Prevalence of osteoarthritis in the joints of the appendicular
skeleton of the cat
By Drs. M.Verruijt
Under supervision of: dr. L.I. Slingerland and prof.dr.H.A.W. Hazewinkel
Department of Clinical Sciences of Companion Animals
Faculty of Veterinary Medicine, Utrecht University
M.Verruijt@students.uu.nl
Table of Contents
pages:
Part one: literature study
Abstract
2
Introduction
2
General Considerations
3
Prevalence
5
Pathogenesis
- the normal joint
- the osteoarthritic joint
7
8
Clinical Symptoms
10
Diagnostic possibilities
10
Radiographic symptoms
13
Therapeutical options
14
Prognosis
15
Discussion
15
Conclusion
16
Part two: retrospective study of radiographs
Abstract
17
Introduction
17
Materials and methods
17
Results
21
Discussion
27
Conclusion
30
Acknowledgements
30
Literature
31
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
1
Part One: Literature study
Abstract
Osteoarthritis in cats is not a widely recognised disease, however veterinarians are becoming
increasingly aware of its existence. It is believed to be a cause of chronic pain in cats. Studies
show a high prevalence in the geriatric cat. No other correlations, for example with obesity,
have been demonstrated.
The pathogenesis of osteoarthritis is thought to be multifactorial and is not totally understood.
The main biochemical change consists of proteoglycan degradation in the joint cartilage.
Only little is described with regard to the clinical symptoms in cats. Cats are thought to be
able to hide their pain and symptoms. Subtile symptoms like stiffness, behavioural changes
and less jumping are indicators for osteoarthritis. These symptoms are often explained by the
owner as part of the cat’s process of ageing. Owners are not aware that these symptoms may
arise from osteoarthritis and from the pain it causes. Therefore the veterinarian is not
consulted. The veterinarian should specifically ask about these symptoms in geriatric cats and
make owners aware of the possibility of osteoarthritis in the geriatric cat.
Diagnosing osteoarthritis in cats is hard using only general and orthopaedic examination of
cats. One of the main concerns is to rule out the possibility of inflammatory arthritis. Often a
radiographic image is needed to diagnose osteoarthritis, possibly after sedation of the cat.
Radiographic changes can vary, but mostly include narrowing of the joint space, subchondral
bone sclerosis and osteophyte formation.
Consideration of the therapeutical options and advice to the owner by veterinarians for cats
with osteoarthritis should not only include pharmacological or surgical treatment, but also
environmental changes. In this way treatment of osteoarthritis in cats is similar to that in other
species. The goal of the treatment is to improve the cat’s quality of life through symptomatic
and supportive measures. These include NSAIDs, weight reduction and for example placing
the food bowls on a low access level for the cat. Osteoarthritis is a non-reversible illness, but
in general an acceptable situation for the cat can be achieved with these therapeutical options.
Introduction
Much is known about osteoarthritis and its clinical importance in dogs. In cats osteoarthritis is
a relatively new research topic, of which the clinical importance may not be fully recognised.
Unlike dogs, cats do not display the symptoms of osteoarthritis in the same clinically
extensive form (8). Dogs are presented at the veterinary clinic because of lameness, unlike cats.
Lameness seems to be a rare phenomenon in cats with osteoarthritis. Clinical osteoarthritis in
cats is described by inability or unwillingness to jump, jumping shorter distances, less playing
behaviour, less grooming behaviour, stiffness and inactivity (3,8,17,34). Because of the lack of
evident clinical symptoms, especially to cat owners, cat osteoarthritis might be an
unrecognised disease. Several risk factors for osteoarthritis in dogs and some for cats are
recognised, but particularly in cats only little is known about osteoarthritis. Risk factors like
obesity, gender and breed have been evaluated in some studies, but were not proven
significant (8,9,17). No definite conclusions can be made with regard to these factors without
further research.
For the first part of this report, evaluation of the available literature concerning osteoarthritis
in the joints of the appendicular skeleton of cats has been performed and a summary of
pathogenesis, risk factors, diagnostic approach, therapeutical options and frequency of
osteoarthritis in cats was made. The search for literature was conducted in several different
ways. The collection of the University Library of the Faculty of Veterinary Medicine in
2
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
Utrecht was searched. At first this was done by hand, by going through the orthopaedic
section of the books in the library. Indexes were searched for the terms “osteoarthritis”,
“degenerative joint disease”, “arthritis”, “osteoarthrosis”, “arthrosis” and “DJD”. Afterwards
the library collection was searched by the use of the digital catalogue for all of the words
described above (the words alone and with the addition of the word “cat” to it) (42). Later on
investigation started considering the published articles about osteoarthritis, in which both
digital magazines as scientific library magazines were assessed. Searching of the articles was
done with assistance of several search engines, c.q. PubMed, VetPortal (including all theses
and proceedings) and IVIS were mostly used (39,40,41). The abovementioned terms were also
used in these search programs.
Subsequently, for the second part of this report, evaluation of the prevalence of osteoarthritis
in the joints of the appendicular skeleton on radiographs from the archives of the Division of
Diagnostic Imaging of the University Clinic for Companion Animals in Utrecht was
performed. In this retrospective study, radiographs were evaluated from cats which were
presented at the Clinic. Together with this evaluation of radiographs, the history of the cats
was evaluated to identify putative risk factors for osteoarthritis in cats. The evaluation of the
radiographs was supervised by a Diagnostic Imaging Specialist.
The objective in this research project is to investigate the prevalence of osteoarthritis in the
joints of the appendicular skeleton of the cat, as it is thought to be higher as yet recognized.
General Considerations
At first the definition of the word osteoarthritis is of great importance. In literature many
names are given for the same disease. To make clear on which disease this report is about, a
brief summary follows.
For the sake of completeness table 1 describes the classification of joint diseases (6).
Table 1: joint disease classification
Non-inflammatory
 Degenerative joint disease/
osteoarthritis/ osteoarthrosis
- primary
- secondary
 Trauma
 Neoplasia
Inflammatory
 Infectious disease
 Non infectious disease
- immunologic
- erosive
- non-erosive
- immune-mediated
Often the word “osteoarthritis” is used. In literature it is defined as “a pathological change of
a diarthrodial synovial articulation characterised by the deterioration of articular cartilage,
osteophyte formation, bone remodelling, changes in periarticular tissue and a low-grade nonpurulent inflammation of variable degree” (5,9,11,25,30,32,34). The description of a diarthrodial
joint is: “two bones, which are covered with joint cartilage and are enclosed by a joint capsule
which contains synovial fluid” (28,30). Synovial joints are composed of two or more articulating
bones, a joint capsule, joint cavity and articular cartilage. Joint cartilage is the main structure
involved in osteoarthritis. Normally the joint cartilage provides a smooth, durable and lowfriction surface which passes on forces from one bone to another and spreads the forces
evenly from one joint surface to the other. Joint cartilage consists of chondrocytes, collagen
(insoluble protein macromolecules), proteoglycans (large extracellular macromolecules) and
water (25,26,31,34). Arthritis is described as inflammation of the joint. With regard to this, a more
correct word for the disease referred to in this report is osteoarthrosis or degenerative joint
disease, because of the minimal inflammatory component of the disease in comparison to
arthritis. Another definition of osteoarthritis is “a non-inflammatory degenerative articular
3
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
joint disease characterised by lack of inflammation in the synovial lining and the presence of a
normal or almost normal synovial fluid”(6). In order to understand this definition, it should be
clear what “normal or almost normal synovial fluid” is. Hardie defines normal synovial fluid
as straw-coloured and viscous fluid, in which the white cell count is low (< 5000 cells/mm3)
and neutrophils are rarely seen (18). The viscosity of the fluid is good or slightly diminished
and the mucin clot test is normal. In inflammatory arthritis the synovial fluid appears to be
yellow to red and the white cell count is high (> 5000 cells/mm3). Neutrophils dominate in the
fluid and viscosity is diminished. The mucin clot test is fair to poor. Normal synovial fluid is
very viscous because of its high concentration of hyalunoric acid (15,18).
