What HTO does to your knee

High tibial osteotomy (HTO) works by changing where your body weight travels through the knee — not by replacing any damaged surface. In a bow-legged (varus) knee, the mechanical axis — the straight line that should run from hip to ankle through the centre of the joint — tilts inward, pushing load onto the medial (inner) compartment. When that compartment's cartilage is worn, every step concentrates force exactly where the joint is least able to tolerate it. Think of it like a table with one cracked leg bearing all the weight: HTO repositions the load onto the sound leg.

The procedure corrects this by making a precise cut in the upper tibia and opening a small wedge on the inner side of the bone. Spreading that wedge shifts the mechanical axis laterally, so it passes through the centre of the knee and weight-bearing force falls onto the healthier lateral compartment instead. The realigned tibia is held open and stable with a locking plate — the TomoFix system is the most widely used — and a biplanar bone cut adds rotational stability. With modern plate fixation, partial weight-bearing can begin around two weeks after surgery.

Critically, HTO preserves your natural knee. No cartilage is removed, no implant is inserted, and the ligaments and bone stock remain intact. The procedure changes the mechanical environment around damaged cartilage rather than replacing it — a distinction that matters both for what HTO can achieve and for what remains possible later if arthroplasty is ever needed.

The patient profile HTO is designed for

Age is a useful starting point, but it is the biological state of the joint that drives the decision. Most candidates are under 60, yet a 58-year-old with largely intact cartilage and an active lifestyle may be a stronger candidate than a 52-year-old with more diffuse wear. The shared profile is a younger, active patient with symptomatic genu varum and osteoarthritis confined to the medial compartment who wants to maintain demanding physical activity — whether that is manual work, running, or field sport — and defer or avoid joint replacement.

The integrity of the lateral and patellofemoral compartments is non-negotiable. HTO shifts load onto the lateral compartment, so if that cartilage is significantly damaged, the procedure trades one worn surface for another. Arthroscopic assessment of the lateral compartment immediately before the osteotomy is standard practice precisely because of this dependency.

Sufficient bone quality is also required — osteoporosis impairs healing at the osteotomy site, and inflammatory arthritis such as rheumatoid disease is an absolute contraindication because the underlying joint pathology is systemic rather than mechanical. Nicotine use is associated with poorer bone healing and is a relative contraindication for the same reason. Where cartilage repair is planned alongside osteotomy, a BMI above 40 is a relative contraindication, as excess load compromises the biological repair environment.

Pain relief after HTO is meaningful in well-selected patients but less predictable than after joint replacement. Setting that expectation honestly at the outset is part of good patient selection — the procedure suits those whose primary goal is to preserve their native knee and maintain physical capacity, accepting that some residual discomfort is possible.

When the balance tips toward joint replacement

Three structural findings categorically redirect the decision toward replacement. A fixed valgus deformity greater than 20° cannot be corrected by the tibial cut used in HTO — the geometry of the problem lies in the wrong bone. Significant ligamentous instability means that realigning the load-bearing axis does not resolve the underlying mechanical problem; the joint cannot hold the corrected position reliably. And when osteoarthritis has extended beyond the medial compartment to involve the lateral side or the patellofemoral joint, the axis-shift rationale collapses: there is no sufficiently healthy compartment to shift load onto. In those patients, unicompartmental or total knee replacement addresses the full extent of the disease in a way osteotomy cannot.

The degree of varus deformity beyond which osteotomy becomes impractical is a more nuanced question. No published threshold defines it, and current evidence leaves this as a matter of clinical judgement informed by imaging, the patient's joint state, and surgeon experience. A degree of varus that sits comfortably within osteotomy range in one patient may be paired with such severe medial cartilage loss that the load-shift produces little gain — making the malalignment angle only one variable among several rather than the deciding factor in isolation.

One further consideration belongs at the start of the conversation rather than the end: a prior HTO can make a subsequent total knee replacement technically more demanding. This does not make osteotomy inadvisable for the right candidate, but it is a factor that should be weighed honestly at the planning stage — evidence that the two procedures exist on a continuum of care rather than as competing alternatives.

HTO, UKA, and TKA side by side

Each of the three procedures addresses unicompartmental medial OA through a fundamentally different mechanism, and that difference — not patient preference alone — determines which fits a given clinical picture.

