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However, use of the Q-angle alone grossly
underestimatesthecomplexityofpatellofemoral
alignment and often leads to errors of diagnosis
and treatment. Furthermore, the Q-angle is
highly variable and unreliable as ameasurement
[5, 6]. These considerations have led the
International Patellofemoral Study Group
(IPSG) to recommend abandonment of clinical
measurement of Q angle, preferring imaging
studies to estimate the lateralizing vector at the
PFJ. The preferred method is to use axial
imaging (CT or MRI) to assess this vector [7].
Careful palpation of both medial and lateral
retinaculum is helpful to localize tenderness.
Studies have shown that 90% of patients with
patellofemoral pain syndrome (PFPS) had pain
in some portion of the lateral retinaculum [8].
Palpation of the specific site of pain can help
guide further investigation of what mechanical
overload, if any, has occurred. The patella
should be displaced to the side undergoing
examination so that while fibers are being
palpated, they are also brought away from
underlying structures in order to avoid
confusion about the site of tenderness.
The term “patellar tracking” refers to the
change in position of the patella relative to the
femur during active knee flexion and extension.
While it is obviously important, no clinically
useful tracking measurement systems exist.
The J sign is a useful but non-specific sign of
patellofemoral pathology. It represents a patella
that does not seat immediately as the knee is
flexed, as well as the rotational torque between
the extensor hood (tendons, retinaculum and
patella) and the femur. But many factors can
contribute to abnormal tracking, such as
trochlear dysplasia, patella alta, and medial
retinacular laxity. Thus, the clinical usefulness
of abnormal tracking in the assessment of
alignment remains unclear because its
relationship to the loading characteristics of the
joint is not a simple one.
Normal tracking of the patella within the
trochlear groove has been described by
translation and tilt, both of which change with
knee flexion angle [9]. As the normal knee
begins to flex, the patella becomes engaged in
the trochlea, causing it to translate medially
approximately 4mm by 20 degrees of knee
flexion. With progressive flexion it then follows
the trochlear groove approximately 7mm
laterally by 90 degrees of knee flexion. While it
is translating laterally, it also tilts medially in a
progressive linear fashion about 7 degrees at 90
of flexion. Deep in flexion, it is more medially
tilted with the odd (far medial) facet articulating
with the medial trochlea. The patella flexes
with the knee at a rate of about 0.7 degrees per
degree of knee flexion [9].
Abnormal patellar tracking may be caused by
muscle weakness, soft tissues deficiencies,
abnormal joint geometry, or limbmalalignment.
Early in flexion the medial retinaculum
(specifically the medial patellofemoral
ligament) provides much of the restraint to
lateral displacement of the patella. Its
contribution to patellar restraint decreases with
flexion from 50% at 0 degrees of flexion to
30% at 20 degrees knee flexion, as the patella
begins to engage the femoral trochlea. The
lowest force required to displace the patella
laterally occurs at 30 degrees of flexion. With
further flexion, the patella engages the trochlear
groove and trochlear geometry becomes the
primary constraint to mediolateral patellar
motion. In cadaver studies where the trochea
has been modified (flattened) to simulate a
dysplastic trochlea, the constraint of the patella
is reduced by 70% [10].
The diagnosis of episodic lateral patellar
dislocation and other conditions associated
with insufficient patellar constraint (e.g. medial
patellar instability following excessive lateral
release) requires documentation of excessive
laxity of the retinacular constraints. Comparison
to the opposite knee can be helpful, provided
that the complaint is unilateral [11]. Patellar
mobility is best assessed both at 0º and at 30º of
flexion (fig. 4). The checkrein often is easier to
recognize at 0º because in this position the
trochlea does not constrain the patella, so it is
easier to feel an “endpoint” as you displace the
patella laterally [12]. At 30º of flexion the
patella is seated in the trochlear groove and it is
easier to quantify the amount of mobility in
each direction [12]. Normal translation should