Pathology & Anatomy

Prearthritic intra-articular hip pathology, including FAI, dysplasia, microinstability, and ONFH, focusing on early diagnosis to prevent premature joint degeneration.

Overview

Acetabular retroversion and femoroacetabular impingement (FAI) management rely on precise characterization of existing lesions and rigorous patient selection to ensure clinical success [2]. Appropriate surgical indications based on preoperative intra-articular cartilage degeneration are paramount for achieving long-term outcomes in periacetabular osteotomy [3]. While acetabular subchondral cysts may not contraindicate hip arthroscopy in FAI patients otherwise indicated for surgery [29], the dysplastic cohort demonstrates outcomes and failure rates similar to rigorously matched controls at midterm follow-up in arthroscopic labral repair [4].

For borderline dysplasia, results represent the work of experienced surgeons selectively managing multiple aspects of hip pathology to optimize outcomes in a defined cohort [11]. Hip arthroscopic surgery with labral preservation and capsular plication in these patients should be performed by surgeons with expertise in advanced arthroscopic techniques using strict patient selection criteria [24]. With improvements in preoperative workup, imaging, and surgical technique, positive results are anticipated in older nonarthritic patients undergoing hip arthroscopy [78].

Current evidence on femoral head fractures regarding indications, variant patterns, surgical approaches, and outcomes has been summarized [74], while understanding emerging technologies in orthopaedic trauma is of critical importance for their utilization [76]. Preoperative planning remains essential to define anatomy and ensure suitable implants are available for total hip arthroplasty in adult hip dysplasia [30]. There is a recognized need for standardized clinical and radiological criteria to guide surgical treatment for FAI [23], as surgeons are reluctant to offer surgical treatment without correction of osseous deformity, particularly for cam-type pathomorphology [60].

Anatomy & Pathophysiology

A comprehensive understanding of hip anatomy and normal function is critical for identifying pathologies and developing successful treatment strategies [1]. Abnormal hip morphology predates arthrosis and is not secondary to the osteoarthritic process [6]. Hip pain in the absence of osteoarthritis may result from a complex combination of dynamic and static mechanical stresses [9]. While variations exist in testing performed by hip specialists, sufficient commonality supports a recommended battery of physical examination maneuvers for evaluation [91].

Osseous Morphology: Male and female patients differ in hip structure, biomechanics, and operative findings of symptomatic labral tears [50]. Observed hip flexion in asymptomatic young women is substantially less than historically reported [25]. Increased mid-sagittal center edge angle remains the sole significant contributor to reduced hip flexion, suggesting a bipolar effect on range of motion [90]. Bony hip morphology was not associated with the risk of groin injuries in male professional soccer players [69]. The greater trochanter classification system, based on anatomy and biomechanics, can distinguish various types of developmental dysplasia of the hip (DDH) and aid in surgical strategy selection [31].

Ligamentous & Capsular Constraints: Both osseous and soft tissue constraints are important to hip biomechanics depending on the direction of applied force [44]. Hip capsular strain varies between ligaments based on both hip position and applied rotational force [72]. A patient with a hip capsular injury demonstrated marked improvement in kinematic and kinetic performance measures, as well as MRI appearance of the torn capsule and gluteus minimus tendon, following treatment [65].

Kinematics & Biomechanics: An understanding of hip joint biomechanics is essential for diagnosing and treating disorders, allowing clinicians to assimilate the effects of motions and deformations from forces acting on the joint to guide interventions [37]. Complex dynamic interplay exists between the hip and spinopelvic parameters; a cam deformity, acetabular undercoverage, and increased spinopelvic angles are predictive of a symptomatic hip state [85]. Hip impingement in femoroacetabular impingement syndrome (FAIS) may routinely occur at flexion angles below 90° in neutral rotation, with males engaging at higher flexion angles than females [89]. Impaired squat performance in FAIS is predominantly predicted by sagittal plane knee and hip biomechanics and hip external rotator strength, and less by frontal plane pelvic range of motion and hip morphology [62]. After an ACL injury prevention program, athletes exhibiting the greatest reduction in knee abduction moments showed greater baseline hip adduction excursion and corresponding improvements in hip flexion, knee abduction kinematics, and hip flexion moments [82]. Total hip arthroplasty significantly alters hip abductor and adductor muscle lengths and moment arms during gait, with the implanted side showing shorter adductor muscles and reduced moment arms compared to the non-implanted side [92].

Clinical Context: Hip injuries in young athletes are being diagnosed with increasing frequency due to advancements in technology and understanding of pathomechanics [63].

Classification

Developmental Dysplasia of the Hip (DDH): A greater trochanter-based classification system distinguishes various types of DDH and aids in surgical strategy selection [31]. For patients aged above 13 years, a classification scheme based solely on the lateral center-edge angle (LCEA) allows for reduced radiation, time, and cost [68]. Future improvements in terminology and classification for congenital hip disease are expected to be based on genetic factors [52].

Fatty Degeneration of Gluteus Muscles: Both the Goutallier classification system and the Quartile system perform equally well in assessing fatty degeneration of the gluteus muscles [58]. These systems show excellent levels of interrater and intrarater agreement for this assessment [58].

