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Patellofemoral instability

117 citationsUpdated Sep 2026

Overview

Patellofemoral instability is a multifactorial condition where each underlying component must be considered to determine appropriate treatment [5]. The 2022 review series synthesized current best practices into a concise, algorithmic approach for the clinical and radiological evaluation and nonsurgical management of this instability [1]. While nonsurgical management is the initial step, surgical intervention remains the mainstay of treatment for recurrent patellofemoral instability that fails conservative measures, with procedure selection guided by specific underlying pathoanatomic mechanisms [2]. A thorough understanding of etiologies, combined with careful preoperative planning and meticulous surgical techniques, optimizes clinical outcomes [3]. This comprehensive approach also optimizes functional outcomes in patients presenting with complex patellofemoral instability and proximal tibiofibular joint instability [4].

Medial patellofemoral ligament reconstruction is a central surgical option, with limited but growing evidence indicating that this ligament-based approach leads to excellent functional outcomes [6]. The procedure is safe and substantially improves knee function, patient quality of life, and activity levels for isolated or combined medial patellofemoral ligament reconstruction [16]. 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]. Isolated medial patellofemoral ligament reconstruction with gracilis tendon autograft in appropriately selected patients serves as an effective long-term treatment with low rates of recurrence [71]. Furthermore, medial patellofemoral ligament 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 [20].

Despite these benefits, the overall reoperation rate after patellofemoral instability surgery remains high, and any reoperation portends worse patient-reported outcomes [26]. The rate of recurrent instability after a primary patellofemoral stabilizing surgery is 6.5% [10]. Medial patellofemoral ligament reconstruction has a high rate of success; however, the complication rate of 26.1% associated with this procedure is not trivial [27]. Many treatment injuries following patellofemoral instability surgery were in principle preventable [15]. Allografts may represent a feasible alternative to traditional autograft for medial patellofemoral ligament reconstruction in selected patients [146], although the current literature lacks clinical evidence on allograft medial patellofemoral ligament reconstruction for adolescent patients with recurrent patellofemoral instability [22]. Good clinical outcomes were demonstrated after patellar cartilage repair with no evidence of inferior results even in complex cases with the need for additional patellofemoral realignment procedures [153]. In selected cases, patelloplasty of the medial facet of the patella has no particular morbidity at intermediate follow-up [43]. The indication for medial closing-wedge patellar osteotomy should be restricted to patients with unsatisfactory intraoperative patellofemoral tracking after trochleoplasty [46]. 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 [40]. Appropriately powered randomized controlled trials are needed to better understand what the adequate indications for surgery in patients with patellar instability and clinical outcomes are [150].

Anatomy & Pathophysiology

Bony Anatomy & Kinematics

The patellofemoral joint comprises the patella and the femoral trochlea, sharing a cartilaginous articulating surface [21]. The patella is a sesamoid bone within the extensor mechanism, functioning to optimize the lever arm of the extensor mechanism around the knee and improve quadriceps contraction efficiency [110]. This extensor lever arm is greatest at 20 to 30 degrees of flexion [110]. Patellar contact with the trochlea progresses with flexion: the inferior articular surface contacts the trochlea at approximately 20 degrees, the midportion at 60 degrees, and the superior portion at 90 degrees [110]. 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 [110].

In normal anatomy, the mean trochlear depth is 4.0 mm [91]. The medial facet contributes 37.4% of the width of the cartilage covering the trochlea, while the lateral facet contributes 62.6% [91]. Decreased trochlear depth reduces the effectiveness of osteochondral restraint and contributes to patellar instability [91]. At flexion angles greater than 30°, the osteochondral constraint of the trochlea provides primary stability to the patellofemoral joint [91]. Patella alta influences kinematics by increasing the extent of knee flexion required before the patella engages within the trochlear groove [91]. This association with instability occurs because the patella may not articulate with the sulcus until higher degrees of flexion, resulting in reduced contact and stability in knee extension and early flexion [60].

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 [110]. Limbs with larger Q angles exhibit a greater tendency for lateral patellar subluxation [110]. Internal rotation of the tibia during flexion centralizes the tibial tubercle or diminishes the Q angle [110]. The patella experiences a joint reaction force dependent on the angle of knee flexion and the magnitude of forces transmitted from the quadriceps and patellar tendons [110]. Patellofemoral joint reaction forces are calculated to be two to five times body weight during activities of daily living [110]. During squatting with knee flexion up to 120 degrees, this force may reach seven to eight times body weight [110]. Radiographic measures of tracking and alignment change with knee motion and are most abnormal at lower flexion angles in knees with instability symptoms [13].

Ligaments & Soft Tissue Restraints

The medial patellofemoral ligament (MPFL) is a fan-shaped ligament extending from the medial femur to the proximal patella [91]. It serves as the primary static restraint to lateral patellar translation within the first 30° of knee flexion [91]. Recent cadaver studies have identified additional fibers extending to the quadriceps tendon, leading to nomenclature such as the medial quadriceps tendon femoral ligament or medial patellofemoral complex [91]. The femoral origin of the MPFL is located 9.5 mm distal and 9.5 mm anterior to the adductor tubercle [91]. 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 [91]. At its patellar insertion, the MPFL merges with the vastus medialis obliquus (VMO) attachment and extends to the medial border of the patella and vastus intermedius tendon [91]. The average width of the MPFL at its insertion is 30 mm [91]. Fifty-seven percent of MPFL fibers attach to the patella, with the remainder attaching to the quadriceps tendon [91]. The average ultimate strength of the MPFL is 178 N [91].

