TIBIAL SLOPE AND ACL RUPTURE: MRI ASSESSMENT
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Two independent reviewers calculated the
angles on each MRI using a modified Hashemi
method which published previously by Lustig
et al.
[5].
According to the procedure described by those
authors, to establish the tibial slope, we used
the proximal tibial anatomic axis (PTAA),
which demonstrates the best correlation with
the tibial shaft anatomic axis (TSAA) [17]. The
PTAA is calculated on the mi-sagittal cut by a
line joining the midpoint between the anterior
and posterior tibial cortices at the level of tibial
tuberosity and at another level 5cm below it.
The angle subtended between the tibial axis to
the horizontal was calculated (Angle TA-H).
The MTP and LTP cuts were used to measure
the medial and lateral tibial slope (MTS, LTS)
respectively.
The PTAA was superimposed on these cuts by
means of TA-H angle. The tibial slope in each
compartment was measured as the angle
between a tangent line connecting the highest
points in the anterior & posterior parts of the
tibial and the perpendicular to the PTTA.
All measurements were positioned as an
overlay and remained in a fixed position on the
complete image series. The meniscal slope
(MS) was defined in the same manner as the
PTS. A tangent to the superior edge of the
meniscosynovial border of the anterior and
posterior meniscus on the sagittal plane was
chosen instead of the tibial plateau cortices.
A posterior inclination to the horizontal was
assigned a positive value, while an anterior
inclination was assigned a negative value. The
measurements were done by two observers and
repeated again after interval of two weeks.
The average PTS and MS angles are reported
as mean angles with standard deviation.The
data was statistically analyzed and the
differences between the bony and soft tissue
slope were compared between the two groups
using independent
t
-test.
RESULTS
The average PTS and MS angles are reported
as mean angles with standard deviation.The
data were initially analyzed for each reviewer
and then the parameters were compared
between the two groups. The maximum and
minimum values for each parameter were also
reported.
Statistical Analysis
The assumption of normality was assessed
with Kolmogorov-Smirnov tests which
revealed that all the measured parameters of
both groups were within normal distribution
(
p
<0.0001).
Inter-observer reliability:
Repeated measures analysis of variance and
95% confidence limits were used to establish
whether the mean slope was altered between
reviewers by means of Intra class Correlation
Coefficient (ICC) and the results showed high
ICC for all the variants which reveal strong
agreement between the observers for all
measurements (table 1).
VARIANT
ICC (95 % CI)
LTS ACL Group
0.9349
MTS ACL Group
0.9148
MMS ACL Group
0.9252
LMS ACL Group
0.9713
LTS CNT Group
0.8841
MTS CNT Group
0.9186
MMS CNT Group
0.8857
LMS CNT Group
0.9159
Table 1:
Inter-observer reliability of the bony and
soft tissue slope for ACL and control (
CNT
) groups.