Developmental Dysplasia of the Hip (DDH)

Introduction and Terminology

Developmental dysplasia of the hip (DDH) is a spectrum of disorders of the developing hip ranging from mild acetabular dysplasia in a stable joint to frank dislocation of the femoral head from the acetabulum. The term “developmental” — preferred since the 1990s over the historical “congenital” — emphasizes that the abnormality is not exclusively present at birth: many cases develop in the days, weeks, or months following birth as the immature hip is exposed to environmental forces, and some cases develop only as the child begins to walk. The spectrum encompasses: the unstable but reduced hip; the subluxable hip (in which gentle stress produces partial displacement); the dislocatable hip (in which gentle stress produces complete displacement); the dislocated but reducible hip (Ortolani- positive); and the dislocated and irreducible hip (in which secondary acetabular changes prevent reduction without surgery). The term “teratological dislocation” is reserved for the rare neonatal hip dislocation associated with arthrogryposis, neuromuscular conditions, and chromosomal disorders, in which the dislocation is fixed at birth and behaves biologically and anatomically differently from typical DDH. This chapter synthesizes content from Tachdjian’s Pediatric Orthopaedics, Apley & Solomon’s, Miller’s Review, and the operative-approach literature to cover the epidemiology and risk factors of DDH, the anatomical and biological basis of the disease, screening and diagnosis in the newborn and infant, the Graf ultrasound classification, treatment of the neonatal and infant hip (Pavlik harness, closed reduction, open reduction), surgical reconstruction of the older child and adolescent (pelvic and femoral osteotomies), the management of residual dysplasia in adolescence and early adulthood, and the special situation of the irreducible neglected dislocation.

Epidemiology and Risk Factors

The incidence of DDH varies substantially with population, screening method, and case definition. Frank dislocation in the newborn is reported at 1-2 per 1,000 live births; instability of any degree (including subluxable and dislocatable hips that subsequently stabilize) at 5-20 per 1,000; and acetabular dysplasia on later imaging at higher rates still. Geographic and ethnic variation is striking: very high prevalence has been reported in some Native American populations (where the practice of swaddling with the hips in extension and adduction is implicated) and in Eastern Europe, while low prevalence is reported in African populations (where the practice of carrying infants on the mother’s back with the hips in abduction is implicated). The classical risk factors form the mnemonic accepted in most pediatric texts: female sex (sixfold increased risk over males), breech presentation (the single most powerful environmental risk factor, with the highest risk for late frank breech rather than complete or footling breech), positive family history (first-degree relative), firstborn child (uterine packing), oligohydramnios, and other “packaging” disorders such as congenital muscular torticollis and metatarsus adductus, both of which should prompt screening of the hip. The left hip is more commonly involved than the right (approximately 60% left, 20% right, 20%

bilateral), and this asymmetry is attributed to the typical fetal position with the left hip in adduction against the maternal sacrum.

Pathological Anatomy

The dysplastic hip exhibits a constellation of bony and soft-tissue abnormalities that progress with continued dislocation and that determine the difficulty of reduction and the long-term outcome. The acetabulum is shallow, sloped, and faces posterosuperiorly rather than laterally; the labrum is thickened, inverted, and forms an inverted-V “limbus” obstructing reduction; the pulvinar (fibro-fatty tissue at the base of the acetabulum) is hypertrophied and fills the empty socket; the transverse acetabular ligament hypertrophies and contracts; the iliopsoas tendon crosses the joint anteriorly and develops an hourglass constriction over the joint capsule, producing the classical “hourglass” or “dumbbell” appearance of the capsule on dye arthrography. The femoral head is small and incompletely ossified, sometimes deformed by pressure against the false acetabulum that develops on the lateral aspect of the iliac wing. The femoral neck is short, anteverted, and progressively becomes valgus with continued dislocation. The hip adductor muscles, particularly adductor longus, become contracted in the dislocated position. Five obstacles to closed reduction are classically described and must be understood: (1) inverted limbus, (2) hypertrophied pulvinar, (3) contracted iliopsoas tendon producing capsular hourglass, (4) contracted transverse acetabular ligament, and (5) capsular contracture. Surgical open reduction must address each of these obstacles.

