The Musculoskeletal System
4.2a The physiology of the musculoskeletal system
The musculoskeletal system consists of the bony skeleton, the joints and the muscles. Its functions are to support the soft tissues of the body, to protect the deep organs and to enable the movements of the body. In addition, as described in Stage 3, the bones contain the marrow spaces in which most of the maturation of the blood cells takes place.
This section considers in turn the physiology of the bony skeleton, the joints and the muscles. It is assumed that the reader has a basic knowledge of the shape, position and names of the bones, joints and muscles.
The physiology of the bony skeleton20
All bone consists of a combination of a hard, non-living substance containing salts of calcium and phosphorus together with a vast number of living bone cells. The non-living part of bone is structured upon a scaffolding of numerous connective tissue fibers. It is this complex material that persists after death when the rest of the body has decayed. Nevertheless, in life, this seemingly fixed aspect of bone is constantly in a state of change, as the bone cells are always active in reshaping this hard material according to the needs of the body.
There are two main types of bone tissue. Compact bone is a dense but very strong material present in all bones at their margins. Cancellous bone is more spongy and filled with red marrow, and is particularly rich in the shafts of the long bones and the ribs, the center of the vertebral bodies and the core of the pelvic bones. In both types of bone a rich network of vessels supplies the bone cells, the osteocytes, with blood and lymph fluid.
The bony skeleton is made up of four different types of bone, categorized according to their shape: the long bones (e.g. the femur and the humerus), the irregular bones (e.g. the vertebrae and the carpal bones), the flat bones (e.g. the sternum and the skull) and the sesamoid bones (e.g. the patella and the pisiform bone). In terms of physiology, the important distinction to be made is between the long bones and the three other types of bone (irregular, flat and sesamoid).
The long bones (see Figure 4.2a-I) in the body are the radius, ulna and humerus of the arm and the femur, tibia and fibula of the leg. They are characterized by a shaft and two widened ends known as epiphyses. The shaft is composed of dense, strong compact bone, with a central hollow that is filled with fatty yellow bone marrow. The epiphyses are the site of bone growth in the child, and are largely composed of soft, spongy cancellous bone containing bloody red marrow, all bounded by a rim of strong compact bone. The epiphyses are covered with hyaline cartilage in the regions where they make joints with other bones; elsewhere the long bones are bounded by a fibrous coat called the periosteum. Underneath the periosteum lie clusters of osteoblasts and osteoclasts, the bone-forming cells responsible for bone remodeling and production. These cells are stimulated to form and reshape new bone when the periosteum or underlying bone becomes damaged. The design of the long bones confers strength, which is necessary for their main functions of locomotion, posture and manipulation.
Figure 4.2a-I The structure of a long bone (partially sectioned)
Short, irregular, flat and sesamoid bones
The short bones are less strong than the long bones because they are composed largely of spongy, cancellous, red, marrow-containing bone, and are bounded by a relatively thin protective rim of compact bone. This structure (see Figure 4.2a-II) supports their functions of intricate movements (in the back, hands and feet), protection (skull bones, pelvis and ribs) and bone marrow production.
Figure 4.2a-II The structure of flat and irregular bones (sectioned)
The blood-forming marrow
It is the red marrow that is the site of the development of the blood cells. This marrow is abundant in the vertebrae and the flat bones of the skull, ribs, sternum and pelvis.
The growth of bone in childhood and adolescence
An understanding of how bones grow is relevant to the pathology of a number of the diseases of bone. In the fetus there is initially no hard bony material. Instead, at the future site of the long and irregular bones, soft cartilage, a form of connective tissue, appears. At the site of the flat bones a soft tissue membrane develops. Gradually, as birth approaches, osteoblast cells within these areas of soft tissue secrete the hard substance that will form the non-living part of bone. This process of transformation of soft tissue into hard bone is called ossification. When bone has ossified, some of the osteoblasts mature into the bone cells situated deep within bone, where they are known as osteocytes.
This means that in the newborn only a small part of each of the bones is mature hard bone. For example, at the time of birth, only the centers of the skull bones have ossified. The edges of these flat bones are still thick membrane, which allows for some flexibility of movement between the skull bones (very important during childbirth). This soft membrane is most prominent in the diamond-shaped soft spot (the fontanel) that can be felt on the top of the head of most babies under one year of age.
