Disruption of the subchondral bone continuity results in bleeding and filling of the defect volume with fibrin clot. Mesenchymal stem cells migrate into the clot, proliferate, and differentiate morphologically into chondrocytes. Usually within six to eight weeks bone is formed within bony defect and fibrous cartilage is formed within chondral defect. Bone marrow stimulation techniques like abrasion, drilling or microfracture are used arthroscopically to disrupt the subchondral plate and provoke chondral formation. They are indicated in focal defects and defectscontained in intact cartilage. Fibrous cartilage is resistant to tension but not as durable to compression as hyaline cartilage is. Patients treated with microfracture improve most during the first year and maximal improvement is seen in two to three years.