Paraspinal muscle changes after single-level posterior lumbar fusion: volumetric analyses and literature review

Posterior lumbar fusion is a widely accepted surgical technique; however, it has been related to the possibility of paraspinal muscle atrophy after surgery. We investigated 1-year postoperative changes in paraspinal muscle volume using a simple formula applicable to magnetic resonance imaging (MRI) or computed tomography (CT) images. Patients with degenerative lumbar spinal stenosis who underwent posterior interbody fusion (PLIF) at the L4/5 level in the period from May 2010 to June 2017 were enrolled in this study. Radiologic parameters were measured using MRI or CT images which were taken before surgery and at 1 year after surgery. The volume of the paraspinal muscles was calculated using a simple formula which was derived from the formula for calculating the volume of truncated elliptic cones. A total of 40 patients were included; 24 were analyzed using MRI and 16 were analyzed using CT. The mean age of the patients was 59.6 ± 12.1 years and 32 (80.5%) were female. When comparing the preoperative and 1-year-postoperative images, multifidus muscle (MF) reduction was consistently observed in the MRI and CT groups, right and left (p = 0.003, p