Biomechanical modeling of finger flexion based on imaging data: Implications on trigger finger surgery

The risk of bowstringing increases significantly after an excessive release of the A2 pulley in patients with trigger finger. However, the safe extent of this release has not yet been determined. Using a biomechanical model of finger flexion, we examined tendon excursion efficiency and moment arms relative to finger joints. This analysis allowed us to determine the safe extent of A2 pulley release.

Computed tomography and magnetic resonance imaging data of eight subjects were used for the modeling. We simulated the incremental release of the A1 and A2 pulleys and compared moment at the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints for each degree of the release. In addition, we calculated the excursion length of the flexor digitorum profundus (FDP) necessary for achieving maximum PIP joint flexion.

With respect to the MCP joint, the moment arm remained unchanged throughout the pulley release. However, with respect to the PIP joint, the moment arm increased significantly when the release reached the proximal half of the A2 pulley. For maximum PIP joint flexion, a significantly larger FDP excursion was required when half of the A2 pulley was released than in the intact finger (26.6 mm vs. 16.3 mm).

Our imaging-based biomechanical model of finger flexion effectively evaluated tendon excursion efficiency and moment arms with respect to the MCP and PIP joints according to the precise level of pulley release. The model demonstrated that extending the release up to the proximal half of the A2 pulley increases the risk of bowstringing. This imaging-based biomechanical modeling may be applied to predict tendon excursion efficiency after various hand surgeries.