Overview
Articular cartilage does not regrow. When a focal patch of it is lost from the end of the femur or the back of the kneecap, the exposed bone hurts, the knee swells with activity, and the defect widens over years toward arthritis. Osteochondral allograft transplantation (OCA) resurfaces that patch with a cylinder of living cartilage and bone from a size-matched donor, restoring a smooth joint surface in a knee that is otherwise healthy.
The aim is a knee that stops swelling and aching with activity, returns to running and sport, and is protected from replacement for decades. Dr. O'Donnell performs the operation as an outpatient at Bayside Surgery Center.
Who It's For
The ideal candidate is under about 50, has a single, well-defined cartilage defect larger than roughly 2 square centimeters on MRI, with pain and swelling that match the location, and healthy cartilage elsewhere in the knee. Common causes are a traumatic cartilage fracture, osteochondritis dissecans, and a defect that persisted after a previous microfracture or debridement. Alignment, ligament stability and meniscus status are assessed and corrected at the same time if needed, since a graft placed in a malaligned or unstable knee fails.
Small defects under about 1 square centimeter are often treated with arthroscopic debridement or microfracture first. Widespread cartilage loss on both sides of the joint is arthritis, not a focal defect, and is better managed non-operatively or, when the time comes, with knee replacement.
A cartilage defect seen on MRI is not by itself an indication for a graft; small and partial-thickness lesions are common in knees without symptoms. Dr. O'Donnell recommends restoration only when the pain, swelling and tenderness localize to the defect on exam, the lesion on MRI is at the same site, and a period of activity change and rehabilitation has not helped. See the cartilage injury page.
What the Procedure Involves
The graft comes from a tissue bank that matches the donor femur to the patient's by size on X-ray, and is transplanted fresh, within about four weeks of recovery, because the cartilage cells must be alive. Under a nerve block plus general anesthesia, the knee is opened through a short incision over the defect. The damaged cartilage and a thin layer of the bone beneath are removed with a cylindrical reamer to create a clean socket of known depth. A matching plug is cut from the same location on the donor condyle, trimmed to the exact depth, and press-fit into the socket so that its surface sits flush with the surrounding cartilage. Fixation comes from the tight fit. Over the following months the patient's bone grows into the donor bone while the cartilage cap stays alive and functional. The operation takes 60 to 90 minutes and patients go home the same day on crutches.
Risks & How They Are Minimized
The risk specific to this operation is failure of the graft to incorporate: the donor bone has to be replaced by the patient's own bone, and if that process stalls the plug loosens or the surface collapses. It is minimized by using fresh grafts with living cartilage, a precise press-fit, strict protection from weight bearing for the first 6 to 8 weeks, and correcting alignment and stability at the same operation. Stiffness is prevented by early passive motion, often with a continuous passive motion machine, which also nourishes the graft cartilage. Infection is uncommon and is addressed with a pre-incision antibiotic. Blood clots are a real concern during the weeks on crutches and are prevented with aspirin, ankle pumps and early motion.
Recovery & Rehabilitation
The graft must be protected from impact and shear while it incorporates. For a femoral condyle defect that means touch-down or non-weight-bearing on crutches for about 6 to 8 weeks; for a patellofemoral defect, weight bearing as tolerated in a brace locked in extension with loaded flexion limited. No running or jumping until cleared, typically 6 to 12 months.
| Phase | Timing | What happens |
|---|---|---|
| Protection & motion | Weeks 0–6 | Weight bearing per lesion location; no loaded flexion of the treated surface. Continuous passive motion or early passive motion, quad sets, straight-leg raises, patellar mobilizations, heel slides within limits. Advance with full extension, a good quad set and controlled swelling. |
| Progressive weight bearing | Weeks 6–12 | Weight bearing advanced gradually to full by about 8 to 12 weeks; crutches weaned. Full motion, stationary bike, pool therapy, closed-chain strengthening in protected ranges. Advance with pain-free full weight bearing, full motion and normal gait. |
| Low-impact strengthening | Months 3–6 | Progressive resistive and single-leg strengthening, elliptical, bike and swimming, hip and core work. No running, jumping or cutting. Advance at 80% strength of the opposite side with no swelling. |
| Return to impact & sport | Months 6–12 | Criteria-based running and plyometric progression, agility and sport-specific drills. Return to sport typically at 9 to 12 months on symmetric strength and functional testing, surgeon-cleared. |
Desk work is possible within 1 to 2 weeks on crutches. Driving resumes once full weight bearing is allowed and the brace is off, about 8 to 12 weeks for a right knee. Cycling and swimming from about 3 months, running from 6 months at the earliest, and sport at 9 to 12 months.
Protocol summary
Precautions: femoral condyle grafts are touch-down or non-weight-bearing on crutches for about 6 to 8 weeks; patellofemoral grafts bear weight as tolerated in a brace locked in extension with loaded flexion limited. Continuous passive motion or early passive motion is used to nourish the graft. No impact activity until cleared, typically between 6 and 12 months.
Criteria: full passive extension and a good quad set end the protection phase; pain-free full weight bearing, full motion and a normal gait end the second; strength of at least 80% of the opposite side with no swelling allows impact to begin; return to sport requires symmetric strength and functional testing, typically at 9 to 12 months.
Physical Therapy Protocol
Osteochondral Allograft Transplantation (Knee) PDF ↗Frequently Asked Questions
How long is the wait for a cartilage graft?
Fresh osteochondral allografts are matched by size to your femur from X-ray measurements, and the wait for a suitable donor is usually a few weeks to a few months. Once a match is found, the graft must be used within about four weeks while its cartilage cells are alive, so surgery is scheduled on short notice.
How long are you non-weight-bearing after osteochondral allograft?
For a defect on the femoral condyle, touch-down or non-weight-bearing on crutches for about 6 to 8 weeks, then a gradual increase to full weight bearing by 8 to 12 weeks. For a patellofemoral defect, you can bear weight from the start in a brace locked in extension, because the graft is not loaded when the knee is straight.
Is cartilage restoration better than microfracture?
For small defects, microfracture is a reasonable first step, but the scar cartilage it produces is softer than the original and often wears out within a few years. For defects larger than about 2 square centimeters, or after a failed microfracture, an osteochondral allograft restores true cartilage and bone and holds up far better over time, which is why Dr. O'Donnell prefers it for larger lesions.
When can I run after cartilage restoration surgery?
Not before 6 months, and only once strength is at least 80% of the other leg with no swelling. Running is introduced as a criteria-based progression in the return-to-impact phase, months 6 to 12, and return to sport is typically 9 to 12 months. Running earlier risks shearing a graft that is still incorporating.
Can my body reject the donor cartilage?
Rejection in the usual sense does not occur. Cartilage has no blood supply and is largely hidden from the immune system, and the bone portion is replaced over time by your own bone. No anti-rejection medication is needed. Donor tissue is screened and tested by the tissue bank.
This page is for general education and is not a substitute for a medical evaluation. The right procedure depends on your individual diagnosis, anatomy, and goals. Kevin O'Donnell, MD sees patients from Coral Gables, Miami, Brickell, Pinecrest and Coconut Grove at 475 Biltmore Way, and out-of-town patients by telemedicine.