Femoro-Epiphyseal Acetabular Roof Index: The modified approach to measuring the femoro-epiphyseal acetabular roof index has better intraobserver and interobserver reliability compared with the original index [67]. Type II and III sourcil types account for the majority of cases in these assessments [67].

Legg-Calvé-Perthes Disease: The Stulberg classification system demonstrates marginally acceptable intra-rater reliability [84]. There is significant variability between classifications assigned by different raters using the Stulberg system, even after intervention [84]. Consequently, the reliability of the Stulberg system calls into question the validity of treatment decisions, outcome evaluations, or epidemiological studies based on it [84].

Femoral Head Avascular Necrosis: A deep learning model exhibits high accuracy in segmenting and grading necrotic lesions according to the Steinberg classification using MRI [66]. Different classification systems for femoral head avascular necrosis demonstrate varying levels of reliability and diagnostic precision [87].

Intra-articular Hip Pathology: Arthroscopic classification of intra-articular hip pathology demonstrates at best moderate interrater reliability [88]. Further development and refinement of multifactorial grading systems for describing labral injury are indicated [88].

Anterior Inferior Iliac Spine (AIIS): Preoperative hip internal rotation does not correlate with AIIS type [95]. Impingement tests do not correlate with AIIS type [95]. The utility of the AIIS classification system in identifying pathologic AIIS anatomy is questioned [95].

Other Considerations: A more accurate set of definitions must be developed to allow for more accurate diagnosis of early hip disease in young adults [96].

Clinical Presentation

A comprehensive understanding of hip anatomy and normal function is critical for identifying pathologies and formulating successful treatment strategies [1]. While clinical assessment can accurately determine the existence of intra-articular abnormalities, it remains poor at defining their specific nature [12]. Consequently, accurate diagnosis is essential for providing valuable care to patients with hip dysplasia [42] and for characterizing lesions in acetabular retroversion to ensure adequate patient selection [2].

Asymptomatic Findings: Abnormal hip morphology predates arthrosis and is not secondary to the osteoarthritic process [6]. FAI morphologic features and labral injuries are common in asymptomatic individuals [8, 35], including asymptomatic adolescent athletes where more than two-thirds show evidence of such lesions on MRI [18]. Similarly, hip and pelvis pathology is frequently uncovered on MRI of asymptomatic hockey players [16], yet this pathology typically does not produce symptoms or result in missed games within four years [16]. Despite the prevalence of these findings, it remains unclear if such pathology is truly common or if radiologic signs require better refinement to define abnormality [35]. Furthermore, the presence of FAI morphology does not necessarily indicate that FAI is the primary source of hip pain [38].

Diagnostic Modalities: Hip pain in the absence of osteoarthritis may stem from a complex combination of dynamic and static mechanical stresses [9]. MRI demonstrated a sensitivity of 50% and specificity of 34% in identifying any pathologic process of the ligamentum teres [20]. Arthroscopy may be necessary to substantiate the diagnosis of pigmented villonodular synovitis in the hip and to assess accompanying damage [39]. A painful squat test provides limited diagnostic utility in CAM-type femoroacetabular impingement [46].

Differential Diagnosis and Red Flags: Extra-articular etiologies of pain represent an important subset of hip disorders that can be accurately identified through physical examination and imaging [14]. The recognition of both hip and lumbar spine pathologies may help reduce the likelihood of misdiagnosis, and managing these entities in the appropriate sequence may reduce persistent symptoms [15]. Other less common causes, such as osteoid osteoma, should be included in the differential diagnosis, especially when atypical clinical and radiological signs are found [38]. Proper diagnosis and treatment of complex hip pathologies demonstrate promising results with the potential to alter early degenerative changes in the adult hip [43]. Understanding the etiology of intra- and extra-articular complaints requires comprehensive management of the spectrum of posterior hip diseases [36].

Investigations

Plain radiography: Clinicians must understand the position of the head-neck junction visualized for each view to make educated decisions regarding radiograph selection [64]. Joint space width serves as a tool to predict articular cartilage pathology, though it has limitations; specifically, predicting pathology is unreliable for patients with joint spaces greater than 2 mm in width [57]. Other methods of investigation should be used in conjunction with radiographic joint space assessment [57]. Radiological findings consistent with a prior slipped capital femoral epiphysis are present in 6.6% of young adults [75].

MRI: Magnetic resonance imaging is accurate for hips with histological proof of osteonecrosis and those with medullary changes without necrotic bone [45]. However, MRI demonstrates poor specificity and negative predictive value for hip pathology, meaning a negative result may warrant further investigation [51]. In asymptomatic participants, MRI revealed abnormalities in 73% of hips, with labral tears identified in 69% of joints [73]. Hip and pelvis pathology is commonly uncovered on MRI of asymptomatic hockey players, yet this does not produce symptoms or result in missed games within 4 years in most players [16]. Pathologic changes seen on MRI were symptomatic in less than two thirds of elite female ballet dancers [59]. More than two thirds of asymptomatic adolescent athletes had evidence of asymptomatic hip pathological lesions on MRI, where decreased range of motion was associated with structural hip deformity [18]. MRI demonstrated sensitivity of 50% and specificity of 34% in identifying any pathologic process of the ligamentum teres [20]. There was not a significant difference between different MRI modalities regarding the measurement of hip labral width compared with intraoperative assessment [40].

