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TIBIAL SLOPE AND ACL RUPTURE: MRI ASSESSMENT
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Under normal loading conditions, patients with a
greater lateral PTS may have greater internal
rotations of the lower leg. The resulting internal
rotation stresses the ACL and may increase the
injury risk [15]. Inconsistency was reported by
Hashemi
et al.
[20] in which the male’s medial
PTSwas associatedwith injurybut not the females.
They also observed an increased medial tibial
plateau depth in conjunction with an increased
PTS in patients with noncontact ACL injuries.
The anterior tibial translation increased
significantly after an ACL rupture [25, 26]. It
suggested that the ACL served as the main knee
stabilizer in tibiofemoral translation, with
specific tension being produced in the course of
internal rotation [15]. When an anterior force is
applied to the tibia of the knee with intact
ligaments, the internal rotation that occurs
imparts considerable stress on the ACL [26].
Tibial slope on lateral tibial plateau undertakes
an important role during extension motion
because it favors internal rotation, which, in
turn, imparts considerable stress on the
extended ACL [25].
The PTS plays an important role in knee
replacement, after total knee arthroplasty
(TKA); the posterior tibial slope affects
anteroposterior stability, range of motion, and
contact pressure within the tibiofemoral joint
[28]. Moreover, an inappropriate cutting angle
of the posterior tibial slope results in
polyethylene wear, component loosening and
posterior cruciate ligament strain [29].
During early weight bearing after ACL
reconstruction, a steep tibial slope might place
increased load on the healing graft and fixation
material and potentially increase the risk of
early elongation or acute failure. Improved
knowledge about the effect of the tibial slope
on the graft after ACL reconstruction might
serve as a basis for individually adapted
postoperative rehabilitation programmes [15].
A small increase in tibial slope, which may
occur inadvertently during medial opening-
wedge HTOs, would not adversely affect
overall A-P knee stability or the in situ forces in
the cruciate ligaments. However, the changes
observed in the resting position with
osteotomies in the sagittal plane may be
important in the treatment of cruciate ligament-
deficient knees [30].
Inconsistencies within and between tibial slope
measurement methodologies have precluded
repeatable demonstration of an “at ACL injury
risk” range of tibial slope values.
Identification of new risk factors is paramount to
prevention. While trends in the current literature
indicate a potential relationship between ACL
injury and PTS, standardized techniques and
more consistent and repeatable data are required
to definitively link the two [25].
The future goal of the research relating tibial
plateau slope to ACL injury risk should be to
establish not only the extent of the role of tibial
slope in injury risk but also the extent to which
that risk can be decreased by prophylactic
interventions such as neuromuscular training.
Such methodologies will also enhance the
objectivity of tibial slope as a factor in the
assessment of post-injury stability and long-
term sequelae [25].
Subjects with an increased tibial slope who are
participating in high-risk activities should
perhaps consider prophylactic precautions.
This could include education on the increased
risk for ACL rupture, as well as injury
prevention training [5].
One of the limitations of the present study is
that we did not have access to the height and
weight of the subjects, and consequently we
did not explore correlations that may exist with
the measured slopes. These parameters should
be tested in future. Secondly, it is important to
note that the MRI voxel resolution, the access
to a sufficient length of the tibia and the ability
to identify landmarks precisely all could have
an impact on the slope measurements.
However, although these factors may influence
the results, they will not influence the large
inter individual differences or the large range
of slope values.