Movement of the distal carpal row during narrowing and widening of the carpal arch width

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.

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.

Changes in carpal tunnel compliance with incremental flexor retinaculum release

Background

Flexor retinaculum transection is a routine surgical treatment for carpal tunnel syndrome, yet the biomechanical and clinical sequelae of the procedure remain unclear. We investigated the effects of flexor retinaculum release on carpal tunnel structural compliance using cadaveric hands.

Methods

The flexor retinaculum was incrementally and sequentially released with transections of 25, 50, 75, and 100 % of the transverse carpal ligament, followed by the distal aponeurosis and then the antebrachial fascia. Paired outward 10 N forces were applied to the insertion sites of the transverse carpal ligament at the distal (hamate-trapezium) and proximal (pisiform-scaphoid) levels of the carpal tunnel. Carpal tunnel compliance was defined as the change in carpal arch width normalized to the constant 10 N force.

Results

With the flexor retinaculum intact, carpal tunnel compliance at the proximal level, 0.696 ± 0.128 mm/N, was 13.6 times greater than that at the distal level, 0.056 ± 0.020 mm/N. Complete release of the transverse carpal ligament was required to achieve a significant gain in compliance at the distal level (p < 0.05). Subsequent release of the distal aponeurosis resulted in an appreciable additional increase in compliance (43.0 %, p = 0.052) at the distal level, but a minimal increase (1.7 %, p = 0.987) at the proximal level. Complete flexor retinaculum release provided a significant gain in compliance relative to transverse carpal ligament release alone at both proximal and distal levels (p < 0.05).

Conclusions

Overall, complete flexor retinaculum release increased proximal compliance by 52 % and distal compliance by 332 %. The increase in carpal tunnel compliance with complete flexor retinaculum release helps explain the benefit of carpal tunnel release surgery for patients with carpal tunnel syndrome.

Three-dimensional stiffness of the carpal arch

The carpal arch of the wrist is formed by irregularly shaped carpal bones interconnected by numerous ligaments, resulting in complex structural mechanics. The purpose of this study was to determine the three-dimensional stiffness characteristics of the carpal arch using displacement perturbations. It was hypothesized that the carpal arch would exhibit an anisotropic stiffness behavior with principal directions that are oblique to the conventional anatomical axes. Eight (n=8) cadavers were used in this study. For each specimen, the hamate was fixed to a custom stationary apparatus. An instrumented robot arm applied three-dimensional displacement perturbations to the ridge of trapezium and corresponding reaction forces were collected. The displacement-force data were used to determine a three-dimensional stiffness matrix using least squares fitting. Eigendecomposition of the stiffness matrix was used to identify the magnitudes and directions of the principal stiffness components. The carpal arch structure exhibited anisotropic stiffness behaviors with a maximum principal stiffness of 16.4±4.6N/mm that was significantly larger than the other principal components of 3.1±0.9 and 2.6±0.5N/mm (p<0.001). The principal direction of the maximum stiffness was pronated within the cross section of the carpal tunnel which is accounted for by the stiff transverse ligaments that tightly bind distal carpal arch. The minimal principal stiffness is attributed to the less constraining articulation between the trapezium and scaphoid. This study provides advanced characterization of the wrist׳s three-dimensional structural stiffness for improved insight into wrist biomechanics, stability, and function.

What does the transverse carpal ligament contribute to carpal stability?

Background The transverse carpal ligament is well known for its involvement in carpal tunnel syndrome, and sectioning of this ligament remains the definite treatment for this pathology. Some authors believe that the transverse carpal ligament is an important stabilizer of the carpal arch, whereas others do not consider it to be significant. Several studies have been performed, both in vivo and in in vitro. Sectioning of the transverse carpal ligament does not seem to have any effect on the width of the carpal arch in the unloaded condition. However, patients will load the arch during their activities of daily living. Materials and Methods A cadaveric study was done with distraction of the carpal bones before and after sectioning the transverse carpal ligament. Results With the transverse carpal ligament intact, the carpal arch is mobile, with distraction leading up to 50% widening of the arch. Sectioning of the transverse carpal ligament resulted in a significant widening of the carpal arch by a further 30%. Conclusions Loading of the carpal arch after sectioning of the transeverse carapal ligament leads to a significant increase in intracarpal mobility. This will inevitably influence carpal kinematics in the patient and might be responsible for some complications after simple carpal tunnel releases, such as pillar pain, palmar tenderness, and loss of grip strength.