Finally osteoarthritis can be seen as a disorder of movable joints characterised by
degeneration of articular cartilage and the production of new bone at articular margins (24,28).
In this report the name osteoarthritis will be used, referring to the non-inflammatory disease
as described above, because it is the most commonly used name in literature.
As described in table 1 osteoarthritis can be classified into primary osteoarthritis and
secondary osteoarthritis. Primary osteoarthritis, often called idiopathic, is degeneration of
cartilage by wear and tear and proceeds with age. Secondary osteoarthritis arises from
diseases, which affect joints and supportive tissues (6,25,27,28,34).
In humans, secondary osteoarthritis can be divided into 4 main categories:
1. articular diseases (like rheumatoid arthritis and septic arthritis)
2. metabolic diseases (like Wilson disease and ochronosis)
3. endocrine diseases (like Diabetes mellitus)
4. structural deformities (like fractures, dysplasia and Calvé-Legg Perthes disease) (11,28,29)
Another way of classifying primary and secondary osteoarthritis is that in primary
osteoarthritis there is no apparent reason for the condition other than increasing age.
Conversely secondary osteoarthritis occurs as a result of abnormal stresses on a joint and any
condition that interferes with normal joint function can cause this (35).
In feline veterinary literature the following classification for osteoarthritis, as displayed in
table 2, is used:
Table 2: osteoarthritis classification in cats
Primary osteoarthritis
 Scottish Fold
Osteochondrodysplasia
 Mucopolysaccharidosis
 Age-related cartilage
degeneration
Secondary osteoarthritis
 Congenital
- Hip dysplasia
 Trauma
- Traumatic joint instability
- Fractures
 Infectious and inflammatory
- Viral (calicivirus, coronavirus)
- Bacterial (mycoplasma, bite wounds)
- Fungal (cryptococcis, histoplasmosis)
 Nutritional
- Hypervitaminosis A
 Neuropathic
 Immune-mediated
- Rheumatoid arthritis
- Progressive Proliferative Polyarthropathy
- Systemic Lupus Erythromatosus
- Idiopathic Polyarthritides
(1,12,25,35)
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
4
Osteoarthritis can also be divided into grades of severeness by the following classification in
humans (11) :
I. destruction of superficial cartilage on areas of highest pressure and movement. No
hyperplasia is present on the margins of cartilage or bone. Joint capsule, synovial
membrane and articular margins are normal.
II. More extensive destruction of cartilage, but still restrained on areas of highest pressure
and movement. No bone is exposed. Early margin hyperplasia (ridge formation) along
the edges of the surfaces. No osteophytes or bone remodelling are present.
III. Total loss of cartilage on one or more pressure points with exposure of bone and often
sclerosis. Distinct osteophytes on the margins of the joint. Change in contour of the
joint surfaces. Fibrosing of the capsule.
IV. Total loss of cartilage on large areas of the joint surface. Subchondral sclerosis.
Irregularity of the joint surface, osteophytes, remodelling, fibrosis of the capsule and
synovial membrane (11).
In the following paragraphs prevalence, pathogenesis, clinical symptoms, diagnostic
possibilities, radiographic symptoms, therapeutical options and prognosis of osteoarthritis in
appendicular joints of the cat are described.
Prevalence
For dogs and humans many studies researching osteoarthritis are available. When it comes to
cats, not much has been investigated yet. Some scientists believe that this is due to the fact
that cats do not show lameness, but hide their discomfort caused by osteoarthritis, for instance
by sleeping more and jumping less high. Because of this hiding, owners do not notice any
discomfort in their cat and the cat is not presented to the veterinarian for an examination
(4,17,22)
. Because of these reasons, the actual prevalence of osteoarthritis is hard to investigate
using clinical symptoms. Several researchers stated that the lack of attention for osteoarthritis
in cats may be due to the fact that cats have a relative small body and because of their ability
to accommodate orthopaedic abnormalities by redistribution of weight bearing forces to other
limbs. Another given reason was that owners do not critically assess the gait of their cats and
therefore do not notice abnormal gaits, mild lameness or joint stiffness (18,32). At last a possible
option for the lack of interest in this disease in the cat, is that signs like stiff gait can be
considered to be “normal” for the elderly cat by the owner. Many owners do not feel the need
to consult their veterinarian about the stiffness of their cat or the decreased ability to jump,
because owners interprete these as normal aged-related changes to which no treatment is
necessary. The veterinarian may need to pay special attention to these changes (7).
Some investigators looked at the prevalence of osteoarthritis in cats. Not all of them separated
spondylosis from appendicular joint osteoarthritis. These terms are different, as osteoarthritis
refers to a process concerning a joint with synovial fluid. Spondylosis on the other hand refers
to a process that includes an articulation without synovial fluid but does involve an
intervertebral disc. By not separating osteoarthritis from spondylosis the total prevalence of
osteoarthritis can be different from the real prevalence. Not in all articles exact prevalence is
given per joint, but only total prevalence is calculated. An overview of the most useful reports
for osteoarthritis is given in table 3.
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
5
Table 3: an overview of relevant research
Research
Criteria for selection
Clarke et al (9)
-
Godfrey
-
(12)
-
Hardie (17)
-
-
Clarke and
Bennet (8)
-
-
-
Kamishina
(21)
-
Assessed joints in
cats (n)
retrospective
218 cats with visible
research
joints on
non-orthopaedic
radiographs of
presentation at clinic which:
cats > 8 years
- 147 shoulders
complete medical
- 189 elbows
record
- 26 carpi
- 113 hips
- 97 stifles
- 33 hocks
- 46 spines
retrospective
292 cats with visible
research
joints on
any sort of
radiographs of
presentation at the
which: unknown
clinic
frequencies of
cats > 1 year
shoulders, elbows,
complete medical
carpi, hips, stifles
record
and tarsi.
Osteoarthritis (n)
in 78 cats, but
spondylosis
deformans was
also included in
this number.
