SPINE Volume 31, Number 3, pp E71–E79 ©2006, Lippincott Williams & Wilkins, Inc. Effects of Pelvic Skeletal Asymmetry on Trunk Movement Three-Dimensional Analysis in Healthy Individuals Versus Patients With Mechanical Low Back Pain Einas Al-Eisa, PhD,* David Egan, PhD,* Kevin Deluzio, PhD,† and Richard Wassersug, PhD* Study Design. Comparative analysis and correlational research design were used to investigate the association between anthropometry and biomechanical performance among asymptomatic subjects and patients with low back pain (LBP). Objectives. To examine the association between pel- vic asymmetry and patterns of trunk motion in asymp- tomatic and LBP subjects. Secondary objective was to investigate the association between restricted trunk mo- tion, laterality of referred pain, and pelvic asymmetry. Summary of Background Data. Subtle pelvic asymme- try (exhibited as either lateral pelvic tilt or iliac rotational asymmetry), which is common among normal individu- als, has not been convincingly linked to abnormalities in back movements. Given the difficulty in diagnosing most LBP, a classification using pelvic asymmetry and patterns of movement could be helpful in establishing a rational treatment plan. Methods. Fifty-nine subjects with no history of LBP and 54 patients with mechanical unilateral LBP were tested. An anthropometric frame was used to measure pelvic asymmetry in standing. Dynamic motion data, comprised of the principal and coupled movements, were collected using the Qualysis Motion Capture System. Results. While the groups did not differ in the total range of lumbar movement, the LBP group exhibited sig- nificantly higher asymmetry in the principal motion. The groups differed significantly in the pattern of coupled ro- tation during lateral flexion. Asymmetry in lumbar lateral flexion was highly related to two types of pelvic asymme- try: lateral pelvic tilt (LPT) and iliac rotation asymmetry (IRA). Asymmetry in lumbar axial rotation was highly related to IRA but weakly related to LPT. Conclusions. This study demonstrates objective differ- ences in patterns of lumbar movement between asymp- tomatic subjects and patients with LBP. The study also demonstrates that subtle anatomic abnormality in the pelvis is associated with altered mechanics in the lumbar spine. We suggest that asymmetry of lumbar movement may be a better indicator of functional deficit than the absolute range of movement in LBP. Key words: pelvic asymmetry, trunk kinematics, low back pain, coupling. Spine 2006;31:E71–E79 Sixty to eighty percent of the general adult population suffers low back pain (LBP) at some point in their lives. 1,2 LBP is also the major cause of disability for patients under the age of 45 in the United States. 3,4 The high cost of LBP can be attributed to its high incidence, high re- currence, and associated disability. Back pain is a symptom rather than a disease diagnosis. 5 Almost 80% of patients with LBP do not have structural pathologic changes (e.g., radiologic signs of degenera- tion, or intervertebral disc herniation). Such patients are classified as having “nonspecific” or “mechanical” LBP, defined as pain in the back that is induced and aggra- vated by mechanical factors such as movement. 6 Cur- rently, functional assessment is the only way to differentiate between various forms of mechanical LBP. Such assess- ment is particularly important in patients with LBP since pain avoidance and the adaptation to pain that take place in the musculoskeletal system may lead to func- tional deficits, 7 such as abnormal movement patterns. 8 Spinal mobility is widely used as an objective clinical assessment of LBP, for both diagnostic and progress evaluation purposes, despite its poor sensitivity and spec- ificity. 9,10 While some studies reported a significant dif- ference in spinal mobility between healthy participants and patients with LBP, 10,11 more recent studies found no significant difference between those two populations in spinal mobility. 9,12 This lack of agreement may be attrib- uted to differences in measurement procedures, methods of analysis, and study populations. Furthermore, there is great variability in trunk motion among both asymptomatic and patient populations, 13 and no general consensus on what constitutes normal trunk motion. Pathology in the low back might affect the pattern of movement rather than only the range of move- ment. 14 Hence, assessment of movement symmetry could indicate abnormality in spinal motion and give some insight to underlying dysfunction. In particular, asymmetries of trunk lateral flexion and axial rotation are presumed to be clinically impor- tant. 15–17 Asymmetry in lateral flexion is useful for iden- tifying subtle lateral lumbar shift, 15,18 especially in cases of lumbar disc herniation. 19 Also, trunk axial rotation is one of the common movements often affected by LBP. 20,21 Trunk axial rotation and lateral flexion are associated with each other, a phenomenon known as “spinal cou- From the *Department of Anatomy & Neurobiology and †School of Biomedical Engineering, Dalhousie University, Halifax, Nova Scotia, Canada. Acknowledgment date: February 18, 2005. First revision date: June 20, 2005. Acceptance date: July 7, 2005. The manuscript submitted does not contain information about medical device(s)/drug(s). Other funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. Address correspondence and reprint requests to Einas Al-Eisa, PhD, Department of Anatomy & Neurobiology, Dalhousie University, 5850 College Street, Halifax, Nova Scotia, B3H 1X5, Canada; E-mail: ealeisa@dal.ca E71