Supramalleolar Osteotomy (Distal Tibia Realignment)

Surgical Indications

Absolute Indications

• Asymmetric (eccentric) ankle osteoarthritis with a correctable deformity: varus OA with medial compartment overload and preserved lateral compartment cartilage, or valgus OA with lateral compartment overload and preserved medial cartilage
• Stage 2-3 ankle OA (Takakura stage II or III): joint space narrowing in one compartment with partial loss of cartilage but salvageable opposing surface
• Varus ankle with TAS angle less than 90 degrees (or valgus with TAS greater than 96 degrees) and symptomatic despite non-operative treatment
• Young, active patient (typically under 55-60 years) who wishes to delay or avoid ankle fusion or replacement
• Mobile subtalar joint with at least 30 degrees of sagittal ankle motion

Relative Indications

• Post-traumatic malunion of the distal tibia or plafond contributing to asymmetric ankle loading
• Ankle OA secondary to distal tibial physeal arrest (e.g. juvenile arthritis, growth disturbance)
• Periarticular deformity with ankle joint subluxation that is correctable
• Patient unsuitable for arthrodesis (bilateral disease, contralateral hindfoot fusion) or TAR (young age, high activity demands)

Contra-Indications

Absolute:

• End-stage (stage 4) concentric ankle OA with complete loss of joint space bilaterally — no compartment to offload to
• Rigid subtalar arthritis (the STJ cannot compensate for residual malalignment)
• Active infection (osteomyelitis, septic arthritis) at or near the ankle
• Severe osteoporosis with insufficient bone stock for plate fixation
• Charcot neuroarthropathy or significant peripheral neuropathy with loss of protective sensation

Relative:

• Rheumatoid arthritis with inflammatory disease activity (optimise medically before surgery)
• Active smoking (significantly elevated nonunion risk — insist on cessation)
• BMI greater than 35 (increased wound complication and nonunion rates)
• Previous ankle trauma with extensive scarring compromising surgical approach
• Diabetes mellitus with peripheral vascular disease

Evidence for Non-Operative Treatment

Non-Operative Management

• Activity modification: Limit impact activities, use a rocker-bottom shoe or ankle-foot orthosis to reduce hindfoot loading
• Physiotherapy: Strengthening of ankle dorsiflexors, plantarflexors, and inversion/eversion muscles; maintain ROM
• Analgesia: Paracetamol and topical or oral NSAIDs; intra-articular corticosteroid injections provide temporary relief (weeks to months) but do not alter disease progression
• Orthotics: Lateral wedge insole for medial compartment overload (varus ankle) to shift load laterally; custom hindfoot orthoses for valgus deformity
• Evidence: Non-operative treatment effectively manages symptoms in early-stage asymmetric OA but does not halt progression. In eccentric OA, the biomechanical abnormality (angulated joint surface, eccentric loading) persists and drives progressive degeneration of the overloaded compartment. SMO addresses the mechanical cause rather than just the symptoms.

Evidence for Supramalleolar Osteotomy

Rationale and Biomechanical Basis

The supramalleolar osteotomy redistributes joint contact pressures by realigning the distal tibial articular surface relative to the talus. In varus ankle OA, the medial compartment bears disproportionate load; after medial opening-wedge correction, contact pressure shifts laterally towards the preserved cartilage. Biomechanical studies show that a 10-degree correction of the TAS angle can shift the centre of contact pressure by 10-20% of the tibiotalar surface area.

Opening-Wedge vs Closing-Wedge

Medial opening-wedge osteotomy:

• Performed through a medial approach to the distal tibia
• Tibialis anterior tendon is retracted anteriorly or partially released
• A wedge of predetermined size is opened medially, the lateral cortex acts as a hinge (or is perforated in a controlled fashion)
• The defect is filled with bone graft (tricortical iliac crest autograft or allograft)
• Fixed with an anatomically contoured anteromedial locking plate
• Preserves bone stock, allows precise correction with a single osteotomy, but requires bone graft and has a theoretically slower union than closing-wedge

Lateral closing-wedge osteotomy:

• Performed through an anterolateral approach
• A calculated wedge of bone is removed from the lateral cortex
• The osteotomy is closed and the tibia translates medially
• Inherent bony contact at the osteotomy site (no graft required)
• Requires fibular osteotomy and more extensive lateral dissection
• Historically associated with risk of transient peroneal nerve palsy from lateral approach

Key Evidence

Distal Tibial Anatomy and the Osteotomy Zone

Distal Tibial Metaphysis

The supramalleolar osteotomy is performed in the distal tibial metaphysis, typically 4-6 cm proximal to the ankle joint line. This region has a robust cancellous blood supply from the nutrient artery and the metaphyseal perforating branches. Cortical thickness increases proximally — the osteotomy site is a transitional zone where the cortical bone is thick enough to hold plate fixation but cancellous enough to allow vascular ingrowth for healing.

