Fatty Degeneration of the Paraspinal Muscle in Patients With Degenerative Lumbar Kyphosis A New Evaluation Method of Quantitative Digital Analysis Using MRI and CT Scan

Study Design: A comparative case-control study. Objective: The aim of this study was to quantify the degree of paraspinal muscle changes in degenerative lumbar kyphosis (DLK) patients using magnetic resonance imaging and computed tomography scanning. Summary of Background Data: Although the pathophysiology of DLK is not completely understood, extensive degeneration and weakness of the lumbar extensor muscles are thought to underlie the condition in most patients. However, there is no ideal method to quantify the degree of fat infiltration and atrophy of the paraspinal muscles in patients with DLK. Materials and Methods: The study group comprised 20 patients with DLK and 20 healthy volunteers. The cross-sectional areas of the psoas, erector spinae (ES), multifidus (MF), quadratus lumborum, and vertebral body were measured. The ratio between the cross-sectional area of the muscle and the vertebral body was used to evaluate lumbar muscularity. The degree of fatty change was evaluated by measuring the ratio between the mean signal intensity of the muscle and that of the subcutaneous fat within regions of interest. Results: Muscularity in the MF and ES was not significantly different between the DLK and control groups at L1, L2, or L3, but was significantly different at L4 (ES, P= 0.001; MF, P= 0.001) and L5 (ES, P= 0.001; MF, P= 0.015). The mean signal intensities of the ES and MF were higher in the DLK group than in the control group at all levels. The degree of fatty change in the ES and MF was significantly higher in the DLK group than in the control group (P< 0.05). Conclusions: Quantitative analysis using magnetic resonance imaging and computed tomography scanning showed differences in paraspinal muscle volume and fatty degeneration between patients with DLK and healthy volunteers. This evaluation method may be useful for measuring the extent of paraspinal muscle degeneration.