When a cartilage defect is too large for other repairs

Cartilage repair in the knee is not a single procedure — it is a size-and-complexity ladder, and osteochondral allograft (OCA) sits at the top of it.

For isolated surface defects below roughly 2 cm², marrow-stimulation techniques or a small osteochondral autograft transfer (OATS) can address the problem in one stage. As defect area grows into the 2–10 cm² range, cell-based approaches such as MACI become relevant competitors. What pushes a case toward OCA is a combination of size and depth: when a lesion extends into the subchondral bone beneath the cartilage layer — not just the surface — a graft that replaces both tissue types in a single procedure has a meaningful structural advantage. For defects exceeding approximately 4 cm² with bone involvement, OCA is generally preferred because it addresses the full depth of damage at once, without the staged recovery that cell-based methods require.

Size alone does not always determine the choice. OCA is also the appropriate option after earlier procedures — microfracture, ACI, or mosaicplasty — have failed, because repeated marrow stimulation can compromise the subchondral bone plate and make cell-based repair less viable as a rescue strategy. Microfracture in particular has a declining role in current practice; evidence consistently shows fibrocartilage breakdown within two to three years and residual subchondral damage that can complicate later repair.

Critically, OCA targets focal, symptomatic defects in a joint that is otherwise structurally sound. Diffuse or end-stage osteoarthritis is a different condition and falls outside the scope of cartilage repair entirely. Beyond defect size, candidacy also turns on age, anatomy, limb alignment, and the condition of the surrounding joint — all of which the next section addresses in detail.

Candidacy factors beyond defect size

Several factors shape whether OCA is the right choice for a given patient — and understanding them helps explain why two people with similarly sized defects may receive different recommendations.

Age is one of the strongest predictors of long-term success. The most compelling survivorship data come from patients aged 30 or under, where published series report 99% graft survival at 10 years in the best-matched cohorts. Suitability generally extends to the mid-forties, though as age rises, the condition of the surrounding joint and subchondral bone becomes a more careful consideration.

Lesion location also matters. Femoral condyle and trochlear defects carry the strongest and most consistent evidence base; the medial condyle is the most frequently treated site in practice. Patellar and tibial plateau lesions are technically more demanding and require specialist assessment to determine feasibility.

Activity level and goals inform the conversation significantly. OCA is particularly well-suited to patients who want to return to sport or physically demanding work — published data in athletes show a 72% return-to-sport rate, with the majority returning at the same level or higher.

Limb alignment is assessed carefully at the same consultation. A valgus knee with a lateral condyle defect, for example, places abnormal load through the graft and is a relative contraindication if left uncorrected. A concurrent distal femoral osteotomy (DFO) can realign the joint at the same time as OCA, giving the graft the mechanical environment it needs to survive long term.

Meniscal and ligamentous integrity round out the assessment. A deficient or absent meniscus alters load distribution across the graft; untreated ligamentous instability adds abnormal shear. Both are evaluated at the same appointment, and where needed, concurrent stabilisation or reconstruction is planned as part of a single coordinated strategy.

What the procedure involves

During an OCA transplantation, the surgeon removes all damaged cartilage and the compromised bone beneath it, shapes a precisely matched plug of donor tissue to fit the resulting cavity, and press-fits it into place — sometimes adding fixation screws or pins for larger grafts. The whole process is completed in a single operation, with no need for a prior biopsy or a second-stage procedure.

The donor tissue is fresh — not frozen — and this distinction matters biologically. Living chondrocytes within the graft matrix are what allow the transplanted cartilage to integrate and survive over years; freezing destroys them. Storage conditions between harvest and implantation are therefore tightly managed, and optimising preservation protocols — temperature, duration, and media composition — remains an active area of research.

On the question of donor matching, size is the critical variable: the plug must fit the patient's anatomy accurately. Sex matching is less decisive than patients sometimes expect. Published data on 285 patients found no significant difference in overall graft survivorship between sex-matched and sex-mismatched donors, though among the small proportion of grafts that do fail, mismatched pairs tended to fail earlier — at a median of 353 days compared with 864 days in matched cases.

An emerging surgical adjunct is bone marrow aspirate concentrate (BMAC), injected at the graft site during the same operation. A 2025 randomised controlled trial found a significantly lower subsequent reoperation rate in the BMAC group (5.3% versus 35.3%), though patient-reported outcome scores at two years were not yet significantly different between groups. BMAC should be understood as an adjunct to the transplantation, not a standalone treatment.

