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PHYS THER
Vol. 87, No. 4, April 2007, pp. 441-454
DOI: 10.2522/ptj.20050370
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Research Reports

Patterns of Lumbar Region Movement During Trunk Lateral Bending in 2 Subgroups of People With Low Back Pain

Sara P Gombatto, David R Collins, Shirley A Sahrmann, Jack R Engsberg and Linda R Van Dillen

SP Gombatto, PT, MS, is a doctoral candidate in the Program in Physical Therapy, Washington University School of Medicine, Campus Box #8502, 4444 Forest Park Blvd, St Louis, MO 63110 (USA)
DR Collins, PhD, is Independent Consultant to the Musculoskeletal Analysis Laboratory, Program in Physical Therapy, Washington University School of Medicine
SA Sahrmann, PT, PhD, FAPTA, is Professor of Physical Therapy/Neurology/Cell Biology & Physiology, Program in Physical Therapy, Washington University School of Medicine
JR Engsberg, PhD, is Associate Professor, Department of Physical Therapy, Doisy College of Health Sciences, Saint Louis University, St Louis, Mo
LR Van Dillen, PT, PhD, is Assistant Professor, Program in Physical Therapy, Washington University School of Medicine

Address all correspondence to Ms Gombatto at: spgombat{at}artsci.wustl.edu


Submitted November 23, 2005; Accepted November 29, 2006


   Abstract
 
Background and Purpose: The movement system impairment (MSI) system is one proposed system for classifying low back pain (LBP) problems. Prior clinical data and observations for the MSI system suggest that different LBP subgroups demonstrate different patterns of movement during clinical tests, such as trunk lateral bending (TLB). The purpose of this study, therefore, was to examine the validity of the observation that lumbar region (LR) movement patterns during TLB are different between 2 subgroups of people with LBP: lumbar rotation with extension (Rotation With Extension) and lumbar rotation (Rotation).

Subjects: Participants were 44 people (28 men and 16 women; age [X±SD], 28.5±8.4 years) with chronic or recurrent LBP.

Methods: Each participant's LBP problem was classified with the MSI system. Kinematic variables were measured, and LBP symptoms were recorded during the TLB test.

Results: People in the 2 LBP subgroups demonstrated different patterns of LR movement during TLB. People in the Rotation With Extension subgroup displayed an asymmetric (right versus left) pattern of LR movement across the TLB movement, whereas people in the Rotation subgroup displayed a symmetric pattern of LR movement. Equal proportions of people in the 2 subgroups reported an increase in symptoms with the TLB test.

Discussion and Conclusion: The patterns of LR movement across the TLB movement were different in 2 subgroups of people with LBP. The difference in the LR movement patterns between subgroups may be an important factor to consider in specifying the details of the interventions for these 2 LBP problems.


   Introduction
Top
 Abstract
 Introduction
Method
 Results
 Discussion
 Conclusion
 References
 
A number of systems, including the McKenzie system,1 the treatment-based classification system,2 and the movement system impairment (MSI) system,3 have been proposed to classify people with low back pain (LBP) into homogeneous subgroups. Classification into subgroups is important because it allows the examination of potential mechanisms underlying different LBP problems and, as a result, provides a basis for classification-specific interventions with the goal of improving outcomes.

Of interest in the present report is the testing of one aspect of the validity of the MSI system, which is based on the kinesiopathologic model of movement (KPM).3 The basic premise of the KPM is that musculoskeletal pain develops when movements and alignments are repeated in the same direction across daily activities. Low back pain, in particular, is proposed to develop when an individual repeatedly moves or aligns the lumbar region (LR) in the same direction.

As with earlier descriptions of alterations in the neutral zone in people with LBP,4,5 the KPM suggests that repeated movements and alignments of the LR have the potential to increase the flexibility of lumbar segments in a specific direction. The increase in flexibility is proposed to reinforce the use of direction-specific movement and alignment strategies that subsequently can become generalized across many activities. The exposure of spinal tissues to repeated low-magnitude loading in the same direction is proposed to contribute to the accumulation of excessive tissue stress, microtrauma, and eventually LBP.

Typically, clinical examinations to classify LBP include tests in which trunk movements and alignments are examined and LBP symptoms are assessed. A variety of tests are included, with the goal of identifying the pathoanatomical source of symptoms1,6 and classifying LBP problems into subgroups on the basis of identified impairments to direct physical therapy interventions.1–3,7,8 The specific purpose of the clinical examination associated with the MSI system is to identify the direction of movement and alignment that appears to be contributing to an individual's LBP problem.

