Microfracture: indications, technique, and results.

The so-called "marrow stimulating" technique of microfracture uses an awl to penetrate the subchondral bone in cartilage defects. Disruption of the subchondral bone induces fibrin clot formation in the area of the chondral defect. This clot contains pluripotent, marrow-derived mesenchymal stem cells, which are able to differentiate into fibrochondrocytes, resulting in a fibrocartilage repair with varying amounts of type I, II, and III collagen content. Microfracture is a single-stage procedure that is ideally suited for small, well-contained, Outerbridge grade 3 to 4 cartilage lesions. Most clinical studies of the outcomes after microfracture in the knee show improvement in knee function in 70% to 90% of patients. The long-term results vary. Almost all studies report significant improvement in the first year after surgery; some report a decline in activity levels after 1 year, especially in elite athletes. Other studies have shown a continuation of good results for up to 7 years. Recent studies have shown that a body mass index greater than 30 kg/m(2) and incomplete fibrocartilage fill of a lesion as observed on MRI correlate with a poor outcome. The technical simplicity of the procedure, cost-effectiveness, and relatively low patient morbidity make microfracture an invaluable tool for the treatment of small full-thickness cartilage lesions. Microfracture is a good first-line procedure because it does not prevent the application of other cartilage repair procedures that may be needed in the future.