Advances in the Canine Cranial Cruciate Ligament, 2nd edition

Intra-Articular Repair for Cranial Cruciate Ligament Rupture in the Dog 205

1986). At 1 year, both grafts had a similar
appearance on histopathology. In a study of 25
dogs, central-third patella tendon deep-frozen
allografts were implanted and showed evidence
of revascularization at 6 weeks, and a similar
histopathologic appearance to the native CrCL
at 30 weeks (Shinoet al. 1984). In a similar study
comparing frozen CrCLallografts to CrCLauto-
grafts (Kirkpatricket al. 1996), allografts were
weaker than autografts, and appeared to have
delayed revascularization at all time points up
to 24 months.
Gamma-irradiation is effective at decreas-
ing negative biological reactions in the
recipient, but can greatly alter mechanical
properties (Fuet al. 1999); this effect seems
to be dose-dependent (Fideler et al. 1995).
Goertzen reported that bone-ligament-bone
CrCL grafts deep-frozen and sterilized with
gamma-irradiation had similar strength as
non-irradiated frozen grafts. At 12 months after
implantation, the grafts had 60–70% strength
of the normal CrCL and a similar collagen
pattern (Goertzen et al. 1995). Although 60
dogs were studied, limitations included the
fact that limbs were immobilized for 5 weeks
after surgery, and functional outcome was not
assessed. Ethylene oxide has minimal effects of
mechanical properties, but residues could be
either inflammatory or carcinogenic (Silvaggio
et al. 1993; Bechtoldet al. 1994).

A final emerging technique to decrease

immunogenic potential while maintaining

mechanical integrity of the graft is called

decellularization. This refers to the process of

removing cells from the tissue while preserving

the structural and functional proteins that

constitute the ECM. Decellularized tissue scaf-

folds have the potential to provide available

biocompatible graft material that can resemble

native tissue structurally, biochemically, and

biomechanically (Hogansonet al. 2010; Pridgen

et al. 2011). Many different decellularization

protocols have been described, and evaluation

of the process is in its infancy. Potential nega-

tive effects include impairment of the viability

of colonizing cells with chemical residues,

wash-out of growth factors bound by the ECM,

loss of ECM structure, and the induction of

sterile inflammation (Schultze-Tanzil et al.

2012). In veterinary medicine, a described

protocol reduced the mean DNA content by

between 44% and 83% in an equine tendon

(Youngstromet al. 2013). In addition to verify-

ing the removal of antigenic debris, it is also

necessary to confirm that desirable components

of the ECM (i.e., glycosaminoglycans, collagen,

protein) are retained. A similar protocol was

evaluated on the canine deep digital flexor

tendon and superficial digital flexor tendon

(Baloghet al. 2016) (Figure 26.1). The histolog-

ical, biochemical, and mechanical results of

Figure 26.1 Image of a decellularized deep digital flexor tendon being prepared for implantation as a cranial cruciate
ligament allograft.