Developmental Dysplasia of the Hip (DDH)

Developmental dysplasia of the hip (DDH) is a spectrum of abnormal hip development ranging from a shallow dysplastic acetabulum to a frankly dislocated femoral head. It is one of the most heavily examined paediatric orthopaedic topics in NEET PG because almost every angle is testable: screening manoeuvres, ultrasound grading, radiological indices, and the age-dependent treatment ladder.

Definition and terminology

The older term "congenital dislocation of the hip (CDH)" has been replaced by developmental dysplasia of the hip because the abnormality is not always present at birth and frequently develops over the first weeks to months of life. The term encompasses a continuum:

• Dysplasia — shallow, abnormally oriented acetabulum, but femoral head still seated.
• Subluxation — partial loss of contact between femoral head and acetabulum.
• Dislocation — complete loss of contact. May be reducible (Ortolani positive) or irreducible (teratologic).

A teratologic dislocation occurs antenatally, is fixed/irreducible at birth, and is associated with neuromuscular conditions (arthrogryposis, myelomeningocele, chromosomal syndromes).

High-yield: DDH is a spectrum, not a single entity. The "developmental" terminology was adopted precisely because many hips are normal at birth and become dysplastic later — which is why a single normal newborn examination does not exclude DDH.

Epidemiology and risk factors

Incidence of frank dislocation is roughly 1–2 per 1000 live births; dysplasia/instability is far commoner (up to ~1 in 100 if instability is included). The left hip is most commonly affected (because the usual left occiput anterior intrauterine position adducts the left hip against the maternal sacrum). Bilateral involvement is next, and isolated right hip is least common.

Classic risk factors — remember the mnemonic "6 Fs / the breech-girl-firstborn triad":

Risk factor	Why / note
Female sex	4–8× more common; maternal relaxin makes the female fetal pelvis laxer
Breech presentation	Single strongest mechanical risk factor (especially frank breech with extended knees)
Family history	Positive first-degree family history; polygenic + ligamentous laxity
Firstborn	Tight, unstretched primigravid uterus and abdominal wall
Oligohydramnios	Reduced intrauterine space restricts fetal movement
Postnatal swaddling	Tight swaddling in extension + adduction ("packaging") promotes dislocation

The condition is part of the "packaging / moulding" disorders and is associated with other intrauterine-crowding deformities: congenital muscular torticollis, metatarsus adductus, and plagiocephaly — always examine the hips when you find these.

High-yield: Breech presentation + female sex + positive family history is the most testable risk triad. The single most powerful individual risk factor is breech presentation.

Pathophysiology

The primary lesion is abnormal acetabular development. Normal acetabular deepening depends on a concentrically reduced, spherical femoral head acting as a template. When the head is subluxated or dislocated:

• The acetabulum stays shallow and the roof becomes oblique (rising acetabular index).
• Secondary soft-tissue blocks to reduction develop over time — inverted limbus (labrum), hypertrophied pulvinar (fibrofatty tissue), hourglass-constricted capsule, tight iliopsoas tendon crossing the capsule, and a taut transverse acetabular ligament.
• The ligamentum teres hypertrophies and elongates.

The classic mnemonic for obstacles to reduction is the "5 obstacles": limbus, pulvinar, ligamentum teres, transverse acetabular ligament, and iliopsoas tendon (capsular constriction being the sixth). These are the reason that the longer a hip stays dislocated, the less likely closed reduction will succeed.

Clinical features — by age

Clinical signs are strongly age-dependent, and this is a favourite exam concept.

Neonate (0–3 months): instability tests

The hallmark examinations are the Ortolani and Barlow tests, performed one hip at a time with the infant relaxed, hips and knees flexed to 90°.

• Ortolani test ("O for Out → In"): The examiner abducts the flexed hip while lifting the greater trochanter anteriorly. A palpable "clunk" of reduction as a dislocated head relocates into the acetabulum = positive (reducing a dislocated hip).
• Barlow test ("B for Back / dislocatable"): The flexed hip is gently adducted with posterior pressure; a dislocatable hip slips out over the posterior rim. It is a provocative test that dislocates a reducible hip.

High-yield: Ortolani relocates a dislocated hip; Barlow dislocates a reducible (located) hip. A high-pitched soft click (ligamentous) is benign; a clunk is significant. Both tests become negative after ~3 months because soft-tissue contractures fix the hip — so absence of Ortolani/Barlow after this age does NOT exclude DDH.

Infant (3–12 months): limited abduction

Once contractures set in, the instability signs disappear and you rely on:

• Limited/asymmetric hip abduction (most reliable sign after 3 months).
• Galeazzi / Allis sign — with hips and knees flexed, the affected knee is lower (apparent femoral shortening). Useful only in unilateral disease.
• Asymmetric thigh/gluteal skin creases (unreliable alone; present in many normal babies).
• Klisic test, Barlow positivity fading.

