Rotator cuff tendinopathy

The results of post-mortem studies suggest that it is common, by the fifth decade of life, to find degenerative changes in the rotator cuff tendons, particularly thinning and fibrillation at the ‘critical zone’ (the hypovascular area) of the cuff. These changes are thought to be those of physiological ageing, but it seems that under some conditions, as degeneration increases, repair mechanisms fail and micro-tears develop, which can become macro-tears; epidemiological studies suggest that these changes are a frequent cause of painful shoulder symptoms . There may also be inflammation of the tendons or bursa. Typically, the pain is made worse by sleeping on the affected shoulder and moving the shoulder in certain directions, and there can be pressure on the tendons by the overlying bone when lifting the arm up, the phenomenon being described as ‘impingement’. Cyriax wrote that the involved tendon could be differentiated by physical examination findings: supraspinatus tendinitis by pain on resisted abduction, infraspinatus tendinitis by pain on resisted external rotation and subscapularis tendinitis by pain on resisted internal rotation . However, the evidence that these signs perform well in clinical practice, at least in population and workplace studies, is lacking.

Biceps tendinopathy

The biceps tendon is also prone to tendinopathy, resulting in anterior shoulder pain. Cyriax described the classical findings of bicipital tendinitis as pain on resisted elbow flexion (Speed’s test) and pain on resisted supination of the forearm (Yergason’s test) . It is worth noting that few epidemiological studies have involved an examination component that specifically attempted to discriminate bicipital tendinitis. Of those that have, most have used criteria based upon those of Cyriax: shoulder pain, local tenderness over the tendon and pain on resisted isometric elevation of the arm and/or resisted isometric flexion of the elbow . It is thought that isolated biceps tendinopathy is relatively uncommon and that the condition more commonly coexists with rotator cuff pathology and impingement.

Adhesive capsulitis (frozen shoulder syndrome)

The term ‘frozen shoulder’ appears to have been first coined by Codman in 1934, for a ‘class of cases which are difficult to define, difficult to treat and difficult to explain from the point of view of pathology’ . Codman wrote that the primary cause was a localised supraspinatus tendinitis with subsequent extension to the other components of the rotator cuff, the subacromial bursa and finally the capsule and extra-capsular ligaments. This view has been disputed , and there is generally no agreement as to the underlying pathophysiology. One arthroscopic study found histological appearances of the capsule similar to those seen in Dupuytren’s contracture, suggesting that frozen shoulder may be one of the fibromatoses . However, these were in a highly selected group of patients (those with severe symptoms of sufficient duration to warrant referral to orthopaedic clinics and surgical intervention).

Capsulitis has been described as having three characteristic phases. During the first painful phase, the shoulder complex is severely painful, often during rest, and this phase can last anything from 3 to 6 months. Subsequently, during the adhesive phase, pain resolves but significant restriction of movement, active and passive, occurs in all planes. In the final resolution phase, recovery of function is said to occur. The transition through these stages is thought to take an average of 30 months, but it may be considerably longer and it is not clear that complete recovery occurs: one study found that as many as 50% of patients failed to regain a normal range of movement, even at follow-up after 7 years .

To diagnose capsulitis, Cyriax required restricted passive motion of the shoulder joint in a ‘capsular pattern’ – that is, limitation of external rotation more than abduction, and more than internal rotation. Broadly, the case definitions used in epidemiological surveys have parallelled this description. Chard et al., for example, used the following definition: ‘marked restriction of all active and passive movements with external rotation reduced by at least 50% of normal, in the absence of bony restriction’ . Other studies have introduced the element of duration: Ohlsson et al. , Viikari-Juntura and Waris et al. required shoulder pain and progressive stiffness of the shoulder over a 3–4-month period. Although broadly similar, it is worth noting that none of these classifications included a definition of ‘normal range of movement’, or the cut-off value below which restriction would be diagnosed.

Acromioclavicular joint syndrome

The acromioclavicular joint is a plane synovial joint between the clavicle and the scapula. Normal function of the joint is required for full active painless elevation of the shoulder to take place, and dysfunction causes localised pain, tenderness and swelling and pain felt maximally on full abduction of the shoulder. Horizontal adduction of the joint with the arm extended is also said to provoke local pain (the so-called ‘scarf test’) . In practice, studies of shoulder disorders have rarely included diagnostic tests specific to this condition. Where they have , the classification criteria have been similar but not identical.

Although many of the clinical diagnostic criteria for these specific shoulder disorders have been widely published and taught, perhaps because of the complex anatomical and functional structure, there is evidence to suggest that these patho-anatomical classification systems do not generally perform reliably in practice . Their validity, at least in population and workplace studies, has also been questioned.

