What HTO does to your knee and why alignment matters

Think of a car tyre that wears unevenly along one edge because the wheel is slightly out of alignment — run it long enough and the rubber on that side grinds down far faster than the rest. A varus knee works in a similar way. With every step you take, forces equivalent to three to eight times your body weight travel through the joint; when the leg is bowed inward, the bulk of that load falls on the inner (medial) compartment rather than being shared evenly. Cartilage on that side deteriorates faster, the joint narrows further, and the bowing worsens — a self-reinforcing cycle that conservative measures alone cannot reverse.

High tibial osteotomy interrupts that cycle at its mechanical root. The surgeon cuts and reshapes the upper section of the tibia, then holds the corrected position with angle-stable locking plates while the bone heals. The result is that the weight-bearing axis of the leg shifts away from the worn medial side toward the healthier lateral compartment, reducing the abnormal load that was driving cartilage breakdown.

The medial open-wedge technique is now standard practice. A biplanar variant — where two intersecting cut planes are used rather than one — adds rotational stability and is increasingly preferred. The aim is to restore the mechanical axis so that it passes through the midpoint of the knee, with approximately 10 mm of intact lateral cortex left as a hinge to maintain stability during healing.

This is a load-redistribution procedure, not a cartilage repair. It improves the mechanical environment for the cartilage that remains, and evidence suggests this can slow ongoing wear and reduce pain — but it does not regenerate the tissue that has already been lost.

The right candidate profile — and who is not suitable

Not every patient with medial knee pain is a candidate for HTO, and understanding where the boundaries lie is the most useful starting point for anyone considering the procedure.

The strongest candidates share a recognisable profile: typically under 60–65 years old, physically active, with a BMI below 30, and a confirmed diagnosis of isolated medial unicompartmental osteoarthritis driven by correctable varus malalignment. Crucially, the lateral and patellofemoral compartments must be in good condition. Because HTO transfers load toward the lateral side, any existing damage there would simply be accelerated by the procedure — which is why pre-operative arthroscopy is considered mandatory to assess the compartment that will bear increased load after realignment. Ligamentous stability is equally important, as is adequate range of motion: a flexion contracture greater than 15 degrees, or less than 90 degrees of knee flexion, rules out the procedure.

Contraindications should be understood clearly. Lateral or patellofemoral OA, inflammatory arthritis (such as rheumatoid arthritis), diffuse or bicompartmental disease, BMI above 30, and significant ligamentous instability are all absolute reasons to look at alternative pathways. BMI is worth noting specifically — some older literature cited a threshold of 35, but the weight of current evidence and clinical practice points to 30 as the relevant limit, though the precise cut-off is one detail a thorough consultant assessment will individualise.

The Lincolnshire Knee Clinic frames candidacy using what it calls the 'joint-preservation window' — a concept that shifts the conversation away from a hard age rule and toward an intersection of structural and functional variables. A fit, active 62-year-old with contained medial wear and a healthy lateral compartment may remain well within that window. A 48-year-old with bicompartmental damage or uncontrolled inflammatory disease may not. Age, in other words, is a guide rather than a gate.

If the profile above broadly describes your situation, a consultant assessment is a reasonable next step — not a commitment to surgery.

How long HTO realistically delays knee replacement

The headline figure from a prospective cohort of 556 patients (643 procedures) is that 79% of knees had not required replacement ten years after medial open-wedge HTO — a cumulative conversion rate of just 5% at five years, rising to 21% at the decade mark. The widely cited clinical estimate drawn from this and comparable data is that HTO defers the need for arthroplasty by an average of 10–15 years in well-selected patients.

Two points are worth stating plainly. First, HTO is a bridge, not a cure. The underlying arthritic process is slowed by the improved mechanical environment, but it is not halted permanently; the majority of patients will eventually need a replacement, and they should be counselled with that honesty from the outset. Second — and this matters to patients who worry about burning bridges — a 2020 systematic review confirmed that having had a prior HTO does not worsen the clinical or radiological outcomes of a subsequent total knee replacement. The conversion surgery is technically more demanding for the operating surgeon, but the patient's result is equivalent to a primary TKR.

Beyond the 15-year horizon, the evidence base becomes thinner, particularly for patients who combined HTO with a cartilage restoration procedure. When patients ask what to expect past that point, the honest clinical answer is that the trajectory depends heavily on how much healthy joint was preserved before surgery, how well the correction holds, and how the remaining cartilage responds over time — which is why getting the initial patient selection and correction target right carries so much weight.

Factors that predict whether HTO will last

Several independent factors shape how long an HTO is likely to hold, and understanding them helps patients set realistic expectations before surgery rather than encountering surprises afterwards.

