Why surgeons recommend HTO before knee replacement

When a surgeon recommends a high tibial osteotomy (HTO) rather than a knee replacement, the natural question is: why not go straight to the replacement and be done with it? The answer lies in what HTO actually does — and for whom it is designed.

The procedure targets a specific mechanical problem. In medial compartment knee osteoarthritis, the leg bows inward (varus, or 'bow-legged' alignment), pushing most of the body's weight through the inner side of the knee where cartilage has already begun to break down. HTO corrects that alignment by making a precise cut in the upper tibia and adjusting the bone so the weight-bearing axis shifts toward the healthier outer compartment. Nothing is removed or replaced; the joint itself is preserved. By redistributing load away from the worn area, the surgery reduces pain and may slow further deterioration of the medial compartment.

This makes HTO a deliberate preservation strategy, not a fallback when everything else has failed. The goal is to extend the working life of the patient's natural knee — ideally by a decade or more — in someone who is active, relatively young, and not yet at the stage where joint replacement is the only realistic option.

The trade-off is real, however. HTO works well for the right patient and adds surgical complexity without proportionate benefit for the wrong one. Patient selection is therefore central to the decision, and most surgeons will discuss it in detail before recommending the procedure.

The patient profile most likely to benefit

Several factors tend to predict who does well with HTO, and understanding them can help frame the conversation with a specialist before any decision is made.

The strongest predictors of a durable result are age under 55, a BMI below 30, and a physically active lifestyle — not because older or heavier patients are automatically excluded, but because these factors consistently show up in long-term data as markers of success. A 20-year prospective study found that patients meeting this profile achieved 62% survivorship at two decades, compared with 44% overall — and 97% of those whose HTO was still functioning reported satisfaction with the outcome. Activity level matters too: higher pre-operative Tegner scores (a measure of physical function) are independently associated with a lower risk of eventually needing joint replacement.

The key mechanical feature is varus malalignment — the bow-legged alignment where the tibia tilts inward, overloading the inner knee. Without this, HTO has no useful biomechanical target. Just as important is that the damage remains confined to the medial compartment, with some intact cartilage still present in the outer (lateral) compartment, which will take on extra load once alignment is corrected. This is why pre-operative arthroscopy is often recommended before committing to the procedure: it allows the surgeon to assess the lateral compartment directly and confirm it is healthy enough to handle the shift.

Some conditions make HTO unsuitable rather than simply less ideal. Rheumatoid arthritis, a fixed valgus deformity greater than 20°, and significant ligamentous instability are absolute contraindications — they fundamentally alter the risk-benefit equation. Nicotine use and osteoporosis affect bone healing after the osteotomy and are treated as relative contraindications; they shift the balance rather than close the door entirely.

None of these factors should be read in isolation. Someone who ticks most boxes but has one borderline result on imaging may still be an excellent candidate; someone who appears to fit may have findings on closer assessment that point elsewhere. The decision ultimately rests on a full review of imaging, activity history, and individual goals with an experienced specialist.

Combining HTO with cartilage repair

Repairing damaged cartilage inside a joint that is still mechanically misaligned is, in principle, a losing strategy: the repaired surface is subjected to the same abnormal loading that caused the damage in the first place. This is the core argument for combining HTO with a cartilage restoration procedure — the osteotomy creates the mechanical conditions in which biological repair can actually take hold.

Evidence supports this logic. In a study of medial OA patients treated with combined medial opening wedge HTO and osteochondral autologous transfer (OATS), Kaplan-Meier survivorship reached 96.7% at a mean of 9.5 years. Second-look arthroscopy confirmed 100% cartilage regeneration across assessed knees, with hyaline-quality cartilage in 86% — a markedly better outcome than load redistribution alone would be expected to produce. Knee Society Scores improved from 48.3 to 90.4 over the follow-up period.

Cell-based repair produces similarly encouraging figures. A 10-year study with angular stable plate fixation found that the HTO combined with autologous chondrocyte implantation (ACI) subgroup achieved 94.3% TKA-free survival, compared with 82.2% for the HTO-alone group treated for established medial OA — a meaningful difference at a decade of follow-up.

