Introduction: Perioperative blood losses in TKR (total knee replacement) are significant and it has been determined that hidden blood loss is frequently more significant than visible blood loss. The aim of this study is to determine if there were any differences in blood loss due to the timing of ischemia cuff release during TKR.

Materials and methods: We studied 103 patients divided into 2 groups; in group A, of 41 patients, the cuff was released when all the bon cuts had been carried out, hemostasis of bleeding blood vessels was carried out and pressure was elevated until the end of surgery and placement of the compressive bandage. In group B, of 62 patients, once the prosthesis was cemented the cuff was released, hemostasis was applied, the wound was sutured and the compressive bandage was put in place without elevating the cuff pressure. In both groups we recorded intraoperative blood loss, both external blood loss and through the drainage, which was removed at 36–48 hours. Hidden blood loss was determined using the formula of Naddler et al that considers sex, weight, height and preoperative hemoglobin and hemoglobin 4 days after surgery.

Results: In group A the mean volume drained was 502 ml, hidden blood 928 ml, with a total loss of 1429 ml. In group B the mean volume drained was 567 ml, hidden blood 764 ml and total loss of blood 1331. There were no significant differences between both groups.

Conclusions: The significance of blood loss in TKR is therefore confirmed, especially hidden blood loss. There were no statistically significant differences according to the moment at which the ischemia cuff was released.

Total knee arthroplasty had been reported to present similar amount of blood loss in external and hidden form. We studied whether lateral patellar release made any differences on both forms of blood loss.

Material and methods: We studied 91 patients (83 women an 8 men) undergoing primary unilateral total knee arthroplasty cemented posterior stabilised with patellar substitution, in 40 lateral patellar release were performed. Surgery is performed under tourniquet. The blood drain was recorded. We assumed that blood volume on the fourth postoperative day was the same as before surgery. Blood volume was estimated taking sex, body mass and height into account. Haemoglobin was recorded on preoperative and four days postoperative.

Results: We found more external blood loss in patients without lateral patellar release (p< 0,05) but no statistical differences in total and hidden blood loss. The amount of hidden blood in both groups were more than twice (975 mL) the external blood loss (443 mL). No relationship was found between body mass and any type of blood loss.

Conclusions: Lateral patellar release made no difference in the amount of total blood loss. In total knee arthroplasty hidden blood loss doubled external blood loss.