Proximity of collateral ligament origin to the axis of rotation of the proximal interphalangeal joint of the finger.

Study Design: Descriptive anatomical study.

Objective: To determine the proximity of proximal interphalangeal (PIP) joint collateral ligament origin to the axis of rotation (AOR) of the joint.

Background: Normal function of the PIP joints of the hands requires competent collateral ligaments. Studies of the collateral ligaments of the PIP joint have led to a hypothesis that the collateral ligaments of the PIP joints originate at the joint AOR. However, no studies have yet provided quantitative evidence to support this assertion.

Methods And Measures: A total of 30 collateral ligament specimens were prepared from the radial and ulnar halves of 16 fingers (digits 2 through 5) from the right hands of 5 formalin-embalmed cadavers. A geometric method was employed to estimate the PIP joint AOR. The proximity of collateral ligament origins to the estimated AOR of the PIP joint was determined.

Results: Collateral ligaments were found to have their proximal attachment an average of 0.02 mm distal and 0.24 mm palmar to the PIP joint AOR. For 90% of specimens the center of the collateral ligament origin was within 1.00 mm of the joint AOR.

Conclusions: These results support the hypothesis that PIP joint collateral ligaments originate at the joint AOR. This finding predicts that the linear distance between the attachments should remain constant as the PIP joint moves through its range of motion. The modest changes in PIP collateral ligament length described in other studies can be attributed primarily to travel of the ligament across a small condylar tubercle at approximately 15 degrees to 20degrees of PIP joint flexion. The practice of immobilizing the PIP joint in 15degreesto 20" egreesof flexion is supported by these findings. J O rthop