Knee

the joint between the upper and lower parts of the leg. It is the largest and most complicated in the body, and it can be analysed separately as three major areas: the medial femorotibial space, the lateral femorotibial space and the patellofemoral space. The articulating bones of the knee include the femur, tibia, and largest sesamoid bone of the body, the patella. Other important structures of the knee are the meniscus, ligaments, fat pad, bursae and recesses. Also, see knee.

2. Pathology

In rheumatoid arthritis alterations usually affect both medial and lateral femorotibial compartments to an equal degree. Other possible findings are diffuse loss of interosseous space in the medial and lateral compartments, osteoporosis, marginal or central osseous erosions, and subchondral sclerosis. Varus angulation or valgus angulation of the knee may ensue. Tricompartmental abnormalities that are of equal severity are most suggestive of rheumatoid arthritis.

Ankylosing spondylitis, psoriatic arthritis and Reiters syndrome can affect one or both knees, sometimes with a tricompartmental distribution. Periosteal proliferation or whiskering may be pronounced.

In osteoarthritis, bicompartmental rather than tricompartmental findings are evident on radiographs. The medial femorotibial compartment is more severely affected, often leading to varus deformity. Some patients, especially women, may have severe alterations in the lateral femorotibial compartment and valgus deformity, however.

Calcium pyrophosphate dihydrate crystal deposition disease frequently has a distribution of abnormalities identical to that in osteoarthritis. Valgus angulation of the knee may be present.

In addition to subperiosteal resorption of bone along the medial aspect of the tibia, hyperparathyroidism can produce distinctive types of joint abnormality on knee radiographs, consisting of subchondral resorption of bone in any compartment (poorly defined erosion and sclerosis) especially in the patellofemoral areas.

Septic arthritis can involve any compartment of the knee. As in rheumatoid arthritis, the alterations can spread to all areas of the joint, producing tricompartmental disease. In neuropathic osteoarthropathy accompanying tabes dorsalis or other diseases with neurologic deficit, sclerosis, fragmentation, subluxation and disorganization of the joint may be evident.

Calcium hydroxyapatite crystal deposition disease and mixed calcium phosphate crystal deposition disease show predominant involvement of the lateral femorotibial compartment, leading to bone collapse and fragmentation; alterations in the shoulder may also be present.

Ischaemic necrosis commonly involves the distal portion of the femur or sometimes the proximal part of the tibia. The medial side of the knee is typically affected in spontaneous osteonecrosis about the knee.

Wilsons disease is associated with abnormality of the patellofemoral compartment. In alkaptonuria, changes resemble those of osteoarthritis. Considerable bone collapse and fragmentation may be evident.

Other abnormal conditions of the knee include joint effusion, haemarthrosis, lipohaemarthrosis, synovitis, synovial plicae, synovial and ganglion cysts, tumours and tumour-like lesions.

DR

DR