Sonographic Measurements of Subsynovial Connective Tissue Thickness in Patients With Carpal Tunnel Syndrome

Objectives A major pathologic finding in patients with idiopathic carpal tunnel syndrome is noninflammatory fibrosis and thickening of the subsynovial connective tissue. The objective of this study was to determine the ability of sonography to depict this thickening by comparing subsynovial connective tissue thickness in patients with carpal tunnel syndrome and healthy control participants. Methods Longitudinal sonograms of the middle finger superficial flexor tendon and subsynovial connective tissue were obtained at 3 levels: at the wrist crease (proximal tunnel), at the hook of the hamate (mid tunnel), and at the distal edge of the transverse carpal ligament (distal tunnel). The thickness of the subsynovial connective tissue perpendicular to the direction of the tendon and the diameter of the flexor digitorum superficialis tendon at the same level were measured. Then, a thickness ratio was created. Results At all 3 levels, the subsynovial connective tissue was thicker in patients than in controls ( P < .0001) with a thickness ranging from 0.60 to 0.63 mm in patients and 0.46 to 0.50 mm in controls. The thickness ratio was significantly greater in patients at the hamate and distal levels ( P = .018 and .013, respectively). Conclusions With this study, we have shown that it is possible to measure subsynovial connective tissue thickness with sonography, and the tissue is thicker in patients with carpal tunnel syndrome than in healthy controls.