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 as well as to the GMK UC Mobile Bearing during level walking, stair descent and downhill walking by means of videofluoroscopy.

Total arthroplasty of the knee (TKA) aims to relieve patient pain and improve functionality of the joint. To maintain sufficient range of motion, but also not overload the surrounding soft tissue structures, reproduction of tibio-femoral kinematics of the healthy knee is thought to be beneficial. In previous studies, it has been shown that the medial condyle, described by the centre of the medial condylar sphere, does not move anterioposteriorly during progressing joint flexion, whereas the lateral condyle has been observed to translate in a posterior direction producing tibial internal rotation with flexion (Freeman and Pinskerova 2003, Pinskerova, Johal et al. 2004, Freeman and Pinskerova 2005). The GMK Sphere prosthesis is specifically designed to mimic the healthy kinematics with providing a medial pivot.

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 as well as to the GMK UC Fixed Bearing. The study includes the simultaneous assessment of the 3D kinematics of the TKA by means of an automated moving fluoroscope and subsequent 2D/3D registration based on CAD models of the TKA, whole leg kinematics by means of skin markers and ground reaction forces during level walking, stair descent and downhill walking a 10° inclined slope. Precisely, the aim is to assess tibio-femoral kinematics in 8-10 TKA subjects implanted one or more years previously with the GMK Sphere prosthesis. In addition, 8-10 conventional GMK PS Fixed Bearing TKA subjects, as well as 8-10 GMK UC Mobile Bearing TKA subjects will be measured to provide a comparison against the GMK Sphere prosthesis kinematics.

Inclusion Criteria:

• Female or male
• Age: 40 to 100 years
• Unilateral TKA
• ≥ 1 years postoperatively
• BMI ≤ 33
• Good outcome, WOMAC between 0 to 28 (0-14 (Excellent), 15-28 (Good)) No pain subjects, VAS ≤ 2
• Good health condition, adequate for test procedure

Exclusion Criteria:

• Other actual significant problem on lower extremities
• Any other arthroplasty at the lower extremities
• Subject incapable to understand and sign informed consent
• Pregnancy at time of testing
• Incapable of performing the motion tasks
• Misaligned TKA (≥ ± 3° from mechanical axis)

Participants fulfilling all of the following inclusion criteria are eligible for the study. The presence of any one of the following exclusion criteria will lead to the exclusion of the participant.