Distal soft-tissue restraints originate on the distal inferomedial patella and comprise the medial patellotibial ligament and medial patellomeniscal ligament [91]. These structures play a role in patellar stability at greater knee flexion angles than the MPFL [91]. Specifically, they restrict lateral patellar translation, tilt, and rotation at 90° knee flexion [91]. The VMO provides a dynamic restraint to lateral translation [91]. Increasing VMO force decreases maximum lateral patellofemoral contact pressure and lateral patellar shift at multiple flexion angles [91]. Conversely, administering a motor branch block to the VMO increases lateral patellar shift during knee extension [91]. A significant delay in VMO activation relative to the vastus lateralis is found in individuals who later experience patellofemoral pain [91]. Measurements of lateral patellar translation and tilt correlate with this delay in VMO activation in patients with pain [91]. An increase in the activation ratio of the vastus lateralis to the vastus medialis is associated with increased lateral patellar tilt [91].

The lateral patellofemoral ligament (LPFL) injury most commonly occurs secondary to iatrogenic disruption [80]. Surgical procedures violating the deep lateral retinacular layer, such as lateral retinacular release, lateral parapatellar arthrotomy, and aggressive lateral dissection, may compromise LPFL integrity [80]. Medial patellar instability attributable to lateral-sided soft-tissue insufficiency has been described without prior surgery [80]. Traumatic or atraumatic LPFL insufficiency can occur in the absence of prior lateral-sided surgery, most frequently in patients with generalized ligamentous laxity, connective tissue disorders, or significant coronal or rotational malalignment [80]. Acute traumatic medial dislocations have been reported in high-level athletes following direct lateral knee impact or noncontact mechanisms resulting in lateral retinacular disruption [80]. Characteristic bone contusion patterns for acute traumatic medial dislocation involve the lateral patella and anteromedial femoral condyle [80].

Pathophysiology & Risk Factors

Patellofemoral instability represents a complex pathology with numerous influencing factors, requiring a detailed understanding of anatomy and kinematics to identify underlying pathologies [12]. Multiple factors contribute to joint stability, including static restraints, dynamic restraints, osteochondral constraints, and lower extremity alignment [11]. The etiology is multifactorial, and successful surgical management requires identifying and considering these contributing factors [11]. In 15–20% of cases, mostly children, the first episode of patellar dislocation is followed by recurrent dislocation or subluxation after minimal stress [19]. Recurrent patellar dislocation is due in some measure to disruption or stretching of 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, which may result in further flattening of the condyle and facilitate 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 [24]. Common injuries occurring during a patellar instability event include a torn MPFL and/or medial retinaculum, avulsion fracture of the medial patella at the MPFL insertion, osteochondral injuries resulting in intra-articular loose bodies, and bone bruising of the patella and lateral femoral condyle [24].

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 [24]. Abnormalities in lower extremity alignment influence the kinematics of the patellofemoral joint [91]. Measurements of femoral anteversion and genu valgum are greater in knees with patellar instability than in healthy control knees [91]. Increased lateralization of the tibial tuberosity relative to the trochlear groove is a common type of lower extremity malalignment [91]. Radiographic measurements of malalignment are significantly correlated with increased lateral shift and tilt of the patella in patients with patellar instability [91]. Radiographic measurements of patellar height are significantly greater in patients with patellar instability than in those without [91]. Patella alta is associated with abnormal patellar tracking, demonstrated by greater lateral shift and tilt of the patella in subjects with an increased patellar height index [91].

The altered function of the patellar tendon in anterior cruciate ligament deficiency results in altered patellar tracking and patellofemoral cartilage contact [75]. Recurrent patellofemoral instability is causing cartilage degeneration [98]. Surgical restoration of the anatomy and biomechanics of the patellofemoral joint may significantly reduce the risk of osteoarthritis [98]. Patellofemoral joint cartilage lesions are associated with blunt trauma, lateral patella dislocations, or as a secondary development in the setting of abnormal joint loading [21]. The understanding of the complexity of the medial patellar stabilizers continues to evolve [64]. There is much heterogeneity among clinical case series and a lack of comparative studies to allow clear indication for the role of isolated or combined surgical reconstruction in patellar stabilization [40]. Distinct anatomical phenotypes underlie dynamic patellar maltracking [109]. Increased understanding of trochlear morphology and sagittal knee balance as they relate to patella alta will be important for defining the factors that affect patellofemoral stability [106].

Vascular Supply

The patella has an extraosseous blood supply consisting of an anastomotic ring that encircles the patella and receives blood from all the geniculates [51]. The intraosseous blood supply of the patella is damaged during resurfacing, theoretically leaving only the superior lateral genicular artery after surgery [51].

Classification

Patellofemoral disorders are broadly classified into three categories: soft-tissue abnormalities, patellar instability, and patellofemoral arthritis [18].

WARPS/STAID: This classification system was introduced specifically for patients with patellofemoral instability and has established validity and reliability in subjects with the condition [44]. Statistically significant evidence demonstrates that certain demographics and pathoanatomies are more prevalent in each of the WARPS and STAID subtypes [68].

Segmental Femoral Torsion: A novel classification system was established for patients with recurrent patellar subluxation and excessive femoral torsion, based on segmental femoral torsion analysis [87].

MRI-Based Morphology: An MRI-based classification system utilizes objective measurements of trochlear and patellofemoral morphology. Specifically, a 2-measurement combination of sulcus angle and LPFA yielded excellent diagnostic accuracy for pediatric patellofemoral instability [116].

Wiberg: The Wiberg classification is a potential risk factor for recurrent lateral patellofemoral instability, though its clinical utility in this population remains unclear [170].

Other Considerations: Developing a standard battery of reliable and reproducible radiographic measures of patellofemoral instability is a challenge; current imaging parameters cannot be used to predict when to operate, what procedure(s) to perform, or how the patient might do [29]. Common physical examination tests for patellofemoral instability demonstrate weak inter-rater reliability [45]. The Banff Patella Instability Instrument (BPII) 2.0 is a reliable and valid instrument for the evaluation of patients who present with patellofemoral instability [70]. Separation of injury patterns into distinct classifications for knee dislocations and multiple ligament knee injuries shows potential for assisting in patient prognosis [140].

