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The pisiform is a sesamoid bone, with no covering membrane of periosteum. It is the last carpal bone to ossify. The pisiform bone is a small bone found in the proximal row of the wrist . It is situated where the ulna joins the wrist, within the tendon of the flexor carpi ulnaris muscle. [1]: 199, 205
The pisiform bone is somewhat unusual, in that it first appears in primitive reptiles, and is never found in amphibians. Because many tetrapods have fewer than five digits on the forelimb, even greater degrees of fusion are common, and a huge array of different possible combinations are found.
The articular capsule is a thin membrane which connects the pisiform to the triangular; it is lined by synovial membrane. The two volar ligaments are strong fibrous bands; one, the pisohamate ligament, connects the pisiform to the hamate, the other, the pisometacarpal ligament, joins the pisiform to the base of the fifth metacarpal bone. These ...
Ulnar nerve enters the palm of the hand via the Guyon's canal, superficial to the flexor retinaculum and lateral to the pisiform bone. [7] Here it gives off the following branches: [8] Superficial branch of ulnar nerve - supplies the palmaris brevis and gives digital branches to the medial one and a half fingers. [7]
Some reliable sesamoid bones such as the pisiform are counted, while others, such as the hallux sesamoids, are not. Individuals may have more or fewer bones than the average (even accounting for developmental stage) owing to anatomical variations.
On the ulnar side, the flexor retinaculum attaches to the pisiform bone and the hook of the hamate bone. On the radial side, it attaches to the tubercle of the scaphoid bone, and to the medial part of the palmar surface and the ridge of the trapezium bone.
The hamate is an irregularly shaped carpal bone found within the hand. The hamate is found within the distal row of carpal bones, and abuts the metacarpals of the little finger and ring finger. [4]: 708–709 Adjacent to the hamate on the ulnar side, and slightly above it, is the pisiform bone.
Volar surface showing its insertion into the pisiform bone and then via ligaments into the hamate bone and 5th metacarpal bone, acting to flex and adduct the wrist joint. Cross-section through the middle of the forearm.