HTO keeps the native joint intact. Once the bone has healed, it places no long-term ceiling on physical demands — a meaningful distinction from either arthroplasty option. Against that, the recovery is longer and symptom relief is less predictable: some patients achieve near-complete resolution; others retain residual discomfort. HTO suits patients whose joint still has biology worth preserving and whose priority is sustained physical capacity.

UKA (such as the Oxford medial partial replacement) sits further along the pathway. By resurfacing only the damaged compartment, it avoids the extent of a full replacement and offers a shorter recovery than TKA; the cruciate ligaments and remaining compartments stay intact. Candidacy is stricter than for TKA — lateral compartment health and ligamentous stability must both be sound — and activity expectations after UKA are more conservative than after a healed osteotomy. It is appropriate when the medial cartilage is beyond biological salvage but disease remains genuinely single-compartment. Describing UKA as combining the advantages of both other options overstates the evidence; it is a distinct procedure with its own indications and limits.

TKA delivers the most consistent pain relief and is the appropriate choice when disease involves more than one compartment or when other surgical options have failed. For isolated medial OA it is the most invasive approach and involves long-term activity modification that osteotomy does not.

Comparative long-term outcome data between HTO and UKA in matched single-compartment populations remain limited, so the choice between them rests on individual anatomy, imaging findings, and clinical examination rather than a settled evidence hierarchy. These procedures occupy different positions on a treatment continuum; selection is not a matter of ranking one above another.

Combining HTO with cartilage repair

Malalignment and chondral damage are not always separate problems. When varus deformity coexists with cartilage damage in the medial compartment, addressing one without the other risks undermining the result: correcting the axis reduces load on the damaged surface but does not repair it, while treating cartilage in a mechanically hostile environment reduces the likelihood of successful healing and integration.

HTO can be staged before or combined with cartilage repair procedures — autologous chondrocyte implantation (ACI), microfracture, or osteochondral transplantation (OAT/OATS) — depending on the extent and depth of the lesion. The sequence matters: realigning the knee first creates a more favourable mechanical environment within which a cartilage repair is more likely to integrate. For smaller lesions, a single combined procedure may be appropriate; larger or more complex defects often warrant a staged approach to allow healing between interventions.

Precise pre-operative characterisation is essential. MRI with cartilage-sensitive sequences — including T2 mapping, which reflects cartilage composition rather than just structure — helps define lesion depth, distribution, and subchondral bone condition, guiding both the choice of cartilage technique and the timing of each stage. Arthroscopic assessment of the contralateral compartment immediately before the osteotomy provides a direct qualitative check of the cartilage that will bear increased load after realignment.

Combining procedures adds recovery time and surgical complexity. Individual assessment, rather than a fixed protocol, determines whether staging or simultaneous intervention is appropriate.

Getting assessed and making the decision

Deciding between osteotomy and replacement requires a structured clinical workup — a single scan is not sufficient on its own. Weight-bearing alignment X-rays map how load is distributed across the knee in the standing position, showing the degree of malalignment that imaging taken lying down can understate. MRI then assesses compartment-specific cartilage integrity, subchondral bone condition, and the state of the structures that would carry increased load after any realignment. Where available, objective gait or biomechanical assessment adds a functional dimension that static imaging cannot capture, quantifying how malalignment translates into dynamic load during everyday movement.

The consultation itself should cover more than anatomy. Activity goals, occupation, tolerance for a longer rehabilitation, and the patient's priority between predictable symptom relief and a preserved native joint all inform which pathway fits a particular clinical picture. Both osteotomy and replacement are legitimate answers; the question is which is appropriate given imaging findings, the degree of malalignment, age, and what the knee is expected to do after recovery.

Patients who have been waiting months without a clear diagnosis or a named pathway can access this type of assessment sooner than they may expect: Lincolnshire Knee is part of the MSK Doctors group and accepts patients without referral — book an assessment at lincolnshireknee.co.uk.

1. [1] High tibial osteotomy. https://en.wikipedia.org/?curid=42896695 https://en.wikipedia.org/?curid=42896695
2. [2] Unicompartmental knee arthroplasty. https://en.wikipedia.org/?curid=16991704 https://en.wikipedia.org/?curid=16991704