Effect of Edema on Flexor Tendon Tensile Forces Following Zone II Repair: A Biomechanical Analysis in a Cadaveric Model.

Abstract

The effect of digital edema on tensile forces in zone II flexor tendon injuries has not been extensively investigated. The purpose of this study was to examine the effect of digital edema on flexor tensile forces following six-strand repair of a zone II flexor tendon laceration and to assess how these forces change throughout the total arc of motion. Eight cadaveric upper extremities were used in the study. All specimens were placed in a dorsal blocking splint with the wrist in neutral and metacarpophalangeal joints at 45° of flexion. Continuous force-displacement curves were generated for the following experimental conditions: at baseline; following zone II flexor digitorum profundus six-strand repair, with mild, moderate, and severe edema; and with self-adherent wrap in place. The force required to produce 3 millimeters of tendon gap was measured as the load to failure in this model. A linear mixed effect model was used to evaluate differences in average flexion force among experimental groups. The average peak force to achieve 270° of flexion for each experimental condition was 10.3 N, 16.1 N, 21.4 N, 28.1 N, 34.3 N, and 47.5 N. The average load to failure was 44.6 N. Digital flexion forces increased nonlinearly throughout the arc of motion. At 180°, moderate edema, severe edema, and self-adherent wrap resulted in significantly increased tensile forces compared to the control and postrepair measurements. Flexion forces increase exponentially throughout the arc of motion and increase significantly with moderate and severe edema beyond 180° in this model. In the setting of moderate to severe edema, active flexion should be limited to the first half of the arc of motion. This is a biomechanical study that quantifies the effect of edema and self-adherent wrap on flexor tendon tensile forces throughout the arc of motion. The patient and therapist should be aware of this kinetic pattern to avoid complications after surgery.