Carpal arch and median nerve changes during radioulnar wrist compression in carpal tunnel syndrome patients

Localization of the Median Nerve and Flexor Pollicis Longus at the Carpal Tunnel Inlet in Patients With and Without Carpal Tunnel Syndrome Using Ultrasound

BACKGROUND

Current illustrations of the carpal tunnel vary greatly. The relative positions of the components such as the median nerve and flexor pollicis longus (FPL) tendon seem often arbitrarily chosen. The purpose of this study was to determine the locations of the median nerve and FPL in the carpal tunnel using ultrasound (US) and to determine whether the position of the median nerve changes in carpal tunnel syndrome (CTS).

METHOD

Patients with and without CTS underwent US examination of the wrist. A 4 × 10 grid was fitted to each saved cross-sectional image. The center points of the median nerve and FPL were identified, and their horizontal and vertical coordinates were recorded.

RESULTS

The median nerve was identified in 115 wrists (average x = 0.70, y = 0.82), and FPL was identified in 90 wrists (average x = 0.86, y = 0.59). A scatter plot was created by stacking all US images to demonstrate the average positions of the median nerve and FPL. There were 97 wrists without CTS (No CTS) and 17 wrists with CTS. There was a significant difference in the vertical position of the median nerve between No CTS and CTS wrists (P = .0006).

CONCLUSIONS

The locations of the median nerve and FPL within the carpal tunnel were determined using US of 115 wrists, and a heat map was created to illustrate these locations. The median nerve was found to be more superficial in the setting of CTS.

Non-Surgical Carpal Arch Space Augmentation for Median Nerve Decompression

The carpal tunnel is a tightly bounded space, making the median nerve prone to compression and eventually leading to carpal tunnel syndrome. Carpal tunnel release surgery transects the transverse carpal ligament to expand the tunnel arch space, decompress the median nerve, and relieve the associated symptoms. However, the surgical procedure unavoidably disrupts essential anatomical, biomechanical and physiological functions of the wrist, potentially causing reduced grip strength, pillar pain, carpal bone instability, scar tissue formation, and perineural fibrosis. It is desirable to decompress the median nerve without surgically transecting the transverse carpal ligament. This paper is to review several approaches we have developed for nonsurgical carpal arch space augmentation (CASA), namely, radio ulnar wrist compression, muscle-ligament interaction, palmar pulling, and collagenolysis of the transverse carpal ligament. Briefly summarized is the research work on the CASA topic about theoretical considerations, in vitro and in situ experiment, computational modeling, and human subject studies with asymptomatic and carpal tunnel syndrome hands.

Spatial Relationship of the Median Nerve and Transverse Carpal Ligament in Asymptomatic Hands

The spacing between the median nerve and transverse carpal ligament (TCL) within the carpal tunnel can potentially affect the nerve morphology. This study aimed to quantify the spatial relationship between the median nerve and transverse carpal ligament in asymptomatic hands. Twelve subjects were recruited to image the carpal tunnel using robot-assisted ultrasound. The median nerve and TCL were segmented from each image and three-dimensionally reconstructed using kinematic information from the robot. The TCL-median nerve distance, nerve cross-sectional area, circularity, and position were measured along the entirety of the nerve length within the carpal tunnel. Results were averaged at every 5% of nerve length. At the nerve length percentages of 0% (distal), 25%, 50%, 75%, and 100% (proximal), the TCL-median nerve distance (±SD) was 0.7 ± 0.4, 0.7 ± 0.2, 0.5 ± 0.2, 0.5 ± 0.2, and 0.6 ± 0.3 mm, respectively. The corresponding nerve cross-sectional area was 9.4 ± 1.9, 10.6 ± 2.6, 11.2 ± 2.1, 11.2 ± 1.7, and 9.7 ± 1.9 mm2. A one-way analysis of variance showed no significant differences between the respective percentages of nerve length for TCL-median nerve distance (p = 0.219) and cross-sectional area (p = 0.869). Significant (p < 0.0001) but weak correlations were observed between the TCL-median nerve distance with cross-sectional area (r = -0.247) and circularity (r = -0.244). This study shows that the healthy median nerve morphology is consistent along the continuous nerve length within the carpal tunnel, supporting the use of 2D imaging in the evaluation of the healthy nerve.

