This is a prospective multicenter cohort study to evaluate the prognostic value of new biological markers in predicting thrombotic events after orthopedic surgery. According to the inclusion and non-inclusion criteria below, the study will include 387 major subjects who will undergo first-line total knee replacement and will receive the same standard prophylactic treatment: anticoagulation with Lovenox® (enoxaparin) 4000 IU/d subcutaneously 6 to 8 hours postoperatively and then daily for 15 days in combination with compression stockings.

Recruitment and follow-up of patients will be carried out in 3 hospitals by the respective orthopedic teams. Three hundred and eighty-seven patients will be included in the study, over a period of 36 months: 200 in Marseille, 100 in Nice and 87 in Nîmes.

The objective of the study was to evaluate the prognostic capacities of the coagulolytic balance of MVs measured after surgery at D0 in the occurrence of a symptomatic or asymptomatic venous thromboembolic event revealed by echodoppler at 1 month after total knee replacement surgery.

The management of the subjects is unchanged from the current recommendations and will be homogeneous between the three inclusion centers. Patients will be hospitalized for 5 days and will receive the usual prophylactic anticoagulant treatment with Lovenox® (enoxaparin sodium; LMWH) 4000 IU/d subcutaneously 6 to 8 hours postoperatively and then daily for 15 days in combination with compression stockings, which corresponds to the management of a PTG according to current recommendations.

Inclusion Criteria:

• Subject, male or female, aged 18 to 85 years (upper age limit classically used in the literature of PTG79-81)
• First-line TKP (knee native to any prosthesis) performed to treat primary or secondary osteoarthritis.

In case of contralateral PTG, a delay of 12 months between the 2 prostheses will be respected according to the habits of the inclusion centers.

• ASA score <4 (American Society of Anesthesiologists)
• No contraindication to prophylactic treatment with low molecular weight heparin (LMWH)
• Subject not taking anticoagulant or antiaggregant therapy at therapeutic dose
• Subject who has signed the informed consent form
• Subject affiliated to the social security system

Exclusion Criteria:

• Subjects with a history of sepsis, tumor or trauma in the considered joint
• Subject with sepsis or acute infection
• Immunocompromised subject (HIV, transplant, chemotherapy, leukemia, glucocorticoids >3 months)
• Subjects with severe respiratory, circulatory or cardiac pathologies involving anticoagulant treatment likely to influence the coagulolytic balance.
• Subject with severe renal insufficiency (creatinine clearance < 30ml/min)
• Subject refusing to participate in the study or not signing the informed consent or unable to adhere to the study procedures
• Subjects who are minors, pregnant or breastfeeding, not affiliated with the social security system, or deprived of liberty
• Subject already included in an interventional trial (which may alter the results of that study)