Ultrasound examination of m. erector spinae in patients with thoracic scoliosis after dynamic and rigid fixation

Objective. To assess the condition and functional parameters of m. erector spinae in patients who underwent dynamic anterior and rigid posterior fixation for thoracic scoliosis, using ultrasound diagnostics (US) and a proprietary methodology. Materials and Methods . The comparative study involved 95 patients aged 15–55 years with idiopathic right-sided thoracic scoliosis (Cobb angle 35–60°): 33 of them after dynamic fixation, 32 after rigid fixation, and 30 patients awaiting surgery (control group). The follow-up period exceeded 12 months. Ultrasound examination included measuring of the fiber pennation angle, muscle thickness, contractility index, and relative asymmetry at the apex of the scoliotic curve. Measurements were performed in two patient positions: at rest and during maximum extension (30°, controlled by a goniometer). Results. Statistically significant differences ( p ≤ 0.05) between the groups were found. At rest, the pennation angle after dynamic fixation (20.06° ± 0.15°) was 26.5% higher than after rigid fixation (15.85° ± 0.62°), but lower than control values (23.57° ± 0.93°). The thickness of m. erector spinae with dynamic fixation (1.23 cm ± 0.01 cm) was close to the control (1.35 cm ± 0.02 cm), whereas with rigid fixation a pronounced decrease in thickness was observed (0.89 cm ± 0.01 cm). During extension (30°), the pennation angle in patients operated on with the dynamic system sharply increased to 39.5° (close to the control value of 40.5°), which was 2.4 times higher than the indicator (16.2°) in the group with rigid fixation. The thickness of m. erector spinae (2.15 cm ± 0.05 cm) under load after dynamic fixation corresponded to the control (2.20 cm ± 0.03 cm), while rigid fixation showed thinning (1.21 cm ± 0.14 cm). The mean contractility index after dynamic fixation was significantly lower ( p < 0.05) than that (84.65% ± 0.35%) after rigid fixation and close to the control value (53.9%), indicating preservation of muscle contractility. Relative asymmetry was minimal in the dynamic fixation group (1.6%) compared to that in the rigid fixation (2.24%) and control (2.96%) groups. Conclusion. The ultrasound technique used in the study demonstrated high efficiency in assessing the condition of the paraspinal muscles. Anterior dynamic fixation for thoracic scoliosis provided the preservation of m. erector spinae functional activity, the maintenance of natural contraction and improved muscle symmetry, whereas posterior rigid fixation was accompanied by structural changes, including reduced elasticity and degeneration of muscle fibers.