Does alignment need to come before cartilage repair?

Cartilage repair placed into a knee that angles inward (a varus deformity) is attempting to heal in a mechanically hostile environment. The medial compartment — already the site of the damaged cartilage — continues to absorb a disproportionate share of load, and that sustained overload undermines any repair regardless of the technique used. High tibial osteotomy (HTO) addresses this by shifting the weight-bearing line away from the damaged medial compartment toward the healthier lateral side.

The decision about whether alignment correction must accompany cartilage repair is threshold-driven. Current expert guidance sets two cut-points: medial compartment cartilage repair should be combined with an unloading HTO when mechanical varus exceeds 3°; isolated cartilage repair in the medial compartment is contraindicated once varus exceeds 5°.

For many patients this does not mean two separate operations. When the cartilage technique chosen does not require laboratory cell cultivation — microfracture, MACI, or osteochondral autograft transfer — a single combined surgical episode is generally preferred. Staging is a technique-dependent decision, not the default. The sections below set out how that decision is made.

Why a varus knee puts cartilage repair at risk

Think of a crack in a plastered wall: patch it as carefully as you like, but if the building's foundations remain uneven and keep forcing the wall to flex in the same direction, the crack will return. The same principle applies to a varus knee. When the leg bows inward, the mechanical axis — the line along which body weight travels — runs through the medial compartment rather than through the centre of the joint. That single structural fact means the medial side absorbs load it was not designed to carry alone.

The numbers illustrate the scale of the problem. During ordinary daily activities, cartilage on the medial side of the knee experiences diurnal strains of up to 10%. After vigorous activity those strains rise into the 5–15% range, and during dynamic loading such as running they can reach 15–35% — consistently higher than on the lateral side. A cartilage defect in this environment is attempting to regenerate under conditions that the mechanical evidence suggests it cannot easily withstand.

Correcting the alignment with a high tibial osteotomy (HTO) works by redirecting that weight-bearing line toward the centre of the joint, shifting load toward the less-affected lateral compartment. The result is a mechanical environment in which repaired tissue has a more realistic chance of integrating during the months of healing that any cartilage technique requires. Without that correction, the repair site remains under the same structural duress that contributed to the damage in the first place.

The varus thresholds that trigger HTO

Those two cut-points — combine HTO with any medial compartment repair above 3° varus, contraindicate isolated repair above 5° — are best understood as the current consensus position rather than fixed rules. Expert guidance from Lutz et al. (2021) and Aweid, Batty and Getgood (2022, Ch.18) sets them out clearly, but the precise boundaries remain under study rather than confirmed by randomised controlled trial evidence.

What the thresholds do not specify is how far the alignment should be corrected — and on this point the distinction between HTO for osteoarthritis and HTO performed to protect a cartilage repair is clinically important.

In an OA patient, deliberate overcorrection is standard practice. The mechanical axis is shifted past neutral into mild valgus to offload the damaged medial compartment as fully as possible. For a patient with a focal cartilage defect undergoing HTO to create a more favourable healing environment, overcorrection is not the goal. Most authors aim for a straight mechanical leg axis — neutral alignment, not a valgus shift. Pushing the axis too far toward the lateral side would transfer disproportionate load to a compartment that may be entirely healthy and is not the target of treatment.

A further surgical nuance underlines why this type of combined procedure demands specialist experience: diagnostic arthroscopy immediately before the osteotomy cut is mandatory. It allows the surgeon to assess cartilage condition in the lateral compartment — the side that will absorb greater load once the weight-bearing line has been shifted. If that assessment reveals unexpected damage there, the surgical plan may need to change before the osteotomy proceeds. Pre-operative planning must account for this possibility.

One operation or two: how the repair technique decides

The technique chosen for cartilage repair does much of the work in deciding whether surgery happens in one visit to theatre or two — and understanding why makes the planning conversation with a specialist considerably clearer.

