Adaptation of the Transverse Carpal Ligament Associated with Repetitive Hand Use in Pianists

<div><p>The transverse carpal ligament (TCL) plays a critical role in carpal tunnel biomechanics through interactions with its surrounding tissues. The purpose of this study was to investigate the <i>in vivo</i> adaptations of the TCL’s mechanical properties in response to repetitive hand use in pianists using acoustic radiation force impulse (ARFI) imaging. It was hypothesized that pianists, in comparison to non-pianists, would have a stiffer TCL as indicated by an increased acoustic shear wave velocity (SWV). ARFI imagining was performed for 10 female pianists and 10 female non-pianists. The median SWV values of the TCL were determined for the entire TCL, as well as for its radial and ulnar portions, rTCL and uTCL, respectively. The TCL SWV was significantly increased in pianists relative to non-pianists (p < 0.05). Additionally, the increased SWV was location dependent for both pianist and non-pianist groups (p < 0.05), with the rTCL having a significantly greater SWV than the uTCL. Between groups, the rTCL SWV of pianists was 22.2% greater than that of the non-pianists (p < 0.001). This localized increase of TCL SWV, i.e. stiffening, may be primarily attributable to focal biomechanical interactions that occur at the radial TCL aspect where the thenar muscles are anchored. Progressive stiffening of the TCL may become constraining to the carpal tunnel, leading to median nerve compression in the tunnel. TCL maladaptation helps explain why populations who repeatedly use their hands are at an increased risk of developing musculoskeletal pathologies, e.g. carpal tunnel syndrome.</p></div

The shear wave velocities (SWVs) for the ulnar TCL (uTCL) and radial TCL (rTCL) in pianists and non-pianists.

<p>* p < 0.05, *** p < 0.001</p

Experimental setup for acoustic radiation force impulse (ARFI) imaging of the transverse carpal ligament (TCL).

<p>Reprinted under a CC BY license, with permission from the Hand Research Laboratory at Cleveland Clinic, original copyright 2016.</p

A representative ultrasound image with the TCL outlined on both the B-mode side (left) and ARFI side (right).

<p>The hamate (H), trapezium (T), and thenar muscles’ ulnar point (TUP,*) are identified. The vertical line at the TUP represents the location where the TCL was divided into radial and ulnar portions. Reprinted under a CC BY license, with permission from the Hand Research Laboratory at Cleveland Clinic, original copyright 2016.</p

Projection angle for the thumb and index finger.

<p>Each data point represents the average of SA for all the trials within the specified 1-N force interval.</p

Force projection angles for the thumb and index finger.

<p>Each data point represents the average of PA for all trials within the specified 1-N force interval.</p

Experimental setup for the pinch task.

<p>(A) A subject interfacing with the pinch apparatus while viewing the monitor for force feedback. <i>(i)</i> The horizontal line in the middle of the tank serves as the target line; <i>(ii)</i> the vertical bar indicates the real-time pinch force of the subject; and <i>(iii)</i> the pinch apparatus in the experiment. (B) Close-up of the typical pinching posture assumed while the digits are interfacing with the apparatus.</p

Force vector components of the thumb and index finger from one representative trial.

<p>(A) The <i>F_x</i>, <i>F_y</i> and <i>F_z</i> components of the thumb force vector; (B) The <i>F_x</i>, <i>F_y</i> and <i>F_z</i> components of the index finger force vector.</p

Definition of coordinate system and angular parameters.

<p>Definition of coordinate system and angular parameters.</p

Shear force tuning curves for the thumb and index finger.

<p>Shear force tuning curves for the thumb and index finger.</p