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Editor’s Note: This case has been modified from a previous version, which incorrectly identified the dislocation at the carpometacarpal joint.
A 62-year-old woman presents with left thumb pain and deformity that seem to have progressed over the past several months. She denies recent injury or fall. Medical history is significant for metacarpophalangeal (MCP) joint synovitis secondary to rheumatoid arthritis. In the past, rest, bracing, and steroid injections have provided short-term relief. On physical examination, the patient has an obvious deformity of the first MCP joint with limited motion. Anteroposterior radiograph taken in the office shows an MCP joint dislocation (Figure).
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Rheumatoid arthritis causes laxity of the capsular ligaments of the MCP joint, which may result in structural instability and joint impairment. Chronic laxity can cause progressive dislocation of the MCP joint, which results in dysfunction of the thumb; this is usually identified when the patient has trouble pinching or grasping objects. Rheumatoid arthritis of the MCP joint also contributes to rupture of the extensor pollicis brevis tendon from its attachment on the base of the proximal phalanx; this can also cause progressive deformity of the thumb. Patients with rheumatoid arthritis will often have palmar subluxation and ulnar deviation at the MCP joints. Capsular destruction from rheumatoid arthritis also causes dorsal subluxation of the metacarpal base and hyperextension of the MCP joint (swan neck deformity). Patients with early rheumatoid arthritis with good motion and stability are candidates for synovectomy and dorsal hood reconstruction. Patients with a chronically dislocated, unstable MCP joint are best suited for a joint arthrodesis.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
References
- Goldfarb CA, Stern PJ. Metacarpophalangeal joint arthroplasty in rheumatoid arthritis: a long-term assessment. J Bone Joint Surg Am. 2003;85(10):1869-1878.
- Moore D. Rheumatoid arthritis. Available at: https://www.orthobullets.com/basic-science/9085/rheumatoid-arthritis. Accessed September 18, 2018.
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