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Patellofemoral instability

114 citationsUpdated Oct 2026

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Overview

Patellofemoral instability is a multifactorial condition in which each underlying component must be considered when determining treatment [6]. Surgical management serves as the mainstay for recurrent patellofemoral instability that fails nonsurgical treatment, with procedure selection guided by the specific underlying pathoanatomic mechanisms [3]. A thorough understanding of the etiologies, combined with careful preoperative planning and meticulous surgical techniques, is required to optimize clinical outcomes [4].

Isolated or combined medial patellofemoral ligament reconstruction is safe and substantially improves knee function, patient quality of life, and activity levels [17]. However, the overall reoperation rate after patellofemoral instability surgery remains high, and any reoperation portends worse patient-reported outcomes [27]. The rate of recurrent instability following a primary patellofemoral stabilizing surgery is 6.5% [12]. Female sex and skeletal immaturity increase the risk for this recurrence [12]. Additionally, age, body mass index, female gender, and patellofemoral cartilage degeneration predict worse patient outcomes after surgery [17].

Many treatment injuries following patellofemoral instability surgery were in principle preventable [16]. Common reasons for these adverse events include non-anatomical medial patellofemoral ligament reconstruction and failure to address relevant pathologies [16]. Prevailing disagreement exists in the treatment of complex patellar instability cases, highlighting the need for established treatment guidelines and algorithms [11].

Anatomy & Pathophysiology

Bony Anatomy & Alignment

The patellofemoral joint comprises the patella and the femoral trochlea, sharing a cartilaginous articulating surface [30]. The patella is a sesamoid bone within the extensor mechanism, functioning to optimize the quadriceps lever arm around the knee [30]. This lever arm is greatest at 20 to 30 degrees of flexion [105]. Patellar contact with the trochlea progresses with flexion: the inferior articular surface contacts at approximately 20 degrees, the midportion at 60 degrees, and the superior portion at 90 degrees [105]. In extreme flexion beyond 120 degrees, the patella articulates only medially and laterally with the femoral condyles, while the quadriceps tendon articulates with the trochlea [105]. A third medial facet often articulates with the lateral aspect of the medial femoral condyle at flexion angles exceeding 90 degrees [105].

Trochlear morphology significantly influences stability. The mean trochlear depth in normal anatomy is 4.0 mm, differing by sex with a mean of 3.4 mm in women and 4.2 mm in men [84]. The medial facet contributes 37.4% to the width of the trochlear cartilage, while the lateral facet contributes 62.6% [84]. Decreased trochlear depth reduces the effectiveness of osteochondral restraint, contributing to patellar instability [84]. Patella alta is associated with instability because the patella may not articulate with the sulcus until higher degrees of flexion are reached [58]. This condition results in reduced contact and stability in knee extension and early flexion [58]. Patella alta influences kinematics by increasing the extent of knee flexion required for the patella to engage within the trochlear groove [84]. It is also associated with abnormal tracking, demonstrated by greater lateral shift and tilt in subjects with an increased patellar height index [84]. Conversely, patella baja is often the result of fat pad and tendon fibrosis [58].

The Q angle is defined as the angle between the extended anatomic axis of the femur and the line between the center of the patella and the tibial tubercle [105]. Limbs with larger Q angles have a greater tendency for lateral patellar subluxation [105]. Increased lateralization of the tibial tuberosity relative to the trochlear groove is a common type of lower extremity malalignment [84]. Radiographic measurements of malalignment are significantly correlated with increased lateral shift and tilt of the patella in patients with patellar instability [84]. Measurements of femoral anteversion and genu valgum are greater in knees with patellar instability than in healthy control knees [84].

The patella experiences a joint reaction force as the trochlea opposes its posterior displacement [105]. Patellofemoral joint reaction forces are calculated to be two to five times body weight during activities of daily living [105]. During squatting with knee flexion up to 120 degrees, the patellofemoral joint reaction force may be seven to eight times body weight [105].

Soft Tissue Restraints

The medial patellofemoral ligament (MPFL) is a fan-shaped ligament extending from the medial femur to the proximal patella [84]. It serves as the primary static restraint to lateral patellar translation within the first 30° of knee flexion [84]. Recent cadaver studies have highlighted additional fibers extending to the quadriceps tendon, leading to nomenclature such as the medial quadriceps tendon femoral ligament or medial patellofemoral complex [84]. The femoral origin of the MPFL is described as 9.5 mm distal and 9.5 mm anterior to the adductor tubercle [84]. Radiographically, this origin correlates with a point 1 mm anterior to a line extending along the posterior cortex, 2.5 mm distal to the posterior origin of the medial femoral condyle, and proximal to the posterior aspect of the Blumensaat line [84]. At its patellar insertion, the MPFL merges with the attachment of the vastus medialis obliquus (VMO) and extends to the medial border of the patella and vastus intermedius tendon [84]. The average width of the MPFL at its insertion is 30 mm [84]. 57% of the MPFL fibers attach to the patella, with the remainder attaching to the quadriceps tendon [84]. The average ultimate strength of the MPFL has been measured to be 178 N [84].

Distal soft-tissue restraints originate on the distal inferomedial patella and comprise the medial patellotibial ligament and medial patellomeniscal ligament [84]. These structures play a role in patellar stability at greater knee flexion angles than the MPFL [84]. Specifically, they restrict lateral patellar translation, tilt, and rotation at 90° knee flexion [84]. At flexion angles greater than 30°, the osteochondral constraint of the trochlea provides primary stability to the patellofemoral joint [84].

The VMO provides a dynamic restraint to lateral translation [84]. Increasing the force applied by the VMO decreases the maximum lateral patellofemoral contact pressure and lateral patellar shift at multiple flexion angles [84]. Administering a motor branch block to the VMO increases lateral patellar shift during knee extension [84]. A significant delay in activation of the VMO with respect to the vastus lateralis is found in individuals who later experience patellofemoral pain [84]. Measurements of lateral patellar translation and tilt are correlated with a delay in the activation of the VMO in patients with pain [84]. An increase in the activation ratio of the vastus lateralis to the vastus medialis is associated with increased lateral patellar tilt [84].

In the skeletally immature population with recurrent dislocation, the MPFL is often injured at the patellar insertion [134]. The MPFL may be attenuated or deficient in multiple sites in patients with recurrent dislocation [134].

Pathophysiology & Mechanisms

Patellofemoral instability represents a complex pathology with a considerable number of different influencing factors [20]. Multiple factors contribute to the stability of the patellofemoral joint, including static restraints, dynamic restraints, osteochondral constraints, and lower extremity alignment [13]. In 15–20% of cases, mostly children, the first episode of patellar dislocation is followed by recurrent dislocation or sublocation after minimal stress [19]. Recurrent patellar dislocation is due in some measure to disruption or stretching of the medially based ligamentous structures, such as the MPFL [19]. In a significant proportion of cases, there is no history of an acute strain and the initial episode is thought to have occurred spontaneously [19].

Predisposing factors for patellar dislocation include generalized ligamentous laxity, underdevelopment of the lateral femoral condyle, flattening of the intercondylar groove, maldevelopment of the patella, valgus deformity of the knee, external tibial torsion, and a primary muscle defect [19]. Repeated dislocation damages the contiguous articular surfaces of the patella and femoral condyle [19]. Damage to articular surfaces may result in further flattening of the condyle, facilitating further dislocations [19]. Patellar dislocation is almost always towards the lateral side [19]. Medial dislocation is seen only in rare iatrogenic cases following overzealous lateral release or medial transposition of the patellar tendon [19]. More than 90% of patellofemoral instability events occur with lateral patellar translation [26].

Common injuries occurring during a patellar instability event include a torn MPFL and/or medial retinaculum, avulsion fracture of the medial patella at the insertion of the MPFL, osteochondral injuries resulting in intra-articular loose bodies, and bone bruising of the patella and lateral femoral condyle [26]. Risk factors for patellofemoral instability include valgus alignment, increased quadriceps angle, excessive femoral anteversion, excessive external tibial torsion, trochlear dysplasia, patella alta, previous patellar dislocation, skeletal immaturity, and disorders that affect ligamentous laxity such as Ehlers-Danlos or Down syndrome [26]. Patellofemoral subluxation or dislocation can result from a direct blow forcing the patella out of place or from noncontact mechanisms [26].

Ligament deficiency may occur over time from microtrauma secondary to chronic overload or acutely, as with a traumatic dislocation [24]. Strength deficiency secondary to pain inhibition, effusion, or direct injury results in relative overload of other tissues unless activity is decreased [24]. Tissue failure such as chondromalacia, arthrosis, or microtrauma ligament failure can occur if overload is of sufficient magnitude and duration or is repeated often enough [24]. When structural failure such as arthrosis or chondromalacia occurs, other tissues such as underlying bone and surrounding soft tissues must absorb increased stresses unless the absolute load is decreased [24]. Asymmetric failure, such as lateral facet arthrosis, can affect alignment [24].

Recurrent patellofemoral instability is causing cartilage degeneration [92]. Surgical restoration of the anatomy and biomechanics of the patellofemoral joint may significantly reduce the risk of osteoarthritis [92]. Nonanatomic surgery and surgical over-constraint may cause osteoarthritis [92]. Abnormal MPFL kinematics may cause overconstraint and increased cartilage pressures of the medial patellofemoral joint [111].

Classification

Patellofemoral disorders are broadly classified into soft-tissue abnormalities, patellar instability, and patellofemoral arthritis [18]. Specific classification systems address distinct anatomical and pathological features of these conditions.

WARPS/STAID: This system classifies patients with patellofemoral instability and has established validity and reliability in this population [45]. Statistically significant evidence indicates that specific demographics and pathoanatomies are more prevalent in each of the WARPS and STAID subtypes [68].

MRI-based Morphology: An MRI-based classification utilizes objective measurements of trochlear and patellofemoral morphology, specifically a 2-measurement combination of sulcus angle and lateral patellofemoral angle (LPFA), yielding excellent diagnostic accuracy for pediatric patellofemoral instability [112].

Segmental Femoral Torsion: A novel classification system for patients with recurrent patellar subluxation and excessive femoral torsion is based on segmental femoral torsion analysis [81].

Lateral Patellofemoral Ligament (LPFL): No validated classification system currently exists to define the severity or pattern of LPFL injury [181]. Injuries to the LPFL are conceptually categorized as traumatic or iatrogenic [181]. The development of a standardized classification for LPFL injury represents an important area for future research [181].

Wiberg Classification: Patellar morphology is most commonly described by the Wiberg classification, which serves as a potential risk factor for recurrent lateral patellofemoral instability [167]. The clinical utility of the Wiberg classification in the population of patients with recurrent lateral patellofemoral instability remains unclear [167]. Patellar dysplasia is graded according to the Wiberg classification, with grades IV and V serving as exclusion criteria in specific surgical contexts [186].

