Introduction – Musculoskeletal physiotherapy is a specialist area of professional physiotherapy practice concerned with the assessment, diagnosis and management of the musculoskeletal pain and dysfunction. The main aims of musculoskeletal physiotherapy are to reduce pain, maintain/regain joint movement, and maximize function and health-related quality of life without adverse effects, enabling people to cope better with ill health.
Traditionally, musculoskeletal physiotherapists have followed a very simplistic model of management, which included identification of a single anatomical structure like muscle, bone, joint, nerve, tendon, ligament, cartilage, and spinal disc etc and immediate intervention with exercises or passive modalities like thermotherapy, manual therapy or electrotherapy. Over the years, musculoskeletal physiotherapists have developed a better understanding of the underlying pain mechanisms and movement impairments. This has led to development of holistic self management strategies, which incorporate the biomedical, psychosocial and neuroscience aspects of pain and dysfunction. Thus, motor control retraining, education and advice, motor imagery, mirror therapy and cognitive behavioural interventions have become important part of the repertoire of techniques of musculoskeletal physiotherapists. Motor Imagery (MI) is an emerging new rehabilitation strategy for chronic pain conditions, though extensively used in athletes and neuro rehabilitation in the past. This technique is based on classical paradigm of cognitive psychology which has been used extensively during the last four decades to study perception, memory and other brain functions. This paper will look into the basics of MI, the treatment process and explore the evidence underpinning the effects of MI in management of chronic pain.
Motor imagery: Motor imagery (MI) represents the result of conscious access to the content of the intention of a movement, which is usually performed unconsciously during movement preparation. It has been reported that brain regions activated during movements are the same as those activated during MI, including the primary sensorimotor cortices, lateral and dorsal pre-motor cortices, pre-supplementary and supplementary motor areas, cingulatemotor area, intraparietal sulcus and supramarginal gyrus. It is a complex cognitive operation that is self-generated using sensory and perceptual processes, enabling the reactivation of specific motor actions within working memory. Therefore, sensory-perceptual, memory, and motor mechanisms are included in broader definitions of the term. Converging evidence from several sources indicates that motor imagery pertains to the same category of processes as those which are involved in programming and preparing actual actions, with the difference that in the latter case, execution would be blocked at some level of the cortico-spinal flow. Evidence for neural reorganization as a result of MI training is emerging as well. In addition, extensive evidence in the literature shows similarity between imagined and executed movements, including involvement of neural substrates, characteristics of movements, such as autonomic reactions, kinematic constraints, temporal properties, and the relation to motor learning and performance enhancement. There is an extensive body of literature which demonstrates the positive effects of MI on motor function including muscle strength, range of motion, postural control and perceptuo -motor professional skills like surgery. In athletes, MI has been demonstrated to improve speed, performance accuracy and movement dynamics.
In patient populations, MI has been used extensively in neurological rehabilitation. There are numerous reports of greatest improvements with a combination of MI practice and physical practice followed by physical practice alone and MI practice alone, which is superior to no practice at all.For chronic, intractable pain, Moseley et al have devised an evidence based sequence of strategies to manage non pathoanatomical brain obstacles to rehabilitation known as GMI. It has been successfully utilized in the management of Chronic regional pain syndrome type 1 (CRPS1), phantom limb pain. Further research is being carried out on its effects in whiplash, hand osteoarthritis and facial pain.
Stages in Graded Motor Imagery Training –
Laterality Reconstruction: Laterality recognition is the body’s ability to differentiate between right and left sides. This involves the activation of the pre-motor cortex areas of the brain, whereas explicit movements activate the primary motor cortex. In chronic, intractable pain states as in CRPS and phantom limb pain, this ability is altered or lost. This is probably a defence mechanism to close down motor output, as if the brain fails to identify the side, it can lead to synaptic stress and increase the pain stimulus. It can be tested using the ‘Recognise’ software developed by the Moseley et al. A simpler method is to use a magazine asking people to pick out left or right hands or legs. Though normative data for the laterality recognition are not available at the moment, Neuro Orthopaedic Institute, Australia (NOI) is conducting an online study to collect the same. Once the deficit has been identified, therapists can start retraining the brain to differentiate between the left and right side. Tools include using flash cards showing left and right limbs; over time, patients get better at picking out the relevant limb. Another method involves using a digital camera to photograph a certain number of right or left hands or legs each day, in different settings. This allows the patient to carry out the tasks in different contexts, whether that be place, time of day or even whether the patient is feeling happy or sad at the time. It is also important that the task is practised repeatedly as even though the results might be quick, there might be a tendency to revert back.
Imagined Movements: The second phase starts once the laterality recognition is in place and the patients are able to differentiate their left and right sides. This stage involves watching people move and imaging their movements. It is important to note that the patients should not perform the movement, as it would lead to firing of the primary motor cortex as explained above and probably lead to symptom aggravation. The key is to imagine your right or left hand, as appropriate, replacing that of the person watched, to exercise the brain. The emphasis during this stage is placed on accuracy and not on speed of movements. In order to facilitate imagery practice, however, some established facts should be considered. First, challenging or unfamiliar actions are more difficult to imagine than simple or familiar ones. Second, closed loop skills are easier to practice than open loop skills. Third, gains from mental practice may be higher when imagery is used at the initial or cognitive phase of motor skill acquisition.
