[home] [Personal Program] [Help]

---

Session: Poster session II
Session starts: Thursday 24 January, 16:00

---

Mauricio Saldivar (Delft University of Technology / Radboudumc)
Thomas Anijs (Radboudumc)
Dennis Janssen (Radboudumc)
Nico Verdonschot (Radboudumc)

Abstract:
In cementless total knee arthroplasty (TKA) high micro-motions at the implant-bone interface are found to prevent local bone ingrowth, which can result in early aseptic implant loosening. In this study, micro-motions underneath a primary tibial tray are computed using the finite element method (FEM). Representation of intra-surgical bone damage is one of the factors which should be taken into account to simulate realistic micro-motion conditions. METHODS: A tibial FEM model was used to compare influence of four material models; a linear elastic model, a softening Von Mises (VM) criterion model, and respectively an ideal and a hardening isotropic crushable foam plastic model (CFM). Geometry and material properties were based on a calibrated CT-scan; the resulting tibia was virtually resected and implanted with a trabecular metal tibial component. An implantation test was performed to predict intra-surgical damage. Loading conditions representing consecutive cycles of walking, sitting, stair climbing and cycling were applied to estimate micro-motions during daily living. A micro-motion threshold of 40 μm is used to determine the extent of local bone ingrowth. RESULTS SECTION: The softening VM criterion model was the plastic material model in which the highest volume of excessive deformation, was found, followed by the hardening and ideal isotropic CFM respectively. Ingrowth distributions underneath the baseplate of the LE model was in line with both CFM’s, while less extensive in the VM model. Distinct differences between the LE and plastic models were found around the pegs, since relative LE ingrowth was very low. DISCUSSION: Current findings stress the importance of using an adequate plastic material model and inclusion of the implantation process when considering initial implant stability in TKA. When interpreting the extent and distribution of ingrowth, it is important to keep in mind non-implant specific native knee loads and an assumed binary micro-motion threshold of 40 μm are used. Also other mechanical stimuli may be involved in primary stability of press-fit implants, as increased strains are also linked to ossification. SIGNIFICANCE: Realistic simulations of peri-prosthetic micro-motions and related bone ingrowth can prevent cases of implant loosening and improves analyses of subsequent long-term bone remodeling in cementless implants.