Dejour Classification: Trochlear dysplasia is classified into types A, B, C, and D according to the Dejour classification [185]. Indications for trochleoplasty are based on objective patellar instability associated with high-grade B or D dysplasia [9]. Medial patellofemoral ligament reconstruction should be systematically associated with trochleoplasty for high-grade B or D dysplasia [9].

Other Considerations: The medial patellofemoral ligament (MPFL) is a single continuous structure with no functional difference between its inferior-straight and superior oblique bundles [186]. The medial patellotibial ligament (MPTL) and medial patellomeniscal ligament (MPML) are considered secondary restraints of patellar stability [186]. The contributions of the MPTL and MPML against lateral translation increase from 26% in extension to 46% at 90° of flexion [186]. At 90° of flexion, the MPTL and MPML are responsible for 72% of patellar tilt and 92% of patellar rotation [186]. Osteochondral lesions in recurrent patellar dislocation are classified according to the International Cartilage Repair Society (ICRS) rating system [186]. Patella alta is defined by an Insall-Salvati index greater than 1.2 [186]. Retropatellar cartilage damage is graded according to the Outerbridge classification [183]. Complications following tibial tubercle osteotomy are categorized into 'minor' and 'major' groups using a modified Clavien-Dindo Classification [78].

Clinical Presentation

History and Symptoms

Patellofemoral disorders present clinically as either pain or instability [13]. The primary complaint in recurrent patellar dislocation is that the knee suddenly gives way, causing the patient to fall, which may be accompanied by pain or the knee getting stuck in flexion [19]. Patients with patellofemoral instability may report a noncontact twisting mechanism or contact with a direct blow as the mechanism of injury [26]. In cases of frank dislocation, the patella may spontaneously reduce or may require positioning with the leg in hip flexion and knee extension for reduction [26]. A clear description of symptoms is necessary to distinguish patellar subluxation from knee buckling caused by pain or weakness [36]. The mechanism of injury, chronicity, number of episodes, and type of episode (dislocation versus subluxation) are important historical elements for evaluation [36]. Knowledge of prior treatments and surgical procedures aids in determining treatment options for patellofemoral instability [36].

Patellofemoral instability is a debilitating condition that primarily affects young athletes [31]. Patellofemoral instability injury rates vary by sport, sex, and type of exposure (competition versus practice) [37]. Girls are affected more commonly than boys, and the condition is often bilateral [19]. The incidence of bilateral patellofemoral instability is 37.8% [66]. In 15–20% of cases, mostly in children, the first episode of patellar dislocation is followed by recurrent dislocation or subluxation after minimal stress [19]. In a significant proportion of recurrent dislocation cases, there is no history of an acute strain, and the initial episode is thought to have occurred spontaneously [19]. Female patients with patellofemoral instability have a higher prevalence of anatomical risk factors and worse outcomes after standard stabilization surgery [34]. Patients with joint hypermobility syndromes experience significantly increased rates of patellofemoral instability and subsequent surgery compared to a matched cohort [64].

Dislocation is almost always towards the lateral side, while medial dislocation is seen only in rare iatrogenic cases following overzealous lateral release or medial transposition of the patellar tendon [19]. Although the patella always dislocates laterally, patients may perceive it as displaced medially because the uncovered medial femoral condyle stands out prominently [19]. Repeated dislocation damages the contiguous articular surfaces of the patella and femoral condyle, which may result in further flattening of the condyle and facilitate further dislocations [19]. Patellar dislocation is a significant risk factor for patellofemoral arthritis, with nearly half of patients having symptoms and radiographic changes consistent with arthritis at 25 years after lateral patellar dislocation [124]. Recurrent patellofemoral instability is multifactorial, and each component must be considered in determining treatment [6]. The etiology of patellar instability is multifactorial, and successful surgical management requires identifying and considering the contributing factors [13]. Patellofemoral syndrome is multifactorial, and the true anatomic reason for each patient's individual pathology must be determined before surgery proceeds [21].

Physical Examination

The main objective in evaluating patellofemoral dysfunction is to identify contributing factors and differentiate between pain and instability [36]. A systematic examination extends beyond the patellofemoral joint to identify multiple factors contributing to symptoms [36]. General ligamentous laxity is associated with an increased risk of patellar instability and can be identified using criteria such as the Beighton hypermobility score [36]. Assessment of alignment begins with the patient in a standing position, where Q angle, genu valgus, and lateralization of the tibial tuberosity can be assessed [36]. Rotational malalignment due to excessive femoral anteversion can often be detected in hip range of motion [36]. "Squinting patellae" are present when the patient stands in a neutral position and are associated with excessive femoral anteversion and tibial torsion [36]. Dynamic assessment of the lower extremity includes the evaluation of quadriceps strength [36]. Deficits in hip strength, particularly in hip abduction and extension, have been identified in patients with patellofemoral pain compared with asymptomatic control patients [36].

Patellar mobility is assessed using the glide test, with translation quantified based on patellar quadrants (25% of the width of the patella) [36]. The apprehension sign can be elicited using a manually directed lateral force on the patella [36]. A positive apprehension test and J sign in the setting of increased lateral glide can represent a loss of patellar stability [36]. A J-sign pattern with more than two quadrants of lateral translation has been correlated with patellar instability [36]. Clinical findings should be correlated with the patient’s description of symptoms to determine whether the patellofemoral joint is functionally unstable [36]. Point tenderness is maximal at the site of the retinacular or ligament tear along its course from the medial epicondyle to the medial patella [26]. An effusion may be subtle or large following a patellar instability event [26]. The apprehension test is typically positive in patients with patellofemoral instability [26]. Evaluation of axial and rotational alignment is performed during the physical examination [26]. The quadriceps angle is assessed during the physical examination [26]. A J-sign may be appreciated during the physical examination [26].

Between attacks, clinical signs are sparse, but the apprehension test is positive and the patient should be examined for features predisposing to patellar instability [19]. There is usually tenderness on the medial side of the joint following a dislocation [19]. Later, the joint becomes swollen, and aspiration may reveal a blood-stained effusion [19]. Common physical examination tests for patellofemoral instability demonstrate weak inter-rater reliability [46]. The management of patellofemoral instability requires synthesis of clinical tests, radiological evaluations, and patient expectations while avoiding over-reliance on strict numerical values [62].

Imaging

Plain radiographs may appear normal or may show an osteochondral loose body [26]. X-rays may reveal loose bodies in the knee from new or old osteochondral fractures [19]. A lateral view with the knee in slight flexion may show a high-riding patella [19]. Trochlear morphology and patellar height and tilt are evaluated on lateral and sunrise views [26]. Tangential views can be used to measure the sulcus angle and the congruence angle [19]. The most sensitive radiographic test for patellar positional abnormalities is the true lateral view in extension [96]. The best specificity for eliminating false positives in patellar positional abnormalities is achieved by the true lateral view in flexion [96]. Patellar positional and dynamic abnormalities are more significant than patellofemoral morphologic abnormalities [96]. Radiographic measures of tracking and alignment changed with knee motion and, in knees with instability symptoms, were most abnormal at lower flexion angles [14].

MRI is helpful and may show signs of previous patellofemoral soft-tissue disruption on the medial side of the knee or trochlear dysplasia [19]. Ordering an MRI after a dislocation is controversial but is advised if a tense knee effusion is present without radiographic signs of an osteochondral injury, as this effusion may signify a chondral loose body [26]. Evaluation of tibial tubercle to trochlear groove (TTTG) distance is part of the imaging workup [26]. Evaluation of skeletal maturity is performed if surgical intervention is planned [26]. Developing a standard battery of reliable and reproducible radiographic measures of patellofemoral instability is a challenge [32]. Imaging parameters currently cannot be used to predict when to operate, what procedure(s) to perform, or how the patient might do [32]. Anatomical patella instability risk factors on MRI show sensitivity without specificity in patients with patellofemoral instability [31]. Anatomical risk factors for patellofemoral instability develop differently between females and males as femoral width increases [60].

Subjects who had dislocated their patella had a flattened trochlear groove, whereas normal knees had a more concave groove [97]. The position of the trochlear groove was more medial in patients with patellofemoral instability compared with normal knees [97]. Groove position was more important than shape when predicting which patellae were likely to dislocate [97]. Signs of patellofemoral dysplasia were found in patients with atraumatic patellar dislocation [53]. Dynamic Q-angle is increased in patients with chronic patellofemoral instability and correlates positively with femoral torsion [94].

Predisposing Factors and Pathoanatomy

Generalized ligamentous laxity is a factor predisposing to dislocation of the patella [19]. Underdevelopment of the lateral femoral condyle and flattening of the intercondylar groove are factors predisposing to dislocation of the patella [19]. Maldevelopment of the patella, which may be unusually small or seated too high, is a factor predisposing to dislocation of the patella [19]. Valgus deformity of the knee is a factor predisposing to dislocation of the patella [19]. External tibial torsion is a factor predisposing to dislocation of the patella [19]. A primary muscle defect is a factor predisposing to dislocation of the patella [19].

Common injuries occurring during a patellar instability event include a torn medial patellofemoral ligament (MPFL) and/or medial retinaculum [26]. Common injuries occurring during a patellar instability event include an avulsion fracture of the medial patella at the insertion of the MPFL [26]. Common injuries occurring during a patellar instability event include osteochondral injuries resulting in intra-articular loose bodies [26]. Common injuries occurring during a patellar instability event include bone bruising of the patella and lateral femoral condyle [26].

Valgus alignment is a risk factor for patellofemoral instability [26]. Increased quadriceps angle is a risk factor for patellofemoral instability [26]. Excessive femoral anteversion is a risk factor for patellofemoral instability [26]. Excessive external tibial torsion is a risk factor for patellofemoral instability [26]. Trochlear dysplasia is a risk factor for patellofemoral instability [26]. Patella alta is a risk factor for patellofemoral instability [26]. Previous patellar dislocation is a risk factor for patellofemoral instability [26]. Skeletal immaturity is a risk factor for patellofemoral instability [26]. Disorders that affect ligamentous laxity, such as Ehlers-Danlos or Down syndrome, are risk factors for patellofemoral instability [26].

Bone geometry and alignment, including torsional deformities, may affect optimal functional load transfer in patellofemoral malalignment [24]. Ligaments stabilize the patella by resisting forces that otherwise could produce abnormal tracking or acute instability [24]. Muscles provide joint acceleration, energy absorption, and stability during active function [24]. Articular cartilage reduces friction and contact stresses between articulating surfaces and absorbs energy [24]. When structural failure such as arthrosis or chondromalacia occurs, other tissues must absorb increased stresses unless the absolute load is decreased [24]. When asymmetric failure occurs, such as lateral facet arthrosis, alignment can be affected [24]. Medial patellofemoral ligament injury patterns vary in skeletally immature patients compared with skeletally mature patients [40]. Certain demographics and pathoanatomies are more prevalent in each of the WARPS and STAID patellofemoral instability subtypes [68]. The WARPS/STAID classification system was introduced for patients with patellofemoral instability and established both validity and reliability [45].

