Intra-Articular Repair for Cranial Cruciate Ligament Rupture in the Dog 207of disease transmission, and the initial strength
and stiffness can be selected. Braided nylon,
Teflon, Supramid, GoreTex and Dacron are just
some examples of materials described for lig-
ament replacement. An early report showed
good subjective outcomes when polyethylene
suture was placed in an intra-articular location
in 98 dogs (Singleton 1969). The limitations of
these scaffolds include their diminished bio-
compatibility, unpredictable degradation rates,
and biomechanical weakening due to degra-
dation (Liuet al. 2008). A canine study evalu-
ated replacement of the CrCLusing Dacron. The
groups included an ‘over-the-top’ placement,
femoral and tibial bone tunnel placement, and
the two techniques with extra-articular aug-
mentation (Parket al. 1985). All grafts were
intact at 12 weeks with no loss in strength, but
at 24 weeks some grafts showed signs of wear
at the origin of the tunnels, with fibrous tis-
sue ingrowth evident. A similar study using
polyester fiber placed in a similar manner pro-
duced equivalent results (Stead et al. 1991).
Studies have also investigated use of pros-
thetic material as a short-term brace for natu-
ral grafts. In dogs with CR, stifles were more
stable at 12 weeks when a fascia lata graft
and poly-L-lactide implant were used com-
pared with the fascia lata graft alone, although
no differences were seen between the groups
by 24 weeks (Laitinen 1994). A separate study
showed that an intra-articular prosthetic graft
allowed improved healing of CrCL elongation
injury compared to an elongated CrCL with no
protection (Lopezet al. 2006).
Given the properties of the materials cur-
rently available, short-term success is often
observed, followed by long-term failure due to
a loss of mechanical strength before replace-
ment with native tissue. If a material that pro-
motes a rapid ingrowth of native cells, while
maintaining mechanical strength and limiting
biologic reaction, could be developed, then
prosthetic ligament replacement could be the
preferred technique for CrCL repair.
Fixation
Three main challenges arise when stabilizing an
intra-articular graft: placement at an ideal loca-
tion, optimal tension at the time of fixation, and
development of a fixation method that will pro-
vide the required strength for recovery.
The CrCL has been described in detail
(Arnoczky 1983), and it is not a simple band.
First, there are two main components, the cran-
iomedial and caudolateral bands, which inter-
act intimately throughout range of motion. The
craniomedial band remains taut throughout a
range of motion as it twists close to 90◦from
proximally to distally. The caudolateral band is
taut only in extension (Arnoczky & Marshall
1977). Intra-articular repair struggles to repli-
cate this anatomy, and the ideal orientation of
an intra-articular graft at the time of fixation
is unknown. Second, the fan-like attachment to
the axial aspect of the lateral femoral condyle
and craniomedial tibia, underneath the inter-
meniscal ligament, make placement of bone
tunnels challenging. One limitation of many
intra-articular repairs previously reported is
that the graft is not placed at the attachment
sites of the CrCL (Baconet al. 1984; Coetzee &
Lubbe 1995). The ‘over-the-top’ technique does
not follow the native path of the CrCL, but
rather passes the graft caudally and over the top
of the lateral condyle. This path also increases
the working length of the graft. When bone tun-
nels are created, the ideal location within the
CrCL attachment site is unknown. In humans,
it has been shown that bone tunnel placement
in the attachment sites of the ACL may not be
perfectly isometric points (Austinet al. 2007). In
dogs, it is suggested that the isometric location
may be caudal to the femoral attachment site of
the CrCL (Palmisanoet al. 2000).
The next challenge with graft fixation is
deciding the ideal tension to be placed on the
graft while it is being secured. This has been
extensively explored in humans, with varia-
tion in recommendations based on the graft
and technique used (Maeet al. 2008; Grunau
et al. 2016). Obviously, too little tension will
result in postoperative laxity, but too much ten-
sion can change the contact mechanics, decrease
the range of motion and affect healing (Austin
et al. 2007; Maeet al. 2008). A study explor-
ing hamstring grafts in dogs found that, when
placed under minimal tension (1 N), graft sur-
vival was superior when compared with high
tension (39 N) (Yoshiyaet al. 1987). Precon-
ditioning grafts with static or cyclic tension
is another highly investigated area of human