A large osteochondral defect affecting the medial femoral condyle

About AMIC Procedure

Larger cartilage defects which are not suitable for an OATS procedure may be suitable for an AMIC (Autologous Matrix-Induced Chondrogenesis) procedure, which uses a collagen membrane to fill the defect. This procedure is suitable in cases where the defect is larger than 2.5cm2, as these cases are not suitable for other types of cartilage surgery.

Although the procedure will involve an arthroscopy to examine the joint surfaces throughout the knee, it is likely that the AMIC procedure itself will be carried out through a small incision. Any loose articular cartilage will be removed. The defect may need some bone graft if there is bone loss as well as a cartilage defect (called an osteochondral defect). This bone graft is usually donated bone.

Stem cells are required to promote the growth of new cartilage. These can either be provided using a microfracture technique, where small holes are made in the bone to promote bleeding. Alternatively, your own bone marrow can be used, which is an excellent source of stem cells.

The defect is then covered with a collagen membrane, which is sealed in place with fibrin glue. The incision is then closed with a dissolvable suture, and you will have a waterproof dressing over the knee. You should be able to go home either on the same day or the day after surgery.

The defect has been filled with donated bone graft and the patient’s own bone marrow aspirate

Rehabilitation

For the first 6 weeks following surgery, the emphasis is on protecting the graft while reducing joint swelling and maintaining your movement.

You will have a brace following surgery, which will be locked in extension for the first 2 weeks, then unlocked to allow flexion. You will be using crutches and only toe-touch weight-bearing at first. The brace can be removed between 2 and 4 weeks, once you have adequate quadriceps control and can raise your leg with the knee straight. You should start building up the weight that you take through the knee from 2 weeks, with the goal of progressing to full weight-bearing by 8 weeks.

From 6 weeks onwards, the goal is to start strength and conditioning work without putting excess stress on the graft. You should be able to return to driving by 8 weeks. A static bike is an excellent rehabilitation tool and can be used from 6-8 weeks, with a gradually increasing load.

The graft begins to mature between 4 and 6 months following surgery. From the 6 month mark, you should begin to return to functional activities and sports-specific training programmes. However, you are unlikely to be able to return to contact sports until the 1 year point.

Outcome of AMIC Procedure

Although results in the femur and tibia are good, the historical results in the patellofemoral joint are less predictable.

The bone graft has been covered with a collagen membrane, which has been sealed in place with fibrin glue

However more recent studies do suggest that good outcomes are achievable. 75% of patients report that their knee function is “good” or “excellent” following AMIC. Follow-up MRI studies have also shown good quality cartilage restoration.

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. Your anonymised data will also be entered onto the International Cartilage Regeneration & Joint Preservation Society registry, which will help to monitor long-term outcomes for this type of surgery.