Investigations

History and Physical Examination

A clear symptom description distinguishes patellar subluxation from knee buckling caused by pain or weakness [36]. The clinician must differentiate between patellofemoral pain and instability based on history and physical examination [13]. The main complaint is that the knee suddenly gives way and the patient falls, which may be accompanied by pain and sometimes the knee gets stuck in flexion [19]. Although the patella always dislocates laterally, the patient may think it has displaced medially because the uncovered medial femoral condyle stands out prominently [19]. There is usually tenderness on the medial side of the joint [19]. Between attacks, clinical signs are sparse; however, the apprehension test is positive and the patient should be carefully examined for features that predispose to patellar instability [19]. The mechanism of injury, chronicity, number of episodes, and type of episode (dislocation versus subluxation) are important historical elements [36].

Alignment and Dynamic Assessment: Alignment assessment in a standing position includes evaluation of Q angle, genu valgus, and lateralization of the tibial tuberosity [36]. Excessive femoral anteversion can be detected in hip range of motion and is often associated with squinting patellae in a neutral standing position [36]. Dynamic assessment includes evaluation of quadriceps strength, as patellofemoral cartilage stresses are sensitive to variations in vastus medialis forces [36]. Deficits in hip strength, particularly in hip abduction and extension, have been identified in patients with patellofemoral pain compared with asymptomatic controls [36]. The apprehension sign is elicited using a manually directed lateral force on the patella [36].

Imaging

Developing a standard battery of reliable and reproducible radiographic measures of patellofemoral instability is a challenge, and imaging parameters currently cannot be used to predict when to operate, what procedure(s) to perform, or how the patient might do [32]. Patellofemoral instability represents a complex pathology with a considerable number of different influencing factors, requiring a detailed understanding of anatomy and kinematics to identify underlying pathologies [20]. The management of patellofemoral instability is a delicate balance between art and science, requiring synthesis of clinical tests, radiological evaluations, and patient expectations while avoiding over-reliance on strict numerical values [62]. Treatment plans for lateral patellar instability should be based on the identification of contributing anatomical factors and tailored to each individual patient, utilizing advanced imaging to guide surgical treatment [172].

MRI: MRI-based patellar tilt measures proved to be an excellent group of measurements for delineating between controls and those with instability [130]. In particular, symptomatic cases with inconspicuous conventional MRI imaging, additional MRI imaging only in the axial plane in a 20° of knee flexion could be beneficial and useful in clinical daily routine [135]. This study demonstrated a comparatively good diagnostic performance for MRI in the evaluation of first and recurrent lateral patellar dislocations, and we therefore recommend MRI for the cartilage assessment after a LPD [157]. These study findings demonstrate a high degree of variability across repeat MRI scans of the same knee in the same patient [158]. However, MRI-based indices frequently indicated preserved patellofemoral engagement despite CDI-defined patella alta, underscoring their complementary role [166]. On MRI, Patellotrochlear Index is the most consistently reliable, whereas ISI and CDI show very good to excellent reliability [180]. Substantial cartilage damage was present in 56% of patients who underwent isolated MPFL reconstruction for recurrent patellar instability, with medial patellar lesions being the most common [176].

Arthroscopy: This study confirms arthroscopic assessment of patella tracking is accurate, reproducible, and a knee flexion angle of greater than 44° correlates with patellar instability diagnosis [168].

Other Considerations: Objective radiographic measurements remain important for characterizing tibial tuberosity position when planning patellar stabilization surgery [175]. The difference between imaging modalities correlated with the degree of knee flexion during image acquisition [49]. There are several bony alterations associated with patellofemoral instability, but our data did not show a significantly smaller lateral patellar facet or relative patellar width that could facilitate a patellar dislocation [173]. The purpose of this paper is to provide a review of the evaluation of patellofemoral instability in the pediatric and adolescent patient with a specific focus on the contributions of coronal and transverse plane deformities, and to provide a framework for the incorporation of bony procedures to address these issues [72]. Furthermore, these findings underscore the need to establish the baseline threshold values of preoperative PROs, clinical exam findings, and imaging parameters specific to patellofemoral instability [48].

Treatment

Non-Operative

Initial management of patellofemoral instability involves immobilization for comfort, rest, ice, compression, and elevation [26]. Physical therapy is initiated to strengthen the injured extremity and address core and hip weakness [26]. A patellar stabilizing brace is used initially for activities of daily living and can be used after the athlete is ready to return to play [26]. Non-operative treatment is usually recommended if patellar dislocation occurs in an anatomically normal knee and osteochondral fracture is ruled out on MRI [169]. Non-surgical treatment achieves better clinical outcomes with respect to a lower patellar instability rate and better subjective function for the overlap-region injury of the medial patellofemoral ligament (MPFL) than for the non-overlap-region injury [163]. Active rehabilitation of the knee without MPFL reconstruction improves patient-reported knee function after one year but does not protect against persistent patellar instability [42].

Operative

Indications: Surgery may be indicated in patients with recurrent instability after unsuccessful nonsurgical treatment [13]. Specific indications for surgical treatment include osteochondral injury with loose body, recurrent instability, and failure of nonsurgical treatment with persistent pain or instability [26]. For the vast majority of adolescents with recurrent patella instability and no prior surgery, isolated medial patellofemoral reconstruction is a rational, safe, efficient, and evidence-based selection [52]. Physeal-sparing medial patellofemoral ligament reconstruction is the treatment of choice for skeletally immature patients with recurrent instability, replacing older nonanatomic techniques [161]. Indications for trochleoplasty are based on objective patellar instability associated with high-grade B or D dysplasia, and medial patellofemoral ligament reconstruction should be systematically associated [9]. The indication for medial closing-wedge patellar osteotomy should be restricted to patients with unsatisfactory intraoperative patellofemoral tracking after trochleoplasty [47]. Patellar lateral closing-wedge osteotomy serves as a useful component of an 'à la carte' surgical strategy for severe patellofemoral instability [179]. A patellofemoral arthrodesis can be regarded safe and also very effective in the relief of pain in extreme patella alta [151]. Indications for MPFL reconstruction following total knee arthroplasty must be based on exact analysis of the reasons for the instability [109].

Surgical Approach / Technique: The surgical procedure should be tailored to the specific dynamic and anatomic variations contributing to the patient’s instability [13]. MPFL reconstruction is an accepted method to restore static medial stabilization for patients with recurrent patellar instability who have failed nonoperative management [155]. There is limited but growing evidence that a medial patellofemoral ligament–based surgical approach to patellofemoral instability leads to excellent functional outcomes [7]. Isolated MPFL reconstruction for recurrent patellofemoral instability provides reliable surgical outcomes [10]. MPFL reconstruction is an effective and reliable treatment in the setting of patellofemoral instability [103]. MPFL reconstruction may serve as a more durable surgical treatment option with lower rates of recurrent instability and failure when compared with other patellofemoral stabilization procedures at up to 10 years after surgery [22]. MPFL reconstruction is a safe and effective treatment for patellofemoral instability without severe trochlear dysplasia and allows most patients to engage in regular sports activities 2 years postoperatively, at least at a recreational level [137]. Isolated MPFL reconstruction with gracilis tendon autograft in appropriately selected patients is an effective long-term treatment for recurrent patellofemoral instability with low rates of recurrence [139]. MPFL reconstruction for recurrent patellar instability could achieve good clinical results, with a good congruous patellofemoral joint and good knee function [61]. Clinical follow-up of the horizontal Y-shaped graft in anatomical two-bundle medial patellofemoral ligament reconstruction confirms the good restoration of the patellar stability and significant improvement of knee function without special complications [39]. MPFL reconstruction had a good outcome in 31 knees with recurrent patellar instability, with improvements in range of motion, Kujala Anterior Knee Pain Scale scores, and radiographic indexes [146]. The largest study to date included 240 consecutive MPFL reconstructions at a single clinic, where the mean Kujala score improved from 62.5 to 80.4 at a minimum 1-year follow-up [146]. A concomitant tibial tubercle osteotomy was done in 23% of patients in the largest study to date of MPFL reconstructions [146]. Some authors have reported excellent results following isolated MPFL reconstruction regardless of the amount of tuberosity lateralization, alta, and trochlear dysplasia [146]. Others have reported better outcome scores when MPFL reconstruction is combined with tibial tubercle osteotomy in patients with a TTTG distance of 17 to 20 mm, patella alta, and preoperative J sign [146]. MPFL reconstruction alone may not be enough to stabilize the patellofemoral joint in a patient with substantial malalignment [146]. Repair of the MPFL has traditionally been considered a good option after an acute first-time dislocation if the location of the tear can be identified, although recent research has cast doubt on this approach [146]. The results of MPFL repair are inferior to those of MPFL reconstruction in a patient with recurrent instability [146]. A case study of isolated MPFL repair for recurrent instability found that 8 of 29 knees (28%) had a later recurrence [146]. Numerous techniques for MPFL reconstruction have been described, using a variety of different graft sources and fixation methods, but no one technique is clearly superior [146]. Recent recognition of the contribution of the other medial soft-tissue structures has led to the development of other surgical techniques such as medial quadriceps tendon femoral ligament reconstruction [146]. Although early results are promising for medial quadriceps tendon femoral ligament reconstruction, more comprehensive results have yet to be published [146]. Modern synthetic material is a safe and effective alternative for medial patellofemoral ligament reconstruction [33].

Implant Selection: The tension of the MPFL construct is set with the patella centered in the trochlea with the knee in 30° of flexion [26]. The location of the graft attachment sites on the patella and femur should be checked to produce an isometric graft with the knee in 0° to 60° of flexion [26]. The femoral attachment can be within 1 to 3 mm from the epiphyseal plate [26]. In younger patients, the femoral attachment site is generally just distal to the physis, but in older adolescents, it can be at or proximal to the physis [26]. Femoral drill tunnels should be aimed away from the physis, which may mean the drill is aimed distal and posterior if starting below the physis [26]. Intraoperative fluoroscopy is useful for achieving optimal tunnel positioning in MPFL reconstruction [146]. Confirmation of normal patellar translation and full knee range of motion is recommended before final graft fixation to prevent overtensioning of the graft [146]. Avoid overconstraining the patella; the patella should have one to two quadrants of medial and lateral translation following repair similar to the native patella [26]. Flexion past 90° will be difficult after overtensioning of the repair or reconstruction [26]. Excessive lateral release can result in iatrogenic medial instability or dislocation [26]. Tibial tubercle osteotomy should be avoided in skeletally immature patients to prevent angular deformity [26]. Quadriceps/femoral nerve stimulation intraoperatively may be helpful to fine-tune the amount of medialization during tibial tubercle osteotomy [26].

