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

Surgical Indications

Absolute Indications

• Moderate-to-severe stable SCFE with Southwick lateral slip angle greater than 30-40 degrees where in-situ pinning would leave clinically unacceptable cam deformity and femoroacetabular impingement
• Selected acute unstable slips (unable to bear weight) with severe displacement in which anatomic reduction under direct vision is judged feasible and the surgeon has specific training in the technique
• Symptomatic residual cam deformity after previous in-situ pinning with documented impingement on CT or MR arthrogram

Relative Indications

• Severe slips (greater than 50-60 degrees) in patients with open physes where the family understands the high learning-curve risk and prefers anatomic realignment over in-situ pinning with later osteochondroplasty
• Bilateral severe slips where staged modified Dunn procedures are planned

Contraindications

Absolute:

• Closed physis (consider intertrochanteric or periacetabular osteotomy instead)
• Active infection
• Surgeon without specific training or institutional support for 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 (consider pinning in situ or salvage)
• Severe medical comorbidities precluding prolonged surgery

Evidence Base and Comparison with In-Situ Pinning

Rationale for Realignment

In-situ pinning of moderate-to-severe slips 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 30-40 degrees have a high rate of symptomatic impingement by 10-15 years. The modified Dunn procedure restores head-neck offset and eliminates the cam while the physis is still open.

Key Evidence

Relevant Surgical Anatomy

Blood Supply to the Proximal Femoral Epiphysis

The epiphysis receives its blood supply almost exclusively from the deep branch of the medial femoral circumflex artery (MFCA). The MFCA originates from the profunda femoris or directly from the femoral artery. Its deep branch runs posteriorly along the intertrochanteric crest, then courses along the posterolateral aspect of the femoral neck approximately 1.5 cm distal to the intertrochanteric line before entering the retinaculum.

Terminal branches: The deep branch gives off 2-4 terminal retinacular vessels that enter the epiphysis at the posterosuperior and posteroinferior margins. These vessels are the sole supply once the physis closes the metaphyseal contribution.

Clinical implication: Any injury to the deep branch or its terminal retinacular vessels during flap development or reduction causes AVN. The vessel is vulnerable during subperiosteal elevation and during tensioning of the flap if the neck is not adequately shortened.

The Retinacular Soft-Tissue Flap

The retinaculum is a fibrous sleeve containing the terminal MFCA branches, periosteum, and the reflected capsule. In the modified Dunn procedure the flap is developed by subperiosteal elevation from the posterior and lateral neck, starting distal to the intertrochanteric line and extending proximally to the epiphyseal margin.

Key technical point: The flap must remain in continuity with the epiphysis. The deep branch must be visualised and protected throughout. Over-dissection or thermal injury destroys the blood supply.

Trochanteric Flip Osteotomy

The osteotomy begins at the posterior border of the greater trochanter (just anterior to the posterior edge) and exits distal to the vastus lateralis ridge. A 1.5 cm thick wafer of trochanter is reflected anteriorly with the vastus lateralis and gluteus medius attached. This preserves the posterior abductor attachment and the MFCA course.

Structures at risk: The sciatic nerve (posterior retraction), the MFCA (if the osteotomy exits too posteriorly), and the superior gluteal neurovascular bundle (excessive proximal extension).

Capsular Anatomy

The hip capsule is opened with a Z-shaped capsulotomy that preserves the inferior flap containing the MFCA. The anterior and superior limbs allow dislocation; the inferior limb protects the vessel. The ligamentum teres is divided during dislocation.

Positioning and Preparation

Patient position: Lateral decubitus on a radiolucent table with the operative hip uppermost. The entire leg is prepped free. A perineal post is used for traction. Image intensifier is positioned to obtain AP and true lateral (frog-leg equivalent) views intraoperatively.

Anaesthesia: General anaesthesia with muscle relaxation. Consider regional block (lumbar plexus or femoral) for post-operative analgesia. Arterial line for blood pressure monitoring during prolonged procedure. Cell saver available.

Consent: Discuss AVN risk (10-25 percent), trochanteric nonunion (3-8 percent), chondrolysis (5-10 percent), leg-length discrepancy (1-2 cm expected), infection, nerve injury, and the possibility of future reconstructive surgery. Emphasise the steep learning curve and that results are volume-dependent.

Step-by-Step Operative Technique (Ganz Surgical Hip Dislocation with Modified Dunn Realignment)

Step 1: Trochanteric Flip Osteotomy

Incision: straight lateral incision from the iliac crest to the mid-thigh, centred over the greater trochanter. Split the iliotibial band. Identify the posterior border of the greater trochanter. Perform the trochanteric osteotomy with an oscillating saw starting just anterior to the posterior edge and exiting distal to the vastus lateralis ridge. Reflect the trochanteric wafer anteriorly with the attached vastus lateralis and gluteus medius. Tag the gluteus minimus insertion.

