Musculoskeletal ImagingOsteophyte
an outgrowth or excrescence of a bone. Osteophytes occur in innumerable musculoskeletal disorders (as for example
acromegaly,
neuropathic osteoarthropathy,
macrodystrophia lipomatosa progressiva,
Wilsons disease,
diffuse idiopathic skeletal hyperostosis DISH and crystal-induced arthropathies, among other conditions).
In osteoarthritis osteophytes are characteristic, and several types are recognized (Table 1). They develop in areas of a joint that are subjected to low stress.
Osteophyte, Table 1. Type of osteophytes in osteoarthritis.
| Type | Mechanism | Radiographic appearance |
|---|
| Marginal osteophyte | Endochondral ossification due to vascularizatoin of subchondral bone marrow | Outgrowth at the margins (nonpressure segments) of the joint producing lips of bone |
| Central osteophyte | Encochondral ossification due to vascularization of subchonddral bone marrow) | Outgrowth at the central areas of the joint producing bumpy contour |
| Periosteal (synovial) osteophyte | Intramembranous type of ossification due to stimulation of periosteal (synovial) membrane with appositional bone formation | Thickening of intraarticular "cortices" producing buttressing |
| Capsular osteophyte | Capsular traction | Lips of bone extending along the direction of capsular pull |
In degenerative disease of the spine, spinal outgrowths due to hyperostosis may occur at the attachment site of fibres of the anulus fibrosus. In spondylosis deformans, they appear as triangular outgrowths located several millimetres from the edge of the vertebral body (see spondylosis deformans (III:1), Fig. 1). Claw osteophytes and traction spurs occur in the spine and frequently cannot be differentiated.
Distinctive hook-like or beak-like osteophytes are observed in the metacarpal heads in haemochromatosis. See haemochromatosis (III:1), Fig. 1.
The acromioclavicular joint may also develop bone outgrowths (i.e. enthesophytes) as an unusual and distinct form of shoulder impingement syndrome; in addition, the clavicle may exhibit excrescences in osteitis condensans of the clavicle and the nasal bone after isotretinoin therapy.
Osteophytes about the hip may be distinguished according to location: in ankylosing spondylitis they occur on the lateral aspect of the femur and form a collar at the femoral head-femoral neck junction; osteophytes are rare in rheumatoid arthritis; and in both osteoarthritis and calcium pyrophosphate dihydrate crystal deposition disease osteophytes occur at the lateral and medial aspects of the femur and may be both femoral and acetabular.
DR