In vivo study of nerve movement and mechanosensitivity of the median nerve in whiplash and non-specific arm pain patients.

Chronic pain following whiplash injury and non-specific arm pain (NSAP, previously termed diffuse repetitive strain injury) present clinicians with problems of diagnosis and management. In both patient groups there are clinical signs of altered nerve movement and increased nerve trunk mechanosensitivity. Previous studies of NSAP patients have identified altered median nerve movement at the wrist. The present study uses high frequency ultrasound imaging to examine changes to median nerve movement and clinical examination to assess altered mechanosensitivity of the median nerve. Longitudinal median nerve movement was measured in the forearm during maximal inspiration in nine post-whiplash patients with chronic neck and arm pain and eight controls subjects. Eight NSAP patients and seven controls were also studied. Transverse median nerve movement at the proximal carpal tunnel during 30 degrees wrist extension to 30 degrees flexion was also measured. A clinical examination of nerve trunk allodynia was performed in all subjects. Longitudinal nerve movement in the forearm was reduced by 71% in the post-whiplash patients and by 68% in NSAP patients compared to controls. In the whiplash patients the pattern of transverse median nerve movement at the proximal carpal tunnel was significantly different to controls (patient mean=2.57+/-0.80 mm (SEM) in a radial direction; control mean=0.39+/-0.52 mm in an ulnar direction). Signs of neural mechanosensitivity (i.e. painful responses to median nerve trunk and brachial plexus pressure and stretch) were apparent in both patients groups. Change in nerve tension and neural mechanosensitivity may contribute to symptoms in whiplash and NSAP patients.