Why is my shoulder hurting?

The meaning of pain expresses how important the central and peripheral nervous systems are for pain processing and pain development. The relevance of pain sensation(s) is necessary and useful information especially during an acute injury. The pain sensation(s) informs us to be cautious (i.e. adjust the balance of physiological function) to a level of activity that can be tolerated by the healing tissue. Consequently following an acute injury for example a blunt trauma or burn the usual reaction would compromise an increase in pain sensitivity in both peripheral (peripheral sensitisation) and central (central sensitisation) pain processing (nociceptive) structures. The artificial division between peripheral and central is at the level of the spinal cord, with the sensitivity at the cord and above deemed ‘central’, while sensitivity peripheral to the cord is deemed ‘peripheral’

 

Conversely the nociception systems (the body’s ability to sense potential harm) are not only common afferent sensors (nerve carrying a message towards the central nervous system) in the event of tissue damage but higher systems such as emotion and mood can have influential and prevailing effects on the peripheral nervous system through the descending modulatory circuitry. The descending circuitry comprises of both direct neural routes and indirect endocrine routes i.e. the hypothalamic-pituitary axis.

 

Therefore the descending systems may not only affect pain perception, but also peripheral tissue homeostasis and healing. To date there is still very limited research and understanding of the peripheral nervous system’s significance of afferent function in tissue homeostasis and healing. Although it is widely accepted that denervation (loss of nerve supply) is harmful to the healing of both bone and ligament (1).

 

Pain may happen in the absence or incidence of tissue damage, and subsequently there is a vast variability in the patterns of peripheral and central changes in patients presenting with shoulder pain. For example some patients may have substantial tissue defects i.e. a rotator cuff tear with a very peripheral pattern of pain sensitivity whereas others may have no substantial tissue defects with a very central pattern of pain sensitivity (2).  However many patients may also present with substantial tissue defects with no presenting pain or functional symptoms (3).

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Pain and Structure

many patients may present with a asymptomatic condition (no noticeable symptoms which are usually associated), with a rotator cuff tear there is still a substantial relationship between the rotator cuff integrity and pain symptoms. Arguably a rotator cuff tendinopathy (RCT) is often the most likely cause of shoulder pain in about three quarters of all patients presented. A study by Oag et al (unpublished) found patients are likely to have symptoms of (RCT) than those without, whilst previous asymptomatic patients are more likely to develop symptoms as the rotator cuff tear increases in size (4).

 

Pain is very complex and many factors may influence the development of pain. It is therefore unlikely that any one precise factor which precisely determines symptom development will ever be found.

 

If a tear occurs and increases in size for example at the glenohumeral joint, the joint kinematics will also change and the abnormality will equally be predominant in both symptomatic and asymptomatic patients (5). Arguably although the tendons of the rotator cuff are often the frequent ‘source’ of pain in the shoulder, any damage to the structures may lead to the development of pain and to other frequent sources i.e. being the glenohumeral joint and capsule, the labrum, acromioclavicular joint and the cervical spine. As you can imagine, it can be extremely difficult and at times be impossible to exactly locate where the exact source of pain is coming from using patient history, examination and radiological investigations for a wide variety of complex reasons. Furthermore the greater degree of a patient being ‘centrally sensitised’ the more problematic it can be to reach a precise diagnosis. For example clinical features may include pain radiating down the arm with tenderness to palpation over a wide area. However it is important to acknowledge that highly centralised patients may have a very treatable peripheral pathology in isolation, but as part of one’s assessment and differential diagnosis it is essential to consider other influential factors such as nerve entrapment in the cervical spine.

 

Patient history, clinical examinations - special tests and findings including diagnostic injections (bursal injection or nerve root blocks) can be very useful and very beneficial but they can also be problematic due to the lack of specificity. For example a C6 nerve root block may potentially eliminate a patient’s ‘cuff tear associated’ shoulder pain due to the result of C6 innervating the shoulder joint. With age rotator cuff tears and cervical spine degeneration become progressively common, meaning that many older people may well have a dual pathology. In the event of a dual pathology this may sometimes be recognised as a significant contributing pathology which may of been missed following unsuccessful surgical intervention.

 

The patient’s tissue abnormality may only identify so much information characterised by the terms of symptomology. The level of individual tissue abnormality and symptoms can be greatly different and likely characterised by individual variations in nociceptive processing both centrally and peripherally.

 

Treating Shoulder Pain

Treating shoulder pain varies greatly due to many different reasons depending on the patient’s specific diagnosis, patient preferences and the therapist’s choice of therapy intervention.  The placebo effect may also have a powerful role and effect on the treatment strategy due to the patient’s expectations and personal beliefs which may greatly help and improve symptomatic variables. The human body has a remarkable capability for reducing pain over time and this process is hardly yet understood.

 

For this same reason patients with significant symptoms may simply feel better over time without consulting a primary or secondary care clinician or specialist to receive therapy intervention even though there has been no improvement or a significant deterioration in their structural tissue abnormality. Therefore many patients do not ‘get better’ but are relatively content to live life with a certain degree of pain and disability. Ageing is also part of normal life and we have to be realistic of what can be achieved by setting realistic patient expectations which is a critical part of any consultation.

 

Summary

There is plenty of research evidence beyond the scope of this health news article without going into great detail for all types of possible treatments for all possible types of shoulder pain diagnoses. However the take home message is;

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"As individuals we are all very different with unique patterns of peripheral tissue changes together with a certain degree of highly variable peripheral and central nervous system changes, and that these drivers of pain symptomology is well worth bearing in mind when considering a rehabilitation treatment intervention".

 

Furthermore everything can be questionable due to the diagnostic sensitivity (how often will the test be positive) and specificity (how good a test is to identify the pathology) and finally we must appreciate that pain is a very complex and confusing entity.