Functional compartmental space: the missing link in the pathogenesis of carpal tunnel syndrome

Abstract

Carpal tunnel syndrome (CTS) is the most common compressive neuropathy, yet its exact aetiology remains unknown. Ultrasonographic examination of the carpal tunnel inlet showed anechoic areas distributed around the nerve and tendons. The areas were measured during fist motion in 10 asymptomatic and 10 CTS-symptomatic individuals, and correlated with the ‘symptom severity’ and ‘functional status’ scores in the Boston Carpal Tunnel Questionnaire (BCTQ). All candidates exhibited a sinusoidal variation of anechoic spaces during flexion-extension, and the maximum anechoic space for each candidate was termed the ‘functional compartmental space’ (FCS). Normal candidates exhibited a greater FCS than CTS-symptomatic candidates, who consequently displayed decreased tendon translation and increased nerve compression against the flexor retinaculum due to a smaller FCS. A larger FCS appears to accommodate flexor-tendon translation and prevents the mechanical impingement of the nerve. This finding may be a conceptual link in CTS pathophysiology and may indicate individual susceptibility to idiopathic CTS.