A knowledge of the normal structure and function of bones and joints will help towards a clearer understanding of the pathological changes which can occur. For such details reference should be made to standard anatomy and physiology textbooks.

afle being strong and resilient, bone is a very active tissue. This will become clearer later in the chapter with the description of some of the principal metabolic diseases. Bones are so structured that they can fulfil three essential mechanical functions:

1. They provide support through their rigidity.

2. They give protection to vital structures as seen in the skull, chest, spinal canal and pelvis.

5. They provide a strong system of levers, linked by joints, which are able to withstand the strong forces of muscle pull required to maintain various postures and produce locomotion.

Bone is a specialised form of connective tissue. There are two types:

(a) Cancellous bone which is formed of a meshwork of trabeculae. Its honeycombed appearance gives the impression of weakness, but it is, in fact, very strong. The trabeculae are laid down in such a way as to enable the bone to withstand the compressive and tensile stresses to which it is exposed. This is clearly shown in the neck and head of the femur (Fig, 5/1).

Co) Compact bone (cortical bone) has a much more solid appearance, although microscopically it consists of systems of fine interlinked canals and spaces.

The shafts of long bones are mainly formed of compact bone which is thicker in the mid-shaft region and is designed to withstand bending stresses. They have a central cavity called the medullary canal. This reduces the weight of the bone without significandy weakening it.

Bones are surrounded by a vascular fibrous periosteum except where the surface is covered by articular cartilage. The inner layer of this membrane contains the osteogenic (bone-forming) cells called osteoblasts. These are the parent cells of the mature bone cells called osteocytes which are unable to divide. The osteoclast is the third type of bone cell. It has a phagocytic action, i.e. it removes bone.

In addition to these cells bone consists of collagen fibres embedded in a ground substance. This is impregnated with calcium salts giving the bone its rigidity.

A bone, although retaining its overall shape, is constantly being laid down and resorbed.

Interference with the structure of bone by a disease process will revent it fulfilling its function to the full. For example, it may be more prone to fracture.

INFECTIONS



These may be divided into acute and chronic infections.

Acute osteomyelitis

This term refers to acute infection in bone. It literally means inflammation of bone and bone marrow. It is the soft tissue components which are involved, i.e. the contents of the medullary cavity, the Haversian systems and the periosteum.

Acute osteomyelitis is caused by a bacterium. This is most frequently Staphylococcus aureus. It occurs most commonly in young children between the ages of two and ten years. In nearly all cases at this age the infecting organism is blood-borne from a distant focus of infection, e.g. a boil, or even a minor skin abrasion. Other portals of entry include the throat, the teeth and the tonsils.

There is often a history of trauma, and it is possible that this might cause minor damage to the bone involved, presenting an area more susceptible to invasion by any circulating bacteria.

It is the more vascular part of the bone which is frequently involved. This is the metaphysis which is that part of a long bone between the shaft and the growth plate. The latter structure acts as a barrier to the spread of infection. However, in young infants, where the growth plate is not fully developed, infection may invade the epiphysis. This in turn may lead to joint infection and growth disturbance

In adults, blood-borne infection is rare. Usually the bacteria are introduced through an overlying wound as, for example, in an open fracture. Such an injury may be associated with road traffic or other accidents. When it does occur, the infection tends to be less acute and is commonly found in the mid-shaft region of the bone.

Osteomyelius commonly involves long bones, particularly the femur and tibia adjacent .to.,the knee. However, no bone is immune;

for example, the mandible may be involved by direct spread from an infected tooth, or the mastoid process from a middle-ear infection. Occasionally there, may be more than one bone involved.

In untreated acute osteomyelitis there are three phases to the pathological process:

1. Suppuration: Pus forms within the cancellous bone. This is a form of abscess. As it is in a confined space and therefore under tension, it is forced along the medullary canal or outward through the Volkmann's canals in the cortical bone to emerge under the periosteum. From there the spr6ad is subperiosteal, lifting this membrane away from the bone. Pus may re-enter the bone at another level or burst through the periosteum into the soft tissues.

2. Necrosis: When its blood supply is cut off, bone dies. Here it may be due to infective thrombosis, rising pressure within the bone cavity, or by stripping of the periosteum. Pieces of dead bone become separated by the action of osteoclasts and form sequestra. These act as foreign body irritants and lead to a discharge through sinuses until they escape or are removed.

