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- The major pain source of rotator…
The major pain source of rotator cuff‐related shoulder pain: a narrative review on current evidence
Key Points
- The reviewed evidence doesn’t appear to support a conclusive, clinically significant relationship between mechanical factors and rotator cuff-related shoulder pain (RCRSP).
- There is moderate-strong evidence for a relationship between chemical processes (inflammatory markers, mediators, growth factors and immune markers) and the intensity of RCRSP, suggesting a different biologic pathway from local tissue inflammation.
- Current evidence for the prevalence of central sensitisation in RCRSP is limited in both study quality and sample size.
BACKGROUND & OBJECTIVE
Rotator cuff-related shoulder pain (RCRSP) is a description of a large number of different pathologies, both traumatic and atraumatic in nature, that present with similar symptoms, including bursitis, rotator cuff tendinopathy, rotator cuff tears and calcific tendinopathy.
In earlier years, atraumatic rotator cuff pain was thought to be caused by either a primary (acromial morphology) or secondary (scapula dyskinesis) reduction in the subacromial space and acromioplasty surgery was widely performed for ‘impingement’ symptoms. While this was successful in relieving symptoms for some, it was not effective for everyone. This has led others to take up the challenge to further examine other causes of rotator cuff-related pain.
The aim of this narrative review was to discuss possible sources of pain contributing to RCRSP according to the mechanisms-based pain classifications.
There does not appear to be a clear clinical association between acromiohumeral distance and critical shoulder angle and atraumatic rotator cuff-related shoulder pain.
METHODS
The authors conducted a narrative review of the literature to review mechanism-based classifications of RCRSP. Mechanism-based pain classifications were introduced in the 1990s and most of the articles reviewed were published after this time. ‘Nociplastic’ pain was only recognized in the mechanism-based classification in 2017 (1). The authors did not provide any information about search terms used or whether they used any inclusion or exclusion criteria, nor any study quality instruments used (which is not unusual in narrative reviews).
RESULTS
The authors found a lack of longitudinal studies that would permit analysis of causation. Instead, almost all studies were cohort, case-control, cross-sectional which can determine the association between the variables and RCRSP but does not permit analysis of causation.
Mechanical Nociceptive Pain
The early descriptions of impingement symptoms caused by compression of the rotator cuff beneath the acromion were proposed by Neer (2). Studies are cited that found a statistically significant but not clinically significant association between acromiohumeral distance and subacromial pain (0.1-0.6mm). Other studies reported no statistical association between acromiohumeral distance and shoulder pain, range of motion or shoulder pain and disability index (SPADI) score.
Scapula dyskinesis has been proposed a cause of secondary external impingement, and an association has been found between scapula dyskinesis and RCRSP, and the development of shoulder injuries in athletes. However, further subclassification of scapula dyskinesis is unreliable and the patterns of dyskinesis were said to vary considerably in the studies reviewed.
Chemical Nociceptive Pain
Molecular changes in rotator cuff tissue samples have been extensively studied to investigate markers of inflammation. There is ample evidence of the presence of inflammatory markers in RCRSP. No clear evidence of a significant correlation between higher concentrations of inflammatory markers and higher pain levels was found, although one study found a significant correlation between higher levels of pain and subacromial bursa thickening/hyperplasia.
Higher concentrations of inflammatory markers, growth factors and immunologic markers were also seen in the glenohumeral joint (GHJ) synovial fluid of people with RCRSP and this was associated with worse scores for pain and function in the RCRSP group. These results suggest that inflammation and other processes are present but are not likely related to local tissue irritation.
Neuropathic Pain
Neuropathic pain is caused by injury or disease to the nervous system which may affect the suprascapular, axillary nerve, brachial plexus or cervical nerve roots causing shoulder pain. Reviewed studies found the prevalence of neuropathic pain diagnosed by PainDETECT and DN4 scores was 10.9%, representing only a small proportion of RCRSP participants.
Peripheral mononeuropathy, brachial polyneuropathy or cervical spine radiculopathy (nerve root pain) may co-exist, or mimic RCRSP, therefore, careful attention to the inclusion criteria in these studies, and vigilance in clinical practice for these differential diagnoses is crucial in understanding the true prevalence of neuropathic pain in RCRSP presentations.
Central Pain
Central sensitisation (CS) is defined as amplification of neural signalling within the central nervous system that elicits pain hypersensitivity (1). This occurs when the degree of local tissue nociception is insufficient to explain the ongoing pain and causes widespread physiologic and functional changes within the nervous system causing widespread pain, allodynia, hyperalgesia, hyperpathia and sensitivity of other body functions (1). The authors found only a small number of studies investigating CS in RCRSP with small sample sizes (< 20). They reported that features of CS (hyperalgesia in remote body parts and reduced pressure-pain threshold) were commonly found.
LIMITATIONS
As with all narrative reviews; no search terms, inclusion or exclusion criteria were provided, and study quality was not reported, making it difficult to evaluate bias and assess the quality of the evidence provided. As the authors pointed out, their intent was to examine the causal link between mechanical, chemical and nociplastic pain features and RCRSP. Due to a lack of longitudinal studies this was not possible, and they were able to report only associations between these pain mechanisms and RCRSP severity.
CLINICAL IMPLICATIONS
There does not appear to be a clear clinical association between mechanical factors (acromiohumeral distance, critical shoulder angle) and atraumatic RCRSP. However in the clinical context, according to current non-surgical management of RCRSP (3), if symptoms can be modified by mechanical methods that influence the subacromial space, treatments that reinforce these methods may be beneficial if symptoms are relieved.
Inflammatory and immunologic pathways are emerging as important factors in many chronic musculoskeletal conditions, including RCRSP. More research is needed to identify whether alternative pharmaceutical treatments are effective at targeting the mediators and growth factors for angiogenesis (versus anti-inflammatory medications) combined with ongoing focus on modifying lifestyle factors that may contribute to pain in chronic musculoskeletal conditions. At present, the prevalence of neuropathic pain appears low, and evidence for CS is limited. However, these should be assessed in the individual patient and managed whenever patients meet the criteria for neuropathic pain or central sensitivity disorders.
+STUDY REFERENCE
SUPPORTING REFERENCE
- Nijs J, Lahousse A, Kapreli E, Bilika P, Saraçoğlu İ, Malfliet A, et al. Nociplastic Pain Criteria or Recognition of Central Sensitization? Pain Phenotyping in the Past, Present and Future. J Clin Med. 2021;10(15).
- Neer CS. Anterior acromioplasty for the chronic impingement syndrome in the shoulder: a preliminary report. J Bone Joint Surg Am. 1972;54(1):41-50.
- Lewis JS. Rotator cuff tendinopathy/subacromial impingement syndrome: is it time for a new method of assessment? British Journal of Sports Medicine. 2009;43(4):259-64.