# Ultrasound Shear Wave Speed of the Transverse Carpal Ligament During Pinching
## 2 Materials and Methods
### Experimental Protocol  
Participants were seated at the testing station (Figure 1). The dominant forearm, with the elbow flexed at approximately 90 degrees, was placed into a container filled with water. The water provides a uniform medium for B-mode ultrasonography and SWE imaging. The palm was oriented supine. Ultrasound gel was placed into a plastic transducer cover. The cover was fitted over an ultrasound transducer (SuperSonic MACH 30, Hologic Inc., Marlborough, MA, USA). The transducer was fixated on a custom-designed ultrasound transducer orientation device. The fixated transducer was lowered into the water and oriented to image the cross section at the distal carpal tunnel. A pinch meter (Go Direct Hand Dynamometer, Vernier, Beaverton, OR, USA) was lowered into the water and placed between the thumb and index finger of the participant in a tip pinch configuration. The width of the pinch meter between the thumb and index finger was approximately 40 mm. A demonstration was given by the operator on how to properly hold the pinch meter. The pinch meter was connected via Bluetooth to a software platform (Vernier Graphical Analysis Pro, Vernier, Beaverton, OR, USA). The graphical interface, which displayed the real-time pinch force data, was shown on a laptop computer and placed within view of the participant.  
The ultrasound transducer was maneuvered near the distal carpal tunnel to find an image of the TCL, ridge of trapezium, thenar muscles, and the thenar muscles' unlar attachment point (TUP). There was no contact between the transducer and the skin. The Qbox, which defines the region of SWS measurement, was oriented with the center of the region approximately at the TUP. Participants were informed of the testing procedure to follow and were allowed time to practice pinching the pinch meter to the prescribed pinch force magnitudes of 10, 20, and 30 N (Figure 2). Testing commenced once participants expressed sufficient comfort with the requirements. Participants were first instructed to apply no force to the pinch meter. A B-mode (Figure 3a) and SWE (Figure 3b) ultrasound image was taken. The frequency of the B-mode and SWE imaging was 19 Hz and 70-800 Hz. The imaging depth was 2.5 cm. With visual feedback, the participants increased the pinch force to 10 N. The 10 N pinch force was held constant for at least 10 s to allow for the SWS readings to stabilize. At this time point, a B-mode and SWE image was taken. Participants then released the pinch effort. After a few seconds of rest, the subsequent pinch force magnitude was tested. The procedure was repeated for pinch force magnitudes of 20 N and 30 N. The pinch force magnitudes were chosen in order to apply appreciable load to the TCL while also allowing the participants to comfortably execute the protocol. The complete imaging and pinch force procedure was repeated for five trials. A 1 min period of rest was allotted between consecutive trials.  
Figure 1: Experimental setup. A seated participant held their dominant hand and forearm in a container of water and gripped a pinch meter in tip-pin configuration. An ultrasound transducer was fixed at the location of the distal carpal tunnel.