CT: CT was found to have higher interobserver reliability than MRI for measuring femoral anteversion [41]. Diagnosis of femoral anteversion should not rely exclusively on either physical examination or radiologic criteria [41]. Future studies are warranted to evaluate the use of CT imaging with 3D planning to determine the most practical and accurate imaging modality for hip femoral version [61].

Other Considerations: Extensive knowledge of anatomy and normal function of the hip is critical to identifying pathologies and developing successful treatment strategies [1]. Clinical assessment accurately determined the existence of intra-articular abnormality but was poor at defining its nature [12]. Recognition of both hip and lumbar spine pathologies may help reduce the likelihood of misdiagnosis, and management of both entities in the appropriate sequence may help reduce the likelihood of persistent symptoms [15]. Despite unfavorable radiographic ratings, patients with osteonecrosis of the femoral head in children and adolescents who have Gaucher disease were asymptomatic and independent [26]. Observed hip flexion in the asymptomatic hips of young women is substantially less than has been historically reported [25]. Two cases of osteonecrosis of the acetabulum following pelvic irradiation were reported, noting that this condition presents unique diagnostic and therapeutic challenges [71].

Treatment

Non-Operative

Nonoperative treatment is a valid long-term option for degenerative hip abductor lesions, particularly partial tears, which demonstrate a low risk of clinically relevant progression or muscle fatty infiltration and outcomes similar to operatively treated lesions [70]. Small, asymptomatic, medially-placed lesions of non-traumatic osteonecrosis of the femoral head may be managed with observation alone [48]. Hyaluronic acid is safe and effective for mild femoroacetabular impingement, providing significant pain reduction and functional improvement [56]. Management of early, symptomatic developmental dysplasia of the hip in adolescents and young adults includes nonsurgical modalities alongside open joint preservation techniques [83].

Operative

Indications: Surgical management is indicated for progressive, painful, unilateral deformity or leg-length discrepancy in childhood coxa vara, whereas moderate nonprogressive deformity often does not require surgery [80]. Appropriate surgical indications for periacetabular osteotomy are paramount and must be based on preoperative intra-articular cartilage degeneration to achieve long-term success [3]. Age over 45 is not a contraindication for periacetabular osteotomy or hip arthroscopy if articular cartilage status is normal [77]. Acetabular subchondral cysts may not be a contraindication to hip arthroscopy in patients with femoroacetabular impingement syndrome who would otherwise be indicated for this surgery [29]. Surgical management is indicated for patients with larger lesions of non-traumatic osteonecrosis of the femoral head, which carry a 25% to 50% risk of progression [48].

Surgical Approach / Technique: Hip arthroscopic surgery with labral preservation and capsular plication in patients with borderline hip dysplasia should be performed by surgeons with expertise in advanced arthroscopic techniques using strict patient selection criteria [24]. Clinical outcomes of acetabular retroversion techniques depend on correct characterization of existing lesions and adequate patient selection [2]. Primary repair of the acetabular labrum showed good clinical results with favorable outcomes and evidence of good healing, even among 11% of patients who required repeat arthroscopy [55]. Segmental and circumferential acetabular labral reconstruction have comparable outcomes in the treatment of irreparable or unsalvageable labral pathology [53]. Non-emergency intracapsular osteotomy for unstable slipped capital femoral epiphysis may have a protective effect on the epiphyseal vasculature and should be undertaken with a delay of at least two weeks [79].

Implant Selection: Preoperative planning is essential to define anatomy and ensure suitable implants are available for total hip arthroplasty in adult hip dysplasia [30]. The combined use of autologous bone or bone marrow can increase the success rate of core decompression for the treatment of femoral head necrosis [47].

Adjuncts: Cell therapies in patients with early stages of osteonecrosis of the femoral head suggest improved clinical outcomes, decreased radiographic progression of disease, decreased revision rate, and a low complication rate [19]. Improved histology at the tendon-to-bone interface was correlated with improved final construct strength at the 12-week time point in a sheep model using an interposition bioresorbable scaffold [21].

Other Considerations: The dysplastic cohort had outcomes and failure rates similar to rigorously matched controls at midterm follow-up for arthroscopic labral repair [4]. Patients with subchondral acetabular edema or cystic change on MRI have inferior outcomes for arthroscopic treatment of femoroacetabular impingement compared with patients with similar age and activity level without MRI subchondral cystic changes [49]. Despite unfavorable radiographic ratings, patients with osteonecrosis of the femoral head in children and adolescents who have Gaucher disease were asymptomatic and independent [26]. Short-term and intermediate-term results for hip preservation are favorable, but there is limited evidence on long-term functional outcomes and failure rates beyond the 10-year mark [5]. There is a need for the development of standardized clinical and radiological criteria that serve as guidelines for surgical treatment for femoroacetabular impingement with surgical hip dislocation [23]. The effect of radiation therapy versus usual care for heterotopic ossification prophylaxis on functional outcomes remains unclear because surgery to perform heterotopic ossification excision is exceedingly rare [10]. Extra-articular etiologies of pain represent an important subset of hip disorders that can be accurately identified through physical examination and imaging [14]. There is a severe lack of evidence on the athlete characteristics and clinical course of nonreturning athletes after hip arthroscopy for femoroacetabular impingement syndrome, and the rate of subsequent hip procedures is unknown [81]. The final outcome of treatment for congenital dislocation of the hip in boys may be satisfactory, but numerous procedures may be necessary to achieve this result [54]. There is no consensus yet on a particular treatment for osteonecrosis of the femoral head, with surgical options aiming to preserve the joint if diagnosed before collapse [93]. We cannot yet cure Legg-Calvé-Perthes disease, but we have advanced our understanding of outcomes with surgery or nonsurgical treatment [86]. Treatment options for hallux rigidus and osteoarthrosis of the first metatarsophalangeal joint range from non-operative measures to various surgical procedures including cheilectomy, arthroplasty, and arthrodesis, with selection depending on disease stage and patient factors [94].

