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M. THAUNAT, C.A. WIJDICKS, P. IMBERT, C. LUTZ, J.M. FAYARD, B. SONNERY-COTTET
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and stiffness of 31 N/mm, when averaging the
values of all 29 unpaired specimens [1,2]. This
structural data provides the rationale to select
the appropriate autografts in conjunction with
adequate fixation methods for reconstruction of
the ALL.
In vitro
robotic assessments of the ALL in the
setting of an ACL injury have defined the ALL
as a significant lateral knee stabilizer [3].
Specifically, as a secondary stabilizer during
internal rotation torque and simulated pivot-shift
test in the ACL-deficient state.
These results were further confirmed by other
investigators utilizing a surgical navigation
system [4]. Twelve fresh-frozen cadaveric
knees were tested in internal rotation at 20° and
90° of flexion and then subsequently tested
using a simulated pivot-shift test consisting of
coupled axial rotation at 30° of flexion. Serial
sectioning of the ACL, ALL, and ITB was
performed. On the contralateral knee,
sectioning was performed in the reverse order.
Measurements were collected using a surgical
navigation system before and after each
sectioning. This study demonstrated that the
ALL is involved in rotational control of the
knee at varying degrees of knee flexion and
during a simulated pivot shift. Concomitant to
an ACL or ITB transection, sectioning the ALL
further increased rotational laxity.
Within the discussion of these two papers, it
became clear that a reconstruction of the
ALL in conjunction with a torn ACL should
be met with critical data, as the significant
biomechanical importance lends itself to the
need for sufficient and reproducible surgical
techniques. Key points in this surgical
treatment would involve techniques that
provide stability without overconstraint while
maintaining a minimally invasive, yet
reproducible, surgical approach for this
secondary stabilizer.
ISOMETRIC BEHAVIOR
Recently, anatomical and functional charac
teristics of the ALL have been reported
demonstrating a structure that originates near
the lateral epicondyle on the femur and inserts
broadly in a fan-like attachment on the tibia
between Gerdy tubercle and the fibular head.
The purpose of the study published by Imbert
[5] was to measure the variations in length
during exion and internal tibial rotation of the
3 different femoral insertions of the ALL
(proximal-posterior; lateral epicondyle; distal-
anterior) while maintaining a xed tibia
insertion (fig. 1). His hypothesis was that the
different femoral insertions will exhibit
different variations in length throughout the
range of motion (ROM) of the knee. This study
shows varying behavior of the ALL dependent
on the 3 different anatomic femoral described
insertions. The proximal and posterior to
epicondyle femoral position is the only position
with a favorable isometry. The presumed
function of the ALL is to prevent excessive
tibial internal rotation near full extension of the
knee as evidenced here at IR20. To assume this
function, the ALL should be maximally
tensioned at IR20. It should also not restrain
knee ROM, gured here by evaluating the
isometry from 0 to 120 of knee exion as well
as at IR90, during which it should stay relaxed.
To answer these requirements, the distance
between the couple of points during knee
motion from full extension to 120 exion and
IR90 should not exceed the maximal distance
at IR20. The proximal-posterior femoral
location was the only position to reveal a
decrease in length during knee exion. This
relaxation when knee going to exion is
appropriate to allow maximal ALL tensioning
at IR20 without restraining the tibial internal
rotation at 90. For rotation, a similar internal
rotation at 20 was observed as in the other
femoral positions, but at 90 the internal rotation
was signi cantly increased as a result of the
relaxation during exion. Both the epicondyle
and distal-anterior femoral locations resulted in
signi cant length increases with knee exion.
Additionally, there were length increases noted
in the distal femoral insertion with internal
rotation forces at both 20 and 90. With
increasing degrees of knee exion in the intact
knee, the internal tibial rotation also increases.
This suggests that the internal rotation restraint
of the knee should relax through knee exion.