204 Surgical Treatment
and lateral third, in combination with the fascia
lata, revealed that no graft was able to mimic
the strength or stiffness of the native CrCL.
Although the central and lateral thirds were
stronger than the medial third, it is likely that
no partial patella tendon graft has the mechani-
cal properties necessary for recovery in the dog
(Butleret al. 1983; Johnsonet al. 1989). In fact, it
has been reported that the entire patellar tendon
is needed to reproduce the mechanical proper-
ties of the CrCL. (Biskupet al. 2014b) Mechan-
ical properties of the patella tendon autografts
at 4, 12, and 26 weeks after surgery revealed
strength and stiffness increasing and elongation
decreasing at each time point, although grafts
never reached the full strength of the intact
CrCL. Compared to extra-articular repairs, both
a third of the patella tendon and a fascia lata
strip showed less stiffness and greater laxity
compared to fibular head transposition and lat-
eral imbrication (Pattersonet al. 1991). Clini-
cal assessment of laxity postoperatively showed
that the lateral third of the patella tendon
with a fascia lata strip placed in an ‘over-the–
top’ technique had increased laxity at 4 weeks
after surgery before decreasing laxity out to
26 weeks. At 26 weeks, laxity of 2.5 mm was still
more than the intact CrCLat 1.8 mm (Hulseet al.
1983).
A limited number of clinical studies have
been conducted with subjective and objective
outcomes to assess the mechanical strength of
common autografts. In one study, examina-
tions were made of dogs with naturally occur-
ring CR repaired with a fascial ‘over-the-top’
graft and assessed with an owner questionnaire
and force platform analysis. With an almost
1.5 year follow-up, owner satisfaction was very
high, although gait analysis revealed signifi-
cantly decreased peak vertical force (Geelset al.
2000). OA also progressed in all dogs. Similar
results were found in 21 dogs with patella ten-
don/fascia lata grafts (Vasseur & Berry 1991).
All owners felt that their dog showed significant
improvement, although instability and progres-
sive OA were documented in most cases.
A unique challenge to autograft collection
is donor site morbidity. A mechanical study
of the patella tendon after removal of its
central third revealed the cross-sectional area
to be dramatically increased over the control
tendon, although strength was significantly less
at 3 and 6 months (Linderet al. 1994). Another
study revealed that the donor patella tendon
decreased in failure strength by 30% compared
to a control at 6 months (Burkset al. 1990).
Although autografts have shown promise, an
autograft with the necessary mechanical prop-
erties that minimize donor site morbidity has
not been described. Further work is necessary
before autografts could be commonly used for
CrCL repair.Allografts
Allograft benefits include a natural ECM scaf-
fold, with the benefit of no donor site morbid-
ity. With allografts, a whole tendon can be used,
such as the entire patella tendon rather than a
third of the patella tendon. The donor tendon
is readily available without needing intraoper-
ative collection, Finally, there is the option of
using a ligament graft, such as the CrCL, as an
allograft. Although allografts have these advan-
tages, they raise concern of disease transmis-
sion, immunological reaction, and alteration of
ingrowth characteristics.
Risk of disease transmission in veterinary
medicine is unlikely, especially if appropriate
donor screening is performed, if grafts are col-
lected in a timely manner with sterile technique,
if post-collection monitoring is performed, and
graft tracking is ensured to record any future
complications. Specific protocols are often read-
ily available from companies providing allo-
grafts commercially.
The detection, reaction, and destruction of
a graft is always a concern when foreign tis-
sue is implanted in the body. The placement of
a fresh allograft would increase the likelihood
of an immune-directed inflammatory response,
although this is not commonly performed,
nor is it currently feasible for CrCL replace-
ment. More commonly, allografts are treated
with an acute deep-freeze, cyclic deep-freeze–
thaw cycles, freeze-drying, gamma-irradiation
or ethylene oxide. The freezing of tendons or
ligaments has been shown to decrease dis-
ease transmission and immunogenic potential,
although some protocols may decrease mechan-
ical properties (Gutet al. 2016). In a dog model,
central-third patella autografts were compared
to similar deep-frozen allografts (Arnoczkyet al.