Who is a good candidate for OCA transplant

After a significant knee injury, one of the first questions a patient typically asks is whether a procedure of this kind — replacing damaged bone and cartilage together — applies to their situation. Several clinical features help define who is likely to benefit.

OCA transplantation tends to suit younger, physically active patients, most commonly under 40 years of age. Evidence consistently shows better clinical outcomes and cartilage fill on imaging in this age group compared with older patients. The underlying damage needs to be a focal, full-thickness defect — meaning it extends all the way through the cartilage into the bone beneath — and typically measures at least 2 cm² in area. Crucially, the damage must affect only one joint surface rather than both sides of the joint; spread across opposing surfaces (a bipolar pattern) is associated with worse results.

Post-traumatic injury is one of the primary reasons OCA is chosen over other cartilage repair methods. When a joint impact or fracture compromises the subchondral bone as well as the cartilage, single-surface repair techniques such as microfracture or osteochondral autograft transfer are often insufficient — OCA addresses both layers in a single operation.

A structurally stable knee is generally preferred. Residual ligamentous instability, if present, is a relative contraindication and may need addressing alongside or before the graft. Absolute or relative contraindications include a BMI above 35, active tobacco use, inflammatory arthritis, and previous removal of the entire meniscus on the affected side.

Eligibility criteria can vary between centres, and a specialist assessment is needed to confirm whether OCA is appropriate for an individual patient's anatomy and history.

What the OCA procedure involves

Fresh allograft tissue — sourced from a deceased donor rather than the patient's own body — sits at the centre of the procedure. A donor knee is size-matched to the recipient's joint, and the surgical team works within a narrow logistical window: chondrocyte viability in fresh allografts falls below the accepted minimum threshold of 70% at roughly 28 days post-procurement. That time pressure shapes scheduling and, in the UK context, limits which centres can reliably offer the procedure depending on tissue-bank access and transport logistics.

In the operating theatre, the surgeon removes the damaged cartilage and the compromised bone beneath it, then press-fits one or more cylindrical allograft plugs into the prepared site. The graft carries both an intact articular surface and its underlying subchondral bone, restoring the full osteochondral unit in a single anaesthetic episode. This contrasts with cell-based approaches such as MACI, which require two separate operations — one to harvest cells, one to reimplant them — and are less suitable when the bone itself has been significantly disrupted by trauma.

Recovery follows a graduated weight-bearing programme. Protected loading in the early weeks gives way to progressive strengthening, with full return to high-impact loading typically taking between 9 and 14 months. Sport and strenuous activity are generally reintroduced only once radiographic evidence of graft incorporation is confirmed, usually no sooner than six months post-surgery.

Why OCA suits post-traumatic defects specifically

When cartilage damage is the only problem, smaller procedures can suffice. Post-traumatic injury, however, rarely stops at the surface: a forceful impact frequently destroys subchondral bone as well, and that changes the calculus for every technique on the repair menu.

Microfracture stimulates marrow to produce fibrocartilage — not hyaline cartilage — and is most reliable for defects below 2 cm². It does not address underlying bone loss at all, and published evidence shows the repair tissue typically begins to deteriorate within two to three years. Post-traumatic defects regularly exceed both of those constraints.

Osteochondral autograft transfer (OATS) extends the ceiling to roughly 4 cm² in mosaic configurations, but it draws on plugs harvested from the patient's own knee — introducing a risk of donor-site pain and functional limitation — and the available graft runs out for larger defects.

MACI and first-generation ACI require healthy, viable subchondral bone as a foundation: the implanted cells need structurally sound bone to adhere to and mature upon. Where a traumatic impact has disrupted that underlying architecture, the biological conditions for successful cell-based repair may simply not exist.

OCA delivers articular cartilage and its underlying bone as an intact unit, independent of host bone quality. The foundational clinical evidence for this specific application is Gross AE et al.'s 2008 long-term cohort (Clinical Orthopaedics and Related Research), which examined fresh allografts in post-traumatic knees with severe subchondral compromise and demonstrated durable outcomes, establishing OCA as the reference standard for this indication.

