Predicting the Long-Term Gains in Health-Related Quality of Life After Total Knee Arthroplasty.

BACKGROUND: We investigated the predictors of long-term gains in quality-adjusted life years (QALYs) from total knee arthroplasty (TKA) and the patient attributes that predicted cost-effective TKA. METHODS: Data on TKA patients (n = 570) from 2006 to 2007 were extracted from a single-institution registry. QALY gains over 7 years post surgery were calculated from health-related quality of life (HrQoL) scores measured preoperatively and annually postoperatively using the short-form health survey (SF-12) instrument. Multivariate linear regression analysis investigated the predictors of QALY gain from TKA from a broad range of preoperative patient characteristics and was used to predict QALY gains for each individual. Patients were grouped into deciles according to their predicted QALY gain, and the cost-effectiveness of each decile was plotted on the cost-effectiveness plane. Patient attribute differences between deciles were decomposed. RESULTS: After exclusions and dropout, data were available for 488 patients. The average estimated QALY gain over 7 years was 0.77 (95% confidence interval [CI] 0.70-0.83). Predictors significantly associated with smaller QALY gains were comorbidities (Charlson comorbidity index 3+ coefficient -0.54 CI -0.15 to -0.92), the absence of severe osteoarthritis in the ipsilateral knee (-0.51 CI -0.16 to -0.85), preoperative HrQoL (standardized coefficient -0.34 CI -0.26 to -0.43), the requirement for an interpreter (-0.24 CI -0.05 to -0.44), and age (-0.01 CI -0.01 to -0.02). The largest difference between cost-effective and non-cost-effective deciles was relatively high preoperative HrQoL in the non-cost-effective decile. CONCLUSION: TKA is likely to be cost-effective for most patients except those with unusually high preoperative HrQoL or a lack of severe osteoarthritis. The poorer outcomes for those requiring an interpreter requires further research.