162 / 460
161
Introduction
Similar to other ligamentous reconstructions,
around the knee, MPFL reconstructions can
lead to complications. These complications
relates to a lack understanding of the biome
chanics of the MPFL ligament and technical
errors made during the reconstruction.
Biomechanics of the
MPFL
The MPFL should be seen as a check rein in
preventing abnormal lateral movement of the
patella, at and near full extension; it is not
suppose to pull the patella medially and is of no
importance once the patella has engaged the
trochlea [15].
In the literature, on reconstruction of the MPFL,
most authors suggest that the reconstructed
ligament should be isometric. So called most
isometric points [25, 27] for the reconstruction
have been suggested.
However in measurements of the normal length
changes in the MPFL it has repeatedly been
shown to be a non isometric ligament [25, 29].
According to Steensen there is a 5.4mm length
change from 0° to 90° of flexion and an average
of 7.2mm length change from 0° to 120°. It is
important to realize that the MPFL is a non
isometric ligament that is at it’s tightest at full
extension and becomes more lax with flexion,
as the patella engages into the trochlea [15].
Victor [33] confirmed the non isometry of the
MPFL and has suggested that there is a
difference in the non isometry of the proximal
and distal fibres of the MPFL; the proximal
fibres are at their tightest at full extension and
the distal at 30° of flexion. In cadaveric studies
it was shown that an anatomic MPFL
reconstruction will restore patella kinematics
better than an isometric reconstruction [22].
The position of the reconstructed ligament on
the patella has very little effect on the isometry
of the ligament. In contrast the position on the
femur has a major effect on the on the isometry
of the ligament.Amore distal position increases
tightness in extension and laxity in flexion;
conversely a more proximal position results in
a graft that is lax in extension and tight in
flexion (fig. 1).
In nearly all patella dislocations there is
underlying causes like patella alta, trochlear
dysplasia, ligamentous hyper laxity, etc. that
predisposes the patient to a patella dislocation.
Patella alta seems to be the most constant
predisposing factor in patella dislocation [16]
Patella height has an influence on the isometry
of the MPFL, the higher the patella the bigger
Complications after MPFL
reconstruction
P.J. Erasmus, M. Thaunat