Mirror Therapy: Though not a part of the traditional motor imagery programs used in sports or neuro rehabilitation motor function enhancement, mirror therapy is a fundamental step in management of chronic pain as advocated by Moseley. The use of visual feedback with the mirror box as a technique for accelerating recovery from phantom pain and stroke was originally invented by VS Ramachandran MD at the University of San Diego. Since then the procedure has undergone placebo-controlled studies and also been employed with success for CRPS and hand injury cases. It is also been increasingly used in motor relearning protocols for stroke as well. While practicing mirror therapy, the patient places the affected limb in what’s known as a mirror box, which keeps the injured part out of view. The corresponding and unaffected limb is then positioned in front of the mirror. An alternative setup is to have the patient sit at a right angle before a mirror so that only one side of the body is reflected back. In either case, the idea is to then move both limbs in a coordinated manner so that they mimic the movement of the other. Studies have shown that the majority of patients typically experience sensations in the hidden limb very quickly after starting this exercise.
Evidence for effect of motor imagery for chronic pain – As mentioned above, there has been considerable research on the use of MI in neuro rehabilitation and sports performance. The research group of G.L. Moseley has focussed on the use of GMI for chronic intractable pain.In a single blind repeated measures, crossover RCT, Moseley evaluated the impact of graded MI (GMI) program on 13 CRPS -1 patients. The patients were randomised to GMI or to the conventional management through a random number table. The outcome measures assessed included – Neuropathic pain scale (NPS) and circumference of the base of second and third digits (as a measure of the swelling). The MI consisted of three stages, each of 2 weeks duration: (i) recognition of hand laterality, (ii) imagined hand movements and (iii) mirror therapy. The principal results of this study were –1) There was a strong effect of treatment group on pain and swelling. The effect size of the treatment was ~ 20 points on the NPS and this was maintained for at least 6 weeks.2) When the control group crossed-over to the MI, they demonstrated similar reductions in pain and swelling.3) 6 weeks after completing the MI, 50% of patients no longer fulfilled the diagnostic criteria for CRPS1.
Though the study presented significant results, these must be interpreted with caution due to small sample size, which was restrictive due to extensive exclusion criteria and included only those patients for whom CRPS1 was initiated by a non-complicated wrist fracture. In addition, as the author acknowledged, the follow up was not long enough to assess the impact on work status or long term quality of life. The study scored 7 on the PEDro scale.In another repeated measures, single blind trial, on 20 subjects with diagnosis of CRPS – 1, Moseley assessed the impact of a motor imagery program (MI) on Neuropathic pain scale and 5 functional tasks, which the patients were finding difficult since the onset of the condition. The imagery program was divided into three components and the subjects were randomly assigned to any of the three groups, which differed in the sequence of the components of MI.
The results of the study showed that patients in the MI group did better than patients in either of the other groups. Second, imagined movements only imparted an effect when they followed hand laterality recognition and mirror movements only imparted an effect when they followed imagined movements. Based on the results of the study, the authors proposed that the sequence of the components in a motor imagery program is important to achieve the sequential activation of premotor and then motor networks. This study is from the same authors as the previous ones and suffers from similar drawbacks including small sample size, lack of adequate follow up and the stringent inclusion and exclusion criteria which would disallow the generalisability of the results to the CRPS 1 patient population. The trial scored 6 on the PEDRo scale. In another study, Moseley randomly allocated fifty-one patients with phantom limb pain or CRPS1 to motor imagery, consisting of 2 weeks each of limb laterality recognition, imagined movements, and mirror movements, or to physical therapy and ongoing medical care. The outcome measures included patient specific task rating scale, McGill pain questionnaire and pain VAS for last 2 days. The mean decrease in pain between pre- and post-treatment was 23.4 for the motor imagery group and 10.5 mm for the control group. Improvement in function was similar and gains were maintained at 6-month follow-up. The authors thus concluded that motor imagery reduced pain and disability in these patients with complex regional pain syndrome type I or phantom limb pain.
The study suffers from some methodological flaws like lack of baseline comparability of the subjects, data collection over a period of 36 months, which could have led to a systematic effect of time or treatment pathway that affected results. The study was graded 5 on the PEDRo scale.In a similar study reported as a short communication in the New England Journal of Medicine, Chan et al concluded that mirror therapy reduced phantom limb pain in patients who had undergone amputation of lower limbs. Such pain was not reduced by either covered-mirror or mental- visualization treatment.In a high quality clinical trial, McCabe et al reported significant pain relieving effect of MI on patients with acute CRPS, but similar results could not be found in the patients with chronic CRPS. In addition to these clinical trials, there have been various published case studies which have explored the effects of MI on patients with chronic pain and have reported complete relief from pain even in intractable cases.
Conclusion: This article has presented the basics of MI and detailed the GMI program in management of chronic intractable pain. Traditionally, recalcitrant conditions like CRPS and phantom limb pain, which pose a dilemma for muscusloskeletal physiotherapists, have been shown to favourably respond to GMI. Based on the above literature, sound conclusion as to the effectiveness of MI in management of chronic pain cannot be drawn, but it does provide useful indicator as to the directions for future research. In addition, though theoretical constructs have been postulated as to the effect of MI on motor cortex, further research needs to be conducted to elucidate the underlying the mechanisms of the effect of MI. Still, it does present the musculoskeletal physiotherapists with a useful tool to manage chronic pain and encourage motor relearning.