Anatomical Variations of the Extrinsic Musculature of Thumb

Abstract

Anatomical variations are commonly encountered during human cadaver dissections. Some of these variations are never discovered unless there is an underlying injury that requires attention. For conceivable clinical and rehabilitation treatments, anatomical modifications may have implications on function therefore it is imperative to report them. This case series depicts the anatomical inconsistency in the muscles and tendons of the extrinsic musculature of the thumb in three human specimens. During a cadaver dissection in physical therapy anatomy course, various anatomical variations were found in three human cadaveric specimens. Cadaver 1 (91- year-old Caucasian female) exhibited a new muscle with a split tendon near the distal posterolateral radius. The author uncovered the supplementary muscle between the Extensor Pollicis Longus (EPL) and Extensor Pollicis Brevis muscles. Cadaver 2 (56-year-old Caucasian male) had two other extrinsic tendons inserted at the thumb. The Extensor Digitorum provided an extra tendon to the pollicis; a similar insertion as the EPL was recognised. In Cadaver 3 (77-year-old Caucasian male) an extra muscle belly was observed within the tendon of the abductor pollicis longus. The other muscle variation was near the distolateral attachment at the base of the first metacarpal joint, between the abductor pollicis brevis and extensor carpi radialis muscles. Understanding the diverse anatomical arrangements could prove beneficial for surgeons and those involved in rehabilitating upper extremities. A detailed understanding of the forearm structural anatomy and anomalies is essential to comprehend the function and movements when lesions affect the normal biomechanics within teaching and clinical environments.

Keywords

• extra thumb tendon
• forearm anatomical variations
• forearm extra muscles