Introduction to Developmental Dysplasia of the Hip (DDH)
Developmental Dysplasia of the Hip (DDH) represents a complex spectrum of anatomic abnormalities involving the growing hip joint, ranging from mild capsular laxity and acetabular dysplasia to frank, irreducible dislocation. While early diagnosis via the Graf ultrasonographic method and prompt intervention with a Pavlik harness yield high success rates in neonates, delayed presentations or conservative treatment failures necessitate definitive surgical management.
The primary objective of surgical intervention in DDH is to achieve and maintain a concentric, stable, and atraumatic reduction of the femoral head within the true acetabulum. This concentric reduction provides the essential mechanical stimulus required for secondary acetabular remodeling. Failure to achieve this results in persistent dysplasia, early-onset osteoarthritis, and severe biomechanical dysfunction.
Clinical Pearl: The biological plasticity of the acetabulum dictates surgical timing. The potential for spontaneous acetabular remodeling diminishes exponentially after 18 to 24 months of age, necessitating concomitant pelvic osteotomies in older children to ensure mechanical stability.
Preoperative Evaluation and Imaging
Meticulous preoperative planning is the cornerstone of successful DDH surgery. The choice of procedure is dictated by the patient's age, the severity of the dysplasia, and the presence of teratologic factors.
Ultrasonography and Radiography
- Ultrasonography (Graf Method): The gold standard for infants under 6 months. It assesses the alpha angle (bony roof) and beta angle (cartilaginous roof). Failure of improvement on dynamic ultrasound after 3–4 weeks of Pavlik harness treatment is a harbinger of conservative failure.
- Plain Radiography: Once the capital femoral ossific nucleus appears (typically 4–6 months), anteroposterior (AP) and frog-leg lateral pelvis radiographs become the primary imaging modalities. Key parameters include:
- Acetabular Index (AI): Normal is < 25° by age 2. An AI > 30° in a walking child often mandates a pelvic osteotomy.
- Shenton’s Line: Disruption indicates proximal femoral migration.
- Center-Edge Angle of Wiberg (CE Angle): Evaluated in older children and adolescents to quantify lateral coverage.
Advanced Imaging
- Magnetic Resonance Imaging (MRI): Post-reduction MRI or CT is mandatory to confirm concentric reduction and evaluate for posterior interposition of the labrum or capsule, avoiding the ionizing radiation of CT where possible, though low-dose CT remains highly effective for assessing bony congruity.
Obstacles to Reduction
Understanding the pathoanatomy is critical. The surgeon must systematically identify and address the anatomical blocks to concentric reduction:
1. Extra-articular Obstacles: Contracted adductor longus, contracted iliopsoas tendon.
2. Intra-articular Obstacles: Hypertrophied ligamentum teres, inverted limbus (fibrocartilaginous labrum), constricted transverse acetabular ligament (TAL), capsular constriction (hourglass capsule), and fibrofatty pulvinar occupying the acetabular fossa.
Open Reduction Techniques
When closed reduction fails or is contraindicated due to excessive required abduction (which drastically increases the risk of avascular necrosis), open reduction is indicated.
The Medial Approach (Ludloff / Ferguson)
The medial approach is typically reserved for children under 12 to 18 months of age presenting with an isolated dislocation without severe bony dysplasia requiring an osteotomy.
Advantages: Direct access to the primary medial obstacles (iliopsoas and adductors); minimal blood loss; cosmetically acceptable scar.
Disadvantages: Inability to perform a formal capsulorrhaphy; limited access to the superior capsule and inverted limbus; higher risk to the medial circumflex femoral artery (MCFA).
Surgical Steps:
1. Positioning: Supine with the affected hip flexed, abducted, and externally rotated (frog-leg position).
2. Incision: A longitudinal incision is made over the adductor longus origin.
3. Superficial Dissection: The adductor longus is isolated and tenotomized at its tendinous origin.
4. Deep Dissection: The plane between the pectineus (femoral nerve) and the adductor brevis/magnus (obturator nerve) is developed.
5. Psoas Tenotomy: The lesser trochanter is palpated. The iliopsoas tendon is isolated and released at its insertion.
6. Capsulotomy: The medial capsule is identified. A crucial step is protecting the MCFA, which courses inferior to the capsule. A longitudinal capsulotomy is performed.
7. Joint Clearance: The ligamentum teres is excised. The transverse acetabular ligament is incised to widen the inferior acetabular entry.
8. Reduction: The femoral head is gently reduced. Stability is assessed in the "safe zone" of Ramsey.
Surgical Warning: The medial circumflex femoral artery (MCFA) is the primary blood supply to the capital femoral epiphysis. Retractors must be placed with extreme caution during the medial approach to avoid iatrogenic avascular necrosis (AVN).
The Anterior Approach (Smith-Petersen)
The anterior approach is the workhorse for DDH surgery in children over 18 months, or in any child requiring a concomitant pelvic osteotomy or capsulorrhaphy.
Advantages: Excellent visualization of all intra-articular obstacles; allows for robust capsulorrhaphy; extensile for concomitant pelvic osteotomies.
Surgical Steps:
1. Incision: A "bikini" incision is made parallel to the iliac crest, extending distally toward the anterior superior iliac spine (ASIS).
2. Interval: The internervous plane between the sartorius (femoral nerve) and tensor fasciae latae (superior gluteal nerve) is developed.
3. Iliac Apophysis: The iliac apophysis is split, and the iliacus is elevated subperiosteally from the inner table of the ilium.
4. Rectus Femoris: The direct head (ASIS) and reflected head (anterior capsule) of the rectus femoris are detached and tagged.
