Why OCA exists as a separate category of cartilage repair

When a surgeon mentions a 'donor graft' for the knee, the question most patients ask first is a reasonable one: why can't the damaged surface simply be resurfaced or stimulated to regrow, the way smaller cartilage repairs work?

The answer lies in depth. Cartilage defects caused by trauma rarely damage just the surface layer — they often destroy the underlying bone as well, leaving a crater that extends through the full osteochondral unit (the combined cartilage-and-bone structure that cushions and loads the joint). Techniques such as microfracture or MACI address the cartilage surface, but they cannot reliably restore a bone bed that has been lost or structurally compromised. OATS — which borrows a small plug of bone and cartilage from a less-loaded part of the same knee — works well for defects up to roughly 2–4 cm², but donor supply within one knee is finite.

An osteochondral allograft (OCA) fills this gap. A size-matched plug of bone and cartilage from a carefully screened donor is shaped and press-fitted into the defect, restoring both layers in a single operation. Crucially, the graft is kept fresh — not frozen — so that living chondrocytes within the cartilage survive to support long-term integration. For the large, deep lesions that post-traumatic injuries typically produce, this combined bone-and-cartilage solution is the most anatomically direct match available.

Who is a realistic candidate

Four overlapping questions shape whether OCA is the right operation — defect character, joint condition, patient factors, and biomechanical environment.

The defect itself. OCA is suited to focal, full-thickness lesions (ICRS grade III–IV) with subchondral bone involvement, generally larger than 2–4 cm², arising from trauma, osteochondritis dissecans, or osteonecrosis. Smaller defects are usually managed with OATS or a cell-based approach; OCA becomes the more logical choice once the bone bed is substantially disrupted and the defect exceeds what autograft supply can fill.

Age and arthroplasty timing. The typical candidate is under 40–45 years and motivated to delay or avoid joint replacement. Survivorship data consistently favour younger patients, and the whole premise of OCA is joint preservation — so alignment with that goal matters.

Factors the team will want to optimise. BMI under 35 and non-smoker status are standard thresholds. Nicotine directly impairs the osseointegration on which large grafts depend, and elevated BMI increases mechanical load on a healing graft; both are addressable before surgery if the patient is willing to engage.

When OCA is not the answer. Diffuse arthritis across the joint is an absolute contraindication — a single graft cannot rescue a globally worn knee. Malalignment and ligamentous instability are relative contraindications only; both can often be corrected at the same sitting via osteotomy or ligament reconstruction.

Bipolar lesions — the harder category. When cartilage loss involves both sides of the joint (the 'kissing lesion' pattern), outcomes are meaningfully lower. Published survivorship in this group falls to roughly six in ten grafts still functioning at fifteen years, compared with considerably higher rates for isolated single-surface defects. The consultant will be frank about this distinction during the planning conversation.

What the long-term survival data actually shows

The headline number for most patients planning around a ten-year horizon: roughly nine in ten freshly transplanted grafts are still functioning at that point for isolated femoral condyle defects, based on a 2019 Bone & Joint Journal series that reported 91% survival at ten years. The trajectory beyond that is a gradual decline rather than a sudden drop — 84% at fifteen years, 59% beyond twenty — meaning many grafts remain viable well into the third decade after surgery.

Pooled figures from Haikal's 2023 narrative review, drawing across mixed-indication cohorts, show a similar but slightly lower curve: approximately 86.7% at five years, 78.7% at ten, 72.8% at fifteen, and 67.5% at twenty years. Assenmacher's 2016 systematic review, following patients to a mean of 12.3 years, reported successful outcomes in 75% of cases.

Most of these registries pool varied causes of cartilage loss together, so post-traumatic-specific long-term data are thinner than the headline figures suggest. That distinction matters, because the subgroup most relevant to post-traumatic injury — large bipolar lesions — shows meaningfully lower survivorship, as the previous section noted.

Even as a second procedure — when a first cartilage repair has failed — OCA remains a credible option: five-year survival of 79–87.8% has been reported in salvage settings, though failure rates rise sharply once defects exceed roughly 9–10 cm².

Realistic expectations for large and bipolar defects

The specific numbers for this subgroup anchor what "harder category" means in practice. A 2025 case series of 89 knees with a mean defect area of 16.7 cm² found graft survivorship of 73.8% at five years, 66.6% at ten, and 58.9% at fifteen — well below the population-wide curves described in the preceding section. The mean time to failure in this cohort was 4.8 years, meaning that when large bipolar grafts do fail, they tend to do so early rather than late.

