In vivo patellar kinematics during total knee arthroplasty

Patellar maltracking after total knee arthroplasty often results in complications, including anterior knee pain, instability and impingement, and is therefore better resolved intraoperatively. Many factors can affect patellar kinematics during knee replacement, including component position, implant design, joint alignment, and soft tissue tensions. However, to our knowledge, the impact of arthroplasty on patellar kinematics has not been previously reported in vivo. A computer-assisted surgery (CAS) system was developed to measure the pre-arthroplasty patellar kinematics, display the distance between this path and the surface of the planned femoral component, and compare the post-arthroplasty path to the pre-arthroplasty path. Three surgeons from three centers used this CAS system to measure the in vivo pre- and post-arthroplasty kinematics of 18 patients. There was a small, but consistent, proximal shift in the tibial joint lines (mean: 4.2 mm), resulting in pseudo patella-baja, i.e., relatively more dist...