Ultrasound Analysis of Human Carpal Tunnel System

The overall goal of this project is to develop a novel ultrasonographic method to characterize the subsynovial connective tissue (SSCT) and detect differences between SSCT, median nerve and tendon motion for the evaluation and diagnosis of patients suspected of having carpal tunnel syndrome (CTS). CTS is usually diagnosed late in its evolution, by measuring electrophysiological changes in median nerve function. Once these changes have occurred, surgery is often the only effective treatment. At an earlier stage of evolution, non-surgical treatment might be more effective. Although ultrasonography and magnetic resonance imaging (MRI) have recently been used to measure changes in median nerve shape in CTS, such approaches also only capture late changes. Thus, a method for detection of CTS that could identify pathology before function or structure of the nerve is compromised could prevent significant morbidity and transition to a permanent neuropathy. One promising opportunity is presented in the subsynovial connective tissue (SSCT), which surrounds the tendons in the carpal tunnel. One of the most characteristic findings in surgically treated patients with CTS is a non-inflammatory fibrosis of the SSCT. Some investigators have suggested that the SSCT may be the cause of the nerve compression in CTS. In our previous work, the investigators have demonstrated differences in the mechanical properties, motion and thickness of the SSCT in patients with CTS compared to normals. More recently, an animal model has been described in which the structural changes in the SSCT have been shown to precede the changes in nerve function.

The investigators have demonstrated in cadaver studies that the normal SSCT can be imaged by ultrasound, and its motion, velocity, and thickness distinguished from that of the nearby tendon and nerve. Here the investigators propose to leverage this work, and study the ability of ultrasound to detect SSCT thickness and motion in individuals with and without CTS. Based on our preliminary research, the investigators formulate the following central hypothesis: An increase in SSCT thickness and changes in sliding velocities of the SSCT with respect to the corresponding tendon are indicative of CTS. In addition, this material property change at SSCT affects median nerve motions and transformations. This is because the SSCT becomes fibrotic in CTS, and the fibrosis alters the normal SSCT-median nerve-tendon functional relationship.