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Soft tissues and TKA
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Protocol
Between January 2013 and July 2014 we
analyzed the behavior of the soft tissues during
knee flexion on eight cadaver knees before and
after TKA implantation. The ethical committee
of our institution approved this investigation.
Cadavers in this study were donated according
to standard procedure. None of these knees had
previous surgery as far as we can judge from
the skin aspect as no clinical information was
delivered from these cadavers. We investigated
the tracking of five specific anatomic structures
from full extension to maximum flexion, before
and after TKA implantation: The Popliteus
Tendon (PT), the Lateral Collateral Ligament
(LCL), the Iliotibial band (ITB), the Medial
Collateral Ligament (MCL), the Quadriceps
Tendon (QT) and the Patellar tendon (PT). The
implanted prosthesis was a copy of the HLS-
KneeTech® (Tornier SA, Montbonnot, France)
provided by the manufacturer and obtained
from additive manufacturing technology:
Fused Deposition Modeling, FDM®, with a
Stratasys Dimension Elite™ (Eden Prairie,
MN USA) using a non radio-opaque and non-
magnetic polymer (Acrylonitrile butadiene
styrene).
The knee was scanned from full extension to
full flexion by 20° increments, before and after
implantation of the TKA. Four knees were
scannedwith a 5TeslaMRI (Siemens Sensation,
Munich, Germany) and four knee with CT-scan
after injection of baryum sulfate into the soft-
tissues. PT and LCL were approached via a
longitudinal lateral incision with the knee at
90° flexion. Ilio-tibial band was then incised
longitudinally and LCLwas identified, between
the head of the fibula and the lateral epicondyle.
After meticulous dissection, the PT was
palpated and progressively visualized crossing
the LCL at its deep face. QT and PT were
approached from a medial parapatellar incision
after patellar eversion and fat pad excision.
MCL was approached from the anterior skin
incision after subcutaneous dissection. The
superficial fibers of the MCL were dissected
from their epicondylar insertion to their distal
tibial insertion. A mixture of glycerol (60%)
and Baryum sulfate (40%) was prepared and
injected meticulously in the different tendons
and ligaments. After application of the contrast
medium, a meticulous multilayer closer was
conducted with separate Vicryl® 2-0 sutures
(Ethicon, Somerville, NJ, USA). After local
preparation all specimens were scanned with
an identical protocol using a helical scanner
(Siemens Sensation, Munich, Germany).
Surgical technique for TKA
implantation
HLS-KneeTech® is a postero-stabilized TKA,
with eight sizes for the tibial component and
ten sizes for the femoral component, with
standard and narrow components for the sizes 3
to 5. Implantation was done through a medial
parapatellar approach and the patella was
everted during the procedure but was not
resurfaced. We used the standard conventional
instrumentation obtained from Tornier SA. An
orthogonal tibial cut was done at the first step,
following an intra and an extra medullar guide.
A 9mm resection was measured from the
palpator. On the femur, the posterior cut was
externally rotated in order to obtain a balanced
knee in flexion. The distal femoral cut followed
the intramedullary rod with a 7° valgus
alignment. Stability and range of motion
(ROM) were tested with the dedicated trial
components and then, the implanted were
cemented in one step. We did not use
conventional surgical cement, with contains
baryum sulfate, but Polyester (Polyester
Demaere, Brussel, Belgium). After TKA
implantation the lower limb was scanned in
supine position from femoral head to ankle
joint so that we could control the alignment.
Sizing of the implants
On the femur anteriorposterior (AP) measu
rement was done with a caliper in order to
avoid anterior notching of the anterior cortex.
Themediolateral dimension (ML) was carefully
adjusted both on the femur and the tibia. We
successively implanted
1)
Normosized TKA:
(the contours of the implants fit exactly with
the contours of the bony section),
2)
Undersized