Use of ultrasonography to evaluate thickness of the erector spinae muscle in maximum flexion and extension of the lumbar spine.

Study Design. An observational study of the changes in thickness of the erector spinae (ES) muscle in three different trunk postures. Objective. To use ultrasonography to evaluate the thickness of the ES muscle in three different trunk postures. Background. Although there has been extensive study of the morphology of the ES muscle during prolonged trunk flexion, we have little information about the changes in thickness of these muscles in various postures of the lumbar spine. Ultrasonography has never been used to measure the thickness of ES muscle. Methods. We studied 30 volunteers with no history of lower back problems. We used ultrasonography to measure the thickness of the ES muscle at each lumbar level (L1, L2, L3, L4, and L5) in maximum flexion, neutral posture, and maximum extension. We tested the reliability of this method by evaluating intraobserver and interobserver differences in 13 subjects. Result. The high correlation between intraobserver and interobserver measurements in the 13 subjects demonstrated that the method provides sufficient reproducibility. When the trunk was flexed maximally, the thickness of the ES muscle was significantly decreased at each lumbar vertebral level. When the trunk was extended maximally, the thickness of the ES muscle was significantly increased at each lumbar vertebral level. Conclusion. The thickness of the ES muscle decreases as the lumbar spine flexes and increases as it extends. We used ultrasonography successfully for quantitative evaluation of changes in thickness of the ES muscle with postural changes in the lumbar spine.