Biomechanical role of the transverse carpal ligament in carpal tunnel compliance

The transverse carpal ligament (TCL) is a significant constituent of the wrist structure and forms the volar boundary of the carpal tunnel. It serves biomechanical and physiological functions, acting as a pulley for the flexor tendons, anchoring the thenar and hypothenar muscles, stabilizing the bony structure, and providing wrist proprioception. This article mainly describes and reviews our recent studies regarding the biomechanical role of the TCL in the compliant characteristics of the carpal tunnel. First, force applied to the TCL from within the carpal tunnel increased arch height and area due to arch width narrowing from the migration of the bony insertion sites of the TCL. The experimental findings were accounted for by a geometric model that elucidated the relationships among arch width, height, and area. Second, carpal arch deformation showed that the carpal tunnel was more flexible at the proximal level than at the distal level and was more compliant in the inward direction than in the outward direction. The hamate-capitate joint had larger angular rotations than the capitate-trapezoid and trapezoid-trapezium joints for their contributions to changes of the carpal arch width. Lastly, pressure application inside the intact and released carpal tunnels led to increased carpal tunnel cross-sectional areas, which were mainly attributable to the expansion of the carpal arch formed by the TCL. Transection of the TCL led to an increase of carpal arch compliance that was nine times greater than that of the intact carpal tunnel. The carpal tunnel, while regarded as a stabile structure, demonstrates compliant properties that help to accommodate biomechanical and physiological variants such as changes in carpal tunnel pressure.

Development of a new calibration procedure and its experimental validation applied to a human motion capture system

Motion capture systems are often used for checking and analyzing human motion in biomechanical applications. It is important, in this context, that the systems provide the best possible accuracy. Among existing capture systems, optical systems are those with the highest accuracy. In this paper, the development of a new calibration procedure for optical human motion capture systems is presented. The performance and effectiveness of that new calibration procedure are also checked by experimental validation. The new calibration procedure consists of two stages. In the first stage, initial estimators of intrinsic and extrinsic parameters are sought. The camera calibration method used in this stage is the one proposed by Tsai. These parameters are determined from the camera characteristics, the spatial position of the camera, and the center of the capture volume. In the second stage, a simultaneous nonlinear optimization of all parameters is performed to identify the optimal values, which minimize the objective function. The objective function, in this case, minimizes two errors. The first error is the distance error between two markers placed in a wand. The second error is the error of position and orientation of the retroreflective markers of a static calibration object. The real co-ordinates of the two objects are calibrated in a co-ordinate measuring machine (CMM). The OrthoBio system is used to validate the new calibration procedure. Results are 90% lower than those from the previous calibration software and broadly comparable with results from a similarly configured Vicon system.

Narrowing carpal arch width to increase cross-sectional area of carpal tunnel--a cadaveric study

BACKGROUND

Carpal tunnel morphology plays an essential role in the etiology and treatment of carpal tunnel syndrome. The purpose of this study was to observe the morphological changes of the carpal tunnel as a result of carpal arch width narrowing. It was hypothesized that carpal arch width narrowing would result in increased height and area of the carpal arch.

METHODS

The carpal arch width of eight cadaveric hands was narrowed by a custom apparatus and cross-sectional ultrasound images were acquired. The carpal arch height and area were quantified as the carpal arch width was narrowed. Correlation and regression analyses were performed for the carpal arch height and area with respect to the carpal arch width.

FINDINGS

The carpal tunnel became more convex as the carpal arch width was narrowed. The initial carpal arch width, height, and area were 25.7 (SD1.9) mm, 4.1 (SD0.6) mm, and 68.5 (SD14.0) mm(2), respectively. The carpal arch height and area negatively correlated with the carpal arch width, with correlation coefficients of -0.974 (SD0.018) and -0.925 (SD0.034), respectively. Linear regression analyses showed a 1mm narrowing of the carpal arch width resulted in proportional increases of 0.40 (SD0.14) mm in the carpal arch height and 4.0 (SD2.2) mm(2) in the carpal arch area.

INTERPRETATION

This study demonstrates that carpal arch width narrowing leads to increased carpal arch height and area, a potential mechanism to reduce the mechanical insult to the median nerve and relieve symptoms associated with carpal tunnel syndrome.