As the name would indicate it is literally creating a tiny break in the bone of the knee joint. This is usually done arthroscopically (using keyhole surgery). The break in the surface of the bone causes bleeding which uses the body’s healing response to create a ‘fake’ joint lining to the chondral (joint cartilage) surface.
The holes which are made in the exposed bone are typically 3 – 4mm apart and are deep enough to reach the bone marrow. This releases the blood and stem cells from the marrow which then clot in the area of the microfracture. This marrow rich clot is the base for new tissue formation and matures into firm repair tissue (fibrocartilage rather than chondral cartilage).
Microfracture is performed when an isolated area of the joint has lost it’s joint lining cartilage but the rest of the joint is in reasonable shape. It creates a ‘new’ surface to cover chondral/cartilage defects where the underlying bone has been exposed. If it works it reduces pain and swelling and helps joint function. Unfortunately the tissue formed is mainly fibrocartilage which is not as good as articular (normal joint lining cartilage) from a biomechanical standpoint.
Typically the patient will have lost the entire thickness of their articular cartilage exposing the underlying bone. They may have unstable flaps of cartilage which need to be removed to stop them catching. Sometimes microfracture can be combined with another substance to promote cartilage formation like JointRep or CarGel.
Microfracture is typically performed on younger patients who have moderate to high activity levels and typically the area of cartilage damage is surrounded by normal cartilage.
Microfracture is typically done as a day only case and you go home the same day of the operation on crutches. It is important to protect the new ‘clot’ which can be dislodged if weight is taken through the knee too soon. Typically you will need to stay off the leg for 6 weeks (Non Weight Bearing on Crutches). It is very important to move the knee during this time to stimulate healing of the tissue though. After 6 weeks progressively more weight is placed though the leg until normal walking resumes at 3 months after the operation. If activities are started too quickly after microfracture surgery, the microfracture may not heal or may heal with poor fibrocartilage (not as durable and likely to break down with time).
Microfracture is not usually used to treat chronic wear and tear (arthritis) articular cartilage damage. The patient will usually have an acute injury which then results in swelling, locking or catching within the knee. Xrays of the knee are often normal but an MRI will show the area of cartilage damage and possibly loose fragments within the knee. The extent of the damage can only accurately be assessed at the time of surgery and not all cartilage lesions are suitable for microfracture or cartilage replacement techniques.
While microfracture is not always successful, multiple studies show ongoing benefit for more than 5 years after the operation. It usually restore people back to a level of moderate function without ongoing swelling and catching in the knee.