The bones do not fully ossify until early adulthood. Until then, there are still some areas of cartilage or membrane that are actively forming new bone and allowing for growth. Because of this, the approximate age of a child can be estimated from an X-ray image of the bones, which shows the state of progression of ossification of the bones. Puberty is a time during which the surge of sex hormones causes an initial spurt of growth of long bones followed by ossification of the growth centers in the long bones (see Section 5.2a). This is why growth slows considerably once puberty has been reached.
The continued growth of bones
After early adulthood the bones do not change significantly in size. Nevertheless, the osteoblasts remain active in secreting new bone. This laying down of new bone is counterbalanced by the activity of another type of bone cell called the osteoclast. The osteoclasts act continually to digest old bone and to return the calcium, phosphorus and other nutrients within the bone back to the circulation for reuse. This process, known as remodeling, allows bones to become stronger in areas in which there is perpetual physical stress (e.g. the upper part of the femur in someone who is physically active) and allows for the repair of bones in the case of fracture.
The rate of remodeling of bone is influenced by various hormones of the endocrine system. The thyroid hormones, growth hormone from the pituitary gland and insulin from the pancreas stimulate the correct development and ossification of the bones. In puberty, testosterone and estrogen stimulate the growth spurt, and also the changes that differentiate the male and female adult skeletons. Estrogen also helps to maintain the calcium content of bones in premenopausal women. In addition, two hormones secreted from the region of the thyroid gland, calcitonin and parathyroid hormone, are essential in the control of the balance of the activity of the osteoblasts and the osteoclasts.
Vitamin D is an essential factor in the maintenance of the non-living (calcified) part of bone. In vitamin D deficiency the bones become softened. This leads to bowing of the bones during childhood (rickets) and pain and weakness in adulthood (osteomalacia). These conditions are discussed in more detail in Section 4.2d.
The structure of the skeleton
The skeleton can be considered as consisting of two parts: the axial skeleton and the appendicular skeleton. The axial skeleton (shaded bones in Figure 4.2a-III) forms the central bony core of the body, and consists of the skull, vertebral bones, sacrum, coccyx, ribs and sternum. All these bones are either flat or irregular, and so each is composed of a core of red marrow-containing cancellous bone surrounded by a thin rim of compact bone. The skull and the vertebral column support and protect the fragile structure of the brain and spinal cord. The ribs and sternum likewise support and protect the lungs and the heart in the thorax, and the organs of the upper abdomen, including the liver, kidneys, pancreas and the spleen.
The appendicular skeleton (unshaded bones in Figure 4.2a-III) is so called because it consists of the appendages to the axial skeleton. These are the shoulder girdle (clavicles and shoulder blades), the upper limbs, the pelvic girdle (the hip bones) and the lower limbs. The bones of the shoulder girdle and the pelvic girdle are flat bones. The bones of the limbs are either long bones or irregular bones.
The healing of bones
Healthy bones are strong and slightly flexible. In health, bones will only break if exposed to significant trauma. Fractures of healthy bone can be classified as simple, compound or greenstick. If a fracture occurs because the bone is weakened in some way by an underlying disease process, it is described as a pathological fracture.
A simple fracture describes when the ends of the bone do not protrude through the skin, whereas a compound fracture involves a break to the skin by the sharp end of the fractured bone. A greenstick fracture occurs in the flexible bones of young children. In this fracture, the break is incomplete, as the bone is far less brittle than the fully ossified adult bone. This means that the bone bends like a green stick, rather than snapping into two.
The healing of broken bones can be compared to the healing of wounds in that it is the formation of a blood clot in the space between the broken ends that initiates the healing process. Figure 4.2a-IV illustrates the stages in the healing of the broken shaft of a long bone. The blood clot stimulates the inward movement of phagocytes and osteoblasts. The phagocytes remove unwanted debris, while the osteoblasts lay down an initially chaotic mass of new bone called callus. The callus is gradually remodeled by osteoclasts into new, ordered compact bone. In adults this process takes weeks to months, but it is significantly quicker in children.
