Each finger except the thumb consists of three bones – the proximal, middle, and distal phalanx. The thumb has only two phalanges – the proximal and the distal.
Sesamoid bones (ossa sesamoidea) seen on both previous pictures are the rounded bones embedded in the muscle's tendons to protect them from excessive friction and redirect the tendon's attachment vector, so the muscle action is more effective1. These bones are almost invariably present in front of the first metacarpophalangeal joint. They are also frequently observed in front of the fifth metacarpophalangeal joint and the thumb's interphalangeal joint.2
1 Amar E, Rozenblat Y, Chechik O. Sesamoid and accessory bones of the hand--an epidemiologic survey in a Mediterranean population. Clin Anat. 2011;24(2):183-187. doi:10.1002/ca.21077.
2 Yammine K. The prevalence of the sesamoid bones of the hand: a systematic review and meta-analysis. Clin Anat. 2014;27(8):1291-1303.
360° rotation of the hand bones
First published: 12/10/2020