SCFE — Modified Dunn Procedure (Surgical Hip Dislocation and Subcapital Realignment)

Indication. Symptomatic moderate-to-severe stable SCFE with a Southwick lateral slip angle greater than 30 to 40 degrees, where in-situ pinning would leave a clinically unacceptable cam deformity and femoroacetabular impingement. It is also used in selected acute unstable slips (the patient unable to bear weight) with severe displacement, when anatomic reduction under direct vision is judged feasible and the surgeon has specific training in the technique, and for a symptomatic residual cam after previous in-situ pinning with documented impingement on CT or MR arthrogram. Contraindications. Absolute: a closed physis (consider an intertrochanteric or periacetabular osteotomy instead), active infection, or a surgeon without the specific training and institutional volume to manage the learning curve. Relative: mild slips less than 30 degrees (in-situ pinning remains the standard), unstable slips presenting after 72 hours with established AVN on MRI, and severe medical comorbidities precluding prolonged surgery. The one decision that matters. For a given slip, three broad strategies exist — and the choice turns on the slip severity, the physes, and the surgeon's training:

Why realign. In-situ pinning of a moderate-to-severe slip leaves a large anterolateral cam deformity that causes cam-type femoroacetabular impingement, labral damage and early osteoarthritis. Long-term studies show that slips greater than 30 to 40 degrees carry a high rate of symptomatic impingement within 10 to 15 years. The modified Dunn procedure restores the head-neck offset and eliminates the cam while the physis is still open.

Special situations. For an unstable SCFE, operate within 24 to 48 hours once physiologically stable; consider pre-operative traction or a gentle closed reduction under anaesthesia before open realignment, and counsel the family extensively about the elevated AVN risk. Bilateral severe slips are managed as staged procedures 6 to 12 weeks apart (single-stage bilateral surgery only in highly selected, medically stable patients with experienced teams). After failed in-situ pinning with a symptomatic cam, prefer arthroscopic or open osteochondroplasty over revision realignment if the physis has closed. Consent specifically for AVN (10 to 25 percent, higher in unstable slips), trochantric nonunion (3 to 8 percent), chondrolysis (5 to 10 percent), an expected leg-length discrepancy of 1 to 2 cm, infection, nerve injury, and the possibility of future reconstructive surgery. Emphasise that results are volume-dependent and that in-situ pinning with later osteochondroplasty is a valid alternative. Setup. Lateral decubitus on a radiolucent table with the operative hip uppermost; the entire leg is prepped free and a perineal post is used for traction. Position the image intensifier to obtain AP and true lateral (frog-leg equivalent) views intraoperatively. General anaesthesia with muscle relaxation, a regional block (lumbar plexus or femoral) for post-operative analgesia, an arterial line, and a cell saver available.

The goal is to anatomically realign the slipped epiphysis at the capital-neck junction while preserving the epiphyseal blood supply, then fix it in the corrected position. The whole operation is built around protecting the deep branch of the medial femoral circumflex artery (MFCA) — the sole supply to the epiphysis — which originates from the profunda femoris (or directly from the femoral artery), runs posteriorly along the intertrochanteric crest and then along the posterolateral femoral neck about 1.5 cm distal to the intertrochanteric line, before giving off 2 to 4 terminal retinacular branches that enter the epiphysis at its posterosuperior and posteroinferior margins. The Ganz surgical hip dislocation exposes the hip without disturbing that vessel, and a subperiosteal retinacular flap carries the terminal branches safely with the epiphysis during realignment.

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Rehabilitation | Phase | Timing | Weight-bearing and precautions | Therapy focus | |-------|--------|--------------------------------|---------------| | 1 | 0 to 6 weeks | Touch-down weight-bearing (10 to 20 kg) with crutches; no active abduction, avoid flexion greater than 90 degrees | Isometric quadriceps, gluteal and core activation; passive and active-assisted hip ROM within safe limits | | 2 | 6 to 12 weeks | Progressive to partial then full weight-bearing once trochanteric healing is confirmed | Active abduction and strengthening; stationary bike, pool therapy | | 3 | 3 to 6 months | Full weight-bearing | Progressive resistance and proprioception; return to low-impact sports when strength and ROM are symmetric | | 4 | 6 to 12 months | Full activity | Sport-specific training; contact sports only after radiographic physeal closure and normal strength | Post-operative protocol - DVT prophylaxis: mechanical compression plus LMWH or aspirin for 4 to 6 weeks.

• Analgesia: multimodal — paracetamol, NSAIDs if renal function allows, gabapentinoids, opioid as needed; a regional catheter for 48 to 72 hours in some centres.
• Wound care: drains removed at 24 to 48 hours; sutures or staples out at 14 to 21 days.
• Monitoring: serial AP and frog-lateral radiographs at 2, 6, 12 and 24 weeks, then 6-monthly until physeal closure; MRI at 3 to 6 months if pain or restricted motion persists; clinical leg-length and abductor strength at each visit. An expected shortening of 1 to 2 cm is common and usually well tolerated. Long-term outcome is dominated by AVN — when it is avoided, the procedure gives high survivorship and little osteoarthritis at 10 years. Complications

Pathoanatomy. In a slipped capital femoral epiphysis the epiphysis displaces relative to the metaphysis through the open physis, and when a moderate-to-severe slip is pinned in situ the residual morphology leaves a large anterolateral head-neck offset — the cam lesion. This cam produces cam-type femoroacetabular impingement, labral damage and early osteoarthritis; long-term data show that slips greater than 30 to 40 degrees carry a high rate of symptomatic impingement within 10 to 15 years. The modified Dunn procedure restores the head-neck offset and removes the cam while the physis is still open. Blood supply recap. The epiphysis is supplied almost exclusively by the deep branch of the MFCA; once the physis closes the metaphyseal contribution is lost and the terminal retinacular vessels become the sole supply. This is why any injury to the deep branch or its terminals during flap development or reduction causes AVN — and why the operation is designed around protecting them.

Key evidence. The Ganz surgical hip dislocation (Ganz, 2001) established that the hip can be fully exposed without avascular necrosis when the MFCA is protected by the retinacular flap — the anatomic foundation of the modified Dunn procedure. Slongo (2010) reported anatomic correction of severe slips with an AVN rate under 10 percent in experienced hands, and Huber (2011) confirmed AVN rates of 10 to 25 percent driven by unstable slips, delayed surgery and excessive tension during reduction. At 10 years, Ziebarth (2017) showed high survivorship and little osteoarthritis when AVN was avoided — confirming that AVN, not the original slip, determines the long-term outcome.