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Hip dysplasia (adult)

143 citationsUpdated Sep 2026

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Overview

Developmental dysplasia of the hip (DDH) encompasses a spectrum of pathologic conditions involving the developing hip, ranging from acetabular dysplasia to complete dislocation [51]. In symptomatic adult patients, deficient anterolateral acetabular coverage of the femoral head is the dominant deformity, resulting in structural hip instability and acetabular rim overload [86]. This condition frequently leads to secondary hip osteoarthritis in adult life, particularly when significant childhood deformities such as the "pistol grip" deformity of the proximal femur are present [7]. Female patients with symptomatic hip dysplasia generally present with acetabular labral tears and rim cartilage lesions [86]. If left untreated, hip dysplasia can result in severe deformities and functional limitations [3].

The long-term prognosis for the symptomatic hip with moderate dysplasia (lateral center-edge angle <15°) treated nonsurgically is very poor [86]. Early diagnosis and treatment are of paramount importance to favorably alter the natural history of the disease [6]. Hip dysplasia is best treated before 5 years of age, and surgery should not be performed unnecessarily [1]. In skeletally mature patients, a reconstructive acetabular osteotomy is the treatment of choice for symptomatic adult hip dysplasia with deficient acetabular coverage [86]. The goal of hip preservation surgery is to alter hip joint morphology to allow more unhindered physiologic range of motion while optimizing hip joint mechanics to delay or halt the progression of hip osteoarthritis [7]. These factors argue for early intervention in both hip dysplasia and hip impingement before the onset of irreversible arthritis [7].

Total hip arthroplasty is the procedure of choice for most patients with symptomatic end-stage coxarthrosis secondary to hip dysplasia, demonstrating a high rate of pain relief and functional improvement [156]. Patients with hip dysplasia can expect reduced pain, improved functional outcomes, and similar revision surgery rates to those with osteoarthritis following primary total hip arthroplasty [23]. Periacetabular osteotomy appears to be effective in delaying prosthetic hip reconstruction when the surgical intervention occurs while the arthritic progression is fairly mild [7]. However, the results of periacetabular osteotomy in patients with more advanced arthritis have been less favorable [7].

Anatomy & Pathophysiology

Definition and Spectrum

Developmental dysplasia of the hip (DDH) is a spectrum of pathologic conditions involving the developing hip, ranging from acetabular dysplasia to complete dislocation [51]. It represents a broad spectrum of disease affecting the femoral head, the acetabulum, or both, ranging from physiologic immaturity of the hip to frank dislocation [15]. The condition is characterized by a developmental anomalous anatomical relationship between the femoral head and the acetabulum [47]. A spectrum of abnormalities may be present including joint instability, ligamentous laxity, acetabular dysplasia, excessive femoral anteversion, hip subluxation, and complete dislocation [47]. Teratologic dislocation of the hip occurs in utero and is irreducible on neonatal examination [51]. Teratologic dislocation is usually accompanied by a pseudoacetabulum [51]. Teratologic dislocation always accompanies other congenital anomalies or neuromuscular conditions, most often arthrogryposis and myelomeningocele [51].

Etiology and Risk Factors

Family history, ethnicity, ligamentous laxity, intrauterine positioning, and postnatal positioning are considered risk factors for DDH [47]. Female sex, firstborn child status, and breech presentation are risk factors for DDH [51]. Disorders of intrauterine packing phenomenon, such as congenital dislocation of the knee, congenital muscular torticollis, and metatarsus adductus, are risk factors for DDH [51]. In affected children, 12% to 33% have a family history of DDH [51]. The risk of DDH is 6% with one affected sibling, 12% with one affected parent, and 36% with a parent and sibling affected [51]. Adequate growth and development of the hip depends on concentric positioning of the femoral head into the acetabular cavity and adequate balance in growth between triradiate and acetabular cartilage [277]. Any alteration in concentric positioning or growth balance leads to hip dysplasia [277]. Most changes that lead to DDH appear in the last months of intrauterine life, as there was no incidence of hip dysplasia among fetuses aborted below 20 weeks of gestation [277]. The mechanical theory suggests that persistent mechanical stimulation can provoke deformity, particularly in periods of high growth [277]. Oligohydramnios, macrosomy, or breech presentation with extended knees are risk factors based on the mechanical theory [277]. The left side is more commonly affected in non-breech newborns [277].

Epidemiology

DDH is one of the most common abnormal conditions present at birth, affecting up to 15% of infants based on ultrasonographic findings [15]. Approximately 5 in 1,000 newborns are ultimately treated for neonatal hip dysplasia [15]. Large cross-sectional studies report the prevalence of hip dysplasia in the adult population is between 3% and 5% [15]. DDH is the most common disorder of the hip in children [51]. One in 1,000 children (0.1%) is born with a dislocated hip [51]. 10 in 1,000 children (1%) are born with hip subluxation or dysplasia [51]. Eighty percent of affected children are female [51]. The left hip is more commonly involved (60%) than the right [51]. Bilateral involvement occurs in 20% of cases [51]. The condition is more common in Native Americans and people of northern Finnish descent [51]. DDH is rarely seen in African Americans [51]. DDH occurs in approximately 1 in 1,000 live births in whites [78].

Normal Hip Anatomy and Biomechanics

The hip is a multiaxial joint formed by the articulation between the pelvis and femur, which connects the axial skeleton and the lower extremity [107]. The hemipelvis comprises three bones: the ilium, ischium, and pubis, which unite at the triradiate cartilage within the concave acetabulum [107]. The shape and depth of the acetabulum are formed by the appearance of ossification centers around the end of the first decade of life, with complete fusion occurring around 18 to 19 years of age [107]. The acetabulum comprises an articular crescent-moon-shaped lunate surface and a nonarticular central fossa that serves as the attachment point for the ligamentum teres [107]. The acetabulum is incomplete inferiorly, forming a notch through which vital blood vessels and nerves pass to supply the joint [107]. The acetabular labrum is a fibrocartilaginous ring attached to the rim of the acetabulum that extends the articulating surface area and increases femoral head coverage [107]. The labrum is triangular in cross section, which contributes to its ability to create a pressurized seal of the central compartment of the hip during loading [107]. Only the external one-third of the labrum contains blood vessels, leaving the majority of the structure avascular and limiting its healing ability following injury [107]. The labrum is highly innervated, with the presence of both mechanoreceptors and nociceptors [107]. The labrum is absent in the area of the inferior acetabular notch, where the transverse acetabular ligament serves as the continuation of the labrum [107]. The femoral head forms two-thirds of a sphere, with a small depression at its center from which the ligamentum teres extends to connect to the acetabular notch [107]. The neck-shaft angle averages 125°, which allows for greater mobility by placing the head and neck more perpendicular to the acetabulum in a neutral position [107]. Normal version, the head-neck angle in the frontal plane, averages 15 to 20° [107]. The angular projection of the femoral head and neck in relation to the obliquely placed acetabulum allows for rotary movements at the hip and prevents impingement [107].

The hip is surrounded by a dense fibrous capsule extending from the periphery of the acetabulum to the intertrochanteric line of the femoral neck [107]. The capsule enhances joint stability by preventing translation of the femoral head in the acetabulum [107]. The Y-shaped iliofemoral ligament is the thickest and strongest of the three main ligaments supporting the hip [107]. The iliofemoral ligament functions to limit external rotation, while its lateral arm limits extension of the joint [107]. The ischiofemoral ligament provides support posteriorly and restricts internal rotation motion [107]. The pubofemoral ligament acts to limit abduction of the joint [107]. Deep fibers from all three ligaments merge to form the zona orbicularis, which circumvents the femoral neck [107]. The hip is a ball-and-socket diarthrodial joint where stability is based primarily on the bony architecture [104]. The fibrocartilaginous labrum deepens the acetabulum, enhancing stability [104]. Labral functions include load transmission, maintenance of vacuum seal, regulation of synovial fluid hydrodynamics, and joint lubrication [104]. The hip joint capsule extends anteriorly to the intertrochanteric crest but posteriorly only partially across the femoral neck [104]. The basicervical and intertrochanteric crest regions are extracapsular [104]. The iliofemoral ligament (Y ligament of Bigelow) is the strongest ligament in the body and attaches the AIIS to the intertrochanteric line in an inverted Y manner [104]. The ischiofemoral and pubofemoral ligaments are weaker but provide additional stability [104]. The capsule is tight in extension and internal rotation, and relaxed in flexion and external rotation [104]. The ligamentum teres arises from the apex of the cotyloid notch and attaches to the fovea of the femoral head [104]. The ligamentum teres transmits an arterial branch of the posterior division of the obturator artery to the femoral head, which is less significant in adults [104].

The average range of motion of a normal hip is approximately 120° of flexion, 30° of extension, 45° of abduction, 20° to 30° of adduction, 35° of internal rotation, and 45° of external rotation [115]. Normal gait function requires hip flexion of 30°, hyperextension of 10°, abduction and adduction of 5°, and internal and external rotation of 5° [115]. The mean femoral neck-shaft angle in the adult is 130° ± 7° [119]. The mean anteversion of the neck is 10° ± 7° [119].

