Background: The purpose of this study was to evaluate the effect of flexor retinaculum division (simulated carpal tunnel release) on the relative motion of flexor tendon, subsynovial connective tissue, and median nerve in human cadaver specimens.
Methods: Using fluoroscopy, we measured the relative motion of middle finger flexor digitorum superficialis tendon, subsynovial connective tissue, and median nerve in twelve human cadavers with simulated fist motion. Measurements were obtained for three wrist positions: neutral; 60 degrees flexion; and 60 degrees extension. The shear index was defined as the difference in motion between two tissues (tendon, subsynovial connective tissue, or nerve) relative to tendon excursion, expressed as a percentage. After testing with an intact carpal tunnel, the flexor retinaculum was cut and the testing procedure was repeated.
Findings: With an intact flexor retinaculum, the wrist flexion position showed significantly less displacement for the subsynovial connective tissue and median nerve relative to tendon displacement, and thus the highest potential shear strain between subsynovial connective tissue-tendon, and tendon-nerve. The wrist extension position also had a significantly higher potential shear strain for tendon-nerve compared to the neutral position. After division of the flexor retinaculum, the differences in shear index among wrist positions were reduced. For the wrist flexion position, the subsynovial connective tissue and median nerve displacements significantly increased, indicating lower shear index values.
Interpretation: These findings suggest that division of flexor retinaculum reduces the potential shear strain and thus possibly the risk of shear injury to tissues with the carpal tunnel.