OBJECTIVE: To evaluate the use of the Hmax/Mmax (H/M) ratio as an outcome measure for acute low back pain and to determine the change of this ratio in acute low back pain patients treated with spinal manipulation.

DESIGN: Randomized clinical trial.

SETTING: Chiropractic college teaching clinic.

PATIENTS: Thirty-six patients with acute low back pain (pain of less than 2 wk duration) were referred by clinicians of the teaching clinic. Eligibility criteria for inclusion into the study consisted of the following: a score of eight or more on the Oswestry questionnaire, 33 mm or greater on a 100-mm visual analog scale, no involvement in litigation related to the low back pain complaint, patient not pregnant and no physical or electrodiagnostic signs of nerve root entrapment.

INTERVENTIONS: The patients were randomly assigned to either a treatment or control group. The treatment group (n = 17) received treatment deemed appropriate by the clinician as long as it included a side-lying manipulation to the appropriate level. The control group (n = 19) received detuned ultrasound, application of a cold pack and 15-30 sec of very gentle soft tissue massage. Patients were treated three to five times over a period of 10 days and were subsequently reevaluated.

MEASUREMENTS: The Hmax/Mmax ratio was calculated from the results of electrodiagnostic testing of the posterior tibial nerve. Extension/flexion ratio of the trunk musculature, Oswestry score and Visual Analog Scale score were also measured.

MAIN RESULTS: The mean difference between H/M ratios pre- and postintervention for the group treated by chiropractic methods was -0.101 on the left and -0.117 on the right. The mean difference for the control group was 0.038 on the left and 0.036 on the right. Although not statistically significant, trends suggest that at the time of final assessment, the group receiving chiropractic care had improved more than the control group.

CONCLUSIONS: The H/M ratio was found to be within normal limits in subjects with acute low back pain. The H/M ratio showed greater change in the group which received spinal manipulation, but the change was subtle. The results indicate that the H/M ratio may be of limited value in clinical practice.

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