Perioperative platelet consumption due to blood loss and coagulation stimulates de novo synthesis of juvenile platelets, which are characterized as RNA rich (reticulated) and HLA-I rich and more reactive. This study was performed to investigate, if prothrombotic juvenile platelets are synthesized in response to major orthopedic surgery, thereby orchestrating the common postoperative increased thrombotic risk.

Twenty-seven patients undergoing total endoprosthesis or adjustment osteotomy were enrolled. Blood was drawn preoperative (day0) and postoperative (day1,3,5), incubated with 550µM Aspirin to equalize platelet function for the postoperative pain therapy and washed platelets were prepared. Juvenile platelets were assessed by measuring the immature platelet fraction (IPF), HLA-I and SYTO13 staining. Platelet activation was assessed via CD62p expression and procoagulant platelet formation (phosphatidyl serine+/CD62p+).

Post surgery, none of the age markers tested, changed significantly (Fig. 1). Therefore, the overall proportion of juvenile platelets remained unaltered postoperatively. Congruently, platelet activation upon TRAP-6 stimulation showed only minor variation (Fig. 2A). Similar results were obtained after stimulation with ADP or CRP. However, postoperative platelet activation greatly differed between individuals (range 1.2-4-fold increase). Furthermore, the proportion of procoagulant platelets upon co-stimulation with TRAP-6 and convulxin remained stable at approximately 10%. Juvenile, HLA-rich platelets (top 20%) expressed 4 times more CD62p compared to HLA-poor platelets (lower 80%) upon TRAP-6 stimulation (p<0.001, Figure 2B). Activation of both subfractions also did not change after surgery.

Major orthopedic surgery does not seem to alter the proportion of juvenile platelets or global platelet function. Activation was higher in the juvenile compared to older platelet population but did not rise significantly postoperative. Consequently, the postoperative increased thrombotic risk is likely not caused by a rise of young hyperreactive platelets. However, a platelet associated risk of thrombosis may be present in individuals showing a more pronounced and persistent enhanced platelet activation pattern after surgery.

Disclosures available upon request