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.

Statistical modeling to characterize relationships between knee anatomy and kinematics

“…The finding that more gradual radius changes through the flexion facet of Mode 1‐ led to reduced posterior tibial translation (or anterior femoral translation) (Figs. 4 and 6) agreed with Clary et al, which observed that an increasing “braking” radius results in less anterior motion and more rollback of the femur with respect to the tibia. Early flexion differences in the lowest point representation were affected by shape of the distal region of the femoral condyles with Mode 1− having a more flattened profile.…”

“…In the natural knee, Hoshino et al identified correlations between the condylar offset ratio and anterior‐posterior (AP) translation and between condylar twist angle and internal–external (IE) rotation . While considering total knee replacement (TKR) implants, Clary et al investigated abrupt versus gradually reducing changes in the femoral sagittal radius of curvature and their impact on TF AP motion, particularly at mid‐flexion …”

Case series report of navigation-based in vivo knee kinematics in total knee arthroplasty with a gradually reducing femoral radius design

“…In a cadaver study, Clary et al. [8] showed that paradoxical anterior translation during mid-flexion occurred at the site where the femoral radius suddenly reduced in the conventional PFCΣ CR, and was improved using Attune CR TKA with a gradually reducing femoral radius. This improvement was caused by the enhanced compatibility of the insert and femoral component.…”

“…indicated that a TKA prosthesis with a gradually reducing femoral radius improved this anterior instability [8]. In this study, we examined if this phenomenon occurs in vivo .…”

Posterior-stabilized total knee arthroplasty: a matched pair analysis of a classic and its evolutional design

“…The most notable difference in the PS femoral component of this system is a multiradius transition at the distal component to posterior condyle region. This has been attributed to conferring greater mid flexion stability as the implanted knee moves from extension to flexion as a result of the more gradual change in the femoral component radius of curvature [12] (Fig. 1).…”