Morphological changes of collagen fibrils in the subsynovial connective tissue in carpal tunnel syndrome

Background: Pathologic changes occur commonly in the subsynovial connective tissue in patients with carpal tunnel syndrome. The purposes of this study were to investigate the ultrastructural changes of the subsynovial connective tissue in these patients and compare them with the findings in cadaver controls. Methods: The diameter and density of collagen fibrils were measured by transmission electron microscopy in specimens of subsynovial connective tissue from ten patients with idiopathic carpal tunnel syndrome and from ten fresh-frozen cadavers of individuals without known symptoms of carpal tunnel syndrome. Results: We noted deformed collagen fibrils with a spiraled appearance in the specimens from the patients. We also observed phagocytosis of elastin fibrils in all of those specimens. These changes were noted only rarely in the cadaver controls. The mean diameter (and standard deviation) of the collagen fibrils was 45.5 ± 8.0 nm in the control group and 54.8 ± 15.2 nm in the patient group (p < 0.05). The mean number of collagen fibrils per 0.04 μm² (density) was 201.38 ± 48.88 in the control group and 157.08 ± 54.38 in the patient group (p < 0.05). Conclusions: These ultrastructural findings suggest that subsynovial collagen in patients with carpal tunnel syndrome is structurally different from that in individuals without carpal tunnel syndrome, but the processes resulting in that abnormal morphology remain to be elucidated. Level of Evidence: Prognostic Level III.