Clinical Examination of the Newborn Hip

The Ortolani and Barlow Maneuvers The Ortolani maneuver, described by Marino Ortolani in 1937, is a test for the dislocated but reducible hip: with the infant supine and relaxed, both hips are flexed to 90°, the thigh is gently abducted, and the examiner’s middle finger placed over the greater trochanter exerts gentle anterior pressure. A positive test is the palpable clunk (not click — clicks are common, soft, and innocuous; clunks are specific) as the dislocated femoral head reduces over the posterior acetabular rim into the socket. The maneuver is sensitive in the first weeks of life when the hip is reducible; it becomes negative once secondary changes prevent reduction. The Barlow maneuver, described by Thomas Barlow in 1962, is a test for the dislocatable hip: with the infant supine and the hip flexed and adducted, the examiner applies gentle posterior pressure on the knee. A positive test is the palpable clunk as the femoral head dislocates posteriorly over the acetabular rim. The maneuver identifies the unstable hip that is currently reduced but can be dislocated by stress. Both maneuvers must be performed with care and without force in a relaxed infant, and the examiner must distinguish the high-pitched soft “click” produced by ligamentous or tendinous snap from the deeper “clunk” of true hip displacement.

Other Signs In older infants (>3 months), the Ortolani and Barlow signs become negative as secondary changes develop, and other signs become more important: limited hip abduction (less than 70° in unilateral disease, with asymmetry between the affected and normal sides being the most reliable sign), apparent shortening of the affected limb (the Galeazzi sign, with both hips flexed to 90° and the knees seen at different levels), asymmetric thigh and gluteal skin folds (a non-specific sign that is overemphasized in some teaching), and apparent leg- length discrepancy. The Klisic test, in which the line connecting the greater trochanter to the anterior superior iliac spine passes below the umbilicus in a dislocated hip rather than above (as in a normal hip), is a useful objective sign. In the walking child with an undetected dislocation, the gait is characteristic: the Trendelenburg gait (lateral lurch of the trunk over the affected hip during stance phase, with drop of the contralateral pelvis), apparent leg-length discrepancy with toe-walking on the affected side, and increased lumbar lordosis with bilateral disease.

Screening and Imaging

Universal vs Selective Screening The optimal approach to DDH screening — universal ultrasound for all newborns, selective ultrasound for at-risk infants, or clinical examination alone with referral for at-risk infants — remains debated. Universal ultrasound screening (the German and Austrian model) detects a higher proportion of cases earlier but also identifies a large number of physiologically immature hips that resolve spontaneously, leading to over-treatment. Selective ultrasound screening (the British and many American models) targets the highest-risk infants — breech presentation, positive family history, and any abnormal clinical examination — and produces a better balance of detection versus over-treatment. The American Academy of Pediatrics and the British Society of Paediatric Radiology have published practice guidelines that combine universal clinical screening with selective imaging. Graf Ultrasound Classification The Graf classification, developed by Reinhard Graf in the 1980s, is the standard ultrasound classification of the infant hip and is universally used in centers performing screening ultrasound. The technique involves a standardized coronal-section ultrasound image of the hip with the infant in lateral decubitus, in which two angles are measured: the alpha angle (the angle between the iliac line and the bony acetabular roof, a measure of acetabular depth) and the beta angle (the angle between the iliac line and the cartilaginous labrum, a measure of labral coverage). The classification produces four primary types: Type I: Normal mature hip. Alpha angle ≥60°. Type II: Immature or dysplastic hip. Alpha angle 43-59°. Subtypes IIa (physiologically immature, <3 months, with no treatment if resolution by 6 weeks), IIb (delayed maturation,

>3 months, requiring treatment), IIc (critical zone, alpha 43-49°, beta <77°, requiring treatment), and IId (decentered, beta >77°). Type III: Dislocated hip with eccentric femoral head. The labrum is everted but not deformed. Type IV: Dislocated hip with displaced femoral head and inverted, deformed labrum. The Graf classification has the great advantage of being highly reproducible when performed by trained operators with a standardized technique, and it provides clear treatment recommendations: Type IIa-minus and IIc and worse require treatment, while Type IIa-plus and I do not.

