Figure 9.3 The effect of wrist posture on carpal tunnel pressure and median nerve contact stress. Hydrostatic pressure was measured by catheter and contact stress by a tubular rubber transducer replacing the excised median nerve (Keir et al., 1997)

There exist models of contact stress as well hydrostatic pressure in the carpal canal. There are few data on nerve stretch during work or other activities. Drury (1987) calculated an exposure parameter (which he termed daily damaging wrist motions) when wrist flexion and force exertion coincided. Moore et al. (1991) calculated median nerve contact stress and its time integral during four kinds of simulated manual work in the laboratory. Under ‘natural’ conditions participants elected to work with the wrist in extension as they squeezed the tool. Even under ‘forced’ conditions where the work was configured to require flexed wrist postures, wrist postures varied close to straight and little loading on the median nerve by the tendons was predicted.