Pathophysiology of Dysplasia

The normal development of the acetabulum depends on the concentric centralization of the femoral head into the acetabular cavity, with the presence of articular motion [47]. Minimal femoral head displacement from the center of the acetabular cavity may predispose to abnormal acetabular development and further instability [47]. The natural history of DDH presents via three evolutional courses: spontaneous resolution, progression to subluxation or dislocation, or subclinical instability with persistent acetabular dysplasia [47]. It is unclear whether acetabular dysplasia diagnosed during adolescence or later is a residual deformity of childhood DDH or a distinct acetabular growth abnormality with later presentation [47]. Late dysplasia is more likely to be bilateral [47]. DDH is a gradually progressive disorder associated with distinct anatomic changes, many of which are initially reversible [113]. At birth, the affected hip will spontaneously slide into and out of the acetabulum [113]. For spontaneous sliding to occur, the posterosuperior rim of the acetabulum has to have lost its sharp margin and become flattened and thickened in the area over which the femoral head slides [113]. A ridge of thickened articular cartilage called the neolimbus arises along the posterosuperior acetabular wall as the head rides in and out of the socket [113]. The neolimbus is the structure that produces the "clunk" felt as the head slides over it [113].

In hips that remain dislocated, secondary barriers to reduction develop [113]. The fatty tissue known as the pulvinar thickens in the depths of the acetabulum and may impede reduction [113]. The ligamentum teres elongates and thickens, taking up valuable space within the acetabulum [113]. The transverse acetabular ligament is often hypertrophic and may impede reduction [113]. The inferior capsule of the hip assumes an hourglass shape, eventually presenting an opening that is smaller in diameter than the femoral head [113]. The iliopsoas muscle, pulled tight across the capsular isthmus, contributes to the narrowing of the acetabular orifice [113]. The capsule narrows through a "Chinese finger-trap" mechanism [113]. Femoral changes in dislocated hips include an increase in anteversion and some flattening of the femoral head as it lies against the ilium [113]. When attempting to reduce the hip against the narrowed capsule, the femoral head abuts the cartilaginous acetabular lip and tends to push this rim into the acetabulum [113]. The constricted hip capsule forces the head against the acetabular rim, and the capsule must be released or stretched to allow the head to move beneath the acetabular rim and enter the acetabulum [113]. The blocking structure encountered in patients with DDH is not only the labrum but also a significant portion of the cartilaginous acetabulum itself [113]. The cartilaginous acetabular anlage is essential for the normal growth and development of the acetabulum and should not be excised [113]. After reduction, the acetabular rim may still impede the deep seating of the femoral head because the rim has become thicker than normal [113].

In the subluxated hip, asymmetric pressure causes progressive flattening of the posterior and superior acetabular rim and medial femoral head [78]. In the completely dislocated hip, dysplasia occurs because normal joint development requires concentric motion with normally mated joint surfaces [78]. The shallow, deformed dysplastic joint surfaces predispose to further mechanical instability and the inexorable progression of the disorder [78]. Displacement of the femoral head in the infant is proximal (posterior and superior) because of the pull of the gluteal and hip flexor muscles [78]. The neonatal hip is a relatively unstable joint because the muscle is undeveloped, the soft cartilaginous surfaces are easily deformed, and the ligaments are lax [78]. Exaggerated positioning in acute flexion and adduction in utero may occur, especially in breech presentation [78]. This positioning may cause excess stretching of the posterior hip capsule, which renders the joint unstable after delivery [78]. Laxity may reflect family history or the presence of maternal relaxin hormone in the fetal circulatory system [78].

Adult Hip Dysplasia and Osteoarthritis

More subtle deformity of the hip has been implicated in the development of osteoarthritis in patients who previously were thought to have "primary osteoarthritis" of the hip [7]. Many patients who would formerly have been thought to fall within the primary osteoarthritis group are now believed to have had hip impingement leading to osteoarthritis over time [7]. As early as 1965, Murray described the subtle "tilt deformity" of the proximal femur that he believed would lead to osteoarthritis [7]. In 1975, Stulberg et al. coined the term "pistol grip" deformity of the proximal femur [7]. In the mid-1990s, Ganz et al. refined the description of hip impingement caused by femoral and acetabular deformity [7]. The articular damage resulting from hip impingement can occur while symptoms remain relatively mild and intermittent [7]. The goal of hip preservation surgery in both dysplasia and impingement is to alter the hip joint morphology to allow more unhindered physiologic range of motion while optimizing hip joint mechanics to delay or halt the progression of hip osteoarthritis [7].

Hip dysplasia is characterized by a shallow acetabulum with deficient coverage of the femoral head [162]. If undiagnosed or untreated, dysplasia can persist after the closure of the triradiate cartilage [162]. Adult dysplasia frequently leads to pain, functional limitations, and early osteoarthritis, as early as the third or fourth decade of life [162]. Premature joint degeneration in dysplasia is a result of significantly altered mechanics resulting from a shallow, more vertical acetabulum [162]. These altered mechanics lead to increased edge loading, decreased contact areas, and increased contact pressures [162]. The dysplastic hip is inherently unstable [162]. Adaptive changes in the dysplastic hip include labral and iliocapsularis muscle hypertrophy, and abductor fatigue in an attempt to stabilize the femoral head within the acetabulum [162]. Despite these adaptations, instability and excessive stress on the articular cartilage ultimately lead to osteoarthritis if left untreated [162].

DDH results in decreased anterolateral acetabular coverage of the femoral head [74]. The hip center is lateralized in DDH [74]. Eccentric joint loading in DDH can result in progressive joint degeneration [74]. The proximal femur is often involved in DDH, with asphericity of the femoral head, head-neck offset malformations, and increased femoral anteversion potentially present [74]. Acetabular dysplasia describes a shallow hip socket without frank dislocation of the femoral head but with varied degrees of superior lateral subluxation of the femoral head [148]. The shallow hip socket in acetabular dysplasia results in high articular cartilage contact stresses near the superolateral rim of the acetabulum [148]. Concurrent labral tears and progressive lateral subluxation of the femoral head occur in acetabular dysplasia, known as the acetabular rim syndrome [148]. Patients with acetabular dysplasia may present with groin pain or abductor muscle fatigue [148].

Classification

Radiographic Parameters and Thresholds

The lateral center-edge angle (LCEA) of Wiberg reflects lateral acetabular coverage and is measured on the AP radiograph as the angle subtended between a vertical line and a line from the center of the femoral head to the lateral border of the sourcil [255]. Normal LCEA values are greater than 25° [255], with angles between 20° and 40° considered normal and 20° to 25° considered borderline [20]. A CE angle ≤ 20° is mostly considered dysplastic, whereas a CE angle between 20° and 25° is considered borderline, and a CE angle > 25° is considered normal [208]. Hip dysplasia was classified when the LCEA was < 25° or the Tönnis angle was > 10° [40]. The anterior center-edge angle reflects anterior acetabular coverage and is measured on the false-profile view as the angle formed between a vertical line and a line from the center of the femoral head to the anterior border of the sourcil [255]. A normal anterior center-edge angle value is greater than 20° [255].

The Tönnis angle reflects acetabular inclination and is determined from an AP radiograph as the angle formed between a horizontal line connecting the radiographic teardrops and a line connecting the medial and lateral edges of the sourcil [255]. A normal Tönnis angle value is less than 10° [255], with angles between 0° and 10° considered normal [20]. The femoral head extrusion index is defined by the length of the femoral head that lies beyond the acetabulum as a percentage of the total horizontal width of the femoral head [20]. Values greater than 25% are considered abnormal [20]. Radiographs underestimate lateral center-edge angle and Tönnis angle measurements compared to computed tomography scans in the assessment of borderline and frank acetabular dysplasia [40]. An isolated assessment of the LCEA is an oversimplistic approach that may jeopardize appropriate classification and may provide insufficient data to guide the treatment of hips with additional features of dysplasia and instability [90].

Adult Classification Systems

Crowe: This classification uses the proportion of subluxation to divide disease severity into four classes [208]. Grade 1 corresponds to subluxation < 50% [208]. Grade 2 corresponds to subluxation between 50 and < 75% [208]. Grade 3 corresponds to subluxation between 75 and 100% [208]. Grade 4 corresponds to total luxation [208].

Hartofilakidis: This system categorizes dysplastic hips into three classes by considering the deformation of the acetabulum in addition to the degree of subluxation [208]. A dysplastic hip is defined as one where the femoral head is contained within the original acetabulum despite the degree of subluxation [208]. Low dislocation is defined as the femoral head articulating with a false acetabulum that partially covers the true acetabulum to a varying degree [208]. The system describes three types of developmental hip dysplasia (dysplasia, low dislocation, and high dislocation) to guide surgical management by anticipating implant type and the need for augmentation [111].

Instability-Based Frameworks: A diagnostic framework groups symptomatic dysplastic hips into one of 3 categories based on the primary direction of instability: anterior, posterior, and global [32]. Classifying acetabular dysplasia into 3 groups based on the plane of instability could optimize the planning of periacetabular osteotomy by giving a better understanding of the 3-dimensional deformity [171]. Three distinct morphologic subtypes of acetabular deficiency are common in young adult patients with acetabular dysplasia [166]. Recognition of distinct morphologic subtypes of acetabular deficiency is important for diagnostic and surgical treatment considerations to optimize acetabular correction and avoid femoroacetabular impingement [166]. Both the Crowe and Hartofilakidis classification systems assess different aspects of developmental dysplasia of the hip in adults [27]. The authors argue that current classification of borderline hip dysplasia based solely on lateral center edge angle is insufficient and that the focus must shift to assessing hip instability to better predict treatment outcomes and the need for bony realignment [164].