How long OCA grafts last

Survival data for OCA grafts follow a consistent pattern across multiple large datasets. Familiari et al.'s 2018 systematic review — 19 studies, 1,036 patients — is the most-cited benchmark: pooled Kaplan-Meier figures show approximately 87% of grafts surviving at five years, 79% at ten years, 73% at fifteen years, and 68% at twenty years. A 2022 narrative review by Lai et al. corroborates these figures with pooled data drawn from hundreds of patients at each time horizon, and an independent cohort analysis of 65 grafts found 68% in situ and functioning at a mean follow-up of 12.9 years — a result broadly consistent with the larger pooled estimates.

For younger patients weighing long-term prognosis, the trajectory matters as much as the headline figures: the decline from five to twenty years is gradual and reasonably predictable rather than abrupt, which can help set realistic expectations over the course of a working life.

One figure that frequently causes misinterpretation is reoperation rate, recorded at 34–53% across studies. Reoperation is not the same as graft failure. Many secondary procedures — hardware removal, débridement, or minor arthroscopic work — leave the allograft itself intact and functioning. The weighted mean failure rate in Familiari et al. was 18.2%, not 34–53%.

Certain characteristics are associated with worse durability: bipolar lesions (damage on both sides of the joint), patellar location, older patient age, and revision rather than primary surgery. Grafts placed as a second OCA show a failure rate of around 16.6%.

It is worth noting plainly that most of what we know comes from cohort studies and case series — Level IV evidence — rather than controlled trials. No large randomised trials have compared OCA directly to MACI or ACI in post-traumatic subgroups. The consistency of the survival pattern across many independent cohorts lends confidence to the figures, but they should not be read as guarantees for any individual.

Return to sport after OCA transplant

Roughly three in four patients who undergo OCA transplantation return to sport — pooled data from 13 studies covering 772 patients places the rate between 75% and 82%. Within that group, isolated OCA (without concomitant procedures) appears to perform better: a 2024 case series by Allahabadi et al. (PMC10896054), focused on professional athletes, recorded an 87.5% return-to-sport rate for isolated grafts, with 91% of those who returned competing at the same or higher level than before surgery.

Those figures are worth contextualising carefully. Professional athletes represent a highly motivated, intensively rehabilitated population — their outcomes are best read as an indicative upper bound rather than a universal expectation. For patients in general active populations, the broader 75–82% range from systematic review data is the more applicable reference.

The timeline also demands honest framing. In the Allahabadi cohort, return to sport occurred at a mean of approximately 14 months post-operatively — longer than most patients anticipate, and longer than recovery timelines for many other knee procedures. Rehabilitation milestones, including radiographic evidence of graft integration, typically need to be met before sport is reintroduced.

Beyond the early return window, evidence becomes thin. Only 3 of the 13 studies in the systematic review provided data beyond three years of follow-up. Whether patients maintain their activity level across five or ten years after OCA is a genuine gap in the literature — a limitation of the evidence base, not a negative finding.

Risks, reoperation, and what happens if the graft fails

Several pre-operative characteristics genuinely alter the probability of a good outcome — and some of them are within the patient's control. Active smoking and a BMI above 35 are both listed as contraindications in most clinical criteria, and the reasoning is straightforward: impaired tissue healing and excess joint load each place additional stress on a graft that depends on biological integration to succeed. Ligamentous instability and inflammatory arthritis carry similar weight. Addressing these factors before surgery — stopping smoking, achieving a healthier weight, stabilising an inflammatory condition — is not merely advisable formality; evidence suggests it materially affects results.

Where risk factors cannot be modified, patients should expect a frank discussion with their surgeon about what a realistic outcome looks like. It is worth noting that candidacy criteria are not uniform across UK centres: age thresholds, BMI cut-offs, and prior-surgery restrictions vary, which can explain why patients with similar clinical profiles receive different recommendations in different hospitals.

Revision OCA — a second allograft after a first has failed — is technically feasible, though the evidence base is thinner and outcomes are less predictable than for a primary procedure.

If OCA ultimately fails despite appropriate patient selection, total knee replacement remains an accessible end-stage pathway. OCA does not foreclose that option, and the procedure is generally regarded as a joint-preserving step — not a gamble that exhausts alternatives.