ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

EVALUATION OF FEMORAL COMPONENT MICROMOTION
AFTER TOTAL KNEE ARTHROPLASTY: AN EXPERIMENTAL
STUDY
1. ABSTRACT
N. Conlisk 1 , P. Pankaj 2 and C.R. Howie 3
Orthopaedic surgeons use stems in revision knee surgery to obtain stability when
damaged metaphyseal bone is encountered, however no consensus exists regarding stem
size or method of fixation. This in-vitro study investigated the influence of different
stem lengths and types of fixation on the pattern and level of micromotion at a range of
flexion angles. Micromotions were found to increase with flexion angle, indicating that
laboratory testing in extension is insufficient. Stemmed implants reduced micromotions
in comparison to stemless for uncemented cases. Cemented implant micromotions were
found to reduce to 1/3 of their equivalent uncemented levels. This study suggests that
the use of stems in revision knee surgery may not be necessary for cemented implants
when the metaphyseal bone is intact.
2. INTRODUCTION
Revision knee arthroplasty is predicted to increase worldwide [1]. There is a general
consensus among orthopaedic surgeons that stemmed tibial and femoral components are
required to obtain initial mechanical stability when there is deficient metaphyseal bone.
However little to no consensus exists regarding the appropriate selection of stem size,
length or method of fixation. Surgeons choose between cemented fixation, cementless
fixation and “hybrid” fixation of a cementless stem coupled with a cemented
metaphyseal component. All of these methods have theoretical advantages and
disadvantages. All have their proponents in the orthopaedic community. A recent
review of the current literature of long-term clinical outcomes did not demonstrate
sufficient evidence to recommend one method over the other [2].
Extensive literature exists on biomechanical testing of the tibia, in contrast relatively
few studies have been conducted on the distal femur [3-7]. Studies which have focused
on the distal femur have often been limited to loading in extension [3, 7]. Work carried
out by Wackerhagen et al. [4] investigated femoral component micromotion through the
use of a custom built dynamic knee rig capable of a range of flexion angles from 0°-90°.
Later work by Cristofolini et al. [5,6] employed a modified knee wear simulator to
investigate the long term loosening behaviour of both cobalt chromium and ceramic
1
PhD student, Edinburgh Orthopaedic Engineering Centre, RM 3.13, A.G.B Building, The Kings
Buildings, The University of Edinburgh, EH9 3JL, Edinburgh, UK
2
Senior Lecturer, School of Engineering, The Kings Buildings, The University of Edinburgh, EH9 3JL,
Edinburgh, UK
3
Consultant Orthopaedic Surgeon, Edinburgh Orthopaedic Engineering Centre, The University of
Edinburgh, EH16 4SA, Edinburgh, UK