110 Clinical Features
that experience bilateral CrCL rupture tend to
be younger than dogs with unilateral ruptures
(Cabreraet al. 2008; Griersonet al. 2011).
Gender
It is unclear whether gender differences have
an effect on the incidence of CR. Multiple stud-
ies have reported an increased prevalence of CR
in spayed females compared to other gender
groups (Whitehairet al. 1993; Lampmanet al.
2003; Powerset al. 2005; Adamset al. 2011),
while others have reported no significant dif-
ferences (Witsbergeret al. 2008) or an increased
risk in males (Griersonet al. 2011). The major-
ity of study results agree that neutered dogs of
either gender are at increased odds of devel-
oping CR compared to intact dogs (Whitehair
et al. 1993; Duvalet al. 1999; Lampmanet al.
2003; Slauterbecket al. 2004; Duerret al. 2007;
Witsbergeret al. 2008; de la Rivaet al. 2013).
A recent study of 360 Golden Retrievers (de
la Rivaet al. 2013) reported that early neuter-
ing (<1 year) significantly increased the likeli-
hood of CR. In fact, there was no occurrence of
CR in studied dogs that were intact (n=122).
Occurrence in early neutered males and females
was reported at 5.1% and 7.7%, respectively. The
effect of early neutering persisted after adjust-
ing for differences in body condition score (de
la Rivaet al. 2013). This is an important observa-
tion, as weight gain is often cited as an explana-
tion for the increased incidence of orthopaedic
disease among neutered dogs (Whitehairet al.
1993; Duvalet al. 1999; Buoteet al. 2009). If not
through weight gain, how does early neuter-
ing affect the CrCL? It has been suggested that
an absence of gonadal hormones leads to atyp-
ical growth plate closure and thus altered con-
formation (de la Rivaet al. 2013). Indeed, early
neutering has been reported to be a significant
risk factor for the development of excessive tib-
ial plateau angles in large-breed dogs (Duerr
et al. 2007). Additionally, an absence of gonadal
hormones may affect the size, shape, or mate-
rial properties of the CrCL itself (Slauterbeck
et al. 2004). A study investigating the effect of
gonadectomy on CrCL collagen homeostasis in
rabbits found that collagen concentrations were
lower and fiber diameters greater in the absence
of gonadal hormones, which may predispose
them to rupture (Lightet al. 2012). Research con-
firming a direct role for gonadal hormones on
the canine CrCL matrix architecture is not cur-
rently available.Obesity
An association between higher body weight
and increased risk of CR has been reported
(Whitehairet al. 1993; Duvalet al. 1999). While
this is an important finding, evaluating weight
alone does not distinguish between large-size
dogs and dogs that are truly overweight. Other
work has attempted to evaluate body condition
more objectively. A study of 755 dogs reported
that those with overweight or obese body condi-
tion scores were twice as likely to be diagnosed
with CR compared to dogs of normal weight
(Lampmanet al. 2003). A similar study eval-
uated body weight as a percentage of recom-
mended breed weight and found that dogs in
the obese category were nearly fourfold more
likely to sustain a CR compared to dogs of nor-
mal weight (Adamset al. 2011). Mechanical, as
well as metabolic, factors explain the increased
risk associated with obesity. From a mechanical
standpoint, obese animals experience increased
loading in their limbs, which in turn may over-
stress the CrCL and predispose it to rupture
(Whitehairet al. 1993; Adamset al. 2011). Addi-
tionally, there has been interest in the endocrine
function of adipose tissue and its role in CR
pathophysiology. Pro-inflammatory adipokines
released by adipose tissue may contribute to the
degenerative process underlying CR (Palluet al.
2010; Adamset al. 2011; Comerfordet al. 2011;
Koskinenet al. 2011).Conformation
The anatomy of the stifle joint has been eval-
uated extensively for risk factors that may
be associated with the development of CR.
Anatomic features investigated include inter-
condylar notch dimensions (Comerfordet al.
2006; Lewiset al. 2008), overall limb alignment
(Dismukeset al. 2008; Mostafaet al. 2009), and
proximal tibial conformation (Selmi & Padilha
Filho 2001; Maciaset al. 2002; Reif & Probst
2003; Dennleret al. 2006; Osmondet al. 2006;