Knee Joint

The knee joint is complicated anatomically and consists of three articulations: two between the condyles of the femur and the tibia, and the third between the femur and the patella. The synovial cavity is common to all three joints, but is indented by the two menisci between the femur and the tibia. These menisci are best seen on the MRI.

Fractures of all three bones can occur and can be visualized on these views. A fracture of the patella may only be visible on the skyline view. It should not be confused with a congenital bipartite patella, which is often present bilaterally. To assess whether there is free fat within the joint space, an x-ray with a horizontal beam should be performed and, if positive, is a fair indication of bone damage. A tunnel view has not been included, but is of use when looking for a loose body or evidence of osteochondritis dissecans. Note also on the skyline view that the lateral femoral condyle projects higher than the medial condyle to resist lateral dislocation of the patella.

The tibia and fibula are connected by an interosseous membrane similar to that of the forearm. Again, with paired long bones, fracture of one bone is often accompanied by a fracture of the other. As mentioned before with the forearm radiograph, if one bone is fractured with considerable displacement, then both proximal and distal joints should be checked for dislocation of the other bone. Note that the head of the fibula does not form part of the knee joint, but has a separate synovial joint with the tibia. Fractures of the tibia and fibula are often compound because of the lack of soft tissues anteriorly. Fractures of the mid-tibial shaft are prone to non-union because of the apparent poor vascularity. Paget's disease and syphilis are causes of 'sabre tibia'.