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center of the native ACL femoral attachment
site. Using the center of the nativeACL femoral
attachment site as a defined anatomic reference
point, the surgeon may choose to alter the
location of the ACL femoral tunnel within the
ACL femoral attachment site based on different
philosophies.
• A central position within the native ACL
femoral attachment site is favored by many
surgeons based on biomechanical studies
demonstrating that a single-bundle ACL graft
positioned at the center of the native ACL
femoral and tibial attachment sites best
controls anterior tibial translation and tibial
rotation during a simulated pivot shift test
and more closely restores knee kinematics to
that of the normal knee compared with other
anatomic ACL graft placements (fig. 5).
• Moving the center of the ACL femoral tunnel
towards the region of the center of the
anteromedial (AM) bundle attachment site
will result in an ACL graft that has smaller
graft-length changes (isometric) and
experiences lower and relatively constant
in
situ
ACL graft forces. Lower
in situ
ACL
graft forces may theoretically reduce the risk
of ACL graft re-rupture compared to a
centrally placed ACL graft which experiences
higher
in situ
ACL graft forces. However,
moving the center of the ACL femoral tunnel
towards the center of the AM bundle
attachment site often results in a more vertical
orientation of the ACL graft that is not as well
aligned as a centrally placed graft to control
the pivot-shift phenomena (fig. 6).
• Moving the center of the ACL femoral tunnel
towards the center of the posterolateral (PL)
bundle attachment site results in an ACL graft
that experiences larger graft-length changes
and higher
in situ
ACL graft forces in
extension. Although this femoral tunnel
position results in a more horizontal ACL
graft orientation that is better aligned to
control the pivot shift, higher
in situ
ACL
graft forces and greater ACL ligament strain
could theoretically increase the risk of ACL
graft re-rupture (fig. 7).
Recent studies have demonstrated that the ACL
fibers in the region of the direct insertion
contribute more restraining force to anterior
tibial translation and the pivot shift phenomena.
To restore more of these fibers, the ACL
femoral tunnel is positioned higher in the
attachment site closer to the lateral
intercondylar ridge and midway between the
center of the AM bundle and the center of the
native attachment site (fig. 8).
Fig. 5