Osteochondral Allograft Transplantation (OCA)

Why this approach — at MOS

Osteochondral allograft is a powerful procedure in the right hands for the right indication, but it requires honest patient counseling about what it can and cannot accomplish. The goal is cartilage preservation and pain relief in a patient who still has good bone stock and a focal rather than diffuse disease pattern. It is not a replacement for knee replacement when diffuse arthritis is present.

We obtain standing alignment radiographs and full-length leg X-rays on every patient before planning OCA to ensure any varus or valgus deformity is identified and addressed — either concurrently with OCA or in a staged fashion. An allograft placed in a malaligned knee will fail faster than one placed in a well-aligned knee because abnormal load distribution concentrates stress on the graft.

Graft selection from the tissue bank specifies not only size (diameter) but also condylar radius of curvature. A graft that does not match the patient's condylar geometry will create contact incongruity — a known cause of early graft failure. We are selective about which grafts we accept, and occasionally delay surgery to await a better-matched specimen.

Who is a candidate?

Indications

• Large focal osteochondral defect (>3–4 cm²) not amenable to autograft due to size
• Defects with significant bone loss requiring restoration of the osseous substrate as well as cartilage
• Failed prior cartilage surgery (microfracture or OATS) with persistent symptoms
• Osteochondritis dissecans (OCD) with large unstable or failed-fixation fragments
• Avascular necrosis of the femoral condyle (early-to-moderate stage with contained involvement)
• Young patients (<50) with focal disease and otherwise preserved joint space

Contraindications

• Advanced diffuse osteoarthritis — allograft treats focal defects, not whole-joint arthritis
• Inflammatory arthritis — ongoing synovial inflammation destroys transplanted cartilage
• Uncorrected malalignment — must address before or concurrently with allograft
• BMI >35–40 — significantly increases failure risk
• Active joint infection
• Inability to comply with post-operative weight-bearing restrictions

Conservative Treatment First

Focal cartilage defects — even large ones — should be managed conservatively when symptoms are mild. Physical therapy, activity modification, corticosteroid injection, and hyaluronic acid injection can reduce pain and inflammation associated with cartilage defects. When these measures fail to provide adequate functional improvement in an active patient with a confirmed large focal defect, osteochondral allograft transplantation becomes an appropriate consideration — particularly when the alternative would be eventual knee replacement at a young age.

The procedure

What Is Osteochondral Allograft Transplantation (OCA)?

Osteochondral allograft transplantation (OCA) replaces a large or complex cartilage defect in the knee using a matched donor graft — fresh cartilage and bone from a tissue bank — that is shaped and implanted to restore the joint surface. It is indicated for defects too large for autograft or when prior cartilage surgery has failed, and provides true hyaline cartilage coverage.

When a focal cartilage defect is too large for autograft (OATS) — generally above 3–4 cm² — or involves significant bone loss, the patient's own knee cannot provide enough donor material. In these cases, a fresh osteochondral allograft from a tissue bank is used. The allograft is a segment of joint surface with its full-thickness cartilage and underlying bone, obtained from a donor and processed to maintain cartilage cell viability while reducing immune response risk.

Unlike the synthetic materials used in joint replacement, an osteochondral allograft is biological — living cartilage tissue. When correctly matched, transplanted, and allowed to integrate, the allograft cartilage maintains its cellular viability and provides a durable joint surface. Published studies show satisfactory function in 70–80% of patients at 10 years in appropriately selected patients.

The procedure requires pre-operative tissue matching for graft size and shape, which introduces a scheduling delay — the tissue bank must identify a graft of appropriate dimensions and curvature, which may take several weeks. This is not immunological matching (no anti-rejection medication is required); it is dimensional matching to ensure the graft conforms to the patient's condylar geometry.

What Happens During Osteochondral Allograft Transplantation?

Tissue Acquisition

Several weeks before surgery, size measurements from the patient's MRI are submitted to the tissue bank. A fresh (not freeze-dried) osteochondral allograft matched to the patient's condylar dimensions is procured. Fresh allografts maintain higher chondrocyte viability than frozen grafts and are preferred for OCA.

Surgery

The procedure is performed at the ambulatory surgery center under general or regional anesthesia. An arthroscopic examination is performed first to assess the defect and surrounding structures. The knee is then opened through a small arthrotomy to gain direct access to the defect site — this provides better visualization and precision for the large recipient socket preparation than fully arthroscopic technique.

The defect is measured and prepared using cylindrical reamers to create a recipient socket with vertical walls and a flat bone base. The allograft is prepared on a side table — matching-diameter cylindrical cores are harvested from the donor segment using the same reamer system, maintaining the cartilage-to-bone architecture. The allograft plug is gently impacted into the recipient socket to achieve press-fit fixation, with the articular surface flush to the surrounding cartilage. In some cases, additional fixation with absorbable pins or screws is used.

The arthrotomy and portals are closed. Post-operative weight-bearing restrictions are initiated.

Recovery timeline

Frequently Asked Questions