Title:
Changes in shape and length of the collateral and accessory collateral ligaments of the metacarpophalangeal joint during flexion.

Abstract:
Although the collateral and accessory collateral ligaments of the metacarpophalangeal joint contribute to the stability of this joint, the functional role of the various portions of these ligaments during flexion is unclear. We investigated changes in the three-dimensional shape and length of the collateral and accessory collateral ligaments during flexion to determine how each portion stabilized the metacarpophalangeal joint.
Twelve fingers from three embalmed cadavers were examined. The origin and the insertion point of the dorsal, middle, and volar portions of the radial and the ulnar collateral ligament and of the radial and the ulnar accessory collateral ligament were precisely identified. Microcomputed tomograms were obtained at 10° intervals during passive flexion from 0° to 80°. We created three-dimensional models of the metacarpal, the proximal phalange, and the paths of the twelve ligament portions. Finally, we calculated the change in the shape and length of the path of each ligament portion during flexion.
The region of contact between each collateral ligament and the lateral edge of the metacarpal gradually lengthened during flexion of the joint, and the ligament gradually stretched to pass around the convex radial or ulnar surface of the metacarpal head. In contrast, each accessory collateral ligament curved around the volar tubercle of the metacarpal head at all flexion angles. The length of the volar portion of each collateral ligament and the length of the dorsal and middle portions of each accessory collateral ligament underwent little change during flexion. However, the lengths of the dorsal and middle portions of each collateral ligament increased significantly during flexion, and the length of the volar portion of each accessory collateral ligament decreased significantly.
The collateral and accessory collateral ligaments can each be functionally divided into three portions-dorsal, middle, and volar. The volar portion of each collateral ligament and the dorsal and middle portions of each accessory collateral ligament are nearly isometric, the dorsal and middle portions of each collateral ligament become taut only in flexion, and the volar portion of each accessory collateral ligament becomes taut only in extension.