Paediatrics Series: DDH - From Screening to Treatment

Visual Element: An interactive "Age Slider". As the user slides from "Newborn" to "4 Years", the treatment algorithm and imaging modality (US -> X-ray) changes dynamically.

Developmental Dysplasia of the Hip (DDH) represents a complex spectrum of pathology ranging from mild, asymptomatic acetabular dysplasia to frank, irreducible dislocation. It is the most common orthopaedic condition in the newborn, with an incidence of neonatal instability approaching 1 in 100, though true dislocation is closer to 1.5 per 1,000 live births. Failure to diagnose and effectively manage DDH early leads to devastating consequences, including early-onset osteoarthritis, significant leg-length discrepancy, and profound disability in young adulthood. In fact, undetected DDH remains a leading cause of total hip arthroplasty in patients under the age of 40.

The terminology shift from "Congenital" (CDH) to "Developmental" (DDH) is crucial for orthopaedic surgery trainees to understand. It reflects the clinical reality that the condition is dynamic and can evolve long after birth. A hip that appears clinically and sonographically normal at birth can become dysplastic at 6 months of age. This mandates that clinical surveillance must be ongoing throughout early childhood, rather than treated as a single isolated screening event in the neonatal unit.

Part 1: Etiology and Risk Factors

The pathogenesis of DDH is multifactorial, representing an interplay between genetic predisposition, hormonal influences, and mechanical "packaging" issues in utero. A thorough understanding of these risk factors is essential for fellowship exam preparation and guiding screening protocols.

• The 4 F's (The Classic Paradigm):
  • Female (80%): Female infants have an increased susceptibility to maternal relaxin, a hormone that crosses the placenta to facilitate pelvic expansion during birth, inadvertently causing ligamentous laxity in the infant's joints.
  • First-born: The unstretched primigravida uterus exerts greater mechanical compressive forces on the fetus, restricting movement and altering hip development.
  • Feet-first (Breech Presentation): This is the single most significant risk factor. A "frank breech" position (hips flexed, knees extended) places immense tension on the hamstrings, which acts as a deforming force, mechanically pulling the femoral head out of the developing acetabulum.
  • Family History: DDH exhibits a polygenic inheritance pattern. The risk jumps significantly if a sibling or parent is affected.
• Associated "Packaging" Conditions: Conditions resulting from severe intrauterine crowding often present concurrently. Look for Torticollis (up to a 20% association with DDH), Metatarsus Adductus, and congenital knee dislocation. In exam scenarios, if a child presents with a severe torticollis, always actively investigate the hips.
• Post-natal Environmental Factors: The practice of tight swaddling with the hips forced into extension and adduction (traditional in some cultures) increases the risk of DDH up to 10-fold. Safe swaddling techniques must allow the hips to remain in a natural state of flexion and abduction.

Part 2: Screening and Diagnosis

The Clinical Exam (The Art)

The clinical examination evolves as the child ages. What works at 2 weeks will not work at 6 months.

• 0-3 Months: The Era of Laxity
  • Barlow Test: Provocative test. Back (Posterior). Flex the hip to 90 degrees, adduct, and apply a gentle posterior force. This tests if a resting, reduced hip is dislocatable.
  • Ortolani Test: Reductive test. Out (Abduct). Gently abduct the hip and apply anterior pressure to the greater trochanter. This tests if a dislocated hip is reducible. You are feeling for a distinct "Clunk" as the femoral head slips over the posterior rim of the acetabulum into the socket. A high-pitched "Click" is usually just the snapping of the iliotibial band or ligamentum teres and is clinically benign.
• > 3 Months: The Era of Contracture
  • As the infant grows, soft tissues contract and the hip becomes stiff. The Barlow and Ortolani tests become negative, even in a dislocated hip.
  • Limited Abduction: This becomes the most sensitive and reliable clinical sign. Normal abduction is ~75 degrees. Restriction to < 60 degrees, or asymmetry > 20 degrees between sides, is highly suspicious.
  • Galeazzi Sign: With the child supine and both knees/hips flexed, a height difference in the knees indicates an apparent leg length discrepancy, secondary to posterior displacement of the femoral head.

Ultrasound Screening (The Science)

Ultrasound is the modality of choice until the proximal femoral ossific nucleus appears (typically 4-6 months). Timing is critical: universal screening immediately after birth has a high false-positive rate due to normal physiologic laxity. Wait until 4-6 weeks for definitive US screening unless the clinical exam is frankly positive.

