Background: To test whether working body schema of the trunk is disrupted in people with back pain using a motor imagery task in which one decides whether a pictured model has their trunk rotated to the left or to the right. We hypothesised that chronic back pain is associated with reduced accuracy of left/right trunk rotation judgements.
Methods: Twenty-one patients with back pain and 14 controls completed two tasks, each involving two trials of 40 images: a left/right hand judgement task, which was used as a control task, and the left/right trunk rotation judgement task. Two (task) x three (group: bilateral back pain, unilateral back pain, control) ANOVAs were undertaken on mean RT and accuracy.
Results: RT was similar across participants and tasks (n.s.). Accuracy was not. Patients with bilateral back pain made more mistakes on the left/right trunk rotation task than patients with unilateral back pain did, who in turn made more mistakes on that task than controls did (Body Part x Group interaction; p<0.001). The mean (95% confidence interval) accuracy for left/right trunk rotation judgements was 53.4% (44.5 – 62.3%) for bilateral back pain patients, 67.2% (60.2 – 74.1%) for unilateral back pain patients and 87% (75 – 98%) for control participants. This pattern was not observed on the left/right hand judgement task, on which all three groups made correct judgements about 83% of the time (n.s.).
Discussion: Chronic back pain is associated with disruption of the working body schema of the trunk. This might be an important contributor to motor control abnormalities seen in this population.