Supramalleolar Osteotomy (Distal Tibia Realignment)

Indication. Symptomatic asymmetric (eccentric) ankle osteoarthritis with a correctable deformity — varus OA with medial compartment overload and preserved lateral cartilage, or valgus OA with lateral overload and preserved medial cartilage — that has failed non-operative treatment (activity modification, a rocker-bottom shoe or AFO, lateral/medial wedge insole, NSAIDs and an intra-articular corticosteroid injection). The patient is typically young and active (under 55 to 60), wishes to delay or avoid ankle arthrodesis or replacement, has a mobile subtalar joint, and at least 30 degrees of sagittal ankle motion. Absolute indications - Asymmetric ankle OA (Takakura stage II or III) with a correctable deformity and a preserved opposing compartment

• Varus ankle with a TAS angle less than 90 degrees (or valgus with TAS greater than 96 degrees) that remains symptomatic despite non-operative care
• Young, active patient (typically under 55 to 60) wishing to delay arthrodesis or total ankle 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 loading
• Ankle OA secondary to distal tibial physeal arrest (growth disturbance)
• Periarticular deformity with correctable ankle subluxation
• 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 — there is no compartment to offload onto
• 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 active inflammatory disease (optimise medically first)
• 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 the approach
• Diabetes mellitus with peripheral vascular disease The three things you must confirm before listing for SMO. These are the selection gatekeepers — miss one and the operation fails.

Opening-wedge or closing-wedge? Both correct the TAS angle back toward neutral; the choice is biomechanical and surgeon-dependent. Medial opening-wedge is the predominant current technique for varus OA.

Consent specifically for nonunion (2 to 8 percent), under- or over-correction (5 to 15 percent), infection (1 to 3 percent), neurovascular injury including transient peroneal nerve palsy (1 to 3 percent), hardware irritation requiring removal (10 to 25 percent), and the possibility of eventual conversion to ankle arthrodesis or replacement if arthritis progresses. Setup. Supine on a radiolucent table; a sandbag under the ipsilateral buttock can help present the medial ankle. Prep the ipsilateral iliac crest into the field if autograft is planned. Thigh tourniquet to 250 mmHg. Position the image intensifier for true AP, lateral and mortise views before draping — fluoroscopy is used repeatedly throughout. Single-dose IV cefazolin 2 g at induction.

The goal: through an anteromedial approach, expose the distal tibial metaphysis 4 to 6 cm above the plafond, perform a controlled incomplete osteotomy with the lateral cortex as a greenstick hinge, shorten the fibula at the same level so the tibia is free to open, correct the TAS angle to neutral, fill the defect with structural graft, and lock a contoured plate across it — restoring a congruent talus under a neutral plafond.

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Lateral closing-wedge — the alternative, in brief. Through an anterolateral incision over the distal tibial metaphysis: osteotomise the fibula at the same level (essential, so the lateral tibial cortices can close and the distal fragment can translate), mark the wedge with K-wires under fluoroscopy, resect a calculated lateral wedge with the saw, close and compress the fragments, and fix with an anterolateral locking plate — no graft is needed because of inherent bone contact. Its specific risks are a higher deep peroneal nerve palsy rate (1 to 5 percent, usually transient) from anterior compartment dissection, and a slightly higher lateral wound breakdown rate on the thin distal tibial skin.

Rehabilitation | Phase | Timing | Immobilisation | Therapy and weight-bearing | |-------|--------|-----------------|----------------------------| | 1 | 0 to 2 weeks | Below-knee posterior splint or cast, ankle neutral, non-weight-bearing | Elevation, toe active range of motion only; wound check at 10 to 14 days | | 2 | 2 to 6 weeks | Removable CAM boot | Touch weight-bearing (10 to 15 kg); gentle active dorsiflexion/plantarflexion in the boot; stationary cycling without resistance | | 3 | 6 to 12 weeks | CAM boot, weaning | Partial to full weight-bearing as callus appears on the 6-week film; progressive active and active-assisted ROM, subtalar mobilisation | | 4 | 3 to 9 months | None (night splint if needed) | Calf raises, resistance bands, proprioception; impact sport only once union is confirmed and strength recovered | Return to function. Office or sedentary work by 4 to 6 weeks; light or standing duties by 8 to 12 weeks; heavy manual work by 12 to 16 weeks or longer. Driving once an emergency stop is safe — typically 8 to 12 weeks for the right (driving) ankle. Low-impact sport (swimming, cycling) from 12 to 16 weeks; running and impact sport from 6 to 9 months once union is confirmed. Radiographs at 6 weeks (early callus), 3 months (confirm union), 6 and 12 months, then annually. Offer hardware removal at 12 to 18 months once union is solid — hardware irritation is the commonest reason for a planned return to theatre. Complications

