DOES COMORBIDITY AFFECT THE OUTCOME OF SURGERY - TOTAL HIP-REPLACEMENT IN THE UK AND JAPAN

Objectives. To assess the impact of comorbidity on the outcome of surg ery in the UK and in Japan; to determine the predictive ability of a n ew measure of comorbidity, the Index of Co-Existent Diseases (ICED); a nd to see if its predictive power could be improved. Design. Logistic regression using data from two retrospective cohorts with prospective outcome data collection. Setting. Six hospitals (three teaching, three non-teaching) in the UK and 15 (12 teaching, three non-teaching) hosp itals in Japan. Study participants. Patients undergoing total hip repl acement (THR) surgery in the UK (n = 268) and in Japan (n = 249). Main outcome measures. Serious complications before hospital discharge and change in three measures of general health status [basic activities o f daily living (ADL); instrumental ADL; social activities]. Results. T he distribution of levels of comorbidity differed between the UK and J apan: none (26.1 versus 42.2%); mild (30.6 versus 43.0%); moderate (23 .5 versus 12.0%); and severe (19.8 versus 2.8%). In the UK, the incide nce of serious complications was higher in patients with moderate (27. 0%) or severe (26.4%) comorbidity than in those with no (14.3%) or mil d (23.4%) comorbidity (P < 0.001). In contrast, no significant associa tion was found in Japan. The relationship between comorbidity and chan ge in health status was weak in the UK and non-significant in Japan. L ogistic regression confirmed that comorbidity was a significant predic tor of serious complications in the UK. The only other significant fac tor was surgical approach (anterior/antero-lateral; odds ratio 2.16, P < 0.05). Attempts to improve the predictive power of the ICED by modi fying its structure and by reclassifying complications was successful in achieving a linear (rather than dichotomous) relationship. The pred ictive power, however, was poor. Conclusions. Comorbidity is a signifi cant determinant of serious complications following THR but not of cha nges in functional or health status. Comparisons of clinical performan ce using post-operative complications must take levels of comorbidity into account if they are to be meaningful. The ICED is of less validit y in the UK and Japan than in its country of origin, the USA. Further work to develop better instruments for the UK and Japan is needed.