Key Anatomical Relationships

The Fibula and Its Role in SMO

The fibula is the lateral strut of the ankle mortise and is a key mechanical constraint during tibial osteotomy:

• Medial opening-wedge: As the tibia opens medially, the lateral cortex hinges (or is perforated) and the tibia widens. The intact fibula prevents the tibia from expanding laterally. Without a fibular osteotomy, the fibula acts as a tension band, resisting opening and causing under-correction. An oblique osteotomy at the same level, with removal of a segment if needed, releases this constraint.

• Lateral closing-wedge: The lateral tibial wedge is removed and the fragments are closed. The fibula must be osteotomised at the same level so that the lateral tibial cortices can appose and the distal fragment can translate medially without the fibula blocking closure.

• Fibular osteotomy technique: An oblique or transverse osteotomy through the fibula at the level of the tibial osteotomy, performed through a separate lateral incision or through the same incision in the lateral approach. A Z-osteotomy or step-cut can be used to control shortening precisely. In opening-wedge technique, a 5-10 mm segment of fibula is sometimes resected to ensure adequate lateral opening.

Distal Tibial Joint Surface Angles

These are the primary radiographic measurements that define the deformity and guide correction:

Tibial Anterior Surface (TAS) angle: Measured on the weight-bearing AP ankle radiograph. The angle between the anatomical axis of the tibia and the distal tibial joint surface. Normal is approximately 93 degrees (range 89-97). A TAS less than 90 degrees indicates varus tilt; greater than 96 degrees indicates valgus tilt. This is the primary angle corrected by SMO.

Tibial Lateral Surface (TLS) angle: Measured on the weight-bearing lateral ankle radiograph. The angle between the anatomical axis of the tibia and the distal tibial articular surface on the lateral view. Normal is approximately 80 degrees (range 76-84). An abnormal TLS indicates sagittal plane deformity (recurvatum or procurvatum) that may require additional correction.

Talar tilt angle: The angle between the tibial plafond and the dome of the talus on the AP view. In varus OA, the talus tilts into the medial compartment. After SMO, the talus should sit congruently under the corrected tibial plafond with restoration of a neutral talar tilt.

Pre-Operative Planning

Radiographic Assessment

• Weight-bearing AP and lateral ankle radiographs: Measure TAS angle (normal 93 degrees), TLS angle, talar tilt, and assess the pattern of joint space narrowing
• Full-length standing radiograph (hip-knee-ankle): Assess the mechanical axis of the lower limb. In varus ankle OA, the mechanical axis may pass medial to the centre of the ankle joint; distinguish whether the deformity is isolated to the ankle (CORA at the joint line) or part of a more proximal deformity
• Stress radiographs: Varus and valgus stress views to assess ligamentous stability and the correctability of the talar tilt. A correctable talar tilt on stress views suggests ligamentous laxity contributing to the deformity and may require concomitant ligament reconstruction
• Broden views: Evaluate the subtalar joint for degenerative changes
• CT scan: Detailed assessment of ankle joint degeneration pattern, subchondral cysts, osteophytes, and subtalar joint surfaces. Helpful for staging with the Takakura classification
• MRI: Assess the condition of the underloaded compartment cartilage — this is the compartment you are relying on to bear load after correction. Full-thickness cartilage loss in the underloaded compartment is a contra-indication to SMO (no compartment left to offload to)

Templating

• Calculate the correction wedge angle: for a varus ankle, if the TAS angle is 84 degrees and the target is 93 degrees, the required correction is 9 degrees. Use trigonometric tables or the sine law: wedge base (mm) at a given osteotomy height and correction angle can be pre-calculated
• Mark the planned osteotomy site: 4-6 cm proximal to the ankle joint, parallel to the joint surface (or at the CORA if the apex is proximal to the joint)
• Plan the fibular osteotomy at the corresponding level
• Select the plate: anatomically contoured anteromedial distal tibial locking plate (for opening-wedge) or anterolateral plate (for closing-wedge). Have sizes available on the tray

Positioning and Preparation

Patient position: Supine on a radiolucent table. A sandbag under the ipsilateral buttock may help present the medial ankle. The ipsilateral iliac crest is prepped and draped into the field if autograft is planned.

