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NexGen MIS LPS-Flex Mobile Implant System
Surgical Technique
MIS Medial Parapatellar Arthrotomy
Minimally invasive total knee arthroplasty has become
a popular procedure with surgeons using a variety
of surgical exposures including the limited medial
parapatellar arthrotomy; the midvastus approach;
subvastus approach; and Quad-Sparing™ approach.
The MIS medial parapatellar arthrotomy is a versatile
approach that can be easily converted to a traditional
approach if necessary. Advantages of this technique
include diminished post-operative morbidity, less
post-operative pain, decreased blood loss, and
an earlier functional recovery.
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However, while
limiting the exposure, the integrity of the total knee
arthroplasty must not be compromised. Following
specific guidelines in patient selection and surgical
technique, the clinical outcome can be predictable.
The MIS medial parapatellar arthrotomy is a versatile
approach because it evolved from the traditional
approach performed by most surgeons. The learning
curve for this technique is short as surgeons gradually
reduce the length of the skin incision and the
arthrotomy into the quadriceps tendon in order to gain
exposure of the knee joint. With lateral subluxation
of the patella, instead of eversion, both the femur
and tibia can be visualized without extending the
arthrotomy high into the quadriceps tendon.
Begin by making a straight anterior midline incision
from the superior aspect of the tibial tubercle to the
superior border of the patella. The skin incision is
made as small as possible in every patient, but should
be extended as needed during the procedure to allow
for adequate visualization and avoidance of excess
skin tension. Skin under the appropriate tension
should form a ‘V’ at the apices. If the skin forms a ‘U’,
the incision should be lengthened.
Following subcutaneous dissection, develop full-
thickness medial and lateral flaps to expose the
extensor mechanism. Release of the deep fascia
proximally beneath the skin and superficial to the
quadriceps tendon facilitates mobilization of the skin
and enhances exposure. In addition, with the knee
in flexion the incision will stretch an average of 3.75
cm due to the elasticity of the skin allowing broader
exposure.
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The goal of minimally invasive surgery is to limit
the surgical dissection without compromising the
procedure. The MIS medial parapatellar arthrotomy
is a shortened version of the traditional approach.
Initially incise the quadriceps tendon for a length of
2-4 cm above the superior pole of the patella. The
arthrotomy should be of a sufficient length to sublux
rather than evert the patella laterally or if the patella
tendon is at risk of injury, extend the arthrotomy
proximally until adequate exposure is achieved
(Figure 6).
Once the exposure is achieved, the bone preparation
begins with the knee flexed at 90°, retractors are
placed both medially and laterally to help aid in
exposure, avoid undue skin tension, and to protect
the collateral ligaments and the patella tendon. In
order to aid visualization and avoid undue tension
to the skin, the surgical assistants are instructed in
proper placement of retractors and positioning of the
knee. This will create a “mobile window” of exposure.
With experience, it will become obvious that the bone
preparation and resection is performed at different
angles of knee flexion. In addition as the bone is
resected from the proximal tibia and distal femur,
there is more flexibility to the soft tissue envelope and
greater exposure is achieved.
Figure 6
