Comparative study of carpal tunnel compliance in the human, dog, rabbit, and rat.

The purpose of this study was to measure the compliance of the carpal tunnel in candidate animal models of carpal tunnel syndrome (CTS), by measuring the resistance when passing a tapered metal rod through the carpal tunnel. Forepaws from 10 dogs, 10 rabbits, and 10 rats with intact carpal tunnels, and 10 fresh frozen human wrist cadavers were used. The slopes of the linear part of the force-displacement curve (a measure of stiffness), normal force, and increasing area ratio (InAR) were significantly different among the four species (p<0.05). Post hoc analysis indicated that the mean slopes for the human carpal tunnel were the largest, indicating the least compliance, whereas those of the rat were the least (p<0.05). The features of the compliance for the dog carpal tunnel were closest to the human. The development of animal models of CTS should consider the compliance of the carpal tunnel, as it will be more difficult to increase pressure in a more compliant tunnel.