Tourniquet: Thigh tourniquet inflated to 250 mmHg before limb preparation. Alternatively, a calf tourniquet can be used but provides a shorter field.

Fluoroscopy: Image intensifier positioned for true AP and lateral views of the ankle. Confirm the C-arm can achieve a true mortise view before draping. Fluoroscopy will be used repeatedly during the osteotomy, correction, and plate fixation.

Antibiotic prophylaxis: Single dose of IV cefazolin 2 g (or appropriate alternative) at induction.

Consent: Specifically counsel regarding nonunion (2-8%), under- or over-correction (5-15%), infection (1-3%), neurovascular injury including peroneal nerve palsy (1-3% transient), hardware irritation requiring removal (10-25%), and the possibility of conversion to ankle arthrodesis if the procedure fails.

Medial Opening-Wedge Osteotomy — Step-by-Step

Step 1: Approach and Exposure

Make a longitudinal incision along the anteromedial border of the distal tibia, centred over the planned osteotomy site (4-6 cm proximal to the medial malleolus). Extend the incision approximately 8-10 cm.

Develop the subcutaneous plane carefully, identifying and protecting the saphenous vein and nerve, which run along the medial subcutaneous border of the tibia.

Deepen to the fascia over the tibialis anterior muscle. Incise the fascia longitudinally and retract the tibialis anterior tendon and muscle belly anteriorly. The anterior tibial neurovascular bundle lies beneath the tibialis anterior — identify it and protect with a Hohmann retractor placed on the lateral subperiosteal surface of the tibia.

Expose the medial surface of the distal tibia subperiosteally. Elevate the periosteum only enough to place the plate; avoid excessive stripping, which compromises the blood supply to the osteotomy site.

Step 2: Osteotomy Planning on Bone

Mark the osteotomy line on the medial cortex under fluoroscopic guidance, 4-6 cm proximal to the ankle joint and parallel to the tibial plafond. Use a sterile marker or Bovie to score the cortex.

Insert two K-wires parallel to the planned osteotomy line, perpendicular to the tibial shaft, under fluoroscopic AP and lateral views. These serve as reference guides for the osteotomy direction.

Step 3: Perform the Tibial Osteotomy

Using an oscillating saw, begin the osteotomy at the marked line on the medial cortex and advance laterally towards, but NOT completely through, the lateral cortex. The lateral cortex is preserved as a hinge (intentional incomplete osteotomy).

Advance the saw to within 2-3 mm of the lateral cortex. Complete the lateral cortex with a series of carefully controlled multiple drill holes (2.5 mm drill) or with gentle osteotome taps, so that the lateral cortex fractures but remains as a greenstick hinge. This controlled fracture prevents unpredictable propagation.

Confirm the osteotomy is complete by inserting a thin osteotome and gently levering — the medial side should open. Do not force it; if resistance is met, the lateral cortex is intact and must be further perforated.

Step 4: Fibular Osteotomy

Make a separate longitudinal incision over the lateral aspect of the fibula at the level of the tibial osteotomy. Develop through the subcutaneous tissue to the fibula, protecting the superficial peroneal nerve branches.

Perform an oblique osteotomy of the fibula at the same level as the tibial osteotomy using an oscillating saw. Remove a 5-10 mm segment of fibula if needed to allow adequate lateral opening of the tibial osteotomy.

Confirm under fluoroscopy that the fibula is completely osteotomised and is not blocking the planned correction.

Step 5: Open the Osteotomy and Insert Bone Graft

Gradually open the medial osteotomy using laminar spreaders or a calibrated osteotomy spreader. Open under fluoroscopic guidance until the desired correction angle is achieved, as measured by the corrected TAS angle on the AP view (target approximately 93 degrees).

Measure the defect at the medial cortex. Prepare a tricortical iliac crest bone graft (autograft) or fresh-frozen structural allograft to match the defect size and shape. For smaller defects (less than 5 mm), cancellous allograft bone chips or synthetic bone substitute may be used as an adjunct, but a structural graft is preferred for defects greater than 5 mm.

