Chronic Musculoskeletal PainBMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f3146 (Published 24 May 2013) Cite this as: BMJ 2013;346:bmj.f3146
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The majority of chronic pain experienced by older adults is musculoskeletal in origin
The symptom experience and impact of this pain varies greatly
Chronic musculoskeletal pain is often associated with reduced activity, sleep disturbance, fatigue and mood alterations, and can result in severe disability
Regional pain in a single joint area is very common. It may be referred from above, or be due to periarticular lesions, as well as arthritis. A good history and careful examination should result in an accurate diagnosis
There are two main forms of arthritis: osteoarthritis (OA) and inflammatory arthritis. Pain in OA does not correlate well with pathology, is largely ‘mechanical’ in nature, and is difficult to treat. The pain of inflammatory arthritis is associated with severe joint stiffness and responds well to anti-inflammatory therapy
Generalised musculoskeletal pain in the absence of peripheral pathology (‘fibromyalgia’) is also common. There is evidence that this condition is due to pain sensitisation and loss of the normal inhibitory mechanisms that help reduce pain
Musculoskeletal pain is ubiquitous – everyone gets it. There are three main causes:
everyday activities that put unusual or repetitive strains on the system;
acute traumatic events;
Everyone is familiar with the aches and pains that generally follow unaccustomed activity and most of us will have had at least one episode of acute post-traumatic pain affecting our muscles, bones or joints. These problems are generally short lasting and not very bothersome. However, huge numbers of us, particularly older adults, also experience chronic, intrusive musculoskeletal pain. Recent surveys suggest that 30–50% of older adults suffer chronic pain, most of which comes from the musculoskeletal system. The spine is the commonest site involved (Back pain is dealt with in Chapter 4) followed by the knees, shoulders and feet. A disease is not always apparent, but of the chronic musculoskeletal disorders that cause chronic pain osteoarthritis is by far the most common.
Although some diseases, such as gout, are renowned for the severe acute, self-limiting pain that they can cause, this chapter only covers chronic musculoskeletal pain and disease.
The Anatomy and Physiology of Musculoskeletal Pain
Figure 1 shows a diagrammatic representation of a synovial joint and its surrounding structures. The articular cartilage is aneural, but the other structures are all richly innervated, with particularly dense sensory innervation seen at the insertions of tendons or ligaments into bone (the entheses), the subchondral bone and the periosteal covering of bones. Nocioceptive systems seen in these structures include the A-delta fibres responsible for acute sharp pain, and the C fibres responsible for chronic dull, throbbing pains (Chapter 4). Sensory input from these structures is an essential part of our function – as we stand or walk the entheses are ‘sensing’ the strain arising from the different muscles and joints, and through spinal pathways adjusting muscle tone accordingly, without our being aware of anything. Normally, these everyday activities, including more strenuous things such as running, do not excite the pain systems, but it now appears that in joint disease, particularly if inflammation is present, the system can become sensitised such that normal everyday activities become painful. In addition, pain sensitisation can occur at the spinal level, and cortical activity can lead to disinhibition of musculoskeletal pain.
The Experience of Musculoskeletal Pain
Healthcare professionals and academics carrying out research on musculoskeletal pain have focused their attention almost entirely on the severity of musculoskeletal pain, with some additional emphasis on whether it occurs at night or not. So, the ‘patient’ is asked how bad the pain is and whether it wakes them at night or not, and management strategies are suggested accordingly. However, it is clear that those with chronic musculoskeletal pain can experience a rich and varied set of symptoms not adequately described by enquiries about pain severity. It is now known, for example, that people with osteoarthritis usually experience two quite different sorts of pain – their ‘usual’ activity-related dull ache, and unpredictable attacks of severe, short lasting, more bothersome pain; and people with inflammatory rheumatic diseases experience severe morning stiffness in joints, which may be their overriding symptom.
Nearly everyone with chronic musculoskeletal pain, be it back pain, fibromyalgia or due to osteoarthritis or rheumatoid arthritis, also experiences four other associated problems:
activities limitations due to pain (with associated lack of participation in life);
The interactions between sleep problems, fatigue, anxiety/depression and pain are complex and not fully understood. The interactions can work in both directions (pain causing depression and depression increasing pain for example), and it is clear that some people can get into a ‘viscious circle’ in which loss of sleep, fatigue and anxiety or depression increase the amount of pain experienced, with the pain also causing sleep and mood problems (Figure 2).
A Classification of Musculoskeletal Disease and Pain
The WHO classification of musculoskeletal disorders breaks them into five groups, which, in rough order of frequency in the population, are shown in Figure 3.
A recent ‘paradigm shift’ in the approach to musculoskeletal (and other) diseases has been the recognition that pain should be thought of as a separate issue – the ‘fifth vital sign in medicine’ and a disease in its own right. In that context the tendency is to classify chronic musculoskeletal pain according to its site(s) of origin – it may be localised to a single joint (such as a shoulder or knee), to a region or limb (the back or the legs for example) or it may be generalised pain (often considered synonymous with fibromyalgia).
Some aspects of regional conditions, arthritis, and fibromyalgia are discussed briefly here.
Regional Pain and the ‘Soft-tissue’ Periarticular Disorders
If someone presents with chronic pain at a single joint site there are three possible causes:
The pain is referred from a more proximal site in the body. The classic musculoskeletal example of this is hip disease presenting with knee pain (Figure 4). Other examples include spinal problems being referred to the arm or leg, and, of course, cardiac problems being referred to the arm. It is essential to examine the structures ‘above’ the affected joint as well as the painful area itself when trying to make a diagnosis of the cause of regional musculoskeletal pain. An additional point to note is that localised tenderness can be referred from above, rather than indicating that the local tissue under the examiners' fingers is diseased.
