Page 232 - Advances in Biomechanics and Tissue Regeneration

228 11. ANALYSIS OF THE BIOMECHANICAL BEHAVIOR OF INTRAMEDULLARY NAILING

FIG. 11.21 Illustration of workflow followed through the acquisition of the geometry, finite element model generation, material assignment, and
eventually simulations developed.

A key issue in the FE models is the interaction between the different constitutive elements of the biomechanical
system, especially when it results in essential conditions affecting the behavior to be analyzed. In this way, the bio-
mechanical behavior of this kind of osteosynthesis depends basically on the conditions of contact between the intra-
medullary nail and bone, so that the correct simulation of the interaction conditions determines the reliability of the
model. The study was focused on the immediately postoperative stage. Thus the interaction at the fracture site did not
take into account any biological healing process. Contact interaction was assumed between the outer surface of the nail
and the inner cortex of the medullary canal of the femur. Tied interaction between screws and cortical bone was con-
sidered, whereas contact between screws and femoral nail was simulated. The selected friction values of bone/nail and
nail/screws were 0.1 and 0.15, respectively, in accordance with the literature [45–47]. Of interest, other similar studies
modeled bone/nail interaction as frictionless [22, 48].
The Abaqus 6.11 program [49] was employed for the calculations and postprocessing the results of the previously
generated models in NX I-DEAS software.
To summarize, a schematic workflow is depicted in Fig. 11.21, exhibiting the overall software used to generate FE
models and perform different simulations.

11.3 TYPES OF FRACTURES AND OSTEOSYNTHESIS

For the treatment of fractures to femurs between the 2 and 5 Wiss zones, an intramedullary nail with corresponding
screws is used. However, the characteristics of this indication are not unique, since there are multiple combinations
according to the geometric design of the nail, its material, the type of surgical approach, locking system, etc. Thus the
use of one or another system depends on the type and location of the fracture, the characteristics of the patient, and the
experience of the surgeon.
To help surgeons choose the best osteosynthesis in each case, two different studies were performed (A and B). The
“A” study consisted of an analysis of the biomechanical behavior of a single system of osteosynthesis for different
types of fracture (in terms of type and position along the femur). On the other hand, the “B” study corresponded

I. BIOMECHANICS