This condition usually occurs in adolescents between the age of 12 to 16. Boys are more commonly affected than girls. Osteochondritis dissecans is characterised by a small localised area of bone death or osteonecrosis on the femur. The causes are yet unknown but several theories exist all trying to explain why a certain area of bone crumbles. Osteochondritis usually affects the outer aspect of the medial femoral condyle. The bone underneath the surface cartilage weakens and the cartilage may break in - similar to the development of a pothole.

Occasionally the whole piece of affected bone together with its cartilage cover is discharged into the joint and may cause locking. Patients usually complain of a dull discomfort or ach after exercise. A history of trauma such as a fall or a twisting injury are possible but their significance is yet unknown. The condition may be associated with locking of the joint. Swelling may be a feature in later stages when the joint surface has developed incongruencies.

If diagnosed early a prolonged period on crutches may help to promote healing of the lesion. Drilling through the lesion with a fine wire may promote re-vascularisation and subsequent healing. If the fragment is already in the process of detaching itself from the femur re-fixation with screws, or biodegradable pins may be successful. In cases were a re-fixation is impossible the clinician has to assess the possibilities of re-establishing normal joint anatomy. In shallow defects, this can be achieved through simple marrow stimulation techniques like microfracture. If the depth of the defect measures more than one cm bone osteoarticular autograft transplantation may be indicated. Currently the option of bone grafting in combination with cartilage cell implantation (ACI, MACI) is under investigation.

In larger and deeper defects which often occur in cases where treatment is delayed a so called sandwich technique can be of benefit, as it allows the filling of the defect with autologous bone graft followed by the application of a cartilage cell impregnated membrane. If possible, this approach obviates the need for a separate bone grafting operation and reduces morbidity. The follow-up is dependant on the size and location of the lesion but usually includes a short period of plaster immobilisation after which the patient will be partially weight bearing for 4 to 8 weeks.