CT measurement of trunk muscle areas in patients with chronic low back pain.

PURPOSE The objective of this study was to determine the cross-sectional area changes of the paraspinal, isolated multifidus, quadratus lumborum, psoas, and the gluteus maximus muscles with CT in patients with chronic low back pain. MATERIALS AND METHODS In this study, we evaluated 36 patients with chronic low back pain and 34 healthy volunteers. The mean age of the patients was 43.2 +/- 6.9 years (range, 30- 58 years) and the mean age of control group was 44.4 +/- 6.9 years (range, 31-61 years). We defined pain that lasts more then one year as chronic pain. Female patients were selected for standardization. All patients were housewives. None of the patients or controls engaged in physical activity other than routine housework. We used a visual analog scale and the Oswestry Pain Questionnaire for clinical evaluation. We made CT cross-sections of the paraspinal muscles at the upper and lower endplates of L4, and of the gluteus maximus at the head of the interfoveal level. RESULTS In the patient group the multifidus, psoas, and quadratus lumborum cross-sectional areas were smaller than in the control group, and the P values were P = 0.002, P = 0.042, and P = 0.047, respectively, at the L4 endplate. At the L4 endplate level, cross-sectional areas of the multifidus and paravertebral muscles in the patient group were smaller than in the control group, and the difference was statistically significant (P = 0.001, P = 0.010, respectively). We did not find any significant difference between the patient and the control groups in gluteus maximus cross-sectional area. CONCLUSION Chronic low back pain caused atrophy of the paraspinal, isolated multifidus, quadratus lumborum, psoas, and the gluteus maximus muscles to varying degrees, which was most prominent in the multifidus. Atrophy was noted in all of the studied muscles, except the gluteus maximus. The reliability of CT in measuring the cross-sectional areas of the back muscles was acceptable.