The effect of body mass index on the risk of post-operative complications during the 6 months following total hip replacement or total knee replacement surgery

Objective: To assess the effect of obesity on 6-month post-operative complications following total knee (TKR) or hip (THR) replacement.Design: Data for patients undergoing first THR or TKR between 1995 and 2011 was taken from the Clinical Practice Research Datalink. Logistic regression was used to assess whether body mass index (BMI) was associated with 6-month post-operative complications [deep vein thrombosis or pulmonary embolism (DVT/PE), myocardial infarction (MI), stroke, respiratory infection, anaemia, wound infection, urinary tract infection or death] after controlling for the effects of age, gender, smoking, drinking, socioeconomic status (SES), co-morbidities and medications.Results: 31,817 THR patients and 32,485 TKR patients were identified for inclusion. Increasing BMI was associated with a significantly higher risk of wound infections, from 1.6% to 3.5% in THR patients (adjusted P <0.01), and from 3% to 4.1% (adjusted P <0.05) in TKR patients. DVT/PE risk also increased with obesity from 2.2% to 3.3% (adjusted P <0.01) in THR patients and from 2.0% to 33% (adjusted P <0.01) in TKR patients. Obesity was not associated with increased risk of other complications.Conclusion: Whilst an increased risk of wound infection and DVT/PE was observed amongst obese patients, absolute risks remain low and no such association was observed for MI, stroke and mortality. However this is a selected cohort (eligible for surgery according to judgement of NHS GPs and surgeons) and as such these results do not advocate surgery be given without consideration of BMI, but indicate that universal denial of surgery based on BMI is unwarranted.