Pediatric and Infant Classification Systems

Tönnis: This system classifies displacement of the femoral head according to the level of the ossific nucleus relative to the lateral margin of the acetabulum [255]. Lesser Tönnis grades of dysplasia correlate with an improved prognosis for satisfactory long-term outcomes [255]. Each increase in the Tönnis grade at the time of diagnosis doubles the likelihood of failure of nonsurgical treatment [255].

International Hip Dysplasia Institute: This classification system bases the severity of subluxation on the position of the center of the metaphysis relative to a horizontal line connecting the two TRCs (Hilgenreiner line) and a vertical line at the lateral border of the ossified acetabulum (Perkin line) [255]. It has been demonstrated to be both reliable and prognostic for success of closed reduction and need for late pelvic osteotomy [255]. Grade I is defined as the H-point being at or medial to the P-line [255]. Grade II is defined as the H-point being lateral to the P-line and at or medial to the D-line [255]. Grade III is defined as the H-point being lateral to the D-line and at or inferior to the H-line [255]. Grade IV is defined as the H-point being superior to the H-line [255].

Graf: This hip classification includes types I, IIa, IIc, D, III, and IV [228]. Type I is described as a mature hip [228]. Type IIa is described as a dysplastic hip [228]. Type IIc is described as a heavily dysplastic hip [228]. Types D, III, and IV are described as decentered hips [228].

Bucholz and Ogden: This classification system is based on morphologic changes in the capital femoral epiphysis, the physis, and the proximal femoral metaphysis [26]. The Bucholz-Ogden system is the most widely used classification system for avascular necrosis [266]. Type I AVN changes are limited to the femoral head, and the metaphysis is not involved [266]. Type II AVN involves lateral epiphyseal closure which produces a valgus deformity of the head on the neck of the femur [266].

Kalamchi and MacEwen: This classification system is based on morphologic changes in the capital femoral epiphysis, the physis, and the proximal femoral metaphysis [26]. A simplification of the Kalamchi and MacEwen classification scheme has been proposed that combines groups II, III, and IV into a single group B [26]. Kalamchi-MacEwen grade 1 is the same as Bucholz-Ogden type I [266]. Kalamchi-MacEwen grade 2 is the same as Bucholz-Ogden type II [266]. Kalamchi-MacEwen grade 4 is the same as Bucholz-Ogden type III [266].

Ogata et al.: This classification system is a reliable and reproducible radiological indicator for reflecting acetabular cover [172].

Acetabular Index: This measure of the inclination of the ossified acetabulum is determined by the angle formed between a horizontal line connecting the TRCs and a line drawn from the iliac margin at the upper edge of the TRC to the most lateral edge of the ossified acetabulum [255]. The acetabular index progressively decreases with age but will remain abnormally high in a dysplastic hip [255].

Associated Morphologic Features

40% of patients with acetabular dysplasia also had radiographic evidence of cam-type femoroacetabular deformity [21]. The morphology of the anterior inferior iliac spine (AIIS) in patients with acetabular dysplasia is commonly prominent, with 72% of hips having Type II or Type III morphologies [163]. In developmental dysplasia of the hip, AIIS type 3 tends to be more severe dysplasia than AIIS type 1 or 2 [187]. The morphologic features of the AIIS in hip dysplasia may differ between males and females [48]. Patients with acetabular dysplasia have an increased frequency of spinal anomalies seen on standard hip radiographs [39]. Hip dysplasia is a pathoanatomic osseous morphology associated with hip instability that may, in part, be due to hip capsular thickness [19].

Imaging and Diagnostic Methods

Conventional radiographs remain critical in the initial imaging evaluation of the hip [20]. A complete hip series usually is composed of a combination of views, including an anterior-posterior (AP) pelvis, a centered AP hip, a lateral view (frog-leg, cross-table, Dunn 45° or 90°), and a false-profile (Lequesne) view [20]. The Dunn 45° view may be more accurate for determining the alpha angle measurement than CT or MRI [20]. The artificial intelligence model measurements demonstrate a high degree of consistency with manual measurements and exhibit robust diagnostic performance in identifying developmental dysplasia of the hip and borderline developmental dysplasia of the hip [175]. Ultrasonographic classification of hip dysplasia uses Angle α formed by the intersection of the baseline and the acetabular roofline, which is normally greater than 60 degrees [72]. Ultrasonographic classification of hip dysplasia uses Angle β formed by the intersection of the baseline and the inclination line, which is normally less than 55 degrees [72].

Clinical Presentation

General Presentation and Natural History

Hip dysplasia is characterized by a shallow acetabulum with inadequate coverage of the femoral head, resulting in abnormal contact mechanics that cause accelerated degeneration of the articular surface at an early age [71]. Subclinical instability may be present without obvious signs or symptoms, and acetabular dysplasia may persist beyond childhood if not diagnosed correctly [47]. In adults with fully dislocated hips, the femoral head may lie well above the acetabular margin in a markedly thickened hip capsule, a condition described as "high-riding dislocation" [190]. In these cases, the femoral head is oval and flattened medially, while the acetabulum is filled with fibrous tissue, hypertrophied ligamentum teres, and a thickened transverse acetabular ligament [190]. The articular cartilage in adult dislocated hips is either atrophic or absent [190]. Muscles that insert at the proximal femur in adult dislocated hips are foreshortened and more horizontally oriented [190]. Fully dislocated adult hips may remain free from degenerative changes for many years, even for the individual's lifetime [190].

Adolescent and Adult Symptoms

The diagnosis of developmental dysplasia of the hip should be suspected and investigated when a skeletally mature, young, active patient has a predominant complaint of insidious activity-related groin pain and/or lateral hip pain [58]. Lateral hip pain is most often the initial symptom in adolescent hip dysplasia, occurring later in the day as fatigue develops due to altered biomechanics leading to a greater force required to maintain normal walking [83]. Deep anterior groin pain generally indicates pain originating from the joint itself and can occur from joint overload, edge-loading of the acetabulum, labral irritation or injury, or labral chondral injury [83]. Deep groin pain in adolescent hip dysplasia occurs later than lateral hip pain, is reported to be more common, is activity-related, and improves when activity restriction is instituted [83]. Patients with late-presenting acetabular dysplasia complain of aching pain that is worse with exertion and long periods of walking or standing, which may result in a decrease in activity [204]. Symptoms in late-presenting acetabular dysplasia usually increase steadily in frequency and severity over a relatively short time after onset [204]. Patients with late-presenting acetabular dysplasia may limp when tired or uncomfortable [204]. A careful history regarding the presence and location of symptoms is critically important when radiographic dysplasia is seen to help develop the ideal treatment plan [83]. Patients may have radiographic dysplasia without associated pain or discomfort [83].

Physical Examination Findings

The physical examination for adolescent hip dysplasia should include observation of ambulation to assess for an antalgic gait and/or a subtle Trendelenburg gait [83]. A Trendelenburg gait involves centering body weight over the hip as a protective mechanism to avoid pain or to offset relatively weak abductors [83]. Physical findings in late-presenting acetabular dysplasia are usually minimal [204]. Some patients with late-presenting acetabular dysplasia have a Trendelenburg limp or a delayed Trendelenburg sign [204]. Discomfort at the extremes of hip motion may be present in late-presenting acetabular dysplasia [204]. Signs of snapping or popping in late-presenting acetabular dysplasia may be caused by a tear in the labrum [204]. Degeneration of the labrum is commonly present in late-presenting acetabular dysplasia as a result of overload from deficient bony acetabular coverage [204]. Hip range of motion should be examined for restriction in motion and to determine relative femoral version in adolescent hip dysplasia [83]. Pain in late-presenting acetabular dysplasia is exacerbated when the hip is maximally flexed, internally rotated, and adducted (the impingement test) [204]. The impingement test, which assesses pain with flexion, internal rotation, and adduction, should be performed to determine the likelihood of true symptomatic labral pathology [83].

In walking patients with dislocated hips, an obvious limping with abductor insufficiency is present, or the patient toe walks on the side of the dislocated hip [191]. In a child of walking age with an undetected dislocated hip, families describe a "waddling" type of gait indicating dislocation of the femoral head and a Trendelenburg gait pattern [200]. Parents of children with undetected dislocated hips may describe difficulty in abducting the hip during diaper changes [200]. Asymmetric skin folds are commonly mentioned as a sign of DDH but are not always reliable because normal children may have asymmetric skin folds and children with dislocated hips may have symmetric folds [200]. The Galeazzi sign is noted when the femoral head becomes displaced laterally and proximally, causing an apparent shortening of the femur on the side of the dislocated hip [200]. Bilateral dislocations may appear symmetrically abnormal on physical examination [200]. Other clinical findings associated with DDH include asymmetric gluteal folds, Trendelenburg stance in older children, increased lumbar lordosis, and pelvic obliquity [169]. In toddlers with bilateral hip dislocations, hyperlordosis of the lumbar spine is often present [51]. Adolescents with hip dysplasia may manifest fatigue and pain in the hip, thigh, or knee in addition to other signs and symptoms [51].

