62 / 72
Furthermore, the setting in this study does not represent the soft
tissue with peripheral muscle and ligaments which may affect the
biomechanical characteristics. The fixation methods were easier to
perform due to the missing soft tissue when compared to the in vivo
environment. Only the initial stability of the constructs was evaluated,
simulating the early healing stage where no osseointegration is seen.
At this stage the interfragmentary stiffness is negligible and the
constructs stiffness is only dependent on the implant fixation [9,43].
In vivo the strength of the construct would increase over time, as bone
remodeling occurs [41]. However, no conclusion can be drawn about
other clinical data such as blood loss, the prolongation of the operation
time related to the removal of the stem out of the medullary space,
the soft tissue damage, or hardware prominence because of the lack of
in vivo conditions within this biomechanical study.
Even though all stems were implanted with press fit stability,
axial pressure during biomechanical testing caused subsidence of the
stem within the proximal fragment of the sawbones. Among the
different groups a difference in the distance of subsidence was
observed. The lowering of the stem was six times larger when a short
stem combined with a cerclage system was used compared to using a
short stem secured by a plate, which was statistically significant. The
long modular revision stem groups also showed lowering effects but
without statistically significant differences between groups. The
edges of the long modular stem are sharp and have a double
profile, which should prevent the stem from sinking and rotating and
they increase the area of contact with the bone. The modular system
provides the possibility of changing the proximal module while
the distal module remains in the femur. This feature represents a
revision option where it is not necessary to remove the entire stem.
In order to remove the stem the femoral canal would have to be
opened which would influence operation time, the risk of fracture
and blood loss. Further clinical studies are needed to demonstrate the
clinical relevance of stem subsidence and to assess if it can lead not
only to leg length inequality, but even to luxation of the total hip
arthroplasty [24].
Conclusions
Periprosthetic fractures are difficult to treat and ongoing research
how to achieve optimum fixation is desirable. The present biomech-
anical study indicates that periprosthetic Vancouver B1 fractures can
be sufficiently fixed by simple cerclage systems. Revision with a long
replacement stem provides a superior mechanical stability regardless
of type of osteosynthesis fixation and is therefore a viable method in
Vancouver B1 cases. A disadvantage of the cerclage system compared
to plating is that an increased subsidence of the short stem was
observed.
Conflict of interest
The authors have no conflict of interest relating to this manuscript.
Implants were kindly donated by Zimmer Biomet GmbH Vienna,
Austria and Implantec GmbH Mödling, Austria.
Acknowledgements
We thank Zimmer Biomet GmbH, Vienna, Austria for providing NCB
Equipment and Implantec Mödling, Austria for providing primary
stems and CCG Systems. We also thank Jeremy Fredette for his
assistance in language editing.
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