Step 2: Capsulotomy and Hip Dislocation

Incise the capsule in a Z-shaped fashion: the superior limb runs along the acetabular rim, the anterior limb along the femoral neck, and the inferior limb protects the MFCA. Dislocate the hip by flexing, adducting, and externally rotating the leg while applying traction. Divide the ligamentum teres with curved scissors. The femoral head is now fully exposed.

Step 3: Development of the Retinacular Flap

With the head dislocated, identify the posterior neck. Using a periosteal elevator, begin subperiosteal elevation at the distal neck just proximal to the intertrochanteric line. Develop the flap proximally along the posterolateral neck, staying strictly subperiosteal. The deep branch of the MFCA is visualised and protected within the flap. Continue elevation until the epiphyseal margin is reached. The flap now contains the terminal retinacular vessels.

Step 4: Controlled Neck Shortening and Epiphyseal Reduction

With the flap protected, perform a subcapital osteotomy at the physis using a thin oscillating saw or osteotome. Remove a 5-10 mm wafer of metaphyseal bone to allow shortening. Reduce the epiphysis onto the shortened neck under direct vision. The head should sit flush without step-off or tension on the flap. Confirm reduction with fluoroscopy in AP and lateral projections.

Step 5: Fixation

Fix the epiphysis with 2-3 cannulated 6.5-7.3 mm screws inserted from the lateral cortex across the physis into the epiphysis. Screws should be perpendicular to the physis and engage at least 5 threads in the epiphysis. Confirm position with arthrogram or direct visualisation to avoid joint penetration.

Fix the trochanteric osteotomy with 2-3 3.5 or 4.5 mm cortical screws with washers. Aim for compression and at least 3 cortices of distal purchase. Consider a tension-band cable if bone quality is poor.

Step 6: Closure and Perfusion Confirmation

Before final closure, confirm epiphyseal perfusion (laser Doppler or drill-hole bleeding). If flow is lost, release the reduction, add more shortening, or accept slight under-correction. Irrigate the joint. Close the capsule loosely. Reattach the trochanter. Close the iliotibial band and skin over drains.

Post-operative Protocol

Immediate Post-operative (Day 0-14)

• Weight-bearing: Touch-down weight-bearing (10-20 kg) with crutches for 6 weeks. Progress to partial then full weight-bearing at 6-12 weeks once radiographic healing is confirmed.
• Hip precautions: Avoid active abduction and flexion greater than 90 degrees for 6 weeks to protect the trochanteric osteotomy.
• DVT prophylaxis: Mechanical (compression devices) and pharmacological (LMWH or aspirin) for 4-6 weeks.
• Analgesia: Multimodal — paracetamol, NSAIDs (if renal function allows), gabapentinoids, opioid as needed. Regional catheter for 48-72 hours in some centres.
• Wound care: Drains removed at 24-48 hours. Suture or staple removal at 14-21 days.

Rehabilitation Phases

Phase 1 (0-6 weeks): Isometric quadriceps, gluteal, and core activation. Passive and active-assisted hip ROM within safe limits. No active abduction.

Phase 2 (6-12 weeks): Progressive weight-bearing as tolerated. Active abduction and strengthening once trochanteric healing confirmed. Stationary bike, pool therapy.

Phase 3 (3-6 months): Full weight-bearing. Progressive resistance and proprioceptive training. Return to low-impact sports when strength and ROM symmetric.

Phase 4 (6-12 months): Sport-specific training. Return to full activity including contact sports only after radiographic physeal closure and normal strength.

Monitoring for Complications

• Serial AP and frog-lateral radiographs at 2, 6, 12, 24 weeks, then 6-monthly until physeal closure.
• MRI at 3-6 months if pain or restricted motion persists (early AVN or chondrolysis).
• Clinical leg-length and abductor strength assessment at each visit.

Special Considerations

Unstable SCFE

• Surgery within 24-48 hours if physiologically stable.
• Consider preoperative traction or gentle closed reduction under anaesthesia before proceeding to open realignment.
• Higher AVN risk — counsel family extensively.

Bilateral Severe Slips

• Staged procedures 6-12 weeks apart.
• Single-stage bilateral surgery only in highly selected, medically stable patients with experienced teams.

Salvage After Failed In-Situ Pinning

• When residual cam causes symptomatic impingement, consider arthroscopic or open osteochondroplasty rather than revision realignment if the physis is closed.