Where alignment or meniscal issues have been identified at assessment, correction can be performed within the same operation — minimising the total number of procedures the patient undergoes.

Survivorship and outcomes — what the evidence shows

The survivorship data for OCA form a clear spectrum, and where a patient sits on that spectrum depends almost entirely on lesion complexity.

Across the broad published literature, 10-year graft survivorship ranges from 78% to 91% — a consistently strong result for a procedure managing some of the most challenging cartilage pathology the knee presents. Most of this evidence comes from Level III and IV case series, predominantly from high-volume cartilage centres, rather than head-to-head randomised trials; that context is worth holding in mind when interpreting the figures.

At the favourable end of the spectrum, the results are striking. In patients aged 30 or under with an isolated OCD or traumatic chondral lesion on the femoral condyle or trochlea measuring under 8 cm², published series report graft survivorship of 99% at both 5 and 10 years, with 93% of patients satisfied with their outcome. Long-term follow-up data extend this picture further — historical series tracking distal femoral allografts to a mean of 22 years confirm that durable function is achievable in well-selected patients.

Where the lesion is more complex — particularly large bipolar defects averaging around 16.7 cm² in published cohorts — the prognosis is meaningfully different. Survivorship in this group falls to 73.8% at 5 years, 66.6% at 10 years, and 58.9% at 15 years, with a graft failure rate of 34.8%. For patients facing early arthroplasty as the realistic alternative, OCA at these survivorship rates may still represent a worthwhile joint-preservation option; the figures are presented not to alarm, but to support informed consent.

One variable that does not meaningfully shift outcomes is whether the defect sits on the medial or lateral femoral condyle. Published data on more than 300 condyle grafts show 10-year survivorship of 88% for medial and 92.9% for lateral grafts — a difference that does not reach statistical significance.

Return to sport and recovery timeline

Planning a return to sport after OCA is, for most patients, a question of when rather than whether. A 2025 systematic review covering 14 studies and 471 athletes found that 72% returned to sport after the procedure, and of those who did, 84% returned at the same or a higher level of play — a meaningful result for a technique that addresses some of the largest and most complex cartilage lesions treated surgically.

The mean time to return was 11.1 months, with a range of 6 to 26 months across studies. Planning for approximately one year before resuming impact or pivoting sport is a reasonable working expectation. Lesion sizes in the reviewed population spanned 1 to 13.94 cm², which confirms these figures are broadly applicable across the defect sizes encountered in everyday practice, rather than being limited to a narrow slice of presentations.

One caveat deserves plain acknowledgement: competitive and professional athletes made up only around 16% of the patients studied. The 72% and 84% figures are therefore most reliably applied to the recreational and amateur sport context; extrapolating them directly to elite performance carries uncertainty, and athletes at that level should discuss individual expectations at assessment.

Recovery follows a progressive pattern: protected weight-bearing and range-of-motion work in the early weeks give way to strengthening and proprioception training through months three to six, with sport-specific loading introduced gradually thereafter. Long-term athletic performance data beyond five years remain limited in the published literature — a gap worth noting, though the survivorship figures discussed in the preceding section provide a proxy measure of durability.

The individual rehabilitation programme will depend on lesion size, any concurrent procedures, and baseline fitness — factors that a specialist assessment is needed to weigh.

Getting assessed and planning next steps

Taking the step from researching OCA to understanding whether it applies to a specific knee starts with a structured specialist assessment — one that goes well beyond reviewing a scan.

A thorough candidacy evaluation combines a detailed clinical history, physical examination, standing weight-bearing X-rays, and MRI. Together, these characterise defect size, depth, and location; map the health of the surrounding cartilage; and — critically — assess alignment, meniscal integrity, and ligamentous stability. If malalignment or a concurrent meniscal problem is identified, surgical planning for a combined procedure (such as a distal femoral osteotomy alongside OCA) begins at the same appointment rather than as a separate process.

The outcome of that assessment is a clear view of where the patient sits in the treatment pathway — whether OCA is appropriate now, whether a staged approach makes more sense, or whether an alternative technique such as MACI better fits the clinical picture.

At London Cartilage Clinic, based on Harley Street, Professor Paul Y. F. Lee leads specialist assessment for patients with complex cartilage defects where advanced restoration options, including OCA, are under consideration. Patients can arrange an initial consultation through londoncartilage.com.

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