Biomedical Engineering Reference
In-Depth Information
The slanted coating configuration produces a load path that transfers load
directly to the medial calcar region and distributes the load laterally, minimizing
stress protection. Most coating configurations produce a load path that transfers
the load distally bypassing the proximal femur, producing stress protection of the
region.
Finite element analysis [118] and clinical experience [75] demonstrate that the
distal slanted coating of the B-P Femoral Stem reduces stress protection and
resorption of the proximal femur compared to fully, and one-third, coated stems.
The gradual increase in coating length from the medial to lateral stem surfaces
provides a gradual load transfer from prosthesis, to cancellous bone, and then to
cortical bone, producing a gradual transfer of load to the lateral, distal cortex as
shown in Fig. 5.34
.
e)
Proportional Sizing
Proportional proximal sizing in 1mm increments provides a close proximal fit and
maximum proximal flare for torsional resistance to load. Torsional resistance is
provided by the oval cross-section of this proximal flare and by the collar.
Proportional Sizing from 9-16mm
Fig. 5.36
Proportional Femoral Stem Sizing
Finite element analysis demonstrates the important role the collar plays in
resisting torsional loads [115]. Thus, torsion loads are transferred proximally,
thereby avoiding torsional stress protection of the more distal regions and thus,
transferring load more naturally than stems which resist torsional loads in the
shaft. Such distal torsional restriction may contribute to the high incidence of
thigh pain associated with designs that transfer load distally [76]. Clinical
experience with the B-P Femoral Stem indicates a relatively low incidence of
thigh pain [74, 75] which may be attributed to the lack of distal load transfer.