Insert the graft into the osteotomy defect with the cortical surface oriented to resist compression (usually with the cortical surface oriented anteroposteriorly to support the medial opening). Confirm position fluoroscopically.

Step 6: Plate Fixation

Apply an anatomically contoured anteromedial locking plate to the medial surface of the distal tibia, spanning the osteotomy site. The plate typically has 3-4 screw holes proximal and 2-3 holes distal to the osteotomy.

Insert locking screws under fluoroscopic guidance: proximal screws first, then distal. Confirm each screw length on lateral fluoroscopy to ensure no joint penetration.

After final screw insertion, remove the spreader and confirm under fluoroscopy that the correction is maintained: check the TAS angle on AP, the TLS angle on lateral, and the talar congruency on the mortise view.

Assess ankle range of motion intraoperatively — dorsiflexion and plantarflexion should be preserved. Check the stability of the fibular osteotomy site.

Step 7: Wound Closure

Irrigate the wound thoroughly. Close the periosteum and deep fascia over the plate with absorbable sutures. Close the subcutaneous layer and skin in layers. Apply a sterile, well-padded below-knee posterior splint with the ankle in neutral.

Lateral Closing-Wedge Osteotomy — Technique Overview

The lateral closing-wedge technique is an alternative approach, used less commonly than medial opening-wedge in current practice but offering some biomechanical advantages (inherent bone contact, no graft required).

Key Steps

1. Approach: Anterolateral incision over the distal tibial metaphysis, 4-6 cm proximal to the ankle joint
2. Fibular osteotomy: Perform at the same level (through the same or a separate incision) — this is essential to allow the lateral tibial cortices to close
3. Osteotomy: Mark the osteotomy lines with K-wires under fluoroscopy. Remove a calculated lateral wedge of bone using an oscillating saw — the wedge angle corresponds to the planned correction angle
4. Close the wedge: Appose the proximal and distal tibial fragments and compress. Check the corrected TAS angle fluoroscopically
5. Fixation: Apply an anterolateral anatomically contoured locking plate. Confirm correction and screw position on AP and lateral fluoroscopy
6. Closure: Layered closure, below-knee posterior splint in neutral

Specific Risks of Lateral Approach

• Deep peroneal nerve: runs in the anterior compartment and is at risk during the lateral approach and lateral osteotomy. Transient peroneal nerve palsy is reported in 2-5% of lateral closing-wedge cases
• Extensor tendons: the extensor digitorum longus and peroneus tertius tendons cross the field and must be protected
• Wound healing: lateral skin over the distal tibia is thin with limited subcutaneous tissue — wound breakdown and infection risk is slightly higher than the medial approach

Post-Operative Protocol

Immediate Post-Operative Phase (Week 0-2)

• Immobilisation: Non-weight-bearing in a below-knee posterior splint or cast for the first 2 weeks with the ankle in neutral dorsiflexion
• Elevation: Elevate the limb above heart level for the first 48-72 hours to reduce swelling; elevate at night
• Analgesia: Regular paracetamol; NSAIDs for inflammatory pain (caution in opening-wedge — theoretical effect on bone healing, though evidence is mixed); short course oral opioids for breakthrough pain in the first week
• DVT prophylaxis: Mechanical (intermittent pneumatic compression devices) for all patients; pharmacological prophylaxis (low molecular weight heparin or rivaroxaban) for high-risk patients per local protocol
• Wound check: At 10-14 days for suture removal (or wound review if absorbable sutures used); inspect for signs of infection or wound dehiscence

Protected Weight-Bearing Phase (Week 2-8)

• Cast or boot: Transition to a removable below-knee walking boot (CAM boot) at 2 weeks if wound healing is satisfactory
• Weight-bearing: Touch-weight-bearing (toe-touch only, 10-15 kg) from week 2-6, progressing to partial weight-bearing (50%) from week 6-8, guided by radiographic evidence of early union
• Radiographic assessment: AP and lateral ankle radiographs at 6 weeks to assess early callus formation and maintenance of correction. Compare TAS angle to the immediate post-operative film
• Physiotherapy: Gentle active ankle dorsiflexion and plantarflexion within the boot; subtalar joint mobilisation; stationary cycling without resistance once partial weight-bearing begins

