Which patients are candidates for OCA?

The single most practical question at this decision stage is size: how large does a cartilage defect need to be before OCA becomes the right option? The evidence points to roughly 2–4 cm² as the tipping point. Below that threshold, marrow-stimulation techniques such as AMIC or autograft transfer (OATS/mosaicplasty) remain reasonable first-line choices. Above it, those approaches carry progressively worse outcomes, and OCA — which replaces the damaged tissue entirely with matched donor cartilage and bone — becomes the more appropriate step.

In practice, most treated defects are considerably larger. In a series of 156 knees reported by Tírico et al., defects were classified as small (under 5 cm²), medium (5–8 cm²), or large (over 8 cm²), with a mean allograft area of approximately 6.4 cm². These are not trivial lesions, and they rarely arise from wear alone.

Post-traumatic injury is one of the three classic primary indications for OCA — alongside osteonecrosis and failed prior cartilage repair. Articular cartilage has no meaningful blood supply and essentially no capacity for self-repair; after a significant knee injury, a full-thickness focal defect of this size will not fill in on its own. That combination of defect depth, defect size, and clear traumatic cause is precisely what OCA is designed to address.

MRI is the gold-standard tool for characterising these lesions before surgery, confirming defect dimensions, bone involvement, and the condition of the surrounding cartilage.

Why the graft has to be fresh — and why that matters for access

The graft works because living cells come with it. Fresh osteochondral allograft tissue contains viable chondrocytes — the cells responsible for maintaining the cartilage matrix — and preserving that viability is what separates fresh allograft from frozen or synthetic alternatives. Freezing destroys the very cells that make the graft function; the 'fresh' qualifier is a clinical distinction, not a marketing label.

That viability has a strict shelf-life. Chondrocyte survival declines noticeably after Day 14 post-procurement and falls below the accepted clinical threshold of approximately 70% viable cells by around Day 28. This tight window shapes every aspect of how OCA is organised: tissue procurement, matching, scheduling, and surgical availability must all align within roughly four weeks of the donor harvest.

For patients who have previously been told they are not suitable for OATS or mosaicplasty — often because their defect is simply too large for an autograft — OCA carries an important additional advantage: no tissue needs to be harvested from anywhere in their own knee. The donor-site morbidity that can complicate autograft procedures is not a factor here.

The freshness requirement does mean that OCA is not available everywhere. Tissue banking infrastructure, a reliable procurement network, and surgical teams experienced in time-sensitive scheduling are prerequisites. Seeking a centre with established expertise in this pathway is therefore a practical step, not an abstract recommendation.

Long-term survivorship — what the evidence actually shows

Durability is the question that matters most to patients with decades of active life ahead. The longest available dataset — Raz et al. (JBJS Am, 2014) — tracked distal femoral fresh OCA grafts to a mean follow-up of 22 years, providing a meaningful picture of how these reconstructions perform into the third decade. That dataset is directly relevant here: it focuses on the distal femur, the most common site for post-traumatic cartilage loss of the kind OCA is designed to address.

Shorter-term series add important texture. In one cohort of 65 grafts, 44 (68%) remained in situ and functioning at a mean of 12.9 years, with the authors reporting 95% survivorship using graft-in-situ as the endpoint. A separate 39-knee series applied stricter failure criteria — an HSS score below 70, conversion to arthroplasty, or revision surgery — and found survivorship of 82.6% at five years and 69.6% at ten years, with 10 knees (26%) meeting the definition of true failure.

The difference between those two sets of figures illustrates something patients should understand before surgery: survivorship statistics are only as informative as the failure definition behind them. 'Failure' in surgical trials most often means conversion to joint replacement or a formal revision procedure — not the return of some discomfort or a reduction in sport tolerance. A graft that has offloaded a patient from arthroplasty for a decade, even if it eventually requires revision, has already delivered substantial benefit.