Figure 4.2a-III The skeleton: anterior view (the bones of the axial skeleton are shaded)
Figure 4.2a-IV The stages in bone healing
Information box 4.2a-I
The bones: comments from a Chinese medicine perspective
In Chinese medicine, the bones and bone marrow have a relationship with two of the extraordinary Yang organs: the Bones and the Marrow.
The Marrow corresponds to the substance that nourishes and forms nervous tissue and the bone marrow, and which is produced by Kidney Essence. Therefore, if the Kidneys are Deficient, the bone marrow will be weak.
The Bones correspond directly to the physiological bones. They are nourished by Kidney Essence and Marrow, and will also become weak if the Kidneys are Deficient.
The physiology of the joints
The joints are the sites in the body at which two or more bones come together. They are essential for allowing free, but controlled, movement of the body.
There are three categories of joint in the body: the fixed or fibrous joints (e.g. the sutures of the skull), the slightly movable or cartilaginous joints (e.g. symphysis pubis and intervertebral joints) and the movable or synovial joints (e.g. the elbow, knee and ankle).
Fibrous joints involve two edges of bone that are linked by tough strands of fibrous connective tissue. The suture lines of the skull are an example of fibrous joints (see Figure 4.2a-V). The movement at a fibrous joint is limited.
Figure 4.2a-V An example of a fibrous joint: a suture line of the skull
Cartilaginous joints offer the potential for more movement because the bones in these joints are linked by a pad of fibrocartilage, which has more spring and bulk than the fibrous strands of a fibrous joint. In the pubis symphysis and in between the vertebral bodies this fibrocartilage pad has a shock-absorbing function (see Figure 4.2a-VI).
Synovial joints offer the most movement and have the most complex structure (see Figure 4.2a-VII).
Figure 4.2a-VII An example of a synovial joint: section of the knee joint viewed from the side
The internal surface of the bones in synovial joints is lined with glassy smooth hyaline articular cartilage, and the rest of the joint space is bound by a fibrous joint capsule (the capsular ligament). The internal surface of the joint is lined with a fluid-secreting synovial membrane. The term synovial has its root in the Greek word ovum meaning egg. This is because the lubricating fluid contained within these joints has been likened in consistency to the white of an egg. The whole joint is given stability by means of fibrous bands (the ligaments) that link the bones and also by the muscle insertions (the tendons) that cross the joint to insert close to its margins.
Some of the synovial joints have unique additional features; for example, the knee joint illustrated in Figure 4.2a-VII contains thickened C-shaped cartilage pads, which sit on the tibial plateau, and two cruciate (crossing) ligaments, which run through the joint space to provide anterior to posterior stability.
Close to the large joints such as the knee, hip and shoulder are fluid-filled sacs lined with synovial membrane called bursae (singular bursa). The purpose of a bursa is to prevent friction between the layers of tissue overlying the joint.
There is a wide range of structures of synovial joints, although all have the same basic features listed above. Diverse examples include the ball-and-socket joint of the hip, the hinge mechanism of the elbow, the pivot provided by the atlantoaxial joint (between the C1 and C2 vertebrae) and the complementary saddle shapes of many of the small bones of the hands and feet.
Information box 4.2a-II
The joints: comments from a Chinese medicine perspective
The physiological joints are made up of bone, ligaments and synovial fluid, further supported by muscles. In this way their health is dependent on Kidney Essence, Liver Qi and Blood, and Gallbladder Qi, all of which are said to have direct correspondences with these aspects.
The fluid that lubricates the joints in Chinese medicine is called Ye, and is under the control of the Spleen and the Kidneys.
The physiology of the skeletal muscles
The muscles responsible for the movement of the bony joints are all largely composed of skeletal muscle fibers (cells). The muscle fibers run parallel to one another within each muscle, and are bound together by fibrous connective tissue. The muscle fibers converge at two or more fibrous structures, called tendons, at the extremities of the muscle. Tendons usually insert into part of the bony skeleton, but in some muscles they attach to the connective tissue of the skin (e.g. in the muscles of facial expression). The fibrous tissue of muscles (including the tendons) is glistening white and contains blood vessels and fat cells. This is the tissue that gives a raw steak its streaky appearance.