Rationale and biomechanics. 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 a medial opening-wedge correction, contact pressure shifts laterally toward the preserved cartilage. Biomechanical studies show that a 10-degree correction of the TAS angle can shift the centre of contact pressure by 10 to 20 percent of the tibiotalar surface area. Non-operative measures manage symptoms in early asymmetric OA but do not halt progression, because the eccentric mechanical abnormality persists and keeps driving degeneration of the overloaded compartment — SMO addresses that mechanical cause rather than the symptom alone. The radiographic angles. - Tibial anterior surface (TAS) angle — on the weight-bearing AP ankle radiograph, the angle between the anatomical axis of the tibia and the distal tibial joint surface. Normal is about 93 degrees (range 89 to 97). Less than 90 indicates varus tilt; greater than 96 indicates valgus tilt. This is the primary angle SMO corrects. (Do not confuse it with the tibial plateau angle / MPTA, which is proximal and relevant to high tibial osteotomy, not SMO.)

• Tibial lateral surface (TLS) angle — on the weight-bearing lateral film, the angle between the tibial axis and the distal articular surface. Normal is about 80 degrees (range 76 to 84). An abnormal TLS indicates sagittal plane deformity (recurvatum or procurvatum) that may need additional correction.
• Talar tilt — between the plafond and the talar dome on the AP view. In varus OA the talus tilts into the medial compartment; after SMO it should sit congruently under the corrected plafond. Takakura staging of varus ankle OA.

The fibula and its role. The fibula is the lateral strut of the mortise and a key mechanical constraint. In a medial opening-wedge, the intact fibula acts as a tension band resisting lateral opening — so an oblique osteotomy at the same level (often with a 5 to 10 mm segment resected) releases this constraint. In a lateral closing-wedge, the fibula must be osteotomised at the same level so the lateral tibial cortices can appose and the distal fragment can translate medially. A Z-osteotomy or step-cut controls shortening precisely. Inadequate fibular release is the commonest technical cause of under-correction. Outcomes and survivorship. In well-selected patients, approximately 70 to 85 percent report good to excellent results at 5 to 7 years. Krähenbühl's series reported 71 percent good or excellent outcomes with survivorship (free of arthrodesis) of 79 percent at 10 years and 67 percent at 15 years; Takakura stage IV disease and subtalar arthritis were the strongest predictors of failure. Tanaka's varus-OA series showed 73 percent excellent or good results at a mean 8.3 years, better in stage II disease. A 2023 systematic review (547 patients) found a mean AOFAS improvement of 33.2 points, a mean TAS correction of 9.4 degrees and a complication rate of 12.1 percent (nonunion 3.2 percent). Special situations. Where the hindfoot deformity is multiplanar — a varus plafond tilt plus a varus heel — an isolated SMO under-corrects, and a concurrent medial-displacement (Dwyer) calcaneal osteotomy is added through a separate lateral incision; combined correction gives better multiplanar alignment, with survivorship around 80 percent at 7 years in stage II disease. After plafond malunion, pre-operative CT is essential — SMO corrects the coronal deformity but does not address intra-articular step-off. In chronic lateral ligament insufficiency with progressive valgus OA, SMO may be combined or staged with ligament reconstruction. Revision SMO is demanding (hardware removal, scarred biology) and the goals are unchanged: a neutral TAS with a congruent talus.