Effect of race, age, and gender on lumbar muscle volume and fat infiltration in the degenerative spine.

Background: The quantity and quality of spinal muscles in patients with degenerative spinal diseases and various backgrounds such as age, gender, or race is unclear. We quantitatively evaluated the cross-sectional area (CSA) and fatty degeneration of the muscles around the spine, using magnetic resonance imaging (MRI) in patients with degenerative spinal disease, and studied the effects of age, gender, and race in multicenter retrospective study.

Methods: The subjects were Caucasian and Asian patients with degenerative lumbar disease who underwent L4-5 single level spinal fusion surgery at centers in the United States and Japan. Using preoperative axial T2 MRI at the L4-5 disc level, the cross-sectional areas of the psoas and paraspinal muscles were measured. Fat infiltration was measured using the threshold method, and percent fat area (%FA) was calculated for each muscle. The muscle/disc area ratio (MDAR) was used to control for size differences per patient. T-test, Pearson's correlation coefficient, partial correlation, and multiple linear regression were used for statistical analysis.

Results: In total, 140 patients (53 men; 87 women; mean age, 69.2 years) were analyzed. Age was similar in Caucasians (n = 64) and Asians (n = 76). MDARs were larger in Caucasians for paraspinal and psoas muscles (p < 0.005). Percent FA of psoas was similar in Caucasians and Asians, but greater in the paraspinal muscles of Asians (p < 0.05). After controlling for race and gender, age was correlated negatively with MDAR (p < 0.001) and positively with %FA (p < 0.001). In the multiple linear regression analysis, age, gender, and race were independently affected by MDAR and %FA.

Conclusions: Lumbar muscle mass and quality were affected by age, gender, and race, independently, in patients with degenerative lumbar disease.