On the basis of results from the examination, the LBP problem is classified into 1 of 5 subgroups. The subgroups are named according to the directions of LR movements and alignments that are observed across several tests in the examination and that are associated with LBP symptoms. The LBP subgroups are: lumbar flexion, lumbar extension, lumbar rotation (Rotation), lumbar rotation with flexion, and lumbar rotation with extension (Rotation With Extension).

One method used to examine the validity of an LBP classification system is to study clinical tests used during the examination and to test predictions about findings for different LBP subgroups. In the present study, we examined trunk lateral bending (TLB), one of the test movements often assessed in people with LBP.2,3,6,9–17 We consider the TLB movement to be particularly important to assess because characteristics of the movement18–21 and repeated performance of TLB22 have been associated with an increased risk23 of LBP. Trunk lateral bending is also one of a cluster of clinical tests that have been found useful in discriminating between people with and people without LBP.10

The results of the TLB test then are used, along with the results of other tests, to assist in classifying an individual's LBP problem and directing a physical therapy intervention.2,3,6–8 Specifically, with the MSI system, data based on clinical measures suggest that people in the Rotation With Extension and Rotation subgroups demonstrate differences in LR movement patterns and symptom behavior with several clinical examination tests, including the TLB.24 The observation that different subgroups of people with LBP demonstrate different characteristics of LR movement during the TLB, however, has not been validated with instrumented measures.

A number of different methods have been used to quantify the characteristics considered to be important to TLB movement in both people with and people without LBP.2,8,17,25–34 Most commonly, examiners have assessed the end-range symmetry of the TLB movement and LBP symptoms.2,3,6,31,34 Because functional activities are not commonly performed at end ranges of motion, however, examining the characteristics of TLB across the range of motion also may be important.3,35 The approach used in the present study, therefore, was different from that used in earlier work with regard to the use of laboratory measures to examine the patterns of LR movement across the TLB movement.

The purpose of the present study was to examine the validity of the clinical observation that LR movement patterns during the TLB test are different between 2 subgroups of people with LBP: Rotation With Extension and Rotation. On the basis of earlier clinical data and observations, we hypothesized that people in the Rotation With Extension subgroup would exhibit a more asymmetric (right versus left) pattern of LR movement than people in the Rotation subgroup. Examining movement patterns in subgroups of people with LBP during a trunk movement is important because it can provide information to assist the clinician in identifying movement patterns that may be contributing to the LBP problem, classifying an individual's LBP problem, and, more specifically, directing classification-specific interventions that address the movement patterns.


   Method
Top
 Abstract
 Introduction
 Method
Results
 Discussion
 Conclusion
 References
 
Subjects

Forty-four people (28 men and 16 women; age [X±SD], 28.5±8.4 years) with chronic or recurrent LBP36 participated in the study (Tab. 1). The subjects were people who reported regular participation (minimum of 2 times per week) in a sport that placed repetitive rotational demands on the hip and lumbopelvic region and who associated participation in their sport with an increase in their LBP, either during or after play. Subjects were recruited from community sources that included advertisements posted on university campuses, in local newspapers, and at local sports clubs or events. No subject was experiencing an acute flare-up36 of the LBP problem at the time of testing. For the purposes of this study, a flare-up was defined as a phase of pain that is superimposed on a recurrent or chronic course and that consists of a period, usually 1 week or less, when the LBP is markedly more severe than usual. If an individual is not in a flare-up period, then he or she should be able to identify the beginning and the end of a flare-up period.36


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  		Table 1. Differences in Characteristics of Subjects in the Lumbar Rotation With Extension Subgroup and the Lumbar Rotation Subgroup

 
With a forced-choice format (yes/no), people were queried both during the screening portion of the study and on the day of testing to determine whether they had been diagnosed by a physician with any of the following conditions: serious spinal complications (eg, tumor or infection); previous spinal surgery; marked kyphosis or scoliosis; spondylolisthesis; spinal stenosis; spinal instability; spinal fracture; ankylosing spondylitis; degenerative disk disease; disk herniation; lower-extremity impairment, such as previous lower-extremity surgery or leg length discrepancy; severe neurological involvement; rheumatoid arthritis; neurological disease requiring hospitalization; history of unresolved cancer; osteoporosis; or current pregnancy. People were excluded from the study if they responded "yes" to any of the conditions listed.

