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[9]. This could be a result of better visualization
of the articular cartilage but other MRI studies
have actually had means less than 3mm for
patients with patellofemoral instability [18,
21]. The means of trochlear groove depth at the
distal trochlea of our patients were nearly equal
to those at the proximal trochlea.
Lateral trochlear inclination is another measure
ment of trochlear morphology prevalent in
patellofemoral literature [16, 18, 31-33]. These
studies have primarily been performed in MRI
based studies, with Carrillon
et al.
establishing
the cutoff between Controls and those with
patellar instability at 11° [31]. This value is
lower than our means of 21.27°±0.66 and
13.31°±1.36 at the proximal trochlea and
21.74°±0.52 and 15.95°±0.85 at the distal
trochlea. Salzmann
et al.
had values closer to
ours, but their research was based on patients
selected on a radiographic criteria of trochlear
dysplasia [16]. Carrillon’s research was similar
to our own in that patients were selected on
basis of a history and physical examination
consistent with patellofemoral dislocations.
Carillon
et al.
also performed the measurements
at the most proximal slice with complete
articular cartilage. Our data still reflects the
trend that a decrease in LTI results in less
resistance to the lateralization of the patella,
which increases chances of patellar instability.
Facet asymmetry is an aspect of trochlear
dysplasia that has had very limited research
until recently. This has mostly been studied in
MRI based studies [16, 21]. Pfirrmann
et al.
first showed that a facet ratio greater than 5:2
(lateral to medial). Note that Pfirrmann
et al.
reported a facet ratio of less than 2:5 (medial to
lateral). We inverted this ratio to correspond to
our lateral to medial ratio of ETIT. Using ETIT,
Pfirrmann identified those with trochlear
dysplasia with sensitivity and specificity of
100% and 96%, respectively [21]. We found
our means of 1.51 and 2.11 at the 1
st
cut and
1.40 and 1.97 at the 2
nd
cut for Controls and
PFJDs respectively to be lower than the 2.5
cutoff Pfirrmann documented. This difference
may be due to difference in patient selection in
that ours were selected on criterion of patellar
dislocation, while Pfirrmann
et al.
divided
patients based on radiographic evidence of
trochlear dysplasia. Salzmann
et al.
also
researched facet asymmetry in comparing axial
radiographs to MRI. Their research did not find
significance for the measurement, but their
means for MRI saw the facet ratio increase
from 1.6 to 1.9 as the degree of dysplasia
increased [16]. This makes our research unique
in that it was the first application of facet
asymmetry to patellar instability.
Condylar height has thus far had limited
research and it has lacked any clear answers.
Escala
et al.
evaluated lateral, medial, and
central condylar height measurements but none
were found to be significant between Controls
and those with patellar instability [9]. Our data
demonstrated that several measures of trochlear
morphology (LCH, % CCH, MCH and %
MCH) proved significantly different at the
proximal trochlea. LCH presumably has a
mechanical role in resisting lateral patellar
displacement, while MCH may simply reflect
overall hypoplasia of the trochlea or condyles.
Interestingly, we also evaluated condylar
heights as a proportion of epicondylar width as
Biedert
et al.
published in 2009 [34]. At the
distal trochlea, despite having no significance
with our standard condylar heights, all three
condylar heights expressed as a percent of
epicondylar width proved significant. Biedert’s
published means for LCH (Controls 81%;
PFJDs 82%), Central Condylar Height (CCH)
(Controls 73%; PFJDs 77%), and Medial
Condylar Height (MCH) (Controls 76%; PFJDs
79%) [34]. Biedert’s results proved similar to
our own at the lateral condyle of the distal
trochlea, but our groups differed at the central
and medial condyle. Biedert
et al.
and our
group, however, did find a larger difference
between the Normal versus PFJD groups with
the medial and central condylar heights than at
the lateral condyle. The discussion of which