The prevalence and history of knee osteoarthritis in general practice: a case-control study

There is no clear published estimate of the prevalence of diagnosed knee osteoarthritis based on consultation in primary care. Further, little is known about the clinical history of patients who are subsequently diagnosed with knee osteoarthritis.

Our aims were (i) to determine the prevalence of knee osteoarthritis diagnosed in primary care; (ii) to compare the medical history of patients currently diagnosed with knee osteoarthritis with that of controls; and (iii) to determine factors associated with X-ray at the time of first diagnosis.

A case-control study was carried out in one general practice in North Staffordshire. Cases aged > or =45 years were identified from computer searches for knee osteoarthritis between 1 January 1998 and 31 January 2000. Matched controls had no diagnosis of knee osteoarthritis during that same period. The medical records for both groups were examined to identify recorded knee-related symptoms, X-rays and secondary care referrals.

A total of 146 cases and controls were reviewed; 49% of cases and 15% of controls had a previous (pre-1998) diagnosis of knee osteoarthritis. This gives an estimated prevalence of diagnosed knee osteoarthritis in the general population aged > or =45 years of 12.5%. Cases were more likely to have had a prior history of knee-related disorders, X-rays and referral to secondary care than controls. There was no association between an X-ray at first diagnosis and previous knee symptoms (odds ratio 0.98; 95% confidence interval 0.49-1.97) and only weak associations of X-ray with gender (male), age (under 60) of patient and time of diagnosis (pre-1998).

Diagnosed knee osteoarthritis is common in general practice and diagnosed patients often have a long history of knee symptoms prior to diagnosis. Further research might usefully consider what influences GPs' diagnosis of knee osteoarthritis and how diagnosis relates to management and outcome.