T2-weighted MRI defines critical compression in the distal carpal tunnel that is relieved after decompressive surgery

Despite carpal tunnel syndrome (CTS) being the most common entrapment neuropathy, its pathophysiology remains debated. Sub-synovial connective tissues (SSCT) within the carpal tunnel are thought to play a role but are poorly characterised. MRI analysis offers potentially novel insights into SSCT characteristics.

A pilot study of T2-weighted MRI was performed in healthy controls (n = 7), and in CTS patients (n = 16) pre- and 6 months post-surgical decompression. Image analysis was performed to quantify SSCT cross-sectional area, SSCT signal intensity ratio, and wrist index (depth/width) at distal, middle, and proximal wrist landmarks.

Median SSCT signal intensity was lower in the distal carpal tunnel of CTS patients pre-operatively (0.96) compared to controls (1.13; P = 0.008) and normalised post-operatively (1.13, P = 0.001). Median wrist index was also lower in CTS patients pre-operatively (0.60) than in controls (0.67, P = 0.022), and again normalised post-operatively (0.74, P = 0.001). This was attributed to changes in carpal depth in the anteroposterior axis with decompression surgery.

This pilot study successfully demonstrated MRI assessment of SSCT in patients with CTS. The decreased SSCT signal intensities suggest predominant changes at the distal tunnel, potentially indicating reduced SSCT perfusion pre-surgery which normalised post-surgery. Our preliminary findings merit further investigation in a larger cohort.