Associated Pathology and Comorbidities

Proximal femoral deformities are highly prevalent in symptomatic acetabular dysplasia, with 92.6% of hips showing abnormalities [33]. There are sex-dependent, disease characteristic differences in patients with symptomatic acetabular dysplasia, with male patients showing a greater prevalence of findings consistent with concurrent FAI and instability [102]. The morphologic features of the anterior inferior iliac spine (AIIS) in hip dysplasia may differ between males and females [48]. Hip pain related to acetabular dysplasia might result in overdiagnosis of hip involvement by axial spondyloarthritis [64].

Diagnostic Considerations and Imaging Context

The diagnosis of developmental dysplasia of the hip should be suspected when a skeletally mature, young, active patient presents with insidious activity-related groin pain and/or lateral hip pain [58]. Adult hip dysplasia is most commonly diagnosed based on the lateral center-edge angle (LCEA), but the LCEA is an unreliable sole marker for dysplasia and additional radiographic parameters should be utilized [59]. Hip dysplasia is classified when the LCEA is <25° or the Tönnis angle is >10° [40]. The use of the iliofemoral line as a radiographic parameter may enable the earlier detection of borderline and frank hip dysplasia in young adults presenting with hip pain [62]. The center gap is a possible new radiographic predictor of progression of osteoarthritis in developmental dysplasia of the hip, but future studies are needed to validate this marker [66]. Both the Crowe and Hartofilakidis classification systems assess different aspects of developmental dysplasia of the hip in adult patients [27]. An estimated prevalence of 12.8% of hips in symptomatic patients highlights the common decision-making challenges in this population [128]. Almost half of patients undergoing total hip arthroplasty before 50 years of age have osteoarthritis associated with acetabular dysplasia [15]. Fewer than 10% of young adults requiring arthroplasty for dysplasia-associated osteoarthritis had hip instability at birth [15]. The incidence of labral pathology in patients with hip dysplasia is reported to occur in two-thirds of patients [83]. Acetabular cartilage lesions are found in 69% of adult hip dysplasia cases, and combined labral/cartilage lesions are found in 59%, most commonly on the anterior and superolateral acetabulum [83].

Investigations

Plain radiography: The lateral center-edge angle (LCEA) is defined as the angle between a line from the center of the femoral head perpendicular to the transverse pelvis axis and a second line from the center of the femoral head to the superolateral most point of the acetabulum [20]. LCEA values of 20°–40° are considered normal, while angles from 20° to 25° are considered borderline [20]. The Tönnis angle is defined by the angle of the acetabular sourcil and a line parallel to the transverse pelvis axis [20]. Coxa profunda is diagnosed when the ilioischial line touches or is medial to the acetabular fossa line [20]. Although adult hip dysplasia is most commonly diagnosed based on the LCEA, this metric is an unreliable sole marker for dysplasia, and additional radiographic parameters should be utilized [59]. Radiographs underestimate LCEA and Tönnis angle measurements compared to computed tomography in the assessment of borderline and frank acetabular dysplasia [40]. Radiographic reference values for acetabular under- and overcoverage may be used for radiographic evaluation of symptomatic hips, may offer possible predictors for surgical outcomes, and serve to guide clinical decision-making [217]. The center gap is a possible new radiographic predictor of progression of osteoarthritis in developmental dysplasia of the hip, but future studies are needed to validate this marker in larger, more diverse patient populations [66]. Projection of two-dimensional radiographic landmarks contributing to the diagnosis of structural hip deformity into 3D allowed for the identification of the overlapping bony anatomy contributing to radiographically visible anterior and lateral sourcil edges [236]. A diagnostic framework groups symptomatic dysplastic hips into one of 3 categories based on the primary direction of instability: anterior, posterior, and global, to aid clinicians in developing a differential diagnosis and planning appropriate surgical management [32]. Residual radiographic dysplasia following successful reduction for late-diagnosed DDH in young patients is not a "deficiency," but is instead a biologic failure of ossification of the acetabulum [100]. Specific morphological characteristics on pelvis radiographs of AVN hips were predictive for poor outcome, at a very young age [234]. Although radiographic indices improved consistently with time in hips without osteonecrosis, hips with osteonecrosis had abnormal indices of acetabular remodeling throughout followup [220]. A computer-assisted analysis of young adult hip radiographs generally demonstrates substantial to excellent levels of interobserver reliability for most parameters [97].

CT: CT overcomes the limitations of radiography by providing three-dimensional assessment of bony morphology and, to some degree, assessment of soft-tissue abnormalities [63]. CT scans are effective for examining cortical and cancellous bone and can be used to create three-dimensional reconstructions of the hip for use in surgical planning [131]. Measurements of femoral head coverage and acetabular and femoral impingement can also be performed reliably using CT images [131]. The sphericity of the femoral head can accurately be determined on CT [244]. A clear measurement of the α angle can be performed on the sagittal-oblique image parallel to the femoral neck on CT [244]. Cystic changes can be clearly seen within the bone, and ossification of the labrum can be better delineated on CT [244]. CT can accurately determine version of the acetabulum and femoral version independent of patient position [244]. Three-dimensional reconstructions on CT can be easily performed, which can help with preoperative reconstruction planning [244]. Low-dose CT with three-dimensional reformats is particularly useful in surgical planning of complex or borderline deformities [67]. A low-dose CT scan of the pelvis with a few slices through the epicondyles of the knee is useful to determine the pattern of acetabular dysplasia, the version of the acetabulum, and the version of the femoral neck [274]. Three-dimensional CT with pelvic remodeling may be indicated for preoperative planning for reconstruction associated with dysplasia surgery, femoroacetabular impingement (FAI), posttraumatic arthritis, or other complex primary total hip arthroplasty (THA) [154]. The multiplanar and 3D capabilities of CT make it an invaluable tool for assessing bone morphology, but at higher cost and radiation dose [145]. 3D volume renderings are useful to aid in preoperative planning in FAI and subspine impingement [145]. CT arthrography can be used for intra-articular hip assessment in patients with contraindications to MRI [145].

MRI: The soft-tissue contrast of MRI is superior to other imaging modalities in assessing both intra-articular and extra-articular hip pathology [63]. For patients suspected of soft tissue or intra-articular pathology, MRI is the modality of choice, given its superior sensitivity and specificity [131]. Conventional MRI is effective at identifying osteochondral injuries, musculotendinous pathologies, and inflammation [131]. Magnetic resonance arthrography (MRA) is more appropriate to determine injuries to the labrochondral structures and the ligamentum teres and identify the presence of loose bodies and synovial chondromatosis [131]. In the accurate detection and staging of articular cartilage lesions, the utility of MRA is reduced, with sensitivity reported to be less than 50% compared with arthroscopic findings [131]. Recent advances in MRI imaging techniques, such as delayed gadolinium-enhanced MR imaging and T2 mapping, allow for a more in-depth analysis of the structure of articular cartilage [131]. Delayed gadolinium-enhanced MR imaging and T2 mapping were effective at detecting early changes to the articular cartilage surfaces of patients with hip dysplasia and femoroacetabular impingement [131]. MRI or magnetic resonance arthrography provides information regarding the integrity of the acetabular labrum and articular cartilage [67]. The anatomy of the proximal femur as well as the version of the acetabulum and femur may be assessed with MRI or magnetic resonance arthrography [67]. Sensitivity to acetabular rim chondral lesions is limited with MRI or magnetic resonance arthrography [67]. Noncontrast MRI at 3T is generally adequate for diagnosing intra-articular pathology [145]. If 3T imaging is unavailable, MRA can be considered at 1.5T for increased diagnostic accuracy [145]. MRI is helpful in identifying femoral neck stress fracture in athletes and predicting patients that may require surgical intervention [145]. MRI is helpful in assessing complications of conventional and resurfacing hip arthroplasties, particularly those with metal-on-metal bearing systems [145]. Major findings that help predict histologic ALVAL scores include synovial thickening, synovitis, synovial volume, abductor disruption, and soft-tissue edema on MRI [145]. Gadolinium-enhanced MRI arthrogram is useful when labral pathology is suspected, especially when associated with FAI [154]. MRI may identify gluteus medius and gluteus minimus tears in patients with lateral hip pain and abductor weakness [154]. Patients with hip dysplasia have a significantly reduced capsular thickness on MRI and delaminated anterior joint capsule, which could be a sequence of instability [209]. The role of arthroscopic intervention in patients with acetabular dysplasia remains to be clarified, and specific imaging protocols including more than one radiographic measure are essential [223]. The authors encourage thorough preoperative evaluation of radiographs and advanced imaging for all patients being considered for hip arthroscopy [91].

