The purpose of this study was to examine the rate of primary knee, hip, or shoulder replacement among persons with osteoarthritis (OA) of the knee by gender and age comparing two nations in similar periods using electronic health records, but with different health-care systems.
Two electronic health care databases of anonymized information were used to construct cohorts of adults with OA of the knee from the United Kingdom (UK) and the United States. Patients were required to have activity in the database at least 6 months before the first diagnosis of knee OA ("index diagnosis") in the study period to ensure that the patient samples were eligible for medical evaluation. The outcomes (numerator) measured were primary knee, hip, or shoulder replacement or the composite of primary knee, hip, or shoulder replacement. The denominator was the person-time at risk computed from time from the date of the index diagnosis to the date of each outcome separately or to the end of the database period if no outcome was documented.
There were 93,146 subjects in the UK and 1,468,217 in the United States who were aged 18+ years and met the study eligibility criteria. The composite joint replacement rate (hip, knee, or shoulder) ranged from 11.89 per 100 person-years (PY) in the Unites States to 4.13 per 100 PY in the UK Primary knee replacements rates ranged from 10.38 per 100 PY in the Unites States to 3.40 per 100 PY in the UK and occurred at a somewhat higher rate in males than females in both countries. Both primary hip and shoulder replacement rates were higher in the Unites States than in the UK (hip: 1.19 per 100 PY and 0.76 per 100 PY; shoulder: 0.19 per 100 PY and 0.03 per 100 PY, respectively). The median time to a primary hip or knee replacement in the UK was approximately twice as long as in the Unites States.
Knee replacements are not an uncommon event in persons with knee OA occurring throughout the adult life span, with the rate steeply rising in both sexes until aged 75 years. Although the pattern of the age-specific joint replacement rates was similar between sexes, the magnitude of the rates was markedly lower in the UK.