Relative motion between the flexor digitorum superficialis tendon and subsynovial connective tissue is time dependent

Abstract

The subsynovial connective tissue is an integral component of flexor tendon gliding in the carpal tunnel, which is strained during longitudinal tendon displacement. We tested the effects of repetition frequency and finger load on flexor tendon function throughout active finger movement. Eleven participants performed metacarpophalangeal joint flexion/extension of the long finger cyclically at three repetition frequencies (0.75, 1.00, 1.25 Hz) and two finger loads (3.5, 7 N). Relative displacement between the flexor digitorum superficialis tendon and subsynovial connective tissue was assessed as the shear‐strain index with color ultrasound throughout the entire time history of finger flexion and extension. In addition, long finger joint angles were measured with electrogoniometry while flexor digitorum superficialis and extensor digitorum muscle activities were measured with fine‐wire electromyography to characterize the finger movements. The shear‐strain index increased with greater finger flexion (p = 0.001), representing higher relative displacement between tendon and subsynovial connective tissue; however, no changes were observed throughout finger extension. The shear‐strain index also increased with higher repetition frequencies (p = 0.013) and finger loads (p = 0.029), further modulating time‐dependent effects during finger flexion versus extension. Using ultrasound, we characterized the time‐dependent response of the shear‐strain index, in vivo, providing valuable data on flexor tendon function during active finger movement. Our results infer greater subsynovial connective tissue strain and shear during repetitive and forceful finger movements. Future research characterizing time‐dependent effects in carpal tunnel syndrome patients may further elucidate the relations between subsynovial connective tissue function, damage, and carpal tunnel syndrome.

Time‐varying changes in median nerve deformation and position in response to quantified pinch and grip forces

“…32,33 As well, the positional change of the nerve is likely to increase stretching of the adjoining SSCT. 34,35 Accordingly, sustained deformational changes of the nerve during repeated hand force exertions may represent an important pathomechanism in CTS.…”

“…13 Mirrored changes in nerve deformation and displacement may also, in part, reflect strain-related characteristics of adjoining SSCT. 34,35 Future research will aim to determine the contributions of these mechanisms to better understand nerve accommodation in hand force exertion tasks.…”

“…While the nerve's ability to accommodate to changes within the carpal tunnel environment is important, 15,16,20 repeated hand force exertions may cause sustained strain owing to the rearrangement of the nerve's fascicles to facilitate its shape change 32,33 . As well, the positional change of the nerve is likely to increase stretching of the adjoining SSCT 34,35 . Accordingly, sustained deformational changes of the nerve during repeated hand force exertions may represent an important pathomechanism in CTS.…”

“…These changes may represent a reorganization of carpal tunnel structures early in hand force exertion tasks, thereby reducing compressive stress imposed on the nerve 13 . Mirrored changes in nerve deformation and displacement may also, in part, reflect strain‐related characteristics of adjoining SSCT 34,35 . Future research will aim to determine the contributions of these mechanisms to better understand nerve accommodation in hand force exertion tasks.…”