Biomedical Engineering Reference
In-Depth Information
Acetabular component
Stem elbow
Calcar
region
Femoral stem
Proximal
Stem tip
Distal
Medial
Lateral
Figure 10.1
Schematic representation of a total hip
replacement. (Adapted from Ruben
et al
. [2, 3].)
fact, ''small'' relative displacements between bone and stem and ''small'' contact
stresses promote bone ingrowth into the stem porous coating, essential for biologic
fixation [9]. Also, thigh pain is related to an inefficient initial stability and to excessive
contact stresses [10]. In addition, stress shielding effect due to the presence of a
metallic implant inside the femur leads to a proximal bone loss, which promotes
implant loosening and reduces bone stock for a revision surgery.
Stem geometry plays an important role in the biomechanical behavior of the
implant, since it determines the way the load is transferred to bone [11]. Although
the stem design is subjected to several clinical requirements, there are stems with
very different geometries in clinical use. From a biomechanical point of view, stem
geometry. Actually, from a biomechanical point of view, stem geometry and porous
coating length can be studied in order to improve initial stability and, thereby
improving implant durability.
Computational mechanics tools are very attractive for analyzing and designing
medical devices, with finite element method being the most commonly used.
This chapter describes structural optimization methods used to succeed in bone
implant. A multicriteria optimization procedure to determine the stem geometry
that maximizes the initial stability and minimize the stress shielding effect is
presented here. Although the model is developed for the femoral component of a
hip prosthesis, similar models can be used to design other artificial joints.
A concurrent model for bone remodeling and osseointegration was also used in
order to study the long-term effect of optimized stem shapes, and to confirm the
relation between initial conditions and implant durability.
