Immediate Improvements in Side-to-Side Weight Bearing and Iliac Crest Symmetry After Manipulation in Patients with Low Back Pain

Abstract

Background

Although there is good evidence that spinal manipulation is an effective treatment to improve pain and function for patients with low back pain (LBP), there is little evidence to support the mechanism by which manipulation works.

Objectives

To determine if iliac crest (IC) and weight-bearing (WB) symmetry improve after spinal manipulation and to determine if improvements in IC and WB symmetry are associated with improvements in pain and function in patients with low back pain.

Design

Single group, within-subjects, repeated measures design.

Method

Thirty consecutive patients (mean age = 40±13) who came to a spine specialty center for treatment of acute or chronic LBP and who would be receiving spinal manipulation participated in the study (14 male patients). Patients completed a series of self-report measures of pain and function and received a standardized physical examination, including the assessment of IC and WB symmetry. Patients received a standardized manipulative intervention, and immediate and 3- to 4-day follow-up examinations were performed by a blinded examiner. Paired t tests were performed to determine within-group changes, and Pearson product moment correlation coefficients were calculated to determine the relationship between improvements in IC and WB symmetry and improvements in pain and function. To control for the potential that an association between changes in IC and/or WB symmetry and changes in pain and function could be confounded by the baseline outcome measure, simultaneous linear regression was performed on any significant correlation. Partial F tests were used to determine if the additional explained variability was significant.

Results

Patients with LBP demonstrated significant improvements in IC and WB symmetry after manipulation (P<.001). Improvements in WB symmetry were associated with improvements in the patients' self-reported levels of pain 3 to 4 days after manipulation (r=.5, P=.007). Based on the significant association between improvements in WB symmetry and improvements in pain, the final pain score was regressed on the change in WB symmetry, after controlling for the baseline level of pain. The addition of the change in WB symmetry explained a 10% additional increase in variability in the patient's level of pain at the 3- to 4-day follow-up (P = .01). No relationship was found between improvements in IC and WB symmetry and improvements in function as determined by the Oswestry Disability Questionnaire 3 to 4 days after manipulation.

Conclusion

IC and WB symmetry improved immediately after spinal manipulation. Improvements in WB symmetry were related to improvements in the patients' self-reported levels of pain, even after controlling for the baseline level of pain. Improvements in IC and WB symmetry were not related to changes in function. The results of this study provide initial data to elucidate how manipulation may work to improve pain and function in patients with LBP.

Introduction

Many randomized clinical trials1., 2., 3., 4., 5., 6., 7. and several systematic reviews8., 9., 10., 11. have found spinal manipulation to be an effective treatment for improving pain and function in patients with low back pain (LBP). However, there is little evidence to support the mechanism by which this occurs. Researchers have suggested that alterations in muscle electrical activity,12., 13., 14., 15. decreased muscle inhibition,¹⁶ reduced reflex muscle spasm,17., 18. and increased intersegmental joint play¹⁹ are some of the results of spinal manipulation that may explain these improvements. Specific to the sacroiliac (SI) joint, some authors have proposed that manipulation directed to this area would alter the abnormal positional relationships between the ilium and the sacrum.²⁰ However, because there is growing evidence that the amount of motion in the lumbopelvic region between the sacrum and the ilium is too small to be even detectable by palpation (ie, less than 2 mm and less than 2°), this theory has been questioned.21., 22., 23. Using roentgen stereophotogrammetric analysis, Tullberg et al²⁴ reported no alteration in the position of the SI joint after a manipulation procedure directed to the SI region.

Using 2 tests we routinely use in the physical examination of patients with LBP, we have observed that alterations such as asymmetries in iliac crest (IC) level and side-to-side weight-bearing (WB) distribution seem to improve after spinal manipulation. Tests of IC and WB symmetry have both been shown to have sufficient reliability to be used in clinical practice.25., 26. Measurement of IC symmetry is a static palpation test used to determine positional malalignment of the pelvis, antalgic posture, or presence of a leg length discrepancy.²⁷ It has been suggested that positional malalignment of the pelvis may be caused by soft tissue alterations that result from the presence of dysfunction in the lumbopelvic region.²⁶ Measurements of WB symmetry also seem to be associated with the presence of LBP. Recent evidence suggests that patients with LBP exhibit decreased side-to-side WB symmetry (ie, increased side-to-side WB asymmetry) than healthy control subjects without LBP (8.8% vs 3.6% of total body weight, respectively, P < .001).²⁵ Importantly, in the patients with LBP, higher magnitudes of side-to-side WB asymmetry were significantly associated with increased pain (r = .39, P = .021).25., 28.

Because there is no evidence to support the theory that spinal manipulation alters bone or joint positioning, we believe the asymmetries observed in patients with LBP may be a result of soft tissue alterations. It has recently been proposed that manipulation may act at the level of soft tissues in the lumbopelvic region rather than effecting changes in bony alignment per se.²⁴ Perhaps manipulation affects the asymmetric tension of soft tissues in this area, resulting in decreased pain. The more symmetric tension and decreased pain may normalize the transmission of forces through the lumbopelvic region and restore more equal weight-bearing distribution in the lower extremities. However, little research has been conducted to begin investigating such a theory. Clinicians who use spinal manipulation to treat patients with LBP will attest to the notion that they frequently observe changes in lumbopelvic posture and landmark asymmetries in their patients. However, due to the poor reliability of tests used to quantify these asymmetries,29., 30. few studies have investigated objective changes in this region due to a manipulative intervention.

Based on the absence of evidence to explain the mechanism for how manipulation may work, it has recently been suggested that clinicians and researchers pursue this line of research.³¹ Thus, the purpose of this project is to determine if IC and WB symmetry improve after manipulation and if these improvements are related to improvements in pain and function.