3. New bone formation: This occurs in the deep layer of the. periosteum. If it is extensive it forms a new case of bone called an involucrum which may contain holes called cloacae, through which pus emerges.

The patient, who is usually a child, presents with severe localised pain, fever and malaise. He looks ill and toxic. The affected limb is held still. It may look normal at first but later swelling and redness appear. Localised tenderness is felt over the affected part of the bone. There is redness and increased warmth of the overlying skin. The tenderness may be exquisite and the child may not permit the part to be touched.

Although the child may be reluctant to move the affected limb, the neighbouring joint can usually be moved painlessly through a small range, whereas in acute septic arthritis any movement is prevented by intense pain.

TREATMENT

Before antibiotics were discovered, osteomyelitis tended to run the course outlined above. Nowadays prompt intensive use of antibiotics may be sufficient to bring the situation under control. The affected part should be rested in a splint and the patient put to bed. The antibiotics are continued for a minimum of three weeks. Drainage may not be required if antibiotics are given early.

However, if a subperiosteal abscess can be detected, or if the fever and local tenderness persist to the same degree after 24 hours of adequate antibiotic treatment, the pus should be drained by incision. Frequently the medullary cavity is also drained by drilling, although opinions vary about the need for doing this.

As the infection comes under control, the physiotherapist is required to supervise mobilisation of adjacent joints, and instruct the patient in crutch walking, initially non-weight-bearing, then progressing through partial to full weight-bearing.

COMPLICATIONS

1. Septicaemia: This may occasionally be fatal.

2. Metastatic infection: This is the spread of infection to other parts, including bones or joints.

3. Septic arthritis: This may occur: (a) in very young children where the growth plate has not formed a barrier to spread of infection from the metaphysis to the epiphysis; (b) where the metaphysis is intracapsular as in the femoral neck; or (c) by metastatic spread.

4. Altered bone growth: This may arise if the epiphysis is involved and damaged in an infant. It usually leads to shortening and may 15e severe In older children there may be stimulation of the growth plate by the metaphyseal hyperaemia, leading to lengthening of the bone.

5. Chronic osteomyelitis.

Chronic osteomyelitis

Although much less common now because of effective antibiotic treatment, it may Occur as a sequel to acute osteomyelitis.

An area of bone iwhich has been destroyed by acute infection will contain cavities sugrounded by dense bone. Pieces of dead bone are usually present and are surrounded by fibrous tissue and sclerosed bone. Although thus surrounded, they may act as foreign body irritants which will provoke the living tissue to pduce seropus which escapes through sinuses. This tends to perstst because the pieces of dead bone cannot escape.

Bacteria may also be imprisoned in the fibrous tissue. They often lie dormant for many years but may at any tine give rise:to an acute flare-up of the infection.

TREATMENT

This is usually conservative as the discharge may be no more than a nuisance. Antibiotics are probably not very effective as'they do not penetrate the fibrous tissue barrier and sclerotic bone. However, "some of the more recent antibiotics show some ability to do this.

Flares of the infection may occur at any time, giving a picture of acute osteomyelitis. They usually settle in a few days with rest. Occasionally an abscess may form which requires drainage if it remains painful and does not discharge itself.

Sometimes, if there are repeated flares or if there is a constant unpleasant discharge, the condition may become an intolerable nuisance necessitating amputation of the part.

Infection may occur as a complication of the implantation of artificial joints. This constitutes a form of chronic osteomyelitis which is being seen with increasing frequency as more and more joints are replaced.

Another form of chronic osteomyelitis is seen as a Brodie's abscess. This commonly occurs in the tibia. It may remain silent for years or present as recurrent episodes of pain. It constitutes a cavity surrounded by a sclerotic zone of bone. It usually contains clear fluid but sometimes contains pus from which the causative bacteria may be isolated. It is treated by drainage and curettage. Sometimes the cavity is then packed with cancellous bone graft to promote more rapid healing.

Tuberculous osteomyefitis

Tkis. is a form of chronic osteomyelitis. It is caused by the tubercle bacillus. It spreads via the bloodstream from a primary area of infection which may be in the lung, pharynx or gut. It causes excessive bone destruction over bone formation. It begins in cancellous bone, most commonly in a vertebral body, the small bones of the hands and feet and the ends of long bones. In the latter site it involves both the metaphysis and epiphysis.

