Anatomical Dimensions of the Proximal Carpal Tunnel Entrance and Its Relationship With Carpal Tunnel Syndrome

Background: Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy in humans. It is characterized by paresthesias in the median nerve (MN) area, distal to the carpal tunnel (CT). It is more common in middle‐aged women. Its incidence increases with repetitive manual activity and obesity, although its ultimate etiology is not well known. Our aim was to determine the ultrasound anatomical dimensions of the proximal CT entrance and their relationship with sex, age, anthropometric data, MN, and the presence or absence of CTS and to assess their possible etiological role in this neuropathy. Methods: We analyzed the anatomical measurements of the proximal entrance of 793 CTs using ultrasound—height, width, and ellipsoid area—in patients with CTS (578) and in healthy subjects (215). We also analyzed their relationships with age, sex, height, weight, dominant hand, and degree of nerve involvement. Results: The three anatomical variables studied at the proximal entrance of the CT were height (12.63 ± 1.44 mm), width (22.06 ± 2.01 mm), and ellipsoid area (173 ± 22 mm 2 ). All three measurements studied were higher in cases than in controls and in male than in female. Height and area were strongly associated with the degree of MN involvement. Conclusions: These results suggest that the proximal CT entrance is a site of adaptability rather than the site of greatest biomechanical stress within the CT in the pathophysiology of CTS.