Single bundle ACL reconstruction in medial portal technique: Knee kinematics after femoral tunnel drilling with
conventional over the top aimer in comparison to the new "medial portal aimer”, “MPA"
+1Herbort M. (Muenster), 1Domnick C., 1Lenschow S., 1Roßlenbroich S., 1Raschke M., 2Petersen W., 3Zantop T
2
+1Department of Trauma, Hand, and Reconstructive Surgery, University of Muenster, Germany,
Department of Traumatology, Martin Luther Hospital , Berlin, Germany, 3Sportopaedicum, Straubing, Germany
[email protected]
Introduction: Among clinical surgeons there seems to be a shift from a
transtibial approach to a medial portal approach in ACL reconstruction.
However, femoral aiming devices have been developed for the
transtibial approach and are now used in the medial portal technique.
During an anatomical study we could demonstrate that a specially
designed medial portal aimer ”MPA” (Karl Storz, Tuttlingen, Germany)
hits accurately the center of the anatomic ACL origin, whereas the
conventional over the top guide (OTG) fails the origin (Fig.1).
Therefore the kinematical results after ACL reconstruction using these
two guides in medial portal technique have been investigated.
The specific aim of this study was to investigate the influence of the use
of the “medial portal aimer, MPA” in comparison to a conventional over
the top aimer in medial portal technique on the resulting knee kinematics
of the single bundle ACL reconstructed knee. We hypothesized that
under a simulated KT 1000 and a simulated pivot shift test, an ACL
reconstruction in medial portal technique using the “MPA” for femoral
tunnel drilling will restore the intact knee kinematics more closely when
compared to ACL reconstruction using the conventional over the top
aimer.
Methods: In nine fresh-frozen human cadaveric knees (range 51-83
years) the knee kinematics were examined using robotic/UFS testing
system (KR 125, KUKA Robots, Augsburg, Germany). After the system
determined the passive path, the knee kinematics were evaluated under
an anterior tibial load of 134-N (to simulate a clinical KT-1000 test) and
a combined rotatory load of 10 N-m valgus and 4 N-m internal tibial
torque (to simulate a pivot shift test). Within the same specimen the knee
kinematics under simulated pivot shift and KT 1000 test were
determined in different conditions: intact, ACL-deficient and single
bundle ACL reconstruction using the “MPA” or the over the top guide.
To exclude any interference, the order of the reconstructions was
randomized. The reconstruction has been performed in both groups in
medial portal technique and the grafts have been fixed on femoral side
with cortical fixation. On tibial side a hybridfixation with interference
screw and cortical button has been performed.
Statistical analyses were performed using a Wilcoxon Rank test. (p <
0.05).
Results: Under 134 N anterior tibial load, anterior tibial translation
(ATT) of the intact knee was a mean of (± standard deviation) 9.4 (± 1.4)
mm, 13.9 (± 1.7) mm, 15 (± 1.8) mm, 13.3 (± 1.5) mm and 9.6 (± 1.1) at
0°, 15, 30°, 60°, and 90° of knee flexion, respectively. After transection
of the ACL the anterior tibial translation (ATT) increased significantly at
all tested flexion angles (p<0.05). The resulting difference of ATT in
comparison to the intact knee was a mean of 8.3 (±1.4) mm, 10.5 (± 1.7)
mm, 12.9 (± 1.8) mm, and 9.3 (± 1.5) mm at 15°, 30°, 60°, and 90° of
knee flexion, respectively. After reconstruction using OTG and MPA
guide the ATT could be significantly increased in comparison to the
intact knee (p<0.02). But the ATT after reconstruction using OTG was
significantly increased in comparison to the intact knee in 15°, 30°, 60°
and 90° of knee flexion. (p<0.03)
After reconstruction using the MPA the ATT was significantly increased
in comparison to the OTG reconstruction group in flexion of 0°.
(p<0.05) There were no significant difference in ATT after ACL
reconstruction using the MPA in comparison to the intact knee (p>0.05)
(Fig.2) In response to a combined rotatory load, the anterior tibial ATT
for the intact knee was 4.6 (±0.5) mm, 8.4 (±0.9) mm, 10.8 (± 1.1) mm,
and 11.2 (±1.2) mm for 0°, 15, 30° and 60° of knee flexion, respectively
(Fig. 3). The values increased after sectioning of the ACL to 8.9 (±0.5)
mm at 0°, 15.5 (±0.7) mm at 15°, 18.4 (±1.1) mm at 30°, and 14.6 (±1.6)
mm at 60°. The increase in ATT was statistically significant at all
flexion angles tested (p<0.05).
Fig. 2: ATT under simulated Lachman test
Under a simulated pivot shift test, single bundle reconstruction using the
over the top guide resulted in an ATT from 7.9 (±1) mm at 0°, 11.9
(±1.3) mm at 15°, 14.0 (±1.4) mm at 30° and 13.3 (±1.6) at 60 ° knee
flexion. At these flexion angles the ATT was statistically significant
higher compared to the intact knee (p<0.05).
After using the “MPA” the ATT was significantly increased at 15° and
30° knee flexion in comparison to the over the top guide (P<0.05). There
were no significant difference in ATT after ACL reconstruction using
the MPA in comparison to the intact knee (p>0.05) (Fig.3)
Fig. 3: ATT under simulated pivot shift test
Discussion: The results support our initial hypothesis that a single
bundle ACL reconstruction in medial portal technique using the “MPA”
will restore the intact knee kinematics more closely when compared to a
reconstruction after using the conventional over the top guide.
In a past anatomical study we could show that in ACL single bundle
reconstruction using medial portal technique transtibial aiming devices
(OTG) fail to hit the center of the anatomic ACL origin. The medial
portal aimer on the other hand hits the center of origin with high
accuracy.
During this biomechanical study it could be shown that these anatomical
findings result in better kinematic parameters.
Significance: Clinical relevance of this study is that using the medial
portal aimer for single bundle reconstruction in medial portal technique
can increase the knee stability after ACL reconstruction and can improve
the clinical results.
We do not recommend using the conventional over the top guide in
medial portal technique, because it results in extra anatomical and less
stable reconstruction of the ACL.
Poster No. 0844 • ORS 2012 Annual Meeting