Osteochondritis dissecans of the knee occurs most frequently in preadolescents and adolescents with open physes but may be seen in adults. A variety of potential etiologies and pathophysiologic pathways have been proposed, most of which center around microtraumatic dysvascularization or necrosis of a focal area of subchondral bone. Experts generally consider osteochondritis dissecans to be an idiopathic phenomenon. The knee is by far the most common site of osteochondritis dissecans, with other sites of involvement including the ankle and elbow, and, less commonly, the shoulder and hip. The most common location for knee osteochondritis dissecans is the lateral aspect of the medial femoral condyle. The second most common location is the lateral femoral condyle; such lesions tend to be larger and more advanced at the time of presentation. Trochlear, patellar, and tibial plateau osteochondritis dissecans lesions also occur (listed here in descending order according to incidence) but are more rare. The primary approach for stable osteochondritis dissecans in skeletally immature patients is nonoperative treatment. While there is no clear evidence that synthesizes the most effective form or duration of nonoperative treatment, most authors have described a minimum of three months of treatment to allow for the assessment of potential healing. Therapeutic modalities include protected weight-bearing with crutches, locked hinged knee-bracing, unloader bracing, and simple activity modification with the avoidance of sports and impact activities. For stable osteochondritis dissecans lesions in skeletally immature patients that do not demonstrate healing with nonoperative measures, and for stable osteochondritis dissecans lesions that are first detected in skeletally mature patients, the standard of care for operative treatment is generally drilling of the lesion. The two principal techniques include transarticular drilling, which is usually performed for femoral condylar lesions in retrograde fashion under arthroscopic visualization, and so-called retroarticular drilling, which is usually performed in an anterograde fashion with fluoroscopic guidance. Both techniques, and others, such as intercondylar notch drilling, are designed to disrupt the sclerotic margin of the osteochondritis dissecans lesion and establish multiple channels between the unaffected, healthy adjacent cancellous bone and the affected subchondral bone of the lesion to allow osseous bridging and osseous healing, the time to which has averaged four to six months in most series. For unstable osteochondritis dissecans lesions-which can range from in situ lesions with mild chondral fissuring to frank osteochondral loose bodies that have undergone complete separation-operative treatment most commonly consists of arthroscopic or open fixation of the lesion, with or without debridement of osseous surfaces and/or bone-grafting at the interface of the parent bone and progeny bone of the osteochondritis dissecans lesion. While the largest series have described successful healing of the majority of lesions following fixation, the treatment of lesions that fail to heal and/or those with chondral degeneration or minimal bone on the progeny fragment may require application of more advanced cartilage salvage or resurfacing techniques, such as OATS (Osteochondral Autograft Transfer System; Arthrex, Naples, Florida), osteochondral allograft transfer, or autologous cultured chondrocyte implantation.
