Ability to discriminate between healthy and low back pain sufferers using ultrasound during maximum lumbar extension

Abstract

Objective: To analyze the ability to discriminate between healthy individuals and individuals with chronic nonspecific low back pain (CNLBP) by measuring the relation between patient-reported outcomes and objective clinical outcome measures of the erector spinae (ES) muscles using an ultrasound during maximal isometric lumbar extension.

Design: Cross-sectional study with screening and diagnostic tests with no blinded comparison.

Setting: University laboratory.

Participants: Healthy individuals (n=33) and individuals with CNLBP (n=33).

Interventions: Each subject performed an isometric lumbar extension. With the variables measured, a discriminate analysis was performed using a value ≥ 6 in the Roland and Morris disability questionnaire (RMDQ) as the grouping variable. Then, a logistic regression with the functional and architectural variables was performed. A new index was obtained from each subject value input in the discriminate multivariate analysis.

Main outcome measures: Morphologic muscle variables of the ES muscle were measured through ultrasound images. The reliability of the measures was calculated through intraclass correlation coefficients (ICCs). The relation between patient-reported outcomes and objective clinical outcome measures was analyzed using a discriminate function from standardized values of the variables and an analysis of the reliability of the ultrasound measurement.

Results: The reliability tests show an ICC value >.95 for morphologic and functional variables. The independent variables included in the analysis explained 42% (P=.003) of the dependent variable variance.

Conclusions: The relation between objective variables (electromyography, thickness, pennation angle) and a subjective variable (RMDQ ≥ 6) and the capacity of this relation to identify CNLBP within a group of healthy subjects is moderate. These results should be considered by clinicians when treating this type of patient in clinical practice.

Keywords: Electromyography; Low back pain; Rehabilitation; Ultrasound.