People move differently in pain. Although this statement is unquestioned, the underlying mechanisms are surprisingly poorly understood. Existing theories are relatively simplistic, and although their predictions are consistent with a range of experimental and clinical observations, there are many observations that cannot be adequately explained. New theories are required. Here, we seek to consider the motor adaptation to pain from the micro (single motoneuron) to macro (coordination of whole-muscle behaviour) levels and to provide a basis for a new theory to explain the motor changes in pain.

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Moving differently in pain: a new theory to explain the adaptation to pain.

Many people with recurrent low back pain (LBP) have deficits in postural control of the trunk muscles and this may contribute to the recurrence of pain episodes. However, the neural changes that underlie these motor deficits remain unclear. As the motor cortex contributes to control of postural adjustments, the current study investigated the excitability and organization of the motor cortical inputs to the trunk muscles in 11 individuals with and without recurrent LBP. EMG activity of the deep abdominal muscle, transversus abdominis (TrA), was recorded bilaterally using intramuscular fine-wire electrodes. Postural control was assessed as onset of TrA EMG during single rapid arm flexion and extension tasks. Motor thresholds (MTs) for transcranial magnetic stimulation (TMS) were determined for responses contralateral and ipsilateral to the stimulated cortex. In addition, responses of TrA toTMS over the contralateral cortex were mapped during voluntary contractions at 10% of maximum. MTs and map parameters [centre of gravity (CoG) and volume] were compared between healthy and LBP groups.The CoG of the motor cortical map of TrA in the healthy group was » 2c m anterior and lateral to the vertex, but was more posterior and lateral in the LBP group.The location of the CoG and the map volume were correlated with onset of TrA EMG during rapid arm movements. Furthermore, the MT needed to evoke ipsilateral responses was lower in the LBP group, but only on the less excitable hemisphere. These findings provide preliminary evidence of reorganization of trunk muscle representation at the motor cortex in individuals with recurrent LBP, and suggest this reorganization is associated with deficits in postural control.

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Reorganization of the motor cortex is associated with postural control deficits in recurrent low back pain.

Methodological aspects of SEMG recordings for force estimation--a tutorial and review.

Background. Previous systematic reviews have concluded that the effectiveness of motor control exercise for persistent low back pain has not been clearly established. Objective. The objective of this study was to systematically review randomized controlled trials evaluating the effectiveness of motor control exercises for persistent low back pain. Methods. Electronic databases were searched to June 2008. Pain, disability, and quality-of-life outcomes were extracted and converted to a common 0 to 100 scale. Where possible, trials were pooled using Revman 4.2. Results. Fourteen trials were included. Seven trials compared motor control exercise with minimal intervention or evaluated it as a supplement to another treatment. Four trials compared motor control exercise with manual therapy. Five trials compared motor control exercise with another form of exercise. One trial compared motor control exercise with lumbar fusion surgery. The pooling revealed that motor control exercise was better than minimal intervention in reducing pain at short-term follow-up (weighted mean difference14.3 points, 95% confidence interval [CI]20.4 to 8.1), at intermediate follow-up (weighted mean difference13.6 points, 95% CI22.4 to 4.1), and at long-term follow-up (weighted mean difference14.4 points, 95% CI23.1 to 5.7) and in reducing disability at long-term follow-up (weighted mean difference10.8 points, 95% CI18.7 to 2.8). Motor control exercise was better than manual therapy for pain (weighted mean difference5.7 points, 95% CI10.7 to 0.8), disability (weighted mean difference4.0 points, 95% CI7.6 to 0.4), and quality-of-life outcomes (weighted mean difference6.0 points, 95% CI11.2 to 0.8) at intermediate follow-up and better than other forms of exercise in reducing disability at short-term follow-up (weighted mean difference5.1 points, 95% CI8.7 to 1.4). Conclusions. Motor control exercise is superior to minimal intervention and confers benefit when added to another therapy for pain at all time points and for disability at long-term follow-up. Motor control exercise is not more effective than manual therapy or other forms of exercise.

Motor Control Exercise for Persistent, Nonspecific Low Back Pain: A Systematic Review

The lumbar multifidus: Does the evidence support clinical beliefs?