Instrumentation

A 6-camera, 3-dimensional motion measurement system (EVaRT*) was used to capture data for examining kinematics during each TLB test. The sampling rate of each camera was 60 Hz, and the static resolution of the motion system was 1 mm for a volume of 1 m3. Movement during the TLB test was captured through the use of 24 retroreflective markers placed on predetermined anatomical landmarks of the trunk, pelvis, and extremities. The specific marker locations were as follows: acromion, distal third phalanx, anterior superior iliac spine, iliac crest, greater trochanter, lateral knee joint line, distal aspect of lateral malleolus, posterior aspect of calcaneus, seventh cervical spinous process, fourth thoracic spinous process, seventh thoracic spinous process, tenth thoracic spinous process, first lumbar spinous process, third lumbar spinous process, fifth lumbar spinous process, and second sacral spinous process. All markers were placed bilaterally, except for spine markers, which were placed superficially over specific spinous processes. Markers were attached with double-sided adhesive tape. Markers placed over spinous processes were 1.90 cm in diameter. All other markers were 2.54 cm in diameter.

Procedure

All participants read and signed an informed consent statement approved by the Washington University School of Medicine Human Studies Committee before participating in the study. Testing included completion of self-report measures, laboratory-based movement testing, and participation in a standardized clinical examination to classify the LBP problem.17,37

Self-Report Measures

A series of self-report measures were completed (Tab. 1). The measures included the following: a demographic and LBP history questionnaire, a numerical rating scale (NRS) of symptoms,38 the Oswestry Disability Index (ODI),39 a racquet sports activity questionnaire, and the Baecke Habitual Activity Questionnaire (BAS).40 The demographic and LBP history questionnaire included variables recommended for reporting in studies involving people with LBP.41 The NRS is an 11-point scale (0–10) of average symptoms over the preceding 7 days, with higher numbers indicating higher symptom intensity. The reliability and validity of NRS scores have been well documented, and scores can be treated as ratio scale data.42 We developed the racquet sports activity questionnaire, which we modeled after a questionnaire used by Raty et al43 to survey LBP problems in elite athletes. The BAS is a 16-item questionnaire that measures habitual physical activity over a prolonged period of time.40 The construct validity of the BAS has been examined by principal components analysis,40 and test-retest reliability has been examined and found to be acceptable, with Pearson product moment correlation coefficients ranging from .74 to .88.40

Laboratory-Based Testing

After completing the questionnaires, the subjects participated in laboratory-based movement testing, which included performance of the TLB test. Subjects wore tightly fitting shorts and a jog bra (women) open over the spinous processes. The TLB movement was performed with subjects in a relaxed standing position, with feet shoulder width apart. At a self-selected movement speed, a subject was asked to laterally bend to a side as far as he or she could and then return to the starting position. The subject was instructed to perform the test movement without bending forward, backward, or twisting and without lifting the foot on the side opposite the trunk movement. Each subject was given 10 seconds to complete each test movement. The TLB movement was performed one time to the right and one time to the left. Reports of changes in LBP symptoms with each TLB movement, relative to symptoms in the standing position, were recorded. Possible symptom responses included the following: remained the same, increased, decreased, or eliminated.

Data Processing

All marker data from the motion measurement system were filtered with a fourth-order, dual-pass Butterworth filter at an initial cutoff frequency of 2.5 Hz. That initial cutoff frequency was chosen because the movements being measured were relatively slow. After the data were filtered, the start and end points of the trunk movement were determined, and the movement time was calculated. Because each subject performed each test movement at a self-selected speed, a filtering frequency based on an individual's movement time was used. With the movement time, raw data were filtered at a subject-specific cutoff frequency44 that was calculated from the reciprocal of 15% of the period with the following equation: 1/[.15 x (2 x movement time)].

The start of movement for each segment during TLB was defined as the time at which both of the following criteria were met: the angular displacement of the segment exceeded a threshold of 0.8 degree, and the angular velocity exceeded 20% of the maximum angular velocity for the segment. The end of movement during TLB was defined as the first point at which the total TLB angle reached 98% of its maximum during the TLB movement. The movement start and end then were visually inspected to determine whether the start marked the first point at which there was a consistent change in the slope of the angle-time plot and whether the end marked the overall maximum angle. If these criteria were not satisfied, then an examiner, who was unaware of the LBP subgroup, made visual judgments of the segment start and end, and the values were manually assigned. Approximately 9% of the movement start and end points required manual modification.

Kinematic measures.
Lumbar, lower thoracic, and upper thoracic region angles and the total TLB angle were calculated across time. The LR segment was defined by a vector from a marker superficial to the second sacral spinous process (S2) to a marker superficial to the first lumbar spinous process (L1). The lower thoracic region segment was defined by a vector from the L1 marker to a marker superficial to the seventh thoracic spinous process (T7). The upper thoracic region segment was defined by a vector from the T7 marker to a marker superficial to the seventh cervical spinous process (C7). Each marker position was calculated relative to the local coordinate system of the pelvis. The local pelvic coordinate system was defined as follows: the origin was at the S2 marker, the anterior superior iliac spine marker defined the x-y plane of the pelvis, and the positive z-axis was defined by a vector perpendicular to the x-y plane (Fig. 1).


