Primary arthroplasties are frequent interventions that can present hemorrhagic complications: postoperative hematoma, deglobulization justifying monitoring blood tests and blood transfusion if necessary.

The attitude regarding the drainage of the surgical site supposed to limit these events differs from one surgeon to another, even in the same team. Its use is common practice; for some, systematic. For others, depending on intraoperative findings or the patient's condition. For others, the drain is never laid.

Faced with the divergence of data from the literature on the benefit of the placement of a drain for intra and postoperative bleeding in knee arthroplasty, the lack of randomized prospective studies on large series of patients, and in a desire to homogenization and standardization of the operating procedure of our surgeons, investigators decided to conduct this prospective interventional, comparative and randomized study.

After obtaining the patient's consent and randomisation, the operating surgeon will have the information of placing or not a drain, lately at the end of the intervention so that the course of the intervention is not influenced by the prior knowledge of the patient randomization arm.

Investigators will carry out especially within the framework of this research 3 samples of a total of 10.7 ml of whole blood (appendix. 12.5) distributed as follows:

Sample no. 1 : 2.7 ml of blood in a hemostasis tube (sodium citrate tube) one day before the procedure (D-1) for the determination of the prothrombin level (PT), activated partial thromboplastin time ( TCA) and the INR or International Normalized Ratio.

Sample no. 2 : 4 ml of blood in a purple EDTA tube for NFS, one day before the operation (D-1) for the determination of hemoglobin ( Hb ) and hematocrit ( Hct ) Sample no. 3 : 4 ml of blood in a violet EDTA tube for NFS for the determination of hemoglobin ( Hb ) and hematocrit ( Hct ) on the fifth postoperative day (D5). This last assessment will be prescribed to the patient to be carried out in the rehabilitation center..

The knee prosthesis implantation surgical technique is performed according to the standard operating procedure of the orthopedic surgery team.

According to the operating standard procedure of our orthopedic department, the drain is non-aspirated for 6 hours and then put back under vacuum until the morning after the knee prosthesis operation.

Three months after the intervention the patient will be seen again in consultation and examined.

Inclusion Criteria:

• Patient consent
• Patient aged over 18 years
• Patient scheduled for primary knee arthroplasty

Exclusion Criteria:

• Patient expresses his/her opposition to participating in the study
• Patient scheduled for revision, revision or totalization arthroplasty
• Primary arthroplasty after septic arthritis
• Patient requiring an additional planned or unplanned surgical procedure such as TTTA, osteosynthesis for an intraoperative fracture and/or removal of material