OATS — Osteochondral Autograft Transfer
Fellowship-trained sports medicine surgeons Christopher Raffo, MD and John Christoforetti, MD perform OATS cartilage transfer for focal knee cartilage defects, using the patient's own living cartilage tissue for durable restoration.
What is oats — osteochondral autograft transfer?
OATS (Osteochondral Autograft Transfer System) is a surgical procedure that treats a focal cartilage defect in the knee by transplanting cylindrical plugs of healthy cartilage and bone from a low-load area of the patient's own knee into the damaged area. Using the patient's own tissue provides true hyaline cartilage — not repair tissue — making OATS particularly effective for defects between 1 and 4 cm² in younger, active patients.
Why this approach — at MOS
When evaluating a patient with a focal cartilage defect, we consider three factors: defect size, defect depth (cartilage-only versus bone involvement), and patient age and activity level. These three parameters largely determine whether microfracture, OATS, or osteochondral allograft is the appropriate choice.
For defects between 1 and 3 cm² in young, active patients, OATS provides true hyaline cartilage coverage with excellent durability data in the literature. We take donor plug harvest seriously — the donor site must be in a low-load zone to avoid creating a symptomatic donor defect, and plug diameter and depth must match recipient socket geometry precisely for optimal press-fit and cartilage congruity.
We address any concurrent malalignment or ligament instability before or simultaneously with OATS, because an unloaded or stable mechanical environment is essential for graft survival. Patients who come to our offices in Montgomery County with focal cartilage defects receive a full evaluation of limb alignment and ligament stability before cartilage treatment is planned.
Who is a candidate?
Indications
- Focal, full-thickness osteochondral defect between approximately 1 and 4 cm²
- Younger patients (generally under 45–50) with good bone quality and healthy surrounding cartilage
- Failed prior microfracture — OATS is a reliable salvage for microfracture failure
- Osteochondritis dissecans (OCD) lesion with detached or loose fragment not suitable for fixation
- Active patients with significant functional limitation from confirmed focal cartilage defect
Contraindications
- Very large defect (>4 cm²) — insufficient autograft available from one knee; osteochondral allograft is more appropriate
- Advanced surrounding cartilage degeneration (defect not focal and contained)
- Uncorrected malalignment that loads the recipient site abnormally
- BMI limiting recovery or significantly increasing surgical risk
- Patient unable or unwilling to comply with protected weight-bearing protocol
Conservative Treatment First
Focal cartilage defects causing significant functional limitation should be evaluated for surgical treatment when conservative management — physical therapy, activity modification, corticosteroid or hyaluronic acid injection — has failed to provide adequate relief. For younger, active patients with confirmed focal defects, the window for cartilage preservation procedures is time-sensitive: delay allows the defect to enlarge and the surrounding cartilage to degenerate, eventually closing the window for cartilage-preserving surgery and moving the patient toward eventual joint replacement. The decision to proceed with OATS rather than microfracture or allograft is individualized based on defect size, patient age, and activity demands.
The procedure
What Is OATS — Osteochondral Autograft Transfer?
OATS (Osteochondral Autograft Transfer System) is a surgical procedure that treats a focal cartilage defect in the knee by transplanting cylindrical plugs of healthy cartilage and bone from a low-load area of the patient's own knee into the damaged area. Using the patient's own tissue provides true hyaline cartilage — not repair tissue — making OATS particularly effective for defects between 1 and 4 cm² in younger, active patients.
Articular cartilage cannot repair itself. When a focal defect occurs — from acute injury, osteochondritis dissecans, or prior failed treatment — filling it with the patient's own living cartilage is the most biologically direct approach. The OATS technique uses a specialized hollow coring device to harvest one or more cylindrical plugs (typically 6–10 mm in diameter) from a non-weight-bearing area of the knee, usually the peripheral trochlea or the edge of the intercondylar notch. These plugs contain both the cartilage layer and the underlying bone cylinder.
Matching-diameter sockets are prepared at the recipient site (the defect), and the plugs are press-fit into these sockets, producing a surface covered with living hyaline cartilage at near-native level. When a single plug is insufficient to cover the defect, multiple plugs are placed in a mosaic pattern — a technique called mosaicplasty. The gaps between plugs fill in with fibrocartilage over time.
What Happens During OATS?
OATS is performed arthroscopically or through a small open approach (mini-arthrotomy) at the ambulatory surgery center. After anesthesia, the defect is inspected arthroscopically and its size precisely measured. The defect edges are prepared to vertical stable walls.
Using the OATS coring system, the appropriate number and diameter of cylindrical sockets are prepared at the recipient site. Then the donor area — typically the superior peripheral trochlea — is identified, and matching-diameter plugs are harvested using the coring device. Each plug is gently tapped into its recipient socket to achieve a press-fit, with the cartilage surface flush with the surrounding joint surface. If multiple plugs are used (mosaicplasty), they are placed in a pattern that maximizes cartilage coverage.
The donor sites are either left to fill with fibrocartilage or backfilled with resorbable material. Portals or the mini-arthrotomy are closed, and a compressive dressing is applied. The procedure takes 60–90 minutes depending on defect size and number of plugs required.
Recovery timeline
Weeks 1–6 (Protected)
Non-weight-bearing or toe-touch weight-bearing with crutches. Continuous passive motion may be used. Range-of-motion exercises without load.
Weeks 6–12 (Progressive Loading)
Gradual weight-bearing. Physical therapy progresses from range of motion to low-load strengthening.
Months 3–6 (Functional)
Stationary bike, pool activities, progressive straight-line activity.
Months 6–12 (Return to Sport)
Gradual return to pivoting and impact sport after meeting functional criteria. Most athletes return at 6–9 months.
OATS recovery closely parallels microfracture in its early protected phase. The graft must be protected from excessive load while the bone-to-bone interface heals (osseous integration), which takes approximately 6–8 weeks. Once bony integration is confirmed and loading begins, recovery accelerates. Return-to-sport timing is based on functional testing — quadriceps symmetry, hop testing, and movement quality — not a fixed calendar date. MOS in-house physical therapists follow cartilage-specific protocols through return to full activity.
Frequently Asked Questions
Why is OATS better than microfracture for some patients?
Where does the donor cartilage come from, and does it cause problems?
How long does the transplanted cartilage last?
Can OATS be done arthroscopically?
What happens if OATS does not work?
References
- Hangody L, Füles P. Autologous osteochondral mosaicplasty for the treatment of full-thickness defects of weight-bearing joints. Journal of Bone and Joint Surgery. 2003;85-A Suppl 2:25–32. doi:10.2106/00004623-200300002-00004. PMID: 12721342.
- Gudas R, Kalesinskas RJ, Kimtys V, et al. A prospective randomized clinical study of mosaic osteochondral autologous transplantation versus microfracture for the treatment of osteochondral defects in the knee joint in young athletes. Arthroscopy. 2005;21(9):1066–1075. doi:10.1016/j.arthro.2005.06.018. PMID: 20104156.