Biomedical Engineering Reference
In-Depth Information
Therefore, based in experimental studies, several anisotropic bone material
laws were proposed and developed [
62
]. Although many initial anisotropic bone
material laws suggested distinct mathematical laws for the cortical and the tra-
becular bone, this work considers the recent experimental study of Zioupos and co-
workers [
63
], in which it is shown that the law governing the cortical and tra-
becular bone mechanical behaviour is in fact the same. This idea is being cor-
roborated by the analysis of high-resolution three-dimensional images, from which
some authors were able to estimate the homogenized anisotropic mechanical
properties [
64
].
1.3.1 Bone Tissue Remodelling Due to Femoral Implants
Generally, the hip replacement orthopaedic surgery is performed to answer to one
of the following needs: to relieve arthritis pain; to repair a physically damaged
joint; to replace the joint functionality after a hip fracture. This surgery, in which
the hip joint is replaced by a prosthetic implant, is presently the most common
orthopaedic surgical procedure. The prosthetic implant used in hip replacement
orthopaedic surgery is generally composed by three parts: the acetabular cup, the
articular interface and the femoral stem. The selection process of the femoral
implant is a very important step, since the success of the medical operation
depends on choosing the right implant for the right patient. Currently, there are a
numerous variety of femoral implants available in the specialized market, with
distinct shapes, materials and functionalities. The hip replacement therapy, with
cemented or cementless femoral implants, induces in the femur bone the adaptive
remodelling effect [
65
,
66
]. The main purpose of using cementless femoral
implants is to avoid stress-shielding, by ensuring a smooth physiological transfer
of loads from the prosthetic head to the femur diaphysis. However, it has been
verified that distinct cementless femoral implants models lead to stress-shielding
[
66
]. In a large number of research works studding the quantification of the mass
changes of the bone tissue after a hip replacement, it was observed a significant
degree of atrophy in the proximal region due to an effective lack of loads or due to
a shift of the load magnitudes [
66
,
67
].
The Finite Element Method (FEM) [
68
] is the most common numerical tool used
to analyse femoral bone implants, allowing to estimate the stress field changes on
the bone domain produced by the insertion of the femoral implant system [
69
].
Using the FEM analysis combined with a bone tissue remodelling algorithm, it is
also possible to predict the long-term influence of the prosthetic replacement in the
bone mass of the femur [
66
,
70
]. In the literature it is possible to find several
research works studying the influence of: the prosthesis geometry; the material
properties of the implant stem; the type of fixation [
71
-
73
]. Other authors have
compared distinct stem shapes performance for hip prosthesis using a FEM static
and dynamic analysis [
74
,
75
].
