Articular cartilage is a white, glistening layer which covers the bone on each side of the joint. The smooth cartilage surface is approximately 3/8 of an inch thick and has very low friction. Articular cartilage damage in the knee is relatively common. When it is focal and isolated, it generally is the result of an injury. Articular cartilage surfaces have little potential to heal or regenerate themselves. The loss of cartilage can lead to pain, swelling, and limited function. Running, cutting, and jumping may be difficult with articular cartilage damage which affects the weight-bearing surfaces of the knee. Occasionally, popping and snapping can occur but are nonspecific. Examination may reveal joint line tenderness. Joint swelling, or “water on the knee” can also be present and cause some degree of stiffness particularly with flexion. Plain x-rays are generally normal if the cartilage defects are relatively small. An MRI is able to more accurately determine the size and area of the missing cartilage. Nonsteroidal anti-inflammatories, along with strengthening exercises may be sufficient to minimize pain. When conservative measures fail to alleviate symptoms, minimally invasive arthroscopic surgery may be an appropriate option. A small shaver is used to debride or clean the margins of frayed articular cartilage. The end of the bone is lightly scraped to remove unwanted cartilage remnants. A small drill or wire is then used to make perforations in the bone which allow it to bleed and establish a layer of scar cartilage. A 4-6 week period of protected weight-bearing is generally necessary to allow the new scar cartilage to adhere and establish itself on the bone. For small defects, usually no larger than 1 cm², microfracture can be very effective in the intermediate term. Full recovery may require 5-6 months and generally results in good overall pain relief.