title: The influence of total knee arthroplasty geometry on mid-flexion stability: an experimental and finite element study.
abstract: Fluoroscopic evaluation of total knee arthroplasty (TKA) has reported sudden anterior translation of the femur relative to the tibia (paradoxical anterior motion) for some cruciate-retaining designs. This motion may be tied to abrupt changes in the femoral sagittal radius of curvature characteristic of traditional TKA designs, as the geometry transitions from a large load-bearing distal radius to a smaller posterior radius which can accommodate femoral rollback. It was hypothesized that a gradually reducing radius may attenuate sudden changes in anterior-posterior motion that occur in mid-flexion with traditional discrete-radius designs. A combined experimental and computational approach was employed to test this hypothesis. A previously developed finite element (FE) model of the Kansas knee simulator (KKS), virtually implanted with multiple implant designs, was used to predict the amount of paradoxical anterior femoral slide during a simulated deep knee bend. The model predicted kinematics demonstrated that incorporating a gradually reducing radius in mid-flexion reduced the magnitude of paradoxical anterior translation between 21% and 68%, depending on the conformity of the tibial insert. Subsequently, both a dual-radius design and a modified design incorporating gradually reducing radii were tested in vitro in the KKS for verification. The model-predicted and experimentally observed kinematics exhibited good agreement, while the average experimental kinematics demonstrated an 81% reduction in anterior translation with the modified design. The FE model demonstrated sufficient sensitivity to appropriately differentiate kinematic changes due to subtle changes in implant design, and served as a useful pre-clinical design-phase tool to improve implant kinematics.
authors.affiliation: Computational Biomechanics Lab, University of Denver, Denver, CO, USA. cclary1@its.jnj.com
authors.forename: Chadd W
authors.initials: CW
authors.lastname: Clary
authors.forename: Clare K
authors.initials: CK
authors.lastname: Fitzpatrick
authors.forename: Lorin P
authors.initials: LP
authors.lastname: Maletsky
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Rullkoetter
mesh_terms: D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D005269:Femur / Q000473:pathology / Q000503:physiopathology*; D020342:Finite Element Analysis; D006801:Humans; D007720:Knee Prosthesis; D008954:Models, Biological; D011474:Prosthesis Design; D013977:Tibia / Q000473:pathology / Q000503:physiopathology*