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INTRODUCTION
Rotatory knee laxity is controlled by the
cruciate ligaments and secondary restraints,
such as the capsule, menisci, collateral
ligaments, and the iliotibial band (ITB).
Clinical diagnosis of rotatory knee laxity can
be performed by static and dynamic rotatory
laxity tests. Static laxity testing is simple and
non-invasive. It measures rotation of the tibia
with respect to the femur and is not yet used in
daily clinical practice. The goal of knee laxity
measurements is to identify the laxity pattern
of an individual patient, improve the diagnosis
of anterior cruciate ligament (ACL) and
peripheral injuries as well as the clinical
outcome following ACL reconstruction
surgery. The contribution of rotational laxity in
this concept still needs to be defined.
Historically, Wang and Walkers analyzed
rotational laxity in cadavers. They recorded
torque-rotation graphs from each cadaver knee
they examined and noticed a high inter
individual variability. Our own experiments
showed that cutting the PL bundle of the ACL
lead in average to a 10% increase in rotation,
whereas the section of both bundles induced a
15% increase in rotation with a torque of 5 N/m
at 30° of flexion (Lorbach).
A first attempt to measure rotation in vivo has
been performed by Zarins in 1983. With
increasing awareness of the importance of
rotational control after ACL reconstruction,
several devices to analyze rotation were
developed by groups from Pittsburgh (Musahl),
Vermont (Shultz), Luxembourg (Lorbach,
Mouton, Seil), Decatur (Branch) with devices
analyzing rotation. Each device is different,
and the applied measurement conditions vary
widely, mainly with respect to patient position
ing, knee flexion angle, and the applied torques.
The amount of torque applied usually varies
between 5 and 15 Nm depending on lower limb
fixation and patient comfort. Knee rotation is
higher if the knee is flexed at 90° compared to
20° and if the hip is extended compared to the
flexed position at 90°. To avoid overestimation
of the measurements when rotation is measured
at the foot, a solution is to measure tibial
rotation directly at the proximal tibia
via
electromagnetic sensors (Alam).
In our experimental device, the Rotameter
(Lorbach), the subject is lying prone to
reproduce the dial test position. Hips are
extended and knees flexed at 30°. The Rota
meter overestimates the total range of rotation
at 5, 10, and 15 Nm by an average of 5, 10, and
25°, respectively. Our current version yields
STATIC ROTATIONAL KNEE
LAXITY MEASUREMENTS AND
ANTEROLATERAL INSTABILITY
R. SEIL, C. MOUTON, D. THEISEN