Carpal Kinematics Study
This study investigates the effects of the FCR and STIL division on scaphoid and lunate motion in a cadaveric wrist model. Eight fresh frozen cadaver wrist forearms were selected after exclusion of significant degenerative changes and scapholunate injury. The radius and ulna were transfixed with a Steinmann pins in neutral forearm rotation and the fingers were disarticulated at the metacarpophalangeal joint. A 250g load was applied to the ECRL, ECRB, APL, ECU, FCR, and FCU to simulate normal compression across the wrist due to muscle tone. A magnetic tracking device was used to record the kinematics of the scaphoid, lunate, and the 3rd metacarpal shaft. Kinematic data was collected during flexion, extension, radial and ulnar deviation. Specimens were tested under the following conditions: 1) ligaments intact, 2) SLIL cut, 3) FCR cut, 4) FCR unloaded, 5) STIL cut and FCR unloaded. With STIL division there was a small but appreciable increase in scaphoid extension and radial deviation throughout the flexion and extension arc and with radial and ulnar deviation. With the STIL cut and FCR unloaded the scaphoid assumed an average of 3° of extension and 1° of radial deviation in comparison to the intact specimens. The results of this study suggest that the SLIL helps maintain scaphoid flexion. In addition, unloading or removing the FCR tendon from its insertion or attachment at the scaphoid moves the scaphoid into an extension position. This suggests that the flexion moment exerted by the FCR, both through its attachment to the scaphoid and through its wrapping around the scaphoid, may be important for maintaining the scaphoid position.
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