The intercarpal joints

The carpal bones are arranged in two transverse rows between which is the important midcarpal joint. For the majority, the joints between the adjacent individual carpal bones are of the plane synovial type, permitting only slight movement between the bones involved. The only bone which moves appreciably is the capitate.

Joints of the proximal row

Plane synovial joints exist between the distal parts of the adjacent surfaces of the scaphoid, lunate and triquetral. However, because these bones are bound together by interosseus, dorsal and palmar intercarpal ligaments there is minimal movement between them.

The interosseus intercarpal ligaments are short bands attaching to the margins of the joint surfaces involved in the radiocarpal articulation. They unite the bones along their whole anteroposterior length. The palmar and dorsal intercarpal ligaments are transverse bands passing from scaphoid to lunate and from lunate to triquetral on the anterior and posterior aspects of the bones respectively.

The pisiform rests on the palmar surface of the triquetral and has a separate synovial joint with it, which is completely enclosed by a thin but strong fibrous capsule. The pisiform is also anchored to the hook of the hamate by the pisohamate ligament, and to the base of the fifth metacarpal by the pisometacarpal ligament. These two ligaments resist the pull of flexor carpi ulnaris, and transfer its action to the hamate and base of the fifth metacarapal. In this way these ligaments form extensions of the muscle.

Joints of the distal row

As in the proximal row, the four bones of the distal row are united by interosseus, palmar and dorsal intercarpal ligaments, with the joints between the individual bones being of the plane synovial type. Because of these ligaments, movements between adjacent bones is minimal.

The interosseus ligaments are not as extensive as in the proximal row, leaving clefts between the bones which communicate with the midcarpal joint proximally, and with the common carpometacarpal joint distally. Occassionally, the midcarpal and carpometacarpal joints communicate with each other between the bones of the distal row. This occurs when one of the interosseus ligaments is incomplete so that communication is around the borders of the ligament, or when one ligament is absent(most commonly that between the trapezium and trapezoid). Dorsal and palmar ligaments generally run transversely across the appropriate surfaces of the bones, uniting trapezium to trapezoid, trapezoid to capitate, and capitate to hamate.