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
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.