Ross & Wilson Anatomy and Physiology in Health and Illness (195 page)

Developmental abnormalities of bone

Achondroplasia

This is caused by a genetic abnormality that prevents the proper ossification of bones that develop from cartilage models, such as the long bones of the limbs, leading to short limbs and characteristic dwarfism.

Osteogenesis imperfecta (‘brittle bone syndrome’)

This is a group of conditions in which there is a congenital defect of collagen synthesis, resulting in failure of ossification. The bones are brittle and fracture easily, either spontaneously or following very slight trauma.

Tumours of bone

Benign tumours

Single or multiple tumours may develop for unknown reasons in bone and cartilage. They may cause pathological fractures or pressure damage to soft tissues, e.g. a benign vertebral tumour may damage the spinal cord or a spinal nerve. Benign tumours of cartilage have a tendency to undergo malignant change.

Malignant tumours

Metastatic tumours

The most common malignancies of bone are metastases of primary carcinomas of the breast, lungs, thyroid, kidneys and prostate gland. The usual sites are those with the best blood supply, i.e. spongy bone, especially the bodies of the lumbar vertebrae and the epiphyses of the humerus and femur. Tumour fragments are spread in blood, and possibly along the walls of the veins from pelvic tumours to vertebrae. Tumour growth erodes and weakens normal bone tissue, leading to pain, pathological fractures and destruction of normal bone architecture.

Primary tumours

Primary malignant tumours of bone are relatively rare.

Osteosarcoma

This is a rapidly growing and often metastatic tumour believed to develop from the precursors of osteogenic cells. In young people between 10 and 25 years of age the tumour develops most commonly in the medullary canal of long bones, especially the femur. It is usually well advanced before it becomes evident. In older people, usually over 60 years of age, it is often associated with Paget’s disease and the bones most commonly affected are the vertebrae, skull and pelvis.

Chondrosarcoma

These relatively slow-growing tumours are usually the result of malignant change in benign tumours of cartilage cells. They occur mainly between the ages of 40 and 70 years.

Disorders of joints

Learning outcomes

After studying this section you should be able to:

relate the features of the diseases in this section to abnormal anatomy and physiology

compare and contrast the features of rheumatoid arthritis and osteoarthritis.

The tissues involved in diseases of the synovial joints are synovial membrane, hyaline cartilage and bone.

Inflammatory joint disease (arthritis)

Rheumatoid arthritis (RA, rheumatoid disease)

This is a chronic progressive inflammatory autoimmune disease mainly affecting peripheral synovial joints. It is a systemic disorder in which inflammatory changes affect not only joints but also many other sites including the heart, blood vessels and skin.

It is more common in females than males and can affect all ages, including children (Still’s disease), although it usually develops between the ages of 35 and 55 years. The cause is not clearly understood but development of autoimmunity may be initiated by microbial infection, possibly by viruses, in genetically susceptible people. Risk factors include:

•
age – risk increases with age

•
gender – premenopausal women are affected three times as commonly as men

•
genetic risk – there is a strong familial link in some cases, and some markers on the surface membranes of white blood cells have also been associated with higher risk of the disease.

Almost always (up to 90% of cases), affected individuals have rheumatoid factor (RF-autoantibodies) in their body fluids. High levels of RF, especially early in the disease, are strongly associated with accelerated and more severe disease. Symptoms include joint pain and stiffness, particularly in the morning and after rest. Joints can be visibly swollen, hot and tender.

Acute exacerbations of rheumatoid arthritis are usually accompanied by fever, and are interspersed with periods of remission. The joints most commonly affected are those of the hands and feet, but in severe cases most synovial joints may be involved. With each exacerbation there is additional and cumulative damage to the joints, leading to increasing deformity, pain and loss of function. The early changes, which may be reversible, include hypertrophy and hyperplasia of synovial cells and fibrinous inflammatory effusion into the joint. Progression of the disease usually leads to permanent tissue damage. Growth of inflammatory granulation tissue, called
pannus
, distorts the joint and destroys articular cartilage, exposing the bone below and causing further damage. Fibrosis of the pannus reduces joint mobility. Pain, stiffness and deformity severely restrict the use of affected joints, and as a result the associated muscles start to waste. About a third of patients, usually those with the most aggressive form of the disease, develop nodules of connective tissue (rheumatoid nodules), usually in the forearm or elbow. Extra-articular symptoms can include anaemia, peripheral neuropathy, cardiac abnormalities, pleurisy and vasculitis.

