Cervical muscle dysfunction in the chronic whiplash associated disorder grade II (WAD-II)

Study Design. In a cross-sectional study, surface electromyography measurem ents of the upper trapezius muscles were obtained during different function al tasks in patients with a chronic whiplash associated disorder Grade II a nd healthy control subjects. Objectives, To investigate whether muscle dysfunction of the upper trapeziu s muscles, as assessed by surface electro myography, can be used to disting uish patients with whiplash associated disorder Grade II from healthy contr ol subjects. Summary of Background Information. In the whiplash associated disorder, the re is need to improve the diagnostic tools. Whiplash associated disorder Gr ade II is characterized by the presence of "musculoskeletal signs." Surface electromyography to assess these musculoskeletal signs objectively may be a useful tool. Methods. Normalized smoothed rectified electromyography levels of the upper trapezius muscles of patients with whiplash associated disorder Grade II ( n = 18) and healthy control subjects (n = 19) were compared during three st atic postures, during a unilateral dynamic manual exercise, and during rela xation after the manual exercise. Coefficients of variation were computed t o identify the measurement condition that discriminated best between the tw o groups. Results. The most pronounced differences between patients with whiplash ass ociated disorder Grade II and healthy control subjects were found particula rly in situations in which the biomechanical load was law. Patients showed higher coactivation levels during physical exercise and a decreased ability to relax muscles after physical exercise. Conclusions. Patients with whiplash associated disorder Grade II can be dis tinguished from healthy control subjects according to the presence of cervi cal muscle dysfunction, as assessed by surface electromyography of the uppe r trapezius muscles. Particularly the decreased ability to relax the trapez ius muscles seems to be a promising feature to identify patients with whipl ash associated disorder Grade II. Assessment of the muscle (dys)function by surface electromyography offers a refinement of the whiplash associated di sorder classification and provides an indication to a suitable therapeutic approach.