What OCA offers when a knee defect is too large for other repairs

A post-traumatic knee injury — from a fracture, dislocation, or direct impact — can strip away not just the cartilage surface but the bone beneath it. That combined damage is the clinical problem osteochondral allograft (OCA) transplantation is designed to solve.

OCA replaces the full thickness of the injured zone in a single operation. A size-matched plug of donor tissue — mature hyaline cartilage sitting on its supporting subchondral bone — is shaped and press-fitted into the defect. No second surgery is needed to harvest the patient's own cells or to reimplant them weeks later.

Post-traumatic defects are established indications for OCA, alongside osteochondritis dissecans and avascular necrosis. The procedure becomes the practical choice once a defect exceeds roughly 2–4 cm²: below that threshold, microfracture or osteochondral autograft (OATS) are more commonly used, but autograft supply runs out as lesion size grows.

What sets OCA apart is what it actually replaces. Microfracture stimulates the body to fill a defect with fibrocartilage — a mechanically inferior substitute whose results can deteriorate from around two to three years. MACI and ACI restore a cartilage layer using the patient's own cultured cells, but neither addresses deep bone loss. OCA is the only repair option that delivers both layers — intact mature cartilage and healthy subchondral bone — in one graft, which is precisely why it is suited to the combined osteochondral injuries that post-traumatic defects so often produce.

Who is a suitable candidate

Strong candidates tend to be adults under 50 with a discrete, full-thickness osteochondral defect — most commonly arising from trauma, osteochondritis dissecans, or avascular necrosis — in an otherwise healthy joint. Real-world condyle series confirm that treated areas typically average around 6.4 cm², encompassing a spectrum from small defects below 5 cm² through to large defects exceeding 8 cm²; all fall within OCA's practical range once autograft supply has been exhausted.

Age is a meaningful factor: surrounding cartilage must be sufficiently preserved to support the graft, and most published criteria place the upper age limit at approximately 50 years. Younger patients with intact adjacent surfaces are generally the strongest candidates.

Several factors move a patient towards the less-suitable end of the spectrum. Relative contraindications include a BMI above 40, radiographic joint-space narrowing consistent with Kellgren-Lawrence OA grade higher than 2 (indicating diffuse rather than focal disease), inflammatory arthritis, a history of prior joint infection, and previous malignancy involving the joint. None of these is absolute in every clinical setting, but each substantially raises the threshold for proceeding, and a specialist will weigh them carefully against the likely benefit.

Malalignment — for example, varus or valgus deformity that overloads the graft compartment — is not an absolute disqualification, but it must be corrected at the same time, typically by osteotomy, or graft failure risk rises considerably. Presenting with malalignment means the planning conversation will include that additional step.

Why donor cartilage behaves differently from other repair options

The biological reason OCA works — and why timing matters — comes down to one question: are the cartilage cells in the graft still alive when they reach the operating theatre?

Unlike microfracture, which prompts the body to fill a defect with fibrocartilage (a scar-like tissue that lacks the mechanical resilience of native cartilage), a fresh OCA plug contains mature hyaline cartilage — the same tissue type that was lost to injury. Those cells, known as chondrocytes, must survive the journey from donor to recipient and then remain active long enough to maintain the graft. The subchondral bone component does the structural work below: it bonds with the patient's own bone bed, anchoring the plug and distributing load from above.

Chondrocyte viability is the key quality metric. Below 70% viable cells, graft function is considered compromised. Viability typically falls to that threshold by around Day 28 after procurement — a narrow window. The difficulty is that tissue banks must hold grafts for a minimum of approximately 14 days to complete microbiological and serological safety testing before release. That mandatory hold leaves very little margin between safe release and the point at which cell numbers start to fall critically.

Newer storage protocols using physiologic or room temperatures (around 37°C or 25°C, rather than standard refrigeration at 4°C) may maintain approximately 80% viability at 28 days — an encouraging direction, though this remains an active area of protocol development rather than a fully settled standard. Donors must be aged between 13 and 35, with intact articular cartilage confirmed at the time of procurement.

