ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

cancellous bone of natural joints are increased by 50 to 100% due to implantation of the
prosthesis [13, 22]. Thus, taking into account the increase of the strain between the
implanted and natural states, apparently, a risk of fatigue-failure of cancellous bone
exists after PFA for loads in range of daily activities if the cement is not firmly bonded
to the bone.
As in all numerical studies, the present study had some limitations. For instance, only
the PFJR and TFJR forces were taken into account without consideration for either
quadriceps force or patella ligament force. Nevertheless, those two forces are related to
the PJFR force by the knee flexion angle, and the applied forces are representative of
the major loads acting upon the implant and bone structure. Results might also be
different with more complex cement distribution, bone cuts and more pathological bone.
CONCLUSIONS
From the global results produced, it may be concluded that the cancellous bone of the
femur become vulnerable after the implantation of PF prosthesis. This comparative
study has limitations, but clearly reports the relative effect of PFA with Journey PFJ
prosthesis in bone structure, when compared with the natural joint for loads of daily
living. On the one hand, the stress-shielding effect is an issue, from the moment when
the arthroplasty surgery is performed. On the other hand, bone rupture by fatigue will
probably occur on cancellous bone, when the cement layer becomes inefficient. The
conclusions drawn about this specific PF prosthesis may lead to the improvement of
future PFA systems in order to better protect the integrity of the bone and to avoid the
need for a surgery of revision. In fact, a different geometry of the bone-implant interface
might help to prevent the stress-shielding effect and to reduce the risk of severe
defacement on cancellous bone.
ACKNOWLEDGEMENT
The first author would like to express his gratitude to “Fundação para a Ciência e a
Tecnologia”, through PhD grant SFRH/BD/63882/2009.
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