The Graf Classification (Coronal Plane): Evaluates the bony roof (Alpha angle) and cartilaginous roof (Beta angle).

• Type I: Normal. Alpha > 60°.
• Type IIa: Immature (Alpha 50-59°, age < 12 weeks). Physiologic delay. Observe and repeat US.
• Type IIb: Dysplastic (Alpha 50-59°, age > 12 weeks). Requires treatment.
• Type IIc: Critical / Endangered (Alpha 43-49°). High risk of dislocation. Treat immediately.
• Type III: Dislocated (Alpha < 43°). Cartilaginous roof is pushed upwards.
• Type IV: Dislocated with a grossly distorted, inverted labrum interposed in the joint.

X-Ray Measurements

Once the femoral head begins to ossify, plain anteroposterior (AP) pelvis films become the gold standard. Positioning is vital; the pelvis must be neutral, not rotated or tilted.

• Hilgenreiner's Line: A horizontal line drawn through the bilateral triradiate cartilages.
• Perkin's Line: A vertical line drawn perpendicular to Hilgenreiner's, descending from the most lateral edge of the ossified acetabular roof. The femoral head must reside in the Infero-Medial quadrant formed by these intersecting lines.
• Acetabular Index (AI): The angle formed by the slope of the acetabular roof intersecting Hilgenreiner's line. It should be < 30 degrees at birth and progressively decrease to < 20 degrees by age 2.
• Shenton's Line: A continuous, smooth radiographic arc tracing the medial border of the femoral neck to the superior border of the obturator foramen. A broken arc implies superior migration (subluxation or dislocation).
• Center-Edge (CE) Angle of Wiberg: Used in older children and adults. Measures lateral coverage of the femoral head. Normal is > 25 degrees.

Part 3: Treatment Algorithm by Age

The management of DDH is strictly age-dependent. The goal is always to achieve and maintain a concentric, stable reduction without damaging the delicate blood supply to the developing femoral head.

0 - 6 Months: The Pavlik Harness

The Pavlik harness is the gold standard for reducible dysplastic or dislocated hips in young infants.

• Mechanism: It is a dynamic splint that maintains the hip in the "Human Position" of Flexion (90-100 degrees) and moderate Abduction (45-50 degrees). Crucially, it prevents hip extension. By keeping the femoral head directed toward the triradiate cartilage while allowing active movement, it harnesses the child's own muscle tone to stimulate concentric acetabular remodeling.
• Protocol: Typically worn 23 hours a day. Serial ultrasound evaluations are required every 1-2 weeks to confirm reduction and track morphological improvement.
• Success Rates: Highly effective (90-95%) for Graf II and III hips. The success rate drops precipitously for Graf IV (frank dislocation with interposed labrum) or in syndromic/teratologic dislocations.
• Complications:
  • Femoral Nerve Palsy: Caused by hyperflexion (> 120 degrees). The baby will present with decreased active kicking or absent knee extension. Treatment: temporarily loosen the anterior straps.
  • Avascular Necrosis (AVN): Caused by extreme hyperabduction. This compresses the vulnerable medial circumflex femoral artery against the posterior labrum or psoas tendon.
  • Pavlik Disease: Erosion of the posterior rim of the acetabulum caused by the persistent grinding of a dislocated femoral head that is locked out of the socket but held in the harness.

6 - 18 Months: Closed vs. Open Reduction

By 6 months, the infant is too large, strong, and active for a Pavlik harness to be reliable. Treatment shifts to definitive reduction under general anesthesia.

• Closed Reduction & Spica Casting:
  • Performed via Examination Under Anesthesia (EUA) and dynamic intraoperative Arthrography.
  • The arthrogram evaluates the quality of reduction. A medial dye pool of < 5mm indicates an acceptable concentric reduction.
  • The Safe Zone of Ramsey: The arc of motion between the angle of maximal abduction (where adductors tighten and AVN risk spikes) and the angle of adduction where the hip re-dislocates. If the safe zone is narrow (< 20 degrees), a percutaneous adductor tenotomy is routinely performed to widen it, allowing safe application of a hip spica cast.
• Open Reduction:
  • Indicated if closed reduction fails to achieve a stable, concentric reduction due to anatomical blocks.
  • Approach: Medial (Ludloff/Ferguson) is favored in younger children (<12 months) as it approaches the hip directly from below, allowing easy release of the psoas and transverse ligament without violating the iliac apophysis. The Anterior (Smith-Petersen) approach is extensile, preferred in older children, and allows for concurrent pelvic osteotomy.

