Interphalangeal joint thumb
Both joints are hinge joints. They allow flexion and extension. They are stabilized by strong ligaments. The interphalangeal joint has muscle attachments through the flexor pollicis longus and the extensor pollicis longus. The first metacarpophalangeal joint has muscle attachments for the extensor pollicis brevis, abductor pollicis brevis, flexor pollicis brevis, and the adductor pollicis.
The interphalangeal joints may be affected in a number of musculoskeletal conditions; some disorders show specific involvement of either the proximal or the distal joints. In rheumatoid arthritis, abnormalities may include swan neck deformity (hyperextension at proximal interphalangeal joints and flexion at distal interphalangeal joints), boutonniere deformity (flexion at proximal interphalangeal joints and hyperextension at distal interphalangeal joints) and hitchhikers thumb or Z-shaped deformity of the thumb (flexion at the metacarpophalangeal joint and hyperextension at the interphalangeal joint). Fusiform soft tissue swelling, periarticular osteoporosis, concentric loss of articular space and marginal erosions may become evident at all the proximal interphalangeal and metacarpophalangeal joints. In psoriatic arthritis the best-known manifestation is the destructive arthritis of distal interphalangeal joints of the hand. Initial erosions occur at the margins of the joint and proceed centrally, resulting in separation of the bone surfaces from each other. Adjacent proximal interphalangeal joints are frequently affected, and severe abnormalities may be encountered at the interphalangeal joint of the thumb. At any altered interphalangeal site, radiographic findings may include separated and eroded, well-demarcated bone margins, pencil and cup appearance, whiskering and intra-articular bone fusion. Resorption of phalangeal tufts can also be evident in one or more terminal phalanges. Osteoarthritis of distal and proximal interphalangeal joints of the hand is extremely common, particularly in middle-aged, postmenopausal women. Enlargements of bone termed Heberdens nodes and Bouchards nodes are typical. Small mucous cysts of the soft tissues may appear on the dorsal aspects of involved interphalangeal joints. Radiographs reveal prominent osteophytes and joint space narrowing. The osteophytes may extend proximally, resembling the wings of a seagull (seagull sign). A peculiar form of interphalangeal joint osteoarthritis characterized by acute inflammatory episodes with eventual ankylosis of some joints has been described (erosive osteoarthritis). While dislocation of these joints is unusual, it has been reported. (Mohan BV, Kishan SS, Munshi PP, Pathak RH, Pandit HH. Irreducible dislocation of the interphalangeal joint of the thumb. J Postgrad Med [serial online] 1996 [cited 2004 Nov 20 ];42:30-1. Available from: http://www.jpgmonline.com/article.asp?issn=0022-3859;year=1996;volume=42;issue=1;spage=30;epage=1;aulast=Mohan)
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