Biomechanical study of the abductor pollicis longus & extensor pollicis brevis after release and reconstruction of the first dorsal compartment of the wrist()

BACKGROUND: The purpose of this study was to determine the biomechanical changes after first dorsal compartment release and after Z-plasty of the first dorsal compartment with respect to the excursion and displacement of the abductor pollicis longus and extensor pollicis brevis tendons. MATERIALS AND METHODS: Six fresh frozen cadaveric hand and forearms were obtained and the tendons of the abductor were exposed and separated from surrounding tissues through a palmar incision and tenotomized at the musculotendinous junction. The excursion and displacement of the abductor pollicis brevis and flexor pollicis brevis tendons were measured for all six cadaveric hands. RESULTS: Increases in tendon excursion were observed in both the abductor pollicis longus (29%) and extensor pollicis brevis (30%) while these observations after Z-plasty were 0.04% for abductor pollicis longus and 0.07% for extensor pollicis brevis. With the use of the modified Elftman curve for the Lengths, tension relationship and Brand's data for resting fiber length we found that 1 cm increase of The excursion of the APL and EPB will decrease tension %65 and %80 respectively. There was also a 12.2-mm displacement of the tendons after release and 4.8 mm displacement after z-plasty of the compartment. CONCLUSION: It seems that Procedures such as enlargement plasty of Kapandji or Z-plasty will increase the size of the compartment but will not change the biomechanical behaviors of the tendons significantly.