It generally presents as a locally destructive lesion with normal tissue being replaced by caseous material. This process leads to increasing destruction of adjacent bone. Caseous material and tuberculous pus may be squeezed out of the bone forming a cold abscess. If this becomes subcutaneous a sinus may be formed.

The patient presents with a general illness of gradual onset and a long history. He may feel unwell and may complain of lassitude, poor appetite, weight loss and night sweats. There may be an evening pyrexia.

Tuberculous dactylitis

This affects the metacarpals or phalanges. A fusiform swelling develops and the shaft appears expanded as new bone is laid down on the surface.


Tuberculosis of the spine

This is sometimes referred to as Pott's disease of the spine. The vertebrae are the bones most commonly affected by tuberculosis.The celtre of the vertebral body becomes caseous and the process spreads to destroy the intervertebral disc. This leads to vertebral collapse with an angular kyphus at that level. The angulation together with pressure of caseous material may lead to spinal cord compression and paraplegia.

A paraspinal abscess often develops. Thi may be a psoas abscess which tends to point just bdow the inguinal ligament. In the neck it may present as a retropharyngeal abscess.

TREATMENT

Treatment of tuberculosis is primarily by drugs. However, with drug cover, surgery may be more safely carried out. This may involve the evacuation of abscesses, and excision of diseased areas and dead bone. This may be particularly necessary to decompress the spinal cord.

Bone grafts are put into the defect left following removal of affected bone. Prolonged recumbency may be necessary. This will produce decreased muscular activity. General physiotherapeutic measures will be necessary to prevent wasting of muscles, chest and circulatory problems.

Acute septic arthritis

This is an acute infection of a joint. As in acute osteomyelitis, the causal organism is usually Staphylococcus aureus, but other organisms may be responsible.

The joint may be infected by the following routes:

1. Through a penetrating wound

2. By eruption of a bone abscess into it

3. By blood-borne spread from a distant site.

Untreated, the infection spreads throughout the joint. The articular cartilage may be destroyed, particularly in staphylococcal infection. The ligaments are softened and may give way so that the joint becomes completely disorganised and. even dislocated. Occasionally the capsule may rupture allowing spread of pus to the periarticular tissues, forming an abscess or a sinus. Where there has been destruction of tissues, fibrous or bony ankylosis may occur.

The patient becomes rapidly ill, with severe pain and swelling in the affected joint. He will have a high, swinging temperature. All movements of the joint are very painful. The pain is so intense that they are often totally abolished.

To prevent permanent joint damagtreatment is urgent. The joint should be aspirated or opened and washed out thoroughly, followed by instillation of antibiotics. Intravenous or intramuscular antibiotics are given initially. They are continued orally as the infection begins to settle.

" The joint is rested in a splint. The hip is always treated on traction to prevent disruption and dislocation.

As the patient's condition improves and the joint pain subsides, further damage to the joint is unlikely. At this stage the physiotherapist will commence careful active movements of the joint. The movements should not be passive, and should never be forced. As pain-free movement increases the patient will be allowed up non-weight-bearing on crutches. When the pain has completely settled, weight-bearing will gradually be increased. A careful watch should be kept for any sign of a flare-up of the infection. This will usually be heralded by the recurrence of pain.

If there is evidence of significant destruction of articular cartilage, ankylosis is to be expected. The joint is splinted in an optimum position until the ankylosis is sound.

Tuberculous arthritis

This is a chronic infective arthritis. As in tuberculous osteomyelitis, it is a local manifestation of a generalised disease. It commonly affects one joint, usually a large one. There is marked muscle wasting and the patient is sometimes unwell.

It is one of three main varieties of chronic arthritis, the other two being rheumatoid arthritis and osteoarthritis. In the former, although there is considerable muscle wasting and the patient is usually unwell, more than one joint is usually affected, in particular the small joints of the hands and feet. In osteoarthritis usual.ly only one or two joints are involved, muscle wasting is only slight and the patient is well. This condition differs in that it is not primarily inflammatory. The associated synovitis is secondary to changes in the articular cartilage.

In the active phase of joint tuberculosis there is evidence of inflammation, namely warmth, swelling and associated muscle wasting. This disease starts in the synovium or interior of the bone adjacent to the joint. Initially the articular cartilage is normal. If the disease is arrested at this stage a return to normal in the joint is still possible. However, if the disease advances, the articular cartilage is attacked from both sides. The tuberculous granulation tissue involving the synovial membrane creeps across its surface destroying it. Similar granulations within the subchondral bone invade its deep surface. Once cartilage damage has occurred healing will take place by fibrous ankylosis of the joint.

