Computer navigated total knee replacement is less invasive than traditional methods, as it avoids the use of intramedullary alignment rods. A previous study (Kalairajah et al, 2005) has shown that computer-assisted techniques may reduce blood loss in comparison to traditional methods. Our study uses a more accurate method of assessing blood loss, and the sample size is larger.

136 TKR patients were selected from a prospectively collected database of all those undergoing arthroplasty at our institution; 68 had standard TKR and 68 had a computer assisted TKR. In each group, half had BMI in the range 20–30, and half had BMI between 30–40. There were an equal number of males and females in each group. All patients received a standardised anaesthetic, and had tranexamic acid at the start of the procedure.

Total body blood volume was calculated from patient height, weight and sex, using the model described by Nadler, Hidalgo & Bloch (1962). This was then used, together with pre- and post-op haematocrit and volume re-infused or transfused, to calculate true blood loss, as described by Sehat, Evans, and Newman (2004). This method is considered to be more reliable than measuring drain output, as it takes account of “hidden” (internal) losses.

The average blood loss was 603ml in the standard TKR group, and 448ml in the computer assisted TKR group. Student’s t-test showed that this difference was statistically significant (p = 0.007). Regression analysis showed no significant difference between obese and non-obese patients, nor a difference between sexes. Blood loss in both groups was lower than in a previous study, which we attribute to our department’s routine use of tranexamic acid.

We conclude that computer-assisted total knee replacement leads to significant reduction in blood loss when compared with traditional techniques. This confirms previous reports.