The objective of this research project is to perform a comparative study on the in vivo kinematics of the GMK Sphere prosthesis in comparison to the conventional GMK PS Fixed Bearing TKA and the GMK UC Fixed Bearing TKA.

Inclusion Criteria:

• subjects bearing a TKA with one of the studied prosthesis
• male and female older than 18 years old
• patients who are willing and able to sign an informed consent form

Exclusion Criteria:

• any case not described in the inclusion criteria

8-10 subjects with Medacta GMK Sphere TKA, 8-10 subjects with GMK PS Fixed Bearing TKA and 8-10 subjects with a GMK UC Fixed Bearing TKA will be involved in this project.

The subject recruitment will be based on the clinical reports of the follow-up examination including the standard clinical assessed parameters alignment, the Western Ontario and McMaster Universities Arthritis Index (WOMAC) and the visual analog scale (VAS)