Temporal trend of annual consultation incidence of osteoarthritis between 1992 and 2013 in primary care in England: estimates from the Clinical Practice Research Datalink

The problem

Osteoarthritis (OA) accounts for 3% of all years lived with disability in high-income countries and is projected to become an even greater challenge for population health and health services in the future due to the changing population age structure and increases in obesity. It is unclear whether this is evident as an increased consultation incidence in UK general practice.

The approach

Annual estimates of incident OA were derived from the Clinical Practice Research Datalink (CPRD). Incident cases of OA in each calendar year were defined as having a newly recorded Read Code starting N05... “Osteoarthritis and allied disorders” in the observation year without any such code in the previous three years. Prevalent cases identified by the same 3-year run-in period method were excluded from the denominator to establish the risk population. The incidence density based on exact person time was applied to estimate the annual incidence. Annual incidence of OA was then estimated for each year 1992-2013 for any OA and joint-specific OA (knee, hip, hand) overall and stratified by gender and age (35-44, 45-54, 55-64, 65-74, 75-84, 85+ years). All overall estimates of OA were age-standardised to the population of England in 2013.

Findings

The overall age-standardised annual consultation incidence for any OA increased from 8.38 per 1000 person-years (95% CI: 8.35, 8.40) in 1992 to 9.03 (9.00, 9.05) in 2004, before decreasing to 5.15 (5.13, 5.17) in 2013. The corresponding estimates for females were 9.66 (9.62, 9.70) in 1992, 11.47 (11.43, 11.51) in 2004, and 6.38 (6.35, 6.41) in 2013; in males, 7.00 (6.97, 7.03) in 1992, 6.57 (6.54, 6.60) in 2004, 3.93 (3.91, 3.95) in 2013. Similar temporal trends in annual incidence were observed within each age-stratum and, generally, when separately estimating annual consultation incidence for knee, hip, and hand OA. The decreasing consultation incidence of OA was still seen when restricting observations to practices continuously registered with CPRD. Between 2004 and 2013 we found that OA clinical events as a proportion of all recorded events in CPRD had fallen by almost 20% (from 0.31% to 0.25%).

Consequences

We found an unexpected decreasing temporal trend of consultation incidence of OA using data from CPRD in the period 2004-2013. This is in contrast with historic increases in overweight and obesity in England, preliminary findings from a smaller local general practice network and trends of increasing incidence for QOF indicators for other long-term conditions reported by other studies in CPRD (e.g. incidence of type 2 diabetes increased from 3.91 to 5.15 per 1000 person-years between 2004-2010. We speculate that the findings reflect changes in coding behaviour that requires further investigation, including international comparison, before any conclusion on the trend in OA consultation incidence can be confidently drawn.

Credits

• Dahai Yu
• George Peat
• John Bedson
• Kelvin Jordan