Progression Phase (Week 8-16)

• Weight-bearing: Progress to full weight-bearing as tolerated from week 8-12, provided radiographs show progressive callus formation at the osteotomy site without loss of correction
• Boot wean: Wean from CAM boot between weeks 8 and 12 as comfort and stability allow
• ROM exercises: Progressive active and active-assisted dorsiflexion, plantarflexion, inversion, and eversion out of the boot
• Strengthening: Calf raises, resistance band exercises, proprioception training (single-leg balance)
• Physiotherapy: Formal physiotherapy referral at this stage for progressive loading and functional rehabilitation

Return to Function

• Office work / sedentary: 4-6 weeks
• Light duties / standing: 8-12 weeks
• Manual work / heavy labour: 12-16 weeks or longer
• Driving: When able to perform an emergency stop safely — typically 8-12 weeks for the right (driving) ankle; earlier for the left in an automatic vehicle
• Sport: Low-impact (swimming, cycling) from 12-16 weeks; running and impact sports from 6-9 months, once full union is confirmed and strength has recovered

Long-Term Follow-Up

• Radiographs: At 3 months (confirm union), 6 months, 12 months, then annually
• Clinical review: At 3 months, 6 months, 12 months, then annually — assess pain, function (AOFAS score), range of motion, and signs of arthritis progression
• Hardware removal: Offer plate and screw removal once union is confirmed and the patient has recovered function (typically 12-18 months). Hardware irritation is the commonest indication for planned removal

Special Case: Combined SMO and Calcaneal Osteotomy

When It Is Needed

In some patients with varus ankle OA, the hindfoot deformity is multiplanar — not just the tibial plafond tilt but also a varus heel (calcaneal inclination contributing to hindfoot varus). In these patients, an isolated supramalleolar osteotomy may not fully correct the alignment because the calcaneus remains in varus and the talus continues to sit tilted.

Technique

• Perform the supramalleolar osteotomy as described, correcting the TAS angle
• Through a separate lateral incision, perform a medial displacement (Dwyer) calcaneal osteotomy — an oblique osteotomy of the calcaneus posterior to the posterior facet of the subtalar joint, displacing the calcaneal tuberosity medially and laterally shifting the ground reaction force under the tibia
• Fix the calcaneal osteotomy with a cannulated screw or staple
• Combined correction addresses both the tibial and calcaneal components of the varus hindfoot

Outcomes

Series have shown that combined SMO with calcaneal osteotomy provides better correction of multiplanar deformity than SMO alone in patients with significant hindfoot varus. Survivorship at 7 years is approximately 80% in Takakura stage II disease.

Special Case: SMO After Previous Ankle Trauma or Surgery

Post-Traumatic Malunion

Patients with a prior distal tibial or plafond fracture that has healed in malalignment may develop eccentric ankle OA. The malunion produces the same biomechanical derangement as primary varus or valgus OA — the joint surface is tilted and load is concentrated in one compartment.

• Pre-operative CT is essential to assess the extent of intra-articular step-off and chondral damage
• The osteotomy corrects the coronal plane deformity; intra-articular step-off from the original fracture is not addressed by osteotomy alone
• Outcomes are good if the deformity is extra-articular (supramalleolar malunion) and the intra-articular surface is congruent after correction

Previous Lateral Ligament Reconstruction

In patients with chronic lateral ligament instability and progressive valgus ankle OA, SMO may be combined with lateral ligament reconstruction. The osteotomy corrects the bony alignment while the ligament reconstruction addresses the soft-tissue instability.

• Ensure the subtalar joint is mobile and not arthritic before proceeding
• Stage the procedures: some surgeons perform the osteotomy first and address ligament reconstruction in a second stage if instability persists

Special Case: SMO in the Revision Setting

After Failed Arthroscopic Debridement

Arthroscopic debridement may provide temporary relief in early eccentric OA but does not address the underlying malalignment. Patients with recurrent symptoms after debridement are strong candidates for SMO — the mechanical cause of their arthritis has never been corrected.

After Failed Osteotomy

Revision SMO is technically demanding: prior hardware removal, scar tissue, and altered bone biology from the index procedure. Nonunion of the index osteotomy must be treated with bone grafting and revision fixation. The correction goals remain the same: restore neutral TAS angle with a congruent talus.