In the later stages of the disease, the inflammation and fever are less marked. The extent of disability varies from slight to severe.
Table 16.8
highlights differences between osteoarthritis and rheumatoid arthritis.

Table 16.8 
Features of the two main types of arthritis

Other types of polyarthritis

Polyarthritis means inflammation of more than one joint. This group of autoimmune inflammatory arthritic diseases has many characteristics similar to rheumatoid arthritis but the rheumatoid factor is absent. The causes are not known but genetic features may be involved.

Ankylosing spondylitis

This tends to occur in young adults, and affects the joints of the vertebral column. Calcification of the intervertebral joints and laying down of new bone leads to reduced spinal flexibility and permanent deformity.

Psoriatic arthritis

This occurs in a proportion of people who suffer from psoriasis, especially if the nails are involved. The joints most commonly affected are those of the fingers and toes.

Reiter’s syndrome (polyarthritis with urethritis and conjunctivitis)

This syndrome, it is believed, may be precipitated by infection with
Chlamydia trachomatis
; the affected joints are usually those of the lower limb.

Rheumatic fever

Rheumatic fever (
p. 120
) is a diffuse inflammatory condition that affects many connective tissues. Polyarthritis is a common presenting feature, often involving the wrists, elbows, knees and ankles. Unlike cardiac effects, arthritis usually resolves spontaneously without complications.

Infective arthritis

Joint infection (septic arthritis) usually results from a blood-borne systemic infection (septicaemia, mainly staphylococcal), although it may also be caused by a penetrating joint injury. Often the joint has been damaged by pre-existing disease, making it more susceptible to infection. Normally, only one joint is involved, which becomes acutely inflamed, and the patient is likely to be ill from the associated septicaemia. Complete resolution is possible if treatment is prompt, but permanent joint damage occurs early in the disease.

Traumatic injury to joints

Sprains, strains and dislocations

These damage the soft tissues, tendons and ligaments round the joint without penetrating the joint capsule. In dislocations there may be additional damage to intracapsular structures by stretching, e.g. to the long head of biceps muscle in the shoulder joint, the cruciate ligaments in the knee joint, or the ligament of head of femur in the hip joint. If repair is incomplete there may be some loss of stability, which increases the risk of repeated injury.

Penetrating injuries

These may be caused by a compound fracture of one of the articulating bones, or trauma caused by, e.g., gunshot. Healing may be uneventful or it may be delayed by the presence of fragments of damaged or torn joint tissue (bone, cartilage or ligaments), which cannot be removed or repaired by normal body mechanisms and prevent full joint recovery. Infection is another risk. Development of chronic inflammation can lead to permanent degenerative changes in the joint.

Osteoarthritis (osteoarthrosis, OA)

This is a degenerative non-inflammatory disease that results in pain and restricted movement of affected joints. Osteoarthrosis is the more appropriate name but is less commonly used. In its early stages, OA is often asymptomatic. It is very common, with the majority of over-65s showing some degree of osteoarthritic changes. Articular cartilage gradually becomes thinner because its renewal does not keep pace with its breakdown. Eventually the bony articular surfaces come in contact and the bones begin to degenerate. Bone repair is abnormal and the articular surfaces become misshapen. This is often the reason for reduced mobility of the joint. Chronic inflammation develops with effusion (collection of fluid) into the joint, possibly due to irritation caused by tissue debris not removed by phagocytes. Sometimes there is abnormal outgrowth of cartilage at the edges of bones that becomes ossified, forming
osteophytes
.