IN VIVO DETERMINATION OF DEEP FLEXION KNEE KINEMATICS FOR A FIXED AND MOBILE BEARING DEEP FLEXION TKA

Abstract

Previously, fluoroscopy has been used to determine the in vivo kinematics during gait, step-up maneuvers and flexion to nine tydegrees. Recently, TKAs have been designed for deep flexion maneuvers. Therefore, the objective of this study is to determine the in vivo kinematics for subjects implanted with either a fixed or mobile bearing deep flexion TKA from full extension to maximum knee flexion

Three-dimensional femorotibial contact positions for thirty-nine subjects, implanted by two surgeons, were evaluated using fluoroscopy into deep flexion. Nineteen subjects had a fixed bearing PS deep flexion TKA and 20 subjects were implanted with a mobile bearing deep flexion TKA. Both TKA designs have similar design features, including condylar geometries.

Seventeen of nineteen subjects implanted with a fixed bearing deep flexion TKA experienced posterior femoral rollback, while all 20subjects having a mobile bearing deep flexion TKA experienced poster iorfemoral rollback. On average, subjects experienced -5.1 and -8.1 mm of posterior femoral rollback, for the fixed and mobile bearing TKA, respectively. The maximum amount of posterior femoral rollback was -11.8 and -12.4 mm for subjects having a fixed and mobile bearing TKA, respectively. On average, subjects experienced 6.5 and 5.4 degrees of normal axial rotation for a fixed and mobile bearing TKA, respectively. The average amount of weight-bearing range of motion was 116 and 125 degrees for a fixed and mobile bearing TKA, respectively. Also, subjects having both TKA types evaluated in this study experienced excellent patellofemoral kinematics

This is the first study to evaluate femorotibial and patellofemoral knee kinematics into deep flexion for a fixed and mobile bearing TKA, designed for deep flex-ion activities. Both groups in this study experienced, on average and subject-to-subject comparison, excellent kinematic patterns. Also, both TKA types evaluated in this study achieved excellent weight-bearing range-of-motion, supporting the design goal for these TKA.