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In the last study on the topic of implant augmentation for the
treatment of osteoporotic distal femur fractures we used human
specimens and modified screws to establish and investigate a clinically
applicable procedure [65]. Therefore, seven pairs of fresh frozen human
distal femur specimens with low bone mass (mean age 87 years, all
female) were used. Prior to any testing bone mineral density (BMD)
was measured using QCT. In accordance with the previous studies
the LCP distal femur with an AO 33 A3 fracture model was used.
The femoral shaft has been replaced by a PMMA part and the plate was
fixed in rigid manner. In contrast to the previous studies cannulated
and perforated screws (four 1.1 mm holes in 10 and 15 mm distance
from the screw tip) were used. Thus, cement injection could be
performed after instrumentation through the screw shaft. Testing was
performed with a comparable setup; the force maximum started at
750 N andwas increased at 0.05 N per cycle. To determine failure x-rays
in antero-posterior direction were performed every 250 cycles.
Biomechanical testing showed no significant difference for initial
axial stiffness (augmented 385.5 N/mm vs. non-augmented 366.7 N/
mm;
p
= 0.444). The mean number of cycles to failure was 23483 (SD
5715) for the augmented vs. 17643 (SD 5483) for the non-augmented
group (Figure 6). This differencewas statistically significant (
p
= 0.011).
Furthermore, the mode of failure changed significantly from cut-out in
the non-augmented group to implant failure (plate and/or screw
breakage) in the augmented specimens (Figure 6).
In summary of the above-presented studies [11,64,65] cement
augmentation of an angular stable locking plate shows beneficial
mechanical characteristics in osteoporoticdistal femur fracture fixation.
This method can enhance bone-implant anchorage significantly and
therefore has the potential to increase stability and avoid complications
(e.g. secondary loss of reduction, mal-union, non-union, cut-out). This
treatment option is not only possible for osteoporotic fractures, but also
for the treatment of periprosthetic distal femur fractures with a well-
fixed prosthesis and the possibility for fracture fixation. The additive
augmentation is a further option for surgeons to enhance stability and
reduce complications in osteoporotic
–
and only osteoporotic
–
distal
femur fractures. In our opinion it is a meaningful salvage procedure for
particular patients with severe osteoporotic/periprosthetic fractures.
Conclusion
Periprosthetic fractures continue to be a hot topic and to generate a
lot of interest in the field of trauma surgery. Several options exist in
periprosthetic fracture fixation: Cerclages are ideally suited to fix
radially displaced fragments around an intramedullary implant,
but they are susceptible to axial load and torsion. Due to the bony
surface geometry, cerclages provide a point-contact fixation and do not
compromise periosteal blood supply. Bicortical locking screw fixation
is effective but difficult on the level of the prosthesis stem. Inserted in
the embracement configuration around the intramedullary implant,
bicortical locking screws provide stable fixation in all load directions.
Double plating is another method to enhance construct stability.
Intramedullary implants increase fracture risk. The combination of
a retrograde nail and a hip endoprosthesis doubles the fracture risk
compared to a non-instrumented femur, whereas the combination of
two cemented well-fixed arthroplasty stems does not. Extramedullary
implants seem favorable for distal periprosthetic fracture fixation.
Concerning stability of the interprosthetic region, cortical thickness
of the femoral shaft is the more contributing factor compared to
interprosthetic distance.
Cement augmentation enhances angular-stable screw purchase in
the osteoporotic periprosthetic distal femur. Especially, if plate fixation
of an osteoporotic periprosthetic distal femur fracturewith awell-fixed
femoral component is considered, cement augmentation of the locking
screws increases construct stability and reduces failure rate.
Conflict of interest
The authors have no conflicts of interest.
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