Clinical Presentation

History and Symptoms

Patellofemoral disorders present clinically as either pain or instability [11]. In recurrent patellar dislocation, the primary complaint 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 may perceive the patella as displaced medially because the uncovered medial femoral condyle stands out prominently, even though the patella dislocates laterally [19]. A clear description of symptoms helps distinguish patellar subluxation from knee buckling caused by pain or weakness [32]. The history must capture the mechanism of injury, chronicity, number of episodes, and the specific type of episode (dislocation versus subluxation) [32]. For recurrent instability, the history should include the activities that provoked symptoms, response to prior treatment, severity of pain and swelling, number of instability episodes, and whether knee function was normal between episodes [54].

Epidemiological factors influence presentation. Patellofemoral instability injury rates vary by sport, sex, and type of exposure (competition versus practice) [34]. The incidence of bilateral patellofemoral instability is 37.8% [66]. In 15–20% of cases, mostly in children, the first episode of dislocation is followed by recurrent dislocation or subluxation after minimal stress [19].

Physical Examination

The main objective of the physical examination is to identify contributing factors and differentiate between pain and instability [32]. General ligamentous laxity, identified using criteria such as the Beighton hypermobility score, is associated with an increased risk of patellar instability [32]. Standing alignment assessment includes evaluation of Q angle, genu valgus, and lateralization of the tibial tuberosity [32]. Excessive femoral anteversion can be detected in hip range of motion and is often associated with "squinting patellae" in a neutral standing position [32].

Palpation and dynamic assessment reveal specific pathologies. Point tenderness is maximal at the site of the retinacular or ligament tear along its course from the medial epicondyle to the medial patella [24]. An effusion may be subtle or large, and a large effusion may raise suspicion of an osteochondral fracture [54]. Patellar mobility is assessed using the glide test, with translation quantified based on patellar quadrants (25% of the width of the patella) [32]. The apprehension sign is elicited using a manually directed lateral force on the patella [32]. A positive apprehension test and J sign in the setting of increased lateral glide can represent a loss of patellar stability [32]. A J-sign pattern with more than two quadrants of lateral translation has been correlated with patellar instability [32].

Evaluation of axial and rotational alignment, including femoral anteversion, tibial torsion, and hyperpronation, is performed [24]. The quadriceps angle is assessed during the physical examination [24]. A J-sign may be appreciated during the physical examination [24]. Dynamic Q-angle is increased in patients with chronic patellofemoral instability and correlates positively with femoral torsion [100].

Imaging

Plain radiographs may appear normal or may show an osteochondral loose body [24]. X-rays may reveal loose bodies in the knee from new or old osteochondral fractures [19]. Trochlear morphology and patellar height and tilt are evaluated on lateral and sunrise views [24]. A lateral view with the knee in slight flexion may show a high-riding patella, and tangential views can be used to measure the sulcus angle and the congruence angle [19]. Evaluation of the tibial tubercle to trochlear groove (TTTG) distance is part of the imaging workup [24]. Evaluation of skeletal maturity is performed if surgical intervention is planned [24].

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 [24]. Radiographic measures of tracking and alignment changed with knee motion and, in knees with instability symptoms, were most abnormal at lower flexion angles [13]. 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 [29].

Predisposing Factors and Pathoanatomy

Patellofemoral instability is multifactorial, and each component must be considered in determining treatment [5]. Common injuries occurring during a patellar instability event include torn medial patellofemoral ligament (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 [24]. Chondral defects of the medial facet and the crest of the patella are the most common in patients with recurrent patellofemoral instability [134]. Signs of patellofemoral dysplasia were found in patients with atraumatic patellar dislocation [53].

Several anatomical and systemic factors predispose to dislocation. 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].

Dislocation is almost always towards the lateral side; medial dislocation is seen only in rare iatrogenic cases following overzealous lateral release or medial transposition of the patellar tendon [19]. Girls are affected more commonly than boys, and the condition is often bilateral [19]. Female patients with patellofemoral instability have a higher prevalence of anatomical risk factors and worse outcomes after standard stabilization surgery [17]. Patients with joint hypermobility syndromes experienced significantly increased rates of patellofemoral instability and subsequent surgery compared to a matched cohort [35]. Medial patellofemoral ligament injury patterns vary in skeletally immature patients compared with skeletally mature patients [37].

Anatomical risk factors for patellofemoral instability develop differently between females and males as femoral width increases [25]. There are several bony alterations associated with patellofemoral instability, but data did not show a significantly smaller lateral patellar facet or relative patellar width that could facilitate a patellar dislocation [72]. Subjects who had dislocated their patella had a flattened trochlear groove, whereas normal knees had a more concave groove [102]. The position of the trochlear groove was more medial in patients with patellofemoral instability compared with normal knees [102]. Groove position was more important than shape when predicting which patellae were likely to dislocate [102]. 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 [65].

Investigations

History and Physical Examination

The primary objective of evaluating patellofemoral dysfunction is to identify contributing factors and differentiate between pain and instability [32]. General ligamentous laxity, which increases the risk of patellar instability, is identified using criteria such as the Beighton hypermobility score [32]. Excessive femoral anteversion is detected through hip range of motion assessment and the presence of squinting patellae in a neutral standing position [32]. Dynamic assessment includes evaluation of quadriceps strength, as patellofemoral cartilage stresses are sensitive to variations in vastus medialis forces [32]. Deficits in hip strength, particularly in hip abduction and extension, have been identified in patients with patellofemoral pain compared with asymptomatic controls [32]. Findings from the physical examination should be correlated with the patient’s description of symptoms to determine if the patellofemoral joint is functionally unstable [32].

