Pemberton & Dega Acetabuloplasty

Core indication. Residual acetabular dysplasia in developmental dysplasia of the hip (DDH) with a concentrically reducible femoral head and an open triradiate cartilage (typically age 18 months to 7–8 years) — in particular a persistently high acetabular index after reduction, where the acetabulum is capacious and globally deficient and reshaping (volume reduction) rather than redirection is required. Pemberton — preferred when

• The acetabulum is large and capacious with generalised (multidirectional) deficiency.
• Maximum reduction of acetabular volume is desired.
• A single hinged correction in almost any direction is needed (the triradiate hinge allows anterior, lateral or global redirection of the roof). Dega — preferred when
• Posterosuperior deficiency predominates — classically the neuromuscular / cerebral palsy hip and posterior DDH.
• Selective, directional correction is wanted while preserving the medial wall and inner cortex.
• A more forgiving, "tunable" osteotomy is preferred (depth and posterior extent of the cut titrate the correction). Contraindications.
• Absolute: a closed (fused) triradiate cartilage (no hinge for reshaping); a non-concentric / irreducible hip (reshaping a roof over a subluxated head is futile — reduce first); active hip sepsis.
• Relative: severe incongruity of the joint surfaces (a redirectional osteotomy such as Salter, or a salvage shelf/Chiari procedure, may be more appropriate); marked femoral-sided deformity requiring a primary femoral osteotomy (often combined rather than a contraindication); an older child near triradiate closure with diminishing remodelling potential. The one comparison that matters — Pemberton, Dega and Salter side by side:

Choosing the right pelvic osteotomy — the decision framework:

• Open triradiate plus capacious global dysplasia plus concentric reduction → reshape with Pemberton (maximal, multidirectional volume reduction).
• Open triradiate plus posterosuperior deficiency (especially neuromuscular) → reshape with Dega (directional, preserves the medial and posterior cortex).
• Mild dysplasia plus a congruent hip with an open triradiate → redirect with the Salter innominate osteotomy.
• Skeletally mature / closed triradiate plus a congruent hip → redirect with a periacetabular (Ganz) or triple osteotomy.
• An incongruent hip needing salvage → Chiari medial displacement or a shelf acetabuloplasty (non-articular augmentation). Special case — the neuromuscular (cerebral palsy) hip.
• The deficiency is typically posterosuperior with progressive hip displacement (a rising migration percentage).
• The Dega, hinging on the intact posteromedial cortex, gives directional posterosuperior coverage while preserving the medial wall.
• It is almost always combined with open reduction and a femoral varus-derotation (and shortening) osteotomy, plus soft-tissue releases (adductor/psoas) to address the muscle imbalance driving the displacement.
• Treat early once the migration percentage is rising despite surveillance; balance all three levels — pelvis, femur and soft tissue — for a durable, congruent, low-pressure hip. Consent and setup. Supine with a small bump under the ipsilateral buttock and flank; the whole limb and hemipelvis are prepped free to allow intra-operative assessment of reduction and stability, with an image intensifier available. General anaesthesia with a caudal/regional block for post-operative analgesia; group-and-save, as osteotomy and reduction can bleed (especially when combined with a femoral osteotomy). Consent specifically for avascular necrosis of the femoral head, triradiate cartilage injury/growth arrest, residual or recurrent dysplasia, joint stiffness/over-coverage, neurovascular injury (sciatic nerve, lateral femoral cutaneous nerve), the need for a spica cast and possible future surgery.

The goal: through an anterior (Smith-Petersen / bikini) approach, expose the ilium subperiosteally down to the sciatic notch, confirm a concentric reduction, then make an incomplete pericapsular cut that hinges the acetabular roof down over the femoral head — on the triradiate cartilage for a Pemberton, on the intact posteromedial cortex for a Dega — and hold it with impacted corticocancellous graft. The exposure is laid out in full as the first steps below; it is the foundation of the whole operation.

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Operative sequence

Step 1Position, approach & exposure

• Supine, sandbag under the ipsilateral buttock/flank; the whole limb and hemipelvis are prepped free. Image intensifier available.
• Anterior (Smith-Petersen / bikini) approach. Develop the internervous interval between sartorius / rectus femoris (femoral nerve) and tensor fasciae latae (superior gluteal nerve).
• Identify and protect the lateral femoral cutaneous nerve (LFCN), which emerges near the ASIS and crosses the interval — retract it gently rather than dividing it.
• Ligate the ascending branch of the lateral femoral circumflex artery, which crosses the distal part of the interval.

Protecting the LFCN

Make the interval just lateral to sartorius to keep the lateral femoral cutaneous nerve medial and protected; identify and gently retract it rather than dividing it. The bikini incision gives a cosmetically favourable scar in a child who will live with it for life.

