Duration of pain and muscular adaptations in patients with dysfunction of the cervical spine.

Biopsies of the sternocleidomastoid and omohyoid muscle were taken from 24 patients who underwent arthrodesis for cervical dysfunction of different etiologies. The two muscles, which are involved differently in movements of the head and cervical spine, were investigated histochemically. Muscle fibers were classified as type I, IIA, IIB, or IIC (transitional fibers) according to the pH lability of myofibrillar ATPase and calculated relative distribution. In both muscles, fiber transformations (as evidenced by an increase in the relative amount of type-IIC fibers) were regularly observed within the first 2 years after the onset of the symptoms. The occurrence of the transformation processes was independent of the patient's age and sex and was the same for the different etiologies. Since the overall fiber composition of the muscles remained essentially unchanged, the fiber transformations must occur alternatingly in both directions (from "slow" to "fast" and the reverse). Muscles of patients with a long case history showed no greater signs of fiber transformation. Therefore, fiber transformations in response to cervical dysfunction occur in the initial stage of the disease and involve different types of muscles. The muscles then return to a "stable" condition, independent of the continuation of the dysfunction and the chronic neck pain.