Osteochondral Autograft Transfer (OATS)

Weight-bearing AP, lateral, Rosenberg (45 degree PA) and skyline views. Assess joint space, alignment and established osteoarthritic change. Chronic lesions may show subchondral change or cysts.

Assess lesion size, location, depth and containment. Evaluate subchondral bone integrity. Identify associated meniscal or ligamentous pathology. Assess donor-site availability.

Helpful for precise lesion sizing and bone-stock assessment, particularly in revision cases or complex geometries.

• Position — supine, thigh tourniquet, leg in a holder or over a post so the knee can be flexed through a full range and the lesion brought into view.
• Anaesthesia/analgesia — GA or regional; the donor site is a recognised source of postoperative pain, so plan multimodal analgesia.
• Diagnostic arthroscopy first — probe and measure the lesion, assess the rest of the joint, and rule out bipolar disease and uncorrected instability or malalignment.

• Measure the defect with a calibrated probe in two planes and confirm it is focal (1-4cm squared), contained with stable shoulders, and not bipolar.
• If larger than expected or bipolar, abandon OATS and convert (osteochondral allograft, ACI/MACI, or a staged plan with osteotomy) rather than over-harvest the donor.

• Arthroscopic — feasible for small, well-positioned condylar lesions where a perpendicular trajectory can be achieved through a portal.
• Mini-arthrotomy (most common) — a limited medial or lateral parapatellar arthrotomy gives perpendicular access and the most reliable plug seating.
• Access is the rate-limiting step: choose the exposure that lets the recipient harvester sit perpendicular to the defect. The single reason to convert from arthroscopic to open is inability to keep the harvester perpendicular — a non-perpendicular tunnel produces an oblique plug, surface step-off and point loading. Plan the approach around perpendicular access, not cosmesis.

• Prepare the recipient socket first (per instrument system), drilling to a defined depth (commonly 15-20mm) with the tube harvester held strictly perpendicular.
• Create vertical walls and a fresh bleeding cancellous base; debride unstable cartilage back to a stable rim. Measure socket depth precisely.

• Donor sites (low-load, non-articulating) — the superolateral and superomedial margins of the trochlea (just above the sulcus terminalis, at the periphery of the patellofemoral contact zone) and the lateral wall of the intercondylar notch.
• Harvest perpendicular to the donor articular surface and slightly longer than the recipient socket so the plug can be trimmed and seated flush.
• Limit harvest to 3-4 plugs maximum — donor availability and morbidity, not the lesion alone, cap the technique near 4cm squared.
• Match donor curvature to recipient convexity and orient the plug's cartilage cap to recreate the local surface contour; a flatter trochlear plug placed into a more convex condyle creates a proud edge or a step.

• Depth — donor plug depth must equal recipient socket depth. Trim bone from the base if too long; never trim the cartilage cap.
• Height — seat flush or up to 1mm proud, never recessed. Recessed plugs are load-shielded and integrate poorly; excessively proud plugs (more than 1mm) cause peak contact stress and graft overload.
• Press-fit — an interference (press) fit provides primary stability without screws or supplemental fixation. Deliver with gentle, axial tamping; avoid repeated heavy impaction, which kills surface chondrocytes.

• Place the largest central plug first, then fill the periphery; aim for the highest practical fill.
• Residual 1-2mm gaps between plugs (commonly 10-20 percent of the defect) fill with fibrocartilage from the marrow — this is acceptable. Complete hyaline coverage is not required; aim for maximal practical hyaline fill while keeping every plug flush and perpendicular.

• Take the knee through a range of motion to confirm the plugs are stable, congruent and do not catch.
• Standard layered arthrotomy or portal closure.
• Document defect size, donor sites, number and diameter of plugs, and the final seating (flush versus proud).