The Use of Ultrasound to Quantify the Amount of Muscle Overlying the Carpal Tunnel

Carpal tunnel syndrome (CTS) is a common condition that still lacks a reliable, objective screening test. Many anatomical aspects of the syndrome have been studied including the dimensions of the carpal tunnel and shape of the nerve within the tunnel. We have observed varying amounts of
muscle overlying the carpal tunnel in patients undergoing surgery for the condition. Assuming that this muscle may have a dynamic role in the development of the condition, we attempted to quantify this muscle using ultrasound (US).
The purpose of this study was to devise a technique to evaluate the amount of muscle overlying the carpal tunnel.
The technique includes using the US transducer in a volar position  located half way between Kaplan’s line and the proximal wrist crease on a line drawn from the tip of the flexed ring finger proximally. The thickness of the muscle layer is evaluated in millimeters. We describe the technique and a series of patients in which the amount of muscle visualized on ultrasound was
correlated with the amount of muscle seen during open carpal tunnel surgery.
Ultrasound evaluation of the depth of muscle overlying the carpal tunnel is associated with the depth seen during surgery for CTS. The amount of muscle overlying the carpal tunnel may be useful for early diagnosis of the condition. More study is necessary to compare the amount of muscle in patients with CTS and individuals without CTS.