Peripheral nerves slide and stretch during limb movements to accommodate changes in path length. If nerves are not free to slide, as may happen in compression syndromes such as carpal tunnel syndrome (CTS), then the nerve segment closest to the moving joint will have to accommodate most of the length change. This will lead to elevated strain, possibly sufficient to affect nerve function (Szabo & Chidgey, 1989). It has been suggested that multiple sites of nerve compression may contribute to non-specific arm pain (NSAP) (Greening et al. 2001). Transverse median nerve movements are reduced in these conditions (Nakamichi & Tachibana, 1995; Greening et al. 1999). However, there have been no studies on longitudinal nerve sliding in CTS and NSAP.
Nerve excursion was measured proximal to the carpal tunnel in the forearm during movement of the metacarpophalangeal (MCP) joints. Nineteen control subjects (age 25-58 years), seventeen CTS (age 30-58 years) and five NSAP patients (age 24-41 years) were examined as part of a study approved by the UCL/UCLH Ethical Committee. Each subject was imaged lying supine in 45 or 90 deg shoulder abduction. In each trial the digits were passively extended at the MCP joint from 90 deg flexion to neutral. Images were captured at 10 frames s-1 using a Diasus ultrasound (Dynamic Imaging, UK) with a 10-22 MHz linear array transducer. Sequences of images were analysed offline as described by Dilley et al. (2001).
The median nerve moved distally during MCP joint extension by 2.62 ± 0.15 mm (mean ± S.E.M.) in controls, and 2.20 ± 0.21 mm in CTS and 2.66 ± 0.49 mm in NSAP patients. There was no significant difference between groups.
Thus it seems that nerves can slide normally in the wrists of CTS and NSAP patients and that pain and loss of function cannot be due to major increases in local nerve strain. Transverse median nerve movement is reduced, and may lead to local nerve injury due to repeated stress from flexor tendons. Other changes in the nerve environment, e.g. ischaemia, low levels of inflammation, may also contribute to symptoms in CTS and/or NSAP.
This work was supported by the Arthritis Research Campaign.