Revision Point

Draw a ‘typical’ long bone and write short notes about the following parts: diaphysis; epiphysis; epiphyseal plate; periosteum; medullary canal; hyaline cartilage.

The skeleton has many different functions, including the support of soft tissue and protection of inner structures. It stores and releases several minerals, including calcium, sodium and phosphorus, and produces blood cells in red bone marrow. The skeleton also acts as a store for fats. It provides attachment to tendons and muscles and finally, bones act as levers when muscles contract and these levers then produce movement.

Types of bone

There are two types of bone – cancellous (spongy) and compact (dense). Cancellous bone makes up most of the tissue in short, flat and irregular bones and provide some support and a storage area for bone marrow. Compact bone offers protection and supports the body. Compact bone also helps the long bones, such as the femur, resist the stress of weight bearing.

Cancellous bone contains many spaces filled with red bone marrow (the cells of which are responsible for the production of blood cells). Compact bone is much denser and is made up from structures known as Haversian systems or osteons.

Blood vessels, lymphatic vessels and nerves from the periosteum penetrate compact bone through perforating canals. These vessels and nerves then connect with central (Haversian) canals running longitudinally through the bone. Surrounding these central canals are rings of hard calcified matrix called lamellae. Between the lamellae are spaces containing mature bone cells known as osteocytes. These spaces are called lacunae. Radiating from all directions from the lacunae are small channels known as canaliculi.

These small channels (canaliculi) are filled with extracellular fluid and contain finger-like processes of the osteocytes. The canaliculi connect lacunae with each other and with the central canals. This intricate branching network provides many routes for blood-borne nutrients and oxygen to diffuse through the fluid to the osteocytes and for wastes to diffuse back into the blood. Areas between the Haversian systems (osteons) contain what is known as interstitial lamellae, which also have lacunae and canaliculi. These sections are incomplete remains of older osteons.

Cancellous bones consist of lamellae that are arranged in an irregular lattice of thin columns of bone called trabeculae.

The macroscopic spaces between trabeculae of some bones are filled with red bone marrow which produces blood cells. Within the trabeculae are osteocytes in lacunae and radiating from the lacunae are canaliculi.

Bone formation

Bones form in one of two ways. A small number of bones develop on or within fibrous connective tissue membrane through a process known as intra-membranous ossification. Ossification refers to the process by which bone is formed. Bones which develop in this way include the flat bones of the skull, the mandible and the clavicle. However, most bones of the body develop through a process known as endochondral ossification, where the bones develop within hyaline cartilage (Tortora, 2005).

Bone formation involves the activity of cells known as osteoblasts. These cells are found typically in the medullary canal of long bones and under the periosteum. Cells known as osteoclasts are involved in the removal and breakdown of bone.

The human skeleton consists of 206 bones which are grouped into two divisions – the axial skeleton and the appendicular skeleton.

Axial skeleton

These are bones around the axis of the body, of which there are 80 in total.

The bones of the skull are divided into two groups – the bones of the face (14) and the bones of the cranium (8). A suture is an immovable joint found between the bones of the cranium. There are four prominent cranial sutures, namely the coronal, sagittal, lambdoid and squamous (Tortora and Grabowski, 2004).

The vertebral column (spine) has several functions, including enclosing and protecting the spinal cord, supporting the head, giving attachment for ribs and back muscles, protecting the brain from vertical shock, and the presence of intervertebral discs act as shock absorbers. The vertebral column also allows for some movement of the head and trunk.

Intervertebral discs are found between the vertebrae from the second cervical to the sacrum. These discs have an outer ring of fibro-cartilage and a soft and pulpy inner core (Tortora and Grabowski, 2004). Intervertebral discs contribute to the flexibility of the vertebral column and as stated above also act as shock absorbers.

The thoracic cage protects the vital organs found within the thorax (chest), and is made up from the thoracic vertebrae, the ribs and the sternum (breastbone). There are 12 pairs of ribs, and the sternum is divided into 3 parts – the manubrium, the body and the xiphoid process.

Appendicular skeleton

This refers to the appendages and girdles and amounts in total to 126 bones.