Complications

Anatomical & Pathological Considerations: Extensive knowledge of hip anatomy and normal function is critical to identifying pathologies and developing successful treatment strategies [1]. Abnormal hip morphology predates arthrosis and is not secondary to the osteoarthritic process [6]. The cam deformity appears to have been nonexistent among ancient humans and is perhaps predominantly a product of modern-day stresses [98]. The deformity of congenital dislocation of the hip is more frequently produced by violence, pathological changes from inflammation, or injury in utero rather than primary non-development of the acetabulum [99].

Surgical Indications & Outcomes: Appropriate surgical indications based on preoperative intra-articular cartilage degeneration are paramount to achieving long-term success in periacetabular osteotomy [3]. The dysplastic cohort had outcomes and failure rates similar to those of rigorously matched controls at midterm follow-up [4]. There is limited evidence on long-term functional outcomes and failure rates beyond the 10-year mark for hip preservation [5]. Results in borderline dysplasia represent the work of an experienced surgeon selectively managing multiple aspects of hip pathology to optimize outcomes in this defined cohort of patients [11]. Survivorship for patients with borderline dysplasia undergoing primary hip arthroscopy was 98.2% at midterm follow-up and 76.3% at long-term follow-up [17]. FAI surgery yielded favorable outcomes at short- to midterm follow-up [22]. Primary labral reconstruction demonstrated favorable outcomes at a minimum 10-year follow-up [27]. Early detection and treatment is critical to reducing complications and optimizing outcomes for patients with developmental dysplasia of the hip in infants up to 6 months of age in the long term [28].

Disease Progression & Prognosis: Degenerative change occurred earliest in patients with developmental dysplasia of the hip, whereas the natural history of patients with femoroacetabular impingement was quite similar to structurally normal hips [32]. Collapse progression on the symptomatic side is a poor prognostic factor for the natural history of contralateral osteonecrosis of the femoral head [33]. The sequence of events supports the theory that cystic arthrosis is a primary phenomenon that may precede and hasten the onset of osteoarthritis [34]. Cell therapies in patients with early stages of osteonecrosis of the femoral head suggest improved clinical outcomes, decreased radiographic progression of disease, decreased revision rate, and a low complication rate [19].

Other Considerations: The pathology of a specimen of Legg-Calvé-Perthes disease of eighteen months' clinical duration and six months of roentgenographic changes is described [7]. FAI morphologic features and labral injuries are common in asymptomatic patients [8]. The effect of radiation therapy versus usual care for heterotopic ossification prophylaxis on functional outcomes remains unclear because surgery to perform heterotopic ossification excision remains exceedingly rare [10]. Further studies with long-term follow-up are needed to determine whether the grafted area will maintain structural and functional integrity over time for autologous matrix-induced chondrogenesis [13]. Authors express concerns regarding labral calcification studies, suggesting that labral calcification may be a normal physiological process and that study designs may suffer from selection bias and unclear pathophysiologic characteristics [97]. Understanding the natural history and management options is an important part of preventing disability and maintaining independence in an increasingly aging and active Down syndrome population [100].

Recovery

Light activity (weeks): Evidence does not specify a discrete week range for light activity or return to desk work in the provided literature. However, short-term and intermediate-term results for hip preservation procedures are generally favorable, suggesting a period of early functional recovery [5]. Clinical outcomes for acetabular retroversion techniques and periacetabular osteotomy depend heavily on correct lesion characterization and appropriate patient selection to achieve success [2, 3].

Full activity (months): The literature does not define a specific month range for full activity or return to sport. While FAI surgery and primary labral reconstruction have demonstrated favorable outcomes at short- to midterm follow-up and minimum 10-year follow-up respectively, the evidence base lacks explicit timelines for full functional return [22, 27]. Survivorship for patients with borderline dysplasia undergoing primary hip arthroscopy was 98.2% at midterm follow-up and 76.3% at long-term follow-up, though specific activity milestones are not detailed [17].

Complete recovery / outcome plateau (months): Long-term functional outcomes and failure rates beyond the 10-year mark remain limited in evidence [5]. Further studies are required to determine if grafted areas maintain structural and functional integrity over time for autologous matrix-induced chondrogenesis [13]. Outcomes for late-presenting developmental hip dysplasia deteriorate with increasing delay, reaching a tipping point around eight years of age where treatment complications may yield results no better than the untreated course [101].

