Utilize previously developed mathematical model to determine in vivo knee mechanics (kinematics, forces, stresses, areas and sound) for subjects having a Sigma Posterior Stabilizing (PS) mobile bearing (MB) total knee arthroplasty (TKA). There are several hypotheses for this study, although the most prominent is: Subjects having a Sigma RP PS TKA will experience polyethylene bearing rotation at 10 years post-operative, similar to their previous evaluations at six months, two years and five years.