A biomechanical modeling of injury, repair, and rehabilitation of ulnar collateral ligament injuries of the thumb

Purpose: The use of early active motion protocols after repair of the thumb ulnar collateral ligament (UCL) theoretically could avoid the complications of postoperative immobilization and improve ligament healing. The goals of this study were as follows: (1) to develop an accurate model of acute UCL rupture, (2) to determine the strain pattern in the UCL during constrained active thumb motion in intact and repaired thumbs, and (3) to determine the load to failure and strain of the UCL during rupture in forced abduction.

Methods: Sixteen fresh-frozen adult cadaver thumbs were mounted in a testing apparatus designed for testing the strain in the UCL during constrained active motion and abduction load to failure. Strain data for the UCL during motion were measured. Specimens were tested to failure using an MTS machine. Dynamic strain data were acquired throughout the loading cycle. Repair of the torn ligament was performed with a suture anchor technique. Strain and load-to-failure measurements then were repeated in the repaired specimens. Differences in the strain values and failure forces between the intact and repaired specimens then were compared.

Results: A reliable model of a UCL rupture was created. Strains in the UCL were similar during active motion in both intact and repaired specimens. A significant decrease in maximum load to failure was noted in repaired specimens but failure reliably occurred at strains 3 times greater than expected with active motion.

Conclusions: A controlled active motion therapy protocol after suture anchor repair of a ruptured UCL of the thumb is safe from a biomechanical point of view.