In recurrent dislocation, the main complaint is that the knee suddenly gives way and the patient falls, which may be accompanied by pain and locking in flexion [19]. Although the patella always dislocates laterally, patients may perceive medial displacement because the uncovered medial femoral condyle stands out prominently [19]. Between attacks, clinical signs are sparse, but the apprehension test is positive [19]. An effusion may be subtle or large following a patellar instability event [24]. The apprehension test is typically positive in the physical examination of patellofemoral instability [24]. Evaluation of axial and rotational alignment and assessment of the quadriceps angle are performed during the physical examination [24].

Imaging

Plain radiography: A lateral view with the knee in slight flexion may show a high-riding patella [19]. Tangential views can be used to measure the sulcus angle and the congruence angle [19]. Objective radiographic measurements remain important for characterizing tibial tuberosity position when planning patellar stabilization surgery [177].

MRI: MRI-based patellar tilt measures proved to be an excellent group of measurements for delineating between controls and those with instability [130]. In symptomatic cases with inconspicuous conventional MRI imaging, additional MRI imaging only in the axial plane at 20° of knee flexion could be beneficial and useful in clinical daily routine [136]. This study demonstrated a comparatively good diagnostic performance for MRI in the evaluation of first and recurrent lateral patellar dislocations, and MRI is recommended for the cartilage assessment after a lateral patellar dislocation [159]. Study findings demonstrate a high degree of variability across repeat MRI scans of the same knee in the same patient regarding tibial tuberosity to trochlear groove distance [160]. MRI-based indices frequently indicated preserved patellofemoral engagement despite Caton-Deschamps Index-defined patella alta, underscoring their complementary role [169]. 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 [179].

CT: The difference between computed tomography and magnetic resonance imaging measurements of tibiofemoral rotation correlates with the degree of knee flexion during image acquisition [49].

Other Considerations: Arthroscopic assessment of patella tracking is accurate, reproducible, and a knee flexion angle of greater than 44° correlates with patellar instability diagnosis [171]. Using dynamic ultrasound assessment, medial patellofemoral distance significantly increases with disruption of the MPFC [186]. While a TT-TG distance ≥20 mm was the strongest predictor of recurrent instability, it was relatively insensitive, and sensitivity may be improved by normalizing the TT-TG distance to patient-specific axial and sagittal plane patellofemoral measurements [184]. The management of patellofemoral instability requires synthesis of clinical tests, radiological evaluations, and patient expectations while avoiding over-reliance on strict numerical values [62]. The true anatomic reason for each patient's individual pathology must be determined before surgery proceeds [14]. Identifying and managing the anatomic or functional deficits specific to the individual patient are crucial for directing nonsurgical and surgical treatments [11]. 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 [175]. These findings underscore the need to establish the baseline threshold values of preoperative PROs, clinical exam findings, and imaging parameters specific to patellofemoral instability [47].

Treatment

Non-Operative

The 2022 JAOS review series aimed to synthesize current best practices into a concise, algorithmic approach for the clinical and radiological evaluation and nonsurgical management of patellofemoral instability [1]. Initial management consists of immobilization for comfort, rest, ice, compression, and elevation [24]. Physical therapy is initiated to strengthen the injured extremity and address core and hip weakness [24]. A patellar stabilizing brace may be used initially for activities of daily living and after the athlete is ready to return to play [24]. Non-operative treatment is usually recommended if patellar dislocation occurs in an anatomically normal knee and osteochondral fracture is ruled out on MRI [172]. For overlap-region injuries of the medial patellofemoral ligament (MPFL), non-surgical treatment achieves better clinical outcomes, including a lower patellar instability rate and better subjective function, compared to non-overlap-region injuries, and can be considered the treatment of choice [165]. However, 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 is indicated for patients with recurrent instability after unsuccessful nonsurgical treatment [11]. Specific indications include osteochondral injury with loose body, recurrent instability, and failure of nonsurgical treatment with persistent pain or instability [24]. The surgical procedure should be tailored to the specific dynamic and anatomic variations contributing to the patient’s instability [11]. 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 [17].

Surgical Approach / Technique: Isolated MPFL reconstruction provides reliable surgical outcomes and is currently the most popular technique for stabilizing the unstable patella [8, 145]. It is an accepted method to restore static medial stabilization for patients with recurrent patellar instability who have failed nonoperative management [157]. 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 [20]. 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 [71]. MPFL reconstruction is an effective and reliable treatment in the setting of patellofemoral instability [108]. Both MPFL reconstruction and the combination of MPFL reconstruction with tibial tubercle osteotomy (TTO) are effective and reliable treatments [55]. 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 [138]. MPFL reconstruction for recurrent patellar instability could achieve good clinical results, with a good congruous patellofemoral joint and good knee function [33]. Clinical follow-up of the horizontal Y-shaped graft with respective graft tension angles 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 [36]. Modern synthetic material is a safe and effective alternative for medial patellofemoral ligament reconstruction [30]. MPFL or medial quadriceps tendon-femoral ligament (MQTFL) reconstruction in skeletally immature patients with first-time patellofemoral dislocation demonstrated lower failure rates and improved functional outcomes at a minimum 2-year follow-up compared with nonoperative management [148]. Physeal-sparing medial patellofemoral ligament reconstruction is the treatment of choice for skeletally immature patients with recurrent instability, replacing older nonanatomic techniques [163]. The current literature lacks clinical evidence on allograft MPFL reconstruction in adolescent patients with recurrent patellofemoral instability [22]. There is much heterogeneity among clinical case series and a lack of comparative studies to allow clear indication for the role of isolated or combined surgical reconstruction in patellar stabilization regarding the medial patellotibial ligament and medial patellomeniscal ligament [40]. Various medial patellofemoral reconstructions appear equally efficacious, but medial retinacular imbrication should not be forgotten for traumatic recurrent patellar dislocation [162]. Both methods of surgical treatment for recurrent patellar dislocation are equally effective in maintaining patellar stability and regarding recurrence rates [137]. MPFL reconstruction is superior to active rehabilitation in protecting against further patella dislocations [42].