The muscle fibers contract in unison in response to motor nerve impulses (see Section 4.1a). Each muscle fiber receives electrical impulses from a nerve fiber via a specialized synapse called the motor end plate. At this synapse, the electrical impulse traveling down the nerve fiber leads to the release of a neurotransmitter chemical. This chemical stimulates the changes within the muscle fiber that culminate in a temporary contraction. The contraction is sustained only for as long as the nerve continues to stimulate the motor end plate.
Muscles act because they are attached to at least two separate parts of the body, and because they can contract. When a muscle contracts, it draws the two or more parts of the body to which it is attached closer together, and this leads to movement.
Most skeletal muscles never attain a state of full relaxation. There is always a low level of nervous stimulation to the muscles, which gives them a firmness known as tone. This background level of tone is essential for correct posture. It is generated as a result of reflex nervous activity at the level of the spinal cord, and is modified further by nervous impulses originating from higher control centers in the brain (see Section 4.1a). If the nerve supply to a muscle is cut off, the muscle becomes completely flaccid, and loses the springy quality that is the normal state in good health.
Muscles act in a variety of ways, of which the biceps brachii, the buccinator and the pelvic floor muscles are good examples. These three muscles have the diverse effects of limb movement, facial expression and support of soft tissues respectively. The biceps (brachii) muscle of the upper arm is an example of a muscle that acts over a synovial joint (the elbow). The biceps has two tendon insertions on the scapula at its proximal end and a single distal insertion into the radius. The flat buccinator muscle of the cheek is an example of a muscle that inserts only into the connective tissue of skin to allow for the movements of the mouth. The muscles of the pelvic floor insert into bone (they are slung between the ischium of the pelvis and the sacrum and coccyx), but do not cause movement at a joint. Instead, by contracting they give support to the tissues of the pelvic floor and are important for maintaining continence of feces and urine.
Information box 4.2a-III
The muscles: comments from a Chinese medicine perspective
The muscles are made up of flesh, tendons and sinews. Their health is dependent on healthy Spleen, Liver and Gallbladder Qi.
Spleen Qi is more responsible for the springy fleshy quality resulting from healthy muscle tone, whereas Liver and Gallbladder Qi are responsible for the power of contraction and the movement that results.
The knots and excessive tone often felt in over-tense muscles are usually a reflection of Liver Qi (and Blood) Stagnation. This, in turn, is more likely to occur in muscles that are weak as a result of Spleen Qi Deficiency.21
Information box 4.2a-IV
The musculoskeletal system: comments from a Chinese medicine perspective
A healthy musculoskeletal system is dependent on the health of the Kidney, Liver, Gallbladder and Spleen Organs. Kidney Essence is of particular importance to the bones. Healthy Blood and Yin are important for lubricating and nourishing the muscles and joints, as well as for preventing Stagnation of Qi. Hence, muscle and joint pains, stiffness or inflamed tendons can result if Blood and Yin, in particular, of the Liver, are deficient.
4.2b The investigation of the musculoskeletal system
Diseases of the bones, joints and muscles are investigated within two distinct conventional specialties. Diseases that are likely to require medical treatment with drugs are referred to a physician known as a rheumatologist, while those conditions that are likely to require surgery are referred to an orthopedic surgeon.
An investigation of the musculoskeletal system might involve:
•a thorough physical examination
•investigations to examine the structure of the bones, muscles and joints (X-ray imaging, ultrasound imaging, magnetic resonance imaging (MRI) and bone scans)
•examination of the blood to look for disturbances in the hormones and chemicals that reflect bone disorders and autoimmune diseases
•examination of the synovial fluid of a joint
•arthroscopy, the endoscopic examination of the interior of a joint.
These investigations are considered briefly in turn below.
The physical examination is a very important aspect of the examination of the musculoskeletal system. A skilled examiner can identify the site and nature of a wide range of musculoskeletal problems without the need for further investigations. For each joint and muscle group there is a range of specific physical tests that can be performed to examine for particular disorders. For example, the FABER (flexion, abduction and external rotation) test is used to examine for a painful disorder of the hip joint.
The physical examination of the musculoskeletal system involves the stages listed in Table 4.2b-I.
