In Vivo Comparison of Knee Kinematics for Subjects Implanted With Either a ConforMIS or Traditional Knee Implant

Study Summary

A better understanding of knee joint kinematics is important to explain the premature polyethylene wear failures within total knee arthroplasties (TKAs) and to help design a prosthesis that most closely approximates the normal knee. Previously, most experimental studies of knee kinematics have involved cadaveric, in vitro analyses, or have not tested the knee in a weight-bearing mode. Others have used exoskeletal linkages and skin markers that permit error due to undesired motions between markers and the underlying bone. More recently, fluoroscopy has been used to assess in vivo kinematics for subjects having a TKA. ConforMIS has attempted to follow a clearly different path than the major orthopaedic companies. They have chosen to offer patients a personalized knee implant based off of each patient's femoral and tibial bone geometry. The hypothesis is that these subjects will experience a more normal-like kinematic pattern, eliminating paradoxical anterior sliding during weight-bearing knee flexion. Therefore, the objective for this study is to analyze the in vivo kinematics for 25 patients implanted with a personalized ConforMIS TKA and 25 patients implanted with a traditional TKA design to determine if there are any kinematic differences between these TKA designs.

Primary Outcome

There are multiple parameters captured by fluoroscopy that will be assessed during these 4 activities including: 1. Anterior/posterior medial and lateral condyle contact positions 2. Axial rotation of the femoral component relative to the tibial component 3. Condylar lift-off will be determined by measuring the distances from the medial and lateral condyles to the polyethylene insert surface 4. Weight-bearing range-of-motion.

Interventions

• DEVICE Conformis CR Total Knee Replacement
• DEVICE Off the Shelf