Walking child (>1 year)

• Unilateral: painless limp, positive Trendelenburg sign (abductor lever arm shortened), toe-walking on the affected side, increased lumbar lordosis.
• Bilateral: waddling ("duck") gait, wide perineum, hyperlordosis — often diagnosed late and easy to miss because there is no asymmetry to flag.

Age	Best clinical sign
0–3 months	Ortolani / Barlow (instability)
3–12 months	Limited abduction + Galeazzi sign
Walking, unilateral	Trendelenburg, limp, short limb
Walking, bilateral	Waddling gait, hyperlordosis, wide perineum

Investigations

The imaging modality of choice is age-dependent — another high-yield decision point.

Flow: Age <4–6 months → **Ultrasound** → Age >4–6 months (femoral head ossific nucleus appears) → Plain radiograph (AP pelvis).

Ultrasound — investigation of choice under 6 months

Before the femoral head ossifies (~4–6 months), the head is cartilaginous and invisible on X-ray, so ultrasound is the investigation of choice. The standard is the Graf static technique, measuring two angles on a coronal image:

• Alpha (α) angle — bony acetabular roof; normal ≥ 60°. Higher = better/deeper.
• Beta (β) angle — cartilaginous roof; normal < 55°.

Graf type	Alpha angle	Interpretation
Type I	≥ 60°	Normal mature hip
Type IIa/IIb	50–59°	Immature/mildly dysplastic (IIa physiological <3 mo)
Type IIc	43–49°	Severely dysplastic but reduced
Type D	43–49°, β >77°	Decentring hip
Type III	< 43°	Subluxated (everted labrum)
Type IV	very low	Dislocated

The Harcke dynamic technique adds real-time stress to assess stability (a sonographic Barlow). Note that ultrasound before ~4–6 weeks over-diagnoses physiological immaturity, so selective screening US is often deferred to 6 weeks.

High-yield: Under 6 months → USG (Graf α ≥ 60° normal). Over 6 months → AP pelvis X-ray. The ossific nucleus of the femoral head appears around 4–6 months, which is the crossover point.

Radiographic indices (>6 months)

On an AP pelvis, draw these reference lines:

• Hilgenreiner's line — horizontal line through both triradiate cartilages (Y-cartilage).
• Perkin's line — vertical line through the lateral edge of the acetabulum, perpendicular to Hilgenreiner's. The normal ossific nucleus / femoral head lies in the inner-lower quadrant; in DDH it migrates to the upper-outer quadrant.
• Acetabular index — angle between Hilgenreiner's line and the acetabular roof; normal < 30° at birth, < 25° by 1 year, < 22° by 2 years. A high index = shallow acetabulum.
• Shenton's (Menard's) line — smooth arc from the inferior border of the superior pubic ramus to the inferomedial neck of femur; broken Shenton's line = subluxation/dislocation.
• Centre-edge angle of Wiberg — used in older children/adults; < 20° abnormal (acetabular dysplasia).
• Von Rosen view — AP with hips abducted 45° and internally rotated; the femoral shaft axis normally points to the acetabulum, but in DDH it points above it.

High-yield: A broken Shenton's line and the femoral head in the upper-outer quadrant (Perkin–Hilgenreiner quadrants) are the two classic X-ray signs of dislocation. Acetabular index > 30° indicates a dysplastic acetabulum.

MRI/CT are reserved for confirming concentric reduction after closed reduction in a spica cast (CT or limited MRI), and arthrography is used intra-operatively to define the "safe zone" and obstacles.

Management — the age-based treatment ladder

Treatment is dictated almost entirely by age and reducibility. The guiding principle: achieve and maintain a concentric, stable, atraumatic reduction to let the acetabulum remodel.

Treatment flow: 0–6 months → Pavlik harness (dynamic flexion-abduction) → if fails/irreducible → 6 months–18 months → closed reduction + arthrogram + hip spica (human/Salter position) → if irreducible → open reduction → >18 months–2 years → open reduction + femoral/pelvic osteotomy as needed.

0–6 months: Pavlik harness

The Pavlik harness is the first-line device. It holds the hips in flexion (~100–110°) and gentle abduction, directing the femoral head into the acetabulum and allowing active movement to deepen it.

• Worn 23–24 hours/day, reviewed with serial ultrasound; success ~85–95% for reducible hips.
• Major complications: avascular necrosis (AVN) of the femoral head from excessive/forced abduction, and femoral nerve palsy from excessive flexion. Pavlik harness disease = erosion of the posterolateral acetabulum from a chronically unreduced hip left in the harness.
• Contraindications/failure: if the hip is not reduced by ~3 weeks of harness use, abandon it (continuing risks Pavlik disease). Teratologic dislocations, major muscle imbalance, and ligamentous laxity syndromes (e.g., Ehlers-Danlos) respond poorly.

High-yield: Avoid forced/excessive abduction in any DDH treatment — it is the chief cause of AVN, the most feared complication. The safe abduction is the "human position" (flexion with moderate abduction), not the extreme frog-leg/Lorenz position.

