Biomechanical stability of abductor pollicis longus muscles with variable numbers of tendinous insertions

Background In the course of a study of different variants of the tendon of the abductor pollicis longus (APL) muscle, the unusual finding of a tendon with six subdivisions was observed in the first compartment. Using this preparation and others with various numbers of tendons (2, 3, 4, and 6), we intended to establish whether the multitendoned muscles increased the strength of the thumb. Methods Fifty‐two upper extremities were examined with attention to the tendons of the APL muscle. The strain on each tendon was biomechanically determined using a microcomputer and potentiometer. The stress was measured continuously and plotted against strain. Results Following treatment with elastase, it is seen that the significance of changes in stability and Young's modulus is inversely proportional to the number of tendons arising from the APL. Conclusions Division of the tendon into several parts leads to better mechanical distribution of stress and extension on thumb abduction. In addition, palmar‐flexion in the wrist may be supported. Anat. Rec. 250:475–479, 1998. © 1998 Wiley‐Liss, Inc.