Soft Tissue-to-Bone Healing in Anterior Cruciate Ligament Reconstruction - Structural Interfaces and Attachments in Biology - page 274

graft-tunnel healing using an Achilles tendon autograft fixed with a biodegradable
poly-( D , L -lactide) interference screw [ 22 ]. They found that at 6 weeks only a partial
interstitial fibrous zone existed between the graft and bone tunnel. At 24 weeks, all
specimens had a tunnel entrance site that resembled a normal appearing ligament
attachment site with a bony bridge between the intra-tunnel graft and the insertion
site. At 52 weeks, the insertion site showed the normal four zones associated with
direct tendon-to-bone attachments.
Despite this encouraging result, in their biomechanical analysis the authors
found that in the early postoperative period the mechanical properties of the graft
were significantly decreased [ 48 ]. There was no graft pullout after 24 weeks,
suggesting that long-term fixation was not compromised. Other authors have
also found similar decreases in early load-to-failure of soft tissue grafts fixed
with bio-absorbable interference screws and better early fixation strength with
suspensory fixation [ 49 , 50 ]. The clinical implications of these findings are not
clear, as a recent meta-analysis suggested that fixation of hamstring grafts with
interference screws on the femoral side may be associated with a lower rate of
clinical failures [ 51 ]. However, there is a general tendency for many surgeons to
recommend a less aggressive rehabilitation protocol and timeline with the use
of soft tissue-only grafts.
13.4.3 Bone Tunnel Properties
Although not supported by strong basic science data, it is generally thought that
increasing the amount of graft in the tunnel and making the fit as tight as possible
increase the security of tunnel healing. In an extra-articular canine model, Greis
et al. demonstrated a statistically significant increase in load-to-failure with an
intraosseous graft length of 2 cm vs. 1 cm [ 52 ]. Additionally, a tighter fit of the
graft in a 4.2 mm diameter tunnel also had a significantly higher load-to-failure
compared to a 6 mm diameter tunnel.
Other studies have questioned the need for a snug (“line-to-line”) graft fit and for
maximizing intraosseous length. In an intra-articular canine model, a tunnel diam-
eter difference of 2 mm on the tibial side did not influence ultimate load-to-failure
[ 53 ]. Using the same model to evaluate the effect of intraosseous graft length, it was
shown that with 5 mm of intraosseous graft vs. 15 mm there was no difference in
histological and biomechanical parameters of graft healing at 6 weeks [ 54 ]. How-
ever, in an intra-articular goat model, reconstructions with 15 mm of intraosseous
graft resulted in significantly more anterior translation at 6 weeks vs. those with
25 mm of intraosseous graft [ 55 ]. At 12 weeks, there were no significant differences
with respect to anterior translation, in situ forces, stiffness, ultimate failure load,
and ultimate stress.