OATS / mosaicplasty

Osteochondral autograft transfer moves cylindrical plugs of bone topped with living hyaline cartilage from low-weight-bearing areas of your own knee — the trochlear margins, the intercondylar notch — press-fit into the defect. One plug is OATS; several arranged together is mosaicplasty. Unlike marrow stimulation or cell therapy, the defect is resurfaced with mature hyaline cartilage on day one: the biology to get right is bony integration and surface congruity, not tissue regeneration.

The randomized evidence

A trial of 57 young athletes with femoral condyle defects randomized to OAT or microfracture is the flagship. At mean 37 months: 96% versus 52% excellent-or-good results, and 93% versus 52% returned to pre-injury sport. The same cohort at mean 10.4 years: OAT still superior, failure 14% versus 38%, and 75% versus 37% maintaining their pre-injury activity level. Both arms declined after year 3 — even the winner is not a cure.

Caveats: this is a single-center trial of 57 young athletes. Generalization to older or lower-demand patients is unsupported, and the effect size has not been independently replicated.

Long-term durability

Two systematic reviews frame the long game. Across 610 patients at mean 10.2 years: large score gains (IKDC +42.4, Lysholm +21.1) but 28% failure and 19% reoperation — older age, prior surgery, and larger defects predicted failure. Across 495 patients at mean 15.1 years: return to sport 86–100%, conversion to knee replacement 0–16%, with sustained score improvements. Both pool observational studies, with the survivor and publication bias that implies. Durability is better than microfracture, not perfect.

The donor site

The originator's series of 831 patients reported good-to-excellent results in 92% of femoral condyle cases and claimed 3% donor-site morbidity. An independent systematic review of 1,726 patients tells it straighter: pooled donor-site morbidity was 5.9% when treating knee defects and 19.6% when harvesting the knee to treat the ankle — mainly patellofemoral pain and crepitus. The measured number is 6–20%, not 3%. You are trading a problem in one part of the joint for a smaller, usually tolerable one in another.

Who it suits

Single-stage, no cell culture, cheap relative to MACI — with a hard ceiling: donor tissue is finite, so the practical limit is about 2–4 cm². Beyond that, donor-site cost outweighs benefit, and large defects point to allograft or MACI instead. For athletes, this procedure has the fastest documented return to play among cartilage repairs — typically 6–9 months — with the strongest randomized return-to-sport data.

It is also technically demanding. Plug height mismatch or surface incongruity degrades results; surgeon volume matters.

Questions for your surgeon

• Is my defect within the 2–4 cm² window where autograft makes sense?
• How many of these do you do a year — and how do you handle plug congruity?
• What donor-site symptom rate do your patients actually report?
• If I am also a MACI candidate, why this one? (No adequately powered modern RCT compares them in the overlap zone.)

Safety

Standard knee surgery risks plus the donor site: patellofemoral pain, crepitus, rarely donor-site fracture. No allograft disease risk, no cultured-cell regulatory issues. Open questions include whether backfilling the donor holes reduces morbidity, and the long-term fate of the interface between plugs, where dead space fills with fibrocartilage.