Bony Procedures: 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 [9]. Tibial tubercle osteotomy should be avoided in skeletally immature patients to prevent angular deformity [24]. Procedures which would compromise an open physis, such as tibial tubercle osteotomy or MPFL graft transphyseal tunnel, are contraindications in skeletally immature patients [24]. Patellar lateral closing-wedge osteotomy serves as a useful component of an 'à la carte' surgical strategy for severe patellofemoral instability [182]. The Femoral Sulcus Deepening Trochleoplasty of Lyon reliably protects against recurrent patellar instability, leading to good postoperative clinical outcomes [185]. A patellofemoral arthrodesis can be regarded safe and also very effective in the relief of pain in extreme patella alta [155].

Implant Selection: Patellofemoral arthroplasty is recommended for isolated patellofemoral osteoarthritis to provide a conservative, bone-sparing alternative to total knee arthroplasty, which may not have as good patient satisfaction in young, active patients [38]. Most series report 85% good to excellent results for patellofemoral arthroplasty [31]. Failures of patellofemoral arthroplasty are associated with uncorrected alignment issues and the progression of tibiofemoral arthritis, with a 25% failure rate at 15-year follow-up in one study [31]. The most common reason for failure of second-generation patellofemoral arthroplasty implants is progression of tibiofemoral arthritis [38]. Patellofemoral arthroplasty alone cannot correct patellar malalignment and/or instability [38]. Malalignment and/or instability of the patellofemoral joint is not an indication for patellofemoral arthroplasty [38]. Inflammatory arthritis is a contraindication for patellofemoral arthroplasty [31]. Chondrocalcinosis, with involvement of the menisci or tibiofemoral chondral surfaces, is a contraindication for patellofemoral arthroplasty [31]. Severe patellar maltracking or malalignment is a contraindication for patellofemoral arthroplasty unless a realignment procedure is required in concert with or before arthroplasty [31]. Patellofemoral arthroplasty is not indicated in patients with severe coronal deformity of the knee (valgus of more than 8 degrees or varus of more than 5 degrees) unless the deformity is corrected by osteotomy before arthroplasty [38]. Patients with patella baja from quadriceps muscle atrophy or patellar tendon scarring are not good candidates for patellofemoral arthroplasty [38]. Patellofemoral arthroplasty is currently not recommended in obese patients (BMI > 30) because of concerns about overload of revision to total knee arthroplasty [38].

Other Considerations: Osteochondral injuries should be addressed during surgical treatment of patellofemoral instability [24]. Evaluation of anatomic abnormalities which are risk factors for dislocation is important, as these should be addressed if possible [24]. Anatomic reconstruction of the MPFL is important for optimal outcome [24]. The tension of the MPFL construct is set with the patella centered in the trochlea with the knee in 30° of flexion [24]. The location of the graft attachment sites on the patella and femur should be checked that they produce an isometric graft with the knee in 0° to 60° of flexion [24]. The femoral attachment can be within 1 to 3 mm from the epiphyseal plate [24]. Femoral drill tunnels should be aimed away from the physis [24]. Avoid overconstraining the patella; the patella should have one to two quadrants of medial and lateral translation following repair similar to the native patella [24]. Flexion past 90° will be difficult after overtensioning of the repair or reconstruction [24]. Excessive lateral release can result in iatrogenic medial instability or dislocation [24]. Quadriceps/femoral nerve stimulation intraoperatively may be helpful to fine-tune the amount of medialization during tibial tubercle osteotomy [24]. 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 [145]. In a study of MPFL reconstructions, 10 of the 29 femoral tunnels were found to be malpositioned [145]. Femoral tunnel malpositioning of greater than 10 mm was associated with postoperative complications but did not necessarily lead to an unsatisfactory outcome [145]. Intraoperative fluoroscopy is useful for achieving optimal tunnel positioning [145]. Confirmation of normal patellar translation and full knee range of motion is recommended before final graft fixation to prevent overtensioning of the graft [145].

Outcomes and Complications: Female sex and skeletal immaturity increase the risk for recurrent instability after primary patellofemoral stabilizing surgery [10]. Higher revision stabilization rates are observed in patients with trochlear dysplasia and patella alta after tibial tubercle transfer and medial patellofemoral ligament reconstruction [26]. The most common complications of MPFL reconstruction are recurrent instability, loss of motion, painful hardware, and patellar fracture [145]. A meta-analysis of 25 studies reporting on a total of 629 knees found that a complication occurred in 164 knees (26.1%) following MPFL reconstruction [145]. 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) [145]. The largest study to date reported a 4.6% rate of recurrent dislocation after MPFL reconstruction [145]. In the largest study to date, 14% of patients had a positive apprehension sign, and 12% had a flexion deficit of 10° or more after MPFL reconstruction [145]. Non-anatomical MPFL reconstruction and failure to address relevant pathologies are common reasons for treatment injuries following treatment for patellofemoral instability [15]. Patellofemoral instability surgery for isolated or combined MPFL reconstruction is safe and substantially improves knee function and patient quality of life and activity levels [16]. Age, body mass index, female gender, and patellofemoral cartilage degeneration predict worse patient outcome after patellofemoral instability surgery [16]. At 10-year minimum follow-up, one-third of patients have patellofemoral arthritis after isolated medial patellofemoral ligament reconstruction using gracilis tendon autograft [71]. The complications of patellofemoral instability surgery often can be avoided by using appropriate surgical techniques [11]. Not surgically addressing chondral lesions in patients with overlying meniscus coverage can allow for high functional outcomes and minimal pain after patellar stabilization procedures [181].