Ultrasonography: Ultrasonography provides real-time dynamic assessment of the hip and is useful in diagnosing soft-tissue abnormalities about the hip joint, and to a lesser degree, within the hip joint itself [63]. Ultrasonography is particularly useful in providing real-time guidance during diagnostic and therapeutic procedures [63]. Although ultrasonography is a valuable tool to examine pediatric hip conditions, its utility in evaluating the adult hip is limited [131]. Ultrasonography can be an effective modality to identify musculotendinous disruptions, effusions associated with intra-articular pathology, or inflammatory conditions, such as bursitis [131]. Ultrasonography is also being increasingly used for targeted injections into muscles, tendons, or intra-articularly around the hip, for use with corticosteroids or biologic treatments emerging as a more recognized modality [131]. Ultrasonography allows bedside evaluation of the hip and can be used to guide interventions in the office setting [145].

Other Considerations: Radiographic evidence of FAI is common in active patients with hip complaints [215]. The prevalence of radiographic femoroacetabular impingement was common in Japanese patients who are generally considered to have dysplastic hips [201]. Radiological evidence of symptomatic femoroacetabular impingement was not uncommon in Japanese patients with hip pain, with cam deformity findings being the most common [216]. Up to 51% of patients presenting with symptomatic FAI show an abnormal femoral version, whilst up to 31% demonstrate abnormal acetabular version [224]. Hip arthroscopy can reliably provide durable and clinically meaningful improvements for the treatment of intra-articular pathology and FAIS in patients with acetabular dysplasia at long-term follow-up [14]. Eight patients (17%) developed dysplasia of the contralateral hip, which appears to be a developmental process rather than an unnoticed dysplasia present from infancy [11].

Treatment

General Principles and Natural History

The primary objective of hip preservation surgery in dysplasia is to alter hip joint morphology to allow more unhindered physiologic range of motion while optimizing hip joint mechanics to delay or halt the progression of hip osteoarthritis [7]. Successful management of late-presenting hip dislocation is judged by outcomes well beyond skeletal maturity into adulthood [37].

Non-Operative

Conservative management is primarily relevant in the infant population. The Pavlik harness is the first choice of treatment for children presenting between 2 and 6 months of age [141]. To be effective, the harness must hold the hips in more than 90 degrees of flexion, with the position of the upper femoral metaphysis pointed toward the triradiate cartilage [141]. If reduction is not obtained within 3 to 4 weeks, the harness should be discontinued and other treatment begun [141]. If reduction is confirmed, the Pavlik harness should be continued for approximately 6 weeks after stability is established [141]. Factors associated with failure include patient age of more than 7 weeks at treatment, bilateral hip dislocation, and an absent Ortolani sign [141]. The overall reported rate of avascular necrosis (AVN) when the Pavlik harness is used ranges from 0% to 15% [141]. A comprehensive protocol for nonoperative treatment of infant DDH has shown high rates of success and extremely low rates of residual dysplasia at a mean age of five years [199]. The majority of patients with residual acetabular dysplasia at two years post-brace treatment spontaneously resolved by five years [98]. Femoral nerve palsy in Pavlik harness treatment is strongly predictive of failure of treatment, and its impact is greatest when the developmental dysplasia of the hip is higher in severity [5].

Operative

Indications: Closed reduction is indicated for children with a dislocated hip in whom orthotic treatment has failed and for those with a late-presenting dislocated hip for whom primary Pavlik harness treatment is not suitable [34]. Surgical reduction of congenital hip dislocation is technically challenging and is usually reserved for patients who have failed non-operative treatment or have late diagnosis [213]. In adolescents, acetabular dysplasia is characterized by increased inclination in the coronal and sagittal planes and a lateralized hip joint center [41]. Adolescent hip dysplasia is most commonly treated with PAO with excellent intermediate and long-term outcomes in hips without prior degenerative changes [41]. Periacetabular osteotomy (PAO) appears to be effective in delaying prosthetic hip reconstruction when the surgical intervention occurs while the arthritic progression is fairly mild [7]. In well-selected patients, periacetabular osteotomy should be considered safe and effective in alleviating pain and improving hip function in patients with symptomatic acetabular dysplasia [68]. Patients with hip dysplasia can be treated with PAO to help maintain activity and preserve the native hip [77]. Age over 45 is not a contraindication for PAO/hip arthroscopy if articular cartilage status is normal [134]. PAO is reliable in treating borderline hip dysplasia with favourable mid-term outcomes [139]. Rotational acetabular osteotomy is an effective surgery for treating symptomatic developmental dysplasia of the hip in selected patients [112]. Patient-specific allograft bone shelves could be a serious option for adolescents with severe hip dysplasia [42].

Surgical Approach / Technique: Closed reduction is performed under general anesthesia with hip abduction and an anteriorly directed force on the posterior aspect of the greater trochanter to obtain reduction [34]. Arthrography is used to evaluate the reduction intraoperatively, with a medial dye pool ≤6 mm or 16% of the femoral head diameter both shown to be predictive of a successful reduction [34]. After 18 months of age, there is an increased likelihood of either femoral or pelvic osteotomy [34]. A femoral shortening osteotomy may be indicated if soft-tissue contractures result in excessive pressure on the femoral head in the acetabulum following open reduction [34]. Restoration of a normal hip joint center with improved/normalized acetabular coverage is achieved with triple innominate osteotomies in those with open triradiate cartilage or a periacetabular osteotomy in the skeletally mature patient [41]. Dega acetabuloplasty is effective and reliable in correcting acetabular dysplasia following developmental dislocation of the hip [147]. Open reduction through anterior minimally invasive approach can achieve good clinical effect in the treatment of infantile developmental dysplasia of the hip [248]. A stable, safe but non-concentric reduction achieved before the age of two years appears to improve over time with nearly 80% of hips becoming fully concentric by one year [246].

Other Considerations: The most serious complication associated with treatment of DDH in early infancy is the development of osteonecrosis [26]. Estimated rates of osteonecrosis vary widely, ranging from less than 5% to almost 50% [26]. Meta-analyses have indicated that the presence of the ossific nucleus provides little protective benefit against osteonecrosis after closed or open reduction [26]. Delaying reduction of a dislocated hip until the appearance of the ossific nucleus more than doubled the need for future surgery [26]. Significantly better results have been reported in patients treated early (1 to 3 years after the ischemic insult) with innominate osteotomy than in patients treated later (5 to 10 years after the ischemic insult) [26]. Early innominate osteotomy has been suggested to induce spherical remodeling of the femoral head, with a resultant congruous hip joint [26]. Symptomatic overgrowth of the greater trochanter can be treated in older patients with greater trochanteric advancement, which increases the abductor muscle resting length and increases the abductor lever arm [26]. Periacetabular osteotomy is an effective technique for treating symptomatic developmental dysplasia of the hip and can maintain the natural hip at least 19 years in selected patients [45]. Up to 62% of patients who underwent PAO for hip dysplasia participated in sports after PAO [253]. Abnormal femoral version is a common comorbidity in adult developmental dysplasia of the hip that can aggravate instability and lead to osteoarthritis [146]. Specific indications for femoral derotational osteotomy and the threshold for correction in adult developmental dysplasia of the hip remain controversial and require further research [146].

Hip Arthroscopy

Improved patient-reported outcomes can be obtained with hip arthroscopy in the treatment of concomitant mild acetabular dysplasia and FAI at a minimum 2-year follow-up [13]. Arthroscopic procedures for individuals with mild dysplasia in the absence of frank instability may be effective; however, great caution should be exercised when approaching dysplastic patients with symptomatic hips [260]. Arthroscopic treatment with labral preservation and capsular plication may be an option for mildly dysplastic hips when strict indications are used [165]. The 7-year hip survival rate in hip dysplasia appears inferior compared with that reported in femoroacetabular impingement (78%) [35]. Further research with more patients and longer follow-up is necessary in order to determine specific indications, if any, for hip arthroscopy in adult hip dysplasia [24]. Optimal surgical treatment of hip dysplasia treats both the cause and the effects of dysplasia by combining hip arthroscopy and periacetabular osteotomy into a single intervention [110]. Patients with borderline hip dysplasia aged 40 years and older treated with contemporary hip arthroscopy achieved similar function, pain, and satisfaction at 5-year follow-up but worse sports function and sports-related Patient Acceptable Symptom State achievement compared with patients aged less than 40 years [138].

Total Hip Arthroplasty

Patients who had hip dysplasia and mild OA had similar recovery curves compared to those who had severe OA or who did not have dysplasia [8]. Patients with hip dysplasia can expect reduced pain, improved functional outcomes, and similar revision surgery rates to those with osteoarthritis following primary THA [23]. Periacetabular osteotomy in patients with dysplasia may decrease the need for structural bone grafting if later conversion to arthroplasty is needed [144]. If an osteotomy relieves symptoms for 10 years or more, and then an arthroplasty is required, the patient will have been able to engage in more physical activity, bone stock will have been preserved, and the patient will be older and less physically active and will need the use of an arthroplasty for fewer years [144].

Complications

Osteonecrosis (AVN)

The most serious complication associated with the treatment of developmental dysplasia of the hip (DDH) in early infancy is the development of osteonecrosis [26]. Estimated rates following DDH treatment vary widely, ranging from less than 5% to almost 50% [26]. Proposed risk factors include open reduction with concomitant osteotomies, redislocation after surgical correction, or the need for a secondary procedure after initial closed or open reduction [26]. The rate of osteonecrosis after closed reduction is lower than after open reduction, but remains as high as 10% to 35% after closed treatment [26]. Meta-analyses indicate that the presence of the ossific nucleus provides little protective benefit against osteonecrosis after closed or open reduction [26].

