Can your knee be preserved

Rather than starting with a menu of operations, the useful first split is between a focal cartilage defect and a knee that is generally worn out. Joint-preserving treatment is usually most relevant for symptomatic, localised damage — often in younger or active patients — when the rest of the joint is still reasonably intact. If wear is diffuse across the knee rather than confined to one area, repair is less likely to be the main answer, and arthroplasty enters the picture more seriously.

That decision is not made on cartilage alone. In a 2025 review of knee-preservation surgery, alignment and the compartment involved were central factors, and in practice stability, meniscus status, age and activity level also shape the plan. High tibial osteotomy is a good example: it is mainly used for medial unicompartmental arthritis or malalignment, and may delay replacement in selected cases by shifting load away from the damaged side.

The pathway is usually simpler than the acronyms make it sound: symptom management first, sometimes injection-based support as an adjunct, then cartilage restoration such as MACI or OCA, or unloading procedures such as osteotomy or bracing, and finally knee replacement when preservation is no longer realistic. The focus here is that focal-defect, joint-preservation part of the pathway.

Why defect size changes the plan

In practice, size often changes the shortlist. For a small focal defect, microfracture has historically been used more often, while a larger focal defect is more likely to steer treatment towards MACI. The size boundary is not absolute: an internal cartilage reference describes roughly 2 to 4 cm² as the range where microfracture or osteochondral autograft may still be considered, with larger lesions tending to favour MACI. That matters because the best direct comparison, the phase 3 SUMMIT trial, studied patients with a mean lesion size of 4.8 cm² and found that MACI produced better 2-year KOOS pain and sport/function improvement than microfracture, with similar adverse-event rates. In other words, once the defect is no longer small, microfracture stops looking like the routine default and more restorative options move to the front of the discussion.

The longer-term pattern also helps explain why the two paths separate. Review data suggest microfracture does best in younger patients, in femoral condyle lesions, and in smaller defects. In a systematic review with 10 to 17 years of follow-up and mean defect sizes of about 2.3 to 4.01 cm², outcomes for medium-to-large lesions were much less reassuring: osteoarthritis progression was reported in 40% to 48%, return to sport in only 17.2% to 20%, and 2.9% to 41% later progressed to total knee replacement in some series. So microfracture still has historical and selective relevance, but the evidence does not support presenting it as the modern best first-line answer for larger cartilage defects.

When OCA is considered

OCA sits in a different part of the preservation pathway. In 1 operation, osteochondral allograft transplantation uses a fresh donor graft to replace not only damaged cartilage but also the underlying bone, which makes it a different tool from marrow-stimulation procedures and from cell-based repairs such as MACI. Reviews describe it mainly for large chondral or osteochondral defects, where the problem is more than a small surface lesion.

That is why OCA is often discussed after post-traumatic injury or as “salvage” after a previous cartilage procedure has failed. In those situations, simply trying to stimulate a repair response may be less suitable, especially if the defect extends into the subchondral bone or the damaged area is too extensive for smaller, contained-cartilage techniques.

The key distinction here is structural rather than rhetorical: OCA is considered for a more complex defect pattern, not just as the next step after microfracture. Whether it is suitable depends on the size and location of the lesion, how much bone is involved, overall alignment, and whether a combined procedure such as an osteotomy may be needed to protect the graft.

What OCA recovery usually looks like

OCA recovery is usually measured in months, not weeks. The practical reason is that there is no single timetable: progression depends on lesion size, lesion location, how well the graft appears to be incorporating, and whether other work was done at the same time. In a systematic review of 62 studies covering 3,451 knees, range-of-motion work was most commonly started in the first postoperative week, while progression to weightbearing as tolerated was most commonly reported at about 6 weeks; the same review also found substantial variation between protocols. That is why some surgeons and physiotherapists move faster or slower even when the operation has the same name.

For sport and higher-impact activity, the published pattern is a range, not a promise. Across rehabilitation studies, return to play or full activity was most commonly placed at about 6 months, but reported timelines stretched from 4 months to 1 year. A recent athlete-focused systematic review reported 72% overall return to sport, with 84% of those returners reaching the same or a higher level, at a weighted mean of 11.1 months. Other athlete series commonly report 75% to 82% return, often around 8 to 12 months. Longer-term graft survival is reasonably encouraging rather than guaranteed, with a 2025 review citing 10-year survivorship of 78% to 91%. Taken together, the message is simple: disciplined rehabilitation and realistic pacing matter as much as the operation if the aim is durable graft survival rather than an early comeback.

Where osteotomy and unloader bracing fit

Sometimes the key problem is not a single cartilage spot but where the load is going. If the medial compartment is taking too much force because of malalignment, shifting weight away from that side may reduce pain and create a better environment for joint preservation. That is the role of an unloader brace or an osteotomy: they are mechanical offloading strategies, not cartilage-regeneration procedures in their own right. A valgus unloader brace is the non-surgical option, usually considered when symptoms are clearly compartment-specific and the aim is to manage load before arthroplasty rather than rebuild cartilage.

High tibial osteotomy (HTO) is the more structural option. In younger patients with medial unicompartment osteoarthritis or varus alignment, it changes the leg axis so the worn compartment is less overloaded, and reviews describe it as a classic joint-preserving approach that may delay knee replacement. The same offloading principle is why osteotomy is sometimes combined with cartilage repair: protecting the repaired side may help the tissue mature. In a randomised trial of adults aged 18 to 65 with symptomatic medial-compartment OA, both valgus bracing and HTO were used before arthroplasty, but HTO reduced KOOS pain more at 12 months in that study.

When replacement becomes the better option

The clearest tipping point is the pattern of damage, not the procedure name. A knee with one contained cartilage problem may still be a preservation knee; a knee with severe, diffuse or multi-compartment wear, shrinking day-to-day function, and pain that remains limiting despite physiotherapy, medicines, injections or other joint-preserving treatment is usually moving into knee replacement territory. In that situation, arthroplasty is not a failed detour from the “right” plan; it often reflects that the whole joint has become the problem rather than one repairable area.

By contrast, a focal defect can still leave room for cartilage restoration, alignment correction or, in selected larger defects, osteochondral allograft and related preservation strategies that may delay replacement in the right knee. The decision is usually made from the full picture: scans, alignment, compartment involvement, previous surgery, current symptoms and activity goals. The practical rule of thumb is simple: preserve what is local and salvageable; replace what is globally worn out. Search MSK lists specialists across the UK who offer cartilage repair, osteotomy, bracing and knee replacement assessment, with filters by region and specialty.