Microfracture surgery is an articular cartilage repair surgical technique that works by creating tiny fractures in the underlying bone. This causes new cartilage to develop from a so-called super-clot. The surgery is quick (typically lasting between 30 and 90 minutes), minimally invasive, and can have a significantly shorter recovery time than an arthroplasty (knee replacement). Chronic articular cartilage defects do not heal spontaneously. However, acute traumatic osteochondral lesions or surgically created lesions extending into subchondral bone, e.g. by Pridie drilling, spongialization abrasion or microfracture causing the release of multipotent mesenchymal stem cells from the bone marrow, may heal with repair tissue consisting of fibrous tissue, fibrocartilage or hyaline-like cartilage. The quality of the repair tissue after these "bone marrow stimulating techniques" depends on various factors including the species and age of the individual, the size and localization of the articular cartilage defect, the surgical technique, e.g., how the subchondral bone plate is treated, and the postoperative rehabilitation protocol. History The surgery was developed in the late 1980s and early 1990s by Dr. Richard Steadman of the Steadman-Hawkins clinic in Vail, Colorado. Steadman slowly refined the procedure through research (including tests on horses). The surgery was called "controversial" by many sportswriters, due to a lack of studies on the long-term effects and the fact that an unsuccessful surgery could end an athlete's career. Steadman has also adapted the surgery into a treatment to help reattach torn ligaments (a technique he calls the "healing response"). Procedure The surgery is performed by arthroscopy, after the joint is cleaned of calcified cartilage. Through use of an awl, the surgeon creates tiny fractures in the subchondral bone plate. Blood and bone marrow (which contains stem cells) seep out of the fractures, creating a blood clot that releases cartilage-building cells. The microfractures are treated as an injury by the body, which is why the surgery results in new, replacement cartilage. The procedure is less effective in treating older patients, overweight patients, or a cartilage lesion larger than 2.5 cm. Further on, chances are high that after only 1 or 2 years of the surgery symptoms start to return as the fibrocartilage wears away, forcing the patient to reengage in articular cartilage repair. The effectiveness of cartilage growth after microfracture surgery is thought to be dependent on the patient's bone marrow stem cell population and some think increasing the number of stem cells increases the chances of