Other Considerations: Procedures that would compromise an open physis, such as tibial tubercle osteotomy or MPFL graft transphyseal tunnel, are contraindications in skeletally immature patients [26]. Female patients with patellofemoral instability have a higher prevalence of anatomical risk factors and worse outcomes after standard stabilization surgery; therefore, an individualized 'a la carte' approach addressing specific anatomical risk factors may be more appropriate [34]. MPFL reconstruction and MPFL reconstruction combined with tibial tubercle osteotomy are effective and reliable treatments in the setting of patellofemoral instability [54]. Surgical management for patellofemoral instability in the presence of patella alta consistently led to improvement in clinical and functional outcomes, regardless of the type of procedure performed [15]. A comprehensive approach optimizes functional outcomes in patients with complex patellofemoral instability and proximal tibiofibular joint instability [5]. Combined medial patellofemoral ligament and medial quadriceps tendon femoral ligament reconstruction with semitendinosus allograft for pediatric patients with first-time patella dislocation yields low failure rates and improved functional outcomes compared with nonoperative treatment [148]. Salvage of failed patellofemoral arthroplasty due to instability can be performed using a combined medial patellofemoral ligament reconstruction, tibial tubercle osteotomy, and vastus medialis obliquus advancement [121]. Non-anatomical MPFL reconstruction and failure to address relevant pathologies are common reasons for treatment injuries following treatment for patellofemoral instability [16]. Malpositioning of the femoral tunnel and securing of the graft with excessive tension are associated with medial patellofemoral articular overload, iatrogenic medial subluxation, and recurrent lateral instability [146]. Proper positioning of the femoral tunnel can be difficult, even for experienced surgeons [146]. In a study of MPFL reconstructions, 10 of the 29 femoral tunnels were found to be malpositioned [146]. Femoral tunnel malpositioning of greater than 10 mm was associated with postoperative complications but did not necessarily lead to an unsatisfactory outcome [146]. The risk of patellar fracture from violation of the anterior patellar cortex or large-diameter transverse patellar tunnels has led to the development of numerous alternative graft fixation techniques [146]. Appropriate positioning of the bony tunnels and tensioning of the graft are thought to be crucial to the success of MPFL reconstruction [146].

Outcomes and Complications: Patellofemoral instability surgery for isolated or combined MPFL reconstruction is safe and substantially improves knee function and patient quality of life and activity levels [17]. Recurrent patellofemoral instability rates after MPFL reconstruction techniques are in the range of instability rates after other soft tissue realignment techniques [8]. The clinical relevance of the study on recurrent instability rates is that it provides clinicians with the best currently available evidence on recurrent patellofemoral instability rates after surgical treatment for patellofemoral instability in skeletally immature patients [8]. Studies of MPFL reconstruction reported success rates of 80% to 96%, with few occurrences of recurrent instability [146]. In general, excellent outcomes were reported for MPFL reconstruction, with a high likelihood of resumption of activities of daily living [146]. The most common complications of MPFL reconstruction are recurrent instability, loss of motion, painful hardware, and patellar fracture [146]. The largest study to date reported a 4.6% rate of recurrent dislocation after MPFL reconstruction [146]. In the largest study to date, 14% of patients had a positive apprehension sign after MPFL reconstruction [146]. In the largest study to date, 12% of patients had a flexion deficit of 10° or more after MPFL reconstruction [146]. A meta-analysis of 25 studies reporting on a total of 629 knees found that a complication occurred in 164 knees (26.1%) after MPFL reconstruction [146]. The most common complications in the meta-analysis of 629 knees were recurrent apprehension (52/164 knees), loss of knee flexion (22), painful hardware (19), and patellar fracture (4) [146]. Medial patellofemoral ligament reconstruction has a high rate of success for patients with patellofemoral instability; however, the complication rate of 26.1% associated with this procedure is not trivial [28]. Complications of patellofemoral instability surgery often can be avoided by using appropriate surgical techniques [13]. Complications of patellar instability surgery in skeletally immature patients include arthrofibrosis, recurrent dislocations, premature growth arrest, overcorrection of axial or rotational alignment, and iatrogenic medial dislocation [26]. Osteochondral injuries should be addressed during surgical management of patellofemoral instability [26]. Evaluation of anatomic abnormalities which are risk factors for dislocation is important, as these should be addressed if possible [26]. Anatomic reconstruction of the MPFL is important for optimal outcome [26]. Not surgically addressing chondral lesions in patients with overlying meniscus coverage can allow for high functional outcomes and minimal pain after patellar stabilization procedures [178]. The current literature lacks clinical evidence on allograft MPFL reconstruction in adolescent patients with recurrent patellofemoral instability [23]. There is much heterogeneity among clinical case series and lack of comparative studies to allow clear indication for the role of isolated or combined surgical reconstruction in patellar stabilization [69]. To assess the best indications for different surgical procedures for patients with patella instability, future research is needed to develop a clear and uniform definition of relevant patella alta [116]. This highlights the need for treatment guidelines and algorithms for patellofemoral instability [11].

Complications

Recurrent Instability and Failure Rates

Recurrent patellofemoral instability remains a significant clinical challenge. In a large series, patients with a first-time patellofemoral dislocation had a 30% recurrence rate [38]. The incidence of bilateral patellofemoral instability was found to be 37.8% [66]. In adolescents, 25% experienced recurrent instability after primary patellar stabilization surgery [75]. Green's procedure to stabilize patellofemoral instabilities results in a high failure rate on the long-term and low subjective assessments [70]. Active rehabilitation of the knee without MPFL-R improves patient reported knee function after one year, but does not protect against persistent patellar instability [42]. Following the initial surgical stabilization, the risk of recurrent dislocation decreases to as low as 5.1% [184]. However, failure to adequately address all contributing risk factors may lead to redislocation, with reported rates of 42% at 5 years and 52% at 10 years postsurgery in a retrospective study [184].

Specific Complications and Technical Errors

The complication rate of 26.1% associated with medial patellofemoral ligament reconstruction is not trivial [28]. A 2013 study reported a 16.2% complication rate for MPFL reconstruction in patients younger than 21 years [153]. Forty-seven percent of complications following MPFL reconstruction in patients younger than 21 years were secondary to technical factors and considered preventable [153]. Female sex and bilateral MPFL reconstruction were risk factors associated with postoperative complications in patients younger than 21 years [153]. MPFL femoral tunnel malpositioning (anterior and proximal) can lead to disabling symptoms including iatrogenic medial patella subluxation, medial patellofemoral overload, and recurrent lateral instability [152]. Subjective outcomes and recurrence rates were worse in patients with trochlear dysplasia or an increased TT-TG distance in which isolated MPFL reconstruction was performed [153]. Recurrence rates can be higher in MPFL repair (26.9%) or medial retinacular repair/plication (16.5%) compared with MPFL reconstruction (6.6%) [153].

Patellar / Extensor-mechanism

Patellofemoral complications include patellofemoral instability, patellar fracture, patellar component failure, patellar component loosening, patellar clunk syndrome, and extensor mechanism rupture [55]. Patellar fracture after TKA is uncommon, occurring in less than 1% of patients [55]. A statistically significant association was found between lateral release and patellar fracture in a series of 1146 TKAs [55]. Patellar thickness and sacrifice of the superior lateral geniculate artery were not associated with patellar fracture after TKA [55]. In some patellar fractures after lateral release, pathologic evidence of osteonecrosis has been apparent [55]. Nonunion and hardware failure are frequent after internal fixation of patellar fractures after TKA [55]. Patellofemoral instability can be caused by extensor mechanism imbalance in which the lateral retinaculum is too tight or the medial soft tissues are too loose [55]. Medial retinacular laxity may occur with postoperative rupture of the medial capsular repair, which can be caused by a closure that is too tight or by a traumatic event in the early postoperative period [55]. Suboptimally positioned patellar, femoral, or tibial components also may lead to patellofemoral instability [55]. Excessive lateral patellar facet resection is possible because of the normal asymmetry of the medial and lateral patellar facets [55]. Lateral placement of the patellar component on the cut surface of the patella fails to reproduce the normal median eminence of the patella and can lead to lateral subluxation of the patella in extension [55]. Suboptimal position of the tibial component in an internally rotated position increases the Q angle by moving the tibial tubercle laterally, leading to lateral subluxation [55]. Internal rotation and medial translation of the femoral component move the trochlea more medial relative to the extensor mechanism, leading to lateral subluxation [55]. Distal realignment procedures, such as tibial tubercle osteotomy, should be undertaken only with extreme caution because serious functional loss would result if nonunion of the transferred tibial tubercle occurred [55]. Painful patellofemoral instability can occur secondary to peroperative patellar fracture during bone-patellar tendon-bone autograft harvesting for anterior cruciate ligament reconstruction [76].

Other Considerations

Patients with joint hypermobility syndromes experienced significantly increased rates of patellofemoral instability and subsequent surgery compared to a matched cohort [64]. A single, first-time or infrequently recurring traumatic lateral patellar dislocation is associated with cartilage injury and gradual deterioration over time, potentially leading to generalized knee osteoarthritis [80]. A history of multiple patellar dislocations is not associated with a higher prevalence or increased severity of chondral injury compared to a single patellar dislocation event [182]. At short- to mid-term follow-up, 80% of service members undergoing TTO for patellofemoral instability returned to military duty with significant improvement in pain scores and a moderate perioperative complication and postoperative instability rate [63]. The complications of patellofemoral instability surgery often can be avoided by using appropriate surgical techniques [13].

Recovery

Light activity (weeks): The provided evidence does not specify a typical week range for desk work, driving, or light activities of daily living.

Full activity (months): The provided evidence does not specify a month range for manual work, sport, or full range of motion and strength return.

Complete recovery / outcome plateau (months): The provided evidence does not specify a month range for the stabilization of pain, strength, or final functional outcomes.

Rehabilitation protocol: The provided evidence does not detail physical therapy phasing, immobilisation duration, weight-bearing or range-of-motion progression, or sling and brace removal timing.

Functional milestones: The provided evidence does not report validated patient-reported outcome measure trajectories or specific outcome-measure benchmarks.

Other Considerations: Long-term follow-up data indicate that MPFLR for recurrent patellar instability achieves good clinical results, with a good congruous patellofemoral joint and good knee function [61]. Clinical follow-up confirms the good restoration of patellar stability and significant improvement of knee function without special complications [39]. In selected cases, patelloplasty of the medial facet of the patella has no particular morbidity at intermediate follow-up [44]. At the latest follow-up, 80.8 per cent of patients had a good or an excellent clinical result; only one patient had redislocation of the patella [192]. Regarding joint health, there was no significant radiographic progression of patellofemoral arthritis at a mean of 2.4 years after surgery [43]. The association of definite knee osteoarthritis in medial patellofemoral ligament reconstruction with or without lateral release was small in the long-term follow-up [164]. In contrast to general belief, the development of patellofemoral osteoarthritis at 12-year follow-up did not exceed the findings from other trochleoplasty case series [194]. However, patellofemoral osteoarthritis developed significantly in 43% of patients at midterm follow-up after Insall's proximal realignment [193].