Figure 1
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  		Figure 1. Lumbar region angle ({lambda}) calculated relative to the z-axis of the local coordinate system of the pelvis. Posterior view. L1=reflective marker superficial to the spinous process of the first lumbar vertebra; L ASIS=reflective marker superficial to the left anterior superior iliac spine; LR segment=vector extending from S2 to L1, indicating the lumbar region segment; R ASIS=reflective marker superficial to the right anterior superior iliac spine; S2=reflective marker superficial to the spinous process of the second sacral vertebra; XY=x-y plane of the local coordinate system of the pelvis; +Z=z-axis of the local coordinate system of the pelvis.

 
The LR angle was calculated as the angle across time between the positive z-axis of the local pelvic coordinate system and the LR segment in the frontal (y-z) plane of the pelvic coordinate system (Figs. 1 and 2). The middle thoracic region angle was calculated as the angle between the LR segment and the middle thoracic region segment across time. The upper thoracic region angle was calculated as the angle between the middle thoracic region segment and the upper thoracic region segment across time. The total TLB angle was calculated as the sum of the LR, lower thoracic region, and upper thoracic region angles (Fig. 2).


Figure 2
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  		Figure 2. Kinematic measures for trunk lateral bending test, including lumbar region and total lateral bending angles. +Z=z-axis of the local coordinate system of the pelvis.

 
Using 11 people with healthy backs, we assessed the intrarater reliability of the kinematic measures to examine the consistency of these measures. Each subject performed 3 repetitions of TLB to the right and also to the left with a minimum of 1 minute between the trials. Intraclass correlation coefficients (ICCs)45 were calculated and found to be acceptable for both LR angle (left: ICC[3,1]=.70; right: ICC[3,1]=.92) and total TLB angle (left: ICC[3,1]=.95; right: ICC[3,1]=.90). The ICC for the LR angle during TLB to the left (.70), however, was somewhat attenuated because of the limited range of values obtained across subjects (minimum=9.3°, maximum=18.6°).

Dependent variables.
All trunk kinematics were examined from the start of the TLB movement to the maximum TLB angle. The maximum TLB angle and the maximum LR angle were calculated. Patterns of LR movement during the TLB test were represented by the percent contribution of the LR segment to the total TLB angle (LR angle/total TLB angle) at each 25% time increment for right TLB and left TLB (25%, 50%, 75%, and 100% of TLB movement time).

Clinical Examination and Classification

In the next phase of the study, the subjects participated in a standardized clinical examination to classify the LBP problem.3,18 In brief, the examination included a series of tests of movements and positions. Table 2 provides a list of the tests included in the examination. With each test, a judgment was made as to whether the LR pattern of movement or alignment was different from an operationally defined kinesiology standard (positive test), and LBP symptoms were monitored. Each test was labeled as flexion, extension, rotation, or some combination on the basis of the presumed direction of the LR movement or alignment associated with the test. The judgment of the pattern of LR movement or alignment was made by the examiner on the basis of visual information or both visual and tactile information.


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  		Table 2. Tests and Measuresa Included in Physical Examination for Classifying Low Back Pain Problems17

 
The response options for symptoms with each test included the following: LBP symptoms remained the same, increased, decreased, or were eliminated. If a subject reported an increase in symptoms with the initial test, which was referred to as a primary test, then the test was immediately followed by a secondary test in which the subject's preferred movement or alignment strategy was modified to be more consistent with the kinesiology standard.7,46 The secondary test was performed in an attempt to decrease or eliminate symptoms. Neurological screening and testing for magnified symptom behavior47 also were performed.

At the conclusion of the examination, a subject's LBP was classified on the basis of the direction of LR movement or alignment that is consistently associated with a positive test and LBP symptoms across the entire examination.3,24,37 In deciding on an LBP classification, a test is given more significance in the decision-making process if the primary test produces an increase in LBP symptoms and the associated secondary test results in a decrease in or an elimination of symptoms. The TLB test, therefore, is one of several tests used to assign an appropriate LBP classification. Possible LBP subgroups were: lumbar flexion, lumbar extension, Rotation, lumbar rotation with flexion, and Rotation With Extension.