The shoulder girdle consists of two bones – the scapula (shoulder blade) and the clavicle (collar bone). The bones of the upper extremities consist of the humerus, the radius and ulna, the carpals and the metacarpals and phalanges.

The pelvic girdle consists of three bones – the ileum, the ischium and the pubis. The bones of the lower extremities consist of the femur, the tibia and fibula, the tarsals and the metatarsals and phalanges.

Joints

A joint or articulation is the point of contact between bones, or between cartilage and bones. They are classified by two methods. One is to classify according to the degree of movement allowed by the joint, where some permit no movement between the articulating bones, some permit slight movement and others permit a great deal of movement. The other way to classify them is dependent upon their structure, that is, whether they have a joint space between the articulating bones and what kind of support tissue binds the bones together (Tortora, 2005). Based on the structure, there are three types of joints in the body – fibrous, cartilaginous and synovial.

A fibrous joint lacks a joint cavity and the bones are united by fibrous connective tissue. Generally, they are immovable joints in the adult, although some allow slight movement. Examples include the sutures between bones of the skull, and the joints between the teeth and upper and lower jaw (maxilla and mandible).

A cartilaginous joint lacks a joint cavity and the bones are unified by a plate of hyaline cartilage. They permit little or no movement. Examples include the symphysis pubis and the joints between the bodies of the vertebral bones.

A synovial joint has a joint cavity present. The bone ends are covered with smooth hyaline cartilage. The joint is lubricated by a thick fluid called synovial fluid and is enclosed by a flexible articular capsule, which may be supported by ligaments. These joints allow a great deal of movement. Examples include the hip, knee, shoulder and elbow.

Skeletal muscle

Skeletal muscle is responsible for movement, maintaining body posture and heat production within the body.

Control of skeletal muscles

Skeletal muscle are under voluntary control. Their fibres normally contract only when sufficient stimulus is applied by a nerve ending. Nerves that innervate skeletal muscle divide into several branches before they terminate. Each branch is then distributed to an individual muscle fibre. In this way, a nerve impulse passing along a neurone will result in the simultaneous contraction of all the muscle fibres which are innervated by that particular nerve cell. A group of muscle fibres that receive their innervation from a single neurone is called a motor unit. An individual muscle may contain hundreds or thousands of individual motor units.

A lever system

Bones work as a system of levers, and muscles provide the power to make them move. A skeletal muscle is attached to one bone at one end of a joint, travels across the joint and is then connected to another bone at the other end of the joint. When the muscle contracts, one bone is pulled towards the other.

Posture

The upright posture is maintained by the simultaneous contraction of appropriate sets of muscles. However, not every muscle is required to continually contract in order to maintain posture. In this way, energy is saved, as we are not using the whole muscle (sets of muscle). Energy expenditure in maintaining posture is reduced by other means too:

• As already stated, we use only a part of each muscle – the postural tension of a muscle is maintained by only a small number of its fibres, and these fibres are constantly changing, resulting in the minimising of fatigue.
  
• We use ligaments – ligaments either within or outwith a joint help to hold the joint in place and give general support to the joint.
  
• Balance – when standing in a balanced position, the joints are in their most stable position and minimal muscular energy is required to maintain the posture. Standing off balance puts the body in an unstable position and more muscular energy is required in order to remain upright.

Ageing changes related to mobilising

Bones

The bones, joints and muscles are all affected by changes caused by the ageing process. These changes have a significant effect on the quality of older people’s lives as they can have a considerable effect on functional ability and can impact negatively on the level of independence in older people (Roach, 2001).

The relationship between bone formation and bone absorption is dynamic over the lifespan of an individual. Bone formation (osteoblast activity) exceeds the bone absorption (osteoclast activity) rate during the period from birth to adolescence, but then bone formation and absorption equalise during the twenties. However, with advancing age, the rate of bone absorption changes. Around the age of 30, bone absorption starts to surpass bone formation. From this age, there is a steady and progressive decrease in cancellous bone loss beginning in the thirties and continuing into old age (Matteson et al., 1997).

