Relative motion between the flexor digitorum superficialis tendon and paratenon in zone V increases with wrist flexion angle

The Median Nerve Displays Adaptive Characteristics When Exposed to Repeated Pinch Grip Efforts of Varying Rates of Force Development: An Ultrasonic Investigation

OBJECTIVES

Repeated gripping with high grip forces and high rates of grip force development are risk factors for carpal tunnel syndrome. As the nerve's adaptive ability is crucial to prevent disease progression, we investigated how these risk factors influence median nerve deformation and displacement over the time course of a repeated pinch grip task.

METHODS

Seventeen healthy participants performed a repeated grip task against a load cell while their carpal tunnel was scanned with ultrasound. The grip task involved pulp-pinching three consecutive times from 0 to 40% maximal voluntary exertion (MVE), performed at three different rates of force development (RFD): 40% MVE/1 second; 2 seconds; and 5 seconds. Ultrasound images were analyzed at 10% MVE intervals. Nerve circularity, width, height, and cross-sectional area were measured to assess deformation. Median nerve displacement was assessed by its change in position relative to the flexor digitorum superficialis tendon of the third digit (FD) in both radioulnar and palmodorsal axes.

RESULTS

Linear mixed modeling indicated that median nerve deformation increased, becoming more circular, with each repeated pulp-pinch (P < .01) and with grip force magnitude (P < .01). However, a faster RFD decreased nerve deformation (P < .01). Furthermore, the nerve displaced ulnarly during pulp-pinching, with greater displacement during the fastest (ie, 40% MVE/1 second) RFD (P < .01).

CONCLUSIONS

The median nerve deformed and displaced in response to pulp-pinching; however, faster rates of force development hindered this adaptive response. This likely reflects the viscoelastic properties of the healthy nerve and subsynovial connective tissue, highlighting the importance of tissue compliance in preventing nerve compression.

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

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.

Carpal tunnel tendon and sub-synovial connective tissue mechanics are affected by reduced venous return

BACKGROUND

The effects of blood flow occlusion and sex-specific differences in tendon-subsynovial connective tissue relative strain are not well understood. Thus, the purpose of this study was to investigate the influence of blood flow, biological sex, and finger movement speed on carpal tunnel tendon mechanics to further develop our understanding of carpal tunnel syndrome.

METHODS

Colour Doppler ultrasound imaging quantified relative motion between flexor digitorum superficialis tendon and subsynovial connective tissue in 20 healthy male and female participants during repetitive finger flexion-extension under brachial occlusion of blood flow and two movement speeds (0.75 & 1.25 Hz).

FINDINGS

Flexor digitorum superficialis and subsynovial connective tissue displacement decreased with occlusion (small effect) and fast speed (large effect). Speed × Condition interactions were found for mean FDS displacement and peak FDS velocity, where slow speed with occlusion reduced both outcomes. Movement speed had a small but significant effect on tendon-subsynovial connective tissue shear outcomes, where MVR decreased with fast finger motion.

INTERPRETATION

These results suggest the influence of localized edema through venous occlusion on tendon-subsynovial connective tissue gliding within the carpal tunnel. This insight further develops our understanding of carpal tunnel syndrome pathophysiology and suggests ramifications on carpal tunnel tissue motion when the local fluid environment of the carpal tunnel is disturbed.

Effects of wrist extension on median nerve and flexor tendon excursions in patients with carpal tunnel syndrome: a case control study

Background

Reduced gliding ability of the median nerve in the carpal tunnel has been observed in patients with carpal tunnel syndrome (CTS). The purpose of this study was to evaluate the gliding abilities of the median nerve and flexor tendon in patients with CTS and healthy participants in the neutral and 30° extended positions of the wrist and to compare the gliding between the finger flexion and extension phases.

Methods

Patients with CTS and healthy participants were consecutively recruited in a community hospital. All the subjects received the Boston CTS questionnaire, physical examinations, nerve conduction study (NCS), and ultrasonography of the upper extremities. Duplex Doppler ultrasonography was performed to evaluate the gliding abilities of the median nerve and flexor tendon when the subjects continuously moved their index finger in the neutral and 30° extension positions of the wrist.