Potential sequelae of osteonecrosis include femoral head deformity, acetabular dysplasia, lateral subluxation of the femoral head, relative overgrowth of the greater trochanter, and limb-length inequalities [26]. Osteoarthritis is a common late complication of osteonecrosis [26]. A 14% incidence of total hip arthroplasty (THA) by age 34 years was identified in patients with osteonecrosis secondary to DDH [203].

Arthroscopic Complications and Failure

Mild dysplastic features and female sex are associated with failure of hip arthroscopy [10]. Hip arthroscopy can reliably provide durable and clinically meaningful improvements for the treatment of intra-articular pathology and femoroacetabular impingement syndrome (FAIS) in patients with acetabular dysplasia at long-term follow-up [14]. Hip dysplasia may not be an absolute contraindication for isolated hip arthroscopy and may serve as a viable intervention with consideration of staged future periacetabular osteotomy (PAO) [18]. Borderline hip dysplasia is not associated with a significant difference in hip survivorship or patient-reported outcomes following primary hip arthroscopy for femoroacetabular impingement syndrome [178]. Longer follow-up is required to determine if hip arthroscopy provides added value to a PAO for symptomatic hip dysplasia [54].

Periacetabular Osteotomy (PAO) Complications and Survivorship

Complications associated with the periacetabular osteotomy were documented in a prospective multicenter study [16]. Impingement adversely affects 10-year survivorship after periacetabular osteotomy for DDH [16]. Obesity increases the risk of complications in the surgical treatment of adolescent acetabular dysplasia with a periacetabular osteotomy [16]. Tranexamic acid reduces the blood loss and blood transfusion requirements following periacetabular osteotomy [16].

The 10- and 20-year survivorship of the native hip after PAO is approximately 86% and 60%, respectively [81]. Periacetabular osteotomy can maintain the natural hip at least 19 years in selected patients [45]. Complications were much more frequent in patients with Charcot-Marie-Tooth (CMT) disease undergoing Bernese periacetabular osteotomy (33%) than in those with developmental dysplasia of the hip (13%) [206]. Specific complications in CMT patients undergoing Bernese PAO included osteonecrosis of the femoral head, transient complete bilateral peroneal nerve palsy, inferior rami fractures, and heterotopic ossification [206].

Total Hip Arthroplasty (THA) Complications

Primary or conversion THA performed for developmental dysplasia adds significant complexity to the surgical procedure and risk of complications [181]. Patients undergoing conversion THA faced approximately 20% greater direct costs compared with a matched group of patients undergoing primary THA [181]. Patients undergoing conversion THA experienced significantly greater surgical times, estimated blood loss, length of stay, intraoperative complications, and postoperative complications [181]. Femoral and acetabular complications in complex THA scenarios may be decreased with the use of dual mobility acetabular implants or versatile, conical femoral implants [181].

Patients with hip dysplasia and mild osteoarthritis had similar recovery curves compared to those who had severe osteoarthritis or who did not have dysplasia following THA [8]. Rotational acetabular osteotomy (RAO) does not lead to higher revision rates, compromised Harris Hip Scores, or shortened survivorship in eventual THA for DDH [174].

Other Considerations

Femoral nerve palsy in Pavlik harness treatment for DDH is strongly predictive of failure of treatment [5]. The impact of femoral nerve palsy is greatest when the developmental dysplasia of the hip is higher in severity [5]. Eight patients (17%) with unilateral late-detected congenital dislocation of the hip developed dysplasia of the contralateral hip [11]. Contralateral hip dysplasia in this context appears to be a developmental process rather than an unnoticed dysplasia present from infancy [11]. A family history of DDH is a risk factor for the progression of hip osteoarthritis [173]. Long-term follow-up is recommended because there is a small but significant incidence of late asymmetric epiphyseal closure and acetabular dysplasia [73].

Recovery

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

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

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

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

Functional milestones: Validated patient-reported outcome (PRO) trajectories are documented for specific surgical interventions. Patients with borderline hip dysplasia undergoing primary hip arthroscopy demonstrated significant improvement in PROs at midterm and long-term follow-up [92]. Appropriate selected older patients with dysplasia without significant preexisting hip osteoarthritis experience clinically meaningful improvements in hip pain and function after hip preservation surgery [12]. The absence of differences in early postoperative patient-reported outcomes across multiple age ranges emphasizes that periacetabular osteotomy (PAO) in the setting of symptomatic acetabular dysplasia can be successful regardless of patient age alone [69].

Other Considerations: Long-term survivorship and natural history data inform prognosis but do not define recovery timelines. Periacetabular osteotomy is an effective technique for treating symptomatic developmental dysplasia of the hip and can maintain the natural hip at least 19 years in selected patients [45]. The 10-year survivorship of the native hip after PAO is approximately 86% [81], while the 20-year survivorship is approximately 60% [81]. Twenty-year results from the originating surgical center in Berne showed hip preservation in 60% of hips at 20-year follow-up [99]. Thirty years postoperatively, 29% of hips undergoing PAO for hip dysplasia can be preserved [55], whereas more than 70% will develop progressive osteoarthritis, pain, and/or undergo total hip arthroplasty by 30 years postoperatively [55]. Impingement adversely affects 10-year survivorship after periacetabular osteotomy for developmental dysplasia of the hip [16]. The RAO cohort with a median follow-up period of 14 years demonstrated good survival rates in patients at the preosteoarthritis stage and in patients at the initial stage of DDH [182]. While favorable short-term and midterm clinical outcomes have been reported after arthroscopic treatment of prearthritic hip lesions, greater long-term follow-up is necessary to assess the efficacy of hip arthroscopic surgery in altering the natural history and progressive degenerative changes associated with FAI [275].

Total hip arthroplasty outcomes in dysplasia show favorable results in specific contexts. Hybrid total hip arthroplasty in Chinese developmental dysplasia of hip patients has favorable results at midterm follow-up, even though their lifestyle includes more deep flexion of the hip [88]. Femoral osteotomy and shortening at the subtrochanteric level predictably allows a stable reduction in patients with high developmental dysplasia of the hip and does not lead to any reduction in longterm survival [95]. High survivorship of cemented sockets with roof graft in severe acetabular dysplasia was found at a mean followup of more than 10 years [96].

Natural history and prognostic indicators vary by morphology. Degenerative change occurred earliest in patients with DDH, whereas the natural history of patients with FAI was quite similar to structurally normal hips [76]. For a patient who recently developed Tönnis 1 degenerative change, the probability of undergoing THA in 10 years based on hip morphology was approximately one in three for dysplasia of the hip (DDH) [53]. The approximate probability at 20 years for a patient who recently developed Tönnis 1 degenerative change to undergo THA was two in three for DDH [53]. Several radiographic variables were found to have negative prognostic value including femoral head lateralization greater than 8 mm, femoral head extrusion index greater than 0.2, acetabular depth-to-width index less than 0.3, lateral center-edge angle less than 25°, and Tönnis angle greater than 8° [53].

Pediatric and adolescent outcomes following early intervention show mixed long-term radiographic and functional results. A retrospective study of closed reductions with mean 30-year follow-up reported good or excellent functional outcomes in 90% of patients, but residual radiographic dysplasia in over half of the patients [192]. Rates of secondary surgery for residual dysplasia following closed reduction were reported between 35% and 58% in two recent retrospective studies [192]. A retrospective study of patients undergoing open reduction and innominate osteotomy with mean 43-year follow-up reported hip survivorship of 99% at 30 years, but only 54% by 45 years after initial treatment [192]. Additionally, 19% of patients who underwent open reduction required secondary surgery [192]. Clinical results for the Dial osteotomy in the treatment of high-grade acetabular dysplasia were 73% satisfactory and 27% unsatisfactory at followup [282], with 13% of hips treated with the Dial osteotomy for high-grade acetabular dysplasia failing between 10–20 years [282].