Cancellous bone loss starts before compact bone loss and the ratio of compact bone to cancellous bone increases with age. By the age of 80, men will lose ~27% of cancellous bone, whereas women will lose ~43% of cancellous bone by the age of 90. With the onset of the menopause, there is a sharp increase in cancellous bone loss due to the loss of protection from the hormone oestrogen. Compact bone loss occurs from the age of 45 in women and the age of 50 in men. Not only does compact bone loss occur at an earlier age in women, it also occurs at a faster rate than in men (Matteson et al., 1997). A vast amount of cancellous bone is found in the vertebral bodies, wrist and hip. Consequently, older people are at increased risk of sustaining fractures in all of those areas (Roach, 2001).

Other changes related to the bones occur through the ageing process, including a decrease in height with age and a change in posture as an older adult may become more stooped. Height decrease is more commonly found in women than in men although it occurs in both sexes (Matteson et al., 1997). As much as 1–6 inches (2.5–15 cm) can be lost in height. Shortening of the spinal column results in what is commonly called a dowager’s hump, that is, kyphosis of the upper thoracic spine. These changes are related to loss of fluid in the fibro-cartilage within the intervertebral discs. As a consequence of this fluid loss, the fibro-cartilage becomes drier, thinner and more delicate. This increases the risk of tearing and contributes to vertebral compression and a decrease in a person’s height. As a result of the shortening of the spinal column, a person’s arms and legs can appear to be longer, although there is no change in their length. Accompanying the changes in the fibro-cartilage, bony outgrowths called osteophytes develop on the vertebral column. These growths are typical of changes associated with osteoarthritis. Osteophytes can also develop on the articulating surfaces of bones making up joints. Within these joints, smooth, articular cartilage may be replaced by a rougher cartilage. The cartilage can also become thicker with advancing age and lose some of its elasticity (Timiras, 2003).

The lordotic curve which can be found in the lower back flattens, and both flexion and extension of the lower back are decreased (Lueckenotte, 2000). A combination of all of the bone changes, including increased flexion of the hips and knees, decreased lumbar lordosis, increased thoracic kyphosis and rounded shoulders with protracted scapula impact on and lead to the familiar stooped posture. The stooped posture can lead to the head jutting forward and tilting upward to maintain gaze level. The individual’s centre of gravity is affected and a slower, shorter, more cautious and wider based gait pattern is developed in old age (MacAnaw, 2001). There are slight differences in the gait changes for men and women. In men, the gait becomes small stepped with a wider based stance. Women become bow legged with a narrower standing base, and walk with a waddling gait (Lueckenotte, 2000).

Increased bone re-absorption has an impact on the amount of calcium in the body. The bone loses calcium and the ability to produce material for the bone matrix is diminished. This results in weakening of the intracellular bone, causing bone to become weaker, thus increasing the risk of fracture for older people (Roach, 2001). The recommended daily intake of calcium for younger adults is between 800 and 1300 mg, and 1200 mg daily for adults over 51 years of age (Maher et al., 2002). Also associated with advancing age is a decreased proficiency in the ability of the body to absorb calcium from the digestive system (Matteson et al., 1997).

In some older women, parathyroid hormone levels increase with ageing, but the contribution of this increase to bone loss may be minimal. The increase in parathyroid levels may represent a compensatory response to reduced intestinal absorption of calcium and subsequent low plasma calcium levels (Timiras, 2003). Vitamin D manufacture in the skin may also be affected if an older person is housebound and unable to venture outside due to reduced mobility, and this will further impact on any dietary deficiencies of calcium.

Physical activity increases stress and strain on the skeleton due to muscular contraction and gravity. It improves blood flow to exercising muscles and indirectly increases venous return. Physical activity involving weight loading also stimulates build up of bone minerals. Physical activity includes gentle exercise such as walking and dancing. Engaging in such activities will not only provide a cardiovascular workout for the individual, but also encourage mineralisation of bones as identified earlier. An accumulation of 30 minutes of moderate activity on most days of the week is recommended by the Scottish Government (2006).

