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Given that the medial patellofemoral ligament
is the primary soft tissue restraint preventing
lateral patellar dislocation [1, 2], it is not
surprising that it is usually disrupted to some
degree when the patella dislocates laterally. In
the setting of acute dislocation, the reported
rate of injury to the MPFL is up to 100% [3, 4].
The ligament appears to have a poor capacity
to heal back to a near normal structure. It tends
to heal in an elongated fashion and is thus often
noted to be attenuated in the setting of recurrent
patellar instability.
The precise anatomy of the MPFL has been
extensively studied [5-11]. The patellar
attachment is broader than the femoral
attachment and extends over the proximal one
half to two thirds of the medial border of the
patella. The exact location of the femoral
attachment has been variably described but is
generally agreed to be in the region of the
medial femoral epicondyle to the adductor
tubercle.
It has been reported that the MPFL is frequently
disrupted at more than one site [12], particularly
in children and adolescents [4]. However, the
femoral attachment is the most common
location of injury and occurs in up to 97% of
cases of acute patellar dislocation [13]. The
next most common site is the femoral
attachment. This is relevant in terms of the
location of tenderness in the acute setting.
Physical examination of the MPFL specifically
is essentially comprised of palpation for
tenderness, assessment of laxity of the MPFL,
and identification of patellar apprehension.
Ancillary testing includes assessment of
generalized ligamentous laxity and the
identification of predisposing factors for
recurrent patellar instability.
The identification of tenderness is really only
relevant to the acute patellar dislocation. No
particular site is specific for MPFL injury, but
tenderness in the region of the medial femoral
epicondyle is most common [3]. However this
may also be due to an injury to the medial
collateral ligament, which may be co-existent
and which will usually be associated with pain
when a valgus stress is applied to the knee.
Tenderness at the medial border of the patella
may be associated with injury to MPFL, but
can also reflect capsular injury, tearing of the
insertion of vastus medialis, synovial injury
and associated haemorrhage, and osteochondral
injury of the patella. Tenderness over the mid
portion of the MPFL may similarly reflect
MPFL injury as well as capsular injury.
MPFL insufficiency will result in a decreased
resistance to lateral translation of the patella.
Although the slope of the lateral facet of the
trochlear groove provides the principal
resistance to lateral translation [2], the MPFL
Acute Patellar Dislocation:
Which Examination for Which
MPFL Lesion?
J.A. Feller