Relationship between low back pain and lumbar multifidus size at different postures.

STUDY DESIGN: A prospective study of multifidus images. OBJECTIVE.: To compare the change of the cross-sectional area (CSA) of multifidus in subjects with and without chronic low back pain (LBP) at different postures.

SUMMARY OF BACKGROUND DATA: Ultrasound imaging was shown to be useful in assessing acute LBP patients at rest only.

METHODS AND MEASURES: Thirty-five male adults participated, including 19 normal and 16 chronic LBP patients. The CSAs of multifidus were assessed on ultrasound images acquired on both sides of the L4 and L5 levels with the subjects in prone lying, upright standing, and 25 degrees and 45 degrees forward stooping.

RESULTS: In the control group, the CSA of multifidus increased from prone lying to upright standing and then gradually decreased from 25 degrees to 45 degrees forward stooping. However, a reverse pattern of the CSA changes was identified in patients with chronic LBP.

CONCLUSION: Multifidus contracts maximally at upright standing in the normal group, while maximum contraction of the muscle occurs at 25 degrees forward stooping in the patient group. The role of multifidus may be altered in the stabilization of the lumbar spine of chronic LBP patients. Assessment of the change in muscle size reacting to different postures is found to be helpful.