Abstract
The transverse carpal ligament (TCL) forms the volar boundary of the carpal tunnel and may provide mechanical constraint to the median nerve, leading to carpal tunnel syndrome. Therefore, the mechanical properties of the TCL are essential to better understand the etiology of carpal tunnel syndrome. The purpose of this study was to investigate the in vivo TCL stiffness using acoustic radiation force impulse (ARFI) imaging. The shear wave velocity (SWV) of the TCL was measured using Virtual Touch IQTM software in 15 healthy, male subjects. The skin and the thenar muscles were also examined as reference tissues. In addition, the effects of measurement location and ultrasound transducer compression on the SWV were studied. The SWV of the TCL was dependent on the tissue location, with greater SWV values within the muscle-attached region than those outside of the muscle-attached region. The SWV of the TCL was significantly smaller without compression (5.21 ± 1.08 m/s) than with compression (6.62 ± 1.18 m/s). The SWV measurements of the skin and the thenar muscles were also affected by transducer compression, but to different extents than the SWV of the TCL. Therefore to standardize the ARFI imaging procedure, it is recommended that a layer of ultrasound gel be maintained to minimize the effects of tissue compression. This study demonstrated the feasibility of ARFI imaging for assessing the stiffness characteristics of the TCL in vivo, which has the potential to identify pathomechanical changes of the tissue.
Highlights
The transverse carpal ligament (TCL) forms the volar boundary of the carpal tunnel and plays a critical role in carpal tunnel mechanics
All tissues in the shear wave velocity (SWV) color map captured with compression (Figure 3D) grossly appear to have hues corresponding to greater stiffness when compared to those without compression (Figure 3B)
The in vivo stiffness of the TCL was investigated by measuring the SWV using acoustic radiation force impulse (ARFI) imaging
Summary
The transverse carpal ligament (TCL) forms the volar boundary of the carpal tunnel and plays a critical role in carpal tunnel mechanics. The TCL stabilizes the carpal bones in the transverse direction [1,2], serves as an anchor for the thenar and hypothenar muscles [3], and acts as a pulley for the flexor tendons [4]. The TCL can potentially compress the median nerve, causing carpal tunnel syndrome. The mechanical constraint imposed by the TCL to the median nerve is further illustrated by TCL transection as a standard surgical treatment for carpal tunnel syndrome. Mechanical stimulation to the TCL during thenar muscle contraction may cause tissue remodeling and lead to thickening and stiffening of the TCL [7]. Investigating the mechanical properties of the TCL may lead to a better understanding of carpal tunnel syndrome etiology
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