Recurrence rates remain a significant consideration. In a large series, patients with a first-time patellofemoral dislocation had a 30% recurrence rate [38]. Among adolescents, 25% experienced recurrent instability after primary patellar stabilization surgery [75], and 25% experienced post-operative PFI after primary patellofemoral stabilization surgery [165]. Higher revision stabilization is observed in patients with trochlear dysplasia and patella alta [27]. This long-term risk stratification holds significant potential clinical utility for determination of patients who are at high risk for recurrent instability after primary patellar dislocation [196].

Key Evidence

• [L5] Surgical management is the mainstay of treatment for recurrent patellofemoral instability that fails nonsurgical treatment, with selection guided by underlying pathoanatomic mechanisms. [3] (10.5435/jaaos-d-23-00650)
• [L5] A thorough understanding of the etiologies of patellofemoral instability, careful preoperative planning, and meticulous surgical techniques will optimize clinical outcome. [4] (10.1097/01.blo.0000214415.83593.db)
• [L5] This comprehensive approach optimizes functional outcomes in patients with complex patellofemoral instability and PTFJ. [5] (10.1016/j.eats.2025.103902)
• [L5] Recurrent patellofemoral instability is multifactorial, and each component must be considered in determining treatment. [6] (10.5435/00124635-201101000-00002)
• [L1] There is limited but growing evidence that a medial patellofemoral ligament–based surgical approach to patellofemoral instability leads to excellent functional outcomes. [7] (10.1177/0363546509353132)
• [L1] The clinical relevance of this study is that it provides clinicians with the best currently available evidence on recurrent patellofemoral instability rates after surgical treatment for patellofemoral instability in skeletally immature patients. [8] (10.1007/s00167-019-05656-3)
• [L5] Indications are based on objective patellar instability associated with high-grade B or D dysplasia, and medial patellofemoral ligament reconstruction should be systematically associated. [9] (10.1016/j.otsr.2021.103160)
• [L1] Isolated MPFL reconstruction for recurrent patellofemoral instability provides reliable surgical outcomes. [10] (10.1186/s13018-021-02383-9)
• [L5] This highlights the need for treatment guidelines and algorithms for patellofemoral instability. [11] (10.1007/s00167-020-05936-3)
• [L3] The rate of recurrent instability after a primary patellofemoral stabilizing surgery is 6.5%. [12] (10.1177/2325967125s00275)
• [L3] Radiographic measures of tracking and alignment changed with knee motion and, in knees with instability symptoms, were most abnormal at lower flexion angles. [14] (10.1016/j.arthro.2014.04.036)
• [L1] Surgical management for patellofemoral instability in the presence of patella alta consistently led to improvement in clinical and functional outcomes, regardless of the type of procedure performed. [15] (10.1177/2325967121999642)
• [L2] Many treatment injuries following patellofemoral instability surgery were in principle preventable. [16] (10.1002/ksa.70493)
• [L3] Patellofemoral instability surgery for isolated or combined MPFL reconstruction is safe and substantially improves knee function and patient quality of life and activity levels. [17] (10.1007/s00167-022-06986-5)
• [L5] Disorders of the patellofemoral joint are a common source of knee pain and can be broadly classified as soft-tissue abnormalities, patellar instability, and patellofemoral arthritis. [18] (10.5435/00124635-199701000-00006)
• [L5] Patellofemoral instability represents a complex pathology with a considerable number of different influencing factors, requiring a detailed understanding of anatomy and kinematics to identify underlying pathologies. [20] (10.1007/s00167-018-4860-3)
• [L5] Patellofemoral syndrome is multifactorial, and the true anatomic reason for each patient's individual pathology must be determined before surgery proceeds. [21] (10.1136/jisakos-2018-000260)
• [L3] MPFL reconstruction may serve as a more durable surgical treatment option with lower rates of recurrent instability and failure when compared with other patellofemoral stabilization procedures at up to 10 years after surgery. [22] (10.1177/03635465231182143)
• [L4] Though patellofemoral instability is common in clinical practice, the current literature lacks clinical evidence on allograft MPFL reconstruction. [23] (10.3390/children10050840)
• [L5] [24] (10.1016/s0278-5919(02)00011-x)
• [L4] The overall reoperation rate after patellofemoral instability surgery remains high, and any reoperation portends worse patient-reported outcomes. [27] (10.1007/s00167-021-06784-5)
• [L1] Medial patellofemoral ligament reconstruction has a high rate of success for patients with patellofemoral instability; however, the complication rate of 26.1% associated with this procedure is not trivial. [28] (10.1177/0363546512442330)
• [L5] [30] (10.1007/s00167-016-4103-4)
• [L3] [31] (10.1136/jisakos-2015-000015)
• [L5] Developing a standard battery of reliable and reproducible radiographic measures of patellofemoral instability is a challenge, and imaging parameters currently cannot be used to predict when to operate, what procedure(s) to perform, or how the patient might do. [32] (10.1016/j.arthro.2023.05.026)
• [L2] [33] (10.1007/s00167-017-4711-7)
• [L5] Female patients with patellofemoral instability have a higher prevalence of anatomical risk factors and worse outcomes after standard stabilization surgery; therefore, an individualized 'a la carte' approach addressing specific anatomical risk factors may be more appropriate. [34] (10.1016/j.jisako.2024.03.014)
• [L3] Patellofemoral instability injury rates vary by sport, sex, and type of exposure (competition vs practice). [37] (10.1177/0363546515577786)
• [L3] In this large series, patients with a first-time patellofemoral dislocation had a 30% recurrence rate. [38] (10.1055/s-0034-1398373)
• [L4] Clinical follow-up confirms the good restoration of the patellar stability and significant improvement of knee function without special complications. [39] (10.1007/s00167-014-3005-6)
• [L4] Medial patellofemoral ligament injury patterns vary in skeletally immature patients compared with skeletally mature patients. [40] (10.1177/0363546512457558)
• [L1] Active rehabilitation of the knee without MPFL-R improves patient reported knee function after one year, but does not protect against persistent patellar instability. [42] (10.1007/s00167-022-06934-3)
• [L4] There was no significant radiographic progression of patellofemoral arthritis at a mean of 2.4 years after surgery. [43] (10.1016/j.arthro.2020.04.017)
• [L4] In selected cases, patelloplasty of the medial facet of the patella has no particular morbidity at intermediate follow-up. [44] (10.1016/j.otsr.2011.10.008)
• [L2] This study introduced the WARPS/STAID classification system and established both validity and reliability in subjects with patellofemoral instability. [45] (10.1007/s00167-013-2477-0)
• [L4] [46] (10.1016/j.asmr.2021.01.004)
• [Paper] The indication should be restricted to patients with unsatisfactory intraoperative patellofemoral tracking after trochleoplasty. [47] (10.1016/j.eats.2023.09.023)
• [L2] Furthermore, these findings underscore the need to establish the baseline threshold values of preoperative PROs, clinical exam findings, and imaging parameters specific to patellofemoral instability. [48] (10.1177/2325967126s00378)
• [L3] The difference between imaging modalities correlated with the degree of knee flexion during image acquisition. [49] (10.1177/23259671241304754)
• [L5] For the vast majority of adolescents with recurrent patella instability and no prior surgery, isolated medial patellofemoral reconstruction is a rational, safe, efficient, and evidence-based selection. [52] (10.1016/j.arthro.2023.10.040)
• [L4] Signs of patellofemoral dysplasia were found in patients with atraumatic patellar dislocation. [53] (10.1007/s00167-013-2751-1)
• [L1] MPFLR and MPFLR + TTO are effective and reliable treatments in the setting of patellofemoral instability. [54] (10.1186/s12891-024-07722-5)
• [L4] The findings demonstrate that anatomical risk factors for patellofemoral instability develop differently between females and males as femoral width increases. [60] (10.1177/2325967126s00032)
• [L2] MPFLR for recurrent patellar instability could achieve good clinical results, with a good congruous patellofemoral joint and good knee function. [61] (10.1016/j.arthro.2013.01.030)
• [L5] The management of patellofemoral instability is a delicate balance between art and science, requiring synthesis of clinical tests, radiological evaluations, and patient expectations while avoiding over-reliance on strict numerical values. [62] (10.1302/0301-620x.105b12.bjj-2023-1026)
• [L4] At short- to mid-term follow-up, 80% of service members undergoing TTO for patellofemoral instability returned to military duty with significant improvement in pain scores and a moderate perioperative complication and postoperative instability rate. [63] (10.1055/s-0037-1603639)
• [L3] Patients with joint hypermobility syndromes experienced significantly increased rates of patellofemoral instability and subsequent surgery compared to a matched cohort. [64] (10.1016/j.asmr.2024.100995)
• [L3] The incidence of bilateral patellofemoral instability was found to be 37.8%. [66] (10.1177/2325967123s00271)
• [L3] This study demonstrated statistically significant evidence that certain demographics and pathoanatomies are more prevalent in each of the WARPS and STAID patellofemoral instability subtypes. [68] (10.1007/s00167-016-4346-0)
• [L5] However, there is much heterogeneity among clinical case series and lack of comparative studies to allow clear indication for the role of isolated or combined surgical reconstruction in patellar stabilization. [69] (10.1007/s00167-017-4469-y)
• [L4] Green's procedure to stabilize patellofemoral instabilities results in a high failure rate on the long-term and low subjective assessments. [70] (10.1007/s00402-019-03322-4)
• [L5] The purpose of this paper is to provide a review of the evaluation of patellofemoral instability in the pediatric and adolescent patient with a specific focus on the contributions of coronal and transverse plane deformities, and to provide a framework for the incorporation of bony procedures to address these issues. [72] (10.3390/jcm10143035)
• [L3] In conclusion, 25% of adolescents experienced recurrent instability after primary patellar stabilization surgery. [75] (10.1177/2325967121s00795)
• [L5] The originality of the present case report lies in the unusual and late presentation of the complication and the use of sagittal patellar closing osteotomy to correct the patellar mal-union underlying the patellofemoral instability. [76] (10.1016/j.otsr.2012.05.008)
• [L4] [78] (10.1177/23259671251374307)
• [L4] A single, first-time or infrequently recurring traumatic lateral patellar dislocation is associated with cartilage injury and gradual deterioration over time, potentially leading to generalized knee osteoarthritis. [80] (10.1177/0363546516687549)
• [L3] A novel classification system for patients with recurrent patellar subluxation and excessive femoral torsion based on segmental femoral torsion analysis was established. [81] (10.1186/s13018-024-05123-x)
• [L5] Recent evidence suggests that recurrent patellofemoral instability is causing cartilage degeneration, and stopping this process via surgical restoration of the anatomy and biomechanics of the patellofemoral joint may significantly reduce the risk of osteoarthritis. [92] (10.1016/j.arthro.2022.10.003)
• [L2] [94] (10.1007/s00167-020-06163-6)
• [L3] [96] (10.1016/s0278-5919(01)00007-2)
• [L2] [97] (10.1097/01.blo.0000203478.27044.9a)
• [L1] MPFL reconstruction is an effective and reliable treatment in the setting of patellofemoral instability. [103] (10.1177/0363546521990004)
• [L4] Its indications must be based on exact analysis of the reasons for the instability. [109] (10.1016/j.otsr.2016.03.018)
• [L4] Such abnormal MPFL kinematics may subsequently cause overconstraint and increased cartilage pressures of the medial patellofemoral joint. [111] (10.1002/jor.24872)
• [L3] The authors present an MRI-based classification system utilizing objective measurements of trochlear and patelloemoral morphology, emphasizing a 2-measurement combination of sulcus angle and LPFA that yielded excellent diagnostic accuracy. [112] (10.1177/03635465251411751)
• [L3] To assess the best indications for diferent surgical procedures for patients with patella instability future research is needed to develop a clear and uniform definition of relevant patella alta. [116] (10.1007/s00402-018-2971-4)
• [Case_report] [121] (10.1016/j.jisako.2025.101063)
• [L3] Patellar dislocation is a significant risk factor for patellofemoral arthritis, as nearly half of patients have symptoms and radiographic changes consistent with arthritis at 25 years after lateral patellar dislocation. [124] (10.1177/0363546516680604)
• [L3] MRI-based patellar tilt measures proved to be an excellent group of measurements for delineating between controls and those with instability. [130] (10.1177/0363546512472441)
• [L4] In particular, symptomatic cases with inconspicuous conventional MRI imaging, additional MRI imaging only in the axial plane in a 20° of knee flexion could be beneficial and useful in clinical daily routine. [135] (10.1186/s12891-021-04733-4)
• [L4] Reconstruction of the MPFL is a safe and effective treatment for patellofemoral instability without severe trochlear dysplasia and allows most patients to engage in regular sports activities 2 years postoperatively, at least at a recreational level. [137] (10.1177/0363546514529640)
• [L4] Isolated MPFLr with gracilis tendon autograft in appropriately selected patients is an effective long-term treatment for recurrent patellofemoral instability with low rates of recurrence. [139] (10.1016/j.arthro.2022.07.021)
• [L3] [148] (10.1016/j.arthro.2025.01.021)
• [L4] A patellofemoral arthrodesis can be regarded safe and also very effective in the relief of pain in extreme patella alta. [151] (10.1007/s00167-014-3203-2)
• [L4] MPFL femoral tunnel malpositioning (anterior and proximal) can lead to disabling symptoms including iatrogenic medial patella subluxation, medial patellofemoral overload, and recurrent lateral instability. [152] (10.1016/j.arthro.2011.02.014)
• [L5] MPFL reconstruction is an accepted method to restore static medial stabilization for patients with recurrent patellar instability who have failed nonoperative management. [155] (10.1016/j.csm.2014.03.006)
• [L3] This study demonstrated a comparatively good diagnostic performance for MRI in the evaluation of first and recurrent lateral patellar dislocations, and we therefore recommend MRI for the cartilage assessment after a LPD. [157] (10.1186/1471-2474-11-149)
• [L4] These study findings demonstrate a high degree of variability across repeat MRI scans of the same knee in the same patient. [158] (10.1177/2325967126s00363)
• [L5] Physeal-sparing medial patellofemoral ligament reconstruction is the treatment of choice for skeletally immature patients with recurrent instability, replacing older nonanatomic techniques. [161] (10.5435/jaaos-d-17-00255)
• [L4] Non-surgical treatment achieves better clinical outcomes with respect to a lower patellar instability rate and better subjective function for the overlap-region injury of MPFL than for the non-overlap-region injury, and can be considered as treatment of choice for overlap-region injury of MPFL. [163] (10.1007/s00167-012-2020-8)
• [L4] The association of definite knee osteoarthritis in medial patellofemoral ligament reconstruction with or without lateral release was small in the long-term follow-up. [164] (10.1177/0363546507306161)
• [L3] In conclusion, 25% of adolescents experienced post-operative PFI after primary patellofemoral stabilization surgery. [165] (10.1177/2325967121s00508)
• [L4] However, MRI-based indices frequently indicated preserved patellofemoral engagement despite CDI-defined patella alta, underscoring their complementary role. [166] (10.1177/03635465261426564)
• [L3] [167] (10.1177/23259671251407090)
• [L3] This study confirms arthroscopic assessment of patella tracking is accurate, reproducible, and a knee flexion angle of greater than 44° correlates with patellar instability diagnosis. [168] (10.1007/s00167-019-05532-0)
• [L5] Non-operative treatment is usually recommended if patellar dislocation occurs in an anatomically normal knee and osteochondral fracture is ruled out on MRI. [169] (10.1016/j.otsr.2014.12.001)
• [L5] Treatment plans for lateral patellar instability should be based on the identification of contributing anatomical factors and tailored to each individual patient, utilizing advanced imaging to guide surgical treatment. [172] (10.2106/jbjs.22.00756)
• [L3] There are several bony alterations associated with patellofemoral instability, but our data did not show a significantly smaller lateral patellar facet or relative patellar width that could facilitate a patellar dislocation. [173] (10.1007/s00167-019-05660-7)
• [L3] Objective radiographic measurements remain important for characterizing tibial tuberosity position when planning patellar stabilization surgery. [175] (10.1177/2325967123s00225)
• [L3] Substantial cartilage damage was present in 56% of patients who underwent isolated MPFL reconstruction for recurrent patellar instability, with medial patellar lesions being the most common. [176] (10.1016/j.jisako.2025.100862)
• [L3] The present findings suggest that not surgically addressing chondral lesions in patients with overlying meniscus coverage can allow for high functional outcomes and minimal pain after patellar stabilization procedures. [178] (10.1177/2325967125s00244)
• [L4] It serves as a useful component of an 'à la carte' surgical strategy for severe patellofemoral instability. [179] (10.1016/j.otsr.2015.07.019)
• [L3] On MRI, Patellotrochlear Index is the most consistently reliable, whereas ISI and CDI show very good to excellent reliability. [180] (10.1002/arj.70465)
• [L4] [181] (10.2106/jbjs.rvw.26.00085)
• [L3] A history of multiple patellar dislocations is not associated with a higher prevalence or increased severity of chondral injury compared to a single patellar dislocation event. [182] (10.1177/2325967120s00186)
• [L3] [183] (10.1007/s00402-017-2705-z)
• [Case_report] [184] (10.1016/j.jisako.2025.100860)
• [L3] [185] (10.1002/arj.70549)
• [L4] [186] (10.1016/j.injury.2020.06.028)
• [L3] At the latest followup, 80.8 per cent of the patients had a good or an excellent clinical result; only one patient had redislocation of the patella. [192] (10.2106/00004623-198870060-00010)
• [L4] Patellofemoral osteoarthritis developed significantly in 43% of patients at midterm follow-up after Insall's proximal realignment. [193] (10.1007/s00167-013-2485-0)
• [L4] In contrast to general belief, the development of patellofemoral osteoarthritis at 12-year follow-up did not exceed the findings from other trochleoplasty case series. [194] (10.1007/s00167-017-4602-y)
• [L3] This long-term risk stratification holds significant potential clinical utility for determination of patients who are at high risk for recurrent instability after primary patellar dislocation. [196] (10.1016/j.arthro.2018.09.017)

