Biomedical Engineering Reference
In-Depth Information
the tendon and bone along the length of the bone tunnel. The authors noted
progressive maturation of this interface over time. By 12 weeks, Sharpey's fibers
were clearly present at the interface. At the 2, 4, and 8-week time points, the
specimens failed by pullout of the tendon from the bone tunnel. However, at 12
and 26 weeks, all specimens failed by pullout of the tendon from the loading
apparatus or midsubstance rupture. This progressive strength was accompanied
by increasing amounts of bone ingrowth and mineralization. Other animal studies
have also demonstrated that the mechanical strength of the tendon-to-bone interface
can be correlated to the degree of bony ingrowth, mineralization, and maturation of
the provisional tissue [
29
,
30
].
The degree of healing and Sharpey's fiber presence between the graft and host
bone is not uniform circumferentially along the length of the tunnels [
13
,
20
,
24
,
26
,
32
]. The reasons for this variation are not known, but it may be related to
differences in the mechanical and biologic environments at different points along
the graft. The graft, along its course, may see different degrees of micromotion as
well as different morphologic types of bone with varying capacities to influence
ingrowth into the graft. Both rabbit and rat models have demonstrated that healing
within the tibial tunnel, as determined by histologic analysis, was inferior compared
to the femoral tunnel [
19
,
33
]. It has been suggested that this may be related to the
observation that the femoral aspect of the graft is exposed along its length to
cancellous bone, but the tibial tunnel has dense cancellous bone only at the segment
closest to the articular portion of the graft. This postulation is supported by a study
using a rabbit model that showed better healing when the graft was inserted into a
cancellous bone tunnel vs. a marrow-filled space [
34
].
13.4 Factors Affecting Graft Healing in ACL Reconstruction
13.4.1 Graft Source
Allografts have become a viable option for ACL reconstruction and provide some
potential advantages compared to autograft, including decreased surgical time and
the elimination of donor site morbidity [
35
]. Shino et al
.
[
36
] showed in a dog
model that there were no differences in revascularization, mesenchymal cell infil-
tration, and remodeling between deep frozen patellar tendon allograft and autograft.
The mean maximal tensile strength was similar at 30 weeks. Nikolaou et al. also
found no differences in the histology and revascularization of patellar tendon
autografts and allografts in a dog model [
37
]. The ultimate load-to-failure and
stiffness were similar between both graft types and reached 90% of control ligament
strength by 36 weeks.
Several other studies have found significant differences in the biomechanical
and histologic properties of allografts vs. autografts. In a goat model, comparing
bone-tendon-bone autograft to deep frozen allograft, the autograft group had
Search WWH ::
Custom Search