Stiffness (N/mm)
•Biomechanical Evaluation of an Innovative Vertebral Compression Fracture Treatment System
+1Wilson, D C; 1Zhu, Q A; 1Kingwell, S; 2Kitchel, S H.; 1Cripton, P A; 1Wilson, D R
+1University of British Columbia and Vancouver Costal Health Research Institute, BC, Canada, 2Orthopaedic Spine Associates, Eugene, OR, USA
Senior Author: [email protected]
Introduction
Vertebral compression fractures (VCF) are prevalent and cause
substantial pain and disability. Treatment of VCFs with vertebroplasty
and kyphoplasty procedures, in which cement is injected into the
fractured vertebral body in an effort to stabilize the fragments and
restore height, has become popular. However, cement extravasation,
which can be associated with complications, has been reported for
kyphoplasty and vertebroplasty procedures. An alternative VCF
treatment, the Benvenue KIVA VCF Treatment System, is designed to
reduce and stabilize VCFs by deploying a coiled PEEK implant through
a percutaneous unipedicular approach which is then augmented with
Figure 3: Augmentation with the Benvenue system (Left) and
cement. This system is proposed to provide cement containment and
kyphoplasty (Right).
minimize the required cement volume. In this study our research
question was: does the Benvenue VCF Treatment System stabilize
Results
fractured vertebrae and restore height as effectively as kyphoplasty?
Within each procedure the intact condition was significantly different
to all other conditions for all measurements.
Methods
Immediately after repair, both repair procedures significantly
We tested 6 T9-T11, 7 T12-L2, and 1 L1-L3 specimens from 9 human
increased overall stiffness (Fig. 4) and height (Fig. 5) from the fractured
cadavers (5F/4M, avg. 74yrs). Specimen levels and mean bone mineral
state. For both treatments, after cyclic loading of the repaired specimens,
density were comparable between groups (Benvenue: 0.63±0.09g/cm2;
overall stiffness and height were significantly greater than for the
kyphoplasty: 0.66±0.11g/cm2). The adjacent vertebrae of each specimen
fractured state. We found no significant differences between treatment
were mounted in dental stone, leaving the middle vertebra (T10, L1 or
methods except for cement usage (2.6±0.4ml for Benvenue and 7.5±0.8
L2) and adjacent discs unconstrained.
ml for kyphoplasty (t-test:p<0.01)).
First, each intact specimen was subjected to a compression stiffness
test. A compressive force (15 cycles, 0-600N, 0.1Hz) was applied to the
Overall Stiffness
2000
top of each specimen at the balance point where a pure compression is
1800
presumably produced. Then, wedge fractures were created in the middle
1600
Benvenue
vertebrae using a custom made jig [1] with a protective dental stone collar
1400
kyphoplasty
(Figure 1). After the stiffness test, the vertebral repair procedure
1200
1000
(Benvenue or kyphoplasty) was performed by a trained spine surgeon
800
using fluoroscopic guidance with the specimen under a 100N
600
compressive load (Figures 2 & 3). Cement usage was recorded for all
400
procedures. After implantation, each specimen was subjected to flexion200
compression cyclic loading (200-500N, 50,000 cycles, 3Hz, 3cm
0
Intact
Fractured
Repaired
Cycled
anterior to balance point). The compressive stiffness assessment was
Figure 4: Overall stiffness for 4 conditions of all specimens. Error bars
performed before and after the cyclic loading.
show 1 standard deviation.
Anterior vertebral height was measured in the intact, fractured and
pre- and post- cycling repaired states using fluoroscopy to image
tantalum beads glued to the anterior vertebral endplates with specimens
under a 100N compressive load at the balance point (Figure 3). Overall
stiffness for the same states was defined as the overall change in load
(600N) divided by the maximum compressive displacement of the entire
specimen between 0 and 600 N of load at the 15th loading cycle.
Statistical significance of changes in overall stiffness and height were
determined using repeated measures analysis of variance with p<0.05.
Figure 5: Anterior vertebral body height for 4 conditions of all
specimens. Error bars show 1 standard deviation.
Figure 1: Testing configurations for compression fracture (Left) and the
compression stiffness test (Right).
Discussion
Treatment of vertebral compression fractures with the Benvenue
system yielded comparable overall stiffness and vertebral body height
restoration to kyphoplasty using about 1/3 of kyphoplasty´s average
cement volume. There is also evidence that overall stiffness and height
are maintained after cyclic loading. It should be noted that this in vitro
study simulated immediately post-operative conditions. While testing
was performed at the low end of expected physiological loads, this is
appropriate for the elderly population likely to undergo treatment for
vertebral compression fractures. The lower cement volume required for
the Benvenue procedure may be clinically relevant due to the
relationship between cement volume and extravasation.
Acknowledgements
Funding was provided by Benvenue Medical Inc. This study was
approved by our institution’s Clinical Research Ethics Board.
Figure 2: AP (Left) and lateral view (Right) during Benvenue procedure
before cement injection.
References
1. Kettler A, et al. Clin Biomech. 2006;21(7): 676-82.
Poster No. 1734 • 55th Annual Meeting of the Orthopaedic Research Society