See Also

• Anatomy
• MPFL reconstruction
• Knee osteoarthritis

References

[3] Patellofemoral Instability Part II: Surgical Treatment. Journal of the American Academy of Orthopaedic Surgeons. 2024. DOI: 10.5435/jaaos-d-23-00650

[4] Patellofemoral Instability after Total Knee Arthroplasty. Clinical Orthopaedics and Related Research. 2006. DOI: 10.1097/01.blo.0000214415.83593.db

[5] Surgical Management of Combined Patellofemoral and Proximal Tibiofibular Joint Instability in a Patient With Ehlers‐Danlos Syndrome. Arthroscopy Techniques. 2025. DOI: 10.1016/j.eats.2025.103902

[6] The Role of Trochlear Dysplasia in Patellofemoral Instability. American Academy of Orthopaedic Surgeon. 2011. DOI: 10.5435/00124635-201101000-00002

[7] Reconstruction of the Medial Patellofemoral Ligament for Treatment of Patellofemoral Instability: A Systematic Review. The American Journal of Sports Medicine. 2009. DOI: 10.1177/0363546509353132

[8] Recurrent patellofemoral instability rates after MPFL reconstruction techniques are in the range of instability rates after other soft tissue realignment techniques. Knee Surgery, Sports Traumatology, Arthroscopy. 2019. DOI: 10.1007/s00167-019-05656-3

[9] Trochleoplasty: Indications in patellar dislocation with high-grade dysplasia. Surgical technique. Orthopaedics & Traumatology: Surgery & Research. 2022. DOI: 10.1016/j.otsr.2021.103160

[10] Isolated medial patellofemoral ligament reconstruction for recurrent patellofemoral instability: analysis of outcomes and risk factors. Journal of Orthopaedic Surgery and Research. 2021. DOI: 10.1186/s13018-021-02383-9

[11] Prevailing disagreement in the treatment of complex patellar instability cases: an online expert survey of the AGA Knee–Patellofemoral Committee. Knee Surgery, Sports Traumatology, Arthroscopy. 2020. DOI: 10.1007/s00167-020-05936-3

[12] Poster 183: Female Sex and Skeletal Immaturity increase the risk for Recurrent Instability after Primary Patellofemoral Stabilizing Surgery. Orthopaedic Journal of Sports Medicine. 2025. DOI: 10.1177/2325967125s00275

[13] Orthopaedic Knowledge Update Sports Medicine 6. Patellofemoral Joint Disorders > Summary.

[14] Tibial Tuberosity‐Trochlear Groove Distance and Patellar Tracking in Symptomatic and Asymptomatic knees in Patients with Unilateral Patellofemoral Instability. Arthroscopy. 2014. DOI: 10.1016/j.arthro.2014.04.036

[15] Surgical Management of Patella Alta in Patellofemoral Instability: A Systematic Review and Meta-analysis. Orthopaedic Journal of Sports Medicine. 2021. DOI: 10.1177/2325967121999642

[16] Non‐anatomical MPFL reconstruction and failure to address relevant pathologies are common reasons for treatment injuries following treatment for patellofemoral instability. Knee Surgery, Sports Traumatology, Arthroscopy. 2026. DOI: 10.1002/ksa.70493

[17] Age, body mass index, female gender, and patellofemoral cartilage degeneration predict worse patient outcome after patellofemoral instability surgery. Knee Surgery, Sports Traumatology, Arthroscopy. 2022. DOI: 10.1007/s00167-022-06986-5

[18] Patellofemoral Instability: Evaluation and Management. Journal of the American Academy of Orthopaedic Surgeons. 1997. DOI: 10.5435/00124635-199701000-00006

[19] Apley And Solomon S Concise System Of Orthopaedics And Trauma. PATELLOFEMORAL DISORDERS.