Carpal arch space increased by volar force applied to the skin surface above the carpal tunnel

BACKGROUND

Carpal arch space augmentation can help decompress the median nerve. The augmentation can be achieved by mechanical manipulations utilizing the biomechanics of the tunnel structure. The purpose of this study was to expand the carpal arch in vitro by applying volar forces on the surface of the wrist.

METHODS

The mechanism was implemented in eight cadaver hands by attaching a volar force transmitter to the palmar surface of the wrist and pulling the transmitter volarly at six force levels (0, 3, 6, 9, 12, and 15 N). Ultrasound images of the cross section at the distal carpal tunnel were collected for morphological analysis.

FINDINGS

The carpal arch height, width, and area were significantly altered by the volarly applied force (P < 0.001). The arch height and area were increased but the arch width was decreased by the force. Pearson's correlation coefficient showed that there was a positive correlation between the arch height and force magnitude; and between the arch area and force magnitude. A negative correlation existed between the arch width and force magnitude (P < 0.001). The magnitude of change of the arch height, width, and area was increased as the force magnitude increased.

INTERPRETATION

This study demonstrated that applying external forces on the wrist skin to increase the carpal arch space was feasible. The magnitude of the force influenced its effect on altering the carpal arch. Study limitations include small sample size and inclusion of male specimens. Future in vivo work is needed for clinical translation feasibility.

Carpal tunnel mechanics and its relevance to carpal tunnel syndrome

The carpal tunnel is an elaborate biomechanical structure whose pathomechanics plays an essential role in the development of carpal tunnel syndrome. The purpose of this article is to review the movement related biomechanics of the carpal tunnel together with its anatomical and morphological features, and to describe the pathomechanics and pathophysiology associated with carpal tunnel syndrome. Topics of discussion include biomechanics of the median nerve, flexor tendons, subsynovial tissue, transverse carpal ligament, carpal tunnel pressure, and morphological properties, as well as mechanisms for biomechanical improvement and physiological restoration. It is our hope that the biomechanical knowledge of the carpal tunnel will improve the understanding and management of carpal tunnel syndrome.

A preliminary study of radioulnar wrist compression in improving patient-reported outcomes of carpal tunnel syndrome

Previous studies have shown radioulnar wrist compression augments carpal arch space. This study investigated the effects of radioulnar wrist compression on patient-reported outcomes associated with carpal tunnel syndrome. Subjects underwent thrice-daily (15 min each time 45 min daily) wrist compression over 4 weeks with an additional four weeks of follow-up without treatment. Primary outcomes included Boston Carpal Tunnel Questionnaire symptom and functional severity scales (SSS and FSS) and symptoms of numbness/tingling based on Visual Analog Scales. Our results showed that radioulnar wrist compression improved SSS by 0.55 points after 2 weeks (p < 0.001) and 0.51 points at 4 weeks (p < 0.006) compared to the baseline scale. At the four-week follow-up, SSS remined improved at 0.47 points (p < 0.05). Symptoms of numbness/tingling improved at two and 4 weeks, as well as the follow-up (p < 0.05). Hand motor impairment such as weakness had a lower frequency across carpal tunnel syndrome sufferers and does not significantly improve (p > 0.05). Radioulnar wrist compression might be an effective alternative treatment in improving sensory related symptoms in patients with mild to moderate carpal tunnel syndrome.

The effects of wrist position and radioulnar wrist compression on median nerve longitudinal mobility

BACKGROUND

Carpal tunnel syndrome is an entrapment neuropathy at the wrist characterized by compromised median nerve mobility. The purpose of this study was to investigate the effect of wrist position on median nerve longitudinal mobility in healthy subjects and the effect of radioulnar wrist compression on the median nerve mobility under non-neutral wrist positions.

METHODS

Dynamic B mode ultrasound images captured longitudinal median nerve motion in the carpal tunnel in 10 healthy subjects at wrist neutral position, 30-degree flexion, and 30-degree extension. In each position, RWC of 0, 5, 10, and 15 N were applied. One-way repeated measure analysis of variance (ANOVA), Post-hoc Tukey's tests, and the Friedman Test were used to show the significant differences of median nerve longitudinal mobility at different wrist positions and force conditions.