Dangers at the exposure

Lateral femoral cutaneous nerve traction or transection causes anterolateral thigh numbness (meralgia paraesthetica). Bleeding from the unligated ascending branch of the lateral femoral circumflex artery. Split the iliac apophysis sharply in the midline and reflect both flaps subperiosteally rather than damaging it unnecessarily.

Step 2Subperiosteal exposure of the ilium

• Split the iliac apophysis in the midline and elevate the periosteum from both the inner (medial) and outer (lateral) tables of the ilium subperiosteally.
• Carry the exposure down to the sciatic notch posteriorly and the capsule / AIIS anteriorly.
• Place blunt retractors (e.g. curved Hohmann) into the sciatic notch on both the inner and outer tables to protect the contents and guide the later osteotome.

Dangers at this step

The sciatic notch holds the sciatic nerve and the superior gluteal neurovascular bundle — keep dissection strictly subperiosteal and place protective retractors. Do not enter the hip joint capsule prematurely: these are pericapsular osteotomies, so stay above the capsule.

Step 3Ensure a concentric reduction first

• If the hip is not concentrically reduced, perform an open reduction: a T-capsulotomy, excise the hypertrophic ligamentum teres and pulvinar, divide the transverse acetabular ligament and any inverted limbus, and reduce the head concentrically.
• Confirm a deep, stable, concentric reduction before reshaping — this is the prerequisite for the whole procedure.

Never reshape over a malreduced head

Do not reshape the roof until the head sits concentrically and deeply. A reshaping osteotomy over a malreduced head simply buttresses a subluxation. Confirm a stable concentric reduction first, then decide how much coverage the roof still needs.

Step 4Plan the osteotomy — Pemberton vs Dega

• Mark the cut above the capsule.
• For Pemberton, plan a curved cut from just above the AIIS sweeping posteriorly toward (not through) the triradiate cartilage; both cortices will be divided down toward the triradiate, which acts as the hinge.
• For Dega, plan a transiliac cut preserving the inner (medial) and posterior cortices as the hinge, with the posterior extent chosen according to the direction of deficiency.

Let the deficiency drive the choice

A globally capacious DDH socket gets a Pemberton hinging on the triradiate for maximal volume reduction. A posterosuperiorly deficient cerebral palsy hip gets a Dega — keep the posterior and medial cortices intact and tune the cut posteriorly to cover the back of the head.

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Step 5Perform the osteotomy

• Using curved osteotomes under image guidance, divide the cortices along the planned line.
• For Pemberton, carry the curved cut on both tables down toward — but not through — the triradiate cartilage.
• For Dega, divide the outer cortex and cancellous bone, leaving the inner and posterior cortex intact as the hinge.

Dangers at this step

Propagating the cut INTO the triradiate cartilage or the joint risks premature triradiate fusion, growth arrest and intra-articular damage. Completing the posterior cortex (Dega) or driving the osteotome out the notch loses the hinge and endangers the sciatic notch contents. Cutting too low (into the capsule/joint) rather than pericapsular enters the joint.

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Step 6Lever the roof and assess correction

• Lever the acetabular roof down (and forward/laterally as needed) by opening the osteotomy with an osteotome or lamina spreader.
• Assess coverage and congruency of the head under the reshaped roof — aim for a congruent, stable, well-covered hip without over-coverage or stiffness.

Correct to congruency, not to a number

Open the hinge gradually and keep checking congruency. Correct only enough to normalise the acetabular index and give a stable, congruent hip. Over-hinging a Pemberton creates a tight, over-covered, stiff joint; under-correction leaves residual dysplasia. The intra-operative congruency check is the guide, not a fixed number of degrees.

Step 7Bone graft and fixation

• Harvest corticocancellous wedges from the inner table of the ilium or the iliac crest/apophysis.
• Impact them into the opened osteotomy to hold the roof in the corrected position.
• The cartilage/cortex hinge is usually stable enough that internal fixation is not required; a smooth K-wire may occasionally steady the graft.

Step 8Closure — and femoral osteotomy if indicated

• If the femoral head is high, very anteverted, or the reduction is high-pressure, perform a femoral shortening / varus-derotation osteotomy through a separate lateral incision.
• Repair the capsule (capsulorrhaphy), reattach the apophysis, and close in layers.
• Apply a hip spica cast for immobilisation, maintaining a safe, congruent position (avoid extreme abduction that raises intra-articular pressure and AVN risk).