Long-term survivorship: what the evidence shows

The numbers look contradictory at first glance — but the spread in published survivorship figures reflects genuine differences in how studies defined failure, not a conflict in the underlying evidence.

One femoral condyle cohort applied a stringent composite: a graft was deemed failed if the patient's Hospital for Special Surgery (HSS) score dropped below 70, if they underwent total knee replacement, or if the allograft was revised. On that demanding measure, roughly 8 in 10 grafts were still functioning at 5 years and around 7 in 10 at 10 years (82.6% and 69.6% respectively). A broader analysis of 65 grafts, using graft persistence as the primary criterion rather than a functional score threshold, reported 95% survivorship, with 68% of grafts in situ and functioning at a mean of 12.9 ± 5.1 years — a more favourable picture that may also reflect better patient selection in more recent cohorts.

The longest follow-up data available comes from Raz et al. (JBJS Am 2014), who tracked distal femoral OCA outcomes to a mean of 22 years — a timeframe no autograft technique has matched.

Patellofemoral OCA carries its own distinct profile. In a systematic review of 129 patients, graft survival stood at 87.9% at 5 years and 77.2% at 10 years, with IKDC scores improving from 41.8 before surgery to 68.1 afterwards (P < 0.001). Outcomes at one anatomical site should not be read across to another.

One honest limitation runs through all of these figures: published series rarely disaggregate post-traumatic patients cleanly from those treated for osteochondritis dissecans or avascular necrosis. Gross AE et al. (Clin Orthop Relat Res 2008) remains one of the few studies to specifically examine OCA for post-traumatic knee defects, and etiology-specific survivorship estimates across the broader literature carry genuine uncertainty as a result.

Functional recovery and return to activity

Three-quarters of patients in published series returned to sport or recreational activity after OCA — a figure that, on first reading, sounds straightforward. In a cohort of 149 knees followed for a mean of six years, 75.2% had returned to some form of sport or recreational activity, 71% achieved very good-to-excellent ratings on the IKDC knee function scale, and 79% could participate in high-level activity. The difficulty with 'return to sport' as a headline metric is that the term spans everything from gentle cycling to competitive athletics; the figure is better read as a measure of meaningful activity restoration than as a guarantee of pre-injury performance.

Rehabilitation itself takes time. Low-impact activity is typically possible from around four to six months after surgery; higher-impact sport generally requires nine to twelve months. For patients calibrating their goals against that timeline, it matters that improvement in knee function scores — rather than a full return to pre-injury sport — is the more consistent finding across published series.

Roughly one in four patients in that same six-year cohort did not return to sport, and current published data does not reliably characterise what their functional plateau looked like — an honest evidence gap that a consulting specialist can address on the basis of individual graft site, defect size, and pre-operative activity level.

Finding a specialist and what to ask at your consultation

OCA is performed by surgeons who specialise in cartilage restoration, typically at tertiary MSK or sports-medicine centres with access to tissue bank networks. Arriving at a consultation prepared with specific questions makes the process more productive. Three worth raising:

• Is the defect size, depth, and anatomical location suited to OCA — or would OATS or MACI be a better fit for my situation?
• Does my joint alignment need correcting before, or alongside, the graft?
• What graft storage protocol does this centre use, and what is the typical wait between listing and surgery?

That third question carries practical weight: as the graft biology section described, chondrocyte viability narrows after procurement, and centres vary in how they manage the window between tissue availability and implantation.

Search MSK lists cartilage restoration specialists across the UK who offer OCA and related osteochondral procedures — use the region and specialty filters to find one near you.

For patients who fall outside OCA candidacy — perhaps because of advanced joint-wide arthritis or the BMI and age thresholds outlined earlier — procedures such as MACI, OATS, or AMIC are established restoration options that a specialist in this field can assess in the same consultation.