Morphological and topographic anatomy of sesamoid bones of human thumb

Background. The objective of the present study was to study the morphology and topography of the sesamoid bones of the thumb in a sample south Indian population. Methods. The present study included 25 formalin fixed human cadaveric thumbs, the metacarpo-phalangeal and inter-phalangeal joints of the thumb were dissected. The number of sesamoid bones and the intrinsic muscles containing them were identified. The mean length, breadth and thickness of the sesamoid bones were measured before their removal from thumb by using the digital Vernier caliper. Results. In 92% of cases, there were two sesamoid bones, observed at the metacar-po-phalangeal joint. The medial sesamoid bone was found inside the adductor pollicis muscle and lateral one was found either in the flexor pollicis brevis muscle (64%) or abductor pollicis brevis muscle (28%). The interphalangeal joint of the thumb in 96% of cases exhibited one sesamoid bone in its median plane, which was within the flexor pollicis longus tendon. The microscopic study confirmed the presence of only bone in all the sections. The mean length, width and thickness of the sesamoid bones at the metacarpo-phalangeal and inter-phalangeal joints of the thumb were 3 ± 0.9 mm, 6.2 ± 1.2 mm, 4.8 ± 0.8 mm, 2.7 ± 0.8 mm, 6.4 ± 1.3 mm and 4.7 ± 0.6 mm respectively. Conclusions. The present study has provided the morphometric data of the sesamoid bones and their topographical distribution in the intrinsic muscles of thumb. The data of the present study have implications in plastic surgery and will aid the operating hand surgeon and radiologist.