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.

Each subject will be asked to perform five activities in one continuous sequence: (1) stand up from a chair, (2) walk up stairs, (3) walk down stairs, (4) level walking, and (5) a deep knee bend. Subjects will be video recorded from the waist down while performing the activities. The speed level of each trial will be based on the comfort level of the patient. The fluoroscopic images will be stored digitally for subsequent analysis on secure servers and workstations at the University of Tennessee.

Inclusion Criteria:

• At least 6 months post-op
• Between 40-70 years of age
• Body weight of less than 250lbs
• TKA patients will be judged clinically successful with an American Knee Society score of greater than 90
• Must have post-op passive flexion of 100 degrees with no ligamentous laxity or pain
• Participants must be able to walk on level ground without aids and ascend/descend stairs without assistance.
• Subjects will either a ConforMIS™ TKA or a traditional TKA manufactured by any other orthopaedic company.
• Patients must be between 160cm (5'3) and 193cm (6'4) tall.

Exclusion criteria:

• Subjects not willing to sign the Informed Consent and HIPAA forms to participate in the study
• BMI >40
• Pregnant females
• Surgical procedures conducted within the past 6 months other than TKA
• Subjects from the physician's list who do not meet study requirements
• Unwilling or unable to comply with study requirements
• Participation in another clinical study which would confound results

Patients who are at least 6 month post-op with a ConforMIS knee replacement or a standard total knee replacement who meets the inclusion/exclusion criteria