FINDINGS

Median nerve longitudinal mobility was found to be significantly influenced by wrist position (P < 0.05). The mobility under wrist neutral position was 3.02 mm/s, 38% higher than under wrist flexion (2.18 ± 0.60 mm/s), and 32% higher than under wrist extension (2.29 ± 0.43 mm/s). The impaired median nerve mobility was significantly restored under 10 N radioulnar wrist compression (P < 0.05), by 34.4% under wrist flexion (3.03 ± 0.85 mm/s), and 38.9% under wrist extension (3.07 ± 0.79 mm/s).

INTERPRETATION

Non-neutral wrist positions compromise median nerve longitudinal mobility, but moderate radioulnar compressive forces are beneficial in the recovery of median nerve longitudinal mobility, and may help to prevent symptoms associated with carpal tunnel syndrome.

Three-Dimensional Carpal Arch Morphology Using Robot-Assisted Ultrasonography

OBJECTIVE

The morphology of the carpal arch implicates the available space for the median nerve within the carpal tunnel. The purposes of this study were to 1) reconstruct the three-dimensional (3D) carpal arch by robot-assisted ultrasonography with a linear array transducer using cadaveric hands, and 2) investigate the 3D morphological properties of the carpal arch.

METHODS

An ultrasound probe with two-dimensional (2D) linear array was integrated on a robotic arm and maneuvered over the cadaveric carpal tunnels to scan the entire transverse carpal ligament and its osseous attachments to carpal bones. The acquired series of 2D ultrasound images together with robot positioning were utilized to reconstruct the 3D carpal arch for morphometric analyses.

RESULTS

Total carpal arch volume was 1099.4 ± 163.2 mm³ with the distal, middle, and proximal regions contributing 18.2 ± 1.5%, 32.7 ± 1.2%, and 49.1 ± 2.3%, respectively. The ligament surface area was 420.1 ± 63.9 mm². The carpal arch width, height, curvature, length, area, and palmar bowing index progressively increased from the distal to proximal locations within the tunnel (p < 0.01).

CONCLUSION

The incorporation of the robot technology with the ultrasound system advanced the applications of traditional 2D ultrasound imaging for a 3D carpal arch reconstruction, allowing for comprehensive morphological assessment of the carpal arch.

SIGNIFICANCE

The developed workflow can be used for the reconstruction and analysis of other anatomical features in vivo.

Carpal Arch Changes in Response to Thenar Muscle Loading

This study investigated the biomechanical effects of thenar muscles (abductor pollicis brevis (APB), superficial head of flexor pollicis brevis (sFPB), opponens pollicis (OPP)) on the transverse carpal ligament formed carpal arch under force application by individual or combined muscles (APB, sFPB, OPP, APB-sFPB, sFPB-OPP, APB-OPP, and APB-sFPB-OPP). In ten cadaveric hands, thenar muscles were loaded under 15% of their respective maximal force capacity, and ultrasound images of the cross section of the distal carpal tunnel were collected for morphometric analyses of the carpal arch. The carpal arch height and area were significantly dependent on the loading condition (p < 0.01), muscle combination (p < 0.05), and their interaction (p < 0.01). The changes to arch height and area were significantly dependent on the muscle combinations (p = 0.001 and p < 0.001, respectively). The arch height and area increased under the loading combinations of APB, OPP, APB-sFPB, APB-OPP, or APB-sFPB-OPP (p < 0.05), but not under the combinations of sFPB (p = 0.893) or sFPB-OPP (p = 0.338). The carpal arch change under the APB-sFPB-OPP or APB-OPP loading was greater than that under the loading of APB-sFPB (p < 0.001). This study demonstrated that thenar muscle forces exert biomechanical effects on the transverse carpal ligament to increase carpal arch height and area, and these increases were different for individual muscles and their combinations.

Ligament and Bone Arch Partition of the Carpal Tunnel by Three-Dimensional Ultrasonography

