Why do some patients keep hurting their back? Evidence of ongoing back muscle dysfunction during remission from recurrent back pain
From: Pain. 2009 Jan 29. [Epub ahead of print]
Approximately thirty-four percent of people who experience acute low back pain will have recurrent episodes. It remains unclear why some people experience recurrences and others do not, but one possible cause is a loss of normal control of the back muscles. We investigated whether the control of the short and long fibres of the deep back muscles was different in people with recurrent unilateral low back pain from healthy participants. Recurrent unilateral low back pain patients, who were symptom free during testing, and a group of healthy volunteers, participated. Intramuscular and surface electrodes recorded the electromyographic activity of the short and long fibres of the lumbar multifidus and the shoulder muscle, deltoid, during a postural perturbation associated with a rapid arm movement. Electromyographic activity onsets of the short and long fibres, relative to that of deltoid, were compared between groups, muscles, and sides. In association with a postural perturbation, short fibre electromyographic activity onset occurred later in participants with recurrent unilateral low back pain than in healthy participants. The short fibres were active earlier than long fibres on both sides in the healthy participants and on the non-painful side in the low back pain group, but not on the previously painful side in the low back pain group. Activity of deep back muscles is different in people with a recurrent unilateral low back pain, despite the resolution of symptoms. Because deep back muscle activity is critical for normal spinal control, the current results provide the first evidence of a candidate mechanism for recurrent episodes.