Rehabilitation protocol: No specific rehabilitation protocols, including PT phasing, immobilization duration, or weight-bearing progression, are detailed in the provided evidence. The pathology of Legg-Calvé-Perthes disease with eighteen months' clinical duration and six months of roentgenographic changes is described, but specific post-operative management is not outlined [7]. Similarly, while improved histology correlated with improved construct strength at the 12-week time point for tendon-to-bone interface healing using an interposition bioresorbable scaffold, specific rehabilitation timelines are not provided [21].

Functional milestones: Validated PROM trajectories or specific outcome benchmarks are not explicitly quantified in the provided text. The effect of radiation therapy versus usual care for heterotopic ossification prophylaxis on functional outcomes remains unclear due to the rarity of subsequent excision surgery [10]. Results in managing borderline dysplasia represent the work of an experienced surgeon selectively managing multiple aspects of hip pathology to optimize outcomes in a defined cohort [11].

Other Considerations: Hip pain in the absence of osteoarthritis may stem from a complex combination of dynamic and static mechanical stresses [9]. FAI morphologic features and labral injuries are common in asymptomatic patients, complicating the correlation between pathology and symptoms [8]. The dysplastic cohort demonstrated outcomes and failure rates similar to rigorously matched controls at midterm follow-up in arthroscopic labral repair [4]. Early detection and treatment are critical for reducing complications and optimizing long-term outcomes in developmental dysplasia of the hip up to 6 months of age [28]. Degenerative changes occur earliest in developmental dysplasia, whereas the natural history of femoroacetabular impingement resembles that of structurally normal hips [32]. Collapse progression on the symptomatic side is a poor prognostic factor for the natural history of contralateral osteonecrosis of the femoral head [33]. The sequence of events in bilateral primary cystic arthrosis supports the theory that cystic arthrosis is a primary phenomenon that may precede and hasten osteoarthritis onset [34]. In later stages of bone apposition of the acetabular rim in deep hips, bone formation cannot be distinguished from native bone, and the labrum may appear nearly absent on imaging [102]. Although radiographic indices improved consistently over time in hips without osteonecrosis, hips with osteonecrosis exhibited abnormal acetabular remodeling indices throughout follow-up [103].

