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Lateral-Sided Surgery with MPFL Reconstruction: When is this needed?
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When to release or lengthen the
lateral soft tissue structures:
With the above discussion as a prologue, one
can attempt to answer the question “When are
lateral sided structures a deforming force
restricting a balanced patella?”.
The most correct statement would be: one
should relax the lateral structures by lengthening
and/or releasing the lateral structures when
they offer resistance to normalization of patella
position in early flexion. The harder question
is: how does one determine this?
The discussion of when to release/lengthen
lateral sided retinacular structures will be
restricted to those cases that one assumes the
major feature preventing normalization of the
patella position is a soft tissue structure, not the
trochlea. Certainly, the morphology of the
trochlea in early flexion can also be a reason to
have excessive lateral patella tilt [11].
However, when one is talking about high-grade
trochlear dysplasia associated with large
degrees of patella tilt, one nearly always needs
to lengthen or release the lateral structures; that
is not what is under discussion in this article.
This article attempts to address those more
subtle cases of “isolatedMPFLreconstructions”
that may or may not need a lateral retinacular
lengthening/release.
An ideal candidate for an isolated MPFL
reconstruction (without bony work (eg) tibial
tubercle osteotomies/trochleoplasties) might
have the following profile of risk factors:
- Trochlear dysplasia, type A, or normal
trochlea.
- A tubercle sulcus angle of 0 to 5° valgus/or
TT-TG less than 20mm. (no significant mal-
alignment of the patellofemoral joint).
- Patella alta less than 1.3 (Insall/Salvati or
Caton/Deschamps index) and/or “reasonable”
overlap of the patella and trochlea surfaces on
sagittal MR [12] (functional patella engage
ment with the trochlea).
In regards to lateral lengthening, the author
reviews the following pre-operative factors to
aide in the decision of how to manage the
lateral soft tissue structures.
- Lateral patella tilt less than 20° utilizing axial
image with posterior femoral condyles as a
reference, measured on an image without
notable knee effusion (in a non-acute injury
setting) usually does not need lateral
lengthening.
- If the non-acute axial image in full extension
shows increased lateral patella tilt but the tilt
corrects in early flexion (20° Laurin’s view or
a 30° Merchant’s view), the patella rarely
needs lateral structures lengthened.
- Axial radiographs taken in early flexion
reveal excessive lateral tilt on both sides, with
no injury to the opposite (non-injured) knee;
this is a strong sign that lateral sided deforming
forces are present.
- Patella tilt that has no lateral tightness on
physical exam after the patella is relocated
does not need lateral side lengthening.
(This may be necessary to evaluate intra-
operatively).
The final decision for how to manage lateral
soft tissue structures is made intra-operatively.
One way the author has evaluated lateral sided
tightness intra-operatively when doing MPFL
reconstructions is the following: a K wire is
passed medial to lateral across the patella at the
most superior aspect of the patella’s insertion
of the MPFL, exiting at the lateral border of the
patella. This gives the surgeon a true
representation of the medial to lateral axis of
the patella. One can then test the lateral
tightness by seeing if the K wire remains level
(parallel to the horizon) at full extension, and
then again at 20°, or when the patella is initially
engaged in the trochlear groove. If the K-wire
remains tilted, the author lengthens the lateral
sided structures (fig. 3). This can be referred to
as an “intra-operative patella tilt test”, with a
very visible structure (the K-wire) representing
the long axis of the patella. In the author’s
MPFL technique, this K-wire is used to