Table 4.2b-I The stages in physical examination of the musculoskeletal system
Examination of the gait, posture and general appearance: this can reveal the characteristic features of musculoskeletal disease, such as a characteristic limp, areas of one-sided muscle wasting or postural deformity due to arthritis
Examination of the muscle groups: looking specifically for areas of wasting or fine twitching, feeling for knots or swellings, and assessing the strength of the muscle groups
Examination of the bones: looking specifically for areas of deformity or shortening, feeling for deformity, swellings or areas of tenderness, and percussion of the bones to examine for deep tenderness
Examination of the joints: looking specifically for redness, swelling and deformity, feeling for heat and tenderness, and passively moving a joint to assess range of movement and the strength of the muscles that cause movement of the joint (active movement). In the case of a localized joint problem, the joint is examined using a range of specific tests
X-ray imaging is the most common investigation performed for musculoskeletal disease. This is because it is relatively cheap, quick to perform, and often produces an excellent picture of the bony structure of the body. The disadvantage of X-ray imaging is that it exposes the patient to radiation, although this is considered to be of minimal risk if X-ray imaging is only required on rare occasions during the lifetime of a patient.
However, X-ray images cannot reveal much information about muscle problems, and will only reveal changes of arthritis at a late stage in the condition, when the bony surfaces of the joint have become eroded. For this reason, the general medical view is that X-ray images are not helpful in the diagnosis of most cases of low back pain, which are usually the result of muscle strain, prolapsed disc or early arthritis, none of which are revealed on an X-ray image.
This can be a useful and non-invasive test for the examination of a joint and the soft tissues that surround it. It is of particular value in the examination of the shoulder.
Magnetic resonance imaging (MRI)
MRI provides very high-quality information about joints and muscles, and reveals the structure of the low back in detail. However, it is expensive and can be uncomfortable for the patient to experience.
Bone scans involve the injection of a radioactive substance into the bloodstream. This substance is concentrated in areas of bone in which there is active growth, which are then revealed by scanning the body for radioactivity. This is useful for revealing areas where there may be a fracture or the site of bone cancer.
A DEXA (dual energy X-ray absorptiometry) scan is a specialized form of X-ray imaging used to investigate the condition of osteoporosis. This form of bone scan does not necessitate injection of a radioactive substance. Instead, it uses a low dose of X-rays to assess the degree of osteoporosis. The DEXA scan is most usually performed in menopausal women and other people at risk of osteoporosis to assess need for medical treatment for this condition.
There are numerous blood tests that can give some information about diseases of the musculoskeletal system. For example, a serum sample can give information about the levels of the mineral salts of calcium and phosphorus in the blood, as well as whether or not levels of hormones such as parathyroid hormone and calcitonin are within the normal range.
The erythrocyte sedimentation rate (ESR) and C reactive protein (CRP) tests can indicate whether an inflammatory process is going on. There is a range of autoantibodies that can be assayed from a serum sample if an autoimmune disease is suspected. In the case of a chronic autoimmune disease, such as rheumatoid arthritis, a full blood count (FBC) may reveal anemia of chronic disease.
Examination of the synovial fluid of a joint
Synovial fluid may be withdrawn from a joint by means of a needle and syringe for examination in the case of arthritis. If the joint is very swollen with fluid, this simple procedure may also give the patient relief from discomfort. In some cases, after withdrawal of the fluid, a corticosteroid drug may be injected directly into the joint through the same needle.
The fluid may reveal the microorganisms and pus characteristic of infection, and so can be a guide for appropriate antibiotic treatment. In the case of arthritis due to simple inflammation (e.g. autoimmune disease or osteoarthritis) the fluid will be clear. In gout the fluid will contain the microscopic crystals that are the cause of the pain.
There is a small risk of introducing infection into the joint with this procedure.
Arthroscopy is a procedure that enables the examination of the interior of a joint, usually the knee. It involves the insertion of a fine endoscope into the joint space via a small incision in the skin overlying the joint. A general anesthetic is usually given. In this way, the integrity of the joint cartilage and any other structures, such as ligaments within the joint, can be examined. In some cases, surgery to the damaged structures within the joint (e.g. a tear in the cartilage within the knee) may be carried out at the same time.
