We developed an in situ freeze-thaw model designed to simulate an
ideally placed and oriented autogenous graft of the anterior cruciate
ligament. In this model, the anterior cruciate ligament was exposed, and
the femoral insertion, tibial insertion, and body of the anterior cruciate
ligament were frozen in situ with specially designed freezing probes.
Freeze-thaw cycles were repeated five times. We used the technique in
thirty-three mature goats to study the biological and biomechanical
outcomes of the devitalized and devascularized anterior cruciate ligament
at zero, six, and twenty-six weeks after treatment. Thus, the collagen
fibers of the simulated autogenous graft remain in normal anatomical
position and the simulated graft is fixed under physiological tension. At
twenty-six weeks, no statistically significant differences were noted
between treated and contralateral control (untreated) ligaments relative to
anterior-posterior translation, maximum force to rupture, stiffness in the
linear region of the force-length curve, modulus of elasticity in the
linear region, strain to maximum stress, or maximum stress. The only
statistically significant difference was an increase in cross-sectional
area of the ligament. This increase was 22 and 42 per cent greater than
that in the control ligaments at six weeks and six months. At six months,
the ligaments in the control group had an average mid-cross-sectional area
of 17.7 +/- 1.2 square millimeters and the ligaments in the experimental
group, 25.2 +/- 3.1 square millimeters. Changes in the size and density of
the collagen fibrils also were demonstrated at six months. These
observations are in sharp contrast to our previous studies of replacement
of the anterior cruciate ligament, in which an allograft of the ligament or
an allograft supplemented with a 3M ligament augmentation device (LAD; 3M,
St. Paul, Minnesota) was used. In those studies, an average reduction in
maximum strength of 75 per cent for the allografts and 50 per cent for the
allografts that had a ligament-augmentation device was found at one year.
We concluded that devitalized, devascularized anterior cruciate ligaments
do not lose strength if the anatomical position and the orientation of the
collagen fibers are not altered.