If this occurs the joint is unsound as the fibrous tissue tends to shrink with time leading to increasing deformity. Also tuberclebacilli may be locked up in this tissue. If this is the case, later flare-up may occur. It is likely that tearing of the fibrous tissue by stress may liberate these organisms.

TREATMENT

As well as general treatment of the patient by rest and antibiotic therapy, local management of the active phase of the disease is:

1. Rest: The joint involved is splinted. In the upper limb the joint

may simply be rested in a sling.

2. Traction: This overcomes spasm and prevents collapse of soft bone. As in acute septic arthritis it is particularly, used if the hip is involved. It may be in the form of skin or skeletal traction.

3. Operation: After rest and antibiotic treatment have been in progress for a few weeks, if the disease is not settling rapiy, operation may be considered. Excision of the diseased synovium, together with other tuberculous debris, facilitates the action of the antibiotics and promotes more rapid healing. This may allow a more useful range of movement to be regained.

As in tuberculous osteomyelitis an abscess may form in the surrounding soft tissue if the joint capsule is perforated. If this becomes subcutaneous, it is liable to erupt through the skin gving rise to a sinus. This sinus track communicates with the joint and may allow secondary infection of the joint to occur. If this should be the case, ankylosis of the joint may become bony.

An abscess may be treated by aspiration or incision followed by Closure of the overlying skin under antibiotic cover. Instillation of streptomycin into a sinus track may effect its cure.

As the disease heals, local treatment depends upon the stage at which its arrest occurred. If articular cartilage damage is minimal, good return of function can be expected. Stress of the joint is gradually reintroduced. In the case of the lowe limb, splints are removed but the patient remains in bed on traction. The traction is then removed for increasing periods of time and then altogether. Mobilisation non-weight-bearing is commenced followed by partial, then full, weight-bearing. This allows for gradual reconstitution of the joint and adjacent bones. The patient is carefully observed and at any sign of recurrence of his signs or symptoms he is dropped back a stage in his rehabilitation programme.

In the upper limb treatment is simpler. The splint or sling is gradually removed for increasing periods and is dispensed with as use increases.

If the disease is arrested late, i.e. after articular cartilage has been destroyed, fibrous ankylosis is to be expected. Therefore the joint is splinted in its optimum position while this occurs. Movement is prevented but stress allowed, e.g. weight-bearing in the lower limb. Some form of splint may be required permanently.

In the upper limb the fibrous ankylosis will be longer as gravity exerts a constant traction force. In the shoulder mobilisation is graduated until support is dispensed with. If pain continues the joint is arthrodesed. In the elbow a permanent splint may be used, although a sling may be sufficient and even this may be dispensed with.

In the longer term, in the absence of a flare-up, the only local treatment required may be a removable splint in the upper limb and a raised shoe in the lower limb. If deformity is a major problem particularly in the hip, corrective osteotomy may be of great help.

If a joint should continue painful arthrodesis may be carried out.

TUMOURS

The word tumour means swelling. In pathological terms it refers to a swelling within the tissues and is a manifestation of neoplasia-the term neoplasia meaning new growth: Turnouts are either benign or malignant.

Benign tumours show an excessive proliferation of cells but the tumour remains localised, is non-invasive and does not metastasise, i.e. does not spread to distant tissues.

Malignant turnouts are characterised by:

1. Invasion of surrounding tissue.

2. Recurrence after removal or radiotherapy

3. Metastases, i.e. spread to local lymph nodes or distant tissues 4. Rapidity of growth

5. Abnormal changes in the cell nucleus

6. Anaplasia: A malignant turnout fails to reproduce the structure of the tissue from which it grows whereas a benign tumour may reproduce it perfectly. This lack of differentiation is called anaplasia. The more anaplastic the tumour, the more malignant it is likely to be.

7. Fatal outcome: A malignant tumour as the name implies tends to kill the patient.

Benign bone tumours nearly all occur in adolescents br young adults. On a radiograph their benign character is demonstrated by the clearly defined edges.

Malignant tumours are either primary, i.e. they arise from bone itself, or secondary, i.e. they are metastatic deposits from turnouts of other tissues. Primary malignant tumours of bone are generally highly malignant and fatal. They tend to occur in young people, are painful and do not show a definite edge on the radiograph.

