Does Paraspinal Muscle Mass Predict Lumbar Lordosis before and after Decompression for Degenerative Spinal Stenosis?

Study Design. Retrospective Cohort Study. Objective. The purpose of this study was to determine if muscle mass and quality of the lumbar paraspinal muscles was associated with improvements in lumbar lordosis and other sagittal parameters after isolated posterior lumbar decompression surgery for lumbar spinal stenosis. Summary of Background Data. Over time, either due to degenerative changes or other spinal conditions, individuals may develop sagittal imbalance. In patients with lumbar spinal stenosis, sagittal imbalance can further exacerbate symptoms of pain and radiculopathy. Sarcopenia of paraspinal muscles has been implicated in previous spine research as a variable with influence on surgical outcomes. Methods. Sagittal parameters were measured on preoperative and postoperative lateral lumbar radiographs and included lumbar lordosis (LL), sacral slope (SS), and pelvic tilt (PT). Preoperative MRI images were evaluated at the base of the L4 vertebral body to assess muscles mass of the psoas muscle and paravertebral muscles (PVM) and Goutallier grade of the PVM. Patients were divided into 3 muscle size groups based on PVM normalized for body size (PVM/BMI): Group A (smallest), Group B, and Group C (largest). Results. Patients in Group C had greater LL preoperatively (51.5° vs. 47.9° vs. 43.2, P =0.005) and postoperatively (52.2° vs. 48.9° vs. 45.7°, P =0.043). There was no significant difference in the ∆LL values between groups ( P >0.05). Patients in Group C had larger SS preoperatively (35.2° vs. 32.1° vs. 30.0°, P =0.010) and postoperatively (36.1° vs. 33.0° vs. 31.7°, P =0.030). Regression analysis showed that PVM/BMI was a significant predictor of LL preoperatively ( P =0.039) and postoperatively ( P =0.031), as well as SS preoperatively ( P =0.001) and postoperatively ( P <0.001). Conclusion. Muscle mass of the paravertebral muscles significantly impacts lumbar lordosis and sacral slope in patients with lumbar spinal stenosis before and after posterior lumbar decompression. These findings highlight a need to address risk factors for poor muscle quality in patients with sagittal imbalance.