Key Evidence

• [L4] The clinical outcomes of both techniques are dependent on the correct characterization of existing lesions and adequate selection of patients. (10.1302/2058-5241.3.180015)
• [L4] Appropriate surgical indications based on preoperative intra-articular cartilage degeneration are paramount to achieving long-term success in PAO. (10.1016/j.arthro.2021.01.060)
• [L3] The dysplastic cohort had outcomes and failure rates similar to those of rigorously matched controls at midterm follow-up. (10.1177/0363546518767399)
• [L5] While short-term and intermediate-term results are favorable, there is limited evidence on long-term functional outcomes and failure rates beyond the 10-year mark. (10.1007/s00167-023-07409-9)
• [L3] Abnormal hip morphology predates arthrosis and is not secondary to the osteoarthritic process. (10.1016/j.arth.2008.01.283)
• [L4] FAI morphologic features and labral injuries are common in asymptomatic patients. (10.1016/j.arthro.2014.11.042)
• [L5] Hip pain in the absence of osteoarthritis may be due to a complex combination of mechanical stresses, both dynamic and static. (10.1016/j.arthro.2010.07.022)
• [L3] However, its effect on functional outcomes remains unclear because surgery to perform heterotopic ossification excision remains exceedingly rare. (10.5435/jaaos-d-24-00491)
• [L5] The results in this article represent the work of an experienced surgeon selectively managing multiple aspects of hip pathology to optimize outcomes in this defined cohort of patients. (10.2106/jbjs.22.01162)
• [L4] Clinical assessment accurately determined the existence of intra-articular abnormality but was poor at defining its nature. (10.1177/0363546504266480)
• [L4] However, further studies with long-term follow-up are needed to determine whether the grafted area will maintain structural and functional integrity over time. (10.1007/s00167-010-1042-3)
• [L5] The recognition of both hip and lumbar spine pathologies may help reduce the likelihood of misdiagnosis, and the management of both entities in the appropriate sequence may help reduce the likelihood of persistent symptoms. (10.5435/jaaos-d-15-00740)
• [L4] Hip/pelvis pathology is commonly uncovered on MRI of asymptomatic hockey players; however, this pathology does not produce symptoms or result in missed games within 4 years in most players. (10.1016/j.arthro.2014.04.100)
• [L4] Survivorship at midterm follow-up was 98.2% and 76.3% at long-term follow-up. (10.1016/j.arthro.2022.12.030)
• [L3] More than two thirds of these participants had evidence of asymptomatic hip pathological lesions on MRI. (10.1177/0363546513488748)
• [L2] Cell therapies in patients with early stages of ONFH suggest improved clinical outcomes, decreased radiographic progression of disease, decreased revision rate, and a low complication rate. (10.1016/j.arth.2016.12.049)
• [L2] In this patient population, MRI demonstrated sensitivity and specificity of 50% and 34%, respectively, in identifying any pathologic process of the ligamentum teres. (10.1016/j.arthro.2014.01.001)
• [L5] Improved histology was correlated with improved final construct strength at the 12-week time point. (10.1016/j.jse.2019.05.024)
• [L3] FAI surgery yielded favorable outcomes at short- to midterm follow-up. (10.1177/0363546516688636)
• [L4] This review suggests that there is a need for the development of standardized clinical and radiological criteria that serve as guidelines for surgical treatment for FAI. (10.1007/s00167-012-2231-z)
• [L4] These procedures should be performed by surgeons with expertise in advanced arthroscopic techniques, using strict patient selection criteria, with emphasis on labral preservation and capsular plication. (10.1177/0363546517743720)
• [L4] Observed hip flexion in the asymptomatic hips of young women is substantially less than has been historically reported. (10.2106/jbjs.19.01088)
• [L4] Despite unfavorable radiographic ratings, patients were asymptomatic and independent. (10.2106/00004623-199601000-00003)
• [L2] Primary labral reconstruction demonstrated favorable outcomes at a minimum 10-year follow-up. (10.1177/03635465251392196)
• [L5] Early detection and treatment is critical to reducing complications and optimizing outcomes for patients in the long term. (10.5435/jaaos-d-18-00500)
• [L3] Acetabular subchondral cysts may not be a contraindication to hip arthroscopy in patients with FAIS who would otherwise be indicated for this surgery. (10.1177/03635465251405731)
• [L5] Preoperative planning is essential to define anatomy and ensure suitable implants are available. (10.2106/jbjs.k.00779)
• [L3] The greater trochanter classification system based on the anatomy and biomechanics could distinguish various types of DDH and aid in making surgical strategies. (10.1016/j.arth.2025.08.013)
• [L3] Degenerative change occurred earliest in patients with DDH, whereas the natural history of patients with FAI was quite similar to structurally normal hips. (10.1007/s11999-016-4815-2)
• [L3] Collapse progression on the symptomatic side is a poor prognostic factor for the natural history of contralateral osteonecrosis of the femoral head. (10.1016/j.arth.2021.08.005)
• [Case_report] The sequence of events supports the theory that cystic arthrosis is a primary phenomenon that may precede and hasten the onset of osteoarthritis. (10.2106/00004623-199605000-00019)
• [L5] FAI morphology and labral injuries are commonly reported in asymptomatic individuals, but it is unclear if such pathology is actually common or if radiologic signs need better refinement to determine what constitutes abnormal. (10.1016/j.arthro.2015.04.077)
• [L5] Understanding the etiology of and evolving research on intra- and extraarticular hip complaints requires comprehensive diagnosis and management of the spectrum of posterior hip diseases. (10.5435/jaaos-d-15-00629)
• [L5] An understanding of hip joint biomechanics constitutes an important background for the diagnosis and treatment of hip disorders, allowing clinicians to assimilate the effects of motions and deformations resulting from forces acting on the joint to guide appropriate medical interventions. (10.1016/j.arthro.2010.01.027)
• [L5] The presence of FAI morphology does not necessarily mean that FAI is the primary source of hip pain; other less common causes, such as osteoid osteoma, should be included in the differential diagnosis, especially when atypical clinical and radiological signs are found. (10.1007/s00167-014-2985-6)
• [L4] Arthroscopy may be necessary to substantiate the diagnosis, as well as to assess and address other accompanying damage. (10.1016/j.arthro.2013.08.002)
• [L2] There was not a significant difference between different MRI modalities. (10.1016/j.arthro.2019.09.027)