Without: 48 cats
had osteoarthritis.
Osteoarthritis
(% )
33.9 %, but
without
spondylosis
deformans
22.0%.
in 64 cats.
22 .0%.
retrospective
research
cats > 12 years
all presentations at
the clinic, except
polyarthritis
complete medical
record
100 cats with visible
joints on
radiographs of
which:
- 93 shoulders
- 71 elbows
- 18 hips
- 13 stifles
- 100 spines
In 90 cats, but
spondylosis
deformans was
also included in
this number.
Without: 64 cats
had osteoarthritis.
90.0%, but
without
spondylosis
deformans
64.0%.
prospective research
cats with clinical
signs of
osteoarthritis
possibility of
NSAID
administration
joints were
radiographed under
anaesthesia
post mortem study
mature cats
no present trauma
28 cats with visible
joints on
radiographs
In 28 cats, which
included
- 3 shoulders
- 33 elbows
- 0 carpi
- 27 hips
- 4 stifles
- 5 hocks
45.0 % for the
elbows and
38.0% for the
hips.
In 156 cats,
312 hip joints were
visible on
radiographs
In 22 cats, in
14.1 %, of which
which 11 cats also 7.1 % also had
had hip dysplasia hip dysplasia
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
6
One of the researchers, Clarke et al, retrospectively looked at a population of 218 cats,
selected by going through the archives of the veterinary hospital of Glasgow between July
1998 and October 2003 (9). In this population 33.9 % of cats was diagnosed with osteoarthritis
(78 cats) in at least one joint on the basis of radiographs. These cats were presented at the
university clinic for non-orthopaedic reasons. A note has to be made about this research,
because this prevalence also included spondylosis deformans. Without spondylosis deformans
a total percentage of osteoarthritis can be calculated as 22.0% (9).
Godfrey performed a similar study, in which 22.0% of the cats retrospectively had signs of
osteoarthritis (12). No data is present about the amount of shoulders, elbows, carpi, hips, stifles
and tarsi that have been evaluated. Therefore no conclusions can be made about the
prevalence in these joints, but only about the total prevalence (12).
Hardie et al retrospectively examined a population of 100 geriatric cats above 12 years old, in
which 90.0 % revealed radiological signs of osteoarthritis (17). A note has to be made about
this research, because this percentage of osteoarthritis also included spondylosis deformans.
Without spondylosis deformans a total percentage of osteoarthritis can be calculated as
64.0%. Also no data is present in the article about the prevalence of osteoarthritis in the
graded joints. Therefore no conclusions can be made about the prevalence in these joints, but
only about the total prevalence (17).
Clarke and Bennet investigated a population of 28 cats with clinical osteoarthritis (8). The
study was prospective, to look at the signs and the responses to NSAIDs in these cats. In this
research 45.0% osteoarthritis in the elbows and 38.0 % osteoarthritis in the hips was
mentioned (8).
Kamishina examined 156 mature cats, of unknown age, which were collected from animal
shelters after euthanasia (21). Only the hips were assessed in this study. The prevalence of
osteoarthritis in the hip joints of these cats was 14.1 % (21).
All these studies concluded that osteoarthritis may be an underrecognized problem in elderly
cats. Mostly affected were the elbows, shoulders, stifles and hips (4,7,9,12,17,20,36). More research
is needed to establish the prevalence of osteoarthritis in the appendicular skeleton of the cat.
Thus, the exact prevalence of osteoarthritis in the appendicular skeleton of the cat is not
known yet.
Pathogenesis
The aetiology of osteoarthritis is believed to be multifactorial and is incompletely understood
(5,14,24,27,32)
. The main structure involved is joint cartilage. The function of normal articular
cartilage is to provide a smooth, low-friction joint surface and to pass on and evenly spread
the forces from one bone to another (30). The main biochemical change in osteoarthritis occurs
in the joint cartilage. In order to understand the changes in osteoarthritis, knowledge of the
normal joint is needed.
The normal joint
Cartilage is a non-innervated avascular tissue, which consists of chondrocytes imbedded in an
acellular matrix which exists of proteoglycans, collagen and water. Articular cartilage can
histologically be divided in several layers, as is displayed in figure 1 (31).
The most superficial layer lies farthest from the subchondral bone and is named the tangential
or gliding zone. Cells are flattened and elongated in this layer and are arranged parallel to the
joint surface. The second layer is the large transitional zone, which contains more rounded
cells which are more randomly arranged. Third layer is the radial zone, which has cells in
columns. Last layer is the calcified zone, where the cells are arranged in columns in a
calcified matrix. The calcified layer is supported by the subchondral bone plate and joins the
subchondral bone at the osteochondral junction (5,30,31).
7
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
Figure 1: an overview of joint anatomy
A figure taken from (31)
The joint capsule is composed of an outer and inner layer. The outer layer is mainly fibrous
and, together with the surrounding connective tissue, its function is to support the joint. The
inner layer is the synovium and contains blood vessels and nerves. It is important for
maintenance of the synovial fluid volume. Synovial fluid has a lubrification and transport
function in normal joints (5,30,31).
Normal articular cartilage is arranged as a stiff, gel-like substance, which consists of a loose
collagen network with chondrocytes and proteoglycan-hyaluronate aggregates. The
proteoglycan-hyaluronate aggregates have a high molecular weight and a high charge,
creating an osmotic component that attracts water to the cartilage. Because of this water
attraction, there is an outward pressure which maintains the stiffness of the cartilage. This
arrangement ensures a low-friction interface in the joint, which gives it the possibility to cope
with load (18).
The osteoarthritic joint
The biochemical changes in the joint consist of the loss of proteoglycans. This loss of
proteoglycans is particularly important because of their central role in the maintenance of
cartilage integrity. Proteoglycan degradation results in reduction of the molecular weight of
the aggregates and therefore loss of water from the articular cartilage. This leads to increased
friction and together with the loss of stiffness of the collagen network, it might cause
mechanical disruption of the cartilage (18).
The characteristic structural changes are disorganisation and loss of articular surfaces and
proliferation of tissues in and adjacent to these surfaces. The classic morphological changes of
osteoarthritic articular cartilage begin with fibrillation. This is a local surface disorganization
involving a splitting of the superficial layers of the cartilage. Eventually the splitting extends
deeper, whereby it alters the normal arrangement of the collagen bundles. Splitting may
extend as far as the junction with subchondral bone. As osteoarthritis progresses fibrillation is
joined by synovial hyperplasia and osteophyte formation. The fibrillation and detoriation of
articular cartilage leads to exposure of the subchondral bone and more generalised synovial
changes. In response to these changes sclerosis of the subchondral bone develops by an
incompletely understood pathogenesis. It is believed also the opposite may occur; sclerosis of
the subchondral bone decreases local shock absorption. This increases forces on articular
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
8
cartilage, which is followed by changes in the articular cartilage. The joint becomes shaped
differently, which is called remodelling. This is thought to be a mechanism to cope with the
forces on the joint (46,48,55). Eventually the result is decreased joint motion and function,
deformity, possible joint instability (and later on ankylosis) and also pain (27).