ACI requires a biopsy in a first operation, a period of laboratory cell culture typically lasting several weeks, and then re-implantation in a second procedure. Because that two-stage structure is already built into the technique, the HTO can be planned around the existing stages — timed to coincide with either procedure, depending on the clinical picture and surgeon preference. Guidance from Lutz et al. (2021) confirms that both staging alongside and performing the procedures separately are considered acceptable for ACI; neither is universally mandated.

For techniques that do not require cell culture, a combined single-stage procedure is generally preferred. Microfracture, OATS (osteochondral autograft transfer), and MACI — where cells are seeded on a collagen scaffold but without the same extended culture demands as first-generation ACI — can all be carried out simultaneously with the osteotomy. A single anaesthetic, one recovery period, and a shorter overall treatment timeline follow as a result. MACI and ACI are sometimes grouped together in shorthand; the staging logic differs between them, and the distinction matters for planning.

Access and cost are practical moderators that can narrow the options in any given centre, particularly for cell-based pathways. Whether a single-stage route is feasible depends not only on the anatomy but on what the treating unit can reliably deliver. Patients are well placed to ask their specialist which approach is planned — and whether the answer reflects the technique's requirements, the local service, or a combination of both.

What needs to be in place before combined surgery

Surgery at this level is not the first response when malalignment and cartilage damage coincide. Guidance from Aweid, Batty and Getgood (2022, Ch.18) is clear that patients must have completed an adequately performed neuromuscular rehabilitation programme — and found it insufficient — before combined realignment and cartilage restoration is considered. That prerequisite matters not only as a clinical gate but as a practical filter: some patients improve enough through structured rehabilitation that the case for surgical intervention becomes less pressing or changes in nature.

Beyond the alignment correction itself, the joint environment has two further mechanical contributors that a specialist will evaluate before proceeding. Ligament instability, if present, undermines the repair environment independently of any osteotomy: an unstable joint continues to expose repaired tissue to abnormal shear forces regardless of how accurately the mechanical axis has been corrected. Where instability is identified, reconstruction should be planned before or alongside the combined procedure.

Meniscal integrity is the third element in the assessment. A significantly deficient meniscus amplifies load transmission through the medial compartment, partially negating the benefit of realignment. Where meniscal tissue is substantially compromised, allograft transplantation may be considered within the same surgical episode — making the planning conversation considerably broader than alignment and cartilage repair alone.

What outcomes research shows — and where evidence is still thin

The clearest head-to-head comparison in the published literature comes from a three-arm study recruiting 20 patients treated by HTO alone, 18 treated with HTO combined with ACI, and 18 treated with HTO combined with microfracture. Groups were well matched at baseline — with the exception of BMI — confirming that prospective comparison across these three strategies is achievable. Granular long-term outcome data from this cohort remains limited in what has been published, so the study is better read as evidence that comparative research is advancing than as a settled hierarchy of results.

Sterett and Steadman's work stands as the landmark series supporting the combined approach. Their 2004 paper in the American Journal of Sports Medicine established a clinical basis for chondral resurfacing alongside HTO in the varus knee; a 2010 follow-up from the same authors added survivorship analysis, providing longer-term perspective on how the procedure holds up over time. Matsunaga et al. (2007) added corroborating evidence using microfracture and abrasion arthroplasty alongside osteotomy in medial gonarthrosis.

Negative outcomes reported in some combined ACI-plus-HTO series require careful interpretation. Those series largely involved patients with advanced multi-compartment osteoarthritis — a population for whom ACI is not indicated to begin with. The results do not transfer directly to patients with focal cartilage defects, for whom the combined procedure is designed; conflating the two groups misrepresents what the evidence actually says about appropriate candidates.

Two evidence gaps remain honest to name. The precise varus threshold beyond which osteotomy becomes obligatory rests on expert consensus rather than randomised trial data. And long-term survivorship figures specific to focal defect patients — as distinct from OA populations — are limited. What the existing evidence does establish is that in correctly selected patients, combined surgery is technically reproducible and durable enough to feature in multi-year survivorship analyses.