Plain Radiographs Plain radiographs become useful as the ossific nucleus of the femoral head appears, typically at 3-6 months of age. The standard AP view of the pelvis is interpreted using several reference lines and angles: Hilgenreiner’s line (horizontal through the triradiate cartilages, the basis for further measurement), Perkin’s line (vertical at the lateral edge of the acetabulum), the femoral head ossific nucleus position (which should lie in the inferomedial quadrant defined by Hilgenreiner’s and Perkin’s lines), Shenton’s line (a smooth curve along the inferior border of the superior pubic ramus and the medial border of the femoral neck, broken in dislocation), and the acetabular index (the angle between Hilgenreiner’s line and the acetabular roof, normally <30° in infants).

Treatment of the Neonatal and Infant Hip

Pavlik Harness (0-6 months) The Pavlik harness, invented by Arnold Pavlik in 1944, is the standard treatment for the neonatal dislocated, dislocatable, or dysplastic hip up to approximately 6 months of age. The harness consists of shoulder straps that connect to anterior and posterior chest straps, which in turn attach to boot straps holding the lower limb. The anterior strap, attached at the level of the knee, maintains hip flexion at approximately 100-110°; the posterior strap, attached at the level of the calf, prevents adduction. The hip is therefore held in the “human” position — flexion of 90-110° with gentle abduction — which encourages spontaneous reduction of a dislocated hip (the Ortolani maneuver is, in effect, performed continuously by the harness) and provides the optimal environment for acetabular development. The harness is worn continuously, removed only briefly for bathing, with weekly or fortnightly clinical and ultrasound monitoring of progress. Successful Pavlik harness treatment achieves reduction in 80-95% of cases of Ortolani- positive hips treated before 3 months of age, with success rates falling for older infants and for hips with more secondary changes. Failure of the harness — variously defined as failure to achieve reduction within 3-4 weeks, persistent dislocation on ultrasound after 6-12 weeks of treatment, or the development of complications — is an indication to abandon the harness and move to closed or open reduction; persistence with an unsuccessful harness past a defined treatment failure point produces “Pavlik harness disease” (avascular

necrosis of the femoral head, posterior dislocation of the femoral head from prolonged stretch on the posterior structures, and femoral nerve palsy). The maximum safe period of unsuccessful harness use is variably quoted as 3-4 weeks, beyond which alternative management should be instituted. Hip flexion greater than 120° (excessive flexion) should be avoided because of the risk of femoral nerve palsy; abduction beyond 60° should be avoided because of the risk of avascular necrosis from compression of the medial femoral circumflex artery against the iliopsoas tendon. Closed Reduction and Hip Spica (6-18 months) For infants over 6 months in whom the Pavlik harness has failed or who present late, closed reduction under general anesthesia followed by hip spica casting is the next step. The procedure involves examination of the hip under anesthesia, adductor tenotomy if hip abduction is restricted (typically required if abduction is less than 60-70°), gentle reduction of the femoral head into the acetabulum under image intensification, arthrography to confirm a concentric reduction and to identify any obstacles to reduction, and immobilization in a hip spica cast in the “human” position (flexion 90-100°, abduction 40-50°, neutral or slight internal rotation). The position is critical: the “frog-leg” position of extreme abduction has been abandoned because of the risk of avascular necrosis from compression of the medial femoral circumflex artery. The cast is typically maintained for 3- 6 months, with a change to a less restrictive abduction brace as healing progresses. The success of closed reduction depends on the obstacles identified by arthrography. A medial dye pool of less than 5 mm at the inferomedial acetabulum is acceptable; greater than 5 mm suggests inadequate reduction and indicates conversion to open reduction. The contraindications to acceptance of closed reduction — the so-called “safe zone of Ramsey” — define the range of abduction within which the hip remains reduced; a hip that dislocates with less than 25° from full abduction has an inadequate safe zone and is at risk of redislocation, indicating either continued treatment or open reduction. Open Reduction Open reduction is indicated when closed reduction fails or when secondary changes preclude closed reduction. The standard approaches are: the anterior (Smith-Petersen) approach, the most common in the older infant and toddler; the medial (Ludloff) approach, useful in the younger infant (6-12 months) and providing direct access to the obstacles in the medial aspect of the joint without the morbidity of the anterior approach but without access to acetabular reconstruction; and combined approaches when concurrent acetabular reconstruction is planned. The principles of open reduction are: capsulotomy to enter the joint, identification and excision of the obstacles (limbus, pulvinar, hypertrophied transverse ligament), lengthening or release of the contracted iliopsoas tendon and adductor tendon, capsulorraphy to tighten the redundant joint capsule, and reduction of the femoral head into the deepened acetabulum. After open reduction, hip spica casting follows for 6-12 weeks, with continued bracing or part-time bracing for further months.

