Abstract
Frozen shoulder (adhesive capsulitis) is a severe chronic pain condition that is not well understood and current treatment is suboptimal. In several other chronic pain conditions motor imagery and tactile acuity deficits are present, which are thought to represent associated neuroplastic changes. The aims of this study were to determine if motor imagery performance assessed by the left/right judgement task, and tactile acuity assessed by two-point discrimination, are altered in people with unilateral frozen shoulder. In this cross-sectional, prospective study eighteen adults diagnosed with frozen shoulder in a physiotherapy clinic setting completed a left/right judgement task, response times (RT) and accuracy for the left/right judgement task were determined. Next, tactile acuity over both shoulders was assessed with a novel, force-standardised two-point discrimination test. Results corresponding to the affected side were compared to the pain free shoulder; Left/right judgement task: mean RT (SD) corresponding to the affected shoulder was significantly slower than RT for the healthy shoulder (p = 0.031). There was no side-to-side difference in accuracy (p > 0.05). Neither RT nor accuracy was related to pain/disability scores or duration of symptoms (p > 0.05). Two-point discrimination: mean two-point discrimination threshold of the affected shoulder was significantly larger than the contralateral healthy shoulder (p < 0.001). Two-point discrimination threshold was not related to pain/disability scores or pain duration (p > 0.05); One explanation for these findings is altered sensorimotor processing and/or disrupted sensorimotor cortex representations of the affected shoulder. A case then exists for the use of treatments aimed at reversing these changes, training the brain to reduce chronic shoulder pain.
Highlights
Frozen shoulder is a severe chronic musculoskeletal pain condition, with a typical history of insidious onset shoulder pain, married with progressive stiffness and functional limitation [1] lasting for many months
Participants were of middle age, had chronic symptoms, were suffering moderately severe pain: worst pain numerical pain scales (NRS) mean 8.0/10 (±2.5); average pain NRS mean 5.0/10 (±2.3); and reported moderate levels of disability with a SPADI mean score of 59.2 (±20.4)%
People with frozen shoulder were slower at recognising thatpossible corresponded to theiroffrozen poorer motor imagerytoperformance that the central related to implicit motor Our imagery is shoulder compared images thatiscorresponded to processing their healthy unaffected shoulder
Summary
Frozen shoulder (adhesive capsulitis) is a severe chronic musculoskeletal pain condition, with a typical history of insidious onset shoulder pain, married with progressive stiffness and functional limitation [1] lasting for many months. A ‘frozen’ stage of extreme range of motion restriction; and a ‘thawing’ stage as stiffness resolves [2]. This description of the course of frozen shoulder has been disputed in a recent systematic review [3], and current evidence based physiotherapy guidelines recommend classifying frozen shoulder as ‘pain predominant’ or ‘stiffness predominant’ [4]. Frozen shoulder has been associated with metabolic diseases—diabetes mellitus [5], hyperthyroidism [6]—and chronic musculoskeletal conditions. Public Health 2020, 17, 7464; doi:10.3390/ijerph17207464 www.mdpi.com/journal/ijerph
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