Post-operative protocol | Phase | Timing | Management | |-------|--------|------------| | Immobilisation | 0–6 weeks | Hip spica applied intra-operatively in a safe, congruent position; spica care, skin/cast hygiene, neurovascular checks and carer education; regional block plus simple analgesia (the cast itself reduces pain by stabilising the osteotomy) | | Removal & mobilisation | from ~6 weeks | Spica removed once the osteotomy and graft show radiographic consolidation; gentle mobilisation with gradual return to weight-bearing; hydrotherapy/physiotherapy if stiff (most young children remobilise spontaneously) | | Radiographic surveillance | ongoing | Monitor the acetabular index, head coverage, congruency, ossification of the capital epiphysis (for AVN) and the triradiate cartilage at intervals, to skeletal maturity, to detect AVN, recurrence or growth disturbance | Complications — recognition, prevention, management

Surgical anatomy. The acetabulum is formed by the confluence of three bones — ilium, ischium and pubis — meeting at the Y-shaped triradiate cartilage, which is the growth centre of the acetabulum. Peripheral acetabular growth (the acetabular epiphysis) contributes to depth and coverage, so reshaping relies on continued growth. The anterior inferior iliac spine (AIIS) is the surface landmark for the start of the Pemberton curved cut, just above the capsule; the sciatic notch marks the posterior limit of both cuts, with the sciatic nerve and superior gluteal vessels lying immediately deep. The key principle is that both procedures pass the osteotomy above the joint capsule (pericapsular), so the joint is not entered, and the acetabular roof is levered downward to cover the femoral head. Reshape, redirect or salvage — the pelvic-osteotomy taxonomy:

Key evidence and outcomes. The Pemberton pericapsular osteotomy gives reliable single-procedure correction of the acetabular index: in Balioglu's mid-term series it fell from a mean of 41.9 degrees pre-operatively to 19.5 degrees (p less than 0.001), with Severin Ia/Ib radiographic outcome in 86 percent. The principal risk is avascular necrosis — Wu's long-term analysis of Pemberton acetabuloplasty found osteonecrosis in 25 of 49 hips (51 percent), with excessive inferior displacement of the femoral head the dominant correlate (p less than 0.0001), implicating compression of the lateral epiphyseal branch of the medial femoral circumflex artery. The Dega osteotomy is widely adopted for the neuromuscular hip: Mubarak's single-stage reconstruction (soft-tissue release plus femoral shortening varus-derotation osteotomy plus a pericapsular acetabuloplasty) kept 17 of 18 spastic hips reduced at a mean of 6 years 10 months, and Kim showed the modified Dega is tunable to the direction of deficiency demonstrated on 3D-CT. Acetabuloplasty is frequently combined in one sitting with open reduction and, where the head is high or anteverted, a femoral shortening/varus-derotation osteotomy to achieve a concentric, stable, low-pressure reduction.

1. Pemberton PA (1965). Pericapsular osteotomy of the ilium for treatment of congenital subluxation and dislocation of the hip. J Bone Joint Surg Am 47:65–86. PMID 14256975. — Original description of the pericapsular osteotomy hinging on the triradiate cartilage. 2. Dega W (1964/1969). Transiliac (incomplete) acetabuloplasty for congenital hip dysplasia (original Polish-language descriptions). — The incomplete transiliac (Dega) acetabuloplasty hinging on the intact inner/posterior cortex; not PubMed-indexed. 3. Salter RB (1961). Innominate osteotomy in the treatment of congenital dislocation and subluxation of the hip. J Bone Joint Surg Br 43-B:518–539. — Description of the redirectional innominate osteotomy hinging on the symphysis pubis (key contrast to reshaping osteotomies). 4. Mubarak SJ, Valencia FG, Wenger DR (1992). One-stage correction of the spastic dislocated hip. Use of pericapsular acetabuloplasty to improve coverage. J Bone Joint Surg Am 74:1347–1357. PMID 1429790. — Pericapsular (Dega-type) acetabuloplasty combined with open reduction and femoral osteotomy for the neuromuscular hip (17 of 18 hips reduced at mean 6 years 10 months). 5. Wu KW, Wang TM, Huang SC, Kuo KN, Chen CW (2010). Analysis of osteonecrosis following Pemberton acetabuloplasty in developmental dysplasia of the hip: long-term results. J Bone Joint Surg Am 92:2083–2094. PMID 20810858. — Excessive inferior displacement of the femoral head correlates with osteonecrosis after Pemberton acetabuloplasty. 6. Balioglu MB, Oner A, Aykut US, Kaygusuz MA (2015). Mid-term results of Pemberton pericapsular osteotomy. Indian J Orthop 49:418–424. PMID 26229162. — Acetabular index improved from a mean 41.9 to 19.5 degrees. 7. Kim HT, Jang JH, Ahn JM, Lee JS, Kang DJ (2012). Early results of one-stage correction for hip instability in cerebral palsy. Clin Orthop Surg 4:139–148. PMID 22662300. — Modified Dega osteotomy within single-event multilevel surgery for the cerebral palsy hip.