96 Etiopathogenesis of Cruciate Ligament Rupture
histologic scores were also higher with synovial
debridement than in sham controls, but less
severe than in dogs with a partial cruciate
transection (Bozynski et al. 2015). Although
these models may not accurately represent the
clinical scenario of degenerative non-contact
CR, they reinforce the intimate association
between synovitis and CrCL health.
Synovial assessment
Objective evaluation of the synovial mem-
brane is not routine in clinical veterinary prac-
tice or research, despite the increased use of
arthroscopy and the importance of synovitis
in joint disease. The value of synovial tissue
assessment has been documented in humans
with OA, rheumatoid arthritis, and other joint
conditions (Guermaziet al. 2011; Hayashiet al.
2011). Ultrasound and contrast-enhanced mag-
netic resonance imaging (MRI) have been used
extensively to evaluate synovial membrane
pathology and joint effusion severity in the
human knee, but lack clinical validation in
dogs (Tarhan & Unlu 2003; Guermaziet al.
2011). These non-invasive modalities correlate
well with arthroscopic and histologic grading
(Karimet al. 2004; de Lange-Brokaaret al. 2014).
However, direct macroscopic evaluation of the
synovial membrane using arthroscopy remains
the ‘gold standard’ for the assessment of artic-
ular cartilage and synovium in human joints
(Ayral 1996; Ayralet al. 1996). Arthroscopy also
allows for the collection of synovial tissue for
microscopic assessment and, importantly, cor-
relates well with histologic characteristics of
disease severity (Lindblad & Hedfors 1985).
Arthroscopic features of synovitis are well
described in the human knee and defined
by three baseline parameters: intensity, extent,
and location (Ayral 1996; Ayral et al. 1996).
Af Klint developed an arthroscopic scoring
system that includes the assessment of syn-
ovial hypertrophy, vascularity, and global syn-
ovitis (af Klint et al. 2009). This method is
simple, efficient, and reliable across different
joint diseases in the clinical setting. The terms
early, late, active, or chronic synovitis are often
used to further characterize joint assessment
in people in an attempt to understand mecha-
nisms of initiation of synovitis.
Early comparative advances have been made
to provide objective measures of synovial
inflammation in dogs. Arthroscopic features
of synovitis in dogs were identified (Bleedorn
et al. 2011) and later refined (Littleet al. 2014),
using the aforementioned arthroscopic scoring
system from human knee synovitis (af Klint
et al. 2009). Identical features can be scored
with high intra- and inter-observer reliability in
the canine stifle joint (Figure 12.4) (Littleet al.
2014). Although some regional variation within
the joint exists, it is unclear if this relates to
local areas of cartilage damage as in human OA
(Lindblad & Hedfors 1985). The arthroscopic
features identified correlate well with histologic
assessment in dogs (Bleedornet al. 2011; Lit-
tleet al. 2014). The need for a standardized
system for joint evaluation was a key objec-
tive of the Osteoarthritis Research Society Inter-
national (OARSI) histopathology initiative in
canine research studies (Cooket al. 2010). Key
questions arise with the establishment of cri-
teria for synovial grading. First, what are the
initial, dominant characteristics of CR? Second,
how do synovial thickening or vascular pat-
terns relate to disease mechanisms? Finally, can
these criteria be used to classify populations by
severity or time course?Synovitis in early cruciate rupture
The synovium in stable stifle joints with early
clinical or radiographic evidence of arthritis is
inflamed (Bleedornet al. 2011; Littleet al. 2014).
Radiographic arthritis correlates with arthro-
scopic observations of synovitis but generally
underestimates the severity (Bleedorn et al.
2011). In a recent case series, synovitis was
present without arthroscopically apparent fray-
ing of the CrCL in dogs with lameness and sti-
fle arthritis. Superficial fraying of the CrCL and,
occasionally, the caudal cruciate ligament, was
seen together with synovitis in the remaining
dogs (Bleedornet al. 2011; Littleet al. 2014).
The synovial reflection surrounding the cru-
ciate ligaments in dogs is no longer intact in
early CR, particularly once fiber bundle dam-
age has occurred. Interestingly, dogs with more
severe synovitis in the unstable stifle had more
severe changes in the stable contralateral joint,
suggesting that disease in joint pairs is related,