Testing of the reliability of examiners performing the physical tests and measures from the standardized examination has been reported.17 Examiners have been able to classify a subject's LBP problem with a fair to good level of reliability (kappa=.57, agreement=78%37; kappa=.5648). Earlier samples24,48 and the sample in the present study suggest that the Rotation With Extension and Rotation subgroups are more prevalent than the other proposed subgroups. Therefore, we focused on the analyses of data from these 2 subgroups. Clinical examination findings typical of the Rotation With Extension or Rotation LBP subgroup are provided in Table 3.


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  		Table 3. Typical Findings for People With Low Back Pain in the Lumbar Rotation With Extension Subgroup and the Lumbar Rotation Subgroup

 
Data Analysis

Data analysis was performed with SYSTAT version 10.2 for Windows.{dagger} Frequency counts and percentages of people in the 2 LBP subgroups (Rotation With Extension, Rotation) in our sample were calculated. A chi-square analysis was conducted on the distributions of the 2 LBP subgroups. Descriptive statistics for and tests of differences between the 2 LBP subgroups were calculated for selected subject-, LBP-, activity-, and movement-related characteristics. A 2-way, mixed-model analysis of variance was conducted to test for main and interaction effects of subgroup (Rotation With Extension, Rotation) and side (right, left) on the maximum LR and TLB angles. A 3-way, mixed-model analysis of variance was conducted to test for main and interaction effects of subgroup (Rotation With Extension, Rotation), side (right, left), and time (25%, 50%, 75%, and 100% of TLB movement time) on the percent contribution of the LR angle to the total TLB angle. For significant main or interaction effects, post hoc analyses were conducted. Significance for all analyses was set at P≤.05.


   Results
Top
 Abstract
 Introduction
 Method
 Results
Discussion
 Conclusion
 References
 
Thirty-three (75%) of the subjects were classified into the Rotation With Extension subgroup, and 11 (25%) of the subjects were classified into the Rotation subgroup. The proportions of subjects in the 2 LBP subgroups were significantly different ({chi}21=11.00, P=.001).

Self-Report Measures

Table 1 provides the results of the tests of differences between the 2 subgroups with regard to subject-, LBP-, activity-, and movement-related characteristics. The subgroups were not significantly different with regard to all variables (P>.05 for all comparisons) except sex and the ODI score.39 There was a larger proportion of men than of women in the Rotation With Extension subgroup ({chi}21=6.82, P=.009), whereas the proportions of men and women in the Rotation subgroup were not significantly different ({chi}21=0.82, P=.37). The people in the Rotation subgroup also had a higher ODI score than the people in the Rotation With Extension subgroup.

Kinematic Measures

Maximum angles.
We compared the 2 subgroups (Rotation With Extension and Rotation) with regard to the maximum TLB angle and the maximum LR angle. The maximum angles for each subgroup and for each side are provided in Table 4. With regard to the maximum TLB angle, there were no significant differences between subgroups (Rotation With Extension: 42.0°±7.6° [X±SD], Rotation: 40.7°±7.8°; F1=0.24, P=.62), and there were no significant differences between sides. There was, however, a trend in both groups toward more end-range TLB motion to the right (left: 40.7°±7.9°, right: 42.7°±8.7°; F1=3.66, P=.06). The interaction of subgroup and side for the maximum TLB angle was not significant (Tab. 4). With regard to the maximum LR angle, there were no significant differences between subgroups (Rotation With Extension: 12.7°±3.2°, Rotation: 11.1°±3.1°; F1=2.00, P=.17), and there were no significant differences between sides (left: 12.5°±4.3°, right: 11.8°±3.9°; F1=0.01, P=.94). The interaction of subgroup and side for the maximum LR angle approached significance, with people in the Rotation With Extension subgroup displaying more end-range LR motion to the left than to the right and people in the Rotation subgroup displaying more end-range LR motion to the right than to the left (Tab. 4).


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  		Table 4. Least Squares Mean (±SE) Maximum Lumbar Region Angle and Total Trunk Lateral Bending Angle for the Lumbar Rotation With Extension Subgroup and the Lumbar Rotation Subgroup

 
Percent contribution of LR motion to TLB.
The percent contributions of LR motion to total TLB motion were significantly different, right versus left, between the LBP subgroups across the 4 time points of TLB (subgroup x side x time; F3=4.27, P=.007). People in the Rotation subgroup displayed no significant differences, right versus left, in the percent contribution of LR motion to total TLB motion across the 4 time points of TLB (symmetric contribution) (side x time; F3=0.26, P=.86) (Tab. 5, Fig. 3A). In contrast, people in the Rotation With Extension subgroup displayed a significant difference, right versus left, in the percent contribution of LR motion to total TLB motion across the 4 time points of TLB (asymmetric contribution) (side x time; F3=11.43, P=.000) (Tab. 5, Fig. 3B). The percent contribution of LR motion to TLB motion stayed the same across the TLB movement to the right (F3=0.66, P=.58), but it decreased across the TLB movement to the left (F3=16.30, P=.000).


