Diseases affecting bone

Paget’s disease

This condition seems to involve a dramatic increase in both osteoclasts and osteoblasts in the bone. The bone starts to remodel far too rapidly. The patient complains of bone pain, and over a period of years the bone may gradually change shape, producing a characteristic bowed tibia and an enlarged skull. One bone may be involved in isolation, or several bones can be involved at the same time. The condition becomes increasingly common with age, affecting as much as 10 per cent of the very elderly. The X-ray findings of the bone are quite characteristic. The bone looks larger then it should and there is loss of the clear margin between the cortex and the medulla. The trabecular pattern of the medulla becomes coarse, tangled and confused. The plasma alkaline phosphatase may be markedly raised because of the increased osteoclast activity. The abnormal bone may suffer a pathological fracture. This fracture can be difficult to manage because the bone is deformed and because any attempt to pass a nail down the medulla may produce significant loss of blood. The cortical bone is also extremely hard and it can be very difficult to make drill holes for screws. Surgery on pagetic bone should be approached with great caution by both surgeon and anaesthetist (Fig 26.2 and Fig 26.3).

Osteoporosis

This condition is becoming increasingly common in the Wes­tern world in the elderly but especially in postmenopausal women. It is believed to be related to a fall in oestrogen. The remodelling activity of the bone appears to fall away but osteoblastic activity falls more rapidly than osteoclastic, so there is a gradual thinning of the cortex and trabecular pattern of the bone. The bone gradually weakens until trivial trauma leads to a fracture. The common sites for a fracture are the neck of the femur, a crush fracture of the lumbar or thoracic spine, the head of the humerus and the distal radius. The fractures heal normally but can be difficult to hold with internal fixation because the bone is so soft and spongy.

Rickets/osteomalacia

The failure of bone osteoid to mineralise is called osteomalacia. In children, the disease is called rickets. The cause is a deliciency in vitamin D or in its metabolism. Vitamin D is produced in the skin when exposed to sunlight. It is also absorbed in the diet and is fat soluble. If the patient has a malabsorption syndrome, then vitamin I) deficiency may occur. In the body vitamin D is converted to 25~hydroxycholecalciferone in the liver, then to 1,25~dihydroxycholecalciferone in the kidney. In children who lack vitamin 0, either because of diet or because of an inbuilt error in metabolism, the costochondral junctions enlarge to form the 'rickety rosary’. The skull develops frontal bosses and the long bones bend, especially the lower third of the tibia. The child is also small. Serum calcium and phosphate are normal hut alkaline phosphatase is usually raised. In adults bone deformity is not so marked but the patient may complain of marked muscle weakness. Lytic lesions may appear in the bone called Looser’s zones. These are particularly common in the pelvis and may cause a pathological fracture.

Hyperparathyroidism.

If for any reason there is excessive production of parathormone there is increased osteoclast activity which leads to lytic lesions in the hone, similar to those seen in osteomalacia. These are called ‘Brown tumours and fractures may occur through these. The osteolytic lesions are particularly characteristic in the terminal phalanges and the alveolar margins of the jaws. The patient’s serum calcium is raised and serum phosphorus is lowered with the alkaline phosphatase slightly raised. The treatment is to manage the underlying endocrine condition but fractures should be treated as normal and will heal well.

Ankylosing spondylitis

This progressive disorder has some features in common with rheumatoid arthritis. It is much more common in men than women and starts with the central joints of the body. The ligaments around the joints calcify and then ossify, freezing the patient into their deformed position (Fig. 26.4). The tissue antigen HLA-B27 is very common in patients who have ankylosing spondylitis but is rarely found in the normal population. It is therefore diagnostic.

History

The condition starts in early adult life, and starts with painful stiff joints.

Examination

Reduction of chest expansion is an early physical sign.

Investigation

As mentioned, the HLA-B27 antigen will be positive. The erythrocyte sedimentation rate may be slightly raised and X-rays of the sacroiliac joints show early obliteration with ankylosis. An X-ray of the spine may show ossification of the spinal ligaments (bamboo spine; Fig. 26.5).

Treatment

Early treatment with anti-inflammatories and physiotherapy can reduce the disability. In cases where gross flexion of the spine has occurred an osteotomy can be performed but this is not without risk of causing paraplegia. If the disease includes the hip joints then total hip replacement will help.