Results

Forty-nine patients with CTS and 48 healthy volunteers were consecutively recruited. Significant differences in the Boston CTS questionnaire, physical examination and NCS results and the cross-sectional area of the median nerve were found between the patients and the healthy controls. The degree of median nerve gliding and the ratio of median nerve excursion to flexor tendon excursion in the CTS group were significantly lower than those in the healthy control group in both the neutral and 30° wrist extension positions. Significantly increased excursion of both the median nerve and flexor tendon from the neutral to the extended positions were found in the CTS group. The ratio of median nerve excursion to flexor tendon excursion was significantly higher in the finger flexion phase than in the extended phase in both groups, and this ratio had mild to moderate correlations with answers on the Boston CTS Questionnaire and with the NCS results.

Conclusions

Reduced excursion of the median nerve was found in the patients with CTS. The ratio of median nerve excursion to flexor tendon excursion was significantly lower in the patients with CTS than in the healthy volunteers. The median nerve excursion was increased while the wrist joint was extended to 30° in the patients with CTS. Wrist extension may be applied as part of the gliding exercise regimen for patients with CTS to improve median nerve mobilization.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04349-8.

External Compression and Partial Ischemia Decrease Human Finger Flexor Tendon and Subsynovial Connective Tissue Relative Motion

Cumulative shear strain of the subsynovial connective tissue (SSCT) surrounding finger flexor tendons plays a significant role in the development and progression of carpal tunnel syndrome. Biomechanical risk factors can alter tendon-SSCT shear strain but the effects of external mechanical compression and localized ischemia have yet to be investigated. In a laboratory study with 19 healthy participants, color Doppler ultrasound imaging was used to quantify relative motion between the flexor digitorum superficialis tendon and SSCT during repetitive finger flexion-extension under various conditions of external mechanical compression (palmar and forearm compression), ischemia and different movement speeds (0.75 and 1.25 Hz). Forearm compression reduced tendon displacement (baseline = 28.5 ± 4.1 mm vs. forearm = 27.0 ± 4.6 mm; p = 0.043) and showed a trend for reduced SSCT displacement, while palmar compression had no significant effects on tendon-SSCT motion. Compared with baseline, partial ischemia decreased SSCT displacement (baseline = 22.9 ± 3.3 mm vs. ischemia = 22.0 ± 3.3 mm; p = 0.015), while tendon displacement remained unchanged. In all experimental conditions, faster movements elicited greater tendon-SSCT relative motion. Our findings suggest that palmar compression may not negatively impact tendon-SSCT relative motion, but forearm compression may require further investigation. Localized ischemia in the forearm may alter the gliding conditions within the carpal tunnel and affect tendon-SSCT relative motion, which bridges an important gap between blood flow in the carpal tunnel and shear injury risk. These findings contribute to the growing body of literature, supporting the role that cumulative tendon-SSCT shear injury may have on the pathomechanics of carpal tunnel syndrome. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:1038-1044, 2020.

A Novel Adhesion Index for Verifying the Extent of Adhesion for the Extensor Digitorum Communis in Patients with Metacarpal Fractures

This study aims to determine if the relative displacement between the extensor digitorum communis (EDC) tendon and its surrounding tissues can be used as an adhesion index (AI) for assessing adhesion in metacarpal fractures by comparing two clinical measures, namely single-digit-force and extensor lag (i.e., the difference between passive extension and full active extension). The Fisher–Tippett block-matching method and a Kalman-filter algorithm were used to determine the relative displacements in 39 healthy subjects and 8 patients with metacarpal fractures. A goniometer was used to measure the extensor lag, and a force sensor was used to measure the single-digit-force. Measurements were obtained twice for each patient to evaluate the performance of the AI in assessing the progress of rehabilitation. The Pearson correlation coefficient was calculated to quantify the various correlations between the AI, extensor lag, and single-digit-force. The results showed strong correlations between the AI and the extensor lag, the AI and the single-digit-force, and the extensor lag and the single-digit-force (r = 0.718, −0.849, and −0.741; P = 0.002, P < 0.001, and P = 0.001, respectively). The AI in the patients gradually decreased after continuous rehabilitation, but remained higher than that of healthy participants.