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  		Table 5. Least Squares Mean (±SE) Percent Contributions of Lumbar Region Motion to Total Trunk Lateral Bending (TLB) Motion for the Lumbar Rotation With Extension Subgroup and the Lumbar Rotation Subgroup

 

Figure 3
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  		Figure 3. Least squares mean (±SE) percent contribution of lumbar region motion to total trunk lateral bending motion. (A) Rotation subgroup. Data show symmetric lumbar region contribution, right versus left. (B) Rotation with extension subgroup. Data show asymmetric lumbar region contribution, right versus left. Asterisks indicate a statistically significant difference (P<.01) in percent lumbar region contributions between the trunk lateral bending movement time points (25%–50%, 50%–75%, and 75%–100%) for trunk lateral bending to the left.

 
For TLB movement to the left for people in the Rotation With Extension subgroup, pair-wise comparisons were made to test for differences in the percent contributions of the LR angle to the total TLB angle between the TLB movement time points (25%–50%, 50%–75%, and 75%–100%), with the application of a Bonferroni correction for multiple comparisons (P≤.017). The contribution of LR motion to TLB motion was significantly smaller at 25% to 50% (P=.002), 50% to 75% (P=.005), and 75% to 100% (P=.008) of the total TLB motion to the left (Tab. 5, Fig. 3B). The right-versus-left difference in the contribution of LR to TLB was particularly evident during the early part of the TLB motion. During the first 25% of the TLB motion, the percent contributions of LR motion were 56.4%±6.5% to the left and 29.6%±4.4% to the right (Tab. 5, Fig. 3B).


   Discussion
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
Conclusion
 References
 
The findings from this study provide data to validate the clinical observation that LR movement patterns during the clinical TLB movement test differ between 2 subgroups proposed in the MSI classification system for LBP. The data support the hypothesis that people in the Rotation With Extension subgroup display more asymmetry in LR movement patterns across the TLB movement than people in the Rotation subgroup. The LR contributions to the TLB movement were greater in the early phases of TLB to the left than to the right for people in the Rotation With Extension subgroup. For people in the Rotation subgroup, however, the LR contributions were similar right versus left across the TLB movement. Differences in movement patterns between 2 subgroups of people with LBP are important to consider in specifying the details of interventions and may suggest differences in the movement system-related mechanisms underlying the 2 LBP problems.

Similar to what others have proposed,6,49 in the MSI system, asymmetry with TLB is considered to be an important finding because of the higher frequency of loading of one or more lumbar segments on one side than on the other. Because the asymmetry of LR contributions occurs early in the range of TLB in the Rotation With Extension subgroup and because functional activities are commonly performed in the early and middle ranges of joint motion, rather than at the end ranges, early LR movement could contribute more to the accumulation of tissue stress in the LR than would the asymmetry of end-range TLB motion.3,35,50 Theoretically, if the LR contributes more than other regions early during TLB movement, then the LR potentially moves repeatedly during all functional activities that involve any degree of TLB. The repetition of such LR movement across the day suggests that the amount of time without loading may be insufficient for normal tissue adaptation,51 resulting in the accumulation of excessive tissue stress, microtrauma, and LBP symptoms. Thus, the asymmetry of the LR movement pattern early during TLB is considered to be an important contributor to the LBP problem in the Rotation With Extension subgroup and an important finding for identifying people in the Rotation With Extension subgroup.

People in the Rotation subgroup did not display asymmetrical LR movement early in the range of TLB. Unlike the situation for the Rotation With Extension subgroup, the primary factor proposed to contribute to the LBP problem in the Rotation subgroup is the increased frequency of loading of LR segments during rotation because of the adoption of rotation-related movement strategies across several different movements. One approach to examining how movement patterns contribute to LBP problems in people in the Rotation subgroup would be to compare, between LBP subgroups, the prevalence and magnitude of LR rotation across several different clinical movement tests.