Joints

The effects of ageing are most commonly felt in the freely movable synovial joints including the knees, wrists, elbows and hips. The synovial membrane which lines the joint cavity secretes a lubricating fluid called synovial fluid. As ageing progresses, the amount of synovial fluid secreted diminishes. The articular cartilage which lines the joint surfaces reduces friction within the joint and also acts as a shock absorber. With advancing age, the cartilage frays, thins and erodes, so that the bones may come into direct contact with each other (MacAnaw, 2001). The ligaments also lose their elasticity so that they shorten and become less flexible. The resultant changes lead to a reduced range of movement in the affected joints (Roach, 2001).

Muscles

The major function of skeletal muscle is to provide the power to allow bones to move. Muscle strength reaches a peak between the ages of 20 and 30 and starts to decline during middle age. This decline continues at a more or less constant rate as we age, irrespective of the muscle group considered. By the age of 80, ~50% of maximum muscle mass is lost (Roach, 2001). However, the rate of decline among muscle groups is variable. The diaphragm remains active throughout life and undergoes little change with ageing. In contrast, the soleus muscle of the leg shows reduced strength with ageing. However, it is possible to increase skeletal muscle power by physical training, even in old age (McMurdo, 2000). Thus, this ageing change is not only reversible, it is also preventable.

The number of muscle fibres reduces with age, resulting in a loss of lean body mass (Roach, 2001). This loss of body mass is known as sarcopenia and results in muscle weakness (Timiras, 2003). Muscles of the lower extremities seem to atrophy more and lose more strength than upper extremity muscles. This may be due to the upper extremity muscles being used more frequently for day-to-day living (MacAnaw, 2001).

Muscle tissue regenerates more slowly with advancing age and tissue that is atrophied is replaced with fibrous tissue. This effect can be seen quite clearly when looking at the muscles of the hands, as they become thin and bony, with deep inter-osseous spaces.

Changes in both the musculoskeletal and the nervous systems result in slower movement (Matteson et al., 1997). This occurs because the density of blood vessel capillaries per motor unit diminishes with age, whereas oxygen utilisation per motor unit remains steady. Muscle contraction slows as the result of prolonged impulse conduction time along the motor unit in muscle tissue (Matteson et al., 1997). Increased muscle rigidity contributes to limited movement in areas such as the neck, shoulder, hips and knees (Roach, 2001). The degree of muscle rigidity can be assessed by measuring the amount of resistance to passive movement.

A decline in muscle mass may parallel the decline in muscle strength, but it does not affect endurance. Endurance can be maintained in older age because type 1 muscle fibres do not atrophy with age. Type 1 muscle fibres are slower contracting fibres. High speed performance is affected by type 2 muscle fibres, which are the fast contracting fibres. Ageing athletes are therefore better able to compete in endurance events, rather than events where there are bursts of speed required.

There are significant amounts of lipofuscin (age-related waste material) and fat deposited within skeletal muscle tissue. Skeletal muscle loses the usual red brown colour due to the loss of myoglobin pigment and they become yellow due to the increased deposition of lipofuscin pigment and fat cells (Matteson et al., 1997).

In order to remain balanced, older people require posture and moving equipoise. Balance is the ability to stand steadily, posture is the alignment of body segments in proper relation to one another and moving equipoise is the control of equilibrium in movements (Linton and Matteson, 1997). Information about the length, tension and speed of muscle activity is provided by muscle spindle and tendon proprioception. This can be described as muscle joint sense and is monitored within the brain. The brain responds to these stimuli by bringing about actions which help to maintain balance, posture and controlled integration of movements. In this way, the body responds appropriately to stimuli in order to maintain correct balance and position.

Control of posture diminishes with age, as a result of a decrease in sensory cues from proprioceptors, declining function of stretch reflexes that initiate from muscle spindles and slower processing of information in the brain. Older people come to depend on visual control to maintain postural stability and visual acuity decreases with advancing age.

Postural sway also increases with age. This change affects women more noticeably than men (Matteson et al., 1997).

Age-related health problems

Osteoporosis

Osteoporosis is a metabolic bone disorder where the balance between bone breakdown and bone build up is lost; that is more bone is broken down (re-absorbed) than is built up. This leads to a reduction in bone mass which typically affects the trabeculae without there being a deficit in bone mineralisation. This contributes to the fragility of bones. The bones become lighter and weaker with thinner cortical bone, less trabeculae and widening of the medullary canal. These weaker, brittle bones are therefore susceptible to fracture.

