Digital 3-Dimensional Analysis of the Paravertebral Lumbar Muscles After Circumferential Single-level Fusion

Abstract

A retrospective controlled cohort study was performed for postoperative 3-dimensional muscle evaluation. Our aim was to establish a method for spatially continuous 3-dimensional analysis of the lumbar paravertebral muscles after instrumented circumferential single-level fusion. Paravertebral muscle degeneration is thought to contribute to postoperative low back pain. Previous analysis methods did not regard on implant associated artifacts and on the multisegmental 3-dimensional character of the paravertebral muscles. At 1 week and 12 months postoperatively, thin slice computed tomography scans of the lumbar paravertebral muscles were digitally analyzed and compared for 20 patients with chronic low back pain owing to monosegmental degenerative disc disease ≥ Modic II° and high intensity zones at L4/5. Tissue-specific regions of all slices were determined for automated calculation of fat and muscle volume, and localization of fatty degenerated areas in a 3-dimensional computer reconstruction model. All computed tomography scans were successfully digitally reconstructed and evaluated. A significant decrease of paravertebral muscle volume and an increase in volume fraction of fatty degeneration was observed at 12 months (Vmuscle 127.4±28.5 cm, V%fat 48.67±3.63%) compared with 1 week postoperatively (Vmuscle 217.4±34.2 cm, V%fat 12.57±2.28%). Fat tissue areas were most often located close to the spinal processes and anterolateral, close to the transverse processes. We established a 3-dimensional image analysis method for evaluating postoperative changes in the lumbar paravertebral muscles of patients, after circumferential single-level fusion, consistently accounting for implant-associated artifacts. We were able to demonstrate volume atrophy and an increase of fatty degeneration after 12 months compared with 1 week postoperatively.