Abstract
The pathophysiology of Stanmore Classification Polar type II/III shoulder instability is not well understood. Functional Magnetic Resonance Imaging was used to measure brain activity in response to forward flexion and abduction in 16 patients with Polar Type II/III shoulder instability and 16 age-matched controls. When a cluster level correction was applied patients showed significantly greater brain activity than controls in primary motor cortex (BA4), supramarginal gyrus (BA40), inferior frontal gyrus (BA44), precentral gyrus (BA6) and middle frontal gyrus (BA6): the latter region is considered premotor cortex. Using voxel level correction within these five regions a unique activation was found in the primary motor cortex (BA4) at MNI coordinates -38 -26 56. Activation was greater in controls compared to patients in the parahippocampal gyrus (BA27) and perirhinal cortex (BA36). These findings show, for the first time, neural differences in patients with complex shoulder instability, and suggest that patients are in some sense working harder or differently to maintain shoulder stability, with brain activity similar to early stage motor sequence learning. It will help to understand the condition, design better therapies and improve treatment of this group; avoiding the common clinical misconception that their recurrent shoulder dislocations are a form of attention-seeking.
Highlights
Complex shoulder instability, as a condition, has rarely been included in shoulder instability classifications[7], whose focus is usually on the traumatic aetiology[2,8,9,10]
No significant differences in cortical activation were found between the two types of movement when tested across all participants, and no effect was found for the interaction movement type*patient group (FWE, P < 0.05)
All clusters were located in the left hemisphere and included primary motor cortex (BA4) and supramarginal gyrus (BA40)
Summary
As a condition, has rarely been included in shoulder instability classifications[7], whose focus is usually on the traumatic aetiology[2,8,9,10]. Www.nature.com/scientificreports respond, and a large cohort of these tend to be female and 17–25 years of age, a group in which the instability has a marked effect on quality of life[16,17]. They are often labelled as attention-seeking, or else receive inappropriate surgery which fails to resolve their symptoms[15,18]. Physiotherapy, and other treatment strategies that incorporate visual feedback about motor performance[19], have had success in the treatment of complex shoulder instability This leads us to hypothesise that central cortical activation contributes to the instability. The non-invasive technique of functional magnetic resonance imaging (fMRI) has been important in developing this new understanding, and has led to clinical important developments in conditions such as Alzheimer’s and Parkinson’s disease29. fMRI studies of motor function in stroke[30,31,32], amputees[33,34,35], and movement dystonia[36] have revealed adaptive changes with bilateral activation and cortical re-organisation in the sensorimotor areas, the supplementary motor areas and the cerebellum[37]
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