[20] The complexity of patellofemoral instability. Knee Surgery, Sports Traumatology, Arthroscopy. 2018. DOI: 10.1007/s00167-018-4860-3

[21] Congenital internal rotation deformity of the distal femur presenting as patellofemoral instability and pain. Journal of ISAKOS. 2019. DOI: 10.1136/jisakos-2018-000260

[22] Surgical Stabilization for Recurrent Patellar Instability in Competitive Wrestlers: Outcomes, Reoperations, and Return to Play at 6-Year Mean Follow-up. The American Journal of Sports Medicine. 2023. DOI: 10.1177/03635465231182143

[23] Allografts for Medial Patellofemoral Ligament (MPFL) Reconstruction in Adolescent Patients with Recurrent Patellofemoral Instability: A Systematic Review. Children. 2023. DOI: 10.3390/children10050840

[24] Patellofemoral malalignment: looking beyond the viewbox. Clinics in Sports Medicine. 2002. DOI: 10.1016/s0278-5919(02)00011-x

[26] Aaos Comprehensive Orthopaedic Review 3. Musculoskeletal Conditions and Injuries in the Young Athlete > VII. Patellofemoral Instability.

[27] Outcomes and reoperation rates after tibial tubercle transfer and medial patellofemoral ligament reconstruction: higher revision stabilization in patients with trochlear dysplasia and patella alta. Knee Surgery, Sports Traumatology, Arthroscopy. 2021. DOI: 10.1007/s00167-021-06784-5

[28] A Systematic Review of Complications and Failures Associated With Medial Patellofemoral Ligament Reconstruction for Recurrent Patellar Dislocation. The American Journal of Sports Medicine. 2012. DOI: 10.1177/0363546512442330

[30] Early osteoarthritis of the patellofemoral joint. Knee Surgery, Sports Traumatology, Arthroscopy. 2016. DOI: 10.1007/s00167-016-4103-4

[31] Anatomical patella instability risk factors on MRI show sensitivity without specificity in patients with patellofemoral instability: a systematic review. Journal of ISAKOS. 2016. DOI: 10.1136/jisakos-2015-000015

[32] Editorial Commentary: Evaluation of Patellofemoral Instability Is Complex and Multifactorial. Arthroscopy. 2023. DOI: 10.1016/j.arthro.2023.05.026

[33] Modern synthetic material is a safe and effective alternative for medial patellofemoral ligament reconstruction. Knee Surgery, Sports Traumatology, Arthroscopy. 2017. DOI: 10.1007/s00167-017-4711-7

[34] Specific considerations in female patients with patellar instability: current concepts. Journal of ISAKOS. 2024. DOI: 10.1016/j.jisako.2024.03.014

[36] Orthopaedic Knowledge Update Sports Medicine 6. Patellofemoral Joint Disorders > Clinical Evaluation.

[37] Epidemiology of Patellofemoral Instability Injuries Among High School Athletes in the United States. The American Journal of Sports Medicine. 2015. DOI: 10.1177/0363546515577786

[38] First-Time Patellofemoral Dislocation: Risk Factors for Recurrent Instability. Journal of Knee Surgery. 2015. DOI: 10.1055/s-0034-1398373

[39] The horizontal Y‐shaped graft with respective graft tension angles in anatomical two‐bundle medial patellofemoral ligament reconstruction. Knee Surgery, Sports Traumatology, Arthroscopy. 2014. DOI: 10.1007/s00167-014-3005-6

[40] Age-Related Differences in Medial Patellofemoral Ligament Injury Patterns in Traumatic Patellar Dislocation. The American Journal of Sports Medicine. 2012. DOI: 10.1177/0363546512457558

[42] Medial patellofemoral ligament reconstruction is superior to active rehabilitation in protecting against further patella dislocations. Knee Surgery, Sports Traumatology, Arthroscopy. 2022. DOI: 10.1007/s00167-022-06934-3

[43] Sulcus Deepening Trochleoplasty and Medial Patellofemoral Ligament Reconstruction for Patellofemoral Instability: A 2‐Year Study. Arthroscopy. 2020. DOI: 10.1016/j.arthro.2020.04.017

[44] Medial facet patelloplasty in patellar instability associated with patellofemoral dysplasia: A report of 26 cases. Orthopaedics & Traumatology: Surgery & Research. 2012. DOI: 10.1016/j.otsr.2011.10.008

[45] Introduction of a classification system for patients with patellofemoral instability (WARPS and STAID). Knee Surgery, Sports Traumatology, Arthroscopy. 2013. DOI: 10.1007/s00167-013-2477-0

[46] Common Physical Examination Tests for Patellofemoral Instability Demonstrate Weak Inter‐Rater Reliability. Arthroscopy, Sports Medicine, and Rehabilitation. 2021. DOI: 10.1016/j.asmr.2021.01.004

[47] Medial Closing‐Wedge Patellar Osteotomy in Patients With Patellofemoral Instability. Arthroscopy Techniques. 2024. DOI: 10.1016/j.eats.2023.09.023

[48] Poster 68. Effect of Post-Operative Apprehension and J-Sign on Outcomes following Medial Patellofemoral Ligament Reconstruction for Recurrent Patellar Instability: Data from the JUPITER Cohort. Orthopaedic Journal of Sports Medicine. 2026. DOI: 10.1177/2325967126s00378

[49] Comparing Tibiofemoral Rotation Measurements Between Computed Tomography and Magnetic Resonance Imaging in Patients With Patellofemoral Instability. Orthopaedic Journal of Sports Medicine. 2025. DOI: 10.1177/23259671241304754

[52] Editorial Commentary: Absent Extreme Bony Malalignment: Medial Patellofemoral Reconstruction Is a Sufficient Primary Surgery for Adolescents With Recurrent Patella Instability. Arthroscopy. 2024. DOI: 10.1016/j.arthro.2023.10.040

[53] Medial patellotibial ligament (MPTL) reconstruction for patellar instability. Knee Surgery, Sports Traumatology, Arthroscopy. 2013. DOI: 10.1007/s00167-013-2751-1

[54] Results of medial patellofemoral ligament reconstruction with and without tibial tubercle osteotomy in patellar instability: a systematic review and single-arm meta-analysis. BMC Musculoskeletal Disorders. 2024. DOI: 10.1186/s12891-024-07722-5

[55] Campbell S Operative Orthopaedics 4 Volume Set. PATELLOFEMORAL COMPLICATIONS.

[58] Miller S Review Of Orthopaedics. SECTION 16 PATELLAR TRACKING IN TOTAL KNEE ARTHROPLASTY > PATELLOFEMORAL DISORDERS.

[60] Anatomical Risk Factors for the Radiological Assessment of Patellofemoral Instability Show Gender-Specific Differences in Pediatric Patients: A Retrospective MRI Analysis. Orthopaedic Journal of Sports Medicine. 2026. DOI: 10.1177/2325967126s00032

[61] Medial Retinaculum Plasty Versus Medial Patellofemoral Ligament Reconstruction for Recurrent Patellar Instability in Adults: A Randomized Controlled Trial. Arthroscopy. 2013. DOI: 10.1016/j.arthro.2013.01.030

[62] Towards a better understanding of patellofemoral instability. The Bone & Joint Journal. 2023. DOI: 10.1302/0301-620x.105b12.bjj-2023-1026

[63] Anteromedializing Tibial Tubercle Osteotomy for Patellofemoral Instability: Occupational and Functional Outcomes in U.S. Military Service Members. The Journal of Knee Surgery. 2017. DOI: 10.1055/s-0037-1603639

[64] Increased Risk of Patellofemoral Instability Events and Surgical Management in Patients With Joint Hypermobility Syndromes: A Matched Cohort Analysis. Arthroscopy, Sports Medicine, and Rehabilitation. 2024. DOI: 10.1016/j.asmr.2024.100995

[66] Poster 296: Incidence and Risk Factors for Contralateral Patellofemoral Instability. Orthopaedic Journal of Sports Medicine. 2023. DOI: 10.1177/2325967123s00271

[68] Assessment of demographic and pathoanatomic risk factors in recurrent patellofemoral instability. Knee Surgery, Sports Traumatology, Arthroscopy. 2016. DOI: 10.1007/s00167-016-4346-0

[69] Medial patellotibial ligament and medial patellomeniscal ligament: anatomy, imaging, biomechanics, and clinical review. Knee Surgery, Sports Traumatology, Arthroscopy. 2017. DOI: 10.1007/s00167-017-4469-y

[70] High failure rate 10.8 years after vastus medialis transfer and lateral release (Green’s quadricepsplasty) for recurrent dislocation of the patella. Archives of Orthopaedic and Trauma Surgery. 2019. DOI: 10.1007/s00402-019-03322-4

[72] Coronal and Transverse Malalignment in Pediatric Patellofemoral Instability. Journal of Clinical Medicine. 2021. DOI: 10.3390/jcm10143035

[75] Poster 234: Radiographic Predictors of Failure of Patellar Instability Surgery in Adolescents. Orthopaedic Journal of Sports Medicine. 2022. DOI: 10.1177/2325967121s00795

[76] Painful patellofemoral instability secondary to peroperative patellar fracture during bone-patellar tendon-bone autograft harvesting for anterior cruciate ligament reconstruction. Orthopaedics & Traumatology: Surgery & Research. 2012. DOI: 10.1016/j.otsr.2012.05.008

[78] Incidence of Complications, Recurrent Instability, and All-Cause Reoperations After Tibial Tubercle Osteotomy for Patellofemoral Instability: A Systematic Review and Meta-analysis of the Literature. Orthopaedic Journal of Sports Medicine. 2025. DOI: 10.1177/23259671251374307

[80] Traumatic Patellar Dislocation and Cartilage Injury: A Follow-up Study of Long-Term Cartilage Deterioration. The American Journal of Sports Medicine. 2017. DOI: 10.1177/0363546516687549

[81] Derotational distal femoral osteotomy yields better outcomes in patellar subluxation with proximal femoral torsion compared with distal femoral torsion: A retrospective comparative study. Journal of Orthopaedic Surgery and Research. 2024. DOI: 10.1186/s13018-024-05123-x

[84] Orthopaedic Knowledge Update Sports Medicine 6. Patellofemoral Joint Disorders > Anatomy and Biomechanics.

[92] Editorial Commentary: Patellofemoral Instability Results in Osteoarthritis, and Nonanatomic Surgery and Surgical Over‐constraint May Also Cause Osteoarthritis. Arthroscopy. 2023. DOI: 10.1016/j.arthro.2022.10.003

[94] Dynamic Q‐angle is increased in patients with chronic patellofemoral instability and correlates positively with femoral torsion. Knee Surgery, Sports Traumatology, Arthroscopy. 2020. DOI: 10.1007/s00167-020-06163-6

[96] Comparison of three standard radiologic techniques for screening of patellar subluxations. Clinics in Sports Medicine. 2002. DOI: 10.1016/s0278-5919(01)00007-2

[97] A Laterally Positioned Concave Trochlear Groove Prevents Patellar Dislocation. Clinical Orthopaedics & Related Research. 2006. DOI: 10.1097/01.blo.0000203478.27044.9a

[103] Return to Sport After Medial Patellofemoral Ligament Reconstruction: A Systematic Review and Meta-analysis. The American Journal of Sports Medicine. 2021. DOI: 10.1177/0363546521990004

[105] Campbell S Operative Orthopaedics 4 Volume Set. PATELLOFEMORAL JOINT BIOMECHANICS AND FUNCTIONAL ANATOMY.

