Which option usually fits the defect

In practical terms, the usual first split is between a large post-traumatic focal defect and a smaller contained lesion. For a large full-thickness chondral or osteochondral defect — often described in reviews as roughly >2–4 cm² — fresh osteochondral allograft transplantation (OCA) is the option most often considered, especially in younger, active patients with a salvageable joint. Published reviews also note better OCA results with unipolar lesions and normal or corrected alignment, while end-stage osteoarthritis, uncorrected malalignment, ligament deficiency, meniscus deficiency, and inflammatory joint disease are recognised reasons not to use it. If the problem is diffuse arthritis rather than a focal defect, cartilage repair usually falls out of scope and joint-preservation or replacement discussions become more relevant.

For a smaller focal osteochondral defect, OATS/mosaicplasty is more often the restorative operation raised, because it transfers the patient’s own bone-and-cartilage plugs. Microfracture still appears in the literature, but its longer-term durability looks less convincing. A small randomised trial at 9.8 years found no significant difference between microfracture and OAT, whereas a larger comparative survival study reported more failures after microfracture than OAT (66% vs 51%) and a shorter mean time to failure (4.0 vs 8.4 years). Even here, the evidence base is modest — a Cochrane review found only 3 trials and 133 participants, with mean defect size 2.8 cm² — so defect size alone does not settle the choice.

When OCA makes sense after an injury

A more useful way to separate post-injury cases is this: OCA tends to come into the frame when trauma has left one dominant, focal defect that includes not only the cartilage surface but often the bone beneath it. Reviews describe fresh allograft as a single-stage option for large full-thickness lesions, often beyond roughly 2–4 cm², and for high-grade focal defects caused by trauma or osteonecrosis rather than general wear-and-tear change. That makes it a joint-preserving option more often considered in younger or biologically younger active patients, especially when the aim is to restore a localised impact injury rather than move straight into knee replacement. Published series also suggest candidacy is more favourable in unipolar defects and less favourable once age is over 40 years or the knee already shows advanced arthritic change.

Just as important, the decision is rarely made from the MRI slice alone. A knee with varus or valgus overload, ligament laxity, or meniscal deficiency may need those problems corrected or addressed at the same sitting, because an allograft placed into an unstable or overloaded joint is working against the mechanics that damaged it. This is why OCA is not a universal cartilage fix: the usual exclusions include end-stage osteoarthritis, inflammatory joint disease, uncorrected malalignment, and an unreconstructed ligament- or meniscus-deficient knee. In practical terms, the memorable post-traumatic OCA case is a single large impact lesion in an otherwise preservable knee, not a knee with diffuse degeneration.

How durable is OCA in the long term

Published long-term follow-up suggests OCA is not simply a short-term patch. In a 2008 post-traumatic knee series, fresh osteochondral allograft cartilage remained viable and functional for 25 years or more when the graft achieved a stable bony base. The histology in that report showed viable chondrocytes, a preserved cartilage matrix, and replacement of graft bone by host bone. In practical terms, the strongest long-range evidence suggests that, in the right mechanical setting, the transplant may last for decades rather than only a few years.

The clearest survivorship figures come from a 2019 series of 60 patients with unipolar femoral condylar fresh allografts performed with realignment osteotomy. Graft survivorship was 85.0% at 10 years and 59.8% at 25 years, and the mean modified HSS score improved from 74.1 before surgery to 89.0 at final follow-up. Those numbers support meaningful durability, but they do not promise the same result for every knee. In the same study, persistent postoperative malalignment was linked to a markedly higher risk of failure, with a hazard ratio of 6.55. Some of the best long-term outcomes therefore reflect both the graft and correction of joint mechanics, not the transplant in isolation.

OATS or microfracture for a small defect

For a small, contained knee defect, the OATS-versus-microfracture decision is less clear-cut than a simple league table suggests. The randomised evidence base is thin: a Cochrane review identified only three trials with 133 participants in total, and the mean defect size across those studies was 2.8 cm², so the literature only partly isolates genuinely very small lesions. In the best long-term randomised follow-up, published in 2014, 25 patients with full-thickness femoral chondral lesions were reviewed at a median of 9.8 years, and there was no significant difference between microfracture and OAT mosaicplasty in patient-reported scores, muscle strength, or radiographic osteoarthritis.

The broader durability signal, however, leans towards OAT or mosaicplasty rather than microfracture. In a larger comparative survival study, long-term failure was 51% after OAT versus 66% after microfracture, and mean time to failure was 8.4 years versus 4.0 years; the same pattern was reported in a subgroup with lesions under 500 mm². That does not prove OATS is the better choice for every small lesion, but it helps explain why many surgeons now view it as the more attractive one-stage option for a selected focal defect in an active knee: it transfers an osteochondral plug rather than relying on the older marrow-stimulation approach used in microfracture. Taken together, the direct evidence is mixed, yet the longer-term practical signal is that microfracture is harder to justify as the modern default when the lesion is small, focal, and otherwise repairable.

Why the rest of the knee matters so much

Consider a bow-legged knee with a medial femoral condyle defect after an injury. If the leg still drives extra load through that same compartment on every step, simply filling the cartilage hole may not solve the reason it failed in the first place. The clearest long-term number comes from a 2019 fresh allograft series of 60 patients in which cartilage repair was combined with realignment: persistent postoperative malalignment was associated with a much higher risk of graft failure, with a hazard ratio of 6.55. Although that figure comes from OCA, it illustrates a broader joint-preservation principle: a focal repair may be less durable when the knee keeps recreating the same overload pattern.

A similar problem arises when the meniscus is deficient or the knee is ligament-unstable. A 2024 review of knee OCA lists uncorrected malalignment, ligament deficiency and meniscus deficiency among the important contraindications, and an earlier review linked better outcomes to normal or corrected alignment rather than leaving the mechanics unchanged. That is why some operative plans pair cartilage restoration with osteotomy, ligament stabilisation or meniscal work. In practice, a bigger operation is sometimes the more conservative choice, because it aims to correct the force that damaged the surface, not just the surface itself.

What to ask at your assessment

Most assessments turn on four practical questions rather than the name of the operation. In the 2019 fresh-allograft series, persistent postoperative malalignment was a strong failure signal, and a 2024 review again listed uncorrected malalignment, ligament deficiency and meniscal deficiency among the reasons cartilage grafting may not be suitable.

• “Is this truly a focal, repairable defect?” That usually means defining the size, depth, whether the edges are contained, and whether the bone beneath the cartilage is involved rather than assuming every painful cartilage scan needs repair.
• “What is driving overload in this knee?” Useful points to pin down are alignment, instability, meniscal loss, previous surgery, and sport- or work-specific loading.
• “What result is realistic?” The key discussion is usually about likely gains in pain, day-to-day function, and the level of sport that may still be possible, rather than expecting one operation to recreate a completely normal knee.
• “Is cartilage repair alone enough?” In some consultant-led assessments, MRI review is paired with objective biomechanical analysis to judge whether a graft or plug is enough on its own, or whether off-loading or stabilising work also needs discussion.

A useful rule of thumb is “repair the defect, correct the overload”: a single focal lesion in a mechanically correctable knee may suit preservation, while diffuse wear or unresolved overload often pushes OCA or OATS out of contention; if a consultant opinion on suitability is needed, appointments can be booked online without referral at mskdoctors.com.

1. [1] Osteochondral Allograft Transplantation in the Knee. (2024). https://doi.org/10.1016/j.arthro.2024.01.006 https://doi.org/10.1016/j.arthro.2024.01.006