An investigation of the reliability and validity of posteroanterior spinal stiffness judgments made using a reference-based protocol

BACKGROUND AND PURPOSE

The reliability and criterion-related validity of ratings of posteroanterior (PA) spinal stiffness made using reference values for comparison have not been investigated. In this study, mechanical reference stimuli for points on an 11-point rating scale were used to determine whether using a reference scale may be feasible. Subjects. Five different raters took part in 2 studies in which they rated 40 subjects who were asymptomatic for low back pain.

METHODS

The interrater reliability of ratings was evaluated with intraclass correlation coefficients (ICCs) and standard errors of the measurement (SEMs). Criterion-related validity was evaluated by correlating judgments of PA spinal stiffness assessed manually with measurements of PA spinal stiffness provided by a mechanical device, the "Stiffness Assessment Machine" (SAM).

RESULTS

Although the reliability indices were generally high, with ICCs reaching .77 and with SEMs as low as 0.72 points, the evidence for criterion-related validity (i.e., the ability of the examiner to judge spinal stiffness levels) was not strong, with correlations reaching only .56.

CONCLUSIONS AND DISCUSSION

The reference-based protocol allows for more reliable measures of PA stiffness judgments than previous protocols have; however, the human ratings are not highly correlated with the SAM measures. The protocol will have clinical value if judgments made using it are shown to be reliable in clinically relevant subjects and to have validity for clinical management of patients.

Therapists' conceptualization and characterization of the clinical concept of spinal stiffness

BACKGROUND AND PURPOSE

The clinical concept of spinal stiffness provides one basis for applying spinal manipulation. Because the terms used to describe the perceptual results of manual spinal stiffness testing are poorly defined, the nature and number of attributes contained in the concept remain unclear. This study attempted to clarify the concept of spinal stiffness by examining the relationships among 31 published spinal stiffness descriptors using cluster analysis.

SUBJECTS AND METHODS

Each stiffness descriptor was printed on a magnetized rubber strip. Physical therapists in Houston (Tex) and Sydney (New South Wales, Australia) judged the similarity of the stiffness descriptors by arranging them on a board. The squared Euclidean distance between words was calculated, and cluster analysis was performed using Ward's method.

RESULTS

Cluster analysis reduced the 31 stiffness descriptors to three superclusters (limited mobility, increased mobility, and viscoelasticity) in both the Houston and Sydney data.

CONCLUSION AND DISCUSSION

In a step toward improving the reliability of spinal stiffness judgments, this study has identified the fundamental characteristics of the clinical concept of spinal stiffness. Research is now needed to clearly define these characteristics and then develop protocols that will allow physical therapists to reliably rate these attributes.

Stiffness judgments are affected by visual occlusion

OBJECTIVE

The current protocol for judging posteroanterior (PA) spinal stiffness has been shown to provide unreliable estimates of PA stiffness. It is possible that a failure to standardize therapists' use of vision in the test protocol partly contributes to the disagreement between raters. This study sought to establish whether vision affects stiffness judgments and so needs to be standardized when judging PA stiffness.

DESIGN

Perceptual study using a mechanical device to provide stiffness stimuli with physiotherapists and lay people as judges.

SETTING

University psychophysics laboratory.

INTERVENTIONS

Occlusion of vision via opaque goggles.

MAIN OUTCOME MEASURES

Measures of interstimulus discriminability and bias.

RESULTS

Occluding vision had no effect on judges' ability to discriminate between stiffness stimuli; however, the same stimuli were judged as significantly stiffer under the visual occlusion condition.

CONCLUSION

The data from this study suggest that vision needs to be controlled when using manual tests to judge PA spinal stiffness.

Evaluation of a new device for measuring responses to posteroanterior forces in a patient population, Part 1: Reliability testing

BACKGROUND AND PURPOSE

This study determined the test-retest reliability of measurements of responses to posteroanterior (PA) forces made using a recently developed instrument.

SUBJECT

Twenty-two subjects with nonspecific low back pain participated.

METHODS

The length of the low- stiffness or "toe" region and the slope of the linear portion of the force-displacement curve were measured on two occasions. Reliability of repeated measurements was evaluated by intraclass correlation coefficients and percentage-of-agreement scores. The presence of a systematic change in the response to PA forces was evaluated by a paired-samples t test.

RESULTS

High reliability coefficients were obtained for both indices of the response to PA forces. The t test revealed no systematic change with repeated testing.

CONCLUSION AND DISCUSSION

The new device provides highly reliable measurement of the lumbar PA force-displacement relationship and may prove useful in evaluating theories that have suggested a relationship between spinal symptoms and abnormal PA stiffness.