32 ESTIMATING THE LIFETIME RISK OF TOTAL HIP AND KNEE REPLACEMENT IN THE UNITED KINGDOM

Abstract

Purpose: Establishing a population-based estimate for the lifetime risk of total hip and knee replacement (THR/TKR) is an important epidemiological development which will assist health service planners in assessing the future burden of lower limb arthroplasty. Methods:We used data from the U.K. General Practice Research Database (GPRD) which contains all the computerised records of 6.25m patients, and is representative of the population of the U.K. We collected data on all THRs and TKRs performed between 1991 and 2006, a total of over 27,000 THRs and 24,000 TKRs. We calculated incidence rates for THR/TKR under a Poisson model and combined these rates with mortality rates from the U.K Office for National Statistics (ONS) using a life-table framework. These estimates were then aggregated to produce a simple lifetime risk of THR and TKR by gender for age 50 and above. We also calculated the temporal trend in lifetime risk at age 50 by single calendar year from 1991 to 2006. Results: We estimated that at age 50 the mortality-adjusted lifetime risk of THR was 7.80% for females and 5.05% for males (TKR: 6.66% and 5.04% respectively). The risks of THR for females aged 50 was 54% greater for than for males (32% greater for TKR). The risk percentage decreases with increasing age for both THR and TKR in males and females. At age 80 the gender gap in risk of THR remains in favour of females (53% higher) but in TKR it is two-thirds of that at age 50 (females 21% higher). Between 1991 and 2006, the lifetime risk of THR rose from 3.89% to 10.41% for females and for males from 3.43% to 6.34%. Over the same period, for TKR the risk for females increased from 2.78% to 10.02% and for males from 1.57% to 7.39%.