Bennet described the pathological features of osteoarthritis in cats and dogs at three levels (5) :
Changes in articular cartilage, changes in bone and changes in soft tissue.
With regard to the articular cartilage the following was described:
- Biochemical changes: dehydration and a change in quantity of proteoglycans.
- Loss of surface chondrocytes: cartilage cells are lost from the superficial layers of the
cartilage.
- Flaking and fibrillation: horizontal flaking of the surface layer occurs, followed by
splitting, eventually into the calcified layer. The cartilage can eventually be sheared of,
which exposes subchondral bone. Fibrillation of the cartilage occurs.
- Chondrocyte clumping: formation of clumps or nest of cells. These may be an attempt
to repair damaged cartilage.
For bone the following was described:
- Periarticular osteophytes: marginal proliferations of bone.
- Subchondral bone sclerosis: associated with cartilage loss.
- Subchondral bone cysts: these are seen in dogs.
- Bone remodelling: osteophytes, subchondral sclerosis and cyst formation are parts of
bone remodelling.
For soft tissue the following was described:
- Synovial membrane: hypertrophy and hyperplasia of the lining layer and increased
thickness of the supportive connective tissue.
- Joint capsule: fibrous thickening of the joint capsule regularly occurs.
- Menisci: several changes in menisci occur, as fibrillation, calcification, splitting,
shredding, tearing and osseous metaplasia.
- Vascular changes: hyperaemia of the bone marrow of the bone occurs and vascular
tufts are seen proliferating to the bone-cartilage interface. Vascular proliferation also
occurs with osteophyte formation. Hyperemia of the synovial membrane and joint
capsule can also be present (5).
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
9
Clinical symptoms
Regarding clinical symptoms in cats, relatively little is described. Bennet et al evaluated
symptoms in cats by descriptions of owners on a survey list (4). Most seen was unwillingness
to jump, jumping less or less high and inactivity. Seldomly a clear limp was reported by
owners. In the survey, questions were asked about lifestyle (e.g. jumping on furniture, activity
levels, aggressiveness and lameness) and weight of the cat. No significant correlation was
seen between lifestyle and osteoarthritis and between weight and osteoarthritis. Bennet did see
a higher incidence of osteoarthritis in older cats than in younger cats (4).
Clarke et al also evaluated lifestyle, age, breed, gender and weight of a group of cats to find a
correlation with osteoarthritis (9). Only age was related significantly in cats with osteoarthritis.
Osteoarthritis was diagnosed more frequently in elder cats than in younger ones. No other
correlations were found and Clarke et al stated that this is similar to the human severeness of
osteoarthritis- clinical lameness relationship (9). In this relation the severeness of osteoarthric
changes do not match the clinical symptoms in that human. Sometimes extensive
osteoarthritis is present, but without clinical symptoms.
Hardie et al describes that cats can compensate for their pain and hide symptoms (17). Owners
may see behavioural changes, like grumpiness and more lethargic cats, and inabilities.
Inabilities like inadequate grooming behaviour, missing the cat’s litterbox and not jumping
high. Seldomly lameness is seen. In cats with chronic pain also subtile findings like
constipation, bad posture while urinating or defaecating, incontinence and inadequate
grooming can be seen. Hardie et al stated that osteoarthritis can’t be associated with these
clinical symptoms (17).
Clarke et al researched the effect of meloxicam therapy in cats with osteoarthritis (8). 67.0% of
the cats showed changes in jumping behaviour. Clarke stated that weight loss, anorexia,
depression, abnormal elimination habits, inadequate grooming, aggression, reduction of
jumping, stiffness and lameness are signs of osteoarthritis (8). After therapy 61.0 % of the
owners noticed improvement, but no placebo group was available.
Shires et al names some possible inheritable causes of osteoarthritis like patella luxation in the
Devon Rex, hip dysplasia in Siamese cats and athropathy in Scottish Folds (34). The named
clinical symptoms were inadequate grooming behaviour, trouble with jumping on furniture
and trouble with getting in/out of the litterbox. Increased irritability may also be present.
Obvious lameness was not seen (34).
Lascelles et al hypothesed that subjective evaluation by owners and an activity monitor collar
can be used for pain measurement in cats (22). This research was done because there was no
validated method to measure pain in cats with osteoarthritis. Thirteen cats were part of the
research, which all had less activity according to the owners. The cats received meloxicam
therapy or a placebo. The research showed that activity increased more in cats with
meloxicam therapy than in cats with placebo therapy (22). Activity might be a marker to use
for therapy regulation in cats with pain and reduction in activity might also be used as one of
the predictive symptoms for the level of discomfort in osteoarthritic cats.
Diagnostic possibilities
A proper signalment and history taking are thought to be important steps in the diagnosis of
osteoarthritis. Mostly affected are elderly cats, therefore it is important to pay special attention
to the history in these cats for symptoms like stiffness, behavioural changes and less jumping
(5,7,8,9,14)
. Caney developed a question survey for owners, which can help to identify
locomotion problems like osteoarthritis in cats. The summary of this questionnaire has been
displayed in table 4 (7).
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
10
Table 4: questionnaire summary
Changes in ability or enthusiasm to:
Noticed:
Changes in behaviour:



















Other questions:



Go up and/or down stairs
Use the cat flap
Jump onto/off bed/sofa/lap/etc.
Jump or climb into/onto its favourite bed
Play
Climb trees/fences/etc.
Use scratching posts
Stiff or stilted gait
Limp
Vocalizing or hissing in response to moving
around or being stroked over joints
Grumpy or less happy with people and other
animals
More withdrawn, less interaction
Less active
Sleeping in different locations
Not coming upstairs
Passing urine or faeces in abnormal locations
Purring less
Reduced appetite
Changes in coat condition and/or grooming
behaviour, neglecting certain areas,
overgrooming certain areas
Weight change
Muscoskeletal injuries in the past
Any affected relatives (especially more
common hip dysplasia in Maine Coon and
possible Siamese, Burmese, Tonkinese,
Oriental and Balinese)
(7)
In history taking questions should also be asked to rule out other diseases, especially in the
geriatric cat. Because of the variety of possible causes of osteoarthritis, underlying diseases
must be ruled out. Additionally, profound clinical exam needs to be done, including general
examination and orthopaedic examination. One of the difficulties in the orthopaedic
examination is the fact that cats dislike the consulting room and will not easily display their
gait and jumping behaviour. In order to solve this issue it is possible to ask the owner to
capture the gait and jumping of the cat in his normal environment with a camera. In
orthopaedic assessment it is also hard to link the reactions to the exam to any orthopaedic
pain, because the cat might only resent being handled. Pain score models can be used, but are
still hard to apply in cats. An example of a pain scale model for animal pain, the University of
Melbourne Pain Scale, is given in table 5. (19).
