About OATS procedure

A large cartilage defect within the knee

Osteochondral Autograft Transfer Surgery (OATS procedure) is suitable when there is a slightly larger area of damage to the weight-bearing area of the femur. This can be done as an arthroscopic or small open procedure, depending on the size and location of the cartilage lesion. It is normally performed as a day case procedure.

A core of bone and articular cartilage (between 6 and 10mm in diameter) is harvested from an area of the knee where it is less important as you do not bear weight through that segment. This cartilage is then transplanted into the defect in order to fill the gap in your articular cartilage. Up to two, or rarely three plugs can be transplanted in this manner to fill larger defects.

The operation is often done as a day case, or occasionally one overnight stay is needed. Usually it can be done through keyhole surgery; occasionally a small incision is needed to open the knee joint and perform the operation. You will have stitches that need removing after 7 to 10 days, and you should use ice packs in the first couple of weeks to help decrease the swelling.

Following the surgery, weight bearing is allowed as tolerated with crutches, building up to full weight bearing by six weeks. Early knee movements are encouraged, and cycling using an exercise bike after one to two weeks. Impact exercises can usually restart at around the three-month mark, with graduated return to sports after 6 months.

Risks of OATS Procedure

The defect has been filled with 2 8mm plugs transplanted from the outside of the knee

All operations come with potential attached risks.

Infection – the risk of an infection following an OATS Procedure is very rare. Every effort is taken during surgery to reduce this risk, through the use of alcoholic skin preparation, clean air sterile theatres and antibiotic treatment at the time of surgery. It is estimated that the risk is approximately 1:1000.

Stiffness – It is unlikely that you will develop long-term stiffness, but in the short term your knee will be sore, swollen and stiff. Regular exercises and ice packs should reduce this, but rarely a manipulation under anaesthetic (MUA) may be required to break down scar tissue and get the knee to bend.

Blood clots – A blood clot in the leg (deep vein thrombosis, DVT) or in the lung (pulmonary embolus , PE) would be extremely rare following an OATS procedure. If you are unfortunate enough to develop either of these, then blood thinning medication such as warfarin (or a newer alternative) is usually required for 3-6 months.

Outcome of OATS Procedure

At ten years, over 70% of OATS procedures are doing well with no further surgery. Significant clinical improvement in the form of patient-reported knee scores is also seen. I invite all my patients to submit their knee scores. This helps me to monitor your ongoing recovery, but also assists with research purposes in the future. Please rest assured that any personally identifiable information will not be shared with anyone else, and that all information used for research will be anonymised.

OATS procedures work best where the area of damage is less than 4cm², and if your area of damage is larger than this I am likely to recommend an AMIC Procedure. I prefer not to transplant more than 2 cores of bone and cartilage if possible due to the rare but potential issues of pain or swelling from the donor area if more cores are harvested.