Cortical representations of infraspinatus in rotator cuff tendinopathy

A recent article in Clinical Neurophysiology has demonstrated that alterations in central motor representation increase over time in individuals with rotator cuff tendinopathy.  The authors conclude that chronicity of pain, but not its intensity, appears to be a factor related to lower excitability of infraspinatus representation and thatthat while cortical reorganization correlates with magnitude of pain in neuropathic pain syndromes, it could be more related to chronicity in the case of musculoskeletal disorders.

 

A common complaint

Discomfort and pain around the shoulder are some of the most typical musculoskeletal complaints that lead people to people seek out a physiotherapist, with issues related to rotator cuff tendinopathy accounting for the lion’s share (35% to 50%) of diagnoses.

For the therapist, many management strategies by which to address this issue are available, such as manual therapy techniques, postural education, and a vast range of strengthening and stretching exercises, to name but a few. Yet, regardless of the intervention employed, a third of shoulder pain patients still complain of ongoing pain, dysfunction and recurrence. In the light of these figures the question is raised, ‘what are we missing?’

Peripheral issues

Within any one musculoskeletal disorder there lies a large range of potential, underpinning mechanisms and related, secondary issues. In the periphery, the presence of pain and pathology is seen to alter muscle function in pain, including changes in timing and duration (onset/offset) of activation, decreased or increased activation, and altered patterns of muscle recruitment order.

Central issue

However, observed changes are not merely limited to the periphery, which we could describe as the ‘hardware or branch post offices’ of the body. Central issues are also apparent; the ‘software or central post office’ suffers, too. Alterations within the CNS have been documented in many musculoskeletal disorders such as low back pain, neck pain and whiplash associated disorders. It has been recently hypothesized that part of the deficits associated with rotator cuff tendinopathy are related to reorganization of somatosensory and motor cortices such as in low back pain, phantom limb pain and complex regional pain syndrome (Myers et al., 2006; Roy et al., 2009; van Vliet and Heneghan, 2006, Tsao et al 2011, Tsao et al 2008).

Cortical representations

In light of such findings, the study by Ngomo et al (2015) is worthy of consideration. This group employed transcranial magnetic stimulation (TMS) to investigate possible central motor representation changes of infraspinatus muscle in thirty-nine patients (18 women, 21 men) all with unilateral rotator cuff tendinopathy. Additionally, the authors questioned whether such changes might be related to pain intensity, pain duration and physical disability.

The study revealed there was a significant inter-hemispheric asymmetry of infraspinatus active motor threshold. On the affected side, the active motor threshold was higher compared to unaffected side, indicating decreased corticospinal excitability. Also, the duration of pain (>12 months), but not its intensity, appeared to be a factor related to the lower excitability of the infraspinatus representation. It is interesting to compare that, for example, in phantom limb pain and in other neuropathic pain syndromes cortical reorganization is related to magnitude of pain not the length of pain (Moseley and Flor 2012).

blog pic brainIn the discussion, the researches stated that the results were consistent with the previous reports of alterations in corticospinal excitability for shoulder muscles in patients with other musculoskeletal shoulder disorders. For example, it was found increased active motor threshold (decreased corticospinal excitability) in subjects with non-traumatic shoulder instability (Alexander, 2009). There are also other TMS studies, considering musculoskeletal disorders showing variable alterations in corticospinal excitability; that is, both increased or decreased activation (On et al 2004; Strutton et al 2003; Strutton et al 2003). Therefore, central issues are apparent but variable in nature, in a comparable manner to that seen in the periphery. The up and downregulation of muscles in the presence of pain caused a lengthy debate before a point of clarity was found. The story must be continued for a fully formed picture to realised with regards to cortical representation. The complexity of the systems underpinning human movement must be acknowledged, yet the overt marker of the state of this system can be considered, assessed and modified; movement. Whilst research continues to illuminate the latent mechanisms, movement supplies a route to manage pain and dysfunction.

The message for therapists

  • So, what are the implications for rehabilitation regarding the study in question?People in pain need pain education, reducing fear of pain and fear of movement. It is this fear that might be a contributing factor in pain, maintaining pain’s presence, movement control impairments and ongoing disability.
  • In order to change, modify and improve cortical representation, so as to decrease ongoing pain and dysfunction, there is a need to focus our rehabilitation program on voluntary, cognitive low-threshold motor control retraining. With skilled motor control retraining delivery we can find and build a new, versatile and healthy way to move. It is this ‘delivery’ of movement that supplies a suggested route to alter both central and peripheral deficits, helping to sort the problems in the local and central post offices.

References

  • Ngomo S, Mercier C, Bouyer L J, Savoie A, Roy J S 2015. Alterations in central motor representation increase over time in individuals with rotator cuff tendinopathy.  126, 365-371.
  • Alexander CM 2007. Altered control of the trapezius muscle in subjects with non- traumatic shoulder instability. Clin Neurophysiol 118:2664–71.
  • Moseley GL, Flor H 2012. Targeting cortical representations in the treatment of chronic pain: a review. Neurorehabil Neural Repair 26:646–52.
  • Myers JB, Wassinger CA, Lephart SM 2006. Sensorimotor contribution to shoulder stability: Effect of injury and rehabilitation. Man Ther 11:197–201.
  • On AY, Uludag B, Taskiran E, Ertekin C 2004. Differential corticomotor control of a muscle adjacent to a painful joint. Neurorehabil Neural Repair 18:127–33.
  • Roy JS, Moffet H, Mcfadyen B, Lirette R 2009. Impact of movement training on upper limb motor strategies in persons with shoulder impingement syndrome. Sports Med Arthrosc Rehabil Ther Technol 1:8.
  • Strutton PH, Catley M, Mcgregor AH, Davey NJ 2003. Corticospinal excitability in patients with unilateral sciatica. Neurosci Lett 353:33–6.
  • Strutton PH, Theodorou S, Catley M, Mcgregor AH, Davey NJ 2005. Corticospinal excitability in patients with chronic low back pain. J Spinal Disord Tech 18:420–4.
  • Tsao H, Galea M P, Hodges P W 2008. Reorganization of the motor cortex is associated with postural control deficits in recurrent
low back pain. Brain 131: 2161-2171
  • Tsao H, Danneels L A, Hodges P W 2011. ISSLS Prize Winner: Smudging the Motor Brain in Young Adults With Recurrent Low Back Pain. Spine 36:21;1721-1727
  • Van Vliet PM,Heneghan NR 2006.Motor control and the management of musculoskeletal dysfunction. Man Ther 11:208–13.

 

Gluteal tendinopathy

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