Joint swelling, reduced range of motion and crepitus are not often seen. Joint thickening can
be seen more commonly and the mostly affected joint is the elbow joint (7).
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
11
Table 5: University of Melbourne Pain Scale Model
Category
Physiological data
Response to palpation
Activity
Mental status
Posture
Vocalisation
Descriptor
- Within reference range
- Dilated pupils
- Percentage increase in heart
rate:
> 20%
> 50%
>100%
- Rectal temperature exceeds
reference range
- Salivation
- No change from
preprocedural behaviour
- Guards/reacts when touched
- Guards/ reacts before
touched
- At rest:
sleeping
semiconscious
awake
- Eating
- Restless
- Rolling
- Submissive
- Overtly friendly
- Wary
- Aggressive
- Guarding or protecting
affected area (including fetal
position)
- Lateral recumbence
- Sternal recumbence
- Sitting or standing, head up
- Standing, head hanging
down
- Moving
- Abnormal posture
Score
0
2
- Not vocalising
- Vocalising when touched
- Intermittent vocalisation
- Continuous vocalisation
0
2
2
3
1
2
3
1
2
0
2
3
0
0
1
0
2
3
0
1
2
3
2
0
1
1
2
1
2
A table taken from (19)
When the clinician suspects that the cat might be suffering from osteoarthritis, the next step in
the process should be making radiographic images. The majority of cats can be imaged
properly without sedation. If proper positioning is not possible because of the lack of
cooperation of the cat, it may be needed to sedate the cat, in which care should be taken
because of the age and other diseases of the cat. The ASA classification should be 2 (slightly
12
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
or moderate systemic disease causing no obvious incapacity, geriatric animals) to 3
maximally (mild to moderate systemic disease causing mild symptoms) (16).
Synovial fluid collection and cytological and bacteriological evaluation of this fluid are rarely
indicated in cats. For example an indication to evaluate synovia includes the involvement of
multiple joints, in which case the examiner should try to rule out the option of polyarthritis
(7,15,34)
.
Radiographic symptoms
Diagnostic approach of osteoarthritis in cats is also a new research subject (9,12). Clarke et al
evaluated radiographs of 218 cats, in which 33.9 % (74 cats) showed signs of osteoarthritis (9).
In 65.3% of the osteoarthrotic joints mild osteophyt formation was present, which suggests
that osteophyt formation in the cat is not as extensive as in dogs (9).
Kamishina et al evaluated radiographic images of the hips of cats for signs of osteoarthritis
together with microscopic evaluation of the joints (21). Low correlation between the
radiographically found changes and the microscopic evaluation of the joints was found. In
134 cats in which radiographs were evaluated to be normal, 38 (28.4%) still had mild to
moderate histological cartilage lesions at post-mortem evaluation of the hip joints (21).
Owens et al investigated which radiographical signs can be used as markers for osteoarthritis
(28)
. Narrowing of the joint space, osteofyt formation and subchondral bone sclerosis are often
seen in dogs. Joint deformities and partial to complete ankylosis of the joint are also named in
dogs (28).
Signs of synovial effusion and/ or thickened periarticular soft tissue are seen less commonly
in cats than in dogs. The incidence of intraarticular soft tissue calcification is seen more
commonly in cats than in dogs (25,35).
Van Gastel-Jansen defined classical radiographical symptoms of osteoarthritis including
irregular joint space, narrowing in some areas of the joint space and normal or enlarged joint
spaces within the same joint. The articular surfaces are rough, if the articular cartilage has
been destroyed. Osteolytic areas and bone proliferation can be seen on the joint margins and
also on the periarticular areas. Free bodies can develop in the synovial fluid (10). Caney
describes the following possible radiographic findings: peri-articular new bone formation (in
form of osteophytes or enthesiophytes), narrowing of joint spaces, sclerosis of subchondral
bone, bone remodelling, soft tissue thickening/swelling around the joint (possibly involving
the joint capsule) and joint effusion (7).
Osteophytes are first seen as an area of proliferation of mesenchymal tissue in the transitional
zone between the synovial membrane and the articular cartilage. The tissue undergoes
metaplasia to form bone. After endochondral ossification, it is a prominent feature. It is
associated with the appearance of numerous blood vessels and therefore appears to be a
vascular reaction associated with new bone formation (5).
In order to pathologically score the severeness of the osteoarthritic changes in the cat, the
human gradation system from Ghadailly has been proposed (11). The gradation is as following:
 Degree 1:
Destruction of superficial cartilage, on surfaces of highest pressure and movement. No
hyperplasia on the margins of cartilage or bone. Capsule, synovial membrane and
articular margins are normal.
 Degree 2:
More extensive cartilage destruction, still confined to surfaces of highest pressure and
movement, on which no bone is exposed. Early margin hyperplasia (ridge formation)
along the margins of the surfaces. No large osteophytes or bone remodelling.
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
13


Degree 3:
Total loss of cartilage on one ore more pressure surfaces, with exposure of
subchondral bone and often bone sclerosis. Clear osteophyt formation on the joint
margins. Change of contour of the joint surfaces. Sclerosis of subchondral bone and
fibrosis of the capsule.
Degree 4:
Complete loss of cartilage on large areas of the joint surface. Sclerosis of exposed
bone. Irregularity of the surface, osteophytes, remodelling, fibrosis of the capsule and
synovial membrane (11).
After all of these descriptions of the radiographic and pathologic signs in the osteoarthritic
joint the conclusion can be that osteoarthritis in cats can be characterized by narrowing of the
joint space, articular cartilage destruction, subchondral bone sclerosis and osteophyte
formation (4,6,9,15,21,25,30,31).
Therapeutical options
Similar to other species, consideration of the therapeutical options and advice to the owner by
veterinarians for cats with osteoarthritis should not only include medicamental or surgical
treatment, but also environmental changes. The goal of the treatment of osteoarthritis is to
improve the quality of life of the cat through symptomatic and supportive measures. These
measures should help to increase mobility, reduce pain, reduce the possibility of further joint
damage and improve the total quality of life (7,18).
Medicamental options are mainly Non Steroidal Anti-Inflammatory Drugs (NSAID’s) for
pain relief. Carefulness with the use of NSAID’s is needed, because of the possible side
effects. Side effects include reduction of the appetite, vomiting, diarrhoea, occult faecal blood
loss, apathy, kidney problems, liver problems and clotting disorders (3,22,23,33,37,38). In the
Netherlands a registered NSAID is Tolfenamic acid (Tolfedine®), which has the indication of
pain relief in cats. Recently an oral suspension NSAID for long-term use in the cat was
registered, Meloxicam (Metacam®) (3,13,37,38).
Controversy exists about the use of glucocorticoids, as they have not proven to be efficient.
There is even evidence of inhibition of the proteoglycan and collagen synthesis, which gives
progression of osteoarthritis in stead of reduction (3,18, 26,32).
