POSTER ABSTRACTS - ISAKOS

Jason Boyer, Houston, Texas USA
Jeffrey T White, Houston, Texas USA
Richard H Hallock Camp Hill, PA, USA
Institute of Orthopedic Research and Education,
Houston, TX, USA
Introduction: An articulating discoid spacer
(UniSpacer) has been popularized to reduce pain
and restore bony alignment in the patient with
early OA of the medial compartment of the knee.
While early clinical results are promising, success
seems to be sensitive to appropriate patient
selection, particularly with regard to the integrity
of the soft tissue structures of the knee. The
purpose of this study was to evaluate knee
kinematics after implantation of the UniSpacer
during a functional weight-bearing activity as a
function of the efficiency of the cruciate
ligaments.
Methods: Six fresh-frozen lower limb specimens
were mounted in a 6 degree-of-freedom joint
simulator and loaded with a system of 4 external
forces to generate a deep knee bend from full
extension to full flexion. During knee motion, the
three-dimensional positions of the femur and
tibia were tracked in real time using a motion
analysis system (NDI, Waterloo, CANADA). All
measurements were repeated after medial
meniscectomy and subsequent implantation of a
UniSpacer using standard surgical techniques in
three conditions: 1) with both cruciates intact, 2)
with a deficient ACL, and 3) with both cruciates
deficient. During flexion, the three dimensional
motion of both the UniSpacer and the tibia were
measured using a fluoroscopic imaging system
(Medical Metrics, Inc, Houston TX).
Results: Cruciate integrity significantly affected
the anteroposterior position of the femur relative
to the tibia in full extension and throughout
flexion with both cruciates intact. Implantation of
the UniSpacer shifted the overall dwell position of
the femur an average of 2.0 ± 4.0mm posteriorly
and reduced the net femoral rollback throughout
flexion from 16.9 ± 2.1mm to 14.6 ± 1.2mm.
Resection of the ACL, with the PCL intact, shifted
of the dwell position an additional 4.1mm
posteriorly (6.1 ± 3.1mm) while also reducing the
net rollback to 11.8 ± 3.5mm. Further resection of
the PCL resulted in an additional 4.5mm (10.6 ±
4.3mm) posterior shift in the dwell position and
reduced net rollback to 8.4 ± 3.7mm. Sequential
resection of the cruciates significantly altered the
axial rotation of the knee during flexion to 140 .
The net axial rotation achieved (difference
between the maximum internal rotation and the
maximum external rotation throughout the flexion
arc) was most affected by ACL deficiency, which
resulted in net internal tibial rotation of the intact
knee by 10.8 ± 5.3 .
Discussion and Conclusion: As in the intact knee,
tibiofemoral kinematics are significantly affected
by the integrity of the cruciates after implantation
of the UniSpacer. As full range of motion
following implantation requires substantial intraarticular
motion of this device, compromising
rollback and altering axial rotation may have a
substantial effect on its clinical and functional
performance. Patient selection criteria for
UniSpacer arthroplasty should include the
presence of both cruciates.
E-poster #528
Medial Opening Wedge Tibial Osteotomy
Utilizing a New Fixation System
Alex Hennig, Burlington, VT, USA, Presenter
Stephen J ncavo, Burlington, VT, USA
Bruce D. Beynnon, Burlington, VT, USA
Joseph A. Abate, Burlington, VT, USA
John S Urse, Dayton, OH, USA
Kathryn Coughlin, Burlington, VT, USA
Steve Kelly, Burlington, VT, USA
University of Vermont College of Medicine,
Burlington, VT, USA
Medial opening wedge osteotomy of the tibia is a
treatment option for patients with symptomatic
medial compartment knee arthritis. To maximize
the advantages of both internal and external
fixation techniques, a new plate system has been
developed consisting of a two-piece plate with a
one-way ratcheting mechanism with two degrees
of freedom. In addition to stable fixation, this
device offers intra-operative adjustability and
provides the opportunity to perform postoperative
adjustment should it be necessary. Our
hypothesis is that this new plate can be used in a
safe and effective manner to achieve a successful
proximal opening wedge valgus tibial osteotomy.
Twenty opening wedge tibial osteotomies were
performed using a new, adjustable internal
fixation plate. A variety of concomitant
procedures were performed including arthroscopic
meniscectomy, OATS, tibial tubercle transfer, and
ACL reconstruction. The change in mechanical
tibio-femoral alignment and the overall shift in
lower extremity mechanical axis was determined.
Union rates, complications, and device survival
were reported. The average shift in lower