Rehabilitation: Immediate weight bearing locked in extension is allowed after surgical treatment of patellofemoral instability [24]. Range of motion should be restricted to 0° to 90° for 4 to 6 weeks postoperatively [24]. Early physical therapy is important for quadriceps activation and range of motion [24]. Return to sports or activities may occur when strength and neuromuscular control has returned, generally around 6 months postoperatively [24]. A patellar stabilizing brace may be used for return to play [24].

Complications

Recurrent Instability: Recurrent patellofemoral instability remains a significant concern following surgical stabilization. In adolescents, 25% experienced recurrent instability after primary patellar stabilization surgery [78]. Recurrent patellofemoral instability rates after MPFL reconstruction techniques are in the range of instability rates after other soft tissue realignment techniques [7]. Green's procedure to stabilize patellofemoral instabilities results in a high failure rate on the long-term and low subjective assessments [74]. 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]. A retrospective study reported redislocation rates of 42% at 5 years and 52% at 10 years postsurgery when all contributing risk factors were not adequately addressed [189]. Following the initial surgical stabilization, the risk of recurrent dislocation decreases to as low as 5.1% [189].

General Complication Rates: The complication rate of 26.1% associated with medial patellofemoral ligament reconstruction is not trivial [27]. A 2013 study reported a 16.2% complication rate for MPFL reconstruction in patients younger than 21 years [156]. Forty-seven percent of complications following MPFL reconstruction in patients younger than 21 years were secondary to technical factors and considered preventable [156]. Female sex and bilateral MPFL reconstruction were risk factors associated with postoperative complications in patients younger than 21 years [156]. At short- to mid-term follow-up, 80% of service members undergoing tibial tubercle osteotomy for patellofemoral instability returned to military duty with a moderate perioperative complication and postoperative instability rate [63].

Technical Failures and Specific Surgical Complications: MPFL femoral tunnel malpositioning (anterior and proximal) can lead to disabling symptoms including iatrogenic medial patella subluxation, medial patellofemoral overload, and recurrent lateral instability [73]. Complications following surgery for patellofemoral instability include recurrent instability, stiffness, patellar fracture, patellofemoral arthrosis, and persistent pain [156]. 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 [156]. Recurrence rates can be higher in MPFL repair (26.9%) or medial retinacular repair/plication (16.5%) compared with MPFL reconstruction (6.6%) [156]. Painful patellofemoral instability can occur secondary to peroperative patellar fracture during bone-patellar tendon-bone autograft harvesting for anterior cruciate ligament reconstruction [81].

Patellar / Extensor-mechanism: Patellar fracture after total knee arthroplasty is uncommon, occurring in less than 1% of patients [57]. Patellar fracture has been correlated with multiple factors, including excessive patellar resection, vascular compromise secondary to lateral release, patellar maltracking secondary to component malposition, excessive joint line elevation, knee flexion of more than 115 degrees, trauma, thermal necrosis from PMMA polymerization, and revision TKA [57]. In a series of 1146 TKAs, a statistically significant association was found between lateral release and patellar fracture [57]. Patellar thickness and sacrifice of the superior lateral geniculate artery were not associated with patellar fracture after total knee arthroplasty [57]. Nonunion and hardware failure are frequent after internal fixation of patellar fractures following total knee arthroplasty [57].

Other Considerations: 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 [57]. Suboptimally positioned patellar, femoral, or tibial components also may lead to patellofemoral instability [57]. Excessive lateral patellar facet resection is possible because of the normal asymmetry of the medial and lateral patellar facets and can lead to tilting of the patellar component [57]. 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 [57]. 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 [57]. Internal rotation and medial translation of the femoral component move the trochlea more medial relative to the extensor mechanism, leading to lateral subluxation [57]. 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 [57].

Long-Term Degenerative Outcomes: 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 [85]. Progression of tibiofemoral arthritis is the most common reason for revision to total knee arthroplasty after patellofemoral arthroplasty [38]. First-generation patellofemoral arthroplasty designs failed because of narrow trochlear grooves and high constraint, which often produced maltracking, patellar catching, or persistent anterior knee pain [38].

Recovery

Outcomes and Recurrence: Recurrent instability remains a significant concern following primary patellar stabilization surgery, with 25% of adolescents experiencing recurrent instability [78] and 25% experiencing post-operative patellofemoral instability [167]. The overall reoperation rate after patellofemoral instability surgery remains high [26], and any reoperation portends worse patient-reported outcomes [26]. Specific procedures demonstrate varying success rates; at short- to mid-term follow-up, 80% of service members undergoing tibial tubercle osteotomy returned to military duty with significant improvement in pain scores, alongside a moderate perioperative complication and postoperative instability rate [63]. Lateral release and proximal realignment for patellar subluxation and dislocation yielded good or excellent clinical results in 80.8% of patients at the latest follow-up, with only one patient experiencing redislocation [197]. Trochleoplasty for severe trochlear dysplasia achieved favorable patient-reported outcomes at final follow-up [201]. Horizontal Y-shaped graft two-bundle MPFL reconstruction confirmed good restoration of patellar stability and significant improvement of knee function without special complications [36], while MPFL reconstruction for recurrent patellar instability generally achieves good clinical results with a congruous patellofemoral joint and good knee function [33]. Patellofemoral arthroplasty yields satisfactory outcomes in patients with isolated patellofemoral arthritis [39].

Complications and Long-term Degeneration: Long-term degenerative changes vary by procedure. Patellofemoral osteoarthritis developed significantly in 43% of patients at midterm follow-up after Insall's proximal realignment [198]. In contrast, the development of patellofemoral osteoarthritis at 12-year follow-up after stand-alone lateral condyle-elevating trochlear osteotomy did not exceed findings from other trochleoplasty case series [199]. The association of definite knee osteoarthritis in medial patellofemoral ligament reconstruction, with or without lateral release, was small in long-term follow-up [166].