All primary bone tumours whether benign or malignant are rare. Secondary malignant tumours are, on the other hand, relatively common and occur mainly over the age of 50. Turnouts which most commonly metastasise to bone are carcinoma of breast, kidney, lung, prostate and thyroid.

The principal tumours, benign and malignant, will be summarised and then a more detailed description of osteosarcoma and secondary tumours of bone will be given. The general basis for any classification of bone tumour is based upon the tissue of origin of the t,maour. Recollection of the tissues involved in the formation and structure of bone, briefly outlined at the beginning of the chapter, will serve as a general guide to the possible tumours that may arise.

VASCULAR (ANGIOID) TISSUE TUMOURS

Benign: (a) Angioma

(b) Aneurysmal bone cyst

Malignant: Angiosarcoma

BONE=FORMING TISSUE TUMOURS

Benign: (a) Osteoma (exostosis)

(b) Ostcoblastoma

(c) Ostcoid osteoma

Malignant: (a) Osteosarcoma

(b) Juxta cortical osteogenic osteosarcoma


CARTILAGE TUMOURS

Benign: (a) Osteochondroma (similar to exostosis but includes cartilage)

(b) Chondroma: Within bone=enchondroma. If protruding beyond confines of bone=ecchondroma (c) Chondroblastoma

Malignant: Chondrosarcoma


EMBRYONIC VESTIGIAL TISSUE TUMOUR"

Chordoma (locally malignant, i.e. invades local tissue)

FIBROBLASTIC TISSUE TUMOURS

Benign: Fibroma (variants non-ossifying fibroma, chondromyxoid fibroma)

Malignant: Fibrosarcoma

TUMOURS FROM NON-OSSEOUS CONNECTIVE TISSUE FOUND IN BONE

Benign: (a) Lipoma

(b) Neurofibroma
(c) Neurolemmoma

Malignant: (a) Liposarcoma

(b) Reticulosarcoma

(c) Myeloma

(d) Ewing's turnout

UNDIFFERENTIATED CONNECTIVE TISSUE TUMOUR Giant cell tumour

The treatment of a benign tumour is either by excision or curettage and bone .grafting.

The reasons for carrying out such treatment are:

1. If the turnout is painful, e.g. osteoid osteoma

2. If the turnout interferes with function of a tendon, or causes a. prominent lump which is either disfiguring or prone to being knocked, e.g. exostosis

3. If by weakening the bone the tumour gives rise to a pathological fracture, e.g. enchondroma

4. If the turnout becomes larger, painful and the outline on the radiograph becomes less distinct. This may indicate malignant change and is occasionally seen in an osteochondroma

5. aere there is significant inherent risk of malignant change, e.g. giant cell tumour.

Osteosarcoma (osteogenic sarcoma)

The term sarcoma is given to malignant tumours of connective tissue. An osteogenic sarcoma is, therefore, a malignant, specially! connective tissue tumour arising in bone.

There are three varieties of the tumour which are based upon the principal tissue seen on histological examination. They have in common the fact that they all form osteoid (uncalcified bone matrix) and bone.

Where chondroblasts (cartilage cells) predominate it is called a chondroblastic osteogenic sarcoma. If fibroblasts predominate it is called a fibroblastic osteogenic sarcoma. If bone formation predominates it is called an osteoblastic osteogenic sarcoma.

They most commonly occur in the metaphysis of a long bone, mostly in the lower end of the femur or upper end of the tibia.. They are twice as common in males and the highest incidence is between the ages of 10 and 25 years.

Pain is usually the first symptom. Local swelling will quickly occur as these tumours are rapidly growing. The temperature of the overlying skin may be increased and commonly there are dilated veins in the area. The swelling becomes tender. The tumour commonly metastasises to the lungs.


Diagnosis is confirmed by a biopsy before treatment commences.

TREATMENT

Treatment may be one or a combination of the following: amputation; radiotherapy; chemotherapy.

If there is no evidence of metastases amputation is usually carried out. This must involve removal of the whole bone as so-called skip lesions may occur, i.e. the bone may be involved at levels other than the main tumour mass. For this reason if the lower end of the femur is involved a hip disarticulation amputation is carried out.

If there is metastatic spread, treatment is usually by radiotherapy. However, amputation may be carried out to remove the local turnout which may become very painful and swollen.

