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Primary Patellar Dislocation and Medial Patellofemoral Ligament Injury
59
The clinical importance of an MPFL injury
location was evaluated in one study [28]. In
that study, MPFL disruption at the femoral
attachment was related to more frequent
subsequent instability than patellar or
midsubstance MPFL injuries [28]. The study is
limited by its retrospective nature and the use
of onlymale subjects.MPFLpatellar attachment
injury was recently reported to be at least as
common as femoral attachment injury [6, 27,
29, 30]. Midsubstance MPFL disruption as an
independent injury location is less common [6,
28]. Partial tears or wavy features of the
midsubstance MPFL structure are commonly
seen in cases of patellar or femoral attachment
MPFL disruption [6, 30] Patellar MPFL injury
may include an osteochondral avulsion fracture,
in which the MPFL structure is relatively intact
and attached to the avulsed bone from the
medial margin of the patella [30]. In some
cases, articular cartilage involvement is seen
[14] (fig. 1). Based on these previous findings,
MPFLrepairmay be consideredmore unreliable
than MPFL reconstruction, in terms of
providing sufficient medial soft tissue stability.
MPFL patellar or femoral attachment injury
can be surgically reinserted with satisfying
results and may lead to a better outcome than
nonsurgical treatment [31], although some
controversy exists in the results of prospective
studies [5, 21, 23, 33]. MPFL midsubstance
injuries seem to not benefit from acute repairs
[28]. MPFL injury at the femoral or patellar
attachment can be repaired with sutures or
suture anchors (fig. 2) [31]. Midsubstance
MPFL injury is difficult to repair adequately
and repair is not recommended [5, 21].
Midsubstance MPFL injury should be repaired
only in rare cases with extensive VMO fascial
disruption in a high-energy dislocation. Patellar
attachment MPFL injury can be classified as a
ligamentous or bony avulsion from the medial
margin of the patella [28]. A third type includes
an osteochondral fragment with articular
cartilage involvement from the medial patella
(fig. 1). According to a retrospective study,
ligamentous patellar MPFL avulsion is not
associated with an increased rate of recurrent
instability compared with femoral MPFL
avulsion injury with similar nonsurgical
management
[28].
Articular
cartilage
involvement can be considered an indication
for surgery, and cartilage defects should be
repaired by reduction and fixation of the
fragment [14, 15].
In some cases, the MPFLmay be injured in two
locations [6]. Most likely, MPFL patellar or
femoral attachment disruption can be
accompanied by midsubstance total or partial
tear. Therefore, MPFL reconstruction may be
Fig. 1: Medial osteochondral avulsion fracture with
articular surface involvement (at the patellar
insertion of the medial patellofemoral ligament).
Axial proton-density magnetic resonance image.
Fig. 2: Medial patellofemoral ligament patellar
attachment injury with avulsion fracture from the
medial patellar margin. Suture anchors have been
inserted to the patella for injury repair.