Hip (THR) or knee (KT) prosthetic surgery is a bleeding surgery with an average blood spoliation of about 1 liter and an average decrease of about 3 g/dl in hemoglobinemia (Hb). Consequently, anemia is observed postoperatively in almost all patients (between 85% and 99% depending on the preoperative Hb value). In all cases, anemia-related events delay the patient's recovery, favor the occurrence of complications and prolong the length of stay. The immediate treatment of acute postoperative anemia is based on transfusion of red blood cells (RBCs). However, this presents several risks for the patient. The first is immediate and associated with the procedure: risk of error with ABO/Rhesus incompatibility, sepsis, pulmonary edema, etc. The second is a medium-term risk, with an increased risk of infection after prosthetic hip or knee surgery. In the long term, immediate postoperative blood transfusion is associated with higher mortality. In order to reduce the likelihood of a patient receiving RGCs, strategies have been developed within a "Patient Blood Management" (PBM), which could be translated as "Personalized Blood Transfusion Management". This strategy is based on 3 pillars: preoperatively, to ensure a patient's hemoglobin level of at least 13 g/dl; during the procedure, to limit blood loss; and postoperatively, to limit the indications for blood transfusion and the number of RGCs to the strict necessary. As the main determinant to trigger the prescription of a blood transfusion is the Hb value, the objective is that the lowest value of hemoglobinemia (Hb_nadir) postoperatively is as close as possible to 10 g/dl. The objective of this study is to describe, by means of the data available in the computerized patient record of patients undergoing scheduled THR or PTG operations at the Paris Saint Joseph Hospital, a prediction equation for Hb_nadir < 10 g/dl and, thus, to prescribe iron and ESAs only in patients who require them.

Inclusion Criteria:

- Patient operated on for elective hip or knee arthroplasty within the Paris Saint Joseph hospital site (HPSJ) between January 1, 2019 and December 31, 2021. Over the 36-month period, 1281 patients underwent THP (approximately 60%) or TKP (approximately 40%) surgery.

Exclusion Criteria:

• Patient who received iron infusion and/or injections of erythropoiesis stimulating agents within one month prior to surgery
• Patient who received an infusion of packed red blood cells in the month prior to surgery
• Absence of preoperative hemoglobinemia
• No postoperative hemoglobinemia
• Patient who had surgery in the previous month
• Patient operated on both sides (hip or knee) during the same operation
• Patient operated in emergency
• Patient with a hereditary anemia
• Patient opposing the use of his data for this research
• Patient under guardianship or curatorship
• Patient deprived of liberty
• Patient under court protection

- Patient operated on for elective hip or knee arthroplasty within the Paris Saint Joseph hospital site (HPSJ) between January 1, 2019 and December 31, 2021. Over the 36-month period, 1281 patients underwent THP (approximately 60%) or TKP (approximately 40%) surgery.