POSTER ABSTRACTS - ISAKOS

the Bioknotless suture anchor (Mitek, Westwood,
MA) and the Bio-corkscrew suture anchor (Arthrex,
Naples, FL).
Methods: A standardized template was used to
create 3-cm wide by 1-cm long full-thickness
supraspinatus defects in 7 paired fresh frozen
cadaveric shoulders. Defects were repaired using
either two 6.5 mm Bio-corkscrew anchors (n = 7)
or three Bioknotless suture anchors (n = 7). All
defects and repairs were performed by the primary
investigator. Following placement in a servo
hydraulic device with the loading vector applied at
a 60º abduction angle, constructs underwent
incremental cyclic testing (5-100 N for 1000 cycles
and 5-180 N for 2000 cycles) and load to failure
testing at a rate of 31 mm/sec. Nonparametric
statistical analysis was performed to evaluate
group differences (P < 0.05).
Results: All specimens repaired with the Biocorkscrew
suture anchors (7 of 7) completed cyclic
testing compared to only 3 of 7 specimens
repaired with the Bioknotless suture anchors (P <
0.03, Fisher Exact Test). The Bio-corkscrew suture
anchors displayed superior failure load results
(533.7 ± 237 N vs. 339.7 ± 228 N, P = 0.018,
Wilcoxon Signed Ranks Test). Stiffness and
displacement did not display significant group
differences (P > 0.50).
Conclusions: To our knowledge this is the first
investigation to evaluate the biomechanical
properties of the Bioknotless suture anchor when
used to repair human rotator cuff defects. The
superior performance of the Bio-corkscrew suture
anchor suggests safer patient performance of
routine activities of daily living and functional
rehabilitation exercises during the early postoperative
period with less risk of fixation site
failure.
E-poster #161
Retroscrew System Biomechanical Fixation
Characteristics Differ During Submaximal
Cyclic and Load to Failure Testing in
PorcineTibiae
John Nyland, Louisville, KY, USA, Presenter
Haw Chong Chang, Singapore, SINGAPORE
Akbar Nawab, Louisville, Kentucky USA
David N.M. Caborn, Louisville, KY USA
University of Louisville, Louisville, KY, USA
Introduction: The RetroScrew System (20-mm
long bioabsorbable retrograde screw with 17-mm
long bioabsorbable antegrade ''back-up'' screw)
was designed to facilitate optimum tibial fixation
of soft tissue grafts for ACL reconstruction at the
level of the intercondylar floor conceivably
maximizing both construct biomechanical
characteristics and anatomical placement. The
efficacy of this relatively short screw to provide
secure fixation of soft tissue grafts has been
observed clinically, however basic biomechanical
information is lacking. Methods: This
biomechanical study evaluated double bundle
human tibialis anterior tendon graft fixation in
porcine tibiae during cyclic and load to failure
testing (n = 7). Tibial tunnel and interference
screw diameter matched graft diameter. Detailed
screening of apparent tibial bone mineral density
(BMD) was performed using dual energy x-ray
absorptiometry at the proximal third, middle
third, and distal third regions of interest for tibial
tunnel placement. Following fixation and
placement in a servo hydraulic device with the
loading axis aligned directly with the tibial tunnel,
the constructs were cycled from 10-50N at 0.1 Hz
for 10 cycles before undergoing 500 cycles
between 50-250 N at 1 Hz and a single-cycle load
to failure test at 20 mm/min. Coefficient of
determination (R²) analysis was performed to
establish relationships between apparent BMD
and fixation characteristics (P < 0.05). Results:
Insertion torques were 16.6 ± 5 in-lbs and 9.3 ± 4
in-lbs for the retrograde and antegrade screws,
respectively. All specimens survived cyclic testing
with displacement of 2.1 ± 0.9 mm and stiffness of
105.3 ± 32 N/mm. Load at failure was 728.1 ± 210
N with a stiffness modulus of 214 ± 55 N/mm and
a displacement of 4.9 ± 2 mm. Upper third tunnel
region BMD was 1.07 ± 0.23 g/cm². Middle third
region BMD was 1.32 ± 0.24 g/cm², and distal third
region BMD was 1.06 ± 0.18 g/cm². All constructs
failed by graft pullout. During cyclic testing,
middle third tunnel region BMD displayed a
strong direct relationship with construct stiffness
(R² = 0.94) while displacement displayed a strong
inverse relationship (R² = -0.92). Similar, but less
robust relationships were observed at the other
BMD regions of interest. However, during load to
failure testing, an inverse relationship was
observed between stiffness and middle third
tunnel region BMD (R² = -0.80) and less robust
relationships were observed at the other BMD
regions of interest. Retrograde screw insertion
torque displayed a weak relationship with
maximal load at failure (R² = 0.44), however
stiffness and displacement relationships were not
significant. Antegrade screw insertion torque
failed to display significant relationships with