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NexGen MIS LPS-Flex Mobile Implant System
Surgical Technique
MIS Midvastus Approach
The capsular incision from the superomedial corner of
the patella distally to the tissue overlying the medial
tibia is routine in all medial capsular approaches.
Preserve approximately 1 cm of peritenon and capsule
medial to the patellar tendon to facilitate complete
capsular closure. Split the superficial enveloping fascia
of the quadriceps muscle proximally over a length of
several centimeters to identify the vastus medialis
obliquus (VMO) fibers inserting into the extensor
mechanism. This will help mobilize the quadriceps
and allow for significantly greater lateral translation
of the muscle while minimizing tension on the patellar
tendon insertion.
The approach becomes “midvastus” at a point proximal
to the superomedial pole of the patella. Variations on
the angle at which the proximal part of the capsular
incision enters the muscle belly of the VMO will result
in various amounts of the muscle being incised as well
as variation in the amount of force required to sublux
the patella laterally. Additional variables include the
actual point of insertion of the VMO fibers into the
patella. This insertion is variable and can take place
very high (actually on the quadriceps tendon proper
and not on the patellar border at all), or lower (at the
midpoint of the medial patellar border), or anywhere
in between. The higher the insertion of the VMO,
the shorter the length of the incision into the muscle
proper. The lower the insertion, the more a “low
incision” into the VMO will make the exposure more
like a subvastus approach and may make subluxation
of the patella more difficult. It is very important to
carry the capsular incision all the way to the superior
border of the patella before incising the muscle belly
of the VMO.
After identifying the characteristics of the VMO
insertion, the vastus medialis obliquus muscle belly
is split by sharp dissection approximately 1.5 cm-2
cm (Figure 7). The superficial muscle has only a flimsy
investing fascia and this fascia, along with the muscle
belly, may be split by blunt dissection; however, the
deepest layer of muscle is adherent to the more robust
fascia of the VMO, which should be incised sharply.
The use of a rake to retract the capsular edges
medially will reveal variable amounts of synovium. The
synovium may be minimal, exuberant and inflamed,
or fibrotic. Removal of excessive synovium from the
medial border of the capsule at the most proximal part
of the exposure distally will improve exposure and, if
the synovium is fibrotic, will also reduce the tension
required for exposure.
Routine medial capsular exposure proceeds by sharp
dissection and removal of the anterior third of the
medial meniscus, and is followed by sharp dissection
of the deep medial collateral ligament from its insertion
on the proximal tibia. This occurs while the knee is
flexed but may be carried out in extension at the
surgeon’s discretion. This is adequate for exposure of
the medial side of the knee. The experienced surgeon
may want to proceed with any medial capsular
releases that are predicted to be necessary to align
the limb and balance the knee, or these maneuvers
may be saved for later in the procedure. At this point
the medial capsular retractors are removed from the
wound for exposure of the lateral side.
Figure 7
