Age- and health-related quality of life after total hip replacement: decreasing gains in patients above 70 years of age

Abstract

Background: While age is a common confounder, its impact on health-related quality of life (HRQoL) after total hip replacement is uncertain. This could be due to improper statistical modeling of age in previous studies, such as treating age as a linear variable or by using age categories. We hypothesized that there is a non-linear association between age and HRQoL.

Methods: We selected a nationwide cohort from the Swedish Hip Arthroplasty Register of patients operated with total hip replacements due to primary osteoarthritis between 2008 and 2010. For estimating HRQoL, we used the generic health outcome questionnaire EQ-5D of the EuroQol group that consits or 2 parts: the EQ-5D index and the EQ VAS estimates. Using linear regression, we modeled the EQ-5D index and the EQ VAS against age 1 year after surgery. Instead of using a straight line for age, we applied a method called restricted cubic splines that allows the line to bend in a controlled manner. Confounding was controlled by adjusting for preoperative HRQoL, sex, previous contralateral hip surgery, pain, and Charnley classification.

Results: Complete data on 27,245 patients were available for analysis. Both the EQ-5D index and EQ VAS showed a non-linear relationship with age. They were fairly unaffected by age until the patients were in their late sixties, after which age had a negative effect.

Interpretation: There is a non-linear relationship between age and HRQoL, with improvement decreasing in the elderly.

Figure 1.

The relationship between the EQ-5D index and the EQ VAS one year postoperatively and the patient’s age at surgery. Preoperative EQ-5D index and EQ VAS were set to the most frequently occurring values (index = 0.87; VAS = 50) and are indicated by the horizontal dashed lines. The change before and after surgery is the height above this line, i.e. anything above is an improvement. The 2 lines differ only in height; the solid line with blue confidence interval indicates the optimal combination of covariates (male sex, first hip, and Charnley class A) while the dotted line with pink confidence interval indicates the least favorable combination (female sex, previous contralateral hip surgery, and Charnley class C). The pain VAS was set to the median value, 65 mm.

Figure 2.

The relationship between the EQ-5D index and the EQ VAS one year after surgery in relation to preoperative values. The 2 lines differ only in height. The solid line with blue confidence interval indicates the optimal combination of covariates (male sex, first hip, and Charnley class A) while the dotted line with pink confidence interval indicates the least favorable combination (female sex, second hip, and Charnley class C). Age and pain were set to the median values, 69 years and 65 mm.