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STATIC ROTATIONAL KNEE LAXITY MEASUREMENTS AND ANTEROLATERAL INSTABILITY
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rotational laxity for which the sensitivity and
specificity to detect an ACL injury has been
reported in the literature is the Rotameter. A
threshold of 3.2° for the SSD in internal
rotation at 5 Nm allowed to correctly identify
38% of patients (sensitivity) and reject 95% of
healthy subjects (specificity). This threshold is
similar to the induced changes after sequential
sectioning in cadaveric knees. Hence it shows
that
in vivo
static rotational laxitymeasurements
need to be improved to produce reliable
clinically useful information.
Combining static anterior and rotational knee
laxity measurements as well as exploiting the
features offered by new arthrometers like the
slope of the load-displacement curve improves
the diagnosis of ACL tears. With this
combination, a positive result confirmed an
ACL tear (sensitivity: 81%) regardless of the
sub-type of the ACL tear and the associated
injuries. This performance is similar to the one
reported for MRI (sensitivity 81%, specificity
96%). Despite this high diagnostic precision,
the performance of arthrometers needs to be
improved, especially when it comes to the
measurement of rotational laxity and the effect
of associated intra- or extraarticular lesions.
Tibial rotation being influenced by lesions of
the collateral ligaments, meniscal roots, the
ITB and the Kaplan fibers or other peripheral
capsuloligamentous structures, there is
currently a paucity of both
in vivo
and
in vitro
studies analysing these variables individually.
Knee laxity after anterior cruciate
ligament reconstruction
ACL reconstruction surgery should aim to
restore knee laxity in all directions. Knee laxity
measurements are therefore of interest as a
postoperative control to follow the graft
evolution and detect potential abnormalities
like graft elongation, recurrent tears, increased
postoperative laxities. These may occur in graft
malpositioning or graft failures. Numerous
studies reported knee laxity measurements at a
specific time point after ACL reconstruction.
Their conclusions are difficult to generalize,
due to the diversity of graft types, surgical
techniques, fixations, associated injuries,
rehabilitation approaches, but also the laxity
measurement techniques. Prospective follow-
up studies with systematic measurements of
knee laxity are missing, so that the current
knowledge on postoperative changes like the
influence of the graft ligamentisation process
on knee laxity is poor.
This lack of methodological scientific evidence
may explain why many studies have shown no
difference in anterior laxity after different
types of surgical reconstruction between a
bone-patellar tendon-bone (BPTB) and a
semitendinosus (ST) autograft (Ahlden). The
current knowledge on knee laxity after ACL
reconstructions as well as after many other
surgical interventions thus needs to be
improved. Little is known about the
postoperative changes of ALL reconstructions.
A recent study by Schon
& al.
indicated that
current ALL reconstruction techniques may
lead to a decrease of internal rotation and
overconstraint of the knee joint.
CONCLUSIONS
Static knee laxity measurements offer the
possibility to improve the understanding of the
capsuloligamentous knee envelope, both in
healthy and injured knees as well as after
different types of reconstruction procedures.
The recent development of rotational laxity
measurement devices has added significant
knowledge to the field. The combination of
knee laxities is now possible and has led to the
concept of knee laxity profiles in healthy knees.
The high variability between individuals as
well as the ability to identify knees with
increased physiological knee laxity may be of
interest in the screening and prevention
programs for athletes. Indeed, subjects with
excessive physiological knee laxity may have a
greater risk to sustain an ACL injury as well as
to display inferior outcomes after an ACL
reconstruction.
The combination of multidirectional laxity
assessments in ACL-injured knees improves
the diagnostic capacity of arthrometers.