112 Clinical Features
et al. 2014b). Dogs diagnosed with unilateral
CR often have signs of moderate to severe
osteoarthritis (OA) in the stable contralateral
stifle (de Bruinet al. 2007; Griersonet al. 2011;
Muiret al. 2011; Fulleret al. 2014a; Chuanget al.
2014). The median time to contralateral CR has
been reported in the range of 405 to 1688 days
(Griersonet al. 2011; Muiret al. 2011; Fulleret al.
2014a). Stifle synovitis is likely an early event
that contributes to the progression of CR (Erne
et al. 2009; Bleedornet al. 2011; Muiret al. 2011;
Littleet al. 2014). The radiographic assessment
of OA present in stable stifle joints is correlated
with arthroscopic assessment of synovitis (Blee-
dornet al. 2011). Therefore, dogs at greater risk
for bilateral rupture can be identified through
radiographic assessment. The presence of
radiographic synovial effusion and osteophy-
tosis in the stable contralateral stifle at the time
of diagnosis is a significant risk factor for the
development of contralateral CR (Chuanget al.
2014; Fulleret al. 2014a), with more severe radio-
graphic change associated with decreased time
to contralateral rupture (Chuanget al. 2014).
These results support the practice of obtaining
bilateral stifle radiographs when evaluating a
dog for unilateral CR. The evaluation of both
joints for OA is valuable for patient manage-
ment, as well as client education, and repre-
sents the ‘gold standard’ of care in small animal
practice.
Genetics
The aforementioned risk factors primarily affect
CR disease progression. The only risk factor
that seems to affect the initiation of CR is
genetic effects from breed. It has long been rec-
ognized that certain breeds (e.g., Newfound-
lands, Rottweilers, and Labrador Retrievers) are
predisposed to CR while others, such as the
Greyhound, are almost never diagnosed with
the condition (Whitehairet al. 1993; Witsberger
et al. 2008). Many recent studies have been per-
formed to characterize the genetic basis of CR
(Wilkeet al. 2009; Bairdet al. 2014; Bakeret al.
2017). The heritability of CR is moderate, with
estimates calculated for the Boxer, Newfound-
land, and Labrador Retriever ranging from 0.26
to 0.48 (Nielenet al. 2003; Wilkeet al. 2006; Baker
et al. 2017). Genome-wide association studies
have been carried out in the Newfoundland and
the Labrador Retriever (Bairdet al. 2014; Baker
et al. 2017), the results of which suggest that
canine CR is a highly polygenic complex trait.
Genetic risk is variable for each individual, and
this risk sets the stage for environmental influ-
ence, the progression of disease, and eventual
rupture. A full discussion on the genetics of CR
is presented in Chapter 7.References
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