Three-Dimensional Silicon Mold Analysis of the Carpal Tunnel: A Morphometric Study in Human Cadavers

Purpose. Carpal tunnel syndrome (CTS) is a common entrapment neuropathy with an incidence rate of 6%. The significance of carpal tunnel shape and dimensions in idiopathic carpal tunnel syndrome has long been debated. Recent studies have exam­ined the accuracy of previous morphometric studies, as the reported dimensions have conflicting results. The purpose of this study was to use cadavers to determine the dimensions and shape of the carpal tunnel using a three-dimensional digitization approach. Methods. The carpal tunnels of 35 cadavers were evacuated, and 210 silicon molds were created from 70 hands by inserting them into the soft tissue-carpeted tunnel. The mold was then scanned by a Structured Light Scanner from Steinbichler 3D scanner to obtain a three-dimensional image of the carpal tunnel, from which various carpal tunnel measures were calculated. Results. The width, height, and cross-sectional area (CSA) of the carpal tunnel decreased significantly from proximal to distal, with a narrow CSA at the distal end. Furthermore, the ulnar side of the tunnel was observed to be significantly deeper than the radial side. Conclusions. In this study our measured dimensions render a truncated elliptical cone-shaped carpal tunnel tapering distally. Based on our analysis, the CSA of the distal carpal tunnel may be estimated by knowledge of the proximal tunnel CSA by using the formula (DistalCSA = 22.137 + 0.734 (ProximalCSA). Knowledge of the tunnel’s struc­tural architecture is important in determining the aetiology of carpal tunnel syndrome associated with variant anatomy.