Changes in the functional structure of the tenosynovium in idiopathic carpal tunnel syndrome: A scanning electron microscope study

Background: The subsynovial connective tissue lies between the flexor tendons and visceral synovium in the carpal tunnel. Although tenosynovial fibrosis is nearly universally noted in patients with carpal tunnel syndrome, the relationship, if any, between the fibrosis and nerve abnormalities is unknown. The authors used light and scanning electron microscope imaging of the subsynovial connective tissue to gather information about its organization. Methods: Human subsynovial connective tissue was studied to determine its ultrastructural morphology. Biopsy specimens of 11 patients (12 hands) with idiopathic carpal tunnel syndrome, 14 cadaver controls, and two cadavers with a history of carpal tunnel syndrome were obtained for scanning electron microscopic imaging and histopathologic examination. Results: The visceral synovial layer is an uninterrupted membrane that defines the bursa dorsally. The subsynovial connective tissue consists of fibrous bundles that run parallel to the tendon, interconnected by smaller fibrous fibers. It connects to the synovial membrane and the flexor tendons. During tendon motion, the loose fibers between adjacent layers are stretched. The control tissue showed interconnections between all the parallel layers, whereas in patients with idiopathic carpal tunnel syndrome, these interconnections were absent, replaced with thicker parallel fibrous bundles. Similar changes were found in the cadaver carpal tunnel syndrome specimens. Pathologic changes in the patient and cadaver carpal tunnel syndrome specimens were most apparent close to the tendon and became progressively less severe in more superficial layers. Conclusions: The authors' observation that the most severe changes in the subsynovial connective tissue were found close to the tendon suggests that these changes may be the result of a shearing injury.