Combinations with microfracture or matrix-assisted marrow stimulation are also practised, particularly for younger patients presenting with a discrete focal defect rather than widespread OA. As a general principle, patients selected for these combined procedures tend to be younger than those treated for established osteoarthritis, and the same candidate selection criteria — activity level, BMI, compartmental assessment — apply throughout.

How the surgery is performed and why accuracy matters

The bone cut at the heart of HTO is precise and deliberate. A surgeon makes an incomplete cut across the upper tibia and repositions it slightly — redirecting how load travels through the knee without removing any joint surface.

Two techniques achieve this. The medial opening wedge approach (now the more widely used) creates a small gap on the inner side of the tibia held open with bone graft and secured with a locking plate. The lateral closing wedge removes a thin wedge of bone from the outer side and closes the gap. Both are supported by evidence; the choice depends on the surgeon's experience and the patient's anatomy.

Biplanar osteotomy with angular stable plate fixation is the current standard — it provides stability during healing and tighter control of the final alignment. That precision is directly linked to outcomes. The correction target is slight valgus alignment of less than 3° of mechanical femorotibial angle: enough to shift load away from the damaged compartment, not so much that the opposite side is overburdened. Under-correction is the most common technical pitfall: in one closing wedge series, 30% of patients experienced hypocorrection, which was independently associated with inferior survival, lower function, and reduced satisfaction.

Modern HTO is technically well-refined, not experimental — but the skill with which these tools are applied still varies. Before proceeding, asking the specialist which technique they favour for your anatomy, and what their correction accuracy results look like, is a sensible step.

What the outcome data actually shows

Numbers tell the most honest story here. In the short to medium term, HTO performs well in appropriately selected patients: a closing wedge series reported 87.6% survival at five years and 75.5% at ten years, while a separate series using angular stable plate fixation found 87.2% TKA-free survival at a decade.

'Survival' in this context means remaining free of conversion to knee replacement — not the absence of all symptoms. Some patients within the surviving group will still experience some discomfort over time, and that distinction is worth holding on to when evaluating the figures.

The longer-term picture is more nuanced. A 20-year prospective study of lateral closing-wedge HTO found overall survivorship of 44% — a figure that deserves context rather than reassurance. Amongst the subset meeting the ideal candidate criteria (age under 55, BMI under 30, moderate symptoms), survivorship reached 62% at 20 years. Of those who retained their HTO to that point, 97% reported satisfaction, with a mean KOOS pain score of 91. That figure is genuinely meaningful: it indicates that the procedure, for the right patient, delivers lasting improvement in quality of life even as a proportion of the overall cohort eventually proceeds to arthroplasty.

The gap between 44% overall and 62% in favourable candidates is, in quantitative terms, the case for the selection rigour discussed earlier in this article. Poor candidacy does not simply reduce the chance of success — it shortens the time horizon considerably.

One evidence gap is worth acknowledging plainly: long-term follow-up data specific to the medial opening wedge technique — now the more commonly performed approach — beyond 15 years remain sparse.

Risks, complications, and planning the road ahead

Complication rates for HTO are broadly comparable to those seen in other elective orthopaedic procedures. A systematic review of 71 studies covering 7,836 patients found an intraoperative complication rate of 5.5% and a postoperative rate of 6.9%. The single most common intraoperative event in medial opening wedge procedures is lateral hinge fracture, occurring in 9.1% of cases. When it happens, the surgical team can manage it intra-operatively, but it is the kind of risk worth discussing explicitly before the procedure rather than learning about afterwards. Nonunion, loss of correction, and implant failure each occurred in fewer than 2% of cases in the same review.

The downstream picture matters equally. A meta-analysis of more than 550,000 patients confirms that total knee arthroplasty performed after a prior HTO achieves comparable long-term survival to primary TKA — so HTO does not close the door on replacement. It does, however, make that future surgery more technically demanding, with significantly higher complication rates than would be expected from a first-time replacement. This is not a reason to avoid HTO; it is a reason to select patients carefully from the outset, since the complexity of a potential future conversion is part of the overall risk calculation.

For anyone considering the procedure, surgeon experience is a meaningful variable — both in achieving accurate correction and, where the anatomy supports it, in assessing whether a combined cartilage restoration approach might extend the benefit further.