Relative Motion Extension Splint for Treatment of Flexor Tendon Adhesions: Proof of Concept

Background: Incorporating relative motion extension splints (RMES) during active range of motion (AROM) exercises positions flexor tendons in relative extension, increasing tendon excursion during flexion. Enhanced excursion and differential glide between the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) tendons may facilitate adhesion lysis. Methods: A frozen cadaveric upper extremity was dissected to expose the middle-finger FDS and FDP tendons with associated pulleys. Relative tendon positions were marked with sutures at levels IIA, IIB, and IIC. Differential glide was measured under 6 conditions: isolated FDS motion with and without RMES, isolated FDP motion with and without RMES, and nonisolated FDP motion with and without RMES. After each condition, distances between markers were recorded to quantify tendon glide. A paired t-test statistical analysis was conducted. Results: RMES during isolated FDS motion increased glide at IIA and IIB (0-1 mm to 3 mm), while IIC was unchanged (3 mm). RMES during isolated FDP motion increased glide only at IIC (4 mm to 6 mm), with no change at IIA (3 mm) or IIB (4 mm). Relative motion extension splints during nonisolated FDP motion increased glide across all zones: IIA (4-7 mm), IIB (8-10 mm), and IIC (11-13 mm). The use of RMES resulted in a statistically significant increase in differential glide compared to the unsplinted condition (mean difference = 1.55; paired t-test, P = .005). Conclusions: This study demonstrates that RMES increase tendon excursion and FDS-FDP differential glide during AROM. Importantly, the effects were not uniform across zone II, suggesting regional variability in susceptibility to adhesion formation and therapy resistance. These findings support the use of RMES to enhance tendon motion and potentially improve outcomes following flexor tendon repair.