Total knee arthroplasty (TKA) is a treatment for advanced femoro-tibial osteoarthritis. This surgery is justified in case of significant discomfort and failure of medical treatment.

The functional results of TKA are good with a recovery of 6 months - 1 year. Nevertheless, very few patients forget their prostheses. A United Kingdom study assessed patient satisfaction in a cohort of 10,000 patients more than one year after TKA: nearly 20% were not satisfied with their TKA.

The knee is indeed a complex articulation that works differently in the three space plans. Current knee prostheses are trying to replicate this biomechanics and get as close as possible to the anatomy of a native knee.

Bellemans et al. found in 250 asymptomatic patients 32% of men with a constitutional varus greater than 3 ° and 17% of women. Restoration of normal knee function can also be achieved by restoring a moderate constitutional deformity present preoperatively. The objective of the femorotibial alignment was dogmatically fixed at 180° (mechanical femorotibial alignment). In recent years, some surgical teams have attempted to reproduce the preoperative constitutional deformity in varus or valgus with the prosthesis. This femorotibial alignment is called kinematic alignment. This kinematic alignment has already been studied in several randomized studies and has demonstrated improved functional scores. However, these studies focused on specific TKA, which are posterior cruciate TKA, and the assessment was subjective through functional scores. In addition, these TKA were often made with patient specific instrumentation (PSI). Some studies have evaluated walking kinematics after TKA with kinematic alignment. But it was again TKA retaining the posterior cruciate ligament.

The investigators would like to prospectively evaluate the restoration of the medially stabilized TKA walking kinematics (medial-stable TKA or ball in socket stability) implanted with a kinematic alignment compared to a mechanical alignment.

Inclusion Criteria:

• Both sex
• Adults between 55 and 80 years
• Diagnosis of internal or global disabling femorotibial gonarthrosis Indication of total first knee arthroplasty (unilateral), using a Sphere type prosthesis (Medacta)
• Constitutional deformity in varus between 3 ° and 10 °
• Fulfilling the pass conditions of a KneeKG walking test: Unipodal support possible for 1 minute, run for 5 min at a speed of at least 0.8 km / h
• Affiliated to a social security system
• Patients able to understand and fulfill the requirement of the study

Exclusion Criteria:

• TKA bilateral
• TKA to change an Uni-compartmental prosthesis
• History of femoral or tibial fracture
• History of femoral or tibial osteotomy
• Associated gesture at the same time (allograft, osteotomy)
• External femorotibial gonarthrosis
• Angle Hip Knee Ankle > 178 °
• Constitutional distortion> 10 °
• Refusal to participate in the study
• Persons deprived of their liberty by a judicial or administrative decision, persons under psychiatric care, persons admitted to a health or social institution for purposes other than research
• Adults subject to a legal protection measure
• breastfeeding or pregnant women
• Patient already participating to another clinical trial that might jeopardize the current trial