Abstract
Objective
To determine the use of oral anti-inflammatory drugs use in the year before and the two years after primary total hip (THR) or knee (TKR) replacement, and to assess whether this varied according to the Body mass Index (BMI).
Design
Population based retrospective case control study.
Setting
433 General Practitioner practices contributing to the General Practitioner Research Database.
Participants
28,068 patients who had undergone a THR and 24,364 patients who had undergone a TKR between 1991-2006. 5 controls per case were matched for age, sex and GP practice.
Main Outcome measures
Two categories of oral anti-inflammatory usage: (1)”zero coverage” – patients who were not prescribed any anti-inflammatory medication; (2)”greater than 80% coverage” – patients who were prescribed anti-inflammatory medication for greater than 80% of the days in the year. Secondary subset analysis according to BMI.
Results
At 1 year post surgery the proportion of cases on >80% coverage reduced from 21% (95%CI: 20% to 22%) to 8% (95%CI: 7% to 10%) for THR and 21% (95%CI: 20% to 22%) to 13% (95%CI: 11% to 14%) for TKR, with no ongoing reduction at 2 years. The proportion of THR/TKR cases on zero coverage increased at both 1 and 2 years post op (THR: Pre op 39%, 95%CI: 38% to 40%); 1 year post op 52% (95%CI: 51% to 53%); 2 year post op 66% (95%CI: 65% to 67%) and TKR: Pre op 39% (95%CI: 38% to 40%); 1 year post op 46% (95%CI: 45% to 47%); 2 year post op 58% (95%CI: 57% to 59%).
BMI analysis
>80% coverage increased with BMI in the control groups. The proportion of THR cases on >80% coverage increased with BMI pre op. The magnitude in reduction of >80% coverage post op was similar across all BMI groups. The proportion of TKR cases on >80% coverage pre op was greatest in the extreme BMI categories. Again the magnitude in reduction of >80% coverage post op was similar across all BMI groups.
Conclusion
THR/TKR's reduce the patients' need for anti-inflammatory medication, with implications regarding the side effects of their long-term use. The majority of the benefit from reduction in anti-inflammatory use is observed by 1 year post operatively. Increasing BMI affects anti-inflammatory use in both the general population as well as those undergoing THR/TKR surgery but without strong evidence of a detrimental effect on the benefits of pain relief.