The pain comes from the periarticular ‘soft tissues’ surrounding the joint There are several structures around the joint which can cause pain. The entheses, referred to above are a common cause, small tears in the structures giving rise to inflammation and pain associated with point tenderness at the anatomical site and pain reproduced by putting strain on the affected ligament or tendon. Common examples are lateral or medial epicondylitis at the elbow (tennis or golfer's elbow, respectively), achilles tendonitis, and ‘policeman's heel’ (plantar fasciitis). Problems in the body of the ligament or tendon can also occur, as in some forms of achilles tendonitis, and most commonly at the shoulder, where the tendons of the rotator cuff are often damaged. Problems can also occur with bursae surrounding joints (subacromial bursitis at the shoulder or trochanteric bursitis at the hip for example), in which case there is swelling of the bursa (which may be visible if superficial, as in olecranon bursitis of the elbow – ‘boozer's elbow’, but may only be detectable with imaging techniques such as ultrasound) (Figure 5). Other causes of periarticular problems include inflammation of tendon sheaths (as in ‘trigger finger’ for example), muscle injuries or localised nerve compression (as in carpal tunnel syndrome).
The pain is caused by intra-articular problems – arthritis There are two main sorts of intra-articular disorder – mechanical and inflammatory. Mechanical problems may be due to traumatic damage to an intra-articular structure, such as a knee meniscus, or to osteoarthritis. Unsurprisingly mechanical joint problems are characterised by mechanical symptoms and signs – such as ‘locking’ of a joint or crepitus on examination, while the inflammatory disorders are characterised by warmth and swelling of the affected joints. There are a large number of inflammatory conditions of joints, as mentioned in the next section.
In general, a careful examination can reveal the cause of regional ‘joint’ pain, and many of the disorders mentioned above are referred to as ‘easily curable rheumatism’, as they can be alleviated by simple, logical approaches, such as taking the stress off an affected enthesis, or injecting local steroid to get rid of focal inflammation in a bursa.
A detailed description of the many different types of arthritis and their characteristics is obviously beyond the scope of this chapter.
Osteoarthritis (OA) is a very common condition of older adults; it is characterised by focal areas of loss of articular cartilage associated with subchondral bone change in synovial joints. It affects hands, knees and hips most often (as well as the spine), and may be accompanied by local soft-tissue periarticular problems or by fibromyalgia, making the pain problem difficult to sort out and treat. Radiographs are used to diagnose the disease (Figure 6) but are of little value in management and should not be used routinely. OA pain is largely use-related and often described as a deep ‘ache’, sometimes interrupted by spasms of a more severe and different form of pain. Pain often disturbs sleep. Short-lasting stiffness of joints after inactivity is usually reported as well. Pain management in OA is difficult, but is well summarised in a recent National Institute for Health and Clinical Excellence (NICE) report that stresses the need for an holistic approach, with prominent use of non-pharmacological therapy; there is no effective treatment for the OA disease process other than joint replacement.
Inflammatory arthritis can be caused by several different diseases, most of which are most common in young adults. They include rheumatoid arthritis (RA), the sero-negative spondarthritides (such as ankylosing spondylitis or psoriatic arthritis), crystal-related arthritis, infections of joints and connective tissue diseases. Most of these diseases are characterised by unrelenting inflammation of the synovial lining of joints, bursae and tendon sheaths. RA is the commonest condition and it has a fairly strong female bias; it usually presents with pain, and swelling of the small joints of the hands and feet; this moves to more proximal joints with time and over a period of many years the inflammation may become less intense, but joint damage, due to erosion of cartilage and bone, can become severe (Figure 7). Prominent features of the pain of RA include severe stiffness in the mornings (it may take someone several hours to get washed and dressed in the morning) and fatigue. The pain itself is usually described as fairly constant and severe, and although it has some relationship to use of the joints, this is not generally as strong a feature as it is in people with OA. The pain of RA responds better to anti-inflammatory therapy than it does to analgesics. The management of RA has improved hugely over the last two decades and if early antirheumatic therapy, with agents such as methotrexate or anti-TNF therapies, is used the condition can usually be well controlled.
Fibromyalgia is a common condition of middle-aged adults (more common in women than men), characterised by widespread musculoskeletal pain, devastating fatigue and sleep and mood disturbances. It has overlaps with chronic fatigue syndrome, irritable bowel syndrome and migraine, and features of these conditions may accompany the dominant musculoskeletal pain and fatigue. Tender spots are commonly present in a number of well defined sites (Figure 8).
There is no peripheral pathology apparent in the muscles, joints or periarticular tissues to explain fibromyalgia. There are, however, a number of risk factors and associated phenomena that suggest that is likely to be due to central sensitisation or disinhibition of pain pathways. The risk factors include genetic and family influences, other psychosocial factors and environmental triggers including stress and infections. The associations include other painful conditions (including headache, which is very common) and disturbances of pain thresholds (with abnormal sensitisation and allodynia both being common), autonomic nervous system activity and neuroendocrine function. Fibromyalgia is a difficult condition to manage. Pharmacological approaches include the use of centrally acting agents including antidepressants and pregabalin; non-pharmacological approaches include exercise-based interventions and cognitive behavioural therapy.