Background: Total knee arthroplasty is effective to regain quality of life. Standing up from and sitting down\non a chair and stair stepping motion are important in daily living. We previously reported in vivo kinematics\nof this implant during a stepping exercise. The purpose of this analysis was to assess in vivo knee motion\nduring standing up from and sitting down on a chair and determine the motion pattern in patients with\nthe unique knee prosthesis.\nMethods: A total of 15 patients implanted with Bi-Surface PS were assessed during standing up from and\nsitting down on a chair. The Bi-Surface PS knee is a posterior-cruciate substitute prosthesis with a unique\nball-and-socket joint in the mid-posterior portion of the femoral and tibial components. Patients were\nexamined during standing up from and sitting down on a chair using a two-dimensional to three-dimensional\nregistration technique.\nResults: During standing up from and sitting down on a chair from minimum to 30�° knee flexion, anterior\nfemoral translation was slight. From 30�° knee flexion to maximum flexion, the kinematic pattern was a medial\npivot and rollback.\nConclusions: This study demonstrated that the knee motion kinematic patterns observed in this study were\nnot similar to normal knee kinematics and derived from the unique design of the Bi-Surface PS.
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