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MPFL Reconstruction: Navigation and Angle of Fixation
147
There has been various principles proposed in
literature as related to the degree of knee flexion
and the tension in which to fix the graft MPFL.
Tensioning the graft at 20-30 degrees of flexion
is a widely used option, given that the patellar
instability occurs in this range [2], but others
chose to tension the reconstructed ligament in
greater degrees of flexion, when the patella is
more fully captured by the trochlea [2, 26]. The
authors do not recommend the traditional graft
tensioning between 20° to 30° of flexion. The
exact knee position during fixation is less
important if knee cycling and graft pre-
tensioning precede the final fixation. Testing
the lateral patellar translation in extension (in
order not to exceed 1/3 of patella width), graft
pre-tensioning, and making the femoral fixation
last in order were the key steps of the
reconstruction.
In the presence of dysplasia, a trochlea that
would not serve as a fulcrum for patella stability
in late knee flexion, is a question to be further
studied in all patients with patellar instability
that undergo MPFL reconstruction. The
findings of the previously-published manu
scripts are based on normal knees with no
trochlear dysplasia and with no concern of
abnormal patella height. The presence of a
normal trochlear groove is a prerequisite for
the function of MPFL beyond certain degrees
of flexion. All these are key factors for the
reconstruction of MPFL, which would involve
a construct that serves its native fashion [1, 2,
26]. But in order for this to succeed, a normal
trochlear anatomy is of paramount importance,
and therefore in cases of trochlear dysplasia
(which account for 96% of the objective
patellar instability population [28]), the lack of
trochlear depth and patella containment must
be taken into account. In these cases there is a
trend towards overtensioning the graft to avoid
lateral patellar translation [22].
Conclusions
The material presented demonstrates the
potential use of navigation systems to align
patellar tracking after MPFL reconstruction to
the native state. It also identifies some key
principles that could be used for graft fixation
in the procedure. As intra-operative patellar
tracking becomes common place, with the
resolution of controversies surrounding patellar
kinematics, a customization of the proposed
MPFL reconstruction technique may be
possible in each patient.
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