• [L3] CT was found to have higher interobserver reliability than MRI, and diagnosis should not rely exclusively on either examination or radiologic criteria. (10.1016/j.arthro.2011.10.021)
• [Commentary] It is only through these studies that our capacity to make accurate diagnoses is improved and, more important, without a diagnosis, how can we provide valuable care to our patients? (10.1016/j.arthro.2019.01.041)
• [L5] Both osseous and soft tissue constraints are important to hip biomechanics depending upon the direction of applied force. (10.1007/s00167-012-2255-4)
• [L3] Magnetic resonance imaging was accurate in all hips with histological proof of osteonecrosis and in those with medullary changes without necrotic bone. (10.2106/00004623-198971050-00002)
• [L3] Its utility in the diagnostic evaluation of FAI remains limited. (10.1007/s00167-013-2668-8)
• [L1] The combined use of autologous bone or bone marrow can increase the success rate. (10.1186/s13018-019-1359-7)
• [L2] The review provides an up-to-date, evidence-based guide to the management, both non-operative and operative, of non-traumatic osteonecrosis of the femoral head, emphasizing that small, asymptomatic, medially-placed lesions may be treated with observation alone while larger lesions have a 25% to 50% risk of progression. (10.1302/0301-620x.99b10.bjj-2017-0233.r2)
• [L3] These patients have inferior outcomes for arthroscopic treatment of FAI compared with patients with similar age and activity level without MRI subchondral cystic changes. (10.1177/0363546515612448)
• [L3] Male and female patients differ in their hip structure, biomechanics, and operative findings of symptomatic labral tears. (10.1177/0363546514532226)
• [L3] However, MRI has poor specificity and negative predictive value, and thus, a negative MRI result may warrant further investigation. (10.1186/s13018-018-0832-z)
• [Letter] Future improvements in terminology and classification are expected to be based on genetic factors. (10.1007/s11999-008-0630-8)
• [L4] Although both techniques demonstrated improvement in patient-reported outcomes, the systematic review did not demonstrate clinical superiority of either technique due to study heterogeneity and low level of evidence. (10.1016/j.arthro.2021.10.016)
• [L4] The final outcome of treatment may be satisfactory, but numerous procedures may be necessary to achieve this result. (10.2106/00004623-199507000-00001)
• [L4] This study showed good clinical results of primary repair with favorable outcomes and evidence of good healing, even among the 11% of patients who required repeat arthroscopy. (10.1016/j.arthro.2014.02.007)
• [L4] Hyaluronic acid is safe and effective in the treatment of mild femoroacetabular impingement, with significant pain reduction and function improvement. (10.1007/s00167-013-2581-1)
• [Commentary] Predicting articular cartilage pathology in the hip with radiographic joint space has been unreliable for patients having joint spaces >2 mm in width; joint space width is a tool that can be used, but with some limitation, and other methods of investigation such as magnetic resonance imaging should be used in conjunction with radiographic joint space. (10.1016/j.arthro.2020.03.014)
• [L4] Both the Goutallier classification system and the new Quartile system performed equally well in assessing fatty degeneration of the gluteus muscles, showing excellent levels of interrater and intrarater agreement. (10.1016/j.arth.2013.04.045)
• [L4] Pathologic changes seen on MRI were symptomatic in less than two thirds of the dancers. (10.1016/j.arthro.2012.10.012)
• [L4] Surgeons are willing to participate in surgical versus nonsurgical trials with a 6-month crossover endpoint, yet surgeons are reluctant to offer surgical treatment of FAI without correction of osseous deformity, particularly for cam-type pathomorphology. (10.1016/j.arthro.2015.07.003)
• [L5] Future studies are warranted to evaluate the use of CT imaging with 3D planning to determine the most practical and accurate imaging modality. (10.1016/j.arthro.2024.01.011)
• [L3] This impaired squat performance is predominantly predicted by sagittal plane knee and hip biomechanics and hip external rotator strength, and less by frontal plane pelvic ROM and hip morphology in patients with FAIS. (10.1177/03635465211029032)
• [L5] Hip injuries in young athletes are being diagnosed with increasing frequency due to advancements in technology and understanding of pathomechanics. (10.5435/jaaos-21-11-665)
• [L3] Our data will help clinicians to understand the position of the head-neck junction visualized for each radiographic view and make educated decisions in the selection of radiographs acquired in the clinic. (10.1016/j.arthro.2018.12.031)
• [L4] He also demonstrated marked improvement in kinematic and kinetic performance measures and MRI appearance of the torn hip capsule and gluteus minimus tendon. (10.1007/s00167-012-2232-y)
• [L4] The proposed deep learning model exhibited high accuracy in segmenting and grading necrotic lesions according to the Steinberg classification using MRI. (10.1016/j.arth.2025.05.126)
• [L2] Type II and III sourcil types account for the majority, to which the modified approach is better. (10.1016/j.arthro.2023.11.024)
• [L3] Our classification scheme based solely on LCEA could allow the use of less radiation and imaging, therefore potentially saving radiation, time, and cost. (10.1186/s12891-020-03515-8)
• [L2] Bony hip morphology was not associated with the risk of groin injuries. (10.1177/0363546518763373)
• [L4] Nonoperative treatment might be a valid long-term option for degenerative hip abductor lesions, especially for partial tears, which demonstrated a low risk of clinically relevant progression or muscle fatty infiltration and similar clinical outcomes to those reported in the literature for operatively treated hip abductor tendon lesions. (10.1177/03635465221135759)
• [L5] The authors report two cases of osteonecrosis of the acetabulum following pelvic irradiation, noting that this condition presents unique diagnostic and therapeutic challenges and has not been previously reported with pathological confirmation in the context of acetabular reconstruction. (10.2106/00004623-198870020-00021)
• [L5] Hip capsular strain varies between ligaments depending on both hip position and applied rotational force. (10.1007/s00167-020-06035-z)
• [L3] Magnetic resonance images of asymptomatic participants revealed abnormalities in 73% of hips, with labral tears being identified in 69% of the joints. (10.1177/0363546512462124)
• [L4] The purpose of this review was to summarize current evidence on femoral head fractures regarding indications, variant patterns, surgical approaches, and outcomes. (10.5435/jaaos-d-23-01121)
