Changes in circulating levels of catecholamines, cortisol, glucose, interleukin-6 and C-reactive protein and in the leucocyte count were investigated for 7 days after surgery in 158 patients undergoing hip or knee arthroplasty. We compared the responses to the two operations, and also examined the effects of pathology (osteoarthritis and rheumatoid arthritis) on the changes associated with knee arthroplasty. Exploratory factor analysis was applied to the data to identify the variables and sampling times that could be used in future to provide a concise description of the response. Patients undergoing knee arthroplasty showed significantly greater changes in noradrenaline, adrenaline and glucose levels, but not in cortisol levels, compared with those undergoing hip arthroplasty. Interleukin-6 and C-reactive protein concentrations were also significantly greater in knee patients than hip patients; however, when corrected for pathology, many of these differences were not significant. Minimal effects of pathology (chronic inflammation with rheumatoid arthritis) were found on the hormonal changes in knee patients. In particular, there was little evidence to support the inference from animal data that the hypothalamic–pituitary–adrenal axis is impaired. The expected increases in interleukin-6 and C-reactive protein concentrations were found in the rheumatoid arthritis patients. Exploratory factor analysis showed that the response could be separated into six components, accounting for 60% of the total variance, and identified the variables and sampling times indicative of each. In conclusion, there are differences in the hormonal, but not inflammatory, responses to hip and knee arthroplasty. Little evidence was found for an important effect of pathology on the changes associated with knee surgery. Factor analysis provided a useful summary of the data.

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