an abnormality involving an attachment of a tendon
to bone (enthesis
Inflammatory abnormalities of entheses are prominent findings in seronegative spondyloarthopathies (ankylosing spondylitis, Reiters syndrome, psoriatic arthritis) and may also be present to a lesser extent in rheumatoid arthritis. Frequently oedema, erosion and proliferation of adjacent bones, reactive sclerosis, syndesmophyte formation, and bone eburnation are seen. On radiographs the bones may have a frayed, irregular surface or a fluffy appearance. In the seronegative spondyloarthropathies, the manubriosternal joint, symphysis pubis, discovertebral joints, plantar aspect of the calcaneus, pelvis, patella, iliac crest, ischial and humeral tuberosities and femoral trochanters may be affected. Progressive fibrosis, trabecular thickening and intra-articular ossification may occur in cartilaginous joints. In the discovertebral joints, "osteitis" and syndesmophyte formation may be noted. In rheumatoid arthritis, the entheses on the spinous processes of the vertebrae, inferior surface of the calcaneus, iliac wings, ischial tuberosities and femoral trochanters may be involved. In the spine, synovial inflammation may occur in interspinous bursae.
Degenerative disorders also produce enthesopathies. Fibrous degeneration and bone proliferation are seen, leading to radiographically detectable excrescences on the ischial tuberosity and trochanters and enthesophytes on the calcaneus, ulnar olecranon and patella. Sacrospinous and sacrotuberous ligaments may also reveal calcification or ossification (Fig.1).
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Lateral radiograph of the heel demonstrates ossification in the Achilles tendon and plantar fascia at the posterior and plantar aspect of the calcaneus, respectively.