Specific shoulder disorders and non-specific pain

Much of the available evidence of risk factors for shoulder disorders comes from epidemiological studies. In many of these studies, data were collected using self-completed questionnaires, and the outcome measure has been ‘shoulder pain’ or ‘shoulder pain lasting more than a specified time’ or ‘shoulder pain causing a specified functional impairment’, sometimes with inclusion of a mannequin diagram to confirm the pain distribution . Whilst these studies have informed our knowledge of the risk of certain activities or exposures, they fail to give specific information as to which component of the shoulder complex is affected and this may have hampered progress towards identifying strategies for prevention. It is plausible that, as with other anatomical sites such as the lower back, shoulder pain may be separable into subcategories, some of which reflect specific patho-anatomical strains and for which risk factors and prevention strategies could be identifiable. Moreover, there may also be a subcategory of ‘non-specific shoulder pain’, which has different risk factors and needs other preventive strategies, rather akin to non-specific or ‘mechanical’ low back pain. Given our current limitations in defining subtypes shown to be relevant in terms of prognosis or response to treatment, much of the literature currently available provides risk estimates for exposures in relation to shoulder pain. Using a case definition of ‘shoulder pain, discomfort, fatigue, limited movement, loss of muscle power but without a pattern allowing a specific diagnosis to be made’, there is growing evidence that ‘non-specific shoulder pain’ is more frequently found in the general population and workplace studies as compared with specific shoulder conditions that have clear diagnostic features, such as rotator cuff syndrome . It has been estimated, for example, that non-specific shoulder pain among workers was six times more frequent than specific shoulder conditions .

The lack of a consistent standardised diagnostic approach has possibly hindered our understanding of the extent of the problem in the workplace and across countries, and consequently the development of effective interventions and preventive tools to reduce the burden of musculoskeletal pain, including shoulder problems . With this in mind, there have been a number of initiatives to try to improve diagnostic classification of upper limb disorders. One such endeavour in the UK was instigated by the Health and Safety Executive, and it involved a multidisciplinary group of experts with an interest in soft tissue upper-limb disorders . Using a Delphi technique, this group derived consensus case definitions for, among other disorders, bicipital tendinitis, rotator cuff tendinitis and adhesive capsulitis . Working from these definitions, and after adding diagnostic criteria for acromioclavicular joint dysfunction and subacromial bursitis ( Table 2 ), informed by a literature search, our group developed and tested an examination protocol suitable for use in population-based epidemiological research . We have shown this protocol to have good reliability between observers for the detection of physical signs at the shoulder both among patients attending hospital-based soft tissue clinics (kappa coefficients 0.54–0.93) and among adults of working age from the general population (kappa coefficients 0.29–0.66) .

This examination protocol has been used in a large population study including 6038 working-aged adults. All 411 people reporting shoulder pain were examined by a trained observer according to the Southampton protocol. Diagnoses were assigned by a computerised algorithm according to the predefined criteria. Marked overlap of all diagnoses was observed within the same shoulders, such that, for example, 205 of the 410 subjects with a diagnosis of adhesive capsulitis also received a diagnosis of rotator cuff tendinitis, and among 28 people who received a diagnosis of bicipital tendinitis, 23 also fulfilled diagnostic criteria for adhesive capsulitis. Therefore, it seemed that these criteria had poor specificity at least for the separation of individuals with subtypes of shoulder pain in a general population study .

In primary care in the Netherlands, van der Windt and colleagues have shown that simpler clinical classification systems yielded better intra-observer reliability but the authors concluded that more research was required to demonstrate whether the clinical syndromes that they proposed ( Table 1 ) constituted separate disorders requiring different treatment strategies . A recent (2014) review of this literature by Hanchard et al. similarly found insufficient evidence of usefulness to support the use of many of the diagnostic tests currently taught in clinical practice .

Individual risk factors

A number of individual risk factors for shoulder pain have been established. These include female gender , obesity , older age and coexisting medical disorders (e.g., inflammatory arthritis, polymyalgia rheumatica, fibromyalgia, multiple sclerosis and diabetes mellitus) . There is growing evidence for a role of individual psychological factors (such as distress and depression) in the development of shoulder pain . Nahit and colleagues found that psychological distress was associated with a doubling of the risk of reported pain . A study of prevalence rates of musculoskeletal symptoms and associated disability in workers suggested that cultural factors such as health beliefs and expectations have an important influence on back, neck and arm pain . Smoking has also been linked to musculoskeletal pain in the arm , and it has been associated with an increased risk of long-term sickness absence (>14 days) among employees with neck–shoulder pain [9]. Possible explanations for such findings include a pharmacological effect on pain perception, damage to musculoskeletal tissues or differences in the threshold for reporting symptoms that reflect differences in personality or illness behaviour .

Non-occupational mechanical factors and shoulder disorders

Non-occupational mechanical risk factors are not the main focus of this review, but leisure or home activities may be an important source of confounding when investigating occupational risk factors for shoulder pain . The biomechanical features of many sports have been investigated, and findings indicate that both professional and recreational athletes who participate in contact sports (e.g., ice hockey) and in sports that involve repetitive overhead actions such as golf, swimming and javelin are at an increased risk of rotator cuff tears , acromioclavicular joint dysfunction and impingement syndrome .