In sickness and in health

Pubmed trends showing how the popularity of analyzing comorbidities have increased over time. The search query is "Arthroplasty[MeSH Major Topic] AND (comorbidity OR co-morbidity)",  for the blue bar I also added "AND (Charlson OR Elixhauser)" to indicate that the popularity of using scores that summarize the comorbidities also are increasing.
Pubmed trends showing how the popularity of analyzing comorbidities have increased over time. The search query is “Arthroplasty[MeSH Major Topic] AND (comorbidity OR co-morbidity)”, for the blue bar I also added “AND (Charlson OR Elixhauser)” to indicate that the popularity of using scores that summarize the comorbidities also are increasing.
When I started my PhD-studies I had this idea that if we know the exact medical status of the patients and implant characteristics we will be able to explain why and when people are re-operated after total hip replacements (THR). Three years later I have just published an article in the Bone and Joint Journal about how wrong I was. In this post I’ll try to give some personal reflections on the article.

The results

The main high-lights from the article are

  1. The most commonly used comorbidity measure (the Charlson score) does not aid in predicting re-operations
  2. The best performing score, the Elixhauser score, is still far from good – barely making an impact on the predictive power of the model
  3. Cemented implants are only better for females, the long standing dogma disappears when checking for gender interactions – males actually do OK with uncemented implants

While the point 1 and 2 were disappointing it does seem to explain why age is not a strong confounder, in the period after 2 years it actually turns out that the older you are the lesser the risk of a re-operation. There is a risk of bias due to that age and comorbidities may discourage a surgeon from re-operating, unfortunately I have found no way to fully account for this bias. This could be an area where patient reported outcomes can help out.

The third point is interesting as I have not heard of gender hip implants while gender knees have gained a lot of interest. It is plausible that females have a different anatomy that the current uncemented hips fail to accommodate, it would be exciting to see some research into this field.

Apart from this I can recommend to have a look at my graphs that I developed for this article. The Bone and Joint Journal were actually kind enough to publish them all in color, I’ll try to post some examples soon in the R-section of this blog.

M. Gordon, A. Stark, O. G. Sköldenberg, J. Kärrholm, and G. Garellick, “The influence of comorbidity scores on re-operations following primary total hip replacement Comparison and validation of three comorbidity measures,” Bone Joint J, vol. 95-B, no. 9, pp. 1184–1191, Sep. 2013.

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