Women in Charnley class C fail to improve in mobility to a higher degree after total hip replacement

Abstract

Background: The Charnley comorbidity classification organizes patients into 3 classes: (A) 1 hip involved, (B) 2 hips involved, and (C) other severe comorbidities. Although this simple classification is a known predictor of health-related quality of life (HRQoL) after total hip replacement (THR), interactions between Charnley class, sex, and age have not been investigated and there is uncertainty regarding whether A and B should be grouped together.

Methods: We selected a nationwide cohort of patients from the Swedish Hip Arthroplasty Register operated with THR due to primary osteoarthritis between 2008 and 2010. For estimation of HRQoL, we used the generic health outcome questionnaire EQ-5D of the EuroQol group. This consists of 2 parts: the EQ-5D index and the EQ VAS estimates. We modeled the EQ-5D index and the EQ VAS against the self-administered Charnley classification. Confounding was controlled for using preoperative HRQoL values, pain, and previous contralateral hip surgery.

Results: We found that women in class C had a poorer EQ-5D outcome than men. This effect was mostly due to the fact that women failed to improve in the mobility dimension; only 40% improved, while about 50% of men improved. Age did not interact with Charnley class. We also found that the classification performed best without splitting or aggregating classes.

Interpretation: Our results suggests that the self-administered Charnley classification should be used in its full capacity and that it may be interesting to devote special attention to women in Charnley class C.

Figure 1.

A. An illustration of the difference in impact of Charnley class depending on sex. The results were adjusted to the median age and pain VAS: 69 years and 65 mm. The most frequent EQ-5D index value preoperatively was 0.87. The red area indicates values below the preoperative index value. The dashed line indicates the predictions from a linear regression model while the solid lines depict quantile regression predictions at the different quantiles. B. The same as in panel A but with EQ VAS as outcome. This was adjusted to the most frequent EQ VAS value preoperatively: 50 mm.

Figure 2.

Average change before and after surgery, by EQ-5D dimension (mobility, self-care, activities, pain/discomfort, and anxiety/depression), each stratified by Charnley class. Each dimension may take on 3 different ordered values; thus, the change ranges from –2 to 2 and this average is shown on the y-axis. The confidence interval bars indicate 95% certainty of each average. The maximum influence of the Charnley classes was on the mobility and pain/discomfort dimensions.

Figure 3.

The crossover between Charnley classes from before to after surgery. The patients before surgery are represented on the left while those after surgery are represented on the right. Pink corresponds to the proportion of women in each group while blue corresponds to the proportion of men. The size of the arrow is proportional to the percentage of patients leaving that specific class and the color of the gradient corresponds to the sex proportion for each transition according to the color bar.

Figure 4.

Our directed acyclic graph (DAG) for this study as generated by dagitty.net. The green node indicates the exposure of interest, the green lines the exposures effect pathways, and the blue node with the “I” indicates the outcome of interest. The blue node without “I” is an intermediate to the effect pathway. White nodes are confounders that are adjusted for in the models, while red nodes indicate nodes that should be adjusted for but that are not available.