Introduction / Definition

Developmental dysplasia of the hip (DDH) describes a continuum of pathology affecting the neonatal and infant hip, extending from mild acetabular dysplasia without displacement to subluxation, reducible dislocation, and fixed, irreducible teratological dislocation. Historically referred to as congenital dislocation of the hip (CDH), the nomenclature changed to recognise that the hip may be anatomically normal at birth and develop instability or dysplasia postnatally.

The overall incidence in Caucasian populations is approximately 1 to 3 per 1,000 live births for frank dislocation, but extends upwards of 15 to 20 per 1,000 when dynamic instability and mild acetabular dysplasia are included. DDH predominantly affects females (roughly 80%), with the left hip being affected more commonly (60%) than the right (20%), and bilateral involvement occurring in approximately 20% of cases.

Risk Factors and Pathophysiology

Key predisposing factors are conventionally divided into mechanical and hormonal:

• Breech presentation: The single greatest isolated risk factor (relative risk 4–6x), primarily due to forced knee extension causing hamstring tightness and hip subluxation forces in utero.
• Female sex: Associated with intrinsic sensitivity to circulating maternal relaxins, inducing ligamentous laxity.
• Family history: Approximately 6% risk if one sibling has DDH, rising to 12% if a parent is affected, and 36% if a parent and a sibling are affected.
• Oligohydramnios, primiparity, macrosomia, and post-term birth: Intrauterine crowding mechanics.
• Associated packaging deformities: Metatarsus adductus, congenital muscular torticollis (up to 8-10% co-existent DDH), and calcaneovalgus foot.
• Postnatal practices: Tight lower-limb swaddling with the hips adducted and extended sharply increases the incidence.

Relevant Anatomy & Classification

Normal hip development relies on a reciprocal dynamic equilibrium: a spherical femoral head concentrically located within a hemispherical, pliable cartilaginous acetabulum stimulating normal concentric rim ossification via the triradiate cartilage.

Anatomical Obstacles to Concentric Reduction

In chronic subluxation or dislocation, mechanical barriers evolve to prevent closed relocation:

• Intra-articular obstacles:
  • Inverted/hypertrophic limbus: The fibrocartilaginous labrum becomes inverted, bruised, and enlarged.
  • Pulvinar: Hypertrophied fibrofatty tissue filling the empty acetabular floor.
  • Ligamentum teres: Elongated, thickened, and fibro-fatty.
  • Transverse acetabular ligament (TAL): Contracted and pulled superiorly, closing off the inferior inlet.
• Extra-articular obstacles:
  • Hourglass constriction: Constriction of the fibrous capsule by the crossing iliopsoas tendon.
  • Iliopsoas contracture: Tightly drawn over the anterior joint capsule, forming a mechanical barrier.
  • Adductor longus / brevis contracture: Restricting abduction required for reduction.

Named Classifications

1. Graf Ultrasound Classification (Infants < 6 months)

Evaluates the osseous acetabular roof angle (Alpha, α) and the cartilaginous roof angle (Beta, β) on a coronal standard plane:

• Type I (Mature/Normal): α ≥ 60°, β < 55°.
• Type II (Physiological delay / Dysplasia):
  • IIa: α 50–59$^ circ in infants < 3$ months (physiologic immaturity).
  • IIb: α 50–59$^ circ in infants > 3$ months (delayed maturation).
  • IIc: α 43–49$^ circ, \beta < 77^\circ$ (critical/at risk).
  • IId: α 43–49$^ circ, \beta > 77^\circ$ (decentring / transitional).
• Type III (Subluxated/Dislocated): α < 43°, with superior structural alteration of cartilaginous roof.
• Type IV (Frank Dislocation): Head completely displaced superiorly; α < 43°, inverted labrum.

2. International Hip Dysplasia Institute (IHDI) Classification

Used on pelvic radiographs for children after the development of ossification centers, or when evaluating the midpoint of the proximal femoral metaphysis:

• Uses the H-line (Hilgenreiner's line) and P-line (Perkin's line).
• Grade I: Metaphyseal midpoint medial to P-line.
• Grade II: Metaphyseal midpoint on or lateral to P-line, but medial to a diagonal line drawn at 45° through the intersection of H- and P-lines.
• Grade III: Metaphyseal midpoint lateral to the 45° line, below the H-line.
• Grade IV: Metaphyseal midpoint above the H-line.

3. Tönnis Radiographic Classification

Evaluates the ossified femoral head centre relative to Perkins line and the horizontal line passing through the lower edge of the teardrop.

Clinical Presentation & Examination

Clinical examination depends strictly on patient age.

Neonates and Infants (< 3 Months)

• Ortolani Test (Reduction manoeuvre): Hip flexed to 90° and gently abducted while elevating the greater trochanter anteriorly. A positive test is a palpable, smooth ‘clunk’ as the femoral head reduces over the posterior acetabular rim into the socket.
• Barlow Test (Provocative dislocation manoeuvre): Hip flexed to 90° and gently adducted with gentle axial posterior thrust applied along the femoral shaft. A positive test is a palpable sensation of the head sliding or subluxating out of the acetabulum.
• Note: High-pitched soft clicks are typically benign fascial snaps (e.g. fascia lata) and must not be confused with true low-frequency Ortolani/Barlow thuds.

