Blood loss following total knee replacement in the morbidly obese: Effects of computer navigation.

Computer navigated total knee arthroplasty (TKA) has several proposed benefits including reduced post-operative blood loss. We compared the total blood volume loss in a cohort of morbidly obese (BMI>40) patients undergoing computer navigated (n=30) or standard intramedullary techniques (n=30) with a cohort of matched patients with a BMI<30 also undergoing navigated (n=31) or standard TKA (n=31). Total body blood loss was calculated from body weight, height and haemotocrit change, using a model which accurately assesses true blood loss as was maximum allowable blood loss which represents the volume of blood that can be lost until a transfusion trigger is required. The groups were matched for age, gender, diagnosis and operative technique. The mean true blood volume loss across all BMI's was significantly (p<0.001) less in the computer assisted group (1014±312ml) compared to the conventional group (1287±330ml). Patients with a BMI>40 and a computer navigated procedure (1105±321ml) had a significantly lower (p<0.001) blood volume loss compared to those who underwent a conventional TKA (1399±330ml). There was no significant difference in the transfusion rate or those reaching the maximum allowable blood loss between groups. This study confirms a significant reduction in total body blood loss between computer assisted and conventional TKA in morbidly obese patients. However computer navigation did not affect the transfusion rate or those reaching the transfusion trigger in the morbidly obese group. Therefore computer navigation may reduce blood loss in the morbidly obese patient but this may not be clinically relevant to transfusion requirements as previously suggested.