Preoperative and follow-up variation of the psoas major muscle as a predictor of S1 screw loosening in patients with degenerative lumbar spinal stenosis

Abstract

Abstract Background: It was reported the paraspinal muscle played an important role in spinal stability. The preoperative paraspinal muscle was related to S1 screw loosening. But the relationship between preoperative and postoperative change of psoas major muscle (PS) and S1 pedicle screw loosening in degenerative lumbar spinal stenosis (DLSS) patients has not been reported. This study investigated the effects of preoperative and follow-up variations in the psoas major muscle (PS) on the first sacral vertebra (S1) screw loosening in patients with degenerative lumbar spinal stenosis (DLSS). Methods:212 patients with DLSS who underwent lumbar surgery were included. The patients were divided into the S1 screw loosening group and the S1 screw non-loosening group. Muscle parameters were measured preoperatively and at last follow-up magnetic resonance imaging. A logistic regression analysis was performed to investigate the risk factors for S1 screw loosening. Results: The S1 screw loosening rate was 36.32% (77/212). The relative total cross-sectional areas and relative functional cross-sectional areas (rfCSAs) of the PS at L2–S1 were significantly higher after surgery. The increased rfCSA values of the PS at L3–S1 in the S1 screw non-loosening group were significantly higher than those in the S1 screw loosening group. The regression analysis showed male, lower CT value of L1 and longer segment fusion were independent risk factors for S1 screw loosening, and postoperative hypertrophy of the PS was a protective factor for S1 screw loosening. Conclusions:Compared to the preoperative muscle, the PS size increasedand fatty infiltration decreased after surgery from L2–3 to L5–S1 in patients with DLSS presenting with short-segment fusion. Postoperative hypertrophy of the PS should be considered as a protective factor for S1 screw loosening. MRI morphometric parameters and postoperative selected exercise of PS for DLSS patients after PLIF might contribute to improvement of surgical outcome.