Weight reduction is important for obese cats. As is thought for dogs, in cats weight
normalisation will lead to decreased forces on the joint and thereby possibly less pain while
moving the joint. Another helpful adjustment is placing the food and water bowls on a lower
level, with easy access for the cat. In this way the cat doesn’t have to jump high to eat or
drink. The same can be done with the litter box, it can be placed on a low location and it is
even possible to use a litter box with low edges. The cat has easy access to the litter box and if
missing the litter box has been a problem, this could solve the problem. A step up can be
made between higher objects like the windowsill and the floor, for gradual access instead of a
high jump.
Unlike dogs it is not easily done to walk the cat on a leash, therefore leash exercise is not
always a possible option. Some cats may dislike water, some cats may not, therefore
swimming is also not always an option. A replacement of this is inducing extra exercise by
strategic placement of the litter box, food and drinking bowls. The cat needs to walk for
example to eat or drink. In this way the location is quite easily accessible, but the cat needs to
walk towards it and thereby have some exercise. Tempting the cat with snacks is also a way to
induce exercise, but care is needed with regard to the development of obesity and unwanted
behavioural patterns.
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
14
Some cats with osteoarthritis are not able to groom efficiently. One of the options to help the
cat with this, is to have the owner brush the cat.
The use of padded bedding in the cat‘s basket is recommended for the protection of the joints.
Even heated beds can be used, on which the cat will lie with cold weather (6,7,18,26, 32,33,36).
Several pet food manufacturers are developing special joint diets or mobility diets. These
diets should help the cat with their mobility and reduce osteoarthritic changes in the joints and
reduce pain. Although the diets have not been proven to be efficient, it might be worth to try
for the osteoarthritic cat owners. For example, one of these diets is the Joint Diet (J/D) from
manufacturer Hill’s. Several studies were performed to assess the clinical effectiveness of the
diet, but no conclusive difference was seen between cats that were fed the J/D diet and cats
that were fed a control diet (43).
Last option to be considered is the use of chondroprotective agents and nutraceutical agents.
They are also called Disease Modifiyng Osteoarthritic Drugs. Slow acting disease modifying
products like Cosequin® can be of use in therapy for osteoarthritis and contain chondrotoin
sulphate and glucosamine as main ingredients. Efficacy of the products has not been proven,
but they appear to be safe for use in the cat (2,3,30,31,32,33).
Prognosis
Osteoarthritis is a progressive condition. It is not possible to reverse the changes in the joint.
Therefore the prognosis for complete recovery is not good at all. Prognosis for an acceptable
life for the cat is fair to good. These cases exclude the cats with severe osteoarthritic changes,
that still have extensive pain with analgesics, in which cases euthanasia might even be
considered. For cats with mild to moderate osteoarthritis an acceptable status of living can be
achieved with therapeutical options like medication and changes to the cat’s environment
(18,32)
.
Discussion
The term “osteoarthritis” may (inappropriately) suggest an exclusively inflammatory cause.
Both “osteoarthritis” and other terms are used in literature, although the authors report on the
same disease. Therefore it is quite difficult to find out what disease is discussed and to draw
the right conclusions from that report. Another problem in literature is the fact that not all
authors distinguish between osteoarthritis and spondylosis deformans. If this goes unnoticed
by the reader false conclusions can be made about, for example, prevalence (9,17).
Also the reported prevalence in some reports is not reported as the prevalence per joint.
Therefore no conclusions can be made about the amount of osteoarthritis per joint and
whether one of the joints is more often affected than other joints (12).
Risk factors and prevalence for osteoarthritis in cats are difficult to establish. Obesity is a
thought to be a risk factor, but was not shown to be so in some studies. The only established
risk factor in cats for osteoarthritis is the age of the cat (4,9). More research is needed to
distinguish other risk factors and to obtain a better approximation of the prevalence in the cat.
Assessing pain in animals is a very difficult thing to do. Pain score models for evaluation of
pain in cats have been developed, for instance the University of Melbourne Pain Scale Model
(19)
. One should always compare the cat’s normal behaviour with the behaviour at that time in
the examination room. However, assessing pain remains difficult, as a cat that is continuously
vocalizing may be in pain, but vocalisation could also reflect stress caused by travelling to
and being in the examination room.
Medicamental options for osteoarthritis consists of the use of NSAIDs. Until recently only
tablets were registered for pain relief in cats. Recently a new NSAID (Metacam®) was
registered for the use in cats, which is an oral suspension. For therapy reliability this oral
15
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
suspension could be a good choice, because lots of owners have trouble with giving tablets to
their cats. With this new medicamental therapy, one should also be aware of possible side
effects. Despite the fact this medicament is relatively safe, it is still a NSAID and side-effects
should be monitored by the owners (22,23,33,37,38).
Diets were not proven to be efficient yet, but it might be worth to try for the osteoarthritic cat
owners (43). Nutraceutical agents and chondroprotective agents are also suggested for cats, but
there’s no definitive evidence of the effectiveness of these products. Therefore it is needed to
discuss the possibility of use in the cat with the owner, but it should always be mentioned that
the effectiveness is not proven (2,30,33).
The veterinarian should not only give the owner medicamental options, but should also speak
with the owner about environmental issues. These changes might be of greater importance for
the cat with osteoarthritis, than the medicamental options given and should be discussed
properly (7,18).
Conclusion
Osteoarthritis in cats may be an under recognised disease, which is receiving quite some
attention at the moment. The objective of this literature study was to describe the prevalence
of osteoarthritis in the joints of the appendicular skeleton of the cat, as it has been thought to
be higher as yet recognized. No definitive remarks on prevalence can be made. Differences
and the inclusion of spondylosis deformans in several researches, make it difficult to compare
the studies with each other.
Carefulness is needed when searching for literature with regard to the nomenclature of the
diseases. Often used names are “osteoarthritis”, “osteoarthrosis” and “degenerative joint
disease”.
Radiographic and pathologic signs of osteoarthritis in cats might not be as extensive as the
signs in dogs, but mostly narrowing of the joint space, articular cartilage destruction,
subchondral bone sclerosis and osteophyte formation are named.
Awareness of osteoarthritis in the elderly cat is needed in veterinarians to be able to learn
owners about this new disease in cats. During check-up’s and scheduled vaccination visits
veterinarians should ask questions about the lifestyle of the cat in order to detect signs of
osteoarthritis and other possible diseases. After diagnosing osteoarthritis in cats, the
veterinarian should take time to explain the importance of environmental changes and if
necessary explain the possibility of medication to the owner of the cat. Additionally, weight
normalisation may be discussed.
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
16
Part two: radiographic retrospective study
Abstract
A retrospective study of 471 radiographic images of cats from the archives of the Division of
Diagnostic Imaging of the University Clinic for Companion Animals in Utrecht was
performed. All visible joints were evaluated with regard to osteoarthritic changes. Breed,
gender, age, weight, diagnosis and (history of) trauma were recorded in each cat. This was
done to identify possible risk factors for osteoarthritis in cats. Logistic regression was
performed per joint to evaluate putative risk factors (i.e. breed, gender, age, weight, trauma
and diagnosis) in the development of osteoarthritis in cats.