The most powerful predictor is how advanced the arthritis appears on imaging at the time of the operation. Patients with more severe radiographic OA at surgery are roughly twice as likely to need a knee replacement within ten years (adjusted hazard ratio 1.96) compared with those presenting with milder disease — one of the strongest arguments for acting earlier in the arthritic process rather than later. Female sex independently increases conversion risk by approximately 67% (HR 1.67); each additional decade of age adds around 50% more risk (HR 1.50); and every 5 kg/m² increase in BMI raises it by roughly 31% (HR 1.31).

None of these figures is disqualifying on its own. Their value lies in counselling: a patient near the upper end of the acceptable age range, with a BMI close to 30 and moderately advanced cartilage loss, has a meaningfully higher probability of needing arthroplasty within a decade than a younger, leaner patient with earlier-stage disease. Honest pre-operative discussion around this profile matters — not as a deterrent, but so patients can weigh the timing decision with an accurate picture of likely HTO lifespan.

Objective biomechanical assessment — examining how the joint is actually loaded during walking — can add a functional dimension that standing radiographs alone do not capture. Dynamic loading patterns, including the adduction moment through the medial compartment, may help refine both the correction target and the individual risk conversation.

One qualification worth stating briefly: the precise degree of varus malalignment that tips the balance from continued conservative management into osteotomy has not been established by a single validated threshold. This means patients near the borderline may encounter differing clinical opinions, and a thorough consultant assessment — weighing imaging, biomechanics, activity level, and patient expectations together — remains the appropriate guide rather than any single cut-off value.

Combining HTO with cartilage repair procedures

Reduced load on the medial compartment — established already as HTO's core contribution — is precisely what makes it a useful platform for cartilage repair. A biologic repair procedure placed into a mechanically hostile joint is working against the physics; once the axis is corrected, the same procedure operates in a far more favourable environment for tissue integration and long-term durability.

That observation is reinforced by an important finding in its own right: HTO performed without any adjunct cartilage procedure already promotes measurable cartilage recovery in a meaningful proportion of patients, including those with severe lesions extending to bare bone. Published arthroscopic and MRI assessments, along with subjective scoring using IKDC and Lysholm instruments, document this recovery — suggesting the mechanical correction itself has a biological effect, not merely a symptomatic one.

Where defect size, grade, or clinical presentation warrants a more targeted repair, HTO can be combined in a single or staged approach with several established techniques:

• ACI / MACI — cell-based implantation, suited to larger contained defects (roughly 2–10 cm²); MACI uses a collagen membrane scaffold, reducing some technical drawbacks of first-generation ACI.
• OATS / Mosaicplasty — osteochondral autograft; most appropriate for smaller focal defects (typically 1–2 cm²), with donor-site morbidity a meaningful consideration.
• AMIC — matrix-augmented marrow stimulation; a single-stage bridge between microfracture and cell-based repair.
• Meniscal allograft transplantation — where concurrent meniscal deficiency compounds the loading problem.

Microfracture, historically the default first-line choice for smaller defects, carries known concerns about fibrocartilage breakdown within two to three years and disruption of the subchondral bone plate — reducing its suitability as a combination partner and as a standalone option in this context.

A 2017 analysis (Kahlenberg et al., PubMed 27773639) confirmed that HTO with cartilage restoration provides reliable medium- to long-term functional improvement. The selection of which procedure to pair, however — governed by defect size and grade, patient age, prior treatment history, and surgeon experience — is not yet guided by a single validated algorithm. This remains an active area of clinical investigation, and individual decisions appropriately rest on a thorough consultant assessment of all these variables together.

Getting an assessment at Lincolnshire Knee

The decision about whether HTO is the right next step cannot be made from symptoms alone — it depends on a precise picture of alignment, compartmental cartilage health, and how the joint loads during movement. That diagnostic picture is also, in practice, the answer to the question the preceding sections have built toward: who benefits, how long the correction is likely to hold, and whether a combined cartilage procedure is warranted alongside the realignment.

A thorough assessment typically draws on standing weight-bearing radiographs and MRI to confirm varus deformity and compartmental involvement. AI-assisted analysis such as onMRI™ — which includes T2 cartilage mapping and compartmental segmentation — can add granularity, particularly in identifying lateral compartment disease that would make HTO unsuitable. Objective gait assessment using MAI Motion® can quantify the dynamic adduction moment through the medial compartment, a functional dimension that static imaging does not capture and that informs both the correction target and the candidacy conversation.

Lincolnshire Knee is part of the MSK Doctors group and accepts patients without a GP referral. Book an assessment at lincolnshireknee.co.uk.

1. [1] High tibial osteotomy – Wikipedia. https://en.wikipedia.org/?curid=42896695 https://en.wikipedia.org/?curid=42896695