The carpal tunnel is geometrically irregular due to the complex composition of many carpal bones intercalated by numerous intercarpal ligaments. The purpose of the study was to investigate the relative contributions of the ligament and bone arches to carpal tunnel space at the proximal, middle, and distal tunnel regions. A catheter ultrasound probe acquired fan-like images inside cadaveric carpal tunnels for three-dimensional reconstruction of the tunnel. The total tunnel volume was 5367.6 ± 940.1 mm3 with contributions of 12.0%, 6.9%, and 4.1% by proximal, middle, and distal ligament arches, respectively, and 27.0%, 25.3%, and 24.7% by proximal, middle, and distal bone arches, respectively. The bone arch occupied more tunnel space than the ligament arch at all regions (p < 0.05). The ligament arch was largest at the proximal region of the tunnel and significantly decreased toward the distal region (p < 0.05). However, the bone arch significantly decreased only from the proximal to middle region (p < 0.05) but not from the middle to distal region (p = 0.311). Consequently, it was observed that the ligament arch was the key contributor to the unequal carpal tunnel space across regions. Partitional and regional tunnel morphometric information may provide a better understanding of tunnel abnormality associated with various wrist pathological conditions. The developed framework of ultrasonography and data processing can be applied to other areas of interest in the musculoskeletal system.

Morphological and positional changes of the carpal arch and median nerve associated with wrist deviations

BACKGROUND

Carpal tunnel and median nerve dynamically change with wrist motion. The purpose of this study was to investigate the morphological changes and positional migration of the carpal arch and median nerve, as well as nerve-arch positional relationship associated with wrist deviation in healthy volunteers.

METHODS

Twenty asymptomatic male volunteers performed wrist motion from neutral to deviated positions combining flexion-extension and radioulnar deviation. Ultrasound images of the carpal arch and median nerve at the distal carpal tunnel were collected during wrist motion. Morphological and positional parameters of the carpal arch and median nerve were derived from the ultrasound images.

FINDINGS

Carpal arch height, area, and palmar bowing of the transverse carpal ligament (TCL) increased with flexion related wrist motion and decreased with extension related motion (P < 0.05). Arch width increased with radial flexion and decreased with extension and ulnar extension (P < 0.05). Median nerve circularity increased with flexion and radial flexion but decreased with extension, ulnar extension, and ulnar deviation (P < 0.05). Nerve centroid displaced ulnarly with radial deviation, radial flexion, and radial extension and displaced radially with ulnar deviation, ulnar flexion, and ulnar extension (P < 0.05). Nerve centroid displaced in the dorsal direction with flexion and radial flexion, but in the palmar direction with extension (P < 0.05). Nerve-TCL distance increased with flexion related motion and decreased with extension relation motion (P < 0.05).

INTERPRETATION

The current study advances our understanding the effect of wrist motion on the carpal tunnel and its contents, which has implications for pathomorphological and pathokinematic changes associated with wrist disorders.

Changes of median nerve conduction, cross-sectional area and mobility by radioulnar wrist compression intervention in patients with carpal tunnel syndrome

BACKGROUND

Owing to the compressive nature of the neuropathy, patients with carpal tunnel syndrome (CTS) have prolonged distal motor latency (DML), sensory nerve latency (SNL), median nerve swelling and restricted median nerve mobility. The purpose of this study was to noninvasively augment carpal tunnel space using radioulnar wrist compression (RWC) and evaluate its effects on median nerve pathological properties in patients with CTS. It was hypothesized that the RWC intervention would reduce the median nerve DML, SNL and cross-sectional area (CSA) and enhance longitudinal median nerve mobility in patients. with CTS.

METHODS

Eleven patients diagnosed with CTS participated in this study. A portable RWC intervention splint was developed to apply 10 N of compressive force across the wrist. Three daily sessions of RWC were performed over 4 weeks of intervention (15 min per session, 45 min per day, 7 days per week). Each 15-min session consisted of three 5-min blocks of RWC, with a 1-min rest in between consecutive blocks. Patients were evaluated at Week 0 (baseline), Week 2 (mid-intervention) and Week 4 (end of intervention). DML and SNL of the median nerve were evaluated using established nerve conduction study techniques. Median nerve CSA at the distal wrist crease was obtained by ultrasound imaging. Median nerve motion associated with finger flexion/extension was captured by dynamic ultrasound imaging and quantified using a speckle cross-correlation algorithm. Finger flexion/extension was recorded using an electrogoniometer. The slope of the regressed linear equation of median nerve displacement as a function of finger flexion angle was used to quantify nerve mobility.

RESULTS

Patients with CTS showed significantly decreased DML (p = 0.048) and median nerve CSA (p < 0.001) and increased nerve mobility (p < 0.001) at mid-intervention compared to baseline. However, DML, CSA and mobility of the median nerve did not differ significantly between Weeks 2 and 4 (p = 0.574, 1.00 and 0.139, respectively). Median nerve SNL was not significantly affected throughout the 4-week intervention (p = 0.330 for Week 0 vs. 2; p = 1.00 for Week 2 vs. 4).

