High Tibial Osteotomy
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Direct answer
A high tibial osteotomy (HTO) shifts the weight-bearing line of a varus knee off the worn medial compartment onto healthier lateral cartilage. The ideal candidate is the young, high-demand patient under about fifty with isolated medial compartment osteoarthritis and a correctable varus — too young and too active for arthroplasty economics and implant longevity. Medial opening wedge has become the default technique worldwide, with the lateral closing wedge retained for extreme corrections; the target is an overcorrection to 62.5 percent of the tibial plateau width from the medial edge (the Fujisawa point), roughly three to four degrees of mechanical valgus. Undercorrection, not surgical technique, is the commonest cause of failure.
What you must remember
- Indication sweet spot: age under 50-55, high activity demand, isolated medial compartment OA (KL grade II-III), correctable varus that opens on a valgus stress radiograph, knee flexion more than 90-100 degrees, flexion contracture less than 10-15 degrees.
- Fujisawa point: the postoperative mechanical axis should pass through about 62-63 percent of tibial plateau width from medial (acceptable range 50-75 percent) — a standard viva quotation, conventionally translated as 3-4 degrees of valgus overcorrection.
- Opening versus closing wedge: opening wedge spares the fibula and the peroneal nerve but risks lateral hinge fracture and nonunion, and openings beyond about 10 mm usually need bone graft; closing wedge (Coventry) needs proximal fibular handling, risks peroneal palsy and patella baja.
- Lateral hinge fracture (Takeuchi classification): type 1 exits above the tibiofibular joint (benign, protected weight-bearing), type 2 runs into the lateral articular surface (needs fixation), type 3 extends into the proximal tibiofibular joint — a modern exam favourite.
- Contraindications: inflammatory arthritis, tricompartmental or lateral compartment disease, medial tibial plateau bone loss, marked patellofemoral arthritis, flexion under 90 degrees, smokers (nonunion).
- Complications: undercorrection (commonest), lateral hinge fracture, delayed union or nonunion, compartment syndrome, peroneal nerve injury with closing wedge, hardware irritation needing removal.
- Implant access reality: dedicated locked valgus-producing plates are costly relative to most Indian unit budgets, so closing wedges fixed with staples or standard plates remain common in district practice; the biology tolerates this when the lateral hinge is intact.
- The extension cousin: an anterior closing wedge of the proximal tibia corrects recurvatum, and an open anterior wedge addresses extension loss after ACL surgery — the same geometry rotated ninety degrees.
Planning the correction
The full-length standing radiograph is the planning film, not the knee view. Draw Mikulicz's line from the centre of the femoral head to the centre of the ankle; in a normal limb it crosses the knee at or slightly medial to its centre (classically about 4 mm medial, ±2 mm). Mark the target axis at 62.5 percent from the medial tibial edge, measure the angle between the existing and desired mechanical axes, and transfer that correction angle to the proximal tibia with its hinge just above the tibiofibular joint. The wedge width is worked out trigonometrically from the correction angle and the tibial width — memorised millimetre rules collapse the moment a different-sized tibia arrives. Intraoperatively the correction is verified with an alignment rod or navigation, and the hinge is left a few millimetres short of complete cortical division so the lateral cortical bridge holds the correction and carries biology.
Where the operation fails
Undercorrection dominates the failure list: residual varus keeps loading the very cartilage the operation was meant to unload, and symptoms return within a few years. The second trap is patient selection — operating on an ACL-deficient knee without addressing instability, or on a patient whose radiographs already show lateral compartment wear; adding valgus to a failing lateral side accelerates disaster. Closing wedge operations add their own classic: patella baja from proximal tibial shortening, which converts a knee that bends well into one with anterior pain. In the viva, the follow-up question after any HTO answer is "why overcorrect?" — because a neutral or minimally corrected axis still biases load medially, and the whole point is a genuine lateral shift.
Frequently asked questions
Why overcorrect rather than correct to neutral?
A neutral axis still directs load through the medial plateau; the Fujisawa overcorrection moves the weight-bearing line lateral to the medial spine so the diseased compartment is genuinely unloaded.
Which nerve is at risk in a lateral closing wedge HTO?
The common peroneal nerve around the fibular neck, hence careful fibular head or neck handling and a documented peroneal examination after surgery.
When is bone graft needed in an opening wedge HTO?
Generally when the opening exceeds about 10 mm or the lateral hinge is unstable; tricortical iliac crest graft or a synthetic substitute fills the defect.
How is success judged after HTO?
The mechanical axis on a standing full-limb radiograph at the Fujisawa point, preserved knee motion and pain relief; good series report roughly 80-90 percent survival at ten years.
What is the commonest reason an HTO fails?
Undercorrection — residual varus continues to load the medial compartment, and symptoms recur despite technically sound healing.