A combination of radiotherapy followed by amputation is sometimes used even if there arc no obvious metastases.

More recently some of these tumours have been treated, with some success, by cytotoxic drugs.

If a solitary lung metastasis is formed its excision is now considered worthwhile.

If amputation is carried out the physiotherapist will be closely involved in the rehabilitation programme This will involve stump bandaging, education in walkin with crutches and management of the prosthesis.

Secondary mmours in bone

These are the most common tumours in bone. They occur mainly ater middle age.


TREATMENT

1. Drugs: Analgesics, and, sometimes, hormones as in the case of breast and prostatic carcinoma.

2. Radiotherapy: Pain is often improved. The tumour mass may shrink and therefore paraplegia due to spinal deposits may sometimes improve.

3. Operation: If the tumour should fungate it is probably best excised although radiotherapy may be useful. Surgical treatment of intractable pain from these tumours may sometimes involve division of sensory nerves, nerve roots or nerve tracts in the spinal cord. Secondary deposits in the vertebral colunm may cause pressure on the spinal cord requiring decompression by laminectomy.

4. Fixation of pathological .fractures: Such a fracture may be the presenting feature of a secondary deposit in bone. Internal fixation of a long bone fractured in such a way is the usual method of management.

METABOLIC BONE DISORDERS

While the mechanical functions of bone may be obvious, the fact that they are physiologically very active can easily be overlooked. They play an integral part in calcium and phosphate metabolism, forming a reservoir which contains 99 per cent of the calcium and 90 per cent of the 15hosphate in the body.

Calcium in its free ionised form is necessary for a number of important body functions, namely: 1. Blood coagulation

2. Normal cardiac and skeletal muscle contraction

3. Normal nerve function.

Maintenance of a blood calcium level between very narrow limits is essential to avoid disturbance of these functions. To maintain this level there is a delicate balance between calcium absorption from the gastro-intestinal tract, its excretion by the kidney and its uptake aad mobilisation from bone. Calcium metabolism comes underthe influence of many factors the chief of which are parathyroid hormone and vitamin D.

Parathyroid hormone acts at three sites to increase the plasma calcium level. First, it facilitates calcium absorption from the intestine. Secondly, it causes mobilisation of calcium from bone. Thirdly, it acts on the kidney causing an increased excretion of phosphate, which in turn leads to a fall in the plasma phosphate level which causes a rise in plasma calcium.

Vitamin D is the term used to refer to a group of closely related substances. Some are found in the diet (fish-llver oil is particularly rich in this) and some are produced by the action of ultraviolet light on certain substances found in the skin of mammals. Vitamin D is required for the absorption of calcium from the intestine. It also causes mobilisation of calcium from bone. In vitamin D deficiency, poor absorption of calcium leads to hypocalcaemia and failure of. mineralisation of the protein of newly-formed bone.

An understanding of the normal physiology of bone as it relates to calcium metabolism will provide a good basis for understanding the metabolic diseases of bone, some of which will now be outlined.

Infantile rickets and osteomalacia

A lack of vitamin D, due either to dietary deficiency, insufficient exposure to sunlight or both, results in these conditions.

Infantile rickets as its name implies occurs in children. The disturbance in calcium metabolism is the same as in osteomalacia which is the adult expression of the disorder. The manifestations Of both these disorders only differ in so much that in the child the bones are in a growing phase.

In both conditions there is an abundance of osteoid, that is, uncalcified bone matrix. In children there are added changes involvingthe growth plate cartilage. These zones become wider but the abundant cartilage is not converted into bone.

Lack of vitamin D leads to a decreased absorption of calcium and phosphate. This in turn leads to a fall in the blood calcium level which stimulates secretion of parathyroid hormone. This hormone cannot increase calcium absorption from the bowel in the absence of vitamin D, but it does cause calcium resorption from bone. The result, therefore, of this sequence of events is that calcium, rather than being laid down, is resorbed from bone in order to maintain the blood and tissue fluid calcium at the correct levels.

In thechild, the effect on the growth plates leads to retarded ossification and growth. The bones are generally softened and prone to bend. This is especially noticeable in the weight-bearing bones.