Although we have identified differences in movement patterns between the Rotation and Rotation With Extension subgroups with TLB, we have not yet determined the factors that contribute to the differences. For example, differences in movement patterns between subgroups could be the result of motor control factors, such as altered timing or magnitude of activation of the trunk muscles. Biomechanical factors, such as passive tissue stiffness, anthropometrics, or end-range extensibility, also could contribute to differences in movement patterns. For example, in the Rotation With Extension subgroup, the tissue stress and microtrauma associated with repetitive movements could have contributed to the decreased resistance of LR tissues, allowing early motion with TLB to the left. Such changes in tissue resistance as a result of microtrauma are similar to previously proposed changes in the neutral zone with injury.4,35 An understanding of the factors contributing to differences in movement patterns among LBP subgroups and how these factors interact is needed to provide a basis for classification and effective intervention.

Descriptions of other LBP classification systems have suggested that some people with LBP demonstrate asymmetry of end-range TLB and that information about asymmetry can be useful in classifying LBP problems.2,6,8 In the present study, there were no significant differences, right versus left, in end-range TLB angles between the 2 LBP subgroups (subgroup x side interaction, P=.63). There was a tendency, however, for both subgroups to move more to the right than to the left (average difference for right versus left, {approx}2°, P=.06), suggesting overall asymmetry in end-range TLB angles for both the Rotation With Extension and the Rotation subgroups. Whether such a difference between sides would be meaningful for classification in other systems is not known at this time.

To our knowledge, with the TLB test, the amount of difference in motion between sides required to distinguish subgroups of people with LBP has not yet been documented. We also used methods for measuring end-range TLB movements that were different from those typically used in other examinations for people with LBP.2,6,8 Because people in both LBP subgroups displayed the same differences in end-range TLB motion, right versus left, such end-range TLB motion would not distinguish LBP subgroups in the MSI system. An examination of patterns of LR contributions across the TLB movement, however, results in predictable differences in patterns of movement that are considered to be important in the MSI system for identifying and treating people in the Rotation and Rotation With Extension subgroups.

There was also a trend toward differences in end-range LR angles, right versus left, between the LBP subgroups (subgroup x side interaction, P=.06). People in the Rotation With Extension subgroup, on average, displayed 1.4 degrees more end-range LR motion to the left than to the right with TLB. People in the Rotation subgroup displayed 1.3 degrees more end-range LR motion to the right than to the left. The primary prediction in the present study, however, was a difference between subgroups in the symmetry of LR contributions across the TLB movement. Given the size and direction of the subgroup differences in end-range LR motion, as well as the importance of examining movement across the range of TLB in the MSI system, such end-range differences would not be considered to be important for identifying the Rotation With Extension and Rotation subgroups or for specifying the details of interventions for the subgroups.

Clinical Implications

Identifying the movement patterns during TLB with instrumented measures is important because it allows a level of measurement precision not previously afforded by clinical measures. At present, data obtained with self-report and clinical measures suggest that when the focus of physical therapy intervention is on modifying the movement patterns of the LR during exercise and functional activities, the result is improved short- and long-term outcomes at the impairment, functional limitation, and disability levels.16,52–54 The instrumented measures for TLB, in conjunction with other measures,55 should allow examination of the relationship between changes in the movement patterns of the LR and the lumbopelvic region during clinical movement tests and changes in outcomes with interventions.

Pilot work with such instrumented measures suggests that people who have LBP and who are provided physical therapy interventions consisting of exercise and instruction to modify their movement patterns with TLB demonstrate predictable changes in movement patterns compared with people who have LBP but who are not treated.56 Because such movement patterns can differ among subgroups, such evidence suggests a need to examine the specific movement patterns that an individual displays and that may be related to the LBP problem and to address modification of the specific movement patterns during physical therapy interventions.

Alternative Explanations

There are some potential alternative explanations for the effects obtained in the present study. First, the difference between the LBP subgroups in the patterns of LR movement during the TLB test could have been the result of an unequal distribution of men and women in the 2 subgroups that we examined. A second potential alternative explanation for the reported effects is the finding that, on average, people in the Rotation subgroup reported higher ODI scores than people in the Rotation With Extension subgroup. In addition, because of the small number of subjects in the Rotation subgroup, the present study may not have had sufficient power to detect differences between subgroups in the number of LBP episodes (P=.09) and current symptoms during standing (P=.29). Both of these variables have the potential to contribute to the identified differences between subgroups in movement patterns during TLB.

To be certain that the variables that appeared to be different between the 2 subgroups were not responsible for the effects obtained in the present study (subgroup x side x time interaction), we conducted an analysis of covariance for the percent contribution of the LR angle to the total TLB angle. The covariates included in the analysis were sex, ODI score, number of episodes, and current symptoms during standing. The interaction effect of subgroup x side x time was still present (F3=5.36, P=.002), despite the loss of power associated with the inclusion of multiple covariates. Therefore, although the subgroups may appear to be different with regard to a number of variables, these variables do not appear to contribute to the subgroup differences in movement patterns obtained in the present study.