Oestrogen and testosterone encourage osteoblast activity and synthesis of bone matrix (Tortora, 2005). Oestrogen levels decrease significantly in women at menopause which accelerates the rate of bone loss, whereas levels of testosterone in men only decrease slightly with age. In females, the level of cytokines rises as the levels of oestrogen falls, resulting in increased activity of osteoclasts which break down bone tissue.

Risk factors for the development of osteoporosis include genetic factors, decreasing oestrogen hormone levels at and post menopause, age as bone mineral density decreases with advancing age, gender with women more likely to develop osteoporosis as they have less bone mass compared to men and their bones are smaller than men’s bones (SIGN 71, 2003). Smoking, low BMI, poor intake of calcium and vitamin D and low levels of weight-bearing exercise, all contribute to the development of osteoporosis. Dietary calcium and vitamin D intake must be adequate to maintain bone remodelling and body functions. Vitamin D is necessary for the absorption of calcium and for normal bone mineralisation. Inadequate intake of calcium or vitamin D over a period of years results in decreased bone mass. Weight-bearing exercise slows the rate at which bone mineral density is reduced.

Normal bone remodelling in the adult results in increased bone mass until about the age of 30 (Huether and McCance, 2004). Genetic factors, nutrition, lifestyle choices and physical activity all influence the timing of peak bone mass. Age-related loss begins soon after peak bone mass is achieved.

With osteoporosis, there can be a gradual collapse of spinal vertebrae over a period of time, which may be asymptomatic. This can be observed as progressive kyphosis (increased curvature of the thoracic vertebrae). With the development of kyphosis, there is an associated loss of height.

Assessment and diagnosis

Bone mineral density is the principal measure for the diagnosis and ongoing monitoring of osteoporosis (SIGN 71, 2003). Dual-energy X-ray absorptiometry (DEXA) scans are considered the gold standard for diagnosis of osteoporosis and are used to measure bone mineral density. Sites used to measure bone mineral density include the lumbar spine, the hip and the wrist. SIGN 71 (2003) advise using two separate sites and indicate their preference as the spine and the hip.

Management

Management goals are to prevent osteoporosis, arrest or slow the process down and relieve existing symptoms. Prevention begins early with the identification and education of people at risk. Adequate dietary and/or supplemental calcium, regular weight-bearing exercise and modification of lifestyle all help to maintain bone mass. Weight-bearing exercise should target the spine and hip as these are the two sites commonly affected by osteoporosis (Walker, 2008). Simply going for regular walks can reduce the risk of hip fractures in post-menopausal women (Feskanich et al., 2002).

Calcium and vitamin D intake should be monitored and supplements used where appropriate. Outdoor activities with exposure to sunlight can help as vitamin D is produced by skin in response to exposure to ultraviolet radiation from natural sunlight.

A number of drugs are available that influence bone mineral density, including bisphos-phonates, calcitonin, strontium ranelate, teriparatide and raloxifene. All these drugs help to reduce the risk of fracture in post-menopausal women (Walker, 2008).

Falls in older people

Falls are not an inevitable consequence of ageing; however, the physical and psychological effects of falls can be wide ranging and potentially serious, if not fatal. Thirty per cent of adults over 65 who live in the community and 50% of those over 80 will fall over a 12-month period, while 60% of those who fall once, fall again within the same year (Oliver, 2007). Oliver goes on to state after falling many older adults find it difficult to rise from the ground, resulting in a lengthy period of immobility which can lead to hypothermia, dehydration and pressure area damage.

Older people are also much more likely to die after a fall than younger people because of the risk of fractures and head injuries. Over 90% of fractures results from falls. Approximately 25% of falls, where there is direct impact on the trochanteric area of the hip, result in a fracture. In the hospital setting, ~ 10% of patients who have fallen will die before discharge (Tideiksaar, 1998). According to Holmes (2006), an older person in the United Kingdom dies every 5 hours as a result of a fall at home. The psychological fear of falling can also have a detrimental effect on an older person’s daily activities (Bazian, 2005) and their overall quality of life. A fall can lead to loss of confidence and increasing anxiety for both the older person who falls and their carer (Oliver, 2007).