In the adult, the bones become decalcified giving rise to a ground-glass appearance on the radiograph. Another radiographic characteristic is bands of radio-lucency: These are called Looser's zones or Milkman's fractures after the people who described them. They represent pseudo-fractures and occur most commonly in the upper humerus, scapula, ribs, pubis and femoral neck. The softened bones are more prone to fracture with minimal trauma (pathological fractures). A group of subcapital fractures of the femur occur in osteomalacic patients. These people are older and often housebound. They have a poor diet and little exposure to sunlight. Patients with osteomalacia often feel unwell and complain of generalised pains and muscle weakness.

TREATMENT

The primary treatment of these conditions is by administration of vitamin D with calcium supplements.

Secondary treatment may involve later correction of deformities by osteotomy. Fractures will require appropriate treatment.

Secondary rickets

This may occur in a number of rarer situations. In these, vitamin D deficiency is not the primary cause.

1. Vitamin D resistant rickets: This is due to hypophosphataemia (low blood phosphate). Individuals with this require massive doses of vitamin D for normal bone formation to occur. Because of this it is known as vitamin D resistant rickets.

2. Hypophosphatasia: This is an inherited disease where the enzyme alkaline phosphatase is lacking. Because of this, although the supply of vitamin D and calcium is normal, the calcium is not deposited in bone.

3. Renal rickets: This is due to malfunction of the kidneys. There is a fall in phosphate levels due to failure of its resorption by the kidneys. This gives rise to increased secretion of parathyroid hormone which mobilises calcium from bone. In a child this will produce the picture of rickets, but in an adult osteomalacia will result.

Hyperparathyroidism

In this condition too much parathyroid hormone is secreted. This may be due to a tumour (adenoma) of a parathyroid gland or, occasionally, to hyperplasia of all the glands. The result of this is excessive excretion of phosphate from the kidney giving a low blood phosphate level. There is normally a constant relationship between the calcium and phosphorus levels in blood. If one falls the other rises. In this situation, because there is a fall in blood phosphate levels, calcium is withdrawn from bone with a consequent rise in the blood calcium level. As a result of this there is a rise in urinary calcium excretion with an increased incidence of calcium containing kidney stones.

Disturbances in bone structure may also occur. There is resorption of bone leading to osteoporosis. Many cysts may be formed and there may be an abundance of fibrous tissue. These changes have given rise to the descriptive term, osteitisbrosa cystica. The bones are weakened and are prone to bending and fracture.

Hypoparathyroidism

This is most commonly due to inadvertent removal of the parathyroid glands during thyroid surgery. There is a consequent fall in blood calcium level. This gives rise to neuromuscular excitability which in its full-blown manifestation produces muscular spasms referred to as tetany.

Osteoporosis

In contrast to osteomalacia where there is a lack of calcium deposition in a normal matrix, in osteoporosis there is poor formation of the protein matrix but normal calcium deposition and bone resorption.

It may occur in a variety of conditions, three of which will be considered.



DISUSE OSTEOPOROSIS

This is seen in paralysis or immobilisation of a limb. Osteoblasts lack the normal stimulus of stresses and strains on the bone, so that bone formation is decreased. There is an increase in calcium excretion with a tendency to .form renal stones. General exercises are therefore important for patients who are recumbent for long periods.



POST-MENOPAUSAL OSTEOPOROSIS

Bone formation is influenced by the gonadal hormones (oestrogens and androgens). Lack of these hormones leads to osteoporosis. This is most commonly seen with the fall in oestrogen levels which occurs at the female menopause. Senile osteoporosis.is for the most part based upon lack of these hormones.



HYPERCORTICOSTEROIDISM (CUSHING'S SYNDROME)

Here osteoporosis is due to hypersecretion of adrenocortical hormones, in particular the giucocorticosteroids. It is due to excessive protein breakdown which inhibits new bone formation and causes breakdown of existing bone matrix, an anti .vitamin D action and an increased urinary calcium cxcrctionwhich is secondary to an increased glomerular filtration rate.

A similar effect may be sccn with the administration of steroids therapeutically over a long period of time.

With ostcoporosis thcrcis an increased tendency for bones to fracture. This isdemonstrated by the common occurrence of fractures of the neck of the femur in elderly female patients. There is also a tendency to compression fractures of vertebral bodies leading to spinal deformity (usually kyphosis) and loss of height. Fractures arc treated appropriately. There is some evidence that calcium supplco mcnts in certain forms with vitamin D may give some improvement in this condition. These patients, unlike those with osteomalacia, are not ill and are not affected by generalised pain and muscle weakness. However, sometimes the two conditions may coexist.