Background: The most common histological finding in carpal tunnel
syndrome is noninflammatory synovial fibrosis. The accumulated effect of minor
injuries is believed to be an important etiologic factor in some cases of
carpal tunnel syndrome. We sought evidence of such injuries in the synovial
tissue of patients with carpal tunnel syndrome and in cadaver controls.
Methods: We compared synovial specimens from thirty patients who had
idiopathic carpal tunnel syndrome with specimens from a control group of ten
fresh-frozen cadavers of individuals who had not had an antemortem diagnosis
of carpal tunnel syndrome and who met the same exclusion criteria. Analysis
included histological and immunohistochemical examination for the distribution
of collagen types I, II, III, and VI and transforming growth factor-ß
(TGF-ß) RI, RII, and RIII.
Results: Histological examination showed a marked increase in
fibroblast density, collagen fiber size, and vascular proliferation in the
specimens from the patients compared with the control specimens (p <
0.001). Collagen types I and II were not found in the synovium of either the
patients or the controls, but collagen type VI was a major component of both.
Collagen type-III fibers were more abundant in the patients than in the
controls (p < 0.001). Expression of TGF-ß RI was found in the
endothelial cells and fibroblasts in the patient and control specimens, with a
marked increase in expression in the fibroblasts of the patients compared with
that in the control tissue (p < 0.001).
Conclusions: These findings are similar to those after injury to
skin, tendon, and ligament and suggest that patients with idiopathic carpal
tunnel syndrome may have sustained an injury to the subsynovial connective
Clinical Relevance: The changes demonstrated in the subsynovial
connective tissue not only could lead to an increase in the volume of the
contents in the carpal tunnel but also may alter its material properties, such
as compliance and permeability to fluid flows, and vascularity. These changes
may, in turn, predispose the subsynovial connective tissue to additional
injury and contribute to the elevation in carpal tunnel pressure seen in
patients with carpal tunnel syndrome.