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PURPOSE: To investigate the classification accuracy of motor control testsof the lumbar spine in discriminating 5 subgroups of peripherally mediated mechanical low back pain (LBP) suggested in the classification system developed by Peter O’Sullivan.

RELEVANCE: Identifying clinically relevant subgroups is considered a prioritized area of LBP research. The current study addresses the issue of using accurate, reliable, and standardized tests to guide such classifications.

METHODS: Seventy subjects with nonspecific LBP were classified by anexpert clinician into 5 subgroups based on the direction of motor control impairment and the assumed mechanism underlying the pain disorder (ie, flexion, lateral shift, active extension, passive extension, andmultidirectional pattern). Thereafter, 5 standardized tests of motor control were performed under the supervision of 2 therapists blinded tothe subgroup classification: “waiters bow,” bilateral and unilateral sitting knee extension, and bilateral and unilateral prone knee flexion. Alack of ability to prevent a compensatory movement (motion give) when instructed to maintain neutral lumbar posture was judged as test failure. Multinomial logistic regression was used to analyze the association between tests and subgroups and to determine the tests’ joint classification accuracy.

RESULTS: The motor control tests showed significant associations to thedifferent subgroups (χ2 = 37.08, P = .002, Nagelkerke pseudo R2 = 0.431)and displayed significant discriminative ability, increasing the classification accuracy substantially, 95% above chance level overall, and for allsubgroups except for the multidirectional pattern. The different subgroups were characterized by different association patterns, indicating different tests to be important for different subgroups.

CONCLUSIONS AND CLINICAL IMPLICATIONS: The results indicate a clinical utility of the motor control tests and suggest them to be useful to supplement in subgroup classification of what traditionally have been considered nonspecific mechanical LBP. The findings also support the clinical validity of the approach to subgroup patients according to the direction of motorcontrol impairment.