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Arthritis in childhood is not uncommon. Estimates of the annual incidence of arthritis vary widely, but for all forms of chronic arthritis it is probably between 5 and 10 per 100 000 children aged 16 years or younger.1 2 Acute forms of arthritis are perhaps four times more common.3 Most paediatricians will therefore see several patients with arthritis each year. The aim of this paper and part 2 of the series4 is to give a concise, but moderately comprehensive, overview of this topic which will help in the management of this heterogeneous group of disorders.
Although chronic arthritis can present with a sudden and painful onset of one or more swollen joints, such a presentation should raise suspicions that the arthritis is due to trauma or to a joint or contiguous bone infection.
Trauma
A traumatic cause of joint swelling is usually obvious from the patient’s history, but parents sometimes incorrectly presume that a swollen joint must have been due to an injury. It is unlikely that an injury is the cause of a swollen joint if the child has not had a definite traumatic event that was painful enough to immediately prevent the child continuing with the activity. The exception to this is perhaps a child with haemophilia, who might develop a haemarthrosis after only mild trauma.
If it is uncertain whether the swelling of a joint is due to a joint effusion or simply due to soft tissue swelling, an ultrasound examination of the joint can be helpful and may also be able to determine whether there is blood in the joint. Synovial fluid analysis of a traumatic effusion usually shows a low white cell count (<0.2 × 109/l), but this can occasionally be much higher and mimic fluid from a septic joint. A haemarthrosis …
Footnotes
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This is the first article in a series on rheumatology.