Older Infants (> 3 to 6 Months)

As soft tissues contract, dynamic tests become negative, and static signs predominate:

• Limitation of hip abduction: The single most sensitive and reliable clinical sign in unilateral or bilateral DDH in infants older than 3 months. Normal abduction is ≥ 70°; asymmetric limitation or < 50° is highly suspicious.
• Galeazzi Sign (Allis sign): With the infant supine, hips and knees flexed to 90°, and feet flat on the table, relative shortening of the thigh on the dislocated side is evident due to the femoral head resting posterior/superior to the acetabulum.
• Asymmetric skin folds: Extra groin/thigh cutaneous folds (non-specific; only significant if deep thigh and asymmetric labial/inguinal extension).

Ambulatory Toddlers

• Unilateral dislocation: Trendelenburg gait, short-leg limp, limb length discrepancy with compensatory equinus foot posture.
• Bilateral dislocation: 'Waddling' gait, pronounced lumbar lordosis due to fixed hip flexion, wide perineal gap, and prominent greater trochanters.

Investigations

Ultrasonography (Birth to 6 Months)

Before ossification of the femoral head (typically 4–6 months), ultrasound is the modality of choice. In the UK, the NHS Newborn and Infant Physical Examination (NIPE) programme mandates selective ultrasound screening at 4–6 weeks for clinical abnormality or major risk factors (first-degree family history, breech delivery after 36 weeks or breech at birth, twin breech).

• Graf method: Standard coronal view at the deepest point of the acetabulum showing the mid-portion of the ilium, acetabular labrum, and triradiate cartilage.
• Harcke dynamic ultrasound: Real-time dynamic evaluation in coronal and transverse planes under stress.

Plain Radiographs (Pelvis AP, neutral, and frog-leg lateral)

Primary imaging modality from 4–6 months onwards once the femoral ossific nucleus appears.

• Hilgenreiner’s line (H-line): Horizontal line drawn connecting the superior margins of the triradiate cartilages.
• Perkin’s line (P-line): Vertical line dropped perpendicular to Hilgenreiner's line from the lateral osseous margin of the acetabular roof.
• Quadrants: Normal ossific nucleus lies within the inferomedial quadrant. In DDH, it shifts to the superolateral quadrant.
• Shenton’s line: Smooth, continuous imaginary arc drawn along the inferior border of the superior pubic ramus and medial margin of the femoral neck. Interrupted or 'broken' Shenton’s line signifies subluxation or dislocation.
• Acetabular Index (AI): Angle between Hilgenreiner’s line and a line along the acetabular roof. Normal at birth is < 30°, decreasing to < 20° by 2 years. Values > 30° in older infants indicate persistent dysplasia.
• Centre-Edge Angle of Wiberg (lateral CEA): Used in children > 5 years and adults. Measured from the vertical to the lateral acetabular margin; normal is > 25° (< 20° denotes definite dysplasia).

Management

Treatment principles aim to achieve and maintain concentric, stable, atraumatic anatomical reduction as early as possible without risking avascular necrosis (AVN).

0 to 6 Months: Pavlik Harness

• Dynamic, non-rigid abduction splint allowing active movement within a safe zone.
• Biomechanics: Flexion straps maintain 100°–110° of flexion (guides femoral head opposite acetabular entry). Posterior abduction straps maintain 45°–60° of gentle abduction. Excessive flexion (> 120°) risks femoral nerve palsy; excessive forced abduction (> 70°) compresses the posterosuperior retinacular vessels against the acetabular rim, causing AVN.
• Monitoring: Ultrasound assessment at 1–2 weeks to confirm concentric reduction. If unreduced by 3–4 weeks, the harness must be abandoned to prevent "Pavlik harness disease" (posterior acetabular rim grooving and erosion by the unreduced head).
• Successful reduction rate is approximately 90–95% for simple dysplasia/subluxation and 60–80% for true Ortolani-positive dislocations.

6 to 18 Months: Closed or Open Reduction & Spica

• Indication: Failure of Pavlik harness or late presentation (6–18 months).
• Closed reduction under general anaesthesia:
  • Hip examination under anaesthesia and fluoroscopy/arthrogram (pooling of medial dye > 5–6 mm implies non-concentric reduction or soft tissue interposition).
  • Percutaneous adductor tenotomy (releases adductor longus contracture, widening the Ramsay 'safe zone' of reduction between redislocation and forced abduction).
  • Application of a 1.5-hip hip spica cast in the "human position" (90°–100° flexion, 45°–55° abduction, neutral rotation) for 12 weeks with an interval change at 6 weeks.
  • Post-reduction CT or MRI is mandatory within 24–48 hours to confirm concentric reduction in the spica.
• Open reduction:
  • Indicated if closed reduction fails, if the safe zone is < 20°, or if arthrogram reveals significant soft tissue interposition.
  • Approaches: Anterior (Smith-Petersen, preferred if secondary pelvic osteotomy required) or Medial (Ludloff / Ferguson / medial anterior, ideal in children < 12–18 months without secondary osseous deformity; avoids dissection of abductor muscles).
  • Systematic release/excision: Iliopsoas tenotomy, removal of hypertrophied pulvinar and ligamentum teres, TAL division, and capsulorrhaphy (vest-over-pants plication).