[109] Medial patellofemoral ligament reconstruction for patellar instability following total knee arthroplasty: A review of 6 cases. Orthopaedics & Traumatology: Surgery & Research. 2016. DOI: 10.1016/j.otsr.2016.03.018

[111] Elongation and orientation pattern of the medial patellofemoral ligament during lunging. Journal of Orthopaedic Research. 2020. DOI: 10.1002/jor.24872

[112] Modification of Objective Dejour Criteria Yields Excellent Diagnostic Accuracy for Pediatric Patellofemoral Instability. The American Journal of Sports Medicine. 2026. DOI: 10.1177/03635465251411751

[116] Does patella alta lead to worse clinical outcome in patients who undergo isolated medial patellofemoral ligament reconstruction? A systematic review. Archives of Orthopaedic and Trauma Surgery. 2018. DOI: 10.1007/s00402-018-2971-4

[121] Salvage of failed patellofemoral arthroplasty due to instability: Combined medial patellofemoral ligament reconstruction, tibial tubercle osteotomy, and vastus medialis obliquus advancement - Case report and algorithm-based. Journal of ISAKOS. 2026. DOI: 10.1016/j.jisako.2025.101063

[124] Patellofemoral Arthritis After Lateral Patellar Dislocation: A Matched Population-Based Analysis. The American Journal of Sports Medicine. 2016. DOI: 10.1177/0363546516680604

[130] Magnetic Resonance Imaging–Based Topographical Differences Between Control and Recurrent Patellofemoral Instability Patients. The American Journal of Sports Medicine. 2013. DOI: 10.1177/0363546512472441

[134] Tachdjian S Pediatric Orthopaedics From The Texas Scottish Rite Hospital For Children E Book. Plate 35.2 Scapulocostal Stabilization for Scapular Winging (Ketenjian Technique) > Operative Treatment > Reconstruction of the Medial Patellofemoral Ligament.

[135] Weight-bearing MRI with a knee flexion angle of 20°: a study on additional MRI investigation modalities to support a more accurate understanding of patellofemoral instability. BMC Musculoskeletal Disorders. 2021. DOI: 10.1186/s12891-021-04733-4

[137] Reconstruction of the Medial Patellofemoral Ligament. The American Journal of Sports Medicine. 2014. DOI: 10.1177/0363546514529640

[139] At 10-Year Minimum Follow-Up, One-Third of Patients Have Patellofemoral Arthritis After Isolated Medial Patellofemoral Ligament Reconstruction Using Gracilis Tendon Autograft. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2023. DOI: 10.1016/j.arthro.2022.07.021

[146] Orthopaedic Knowledge Update Sports Medicine 6. Patellofemoral Joint Disorders > Patellofemoral Instability > Medial Patellofemoral Ligament Reconstruction.

[148] Combined Medial Patellofemoral Ligament and Medial Quadriceps Tendon Femoral Ligament Reconstruction With Semitendinosus Allograft for Pediatric Patients With First‐Time Patella Dislocation Yields Low Failure Rates and Improved Functional Outcomes Compared With Nonoperative Treatment. Arthroscopy. 2025. DOI: 10.1016/j.arthro.2025.01.021

[151] Patellofemoral arthrodesis as pain relief in extreme patella alta. Knee Surgery, Sports Traumatology, Arthroscopy. 2014. DOI: 10.1007/s00167-014-3203-2

[152] Technical Failure of Medial Patellofemoral Ligament Reconstruction. Arthroscopy. 2011. DOI: 10.1016/j.arthro.2011.02.014

[153] Orthopaedic Knowledge Update Sports Medicine 6. Patellofemoral Instability and Other Common Knee Issues in the Skeletally Immature Athlete > Patellofemoral Instability > Complications.

[155] MPFL Reconstruction. Clinics in Sports Medicine. 2014. DOI: 10.1016/j.csm.2014.03.006

[157] How reliable is MRI in diagnosing cartilaginous lesions in patients with first and recurrent lateral patellar dislocations?. BMC Musculoskeletal Disorders. 2010. DOI: 10.1186/1471-2474-11-149

[158] Poster 50. High Variability in Tibial Tuberosity to Trochlear Groove Distance on Repeat Knee MRI Scans in Adult Patients. Orthopaedic Journal of Sports Medicine. 2026. DOI: 10.1177/2325967126s00363

[161] Surgical Management of Patellofemoral Instability in the Skeletally Immature Patient. Journal of the American Academy of Orthopaedic Surgeons. 2018. DOI: 10.5435/jaaos-d-17-00255

[163] Non‐surgical treatment for acute patellar dislocation with special emphasis on the MPFL injury patterns. Knee Surgery, Sports Traumatology, Arthroscopy. 2012. DOI: 10.1007/s00167-012-2020-8

[164] Long-term Follow-up and Knee Osteoarthritis Change after Medial Patellofemoral Ligament Reconstruction for Recurrent Patellar Dislocation. The American Journal of Sports Medicine. 2007. DOI: 10.1177/0363546507306161

[165] Radiologic Predictors of Failure of Patellofemoral Instability Surgery in Adolescents. Orthopaedic Journal of Sports Medicine. 2022. DOI: 10.1177/2325967121s00508

[166] Reevaluating Patellar Height Indices in Pediatric Patellofemoral Instability: Comparative Accuracy of Caton Deschamps Index, Patellotrochlear Index, and Sagittal Patellar Engagement. The American Journal of Sports Medicine. 2026. DOI: 10.1177/03635465261426564

[167] Patellar Morphology in Recurrent Lateral Patellofemoral Instability: Associations With Risk Factors and Postoperative Outcomes. Orthopaedic Journal of Sports Medicine. 2026. DOI: 10.1177/23259671251407090

[168] Arthroscopic assessment of patella tracking correlates with recurrent patellar instability. Knee Surgery, Sports Traumatology, Arthroscopy. 2019. DOI: 10.1007/s00167-019-05532-0

[169] Acute traumatic patellar dislocation. Orthopaedics & Traumatology: Surgery & Research. 2015. DOI: 10.1016/j.otsr.2014.12.001

[172] Lateral Patellar Instability. Journal of Bone and Joint Surgery. 2023. DOI: 10.2106/jbjs.22.00756

[173] Neither lateral patellar facet nor patellar size are altered in patellofemoral unstable patients: a comparative magnetic resonance imaging analysis. Knee Surgery, Sports Traumatology, Arthroscopy. 2019. DOI: 10.1007/s00167-019-05660-7

[175] Poster 245: Clinical Measurement of the Standard Q-Angle Correlates Poorly with Tibial Tuberosity to Trochlear Groove Distance in Awake Patients and Anesthetized Patients with Patella Alta and Trochlear Dysplasia. Orthopaedic Journal of Sports Medicine. 2023. DOI: 10.1177/2325967123s00225

[176] Articular cartilage damage is frequently noted at the time of medial patellofemoral ligament reconstruction and is associated with age and patellofemoral anatomy. Journal of ISAKOS. 2025. DOI: 10.1016/j.jisako.2025.100862

[178] Poster 149: Traumatic Lateral Femoral Condyle Lesions associated with Patellofemoral Instability Demonstrate Excellent Outcomes With Non-Operative Management and Patellar Stabilization with Meniscal Coverage at 8-Years Follow-Up. Orthopaedic Journal of Sports Medicine. 2025. DOI: 10.1177/2325967125s00244

[179] Patellar lateral closing-wedge osteotomy in habitual patellar dislocation with severe dysplasia. Orthopaedics & Traumatology: Surgery & Research. 2015. DOI: 10.1016/j.otsr.2015.07.019

[180] Magnetic Resonance Imaging and Radiographic Patellar Height Ratio Measurement Reliability Is Not Degraded by Skeletal Maturity or Patellofemoral Instability. Arthroscopy. 2026. DOI: 10.1002/arj.70465

[181] Lateral Patellofemoral Ligament Reconstruction Remains Poorly Defined: A Review from Anatomy to Surgical Management. JBJS Reviews. 2026. DOI: 10.2106/jbjs.rvw.26.00085

[182] DOES THE NUMBER OF PATELLOFEMORAL INSTABILITY EPISODES CORRELATE WITH THE PREVALENCE AND SEVERITY OF CHONDRAL AND OSTEOCHONDRAL LESIONS IN PEDIATRIC AND ADOLESCENT PATIENTS?. Orthopaedic Journal of Sports Medicine. 2020. DOI: 10.1177/2325967120s00186

[183] Surgical treatment of patellar instability: clinical and radiological outcome after medial patellofemoral ligament reconstruction and tibial tuberosity medialisation. Archives of Orthopaedic and Trauma Surgery. 2017. DOI: 10.1007/s00402-017-2705-z

[184] Concomitant distal femoral osteotomy in managing chronic patellofemoral instability with an associated valgus deformity: A case report and review of literature. Journal of ISAKOS. 2025. DOI: 10.1016/j.jisako.2025.100860

[185] High‐Grade Trochlear Dysplasia Confounds Patellar Height Assessment Using the Magnetic Resonance Imaging‐Derived Patellotrochlear and Radiograph‐Derived Caton‐Deschamps Indices. Arthroscopy. 2026. DOI: 10.1002/arj.70549

[186] Combined medial patellofemoral and patellotibial reconstruction with soft tissue fixation in recurrent patellar dislocation. Injury. 2020. DOI: 10.1016/j.injury.2020.06.028

[192] Lateral release and proximal realignment for patellar subluxation and dislocation. A long-term follow-up.. The Journal of Bone & Joint Surgery. 1988. DOI: 10.2106/00004623-198870060-00010

[193] Patellofemoral osteoarthritis after Insall's proximal realignment for recurrent patellar dislocation. Knee Surgery, Sports Traumatology, Arthroscopy. 2013. DOI: 10.1007/s00167-013-2485-0

[194] A stand-alone lateral condyle-elevating trochlear osteotomy leads to high residual instability but no excessive increase in patellofemoral osteoarthritis at 12-year follow-up. Knee Surgery, Sports Traumatology, Arthroscopy. 2017. DOI: 10.1007/s00167-017-4602-y

[196] The Recurrent Instability of the Patella Score: A Statistically Based Model for Prediction of Long‐Term Recurrence Risk After First‐Time Dislocation. Arthroscopy. 2019. DOI: 10.1016/j.arthro.2018.09.017