Fiber composition and fiber transformations in neck muscles of patients with dysfunction of the cervical spine.

Biopsies of ventral neck muscles (sternocleidomastoid, omohyoid, and longus colli) and dorsal neck muscles (rectus capitis posterior major, obliquus capitis inferior, splenius capitis, and trapezius) were taken from 64 patients who underwent spondylodesis for cervical dysfunction of different etiologies. The muscle fibers were classified histochemically as type I, IIA, IIB, or IIC (transitional or intermediate fibers) according to the pH lability of their myofibrillar ATPase. Signs of muscle fiber transformations were observed in all muscles investigated, as evidenced by an increased relative amount of type-IIC fibers. The transformations occurred independently of (a) the type of muscle (i.e., more "postural" or more "phasic"), (b) the sex and age of the patient, (c) the type of condition, and (d) the presence of additional neurological deficits. Thus, the same pattern of muscular reaction was found in patients with rheumatoid arthritis as in patients with soft-tissue injuries of the neck (e.g., "whiplash injury"). In the ventral muscles and the obliquus capitis inferior, the occurrence of transformations correlated strongly with the duration of symptoms; in the ventral muscles the vast majority of transformations were encountered in patients with a shorter history of symptoms, whereas in the obliquus capitis inferior the reverse occurred. In the other dorsal muscles, no correlation with the duration of symptoms was found. Muscles in which transformations had ceased displayed, on average, a significantly higher percentage of fast type-IIB fibers than were found in muscles with ongoing transformations. This strongly indicates that the transformations proceeded in the direction from "slow oxidative" to "fast glycolytic."