Gross et al. (Clin Orthop Relat Res, 2008) contribute a further anchor: their long-term series focused specifically on post-traumatic defects, making it among the most directly applicable datasets for patients whose knee damage follows an identifiable injury.

Return to sport and functional recovery

For most active patients, the question that shapes the decision is a simple one: will surgery actually get them back to what they were doing before?

The published evidence answers that reasonably well. In a cohort of 149 knees followed for a mean of six years, 75.2% of patients had returned to sport or recreational activity, 71% achieved 'very good' to 'excellent' knee function on the IKDC scale, and 79% were participating in high-level activity — moderate, strenuous, or very strenuous. Those are not provisional or short-term figures; six years is long enough for early failures to have declared themselves.

The timeline is where active patients need an unambiguous picture. Return to low-impact activity is typically achievable at four to six months post-operatively. Return to high-impact sport takes nine to twelve months. That is a meaningful commitment of time and structured rehabilitation — not a six-week procedure. Premature loading before the graft has integrated raises the risk of failure, so the staged approach is not arbitrary caution but a biological requirement.

For a patient who has already worked through earlier-stage interventions — physiotherapy, injection therapy, or marrow-stimulation procedures — without regaining the function they need, a twelve-month rehabilitation investment in a procedure that offers decade-level durability is a proportionate trade.

Technical scope — where OCA can and cannot be applied

OCA is most commonly applied to the femoral condyle, but the technique has been extended to the patellofemoral joint — a 2019 systematic review by Chahla et al. (Am J Sports Med) confirmed its feasibility and clinical utility there, broadening the range of post-traumatic defects that can be addressed.

Wherever the graft is placed, surgical precision is not optional. Koh et al. (Am J Sports Med, 2004) demonstrated that even modest graft height mismatch significantly elevates contact pressure at the repair site. Too proud or too recessed, and the biomechanical environment that the graft depends on for integration is disrupted. This is the primary reason OCA should be performed at a specialist centre by surgeons with specific experience in graft preparation and implantation.

Graft failure does not necessarily foreclose further joint-preservation surgery. Revision OCA — replacing a failed primary graft with a second allograft — is a recognised option; Horton et al. (Am J Sports Med, 2013) found it can be effective in carefully selected patients.

Where mechanical malalignment accompanies the cartilage defect, OCA is sometimes combined with an osteotomy — high tibial (HTO) or distal femoral (DFO) — to offload the repaired compartment and protect the graft from asymmetric loading. Alignment correction and cartilage restoration address different problems in the same joint; addressing both in the same operative plan is sound practice when the anatomy warrants it.

How OCA fits the cartilage repair pathway

One honest gap in the evidence deserves naming: there are no published head-to-head trials directly comparing OCA and MACI in the larger post-traumatic population — the cohort where both techniques are, in principle, relevant. That gap is not a reason for alarm about either option; it is precisely why individual specialist assessment matters more than a protocol flowchart. The decision turns on defect geometry, the degree of subchondral bone involvement, prior treatment history, and the patient's broader mechanical and biological profile. Where subchondral bone loss accompanies the cartilage injury, OCA's capacity to restore both layers simultaneously gives it a practical advantage that cell-based techniques cannot replicate in a single operative stage.

Within the wider pathway, OCA sits at the upper end of cartilage restoration — beyond marrow-stimulation and autograft options, and well short of joint replacement. For patients with post-traumatic defects that have outgrown earlier interventions, it often represents the last substantive joint-preservation option before arthroplasty enters the conversation.

Candidacy assessment draws on detailed MRI review, full clinical history, and — where biomechanical load distribution is a clinically relevant factor — objective motion analysis such as MAI Motion®. No two presentations are identical, and no algorithm substitutes for that workup.

For patients who want to explore their options without a GP referral, a consultation can be arranged directly through mskdoctors.com.

1. [1] Articular cartilage repair — Wikipedia. https://en.wikipedia.org/?curid=19042351 https://en.wikipedia.org/?curid=19042351