Approximately thirty-four percent of people who experience acute low back pain (LBP) 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 LBP from healthy participants. Recurrent unilateral LBP patients, who were symptom free during testing, and a group of healthy volunteers, participated. Intramuscular and surface electrodes recorded the electromyographic activity (EMG) 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. EMG 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 EMG onset occurred later in participants with recurrent unilateral LBP than in healthy participants (p=0.022). The short fibres were active earlier than long fibres on both sides in the healthy participants (p<0.001) and on the non-painful side in the LBP group (p=0.045), but not on the previously painful side in the LBP group. Activity of deep back muscles is different in people with a recurrent unilateral LBP, 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.

Why do some patients keep hurting their back? Evidence of ongoing back muscle dysfunction during remission from recurrent back pain

Study Design. Cross-sectional design. Objective. To compare lumbar multifidus electromyographic activity (EMG) during predictable and unpredictable trunk loading between people with and without recurrent unilateral low back pain (LBP) during symptom remission. Summary of Background Data. Unpredictable loading is a common injury mechanism for LBP. Paraspinal muscle responses to trunk loading differ between people with and without a history of LBP, but whether the response differs between specific regions within the paraspinal muscles is unclear. Differences between deep (DM) and superficial fibers (SM) of multifidus have been implicated in other tasks. It is unknown whether DM and SM EMG differ between people in remission from recurrent LBP and healthy people during trunk loading. Methods. DM and SM EMG was recorded bilaterally at L5 with intramuscular electrodes during predictable and unpredictable trunk loading and compared during 10 milliseconds epochs (250 milliseconds before to 150 milliseconds after loading) between sides, loading conditions, and groups. Results. DM EMG increased above baseline before and after predictable load onset, but returned to baseline at the time of impact. Both DM EMG bursts were less in the remission group and less on the non-painful side. Peak SM EMG amplitude on the previously painful side was earlier in the remission group than healthy participants. DM and SM EMG were less after unpredictable load onset in the remission group than healthy participants. Conclusion. Despite symptom remission, DM EMG during predictable loading and DM and SM EMG during unpredictable loading were less in people with recurrent LBP than healthy participants.

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People with recurrent low back pain respond differently to trunk loading despite remission from symptoms.

New insight into motor adaptation to pain revealed by a combination of modelling and empirical approaches.

A randomized controlled study was done to compare the clinical, radiographic, and quality of life outcomes between posterior-stabilized and cruciate-retaining primary total knee implants. One hundred forty-three patients were enrolled in the study. Patients ranged in age from 57 to 89 years, had a primary diagnosis of osteoarthritis, and an intact functioning posterior cruciate ligament. Patients were excluded if they had a flexion contracture greater than 15 degrees, a varus deformity greater than 20 degrees, or a valgus deformity greater than 15 degrees. Patients were randomized to one of two study groups, posterior-stabilized AMK total knee implants (76 patients) or cruciate-retaining AMK total knee implants (67 patients). One hundred eight patients have had a minimum 2-year followup including 57 patients in the posterior-stabilized group and 51 patients in the cruciate-retaining group. Seventy-three patients have had a minimum 3-year followup including 37 patients in the posterior stabilized group and 36 patients in the cruciate-retaining group. The overall total Knee Society clinical rating score at 2 years averaged 157.1 points in the posterior-stabilized group and 156.5 points in the cruciate-retaining group. At 3 years, the scores averaged 156.8 points in the posterior-stabilized group and 163.5 points in the cruciate-retaining group. The range of motion component of the Knee Society score averaged 113.6 degrees for the posterior-stabilized group and 108.5 degrees for the cruciate-retaining group at 2 years, and 108.3 degrees in the cruciate-retaining group and 108.5 degrees in the posterior-stabilized group. Based on the various parameters analyzed, there were no notable differences between the groups with a posterior-stabilized and a cruciate-retaining total knee implant at 2 years. This trend seemed to be the same at 3 years.

D. A. MacDonald

Papers

Why do some patients keep hurting their back? Evidence of ongoing back muscle dysfunction during remission from recurrent back pain

The lumbar multifidus: Does the evidence support clinical beliefs?

People with recurrent low back pain respond differently to trunk loading despite remission from symptoms.

New insight into motor adaptation to pain revealed by a combination of modelling and empirical approaches.

Posterior-stabilized and cruciate-retaining total knee replacement: a randomized study.