Interphalangeal joint thumb
by Nathan Wei, MD, FACP, FACR
Nathan Wei is a nationally known board-certified rheumatologist and author of the Second Opinion Arthritis Treatment Kit. It's available exclusively at this website... not available in stores.
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The thumb consists of three bones: the first metacarpal, proximal phalanx, and the distal phalanx.
The joint that joins the distal phalanx to the proximal phalanx is called the interphalangeal joint (IP)and the joint that joins the proximal phalanx to the metacarpal bone is called the first metacarpophalangeal joint (MCP).
Both IP and MCP joints are hinge joints which means they allow flexion and extension. They are stabilized by ligaments.
The interphalangeal joint has muscle attachments for 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 arthritic conditions.
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). Soft tissue swelling, bone loss, narrowing of the joint space due to cartilage loss, and bony erosions may be seen.
In psoriatic arthritis, there is destructive arthritis of the joints of the hand. Erosions are noted at the margins of the joint and severe abnormalities may be seen involving the interphalangeal joint of the thumb.
Osteoarthritis of distal and proximal interphalangeal joints of the hand is extremely common, particularly in middle-aged, postmenopausal women. Enlargements of bone called Heberdens nodes and Bouchards nodes are typical. Mucoid cysts may appear on the involved interphalangeal joints. X-rays reveal bone spurs and joint space narrowing.
A form of interphalangeal joint osteoarthritis characterized by acute inflammatory episodes with eventual fusion 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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