6–18 months: closed reduction + spica

Once the child is too big/old for a harness or it has failed:

• Closed reduction under anaesthesia with arthrography to confirm concentric reduction and assess obstacles.
• May be preceded by gradual traction to relax soft tissues.
• An adductor tenotomy widens the "safe zone."
• Immobilise in a hip spica cast in the "human position" (flexion ~95°, abduction 40–55° — NOT extreme). Confirm reduction with CT/MRI.

18 months–2 years and beyond: open reduction ± osteotomy

After walking age and in failed closed reductions:

• Open reduction (medial or anterolateral approach) to remove the obstacles (limbus, pulvinar, psoas, capsule).
• Femoral osteotomy — varus derotation shortening osteotomy when there is excessive femoral anteversion/coxa valga; shortening also reduces pressure → lowers AVN risk.
• Pelvic (acetabular) osteotomies:

Osteotomy	Type / mechanism	Typical use
Salter (innominate)	Redirectional; hinges on pubic symphysis to rotate acetabulum forward/laterally	Children ~18 mo–6 yr; classic NEET answer
Pemberton	Reshaping; hinges on triradiate cartilage, reduces acetabular volume	Younger children, open triradiate cartilage
Dega	Incomplete iliac osteotomy, reshaping	Neuromuscular/posterior deficiency
Chiari	Salvage/medial displacement; provides fibrocartilage cover	Older child, non-congruent hip
Shelf (augmentation)	Salvage; bone graft extends roof	Inadequate lateral cover
Ganz (peri-acetabular, PAO)	Redirectional in skeletally mature	Adolescents/adults with closed triradiate

High-yield: Salter osteotomy hinges on the pubic symphysis and redirects the acetabulum; Pemberton hinges on the triradiate cartilage and reshapes/reduces volume. Salter is the single most commonly asked pelvic osteotomy.

Complications

• Avascular necrosis (AVN) of the femoral head — the most serious iatrogenic complication, from forced abduction/excessive pressure; can produce growth disturbance and a misshapen head.
• Redislocation / residual subluxation.
• Residual acetabular dysplasia → early secondary osteoarthritis in adulthood (DDH is a leading cause of OA hip in young adults, especially women).
• Leg-length discrepancy and limb shortening.
• Coxa magna, coxa vara (post-osteotomy), stiffness, and limp.

Key differential diagnoses

Condition	Distinguishing feature
Septic arthritis of hip	Febrile, toxic, refuses to move limb, raised CRP/ESR — an emergency
Coxa vara (developmental)	Neck-shaft angle reduced, decreased abduction, but head reduced
Proximal focal femoral deficiency (PFFD)	Markedly short, externally rotated thigh; abnormal proximal femur
Neuromuscular hip dislocation	Cerebral palsy, spina bifida — secondary to muscle imbalance
Pathological dislocation	Following neonatal hip sepsis (post-infective)
Transient synovitis	Older child, self-limiting, follows viral illness

Recently asked / exam angle

• Ortolani vs Barlow is the single most repeated question: Ortolani relocates; Barlow dislocates. Image-based questions show the manoeuvre — abduction-with-lift = Ortolani.
• Graf α angle ≥ 60° = normal — direct numerical recall.
• Investigation of choice by age: USG <6 months, X-ray >6 months (because of the femoral head ossific nucleus).
• Salter osteotomy hinges on the pubic symphysis; Pemberton on the triradiate cartilage — frequently paired in match-the-following.
• Most feared complication = AVN, caused by forced abduction; safe "human position" is the answer to "how to immobilise."
• Galeazzi sign is positive only in unilateral DDH; bilateral DDH is the classic "easily missed" presentation with a waddling gait.
• Acetabular index >30° and broken Shenton's line as radiological markers.
• Strongest risk factor = breech presentation; left hip most commonly affected.
• Associations: torticollis, metatarsus adductus, oligohydramnios ("packaging" disorders).

Rapid revision

1. DDH = spectrum: dysplasia → subluxation → dislocation; "developmental," not purely congenital.
2. Left hip most common; breech, female, firstborn, family history, oligohydramnios are risk factors.
3. Ortolani reduces a dislocated hip (clunk in); Barlow dislocates a reducible hip (clunk out).
4. Instability tests become negative after ~3 months due to contractures.
5. After 3 months, limited abduction is the most reliable sign; Galeazzi positive only if unilateral.
6. USG is investigation of choice <6 months (Graf: α ≥ 60° normal, β < 55°).
7. AP X-ray after 6 months when the ossific nucleus appears.
8. Radiology: acetabular index >30°, head in upper-outer Perkin quadrant, broken Shenton's line.
9. Pavlik harness first-line 0–6 months; avoid forced abduction → AVN; avoid excessive flexion → femoral nerve palsy.
10. 6–18 months: closed reduction + arthrogram + human-position spica; >18 months: open reduction ± osteotomy.
11. Salter osteotomy hinges on pubic symphysis (redirect); Pemberton on triradiate cartilage (reshape).
12. AVN is the most feared complication; untreated DDH → early secondary osteoarthritis, especially in young women.