Limitations

There are some potential limitations of the present study. First, the results of this study may not be generalizable to all people with LBP. The cohort of people that we examined consisted of people from the community who regularly participated in a rotation-related sport, such as tennis, squash, or golf. In addition, several conditions assessed during our screening process might have excluded a number of people with LBP from participation in the study. The findings, therefore, may not be generalizable to some people with LBP who would receive care in a physical therapy clinic, to people who do not regularly perform a rotation-related sport, or to people with the conditions listed in the exclusion criteria for the study. We do know, however, from earlier studies of people with LBP that, irrespective of participation in a leisure time activity, LBP problems can be classified with the proposed LBP model.37 Furthermore, many of the people in the earlier work, irrespective of leisure time activity, were assigned to the Rotation With Extension LBP subgroup.16,37

A second potential limitation is that the movement that we studied was a movement performed during a clinical test and, therefore, may not represent movements used during everyday activities. Trunk movement tests, however, are routinely included in many clinical examinations for people with LBP.2,3,6,7,9–17 The basis for the inclusion of trunk movement tests is that the tests provide a clinically feasible method to gain insight into movement patterns potentially used during everyday activities and how movement patterns are related to pain behavior in an individual with LBP. Future studies could focus on examining the relationship between movements performed during clinical tests and movements used during everyday activities.

A third potential limitation is that our kinematic measures of LR and TLB movements were tested for reliability only in people without a history of LBP. We do not know the level of reliability of our measures in people with LBP.

A fourth potential limitation is that movement artifacts can be associated with the use of surface markers to index bone movement.57 Our primary interest in the present study, however, was examination of the relative difference in LR contributions across the TLB movement between LBP subgroups and not absolute measures of trunk motion. Because there are no data to suggest systematic differences in movement artifacts associated with different LBP subgroups, there is no reason to consider that the differences in movement patterns between LBP subgroups could be the result of differences in movement artifacts. In addition, the consistency of the measures used in the present study is acceptable.


   Conclusion
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
 Conclusion
References
 
The findings of the present study suggest that people in 2 different LBP subgroups—Rotation With Extension and Rotation—demonstrate differences in LR movement patterns across a TLB movement. People in the Rotation With Extension subgroup demonstrated an asymmetric LR movement pattern with TLB, right versus left. People in the Rotation subgroup demonstrated a symmetric LR movement pattern with TLB, right versus left. Specifically, in people in the Rotation With Extension subgroup, the LR contributed more to TLB during the early phases of the TLB movement to the left than to the right. On the basis of these findings, the difference in the patterns of LR movement across the TLB movement in different subgroups of people with LBP may be an important factor for clinicians to consider when examining people with LBP and when specifying the details of interventions.


   Footnotes
 
Dr Sahrmann, Dr Engsberg, and Dr Van Dillen provided concept/idea/research design. Ms Gombatto, Dr Sahrmann, and Dr Van Dillen provided writing. Dr Van Dillen provided data collection, and Ms Gombatto and Dr Collins provided data analysis. Dr Van Dillen provided project management, fund procurement, and subjects. Dr Sahrmann and Dr Van Dillen provided facilities/equipment. Ms Gombatto, Dr Collins, Dr Sahrmann, and Dr Engsberg provided consultation (including review of manuscript before submission). The authors acknowledge the assistance of Kevin Hollander, doctoral candidate in the School of Engineering, University of Arizona, for his assistance in development of the original kinematic model and input into calculations of the dependent variables of interest described in the article. They also acknowledge the assistance of James Hsiau, BS, Tom Susco, PT, DPT, MEd, ATC, and Donovan J Lott, PT, MSPT, CSCS, for their assistance in data processing.

This research, in part, was presented at the Combined Sections Meeting of the American Physical Therapy Association; February 23–27, 2005; New Orleans, La.

This work was partially funded by the National Institute of Child Health and Human Development, Division of the National Center for Medical Rehabilitation Research, grant 1 K01HD-01226-05 and grant 5 T32 HD07434-10, and a scholarship from the Foundation for Physical Therapy.

* Motion Analysis Corp, 3617 Westwind Blvd, Santa Rosa, CA 95403. Back

{dagger} Systat Software, Inc, 501 Canal Blvd, Suite E, Point Richmond, CA 94804-2028. Back


   References
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 Abstract
 Introduction
 Method
 Results
 Discussion
 Conclusion
 References
 

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