Department of Mechanical Engineering, Imperial College London
Doi
Abstract
Long-term survivorship of a total knee replacement (TKR) relies on the strength of
bone around the implant and its initial stability. Aseptic component loosening caused
by mechanical factors is a recognised failure mode for knee prostheses. Bone
resorption due to “stress-shielding” of the stiff stemmed implants will potentially lead
to weakened bone strength, and presents a challenge for revision TKR surgery. The
aim of this study was to develop analytical methodologies for the investigation of
fixation performance of TKR, and to gain a better understanding of the prosthetic
design requirements, addressing two major mechanical problems of bone remodelling
and aseptic loosening.
Patient-specific finite element (FE) modelling incorporated with a strain-adaptive
bone remodelling theory was used to simulate bone remodelling responses of the postoperative
tibial fixation. The choice of cementing technique was found to influence
the remodelling behaviour; cemented fixationmodelled as a firm anchorage of the
prosthesis onto the bone, was predicted to induce greater stress-shielding effect
consequently leading to severe proximal bone resorption; for a fixation relying on
biological attachment of bony ingrowthmodelled as a less firmly anchored boneprosthesis
interface, lesser proximal bone resorption was predicted.
The consideration of bone remodelling in FE simulations for fixation analyses is
paramount as it influenced the risk prediction of aseptic loosening between prosthesis
designs. The cement tensile stresses and bone-prosthesis interface micromotions
predicted were different prior to and after bone adaptation. FE predictions of the MIS
mini-keel and standard stemmed prosthesis fixations after simulating six months of
bone adaptation correlated well with the RSA measurements at a similar period.
A modified in-vitro technique of measuring bone-prosthesis relative micromotion was
developed for relating initial stability of the cemented and cementless (press-fit) tibial
prostheses fixations to late aseptic loosening. The developed computational and invitro
methods should be applicable to other joint replacements
