Quantifying lumbar flexion-relaxation phenomenon: theory and clinical applications

Abstract

Purpose of study: The flexion-extension (FR) phenomenon represents lumbar extensor muscle relaxation in electromyograph (EMG) reading near full flexion. It can be reproducibly assessed in normal subjects and found intermittently in CLBP patients. Few recent studies have examined a potential relationship between inclinometric lumbar range-of-motion (ROM) measures and the surface EMG signal. This two-part study described the use of FR in assessing CLBP patients before and after rehabilitation, and establishing a normative database (Part 1), for subsequent use in comparison to CLBP patients (Part 2). We discuss the clinical utility of combined EMG and ROM measurements in assessing the FR phenomenon as a test to potentially assist in planning rehabilitation programs, guide patients' rehabilitation progress and identify early posttreatment failures.Methods used: In Part 1, 12 normal subjects were evaluated to examine reliability of EMG signal readings and ROM measures at both FR and maximum voluntary flexion (MVF). The mean sEMG signal, as well as the gross, true and sacral lumbar ROM measurements were recorded as normative data. In Part 2, 54 CLBP patients referred for tertiary rehabilitation underwent EMG and ROM measurement before rehabilitation. Of this group, 20 patients were not appropriate for rehabilitation or failed to complete the course of treatment and were assessed only once. Program completers were retested with the identical methodology after rehabilitation (n = 34), using the empirically derived cutoff scores for EMG readings at FR and ROM from Part 1 and prior scientific literature. Sensitivity, specificity and predictive values of the EMG to identify abnormal motion were assessed.of findings: The ability of experienced testers to reliably measure ROM and EMG at FR was high (r .92, p < .001). All normal subjects achieved FR at a tightly clustered range of mean EMG signals from 1 to 2.3 μV. Most of the variation between motion at FR and MVF occurred through the hip (sacral) motion component of the gross (or total) motion measured at T12. In Part 2, posttreatment reliability for ROM, EMG and the ability to detect the FR point was also high (r 0.82, p < .001). Sensitivity was variable, but specificity was 100% before and after rehabilitation because of the absence of false positives (patients failing to achieve FR who demonstrated normal motion by any of the ROM criteria). Similarly, positive predictive value was also 100% before and after rehabilitation. Over 30% of all 54 patients demonstrated the ability to achieve FR before treatment, with FR usually associated with higher ROM than the non-FR patients. After treatment, 94% of program completers achieved FR, including all those who achieved FR before treatment. FR was associated with major improvement in ROM.Relationship between findings and existing knowledge: FR measures a point at which true lumbar flexion ROM approaches its maximum in normal subjects. This is also the point at which lumbar extensor muscle contraction relaxes, allowing the lumbar spine to hang on its posterior ligaments. The gluteal hamstring muscles then lower the flexed trunk even further, by allowing the pelvis to rotate around the hips.Overall significance of findings: The FR phenomenon, absent in most CLBP patients, was subsequently found in Part 2 to offer a promising method to individualize rehabilitation treatment, decrease unnecessary utilization, identify potential postrehabilitation treatment failures and assess permanent impairment rating validity.Disclosures: No disclosures.Conflict of interest: No conflicts.