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

and non-constrained. Few studies have been performed for both types of elbow
prosthesis: semi-constrained and non-constrained, but the heterogeneity of the results
leads to a great discussion about its conclusions. In fact, Recent studies, based on
records of orthopaedic Norway and Finland [1, 2], revel no significant differences in
success’ rates between these two types of arthrosplasties, with mean values of 92% at 5
years and 84% at 10 years. In both cases the aseptic loosening is pointed as the main
reason for the revision arthroplasty, and this collapse happens mainly due to the stressshielding
effect. Biomechanical studies, performed with the semi-constrained implants,
confirmed the presence of abnormally levels of tension in the bone around the implant,
which can be associated with the risk of loosening. However, for the non-constrained
implants, biomechanical studies are not available for corroborating a loosening risk, as
identified for the semi-constrained implants. In order to answer this question, a
comparisons in the structural behavior of the elbow joint in his native and arthroplastic
states, were carried out.
3. MATERIALS AND METHODS
For this study a native and arthroplastic finite element (FE) models of the humerus were
considered. According to this, the humerus structure were modeled, as well as the
humeral component of the IBP prosthesis. The models considered were constrained on
the diaphysis of the humerus and all the interfaces between the components were
fastened. The load cases applied to the condylar surface (native and arthroplastic) were
representative of daily activities. The material properties used are those referenced in
Table 1 and were assumed to be homogeneous, isotropic and linear elastic.
Table 1: Mechanical properties of the finite elements models.
Component Elastic module (GPa) Poisson ratio
Cancellous bone 0.155 0.3
Cortical bone 16.7 0.3
Humeral component (Co-Cr-Mo) 210 0.3
Bone cement 2.28 0.3
The load-cases applied were used to access the principal cancellous bone strain, before
and after arthroplasty,
4. RESULTS AND DISCUSSION
In the Figure 1 and 2, we can see the patterns of the principal strains at the cancellous
bone of humerus. Comparing the principal strains of the arthroplastic model, near the
humeral component, with the native model, we observed that the introduction of the IBP
implant tended to increase the bone strains along the implant length, in the metaphyseal
region, with peak strains observed at the implant tip. In fact, the increase of maximal
principal strains was 5.3 (1903 to 12073 µstrain) times and 3.5 (-2170 to -9746 µstrain)
times for the minimal principal strains, relatively to the native case.