Functional recovery after total knee replacement (TKR) is characterized by an incomplete muscle strength due to arthrogenic muscle inhibition (AMI) and tendency to estimate the functional level. These deficits could be related to alteration of sensory feedback, and could influence the ability to modulate patients' motor performance.

To date, there are not studies investigatin the ability to modulate the motor performance in patients with TKR compared to healthy age-matched subjects.

In this study 20 patients with TKR and 20 healthy will be included . Inclusion criteria are: age between 40 and 80 , TKR for primary knee osteoarthritis, knee flexion ≥ 90° and complete knee extension, ability to perform a sit to stand on a 46 cm high chair and to walk for at least 50 meters without aids. Exclusion criteria: patients undergoing TKR after traumas, previous tibial or femoral osteotomy, partial or complete revision surgery. subjects with psychiatric and/or cognitive impairments, or with neurological, musculoskeletal or other disorders that could influence motor or functional recovery will be also exluded.

The aim of the study is to investigate the ability in motor performance modulation in patients after TKR compared to healthy age-mtched subjects.

Primary endpoint is to investigate this ability during a leg extension performed in open kinetic chain. This ability will be also evaluated during a Sit To Stand and during walking (with 10 Meters Walking Test). Secondary endpoint is to investigate pain, rate of perceived exertion and perceived load symmetry during the three tests. In both healthy and TKR groups these outcomes will be detected two times. In particular, in TKR group, patients will be tested the day before surgery and 5 days after surgery.

This study is aimed at conducting a survey in healthy subjects and in a population of subjects undergoing TKR . Participants will undergo an acquisition similar to others already described in the literature and without adverse events. Tests will last about 60 minutes and during them, will be used the equipment of Motion Analysis Lab of "Humanitas Research Hospital".

Inclusion Criteria:

• Age between 40 and 80 years
• TKR because of primary gonarthrosis
• Flexion ≥ 90° and complete knee extension
• Able to perform a Sit to Stand from a 46 cm high chair, without upper limb use
• Able to walk at least 50 meters without walking aids

Exclusion Criteria:

• TKR because of traumatic event
• Patients undergone to tibial or femoral osteotomy
• Partial or Total TKR revision
• Cognitive and psychiatric impairments
• Presence of neurological, internist or musculoskeletal system pathologies that may affect functional or motor recovery

Healthy subjects will have to comply with all the eligibility criteria just mentioned except for the inclusion criterion: Intervention of TKR following primary gonarthrosis

Patients: subjects undergoing total knee replacement intervention because of primary gonarthrosis.

Healty subjects: people with no known significant health problems who are recruited to participate as controls for a patient Group.