Concomitant Femoral and Pelvic Osteotomies

In the older child (typically over 18-24 months) with persistent dysplasia or with neglected dislocation, concurrent femoral and pelvic osteotomies are required to achieve and maintain reduction. The choice of procedure depends on the age of the child, the morphology of the dysplastic acetabulum, the femoral anteversion, and the soft-tissue contractures.

Femoral Osteotomy A femoral varus-derotation osteotomy addresses the typical proximal femoral anatomy of DDH: excessive anteversion and valgus. The osteotomy is typically performed in the subtrochanteric region with a blade plate or angled-blade plate fixation. Indications include excessive anteversion (greater than 50-60°), excessive valgus (femoral neck-shaft angle greater than 150°), and femoral head deformity. The procedure improves congruency, reduces shear forces on the dysplastic acetabulum, and supports acetabular remodeling in the growing child. Pelvic Osteotomies A variety of pelvic osteotomies address the dysplastic acetabulum, and the choice depends primarily on the age of the child and the morphology of the dysplasia. The Salter innominate osteotomy (described by Robert Salter in 1961) is a single-cut osteotomy of the innominate bone through the triradiate cartilage and the supra- acetabular region, with rotation of the distal segment to redirect the acetabulum anteriorly and laterally. The osteotomy depends on the elasticity of the triradiate cartilage and pubic symphysis and is therefore best suited to children between 18 months and 6 years of age. Salter’s procedure is the classical operation for the child with persistent dysplasia after open reduction. The Pemberton osteotomy is an incomplete osteotomy of the supra-acetabular region with the inferior cortex left intact; it pivots on the triradiate cartilage and is used to redirect the acetabulum more steeply than Salter osteotomy can achieve. Indications are similar to Salter but with more severe dysplasia, and it can be performed up to the age of skeletal maturity, though the triradiate cartilage must still be open. The Dega osteotomy is an incomplete osteotomy of the supra-acetabular region similar to Pemberton, used particularly in neuromuscular hip dysplasia (cerebral palsy) where the deficit is principally posterior; the osteotomy hinges on the posterior cortex and redirects the acetabulum anteriorly. The triple pelvic osteotomy (Steel, Tönnis) involves separate osteotomies of the ilium, ischium, and pubis, allowing rotation of the entire acetabular fragment. The procedure is used in older children and adolescents in whom the triradiate cartilage has closed and the Salter and Pemberton osteotomies are no longer possible. The fragment is fixed with screws and may require limited bone graft.

The periacetabular osteotomy (PAO, Ganz osteotomy) is the modern standard for the dysplastic adolescent and adult hip with closed triradiate cartilage. The procedure involves four osteotomies around the acetabulum (ischial, supra-acetabular, partial pubic, and retroacetabular cuts) that free the entire acetabulum as a single fragment while preserving the posterior column of the pelvis intact. The fragment is rotated to provide optimal coverage of the femoral head and fixed with multiple screws. The Ganz PAO is the operation of choice for symptomatic adolescent and adult hip dysplasia with a concentric, congruent joint, and its long-term outcomes — joint preservation and avoidance of arthroplasty — have transformed the management of adult hip dysplasia. The Chiari osteotomy is a salvage procedure for the older child or adolescent with severe dysplasia and a non-congruent joint, in whom redirectional osteotomies are not feasible. The osteotomy involves a cut through the iliac wing immediately superior to the acetabular rim, with medial displacement of the inferior fragment to provide a buttress of bone above the femoral head. The joint is not redirected; rather, the femoral head is provided with additional weight-bearing surface. The procedure produces a metaplastic joint surface that is less durable than the native cartilage but provides useful function for many years. The shelf acetabuloplasty is another salvage procedure in which a cortico-cancellous bone graft is fixed to the lateral acetabular rim to extend coverage of the femoral head. It is used in younger children (typically over 3-4 years) as an adjunct to reduction, and in older patients as a salvage procedure for non-congruent joints.