Key Evidence

• [L5] The goal of this review series was to synthesize current best practices into a concise, algorithmic approach for the clinical and radiological evaluation and nonsurgical management of patellofemoral instability. [1] (10.5435/jaaos-d-22-00254)
• [L5] Surgical management is the mainstay of treatment for recurrent patellofemoral instability that fails nonsurgical treatment, with selection guided by underlying pathoanatomic mechanisms. [2] (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. [3] (10.1097/01.blo.0000214415.83593.db)
• [L5] This comprehensive approach optimizes functional outcomes in patients with complex patellofemoral instability and PTFJ. [4] (10.1016/j.eats.2025.103902)
• [L5] Recurrent patellofemoral instability is multifactorial, and each component must be considered in determining treatment. [5] (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. [6] (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. [7] (10.1007/s00167-019-05656-3)
• [L1] Isolated MPFL reconstruction for recurrent patellofemoral instability provides reliable surgical outcomes. [8] (10.1186/s13018-021-02383-9)
• [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. [9] (10.1177/2325967121999642)
• [L3] The rate of recurrent instability after a primary patellofemoral stabilizing surgery is 6.5%. [10] (10.1177/2325967125s00275)
• [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. [12] (10.1007/s00167-018-4860-3)
• [L3] Radiographic measures of tracking and alignment changed with knee motion and, in knees with instability symptoms, were most abnormal at lower flexion angles. [13] (10.1016/j.arthro.2014.04.036)
• [L5] Patellofemoral syndrome is multifactorial, and the true anatomic reason for each patient's individual pathology must be determined before surgery proceeds. [14] (10.1136/jisakos-2018-000260)
• [L2] Many treatment injuries following patellofemoral instability surgery were in principle preventable. [15] (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. [16] (10.1007/s00167-022-06986-5)
• [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. [17] (10.1016/j.jisako.2024.03.014)
• [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)
• [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. [20] (10.1177/03635465231182143)
• [L5] [21] (10.1007/s00167-016-4103-4)
• [L4] Though patellofemoral instability is common in clinical practice, the current literature lacks clinical evidence on allograft MPFL reconstruction. [22] (10.3390/children10050840)
• [L4] The findings demonstrate that anatomical risk factors for patellofemoral instability develop differently between females and males as femoral width increases. [25] (10.1177/2325967126s00032)
• [L4] The overall reoperation rate after patellofemoral instability surgery remains high, and any reoperation portends worse patient-reported outcomes. [26] (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. [27] (10.1177/0363546512442330)
• [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. [29] (10.1016/j.arthro.2023.05.026)
• [L2] [30] (10.1007/s00167-017-4711-7)
• [L2] MPFLR for recurrent patellar instability could achieve good clinical results, with a good congruous patellofemoral joint and good knee function. [33] (10.1016/j.arthro.2013.01.030)
• [L3] Patellofemoral instability injury rates vary by sport, sex, and type of exposure (competition vs practice). [34] (10.1177/0363546515577786)
• [L3] Patients with joint hypermobility syndromes experienced significantly increased rates of patellofemoral instability and subsequent surgery compared to a matched cohort. [35] (10.1016/j.asmr.2024.100995)
• [L4] Clinical follow-up confirms the good restoration of the patellar stability and significant improvement of knee function without special complications. [36] (10.1007/s00167-014-3005-6)
• [L4] Medial patellofemoral ligament injury patterns vary in skeletally immature patients compared with skeletally mature patients. [37] (10.1177/0363546512457558)
• [L4] PFA yields satisfactory outcomes in patients with isolated patellofemoral arthritis. [39] (10.1007/s00167-014-3202-3)
• [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. [40] (10.1007/s00167-017-4469-y)
• [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] In selected cases, patelloplasty of the medial facet of the patella has no particular morbidity at intermediate follow-up. [43] (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. [44] (10.1007/s00167-013-2477-0)
• [L4] [45] (10.1016/j.asmr.2021.01.004)
• [Paper] The indication should be restricted to patients with unsatisfactory intraoperative patellofemoral tracking after trochleoplasty. [46] (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. [47] (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)
• [L5] [54] (10.1177/2325967117750352)
• [L1] MPFLR and MPFLR + TTO are effective and reliable treatments in the setting of patellofemoral instability. [55] (10.1186/s12891-024-07722-5)
• [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)
• [L5] The understanding of the complexity of the medial patellar stabilizers continues to evolve. [64] (10.1007/s00167-018-5266-y)
• [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. [65] (10.1177/0363546516680604)
• [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)
• [L3] The BPII 2.0 was successfully adapted into German and is a reliable and valid instrument for evaluation of German-speaking patients who present with patellofemoral instability. [70] (10.1007/s00167-017-4673-9)
• [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. [71] (10.1016/j.arthro.2022.07.021)
• [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. [72] (10.1007/s00167-019-05660-7)
• [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. [73] (10.1016/j.arthro.2011.02.014)
• [L4] Green's procedure to stabilize patellofemoral instabilities results in a high failure rate on the long-term and low subjective assessments. [74] (10.1007/s00402-019-03322-4)
• [L4] The altered function of the patellar tendon in anterior cruciate ligament deficiency resulted in an altered patellar tracking and patellofemoral cartilage contact. [75] (10.1177/0363546508314404)
• [L3] In conclusion, 25% of adolescents experienced recurrent instability after primary patellar stabilization surgery. [78] (10.1177/2325967121s00795)
• [L4] [80] (10.2106/jbjs.rvw.26.00085)
• [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. [81] (10.1016/j.otsr.2012.05.008)
• [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. [85] (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. [87] (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. [98] (10.1016/j.arthro.2022.10.003)
• [L2] [100] (10.1007/s00167-020-06163-6)
• [L2] [102] (10.1097/01.blo.0000203478.27044.9a)
• [L5] Increased understanding of trochlear morphology and sagittal knee balance as they relate to patella alta will be important for defining the factors that affect patellofemoral stability. [106] (10.1016/j.arthro.2024.03.008)
