Effect of tibial component position on patellar strain following total knee arthroplasty.

Patellar fracture following total knee arthroplasty has been related to component alignment and tibiofemoral joint-line position. The purpose of this study was to determine the effect of anteroposterior displacement of the tibial component and inferosuperior displacement of the tibiofemoral joint line on patellar strain following total knee arthroplasty with a cruciate-substituting design. Patellar strain increased (decreased) with anterior and inferior (posterior and superior) displacement. When averaged across all flexion angles, the strain changed approximately 1.7%/mm of anteroposterior displacement and 1.0%/mm of inferosuperior displacement. For individual specimens, changes in strain as high as 3.2%/mm of inferosuperior displacement of the joint were seen. These changes in strain may be associated with changes in tibiofemoral joint-line position. These changes in strain may be a biomechanical indicator of the efficacy of retaining the preoperative position of the tibiofemoral joint line.