18 Months - 4 Years: Femoral and Pelvic Osteotomies

In the walking child, simple soft-tissue reduction is rarely sufficient. The acetabulum has lost its plasticity, and bony reshaping is required to provide mechanical stability.

• Femoral Osteotomy: A Varus Derotational Osteotomy (VDRO).
  • Rationale: DDH is typically associated with excessive femoral anteversion and coxa valga. A VDRO corrects this geometry. Furthermore, by intentionally shortening the femur (subtrochanteric shortening), it drastically decompresses the hip joint. This reduces tension on the surrounding musculature when pulling a high, chronically dislocated hip down into the true acetabulum, drastically reducing the risk of AVN.
• Pelvic Osteotomies:
  • Salter (Innominate): A complete, redirectional osteotomy. The cut runs from the sciatic notch to the AIIS. The entire acetabulum is hinged downward and outward at the mobile pubic symphysis. It provides excellent anterolateral coverage and slightly lengthens the leg. Prerequisite: requires an open triradiate cartilage and a concentrically reduced hip.
  • Pemberton: An incomplete, pericapsular osteotomy. The cut hinges on the flexible triradiate cartilage. It actively changes the shape of the acetabulum, bending the roof downward. This reduces the overall volume of the joint, making it ideal for the large, capacious, shallow dysplastic hip.
  • Dega: Similar to a Pemberton, but the inner table of the posterior ilium is left intact. Frequently utilized in neuromuscular dysplasia (e.g., Cerebral Palsy) where posterior deficiency is prominent.

> 4 Years to Adolescence: Salvage Procedures

• Triple Pelvic Osteotomy (Steel, Tonnis): In older children, the pubic symphysis loses mobility, meaning a Salter osteotomy will not hinge. Complete cuts through the Ilium, Ischium, and Pubis free the acetabulum entirely, allowing massive multi-directional reorientation.
• Periacetabular Osteotomy (PAO of Ganz): The absolute gold standard for symptomatic dysplasia in adolescents and young adults with closed triradiate cartilage. The polygonal cuts free the acetabulum while meticulously preserving the posterior column of the pelvis. This maintains pelvic ring stability, allows for early weight-bearing, and does not alter the shape of the true pelvis (preserving the potential for normal vaginal delivery in females).

Part 4: Avascular Necrosis (AVN) - The Enemy

Avascular Necrosis in the setting of DDH is almost entirely an iatrogenic complication. It is the most devastating complication of treatment, altering the trajectory of the child's life.

• Pathophysiology: The blood supply to the developing pediatric femoral head (primarily the lateral epiphyseal branches of the medial circumflex femoral artery) is exceedingly fragile. Extreme positioning (hyperabduction in casting) or forceful reduction of a high dislocation without adequate femoral shortening stretches and tamponades these vessels.
• Consequences: Ischemia leads to growth arrest of the proximal femoral physis. Depending on the zone of injury, this results in a shortened limb, coxa brevis (short neck), severe trochanteric overgrowth, or catastrophic coxa magna (enlarged, deformed head) leading to early joint failure.
• Classification (Kalamchi-MacEwen):
  • Group I: Changes localized to the ossific nucleus. Excellent prognosis.
  • Group II: Damage to the lateral physis. Leads to a valgus tilt of the head.
  • Group III: Damage to the central physis. Leads to a short femoral neck.
  • Group IV: Total damage to the physis and head. Devastating outcome with severe deformity.
• Prevention: Utilizing the "Safe Zone" during casting, abandoning failing Pavlik harnesses early, and aggressively utilizing femoral shortening osteotomies in older children to decompress the joint prior to reduction.

Conclusion

The management of Developmental Dysplasia of the Hip is a marathon, not a sprint. The orthopaedic surgeon's responsibility does not end when a concentric reduction is achieved at 6 months. A biologically reduced hip can still experience growth arrest or late-onset dysplasia as the child's mechanical demands change. Relentless, protocol-driven clinical and radiographic surveillance until skeletal maturity is absolute mandatory to prevent the silent progression to early adult osteoarthritis.

Radiology Cheatsheet

Download a PDF overlay for measuring Alpha angles and Acetabular Indices.