Rheumatoid and seronegative arthropathies of the foot

The foot may be involved with rheumatoid arthritis and its seronegative variants, manifesting many radiographic features common to these arthritides. However, the pattern of joint involvement in the foot and elsewhere in the skeleton, presence or absence of osteoporosis, symmetrical or asymmetrical involvement, bony proliferation or lack of it, and the involvement of the calcaneus are important distinguishing features. Resnick and coworkers have described five target sites of involvement in the calcaneus in these arthropathies: (1) superior surface, (2) posterior surface above the Achilles tendon attachment, (3) posterior surface at the insertion of the Achilles tendon, (4) plantar surface at the attachment of the plantar fascia, and (5) plantar surface anterior to the plantar fascia insertion. In rheumatoid arthritis, calcaneal abnormalities occur predominantly at sites 1 to 4. In psoriatic arthritis and ankylosing spondylitis, sites 2 to 5 are most often involved. In Reiter's syndrome, the calcaneus shows most abnormalities at sites 1, 2 and 4. Awareness of these and other radiographic features of the arthropathies in the foot is essential for proper diagnosis.