Even if no surgery is carried out, many people report that chronic knee pain is relieved (usually temporarily) following arthroscopy.
4.2c The treatment of musculoskeletal pain
This section explores the way in which conventional medicine manages the problem of pain resulting from musculoskeletal disease. The approach to musculoskeletal pain can be broadly categorized into disease modification and symptom relief.
Disease modification involves the use of medication that actually alters the progression of the underlying disease. Because the disease has been slowed or halted, symptoms abate. The disease-modifying treatments are described in the next three sections on diseases of the musculoskeletal system because they vary according to the disease being treated.
Symptom relief involves the use of medication or other therapies to block the sensation of pain. It does not attempt to alter the underlying disease process. Almost by definition, symptom relief is suppressive in nature. The most common form of symptom relief in musculoskeletal pain is the use of painkillers. The medical term for a painkiller medication is an analgesic.
Analgesics in musculoskeletal disease
Musculoskeletal disease is the most common reason for the prescription of analgesics. Analgesics are also used for a wide range of other conditions, including headache, menstrual pain and the pain of cancer. The analgesics used can be broadly categorized into simple analgesics, non-steroidal anti-inflammatory drugs (NSAIDs) and opioid (morphine-like) analgesics. These might be prescribed on their own or in combination with each other. There are, in fact, many analgesic preparations that contain a combination of two drugs that are believed to complement each other in their mode of action (e.g. co-codamol and co-dydramol, which combine paracetamol with codeine and dihydrocodeine, respectively). Other compound analgesics incorporate non-analgesic drugs such as caffeine or decongestant medication.22
A vast range of analgesics is available for direct sale to the public. Many of these are compound preparations.
The simple analgesics are aspirin and paracetamol. Aspirin is anti-inflammatory in action, which means that it inhibits the chemical communication between the leukocytes that maintain the process of inflammation. Therefore, aspirin acts to reduce the heat (fever), redness, pain and swelling that are characteristic of inflammation. Paracetamol has a poorly understood mechanism of action. It is believed not to be anti-inflammatory. However, its effect is similar to that of aspirin in that it can reduce pain and fever.
Aspirin also reduces the tendency of platelets to stick together. This is why it is of value in the prevention of thrombosis and embolism. For this effect, a very low dose (75mg) is required daily. The analgesic dose is much higher (up to 600mg four times a day).
Aspirin tends to irritate the lining of the digestive tract, although in most cases this effect is mild and painless. However, in some people this can result in severe inflammation, with bleeding into the stomach (gastritis). Other side effects include asthma and rashes. In children under the age of 12 there is a very small risk of a severe form of inflammation of the liver called Reyes syndrome.
Paracetamol has few side effects in low doses, but in overdose it is highly toxic to the liver.
Simple analgesics are recommended for mild pain. Aspirin should not be given to children, and ideally should not be taken at analgesic doses for a long-standing (chronic) condition because of the risk of stomach irritation.
Simple analgesics: comments from a Chinese medicine perspective
In Chinese medicine, the reduction in pain from the simple analgesics corresponds to Movement of Stagnation and Clearance of Heat. In pain relief the action is suppressive in nature, as it clears the symptom locally without necessarily addressing the underlying cause.
Aspirin is believed to be generally Warming and Dispersing in nature. In some cases it may enable the Clearing of Wind Cold by causing sweating and the Release of the Exterior. The Warm nature is evidenced by the side effect of Heat in the Stomach. Asthma and rashes suggest that, in some people, aspirin may also depress Lung Qi and permit Wind Heat Invasion.
In high doses, the liver toxicity described in conventional medicine strongly suggests that paracetamol stagnates and damages the Liver Qi from a Chinese medicine viewpoint.
Non-steroidal anti-inflammatory drugs (NSAIDs)
NSAIDs are a family of drugs that have an anti-inflammatory effect similar to that of aspirin. Like aspirin they can reduce pain, fever, redness and swelling, and they also have side effects that include gastric irritation, asthma and rashes. Rarely they can promote cardiovascular thrombotic adverse events.
Commonly prescribed NSAIDs include ibuprofen and diclofenac. Diclofenac is considered to carry more risk of thrombotic events than ibuprofen.