Key Evidence

• [L4] Hip dysplasia is best treated before 5 years of age, and surgery should not be performed unnecessarily. [1] (10.1016/j.otsr.2021.103172)
• [L5] If left untreated, hip dysplasia can result in severe deformities and functional limitations. [3] (10.5435/jaaosglobal-d-23-00291)
• [L3] This complication is strongly predictive of failure of treatment, and its impact is greatest when the developmental dysplasia of the hip is higher in severity. [5] (10.2106/jbjs.j.01210)
• [L3] Patients who had hip dysplasia and mild OA had similar recovery curves compared to those who had severe OA or who did not have dysplasia. [8] (10.1016/j.arth.2024.04.060)
• [L5] When confronted with a controversial topic and treatments for hip dysplasia we need more consistent definitions of hip dysplasia, and then study our outcomes of these treatments in the short, mid, and long term before we adopt them as reliable treatment options. [9] (10.1016/j.arthro.2017.10.021)
• [L3] Mild dysplastic features and female sex are associated with failure of hip arthroscopy, raising concern that isolated hip arthroscopy is being increasingly utilized in patients with acetabular dysplasia. [10] (10.1177/2325967117s00230)
• [L3] Eight patients (17%) developed dysplasia of the contralateral hip, which appears to be a developmental process rather than an unnoticed dysplasia present from infancy. [11] (10.1302/0301-620x.96b9.33768)
• [L3] Our findings show that appropriately selected older patients with dysplasia without significant preexisting hip osteoarthritis experience clinically meaningful improvements in hip pain and function after hip preservation surgery. [12] (10.1016/j.arthro.2024.10.039)
• [L4] This systematic review indicates that improved patient-reported outcomes can be obtained with hip arthroscopy in the treatment of concomitant mild acetabular dysplasia and FAI at a minimum 2-year follow-up. [13] (10.1016/j.arthro.2019.11.122)
• [L4] Hip arthroscopy can reliably provide durable and clinically meaningful improvements for the treatment of intra-articular pathology and FAIS in patients with acetabular dysplasia at long-term follow-up. [14] (10.1177/03635465261429491)
• [L4] These findings suggest that hip dysplasia may not be an absolute contraindication for isolated hip arthroscopy and may serve as a viable intervention with consideration of staged future periacetabular osteotomy (PAO). [18] (10.1177/03635465231197177)
• [L5] Hip dysplasia is a pathoanatomic osseous morphology associated with hip instability that may, in part, be due to hip capsular thickness. [19] (10.1016/j.arthro.2024.07.012)
• [L3] 40% of patients with acetabular dysplasia also had radiographic evidence of cam-type femoroacetabular deformity. [21] (10.1186/s13018-014-0093-4)
• [L3] Patients with hip dysplasia can expect reduced pain, improved functional outcomes, and similar revision surgery rates to those with osteoarthritis following primary THA. [23] (10.5435/jaaos-d-24-01315)
• [L5] Further research with more patients and longer follow-up is necessary in order to determine specific indications, if any, for hip arthroscopy in adult hip dysplasia. [24] (10.1016/j.arthro.2015.12.020)
• [L4] Both classification systems assess the different aspects of developmental dysplasia of the hip in adults. [27] (10.1007/s00402-012-1600-x)
• [L5] The authors propose a diagnostic framework that groups symptomatic dysplastic hips into one of 3 categories based on the primary direction of instability: anterior, posterior, and global, to aid clinicians in developing a differential diagnosis and planning appropriate surgical management. [32] (10.1016/j.arth.2017.02.067)
• [L2] Proximal femoral deformities are highly prevalent in symptomatic acetabular dysplasia, with 92.6% of hips showing abnormalities. [33] (10.1007/s11999-008-0481-3)
• [L3] Overall, the 7-year hip survival rate in hip dysplasia appears inferior compared with that reported in femoroacetabular impingement (78%). [35] (10.1177/0363546517713176)
• [L5] Most patients with borderline hip dysplasia achieve successful outcomes after hip arthroscopy alone, but those with signs of instability may fail and require bony treatment; future studies must identify characteristics that predict failure of an arthroscopic-only approach. [36] (10.1016/j.arthro.2022.10.005)
• [L4] Successful management of late presenting hip dislocation is judged by outcomes well beyond skeletal maturity into adulthood. [37] (10.1302/0301-620x.97b6.35395)
• [L3] Patients with acetabular dysplasia have an increased frequency of spinal anomalies seen on standard hip radiographs. [39] (10.1302/0301-620x.103b8.bjj-2020-2481.r1)
• [L4] [40] (10.1016/j.arthro.2024.10.038)
• [L5] The excellent and predictable functional and radiologic outcomes suggest that patient-specific allograft bone shelves could be a serious option for adolescents with severe hip dysplasia. [42] (10.5435/jaaosglobal-d-24-00382)
• [L4] PAO with concomitant hip arthroscopy for symptomatic hip dysplasia resulted in significant improvements in functional outcomes, with a high percentage of patients achieving important clinical thresholds. [43] (10.1177/03635465251391182)
• [L3] Periacetabular osteotomy is an effective technique for treating symptomatic developmental dysplasia of the hip and can maintain the natural hip at least 19 years in selected patients. [45] (10.1007/s11999-008-0242-3)
• [L3] Staged hip arthroscopy and PAO for hip dysplasia leads to similar PROs at 12-24 months compared to combined procedures. [46] (10.1016/j.arthro.2023.02.017)
• [L4] The morphologic features of AIIS in hip dysplasia may differ between males and females. [48] (10.1016/j.arth.2016.02.018)
• [L3] Surgical outcomes at minimum of 2 years in patients with borderline hip dysplasia in selected patients undergoing PAO or hip arthroscopy were good. [49] (10.1177/2325967120s00209)
• [L1] Longer follow-up will be required to determine if hip arthroscopy provides added value to a PAO for symptomatic hip dysplasia. [54] (10.1016/j.arth.2024.05.035)
• [L3] Thirty years postoperatively, 29% of hips undergoing PAO for hip dysplasia can be preserved, but more than 70% will develop progressive osteoarthritis, pain, and/or undergo THA. [55] (10.1007/s11999-016-5169-5)
• [L4] The diagnosis of developmental dysplasia of the hip should be suspected and investigated when a skeletally mature, young, active patient has a predominant complaint of insidious activity-related groin pain and/or lateral hip pain. [58] (10.2106/jbjs.j.01735)
• [L5] Adult hip dysplasia is most commonly diagnosed based on the LCEA; however, the LCEA is an unreliable sole marker for dysplasia, and additional radiographic parameters should be utilized. [59] (10.1177/0363546519881411)
• [L2] The use of this radiographic parameter as an additional tool may enable the earlier detection of borderline and frank hip dysplasia in young adults presenting with hip pain. [62] (10.1177/0363546517708983)
• [L3] Hip pain related to acetabular dysplasia might result in overdiagnosis of hip involvement by axial spondyloarthritis. [64] (10.1186/s12891-022-05575-4)
• [L5] The center gap is a possible new radiographic predictor of progression of osteoarthritis in developmental dysplasia of the hip, but future studies are needed to validate this marker in larger, more diverse patient populations. [66] (10.1097/corr.0000000000000501)
• [L5] In well-selected patients, this reconstructive osteotomy should be considered safe and effective in alleviating pain and improving hip function in patients with symptomatic acetabular dysplasia. [68] (10.1016/j.arth.2017.02.015)
• [L2] The absence of differences in early postoperative patient-reported outcomes across multiple age ranges emphasizes that PAO in the setting of symptomatic acetabular dysplasia can be successful regardless of patient age alone. [69] (10.1016/j.arth.2021.05.029)
• [L3] Degenerative change occurred earliest in patients with DDH, whereas the natural history of patients with FAI was quite similar to structurally normal hips. [76] (10.1007/s11999-016-4815-2)
• [L4] Patients with hip dysplasia can be treated with PAO to help maintain activity and preserve the native hip. [77] (10.1177/03635465251334770)
• [L3] The 10- and 20-year survivorship of the native hip after PAO is approximately 86% and 60%, respectively, in this cohort. [81] (10.5435/jaaos-d-17-00810)
• [L4] The majority (71%) of active patients with hip dysplasia return to presurgical or higher activity levels after open hip preservation surgery with the periacetabular osteotomy. [85] (10.1177/0363546514535906)
• [L3] Hybrid total hip arthroplasty in Chinese developmental dysplasia of hip patients has favorable results at midterm follow-up, even though their lifestyle includes more deep flexion of the hip. [88] (10.1016/j.arth.2009.07.002)
• [L3] An isolated assessment of the LCEA is an oversimplistic approach that may jeopardize appropriate classification and may provide insufficient data to guide the treatment of hips with additional features of dysplasia and instability. [90] (10.1177/0363546518810731)
• [L5] The authors encourage thorough preoperative evaluation of radiographs and advanced imaging for all patients being considered for hip arthroscopy. [91] (10.5435/jaaos-d-16-00231)
• [L4] Patients with borderline hip dysplasia undergoing primary hip arthroscopy demonstrated significant improvement in PROs at midterm and long-term follow-up. [92] (10.1016/j.arthro.2022.12.030)
• [L2] Our data suggest femoral osteotomy and shortening at the subtrochanteric level predictably allows a stable reduction in patients with high developmental dysplasia of the hip and does not lead to any reduction in longterm survival. [95] (10.1007/s11999-009-1218-7)
• [L4] In contrast to reported series and the common use of cementless cups in patients with developmental dysplasia of the hip, we found high survivorship of cemented sockets with roof graft in severe acetabular dysplasia at a mean followup of more than 10 years. [96] (10.1007/s11999-012-2346-z)
