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

It must be noted however, that in this instance the fixed boundary condition resulted in a
much higher level of stress at the stem tip than the muscle supported femur (Fig. 3
region 4 and Fig. 4).
5. DISCUSSION
Figure 4: Sagittal plane section highlighting the influence restrained
and musculoskeletal boundary condition have on end of stem stress.
In this study FE models of the femur both pre and post total knee arthroplasty were
examined. The main aim of this work was to compare the influence of FE boundary
conditions on the mechanical environment of the femur. Based on the findings of this
study it is suggested that if the mechanical environment of the entire femur is of interest
as in the case of a long stemmed hip or knee implant, then musculoskeletal BCs are
essential to produce reliable results and to avoid artifacts due to unrealistic fixed
boundaries. However, if the mechanical stress/strain field close to the region of load
application is required (e.g. to examine primary stemless knee replacement or
unicompartmental knee replacements) simple restrained boundary conditions can
provide acceptable results at a greatly reduced computational cost.
As with any FE model, there are currently a number of limitations that must be
considered when interpretating the results presented in this study; only one position in a
single gait cycle has been investigated in the current study and as the muscles take a
more active role in the distribution of stress away from the bone in flexion it is likely
that a more noticeable difference between models may be observed. It must also be
noted that simplified loading was applied at the knee joint. In this instance only the
vertical reaction forces and patella-femoral forces were modelled, Shear forces and
moments were not considered. Finally only the passive properties of the muscles
directly connected to the femur were modelled in this study (i.e. Compressive
contribution of muscles running from pelvis to tibia/fibula not considered).