56 / 460
Acute Patellar Dislocation: Which Examination for Which MPFL Lesion?
55
Ahmad
et al.
described what they called the
moving patellar apprehension test [23].
Essentially, a lateral displacement force is
applied to the patellar as the knee is taken from
extension into 90 degrees flexion and back to
extension. The patient is observed for appre
hension. In the second part of the test the knee
is taken through the same range of motion, but
with a medial displacement force applied to the
patellar, which should eliminate apprehension
in the patient with an incompetent MPFL.
Compared to the ability to dislocate the patella
under anesthesia, the moving patellar apprehen
sion test was found to be highly sensitive, and
both accurate and specific.
It is important to consider the amount of lateral
translation of the patellar in terms of the overall
ligamentous laxity of the patient. Generalised
ligamentous laxity is assessed using the signs
described by Beighton and Horan [24]. These
are passive dorsiflexion of the little finger
beyond 90 degrees with the forearm flat on a
table, passive opposition of the thumb to the
flexor aspect of the forearm, hyperextension of
the elbow beyond 10 degrees, hyperextension
of the knee beyond 10 degrees, and forward
flexion of the trunk so that the palms of the
hands can be rested easily on the floor. They
can be scored by assigning a score of zero
(absent) or one (present) to each of the tests
that can be performed bilaterally as well as to
trunk flexion [25]. A total score of 4 or more
out of 9 is considered indicative of generalized
ligamentous laxity.
In summary, the MPFL is almost always injured
in an acute patellar dislocation. The most
frequent site is the femoral attachment and this
is often associated with tenderness. The second
most frequent site is the patellar attachment, but
multiple sites of injury have also been reported,
especially in children and adolescents. Lateral
patellar glide can be assessed with the knee in
extension and also in 20 to 30 degrees flexion.
Displacement of more than 50% of the width of
the patella is considered abnormal. Patellar
apprehension can be assessed at the same time.
Consideration should also be given to the
presence of generalized ligamentous laxity.
Literature
[1] Conlan T, Garth WPJ, Lemons JE. Evaluation of
the medial soft-tissue restraints of the extensor mechanism
of the knee.
J Bone Joint Surg Am. 1993rd ed. 1993 May;
75(5): 682-93.
[2] Senavongse W, Amis AA. The effects of articular,
retinacular, or muscular deficiencies on patellofemoral joint
stability. The Journal of bone and joint surgery.
British
volume. 2005
th
ed. 2005 Apr. 87(4): 577-82.
[3] Sallay PI, Poggi J, Speer KP, Garrett WE.
Acute dislocation of the patella. A correlative pathoanatomic
study.
Am J Sports Med. 1996 Jan. 24(1): 52-60.
[4] Balcarek P, Walde TA, Frosch S,
Schüttrumpf JP, Wachowski MM, Stürmer
KM,
et al.
Patellar dislocations in children, adolescents and
adults: a comparative MRI study of medial patellofemoral
ligament injury patterns and trochlear groove anatomy.
Eur J
Radiol. 2011 Sep.; 79(3): 415-20.
[5] Mochizuki T, Nimura A, Tateishi T,
Yamaguchi K, Muneta T, Akita K. Anatomic study
of the attachment of the medial patellofemoral ligament and
its characteristic relationships to the vastus intermedius.
Knee Surg Sports Traumatol Arthrosc. 2012 Apr. 11.
[6] Amis AA, Firer P, Mountney J, Senavongse
W, Thomas NP. Anatomy and biomechanics of the medial
patellofemoral ligament.
Knee. 2003 Sep.; 10(3): 215-20.
[7] Feller JA, Feagin JA, Garrett WE. The medial
patellofemoral ligament revisited: an anatomical study.
Knee
Surg Sports Traumatol Arthrosc. 1993;1(3-4): 184-6.
[8] Nomura E, Inoue M, Osada N. Anatomical
analysis of the medial patellofemoral ligament of the knee,
especially the femoral attachment.
Knee Surg Sports
Traumatol Arthrosc. 2005 Oct.; 13(7): 510-5.
[9] Smirk C, Morris H. The anatomy and reconstruction
of the medial patellofemoral ligament.
Knee. 2003 Sep.;
10(3): 221-7.
[10] Steensen RN, Dopirak RM, McDonald WG.
The anatomy and isometry of the medial patellofemoral
ligament: implications for reconstruction.
Am J Sports Med.
2004 Sep.; 32(6): 1509-13.
[11] Warren LF, Marshall JL. The supporting
structures and layers on the medial side of the knee: an
anatomical analysis.
J Bone Joint Surg Am. 1979 Jan.; 61(1):
56-62.