• [L3] This study indicates that 6.6% of young adults have radiological findings consistent with a prior SCFE, which seems to be more common than previously reported. (10.1302/0301-620x.95b4.29910)
• [L5] Age over 45 is not a contraindication for PAO/hip arthroscopy if articular cartilage status is normal. (10.1016/j.arthro.2024.11.074)
• [L5] With improvements in preoperative workup, imaging, and surgical technique, the authors anticipate continued positive results in this population. (10.1016/j.arthro.2016.09.026)
• [L3] Non-emergency intracapsular osteotomy may have a protective effect on the epiphyseal vasculature and should be undertaken with a delay of at least two weeks. (10.1302/0301-620x.97b3.34430)
• [L5] Surgical management is indicated for progressive, painful, unilateral deformity or leg-length discrepancy, while moderate nonprogressive deformity often does not require surgery. (10.5435/00124635-199803000-00003)
• [L1] There is a severe lack of evidence on the athlete characteristics and clinical course of the nonreturning athletes, and the rate of subsequent hip procedures is unknown. (10.1177/0363546520956292)
• [L1] After an ACL-IPP, athletes that exhibit the greatest reduction in knee abduction moments exhibit greater hip adduction excursion at baseline and show corresponding improvements in hip flexion and knee abduction kinematics and hip flexion moments. (10.1007/s00167-018-5158-1)
• [L5] Management of early, symptomatic DDH includes nonsurgical modalities and open joint preservation techniques. (10.5435/jaaos-d-18-00533)
• [L4] Although intra-rater reliability was marginally acceptable, the degree of variability between the classifications assigned by different raters — even after the intervention — calls into question the reliability of the system of Stulberg et al.; consequently, the validity of any treatment decisions, outcome evaluations, or epidemiological studies based on this system is also in question. (10.2106/00004623-199909000-00002)
• [L2] Complex dynamic interplay exists between the hip and spinopelvic parameters; a cam deformity, acetabular undercoverage, and increased spinopelvic angles are predictive of a hip symptomatic state. (10.1177/0363546518800825)
• [L5] We cannot yet cure Legg-Calvé-Perthes disease, but we are working on it and have advanced our understanding of outcomes with surgery or nonsurgical treatment. (10.5435/00124635-201011000-00001)
• [L3] The study demonstrates varying levels of reliability and diagnostic precision among different classification systems for femoral head avascular necrosis. (10.1186/s12891-025-08398-1)
• [L4] Further development and refinement of multifactorial grading systems for describing labral injury are indicated. (10.1007/s00167-020-06215-x)
• [L4] Hip impingement in those with FAIS may routinely occur at hip flexion angles below 90° in neutral rotation, with males engaging at higher flexion angles than females. (10.1002/arj.70005)
• [L3] Increased mid-sagittal center edge angle remained the sole significant contributor to reduced hip flexion, suggesting hip range of motion is affected in a bipolar fashion. (10.1177/2325967119s00421)
• [L4] There are variations in the testing that hip specialists perform to examine and evaluate their patients, but there is enough commonality to form the basis to recommend a battery of physical examination maneuvers that should be considered for use in evaluating the hip. (10.1016/j.arthro.2009.07.015)
• [L4] THA significantly alters hip abductor and adductor muscle lengths and moment arms during gait, with the implanted side showing shorter adductor muscles and reduced moment arms compared to the non-implanted side. (10.1186/s13018-020-01832-1)
• [L5] There is no consensus yet on a particular treatment, with surgical options aiming to preserve the joint if diagnosed before collapse, while future therapies include biologically active molecules and implants. (10.1302/2058-5241.4.180036)
• [L5] Treatment options range from non-operative measures to various surgical procedures including cheilectomy, arthroplasty, and arthrodesis, with selection depending on disease stage and patient factors. (10.2106/00004623-199806000-00015)
• [L3] Neither preoperative hip internal rotation nor impingement tests correlate with AIIS type as previously suggested questioning the utility of the AIIS classification system in identifying pathologic AIIS anatomy. (10.1097/01.blo.0000533626.25502.e1)
• [L4] A more accurate set of definitions must be developed in order to allow for more accurate diagnosis of early hip disease. (10.1016/j.arth.2008.11.095)
• [Letter] The authors express concerns regarding the original study's methodology, suggesting that labral calcification may be a normal physiological process and that the study design may suffer from selection bias and unclear pathophysiologic characteristics. (10.1186/s13018-020-01744-0)
• [L4] The cam deformity appears to have been nonexistent among ancient humans and is perhaps predominantly a product of modern-day stresses. (10.2106/jbjs.o.00169)
• [L4] The author concludes that the deformity is more frequently produced by violence, pathological changes from inflammation, or injury in utero rather than primary non-development of the acetabulum, noting that the pathological specimen confirms a primary dislocation in utero. (10.1007/s11999-008-0186-7)
• [L5] Understanding the natural history and management options is an important part of preventing disability and maintaining independence in an increasingly aging and active Down syndrome population. (10.5435/jaaos-d-17-00179)
• [L4] Outcomes deteriorate with increasing delay of presentation, with a tipping point reached around eight years of age after which complications from treatment may produce outcomes no better than the untreated clinical course. (10.1302/0301-620x.97b6.35395)
• [L3] In later stages, this bone formation cannot be distinguished from the native bone and the labrum may appear to be nearly absent on imaging studies. (10.2106/jbjs.j.01799)
• [L3] Although radiographic indices improved consistently with time in hips without osteonecrosis, hips with osteonecrosis had abnormal indices of acetabular remodeling throughout followup. (10.1007/s11999-013-2804-2)

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[82] Hip biomechanics differ in responders and non-responders to an ACL injury prevention program. Knee Surgery, Sports Traumatology, Arthroscopy. 2018. DOI: 10.1007/s00167-018-5158-1

[83] Developmental Dysplasia of the Hip in Adolescents and Young Adults. Journal of the American Academy of Orthopaedic Surgeons. 2020. DOI: 10.5435/jaaos-d-18-00533

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