5. Psoas Release: The psoas tendon is identified over the pelvic brim and tenotomized at the musculotendinous junction.
6. Capsulotomy: A T-shaped or I-shaped capsulotomy is performed. The capsule is meticulously preserved for later repair.
7. Joint Clearance: The pulvinar is removed. The ligamentum teres is excised. The transverse acetabular ligament is radially incised. The inverted limbus is everted (never excised, as it contributes to future acetabular growth).
8. Capsulorrhaphy: Following concentric reduction, the redundant capsule is advanced superiorly and laterally, sutured tightly to maintain the femoral head within the acetabulum.
Concomitant Femoral Osteotomies
In older children (typically > 3 years) or those with high dislocations, reducing the hip places excessive pressure on the articular cartilage and the MCFA.
Femoral Shortening and Varus Derotation Osteotomy (VDRO)
To decompress the joint and correct excessive femoral anteversion and coxa valga, a subtrochanteric femoral shortening osteotomy is performed.
* Biomechanics: Shortening reduces the joint reaction force, mitigating the risk of AVN. Varus and derotation optimize the orientation of the femoral head within the newly reduced acetabulum.
* Technique: A lateral approach to the proximal femur is utilized. A predetermined segment of the subtrochanteric femur is resected. The femur is derotated (usually 20–30 degrees) and placed in slight varus, then rigidly fixed with a pediatric blade plate or locking plate.
Pelvic Osteotomies in DDH
When the acetabular index remains elevated or lateral coverage is deficient, a pelvic osteotomy is required. These are broadly categorized into redirectional, reshaping, and salvage osteotomies.
1. Redirectional Osteotomies (Salter Innominate Osteotomy)
Described by Robert Salter, this osteotomy redirects the entire acetabulum as a single unit, hinging on the pubic symphysis.
* Indications: Children aged 18 months to 6 years with a congruous joint but deficient anterolateral coverage.
* Biomechanics: Provides anterolateral coverage by rotating the true acetabulum. It does not change the volume or shape of the acetabulum.
* Technique: A Gigli saw is passed through the greater sciatic notch and brought out anteriorly above the anterior inferior iliac spine (AIIS). The distal fragment is displaced laterally, anteriorly, and inferiorly. A triangular bone graft from the iliac crest is impacted into the osteotomy site, and the construct is stabilized with two threaded Kirschner wires.
2. Reshaping Osteotomies (Pemberton and Dega)
These are incomplete pericapsular osteotomies that hinge on the triradiate cartilage, thereby changing the volume and shape of the acetabulum.
* Pemberton Pericapsular Osteotomy:
* Indications: Severe dysplasia with a capacious acetabulum.
* Technique: An osteotome is driven through the outer and inner tables of the ilium, curving parallel to the joint capsule down to the ilioischial limb of the triradiate cartilage. It hinges on the flexible triradiate cartilage, allowing the acetabular roof to be levered downward.
* Dega Transiliac Osteotomy:
* Indications: Particularly useful in teratologic or neuromuscular dysplasia (e.g., cerebral palsy) where posterior coverage is deficient.
* Technique: Similar to the Pemberton, but the inner cortex of the ilium is left intact posteriorly, creating a hinge that allows for significant lateral and posterior coverage.
3. Salvage Osteotomies (Chiari Medial Displacement Osteotomy)
When concentric reduction is impossible or the articular cartilage is severely damaged, salvage procedures are employed to provide a mechanical block to subluxation.
* Indications: Older adolescents or adults with severe, uncorrectable dysplasia or incongruency.
* Technique: An extra-articular osteotomy is performed just superior to the capsular attachment. The pelvis is displaced medially. The joint capsule is interposed between the femoral head and the cancellous bone of the proximal iliac fragment, eventually undergoing fibrocartilaginous metaplasia to form a "shelf."
Complications and Management
Avascular Necrosis (AVN)
AVN of the capital femoral epiphysis is the most devastating complication of DDH treatment, directly resulting from vascular insult to the MCFA or excessive mechanical pressure (rigid abduction).
* Kalamchi and MacEwen Classification:
* Type I: Changes limited to the ossific nucleus (excellent prognosis).
* Type II: Lateral physeal damage leading to valgus deformity.
* Type III: Central physeal damage leading to coxa brevis.
* Type IV: Total damage to the epiphysis and physis, leading to severe coxa magna, brevis, and varus.
* Prevention: Avoid extreme abduction in casts (the "frog-leg" position is obsolete; the "human position" of moderate flexion and mild abduction is preferred). Utilize femoral shortening in older children to decompress the joint.
Re-dislocation
Re-dislocation occurs due to inadequate clearance of intra-articular obstacles, failure to recognize excessive femoral anteversion, or inadequate capsulorrhaphy. Immediate return to the operating room for revision open reduction and potential bony realignment is mandatory.
Postoperative Protocols and Rehabilitation
Strict adherence to postoperative immobilization is critical to allow for capsular healing and bony union of osteotomies.
- Spica Casting: Following open reduction, the patient is placed in a 1.5-hip spica cast in the "human position" (100° of flexion, 40° of abduction, neutral rotation).
- Duration: The initial cast is maintained for 6 weeks. Under general anesthesia, the cast is removed, clinical stability is assessed, and a new cast is applied for an additional 6 weeks.
- Hardware Removal: Kirschner wires from a Salter osteotomy are typically removed at 6 to 8 weeks postoperatively once radiographic union is confirmed.
- Long-Term Surveillance: Patients must be followed radiographically until skeletal maturity. The acetabulum continues to remodel for years following a successful reduction. Late manifestations of mild dysplasia or AVN may not become apparent until the adolescent growth spurt, potentially requiring late periacetabular osteotomies (e.g., Ganz PAO).
