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A 53 year old man had a long history of rheumatoid arthritis (RA) necessitating hip, knee and elbow replacements. Hand deformity and pain progressed (right worse), particularly at the metacarpophalangeal (MCP) joints. However, he had congenital short fourth metacarpals and fourth MCP joints which were clinically and radiologically sound. He underwent prosthetic replacements of the right 2nd/3rd/5th MCP joints (fig 1B). A similar picture (preoperative) was seen in the left hand (fig 1A).
Radiographs may underestimate the severity of RA changes, but it is interesting to speculate why an MCP joint of a short metacarpal might be protected against degeneration. There might be an associated MCP joint anomaly, making it less prone to erosive change. However, we suggest that MCP joint biomechanics are important—not only are flexor and extensor functions altered but also the fourth MCP joint is splinted by the neck/head of the 3rd and 5th metacarpals, preventing valgus/varus deviation.
Although RA is appropriately considered an inflammatory condition, these pictures emphasise the importance of mechanical factors in joint failure.
Series editor: Gary D Wright
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