NSAIDs generally have a more powerful effect than aspirin, and are particularly useful in any pain that has inflammation as its root cause. Therefore they are useful in the inflammatory conditions of the musculoskeletal system such as arthritis, tendon and ligament injuries, and most bony pain, including fractures. NSAIDs at maximum dose can be safely used in combination with paracetamol or with opioid analgesics to increase the effect of pain relief.
The side effect of gastric irritation is less marked than for aspirin. Nevertheless, it is recommended that NSAIDs are taken with food. However, NSAIDs can also be toxic to the kidneys in susceptible people, particularly if taken at a high dose for a prolonged period. For this reason they should be used with caution in elderly people or in combination with other medication that may affect the kidney function.
The cyclooxygenase-2 (COX-2) NSAIDs (etoricoxib and celecoxib), which are selective inhibitors, were developed to minimize the risk of upper gastrointestinal bleeding, and short-term data suggest that they do indeed carry a low risk of bleeding events in clinical practice. However, there does seem to be an association between these COX-2 inhibitors and adverse thrombotic cardiac events, and so their use is reserved only for those situations when older-generation NSAIDs cannot be used and risk of cardiovascular disease is low.
For reasons that are unclear, the response in terms of pain relief of an individual to different NSAIDs is unpredictable. For this reason a number of these drugs may be tried in succession before the best effect is found.
Information box 4.2c-II
Non-steroidal anti-inflammatory drugs: comments from a Chinese medicine perspective
In Chinese medicine, the energetic action of NSAIDs is similar to that of aspirin in terms of having a property of Moving Stagnation and Clearing Heat. The side effects suggest that these medications introduce Toxic Heat (rash and gastritis) and can also lead to Stagnation of Blood and Qi (thrombotic events in susceptible people). In the long term, the warming nature of these drugs may deplete Blood and Yin, primarily of the Liver and Kidney (evidenced by long-term damage to both liver and kidney function). They also can adversely affect Lung Qi in some individuals as asthma can be induced by NSAIDs.
Opioid painkillers are so called because their action is similar to that of the naturally occurring drug opium. They all appear to mimic the effect of the body’s natural painkillers, the endorphins, and act within the spinal cord and the brain to reduce the sensation of pain.
Opioid analgesics provide strong pain relief, although they do not reduce inflammation directly. They are generally only used in musculoskeletal conditions when pain is very severe (e.g. after acute trauma such as a fracture). They may safely be used in combination with aspirin, paracetamol or NSAIDs. Opioid analgesics include codeine, morphine, buprenorphine, diamorphine (heroin), dihydrocodeine, pethidine and tramadol.
Opioids are highly addictive, and also induce bodily tolerance to the effects of the drug. With recurrent use increasing doses may be required to maintain a steady level of pain relief. They may induce a sense of euphoria or well-being.
The most common adverse side effect is nausea and vomiting. Therefore, anti-sickness medication may have to be prescribed at the same time. Constipation is also a common side effect. With very high doses the depth of breathing may be inhibited, and the patient may fall into a stupor. In overdose, death may result from respiratory failure.
Information box 4.2c-III
Opioids: comments from a Chinese medicine perspective
In Chinese medicine, the pain-relieving effect of opioids would correspond to the Movement of Stagnation. This effect is suppressive in nature, and the side effects indicate profound energetic disturbance. The side effects of euphoria and stupor may reflect the obstructing effect of Heat (at the Blood Level) on the Heart Organ. Constipation may also be a result of Heat, in this case in the Small and Large Intestine. Itch and rashes also are suggestive of Wind and Heat. Suppression of respiration may reflect a Depression of Lung and Kidney Qi. Nausea and vomiting might be seen as a manifestation of Stagnation of Liver Qi and consequent rebellion of Stomach Qi.
In the long term opiates are addictive and promote dependency. The profound effects of Heat on the Heart will lead to Heart Yin Deficiency and also Stagnation of Liver Qi. The person will therefore feel they need more of the drug in a need to deal with the discomfort of these states of imbalance. In the long term the patient on opiates will show signs of Heart/Kidney Yin Deficiency, with Liver and Spleen Disharmony.23