Analysis of Competitive Posterior Cruciate Retaining (PCR) and Posterior Stabilized (PS) Total Knee Arthroplasty (TKA)

Inclusion Criteria: 1. Subjects will have one of the following implant types: 1) Stryker Triathlon PCR TKA (28 subjects), 2) Stryker Triathlon PS TKA (28 subjects), 3) Zimmer Persona PCR TKA (28 subjects) and 4) Zimmer Persona PS TKA (28 subjects). 2. Patients must be at least three months post-operative. 3. Participants must not experience any pain or other post-operative complications. 4. Participants must have a stable TKA and be capable of performing a deep knee bend activity. 5. Participants must weigh less than 300 lbs., not underweight (BMI \< 18.5) or too obese (BMI\>35). 6. Must be in the age range of 18 years to 85 years (both inclusive). 7. Participants must be able to perform the required activities without concern. 8. Subjects must be willing to sign the Informed Consent (IC) form to participate in the study. 9. Patients who do not have previous surgery on the implanted knee that might restrict their movement. Exclusion Criteria: 1. Pregnant, potentially pregnant, lactating females or of childbearing age. To satisfy radiation protocol, each female subject will be asked if she is pregnant, or possibly could be pregnant. A pregnant person will not be allowed to participate in the study. (All potential female study patients will be asked if they are premenopausal or if they have undergone a hysterectomy. If the possibility of pregnancy exists, a pregnancy kit will be given to the patient at the informed consent meeting, just prior to the fluoro. Results of the test will be recorded in a test log. Any female patient showing a positive test will be excluded from testing.) 2. Subjects without the required type of knee implant. 3. Cannot have pain in other parts of the body that would prohibit the subject from performing the activities). 4. Cannot have ligamentous pain and/or laxity. 5. Unwilling to sign IC/HIPAA form(s). 6. Does not speak English. 7. Patients who have enrolled in a fluoroscopic kinematic study within the past year. 8. Patients currently involved in any personal injury litigation, medical/legal or worker's compensation claims. 9. Patients with known drug or alcohol abuse histories or psychological disorders that could affect ability to complete all aspects of the study. 10. Patients with neurological or musculoskeletal disorders that might adversely affect weight-bearing motion ability.