Reliability of detection of lumbar lateral shift

Abstract

Background and purpose

The poor reliability of lateral shift detection has been attributed to lack of rater training, biologic variation, and test reactivity. This study aimed to remove the potential confounding arising from biological variation and test reactivity and control the level of rater experience/training in making judgments of lateral shift.

Subjects

One hundred forty-eight raters with 3 levels of clinical physical therapy experience and training in the McKenzie method participated.

Method

The raters viewed photographic slides of 45 patients with low back pain. Slides were judged on a numerical scale for presence and direction of a shift. Intrarater reliability was evaluated using the intraclass correlation coefficient (ICC) and interrater reliability was evaluated using both the ICC and κ statistic.

Results

Reliability of shift judgments was only moderate for all groups (eg, ICC [2,1] values ranged from 0.48 to 0.64).

Conclusion

Lateral shift judgements have only moderate reliability, even when trained raters judge stable stimuli. We propose that the photo model employed can be used to explore the source of error in this process.

Introduction

A recent survey of physical therapists in the United States¹ reported that a McKenzie evaluation was one of the most common evaluations performed for patients with low back pain (LBP) and that almost half the therapists viewed the McKenzie method as the most useful management approach for low back pain. Similar results have been reported for British and Irish physiotherapists.2, 3

The method has received support as an effective LBP treatment in a systematic review of activity prescription for back pain⁴ and also in Danish clinical practice guidelines,⁵ based on the 2 existing clinical trials.6, 7 Subsequent to the completion of both reviews, Cherkin et al⁸ published a clinical trial evaluating 3 approaches (chiropractic manipulation, McKenzie therapy, and an educational booklet) and found chiropractic manipulation and McKenzie therapy to have similar effects and costs. However, both treatments provided only marginally better outcomes than an educational booklet.⁸ In this environment, further information about the use of the basic criteria in the method is needed.

The principal aim of the McKenzie assessment is to first determine those suitable for treatment with this approach. Suitable patients must fit one of 3 syndromes: postural, dysfunction, or derangement.⁹ The derangement syndrome is further divided into 7 subsyndromes on the basis of pain location, the behavior of the pain in response to the application of repeated spinal movements, and on the presence or absence of deformities including a lateral shift. Because classification determines the specific treatment used by the treating clinician, accurate classification is believed essential for the effective management of the LBP patient.

In employing the method, the presence of a lateral shift is determined by visual inspection at the time the patient's posture is evaluated. If a lateral shift is deemed to be present, lateral glide movements are performed to assess if these alter the patient symptoms. Where this is the case, the shift is classified as “relevant’ and directs the initial treatment approach.⁹ The initial step of detecting a shift is of paramount importance, because it is only if a shift is identified to be present that its relevance is determined.

A lateral shift is defined as a lateral displacement of the trunk in relation to the pelvis.⁹ The prevalence of a lateral shift has proved hard to establish, probably because of the problems with measurement of this attribute. Porter and Miller¹⁰ suggest that it is an uncommon feature, citing a prevalence of 5.6%; however, later studies report approximate prevalences of 20%¹¹ and 80%.¹²

The reliability of therapists in determining the presence of a lateral shift has been evaluated in 6 studies to date. In the Kilby et al¹³ study, 2 physiotherapists with some training in the McKenzie method simultaneously evaluated 41 patients. There was only 55% agreement on the presence or absence of a lateral shift, a value similar to the findings of Nelson et al,¹⁴ who reported that the detection of lumbar tilt (lateral shift) had high interobserver error. However, these studies did not provide κ values, and there was insufficient data to allow calculation of this statistic.

Riddle and Rothstein¹¹ examined the intertester reliability of assessments of LBP patients made by physical therapists using the McKenzie method. They also aimed to determine whether training in the McKenzie method influenced reliability. Forty-nine physical therapists from 8 clinics examined 363 patients. Sixteen of the therapists had attended at least 1 postgraduate course in the McKenzie method. The paired assessments were completed consecutively, with a time interval between examinations. They found a high error rate in the determination of the presence of a lateral shift (60% agreement, κ = 0.26) and concluded that this was a possible source of error in the determination of the syndrome classifications.

Donahue et al¹² attempted to improve the reliability of the determination of the presence and direction of a lateral shift by using a simple measuring device, but the reported κ value for the decisions indicated very poor reliability. McLean et al¹⁵ investigated 3 different techniques for measuring trunk list and concluded that the use of a plumb line provided the most reliable measures; however, there was no summary reliability statistic reported to allow comparison to other studies.

Improved reliability in determining the presence of a lateral shift (78% agreement, κ = 0.52) was demonstrated by Razmjou et al¹⁶ for therapists observing the same patient assessment. The 2 physical therapists involved in this study were both trained extensively in the McKenzie method and assessed the patients simultaneously in an attempt to reduce the error related to repeated examinations. They visually determined whether a lateral shift deformity was present for each patient.

Based on the research to date, it remains unclear whether a lateral shift can be detected with acceptable reliability. The measuring devices used to date do not seem to improve reliability, and the reliability estimates are in the range poor to moderate. It is therefore worthwhile to explore the source of disagreement.

Two hypotheses have been offered for the poor reliability observed:

• The attribute is inherently unstable and changes with repeated examination.¹⁶

• The attribute is subtle, and clinical experience and training are necessary to reliably measure a lateral shift.¹⁷

One way to explore the first hypothesis is to use a model of clinical practice that allows for greater control than would be possible in the clinic, for example, the use of photographs as the stimuli to be rated rather than real patients. This method avoids the potentially confounding effect of the biologic variation of the shift, allows for an unlimited number of repetitions of the same stimuli, and also allows for a much larger panel of raters than is practical in a traditional clinical reliability study.

To explore the effect of clinical experience and training, we selected a cross section of raters, including first-year undergraduate students, graduate physiotherapists with no formal training in the McKenzie method, and graduate physiotherapists with a minimum of 70 hours training in the McKenzie method.

The aims of the study were to investigate:

• the intrarater/interrater reliability of judgements of lateral shift made from inspection of photographs of patients with low back pain.

• whether interrater reliability and discriminability were influenced by level of education in the McKenzie method.