Three failure pathways dominate this picture. A 2025 prospective cohort of 186 cases found an overall initial failure rate of 23.1%, driven by bone failure (34.9% of failures), meniscus-related failure (30.2%), and progressive joint disease (25.6%). Bone failure is the most common single pathway and reflects the biological challenge of osseointegrating a large graft through creeping substitution — a slow process more prone to incomplete healing across greater defect areas. Where defects reach 9–10 cm² in salvage settings, failure rises to 39% and reoperation to 67%, confirming that size carries independent biological risk rather than simply a technical one.

None of this, however, forecloses meaningful functional recovery. A 2026 technical note applying 3D virtual planning to post-traumatic large OCA — achieving translational accuracy within 2.5 mm — reported Lower Extremity Functional Scale scores rising from roughly 22 to 78–81 out of 100 at over one year, a shift that represents a substantial restoration of everyday function. Where trauma has caused multi-surface bone loss, staged management is part of how those gains are reached: a 2026 case report of a 21-year-old with extensive high-velocity open knee injury demonstrated confirmed graft incorporation at two years, but only after staged debridement and precise size-matched graft selection before the definitive reconstruction.

How grafts fail and which risk factors can be changed

The most common single pathway to graft loss — bone failure — hinges on a process called creeping substitution: the host body must gradually replace the donor bone with its own blood supply, vessel by vessel. When that revascularisation stalls or remains incomplete across a large graft area, the transplanted bone loses structural support. Preclinical work using a locally delivered iron chelator compound (deferoxamine, DFO) has shown improved trabecular bone volume and revascularisation in animal models, suggesting this failure mode may be amenable to augmentation — though DFO remains experimental and is not currently part of clinical practice.

Meniscus-related failure and progressive joint disease account for roughly a further third of failures between them — a reminder that OCA addresses the focal defect but cannot independently arrest broader joint deterioration over time.

Among the contributors patients can actively influence, adherence to the post-operative rehabilitation programme stands out as the most directly controllable variable; smoking status and body weight have already been established as candidacy thresholds rather than post-operative discoveries.

Non-modifiable factors — older age, male sex, and bipolar joint involvement — inform expectation-setting and surgical counselling rather than serving as outright disqualifiers in most cases. Donor-recipient sex mismatch may accelerate early failure in a small subset, though the evidence on this remains preliminary and should not be over-weighted in decision-making.

How the assessment and planning process works

Planning begins with imaging. MRI is the standard first step, characterising defect size, location, depth, and the condition of the underlying subchondral bone — each of which shapes whether OCA is appropriate and how the graft will need to be shaped and seated. Weight-bearing X-rays are taken alongside to assess limb alignment; where malalignment is present, it is better planned for concurrently via osteotomy than left uncorrected, since a well-placed graft in a mechanically compromised joint carries a meaningfully higher failure risk.

Graft sourcing is a logistical step patients benefit from understanding early. Fresh osteochondral allografts come from licensed tissue banks and must be carefully size-matched to the recipient's joint geometry. Availability depends on donor supply, and surgery is typically scheduled around an appropriate match rather than a fixed date — factoring this in from the start avoids unnecessary uncertainty about lead times.

Consultant assessment determines whether OCA is the right pathway or whether a smaller autograft transfer, a cell-based repair, or alignment surgery alone would serve better. At the MSK Doctors centres in Sleaford and Grantham, that assessment draws on on-site imaging and covers the full cartilage-repair pathway alongside OCA — and no GP referral is required to arrange it at mskdoctors.com.

1. [1] Osteochondral Allograft Transplantation as a Salvage Procedure After Failed Index Cartilage Surgery of the Knee: A Systematic Review. (2025). https://doi.org/10.1177/03635465241238466 https://doi.org/10.1177/03635465241238466
2. [2] Mid-term failure rates, timing, and mechanisms for osteochondral allograft transplantation in the knee: Characterizing risk factors and identifying modifiable variables.. (2025). https://doi.org/10.1016/j.jor.2025.03.040 https://doi.org/10.1016/j.jor.2025.03.040
3. [3] Iron Chelators Augment Large Osteochondral Allograft Osseointegration in a Preclinical Canine Model. (2024). https://doi.org/10.1097/BOT.0000000000002881 https://doi.org/10.1097/BOT.0000000000002881
4. [4] Midterm Survivorship and Clinical Outcomes in Fresh Osteochondral Allograft Transplantation for the Treatment of Large Bipolar Lesions of the Knee. (2025). https://doi.org/10.1177/03635465241313139 https://doi.org/10.1177/03635465241313139