A fall can be defined as ‘an unexpected, involuntary loss of balance by which a person comes to rest at a lower or ground level’ (Commodore, 1995). Falls are under-reported as people are ashamed of falling or they are unwilling to admit that they have fallen. They may also think that falling is a consequence of growing older. The term fall is now viewed as a contentious word, as it is perceived to be associated with people who are old, frail and dependant (DH, 2001). Falls in older people should be taken seriously as they may indicate underlying health or social problems.

Causes

The causes of falls are many and varied and have traditionally been divided into intrinsic and extrinsic factors. However, this distinction may not always be useful as falls tend to be multifactorial. In other words, there is normally more than one reason for a fall. Falls are often related to the multifactorial relationship between several risk factors, the external environment and the older person’s own activities and awareness or attitudes to risk. A trip or a fall may be a combination of both intrinsic and extrinsic factors, for example, someone trips over their rug but this may not have happened if their eyesight had been better or they were not hurrying (Oliver, 2007). The descriptions older people use to describe an event is important as they may not have used the word fall but use other descriptions including a slip, trip or an accident (Kelly and Dowling, 2004). The meaning that an older person ascribes to a fall will influence whether they report the fall. Table 9.1 lists the most common factors that are implicated in falls.

However, some of the factors require further explanation. Older people are rarely asked about their alcohol intake and they may have a higher weekly intake than is recommended for a number of reasons, including loneliness or bereavement. There is a range of medications that commonly increase the incidence of falls and they include centrally sedating agents such as sedatives, hypnotics, opiates and anticonvulsants. Drugs that can precipitate postural hypotension such as anti-hypertensives, anti-arrhythmics and diuretics may also increase the incidence of falls (Oliver, 2007). In hospital, the use of bed rails increase the risk of falls as patients may try to ‘escape’ the confines of their bed by climbing over, under or through the bed rails.

The ageing changes related to falls not only involve musculoskeletal changes, but also changes in vision and hearing (see Chapter 4). The ability to maintain balance requires the constant interaction of three fundamental processes: (i) recognition via sensory nerves, for example, eyesight, touch and proprioception (a sense of where the body is in space and where the various parts of the body are located in relation to each other), (ii) interpretation of theses impulses in the CNS and (iii) adjustment via motor nerves such as reflexes, conscious movement and muscular contraction. If one or more of these processes are impaired, then the risk of fall increases (Oliver, 2007).

Table 9.1 Common factors implicated in falls. (Reproduced from Oliver (2007). With permission.)

Where vision is concerned, the lens becomes less flexible as we grow older so that the eye does not accommodate so readily. This is described as presbyopia. Presbyopia can affect depth perception so that when a person is going up or down stairs, it may be difficult for them to judge accurately the depth of steps, which can increase their likelihood of stumbling and falling. Advice here is to use a banister (hand rail) and not to rush. Vision can also be affected by eye glare if a cataract is forming/has formed. Being outside on sunny days or indoors when bright lights shine on polished floor surfaces can also increase the risk of falls due to glare (Kelly and Dowling, 2004).

Changes in the ear include atrophy of the ossicles (malleus, incus and stapes) in the middle ear which causes changes in sound conduction resulting in the potential loss of high tone frequencies. This is called presbycusis. Background noise is amplified and there is a decrease in directional hearing. This decrease in directional hearing increases the risk of falls as it can be disorientating to the person, who can be startled by sudden and unexpected noises.

In the cardiovascular system, the loss of tissue elasticity in arteries leads to a decrease in tissue recoil, resulting in changes in blood pressure with alterations in body position. As a result, older adults who lie flat and rise up suddenly are more likely to experience a drop in blood pressure and a feeling of light-headedness due to this loss of tissue elasticity and recoil. There is also an overall reduction in reaction time which makes it more difficult for older people to correct themselves before they fall (Kelly and Dowling, 2004).

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