CONCLUSION

This study revealed that RWC intervention with 10-N force applied to the wrist in the radioulnar direction could restore impaired neurophysiological and biomechanical functions of the median nerve. The beneficial effects of RWC intervention for the median nerve were in evidence after a relatively short period of two weeks. These functional improvements could be explained by intermittent decompression of the median nerve via RWC-induced augmentation of the carpal arch.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

Biomechanically manipulating the carpal tunnel by RWC decompresses the median nerve and has the potential to become an alternative treatment for CTS.

Enhancement in median nerve mobility during radioulnar wrist compression in carpal tunnel syndrome patients

BACKGROUND

Carpal tunnel syndrome is a compression neuropathy at the wrist associated with compromised median nerve mobility. The purpose of this study was to investigate the effects of radioulnar wrist compression on median nerve longitudinal mobility within the carpal tunnel in carpal tunnel syndrome patients as well as healthy subjects.

METHODS

Dynamic ultrasound images captured longitudinal median nerve motion in the carpal tunnel during radioulnar wrist compression force application in 11 healthy subjects and 11 carpal tunnel syndrome patients.

FINDINGS

We found that median nerve mobility was not significantly affected by radioulnar wrist compression in healthy subjects (P = 0.34), but improved by 10 N radioulnar wrist compression in carpal tunnel syndrome patients (P < 0.05). Analysis of segmental median nerve mobility in carpal tunnel syndrome patients showed significantly improved mobility in the proximal tunnel section under 10 N radioulnar wrist compression force condition compared to the no compression condition (P < 0.05).

INTERPRETATION

Moderate radioulnar wrist compression force application helps restore impaired median nerve mobility and may be effective in improve nerve function and symptoms associated with carpal tunnel syndrome.

Thickness and Stiffness Adaptations of the Transverse Carpal Ligament Associated with Carpal Tunnel Syndrome

The purpose of this study was to investigate the morphological and mechanical properties of the transverse carpal ligament (TCL) in patients with carpal tunnel syndrome (CTS). Thickness and stiffness of the TCL in eight female CTS patients and eight female control subjects were examined using ultrasound imaging modalities. CTS patients had a 30.9% thicker TCL than control subjects. There was no overall difference in TCL stiffness between the two groups, but the radial TCL region was significantly stiffer than the ulnar region within the CTS group and such a regional difference was not found for the controls. The increased thickness and localized stiffness of the TCL for CTS patients may contribute to CTS symptoms due to reduction in carpal tunnel space and compliance. Advancements in ultrasound technology provide a means of understanding CTS mechanisms and quantifying the morphological and mechanical properties of the TCL in vivo.

Subject-specific finite element analysis of the carpal tunnel cross-sectional to examine tunnel area changes in response to carpal arch loading

BACKGROUND

Manipulating the carpal arch width (i.e. distance between hamate and trapezium bones) has been suggested as a means to increase carpal tunnel cross-sectional area and alleviate median nerve compression. The purpose of this study was to develop a finite element model of the carpal tunnel and to determine an optimal force direction to maximize area.

METHODS

A planar geometric model of carpal bones at hamate level was reconstructed from MRI with inter-carpal joint spaces filled with a linear elastic surrogate tissue. Experimental data with discrete carpal tunnel pressures (50, 100, 150, and 200mmHg) and corresponding carpal bone movements were used to obtain material property of surrogate tissue by inverse finite element analysis. The resulting model was used to simulate changes of carpal arch widths and areas with directional variations of a unit force applied at the hook of hamate.

FINDINGS

Inverse finite element model predicted the experimental area data within 1.5% error. Simulation of force applications showed that carpal arch width and area were dependent on the direction of force application, and minimal arch width and maximal area occurred at 138° (i.e. volar-radial direction) with respect to the hamate-to-trapezium axis. At this force direction, the width changed to 24.4mm from its initial 25.1mm (3% decrease), and the area changed to 301.6mm² from 290.3mm² (4% increase).

INTERPRETATION

The findings of the current study guide biomechanical manipulation to gain tunnel area increase, potentially helping reduce carpal tunnel pressure and relieve symptoms of compression median neuropathy.