Avascular Necrosis (AVN) of the Femoral Head as a Complication

The principal iatrogenic complication of DDH treatment is avascular necrosis of the femoral head, produced by compression of the medial femoral circumflex artery against the iliopsoas tendon during excessive abduction. The Kalamchi-MacEwen classification of AVN following DDH treatment recognizes four grades: Grade I, transient changes of the ossific nucleus with full recovery; Grade II, lateral physeal injury with secondary valgus deformity; Grade III, central physeal injury with shortening of the femoral neck and the appearance of a relative trochanteric overgrowth; Grade IV, complete physeal arrest with severe shortening, deformity, and disability. Avoidance of excessive abduction in casting and bracing is the principal preventive measure.

The Neglected and Adolescent Hip

The neglected DDH presents as a unilateral or bilateral dislocation in an older child or adolescent who has not received treatment. The challenges of treatment are formidable: the false acetabulum has developed on the lateral iliac wall, the true acetabulum is small and dysplastic, the femoral head is deformed and the femoral neck is short and anteverted, the soft tissues are severely contracted, and the limb is shortened. Treatment options include open reduction with femoral shortening osteotomy (to allow reduction without excessive tension on the neurovascular structures) combined with pelvic osteotomy, salvage procedures (Chiari, shelf), and acceptance of the dislocated position with later total hip arthroplasty in adulthood. The choice depends on the age of the patient at presentation,

the unilateral or bilateral nature of the dislocation, and the severity of the secondary changes.

Outcomes and Adolescent / Adult Sequelae

The long-term outcome of DDH depends on the age at diagnosis, the success of initial treatment, and the development of residual dysplasia. Early diagnosis and successful Pavlik harness treatment produces near-normal hips in 90-95% of cases. Late diagnosis or failed initial treatment with subsequent open reduction and osteotomy produces less favorable outcomes, with residual dysplasia, AVN, and early osteoarthritis as the principal long-term sequelae. Adolescent and adult hip dysplasia presents with groin pain, hip impingement symptoms, and progressive arthritis, and is managed by periacetabular osteotomy in the appropriate candidate or by total hip arthroplasty in advanced disease.

Summary and Take-Home Points

Developmental dysplasia of the hip is the commonest pediatric hip disorder and the most preventable cause of early adult hip arthritis. Early diagnosis — by clinical examination at birth and at every well-child visit, supplemented by selective ultrasound for at-risk infants — and prompt treatment with the Pavlik harness in the first months of life produce excellent outcomes. The Graf ultrasound classification provides reproducible diagnosis and treatment recommendations in the neonatal and infant hip. The Pavlik harness, applied for 3-6 months in the “human” position, is the standard for the dislocatable, subluxable, or dysplastic hip in the first six months of life. Closed reduction under anesthesia with hip spica casting is the next step for the older infant or failed harness, and open reduction addresses the five classical obstacles to reduction when closed methods fail. In the older child, concurrent femoral varus-derotation osteotomy and pelvic osteotomy (Salter, Pemberton, Dega, triple, or periacetabular) address the secondary bony deformity. Avascular necrosis of the femoral head, graded by the Kalamchi-MacEwen system, is the principal iatrogenic complication and is prevented by avoidance of excessive abduction. Adolescent and adult hip dysplasia is the late consequence of inadequately treated DDH and is managed by periacetabular osteotomy in the appropriate candidate or by total hip arthroplasty in advanced disease.