title: When does subluxation of the first carpometacarpal joint cause swan-neck deformity of the thumb in rheumatoid arthritis: a 20-year follow-up study.
abstract: The aim of our study was to assess the incidence of subluxation of the first carpometacarpal joint (CMC I) and to evaluate which degree of subluxation produces swan-neck deformity of the thumb in rheumatoid arthritis (RA) occurring over 20 years. The hands of 83 rheumatoid factor (RF)-positive RA patients with recent (< or = 6 months) arthritis were evaluated radiographically at onset and at 1, 3, 8 and 15 years; 68 patients were evaluated at 20 years from entry. Subluxation was assessed in millimetres and compared with the MCP-I angle measurement to evaluate the thumb deformity. A statistical end-point analysis was performed between two different grades of subluxation. Subluxation of 2-3 mm was non-specific and only one third of these thumbs showed swan-neck deformity. At the end-point, subluxation of > or = 4mm was present in 17% of the thumbs, 81% of which had the swan-neck deformity; only five thumbs did not show this deformity, but presented deformed and unstable MCP I and interphalangeal joints. The frequency of swan-neck deformity was highly significantly (p < 0.0001) increased in the thumbs with severe CMC I subluxation (> or = 4 mm) compared with lesser subluxation (< 4 mm). When subluxation of the CMC I exceeds 4 mm, the swan-neck deformity of the thumb is a common consequence. This deformity is often progressive, and the hand function of such patients should be followed up carefully, both clinically and radiographically.
authors.affiliation: Rheumatism Foundation Hospital, Heinola, Finland.
authors.forename: E
authors.initials: E
authors.lastname: Belt
authors.forename: K
authors.initials: K
authors.lastname: Kaarela
authors.forename: J
authors.initials: J
authors.lastname: Lehtinen
authors.forename: H
authors.initials: H
authors.lastname: Kautiainen
authors.forename: M
authors.initials: M
authors.lastname: Kauppi
authors.forename: M U
authors.initials: MU
authors.lastname: Lehto
mesh_terms: D000328:Adult; D001172:Arthritis, Rheumatoid / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D004204:Joint Dislocations / Q000150:complications* / Q000000981:diagnostic imaging; D008297:Male; D011859:Radiography; D013933:Thumb / Q000000981:diagnostic imaging / Q000473:pathology*; D014955:Wrist Joint / Q000000981:diagnostic imaging / Q000473:pathology*