Study design: In this study, the authors investigated the superficial multifidus muscle in patients with idiopathic scoliosis. During spinal fusion, biopsies were taken bilaterally at the apex of the curve, and at the upper and lower end vertebrae.
Objectives: To analyze the muscular reactions in response to bracing in patients with idiopathic scoliosis.
Summary of background data: The extent to which intervertebral mobility is restricted by an orthosis is still controversial. In addition, the effect of bracing on the erector spinae has not been investigated.
Methods: Of a total 30 patients, 11 had been treated with a corset for a year or more before surgery. Biopsies were investigated histochemically and the muscle fibers classified as Type I, IIA, IIB, or IIC (transitional fibers). The relative distribution of the fibers was calculated and their diameter was measured.
Results: In unbraced patients, a shift in the fiber distribution (from "slow" to "fast") was observed exclusively at the concave side of the apex. This shift was paralleled by an increased percentage of the intermediate Type IIC fiber (indicative of fiber transformation). In patients who always wore a corset, the relative amount of Type IIC fibers was increased, without preference for a specific location.
Conclusions: Corset treatment elicits muscle fiber transformation processes at different levels along the scoliosis. This general reaction of the paraspinal muscles provides strong evidence against the existence of muscular disorders that are restricted to the area of the apex and are thus causing the scoliosis. As such, it must be assumed that the muscular changes in the apical region are secondary.