Effects of knee flexion following knee arthroplasty on postoperative blood loss: a study on 50 patients

Increased public and medical concerns regarding transfusion-associated infections and the cost involved in blood transfusion necessitate the imperative to justify transfusions. Since knee arthroplasties are often performed under tourniquet control, most blood loss occurs in the postoperative period. This makes this surgery ideally suited for evaluating techniques that decrease postoperative blood loss. A prospective study was carried out on 50 primary knee replacements (25 knees flexed, 25 knees extended) to evaluate the effect of maintaining the knee in 90 degrees of flexion in the immediate (24 h) postoperative period on postoperative need for transfusion. The volume of blood collected in the drains was used to estimate postoperative blood loss. Drop in haemoglobin was estimated by calculating the difference in preoperative and postoperative concentrations. Patients in the group with flexion of the knee lost a mean of 313 ml blood (2.0 g/dl drop in Hb); this was significantly less than that in the control (extension) group which lost 590 ml (3.2 g/dl drop in Hb). This decreased blood loss in the flexion group was reflected in the transfusion rates: 1 patient in the flexion group requiring transfusion compared to 6 patients in the extension group. Knee flexion following knee replacement is a simple yet effective method for decreasing postoperative blood loss and therefore transfusion rates.