Pathogenesis of piriformis syndrome: a magnetic resonance imaging-based comparison study

Abstract

Objective: To assess the morphological parameters of the piriformis muscle through magnetic resonance imaging(MRI) so as to further elucidate the pathogenesis of piriformis syndrome (PS). Methods: From September 2015 to October 2016, 30 suspected PS patients and 30 normal controls were enrolled in this study from the Nanfang Hospital, Southern Medical University. The possible causative factors of the PS in the patients were obtained, and the PS patients were divided into subgroups according to the anatomic site of the tender regions. The parameters of the maximum thickness (cm), area (cm(2)) and the volume (cm(3)) of the piriformis muscle of both groups were measured by MRI and were statistically compared between the groups with the independent-sample t test so as to investigate the pathogenesis of injured sciatic nerve. Results: Twenty-six patients were verified with PS, unhealthy sitting postures presented in 16 patients (61.5%) and no trauma history was recorded in these patients. Fifteen cases (57.7%) with tenderness located at the suprapiriformis foramen region (SPF group, n=15), 11 patients (42.3%) with tenderness at the piriformis muscle (PM group, n=11). The thickness, area and volume of the pathological side piriformis muscle in the PM group were all significantly higher than the corresponding indexes in the control group[(2.24±0.46) vs (1.66±0.30) cm, (14.4±2.2) vs (8.8±2.1) cm(2,) (23.9±3.8) vs (15.2±2.6) cm(3,) respectively, t=4.699, 7.437, 8.291, all P<0.05]and were all higher remarkably than those in the SPF group[(1.62±0.20) cm, (8.7±1.6) cm(2,) (14.1±4.8) cm(3,) respectively, t=4.640, 7.631, 5.589, all P<0.05]. No significant difference was observed in the up-mentioned indexes between the SPF and the control group (t=-0.439, -0.102, -1.083, all P>0.05). Conclusions: Tender region at the buttock indicates the lesion site in the PS patients. The PS patients with tenderness at the suprapiriformis region might originate from another pathogenesis independent of piriformis muscle compression, the injury of the sciatic nerve or its branch maybe due to the indirect crush by the soft tissue of the suprapiriformis region under an unhealthy sitting posture.