• [L1] MPFL reconstruction is an effective and reliable treatment in the setting of patellofemoral instability. [108] (10.1177/0363546521990004)
• [L4] These findings highlight distinct anatomical phenotypes underlying dynamic patellar maltracking. [109] (10.1177/2325967126s00397)
• [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. [116] (10.1177/03635465251411751)
• [Case_report] [124] (10.1016/j.jisako.2025.101063)
• [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] Chondral defects of the medial facet and the crest of the patella are the most common in patients with recurrent patellofemoral instability. [134] (10.1186/s13018-022-02911-1)
• [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. [136] (10.1186/s12891-021-04733-4)
• [L3] Both methods are equally effective in maintaining patellar stability and regarding recurrence rates. [137] (10.1007/s00264-016-3119-1)
• [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. [138] (10.1177/0363546514529640)
• [L5] Separation of injury patterns into distinct classifications for knee dislocations and multiple ligament knee injuries allows researchers to stratify by newer modifications and shows potential for assisting in patient prognosis. [140] (10.1016/j.arthro.2025.05.011)
• [L1] Allografts may represent a feasible alternative to traditional autograft for MPFL reconstruction in selected patients with patellofemoral instability. [146] (10.1007/s00167-021-06569-w)
• [L3] MPFL/MQTFL reconstruction in skeletally immature patients with first-time patellofemoral dislocation demonstrated lower failure rates and improved functional outcomes at a minimum 2-year follow-up compared with nonoperative management. [148] (10.1016/j.arthro.2025.01.021)
• [L2] Appropriately powered randomized controlled trials are needed to better understand what the adequate indications for surgery in patients with patellar instability and clinical outcomes are. [150] (10.1186/s13018-020-02072-z)
• [L4] This comprehensive literature review demonstrated good clinical outcomes after patellar cartilage repair with no evidence of inferior results even in complex cases with the need for additional patellofemoral realignment procedures. [153] (10.1007/s00167-021-06728-z)
• [L4] A patellofemoral arthrodesis can be regarded safe and also very effective in the relief of pain in extreme patella alta. [155] (10.1007/s00167-014-3203-2)
• [L5] MPFL reconstruction is an accepted method to restore static medial stabilization for patients with recurrent patellar instability who have failed nonoperative management. [157] (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. [159] (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. [160] (10.1177/2325967126s00363)
• [L5] [162] (10.1002/arj.70046)
• [L5] Physeal-sparing medial patellofemoral ligament reconstruction is the treatment of choice for skeletally immature patients with recurrent instability, replacing older nonanatomic techniques. [163] (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. [165] (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. [166] (10.1177/0363546507306161)
• [L3] In conclusion, 25% of adolescents experienced post-operative PFI after primary patellofemoral stabilization surgery. [167] (10.1177/2325967121s00508)
• [L4] However, MRI-based indices frequently indicated preserved patellofemoral engagement despite CDI-defined patella alta, underscoring their complementary role. [169] (10.1177/03635465261426564)
• [L3] [170] (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. [171] (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. [172] (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. [175] (10.2106/jbjs.22.00756)
• [L3] Objective radiographic measurements remain important for characterizing tibial tuberosity position when planning patellar stabilization surgery. [177] (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. [179] (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. [181] (10.1177/2325967125s00244)
• [L4] It serves as a useful component of an 'à la carte' surgical strategy for severe patellofemoral instability. [182] (10.1016/j.otsr.2015.07.019)
• [L3] While a TT-TG distance ≥20 mm was the strongest predictor of recurrent instability, it was relatively insensitive, and sensitivity may be improved by normalizing the TT-TG distance to patient-specific axial and sagittal plane patellofemoral measurements. [184] (10.1007/s00167-017-4752-y)
• [Paper] The procedure reliably protects against recurrent patellar instability, leading to good postoperative clinical outcomes. [185] (10.1016/j.eats.2023.01.007)
• [L5] Using dynamic ultrasound assessment, we found that medial patellofemoral distance significantly increases with disruption of the MPFC. [186] (10.1177/23259671221098748)
• [Case_report] [189] (10.1016/j.jisako.2025.100860)
• [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. [197] (10.2106/00004623-198870060-00010)
• [L4] Patellofemoral osteoarthritis developed significantly in 43% of patients at midterm follow-up after Insall's proximal realignment. [198] (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. [199] (10.1007/s00167-017-4602-y)
• [L3] Furthermore, at final follow-up favorable PROs were achieved in patients who underwent trochleoplasty for the treatment of their patellofemoral instability with severe trochlear dysplasia. [201] (10.1177/23259671251321499)

See Also

• Anatomy
• MPFL reconstruction
• Knee osteoarthritis

References

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

[169] 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

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

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

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

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

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[179] 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

[181] 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

[182] 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

[184] Individualizing the tibial tubercle to trochlear groove distance to patient specific anatomy improves sensitivity for recurrent instability. Knee Surgery, Sports Traumatology, Arthroscopy. 2017. DOI: 10.1007/s00167-017-4752-y

[185] The Femoral Sulcus Deepening Trochleoplasty of Lyon. Arthroscopy Techniques. 2023. DOI: 10.1016/j.eats.2023.01.007

[186] Utility of Diagnostic Ultrasound in the Assessment of Patellar Instability. Orthopaedic Journal of Sports Medicine. 2022. DOI: 10.1177/23259671221098748

[189] 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

[197] 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

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

[199] 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

[201] Evaluating the Outcomes of Trochleoplasty in the Treatment of Patellofemoral Instability in the Adolescent and Young Adult Knee With Severe Trochlear Dysplasia: A Minimum 2-Year Follow-up. Orthopaedic Journal of Sports Medicine. 2025. DOI: 10.1177/23259671251321499