EFFECT OF FEMORAL COMPONENT ROTATION AND PATELLAR DESIGN ON PATELLAR FORCES

A force transducer attached to the patella was used to measure patella r contact forces after total knee arthroplasty for neutral femoral com ponent position and for 10 degrees internal and external femoral compo nent rotations. Knees were cycled continuously under load from 10 degr ees to 110 degrees flexion. Two designs of knee replacement with diffe ring degrees of intrinsic tibiofemoral constraint were studied, Additi onally, contact forces for a dome shaped patella and a modified dome s haped patella (a patellar component with a central projection surround ed by a peripheral flat region) were compared, When using the design w ith relatively high intrinsic tibiofemoral constraint, there were no s ignificant changes in patellar contact forces after axial rotation of the femoral component, When using the design with relatively low intri nsic tibiofemoral constraint and averaging over the range of flexion a ngles tested, the mediolateral component of the patellar contact force increased approximately 17% after 10 degrees internal rotation compar ed with neutral rotation, and the normal component of the patellar con tact force decreased approximately 8% after a 10 degrees external rota tion compared with 10 degrees internal rotation of the femoral compone nt, The inferosuperior component of the patellar shear force, when usi ng the modified dome shaped patellar component, was significantly lowe r than for the dome shaped patella.