Biomedical Engineering Reference
In-Depth Information
f)
Wear
The low contact stress associated with the B-P ankle will produce less wear than
the typical fixed bearing ankles that have performed badly. Still the estimated
contact stress in the B-P ankle is somewhat higher than in the NJ LCS knee.
Sliding motion in the ankle is, however, much less than in the knee, mitigating
wear. It is desirable, nevertheless, to provide superior bearing surfaces for
prosthetic ankle articulation. The authors have been developing a ceramic coated
articulating surface since 1988. The first implantation's occurred in 1989. In its
current form the surface is polished to a 0.5micro inch finish so as to minimize
wear. Furthermore, the first author has used highly cross-linked UHMWPe in an
effort to further reduce wear.
g)
Fixation
The fixation of the B-P Mark III Ankle is illustrated in Fig. 4.39.
ANT 3 3mm
Fig. 4.39
Mark III B-P Ankle Fixation Geometry
The dual Peg fixation of the talar component is used for the purpose of
obtaining fixation on both sides of the talus while minimizing disruption of the
talar blood supply. This is expected to minimize talar resorption and associated
talar component tilt, encountered in the earlier single and dual fin designs. The
primary blood supply of the talus is inferior and central to the talus [55, 87]. The
short, anterior, dual pegs minimize this disruption.
The short fixation peg of the tibial component is designed to help resist tilting
forces on the tibia resulting from off-center loads. Early designs with a dual fin
fixation were originally used and worked well in the relatively few cases of
