PURPOSE

To analyze the anatomy and contribution of the oblique retinacular ligament (ORL) to distal interphalangeal (DIP) joint extension force with varying angles of proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joint flexion.

METHODS

Forty fresh-frozen fingers were dissected. The fingers were mounted in a custom jig, and the force required to flex the DIP joint was assessed with the PIP joint flexed 0°, 30°, 60°, and 90° and with the MCP joint flexed 0°, 45°, and 90°. The force was measured in the intact specimen, and then all measurements were repeated following sectioning of the ORL and then the central slip.

RESULTS

The ORL was present on the radial and ulnar aspects of all but 2 fingers. The ORL tended to be the most robust in the ring finger. In the intact specimen, DIP flexion resistance force was maximum at 30° of PIP joint flexion and minimum at 90° of PIP joint flexion. There was a significant difference between the 90° position and all other positions of the PIP joint with respect to flexion force in the intact specimen. This meant that less force was required to flex the DIP joint at 90° of PIP joint flexion. Sectioning of the ORL revealed that it contributed 25% to the total force required to flex the DIP joint with the PIP joint at 0°, 31% at 30°, 18% at 60°, and 3% at 90° of flexion. The MCP joint position had no effect. Sectioning the central slip produced a significant increase in force required to flex the DIP joint at 90° of PIP joint flexion.

CONCLUSIONS

In this study, the ORL was usually present, and it contributed up to 30% of the passive resistance to DIP joint flexion. The intact central slip accounted for the decrease in DIP joint extensor tone at 90° of PIP joint flexion.

CLINICAL RELEVANCE

The ORL plays a small role in passively resisting DIP flexion.