• [L3] A computer-assisted analysis of young adult hip radiographs generally demonstrates substantial to excellent levels of interobserver reliability for most parameters. [97] (10.1177/0363546514542797)
• [L3] The majority of patients with residual acetabular dysplasia at two years post-brace treatment spontaneously resolved by five years. [98] (10.1302/0301-620x.106b7.bjj-2023-1169.r1)
• [L5] [100] (10.2106/jbjs.23.00697)
• [L3] There are sex-dependent, disease characteristic differences in patients with symptomatic acetabular dysplasia, with male patients showing a greater prevalence of findings consistent with concurrent FAI and instability. [102] (10.1007/s11999-015-4155-7)
• [L5] Optimal surgical treatment of hip dysplasia treats both the cause and the effects of dysplasia by combining hip arthroscopy and periacetabular osteotomy into a single intervention. [110] (10.1016/j.arthro.2023.07.046)
• [L5] The Hartofilakidis classification system describes three types of developmental hip dysplasia (dysplasia, low dislocation, and high dislocation) to guide surgical management by anticipating implant type and the need for augmentation. [111] (10.1097/corr.0000000000000802)
• [L3] Rotational acetabular osteotomy is an effective surgery for treating symptomatic developmental dysplasia of the hip in selected patients. [112] (10.1007/s00402-017-2636-8)
• [L1] Additionally, an estimated prevalence of 12.8% of hips in symptomatic patients highlights the common decisionmaking challenges in this population. [128] (10.1177/23259671211040455)
• [L5] Age over 45 is not a contraindication for PAO/hip arthroscopy if articular cartilage status is normal. [134] (10.1016/j.arthro.2024.11.074)
• [L3] Patients with borderline hip dysplasia aged 40 years and older treated with contemporary hip arthroscopy achieved similar function, pain, and satisfaction at 5-year follow-up but worse sports function and sports-related Patient Acceptable Symptom State achievement compared with patients aged less than 40 years. [138] (10.1177/03635465251397621)
• [L4] PAO is reliable in treating borderline hip dysplasia with favourable mid-term outcomes. [139] (10.1302/0301-620x.105b7.bjj-2022-1058.r2)
• [L4] Abnormal femoral version is a common comorbidity in adult developmental dysplasia of the hip that can aggravate instability and lead to osteoarthritis, yet specific indications for femoral derotational osteotomy and the threshold for correction remain controversial and require further research. [146] (10.1530/eor-23-0145)
• [L4] Dega acetabuloplasty is effective and reliable in correcting acetabular dysplasia following developmental dislocation of the hip. [147] (10.1016/j.otsr.2013.12.015)
• [Letter] While both hip arthroscopy and periacetabular osteotomy offer potential benefits for patients with borderline hip dysplasia, the authors argue for moving beyond generalized results to identify specific patient subgroups who do not do well with hip arthroscopy alone and should be considered for initial treatment with periacetabular osteotomy. [152] (10.1016/j.arthro.2025.01.057)
• [L5] Total hip arthroplasty is the procedure of choice for most patients with symptomatic end-stage coxarthrosis secondary to hip dysplasia, demonstrating a high rate of pain relief and functional improvement. [156] (10.5435/00124635-200209000-00005)
• [L4] The morphology of the AIIS in patients with acetabular dysplasia is commonly prominent, with 72% of hips having Type II or Type III morphologies. [163] (10.1097/corr.0000000000001547)
• [L5] The authors argue that current classification of borderline hip dysplasia based solely on lateral center edge angle is insufficient and that the focus must shift to assessing hip instability to better predict treatment outcomes and the need for bony realignment. [164] (10.1016/j.arthro.2023.10.023)
• [L5] They suggest that while open treatment remains the gold standard, arthroscopic treatment with labral preservation and capsular plication may be an option for mildly dysplastic hips when strict indications are used. [165] (10.1177/0363546519825641)
• [L4] Recognition of these distinct morphologic subtypes is important for diagnostic and surgical treatment considerations to optimize acetabular correction and avoid femoroacetabular impingement. [166] (10.1007/s11999-016-5150-3)
• [L3] Classifying acetabular dysplasia into 3 groups based on the plane of instability could optimize the planning of PAO by giving a better understanding of the 3-dimensional deformity. [171] (10.1177/0363546521992108)
• [Paper] The Ogata et al. classification system is a reliable and reproducible radiological indicator for reflecting acetabular cover. [172] (10.1007/s00402-001-0376-1)
• [L3] A DDH family history is a risk factor for the progression of hip OA. [173] (10.1016/j.arth.2023.08.026)
• [L3] Our midterm results demonstrated that RAO does not lead to higher revision rates, compromised HHSs, or shortened survivorship in eventual THA for DDH. [174] (10.1007/s00402-015-2154-5)
• [L4] The artificial intelligence model measurements demonstrate a high degree of consistency with manual measurements and exhibit robust diagnostic performance in identifying developmental dysplasia of the hip and borderline developmental dysplasia of the hip. [175] (10.1186/s12891-024-08035-3)
• [L3] Borderline hip dysplasia is not associated with a significant difference in hip survivorship or patient-reported outcomes following primary hip arthroscopy for femoroacetabular impingement syndrome. [178] (10.1016/j.arthro.2023.09.003)
• [L3] The RAO cohort with a median follow-up period of 14 years demonstrated good survival rates in patients at the preosteoarthritis stage and in patients at the initial stage of DDH. [182] (10.1016/j.arth.2025.06.021)
• [L3] In DDH, AIIS type 3 tends to be more severe dysplasia than AIIS type 1 or 2. [187] (10.1016/j.jisako.2023.03.068)
• [L3] Our comprehensive protocol for nonoperative treatment of infant DDH has shown high rates of success and extremely low rates of residual dysplasia at a mean age of five years. [199] (10.1302/0301-620x.105b8.bjj-2023-0149.r1)
• [L3] The prevalence of radiographic femoroacetabular impingement was common in Japanese patients who are generally considered to have dysplastic hips. [201] (10.1302/0301-620x.98b9.37267)
• [L3] We identified a 14% incidence of THA by age 34 years in patients with osteonecrosis secondary to DDH. [203] (10.1186/s12891-024-07517-8)
• [L4] [208] (10.1186/s12891-024-07244-0)
• [L3] Patients with hip dysplasia have a significantly reduced capsular thickness on MRI and delaminated anterior joint capsule, which could be a sequence of instability. [209] (10.1007/s00167-022-07022-2)
• [L5] Surgical reduction of congenital hip dislocation is technically challenging and is usually reserved for patients who have failed non-operative treatment or have late diagnosis. [213] (10.1016/j.otsr.2017.04.021)
• [L2] Radiographic evidence of FAI is common in active patients with hip complaints. [215] (10.1007/s11999-010-1233-8)
• [L4] Radiological evidence of symptomatic femoroacetabular impingement was not uncommon in these Japanese patients with hip pain, with cam deformity findings being the most common. [216] (10.1302/0301-620x.96b2.32680)
• [L3] They may be used for radiographic evaluation of symptomatic hips, may offer possible predictors for surgical outcomes, and serve to guide clinical decision-making. [217] (10.1007/s11999-014-4038-3)
• [L3] Although radiographic indices improved consistently with time in hips without osteonecrosis, hips with osteonecrosis had abnormal indices of acetabular remodeling throughout followup. [220] (10.1007/s11999-013-2804-2)
• [L5] The role of arthroscopic intervention in patients with acetabular dysplasia remains to be clarified, and specific imaging protocols including more than one radiographic measure are essential. [223] (10.1302/0301-620x.99b6.bjj-2017-0491)
• [L2] Up to 51% of patients presenting with symptomatic FAI show an abnormal femoral version, whilst up to 31% demonstrate abnormal acetabular version. [224] (10.1007/s00167-021-06643-3)
• [Paper] [228] (10.1055/a-0924-5491)
• [L3] Specific morphological characteristics on pelvis radiographs of AVN hips were predictive for poor outcome, at a very young age. [234] (10.1302/0301-620x.103b5.bjj-2020-1485.r1)
• [L4] Projection of two-dimensional radiographic landmarks contributing to the diagnosis of structural hip deformity into 3D allowed for the identification of the overlapping bony anatomy contributing to radiographically visible anterior and lateral sourcil edges. [236] (10.1097/corr.0000000000003268)
• [L3] A stable, safe but non-concentric reduction achieved before the age of two years appears to improve over time with nearly 80% of hips becoming fully concentric by one year. [246] (10.1302/0301-620x.102b5.bjj-2019-1496.r1)
• [L4] Open reduction through anterior minimally invasive approach can achieve good clinical effect in the treatment of infantile developmental dysplasia of the hip. [248] (10.1186/s12891-023-06582-9)
• [L2] Up to 62% of patients who underwent PAO for hip dysplasia participated in sports after PAO. [253] (10.1177/03635465251385258)
• [L4] Arthroscopic procedures for individuals with mild dysplasia in the absence of frank instability may be effective; however, great caution should be exercised when approaching dysplastic patients with symptomatic hips. [260] (10.1016/j.arth.2017.02.022)
• [L5] While favorable short-term and midterm clinical outcomes have been reported after arthroscopic treatment of prearthritic hip lesions, greater long-term follow-up is necessary to assess the efficacy of hip arthroscopic surgery in altering the natural history and progressive degenerative changes associated with FAI. [275] (10.1177/0363546513476281)
• [L5] [277] (10.1302/2058-5241.4.180019)
• [L4] Clinical results at followup were 73% satisfactory and 27% unsatisfactory, with 13% of hips failing between 10–20 years. [282] (10.1097/01.blo.0000153992.17554.67)

See Also

• Hip osteoarthritis
• Periacetabular osteotomy
• Femoroacetabular impingement
• Hip arthroscopy

References

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