18 to 24 Months: Open Reduction and Osseous Procedures

At this age, acetabular remodelling potential diminishes, and excessive femoral anteversion/coxa valga may prevent stability. Most patients require concomitant open reduction, femoral derotation/varus osteotomy (VDRO), and a pelvic osteotomy.

Pelvic Osteotomies (Age > 18–24 Months)

Categorised functionally into reconstructive (reshaping/re-orienting) and salvage:

1. Redirection (Acetabular Reorientation - triradiate cartilage must be open or closed based on type):

   • Salter Innominate Osteotomy: Transverse cut from the sciatic notch to the anterior inferior iliac spine (AIIS). Rotates the acetabulum around the symphysis pubis anterolaterally. Corrects acetabular index by up to 10°–15°. Requires an open triradiate cartilage.
   • Triple Pelvic Osteotomy (Steel, Tönnis): Complete division of ilium, ischium, and pubis; used in older juveniles with an open or closing triradiate cartilage requiring marked acetabular rotation.
   • Ganz Periacetabular Osteotomy (PAO): Indicated in adolescents and young adults with a closed triradiate cartilage and congruent, preserved articular cartilage. Retains the posterior column, allowing immediate mobilisation and high degrees of 3D correction.

2. Reshaping (Volume reduction/acetabuloplasty - triradiate cartilage must be open):

   • Pemberton Osteotomy: Incomplete osteotomy from AIIS curving downward into the ilio-ischial limb of the triradiate cartilage. Hinging occurs through the triradiate cartilage, reducing acetabular volume and providing significant anterior and lateral coverage.
   • Dega Osteotomy: Incomplete transcortical osteotomy directed towards the triradiate cartilage, leaving the inner pelvic cortex intact. Allows customised anterior, lateral, or posterior overhang alteration (popular in neuromuscular hip dysplasia).

3. Salvage Procedures (Congruent reduction unobtainable; triradiate usually closed):

   • Chiari Medial Displacement Osteotomy: Horizontal osteotomy directly above the joint capsule; the distal fragment is displaced medially, allowing the shelf of the iliac cut to cover the head with metaplastic fibrocartilage.
   • Shelf Procedure: Extra-articular augmentation using structural autograft positioned over the superior joint capsule.

Complications

• Avascular Necrosis (AVN) of the Femoral Head: The most devastating complication (0–73% incidence depending on series and technique). Primarily iatrogenic, driven by excessive abduction in casts or braces, forceful reduction, or posterior dissection jeopardising the medial femoral circumflex artery (MFCA). Classified according to the Kalamchi and MacEwen system (Grade I: temporary changes; Grade II: lateral physeal damage leading to valgus head; Grade III: central physeal arrest; Grade IV: complete head collapse and short femoral neck).
• Redislocation / Persistent Subluxation: Often secondary to unrecognised intra-articular blocks, inadequate capsular tightening, or uncorrected acetabular/femoral retroversion/anteversion.
• Femoral Nerve Palsy: Occurs with excessive hip flexion in a Pavlik harness (> 120°). Characterised by loss of active knee extension. Harness must be removed immediately; generally resolves spontaneously.
• Chondrolysis and Early Osteoarthritis: Resulting from repetitive forceful closed manoeuvres or persistent joint incongruity.

Exam Pearls

• The medial circumflex femoral artery (MFCA) is the primary vascular supply to the infant and paediatric femoral head; damage to its deep ascending terminal branches during medial approaches (Ludloff/Ferguson) or capsulotomy produces catastrophic AVN.
• Remember the Safe Zone of Ramsay: The angular difference between the angle of abduction required to achieve reduction (reduction arc) and the angle of adduction at which redislocation occurs (redislocation arc). A narrow safe zone (< 20°) is an absolute indication for adductor tenotomy or open reduction.
• A broken Shenton’s line on a plain pelvis radiograph is the most dependable initial sign of hip displacement in older infants.
• Pemberton vs. Salter: Salter rotates the entire acetabulum using the pubic symphysis as a hinge (requires bone graft block in the osteotomy gap and intact triradiate cartilage); Pemberton reshapes the acetabular roof by hinging through the triradiate cartilage itself and alters the acetabular volume (does not require internal fixation).
• Always check the status of the triradiate cartilage in the exam before choosing an osteotomy: Salter and Pemberton require an open triradiate cartilage; Ganz PAO is indicated strictly when the triradiate cartilage is closed.