The prevalence of osteoarthritis in cats in this study was 36.7%. A significant relation was
found between age and the degree of osteoarthritic changes in the shoulders (P<0.001),
elbows (Pelbow1<0.001 and Pelbow2=0.015) and stifles (P=0.002). Cats are more likely to have
osteoarthritic changes, as their age advances. Depending on the joint, the odds of having
osteoarthritis increased with a factor of approximately 1.3 per extra year of age. No other
putative risk factors were found to be significant.
The prevalences of osteoarthritic changes in the evaluated joints are summarised. Not enough
data was available to draw conclusions on the prevalence of osteoarthritis in the carpus and
tarsus. Most of the osteoarthritic changes in the joints were graded as mild osteoarthritic
changes. Less often the changes were graded as severe osteoarthritic changes.
Osteoarthritis more often occurs bilaterally than unilaterally in shoulders and hips (P<0.001
for both). If one of the shoulder or hip joints was positive for osteoarthritis, in 86%
(shoulders) and 95% (hips) of the cases osteoarthritic changes were also found in the
contralateral joint.
This report demonstrates an increased odds of having osteoarthritis in the joints of the
appendicular skeleton of cats with increasing age, confirming the results of several other
researches. Osteoarthritis in the elderly cat may be a new disease for the veterinarian to assess
in the geriatric cat.
Introduction
As a second part of this research project, evaluation of the prevalence of osteoarthritis in the
joints of the appendicular skeleton on radiographs from the archives of the Division of
Diagnostic Imaging of the University Clinic for Companion Animals in Utrecht was
performed. In this retrospective study, radiographs were evaluated from cats which were
presented at the University Clinic. Together with this evaluation of radiographs, the history of
the cats was evaluated to identify putative risk factors for osteoarthritis in cats (for example
weight, age, trauma and other diseases). The evaluation of the radiographs was supervised by
a Diagnostic Imaging Specialist.
The objective of this report was to find out if the prevalence of osteoarthritis in the joints of
the appendicular skeleton of the cat is higher as yet recognized.
Materials and methods
At first a selection of radiographic material from the department of Diagnostic Imaging of the
University Clinic for Companion Animals in Utrecht was made by collecting all radiographic
material from cats from May 26th 2004 until January 17th 2007, on which one or more joints
are visible. Whenever only a part of the joint was visible or the joint was superimposed on
another radio dense structure, the joint was not included in the research. Shoulders were only
17
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
evaluated, when both shoulders were visible and gradable. The other joints were always
named 1 (i.e. elbow 1 or stifle 1) if only one of these joints was present on the radiographs. If
the contralateral joint of a cat was also visible and gradable, this joint was named 2 (i.e. elbow
2, stifle 2, etcetera).
Age, breed, gender, weight, diagnosis and (history of) trauma of the cats were also recorded.
These were used to find possible relations between these variables and osteoarthritis.
Descriptives of these variables are outlined in the following paragraph:
Age: the age of the cat on the day of the radiographic imaging was calculated in years and
months, i.e. a cat was for instance 6 years and 3 months old. The ages were then converted to
a decimal scale. Age was considered to be a continuous variable for statistical analysis.
Breed: Cats from 25 different breeds were included. Each breed was given a number, as
described in table 6. The breed selection was done by the information on the chart of the
patient. Breed was considered to be a nominal variable for statistical analysis.
Table 6: breed classification
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Domestic Shorthair
European Shorthair
Siamese
Persian
Maine Coon
Abyssinian
Norwegian Forest cat
Cornish Rex
British Shorthair
Havanna Brown
Eastern Shorthair
Selkirk Rex
Turkish Angora
Burmese
Crossbred
Exotic Shorthair
Sphinx
Holy Birman
Bengalese
Tonkinese
Ragdoll
Somali
Siberian
Russian Blue
Devon Rex
Gender: 5 different gradations were made for the gender, as described in table 7. Only
complete gender information on the charts was used. Gender was considered to be a nominal
variable for statistical analysis.
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
18
Table 7: gender classification
1
2
3
4
99
Male neutered
Female neutered
Male
Female
Unkown
Weight: at presenting of the cat at the university clinic, many cats were weighed. All available
weights were recorded. The weights were rounded to one decimal. Weight was considered to
be a continuous variable for the statistical analysis.
Diagnosis: when final diagnosis of a disease in a cat was made, this was also recorded. Later
on the diagnoses were grouped into main categories. These categories are described in the
table below. Diagnosis was considered to be a nominal variable for the statistical analysis.
Table 8: diagnosis classification
1
Main categories of diseases
Cardiovascular
2
Pulmonary
3
4
5
6
7
8
9
Gastrointestinal
Orthopaedic
Nervous
Kidney/Urinary tract
Endocrine
Hepatic
Haematologic
10
11
12
Ear nose throat
Fever of unknown origin
Traumatic cases
13
Neoplasia
14
15
99
Multiple problems
Other
No Diagnosis
Descriptive
Hart failures, cardiomyopathies. Special note:
liquothorax & HCM is described as cardiovascular.
Bronchitis, liquothorax, hernia diaphragmatica (nontrauma), asthma and tracheal problems. Primary
lungtumors and lung metastasis were noted as
neoplasia.
All gastrointestinal diseases, including corpora aliena
Non-traumatic orthopaedic cases
Central nervous system and peripheral nervous system
Urinary tract problems and kidney problems
All endocrine disorders
All hepatic and cholangial diseases
Haematologic disorders, including immune mediated
haemolytic anaemia
All ear, nose and throat problems
Cat presented with fever of unknown origin
Car accidents, falling from heights, gunshot wounds,
bone fractures, pneumothorax (traumatic), hernia
diaphragmatica (traumatic), bite trauma
All sorts of tumors, including abdominal,
cardiovascular and pulmonary neoplasia
Several diseases simultaneously, except trauma
Diseases which can not be categorised
No definitive diagnosis/ symptoms
Trauma: trauma was graded as no known trauma, trauma in present, trauma in past and a
combination of trauma in past and present, as described in table 9. For further statistical
analysis (logistic regression) the cases were classified as with (a history of) known trauma (1)
or not (2). Trauma was considered to be an ordinal variable for the statistical analysis.
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
19
Table 9: trauma classification
0
1
2
3
No known trauma
Trauma
Trauma in past
Trauma + trauma in past
Osteoarthritis: the visible joints on the obtained radiographic images were graded per joint
with regard to visible osteoarthritic changes, as described in table 10. For the logistic
regression analysis the cases were regrouped into a group with osteoarthritic changes (1) and
a group without (2). Osteoarthritis was considered to be an ordinal variable for the statistical
analysis.
Table 10: osteoarthritis classification
0
1
2
99
No osteoarthritic changes
Mild osteoarthritic changes
Severe osteoarthritic changes
Joint not visible
Overall formation of the joint, osteophyte formation, subchondral bone sclerosis and other
abnormalities are evaluated and scaled. The difference between mild and severe osteoarthritic
changes was the appearance of a loose fragment in the joint, extensive irregularity of the joint
surface and the appearance of large osteophytes. Minimal irregularity of the joint surface and
small osteophytes were graded to be mild osteoarthritis.
All gradable joints were placed in an excel sheet, whereby also the directions of the taken
radiographs were recorded. Mostly these included a dorso-ventral and dextro-sinistral image
of the shoulders; a ventro-dorsal and dextro-sinistral image of the hips; a medio-lateral and a
posterior-anterior image of the elbows, stifles, carpus and tarsus. If only a ventro-dorsal view
of the hips or a dextro-sinistral view of the shoulders was present, this radiograph was also
evaluated and graded. Whenever only a dextro-sinistral view of the hips (or a dorso-ventral
view of the shoulders) were available for evaluation, these joints were not included in the
study, because of not being able to evaluate the complete joint surface.
After collection the data was entered into the statistical program “ SPSS 12.0.1 for windows”.
Each continuous variable (i.e. age, weight) was tested for normality using the KolmogrovSmirnov test with Lillifors significance correction. The aim of this test was to find out if the
continuous variable was distributed parametrically or not. For each joint the frequencies of
each grade were tabulated. The prevalence of osteoarthritis per joint was calculated as the
number of affected joints divided by the number of included joints.
Univariate logistic regression was performed per joint to separately evaluate each putative
risk factor (i.e. breed, gender, age, weight, trauma and diagnosis) in the development of
osteoarthritis in cats. The Hosmer-Lemeshow goodness-of-fit test was used to evaluate the fit
of the regression model. Whenever univariate regression analysis per joint revealed more than
one putative risk factor (P<0.05), these risk factors were analysed together using multivariate
logistic regression. A backward stepwise (based on likelihood ratio) approach was used.
Variables with P>0.05 were removed from analysis. P<0.05 was considered to be significant.
A binominal test was performed to investigate the gender distribution in the cats in this report.
A Chi-square test was used to determine if the risk of having osteoarthritis in one shoulder or
hip was higher if the contralateral joint was already diagnosed with osteoarthritis. Within the
group of cats with unilateral osteoarthritis it was assumed that osteoarthritis occurred in the
right joint as frequently as in the left joint.
20
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
Results
Frequency tables were made of all assessed variables. These are displayed in the tables below.
For general view table 11 was made considering the frequencies of ages from the cats.
Table 11: age frequencies
Age number
1
2
3
4
5
Total
Age
0-5 years
>5- 10 years
>10-15 years
> 15 years
Missing
Frequency (n)
185
138
116
25
7
471
Frequency (%)
39.3
29.3
24.6
5.3
1.5
100.0
The age frequencies of the cats in the research are also displayed in the histogram in figure 2.
Figure 2: age frequencies
50
Frequency
40
30
20
10
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Age (years)
Subjectively, in figure 2 it seems that the amount of younger cats is higher than the amount of
elderly cats in this research. In the first two categories 42 and 50 cats are present, which
seems to display that more younger cats (until 2 years of age) are presented at the Division of
Diagnostic Imaging of the University Clinic for Companion Animals in Utrecht for
radiographic imaging. After 14 years of age the amount of cats presented for a radiographic
image diminishes, which may be explained by the average age cats are becoming these days.
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
21
The variables age and weight were not distributed parametrically (P<0.001 and P=0.038,
respectively) Therefore the median and range are reported in table 12.
Table 12: age and weight distribution
Age
Weight
Distributed
parametrically
No
No
Median
Range
7.0850
4.00
0.25 – 17.17
1.10-8.20
To assess the average bodyweights of the cats versus the age of the cats in the research a
histogram has been made. The average weight (with 95% confidence interval) per age
category are displayed in figure 3.
Figure 3: weight versus age distribution
Weight seems to be quite constant throughout the age categories.
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
22
The frequencies of different breeds were assessed and outlined in table 13.
Table 13: breed frequencies
Breed number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Breed
Domestic Shorthair
European Shorthair
Siamese
Persian
Maine Coon
Abessian
Norwegian Forest cat
Cornish Rex
British Shorthair
Havanna Brown
Eastern Shorthair
Selkirk Rex
Turkish Angora
Burmese
Crossbred
Exotic Shorthair
Sphinx
Holy Birman
Bengalese
Tonkinese
Ragdoll
Somali
Siberian
Russian Blue
Devon Rex
Frequency (n)
121
212
18
18
20
2
7
2
20
1
8
1
2
3
14
1
3
7
1
1
3
2
1
2
1
Frequency (%)
25.7
45.0
3.8
3.8
4.2
0.4
1.5
0.4
4.2
0.2
1.7
0.2
0.4
0.6
3.0
0.2
0.6
1.5
0.2
0.2
0.6
0.4
0.2
0.4
0.2
Domestic shorthairs and European shorthairs together represented more than 70% of the
presented cats. Most of the cats were European shorthairs (45.0%), followed by Domestic
shorthairs (25.7%), Maine Coons (4.2%), Siamese (3.8%), Persians (3.8%) and Crossbreds
(3.0%).
The distribution of the genders is outlined in table 14.
Table 14: gender frequencies
Gender number
1
2
3
4
99
Gender
Male neutered
Female neutered
Male
Female
Unknown
Frequency (n)
230
172
36
32
1
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
Frequency (%)
48.8
36.5
7.6
6.8
0.2
23
Slightly more neutered males were present in the cases and somewhat less neutered females,
as confirmed by a binomial test, which showed a higher prevalence of neutered males (57.0%,
P=0.004). Intact males and females were not presented as much.
All cases were assessed for any trauma in past or present. The frequencies are displayed in
table 15.
Table 15: trauma frequencies
Trauma number
0
1
2
3
Trauma
No known trauma
Trauma
Trauma in past
Trauma + trauma in past
Frequency (n)
382
84
4
1
Frequency (%)
81.1
17.8
0.9
0.2
The table shows that 18.9% of the cases were presented for a history of trauma or had trauma.
In 81.1 % of the cases there was no known (history of) trauma. Sixty-six percent of cats with
a history of trauma (in the past, recent or both) were male.
Finally, all diagnoses were categorized into disease categories. These are displayed below in
table 16.
Table 16: disease frequencies
Disease number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
99
Disease category
Cardiovascular
Pulmonary
Gastrointestinal
Orthopaedic
Nervous
Kidney/Urinary tract
Endocrine
Hepatic
Haematologic
Ear nose throat
Fever of unknown origin
Traumatic cases
Neoplasia
Multiple problems
Other
No Diagnosis
Frequency (n)
31
105
25
9
16
18
3
5
7
6
6
80
88
59
6
7
Frequency (%)
6.6
22.3
5.3
1.9
3.4
3.8
0.6
1.1
1.5
1.3
1.3
17.0
18.7
12.5
1.3
1.5
The main disease categories are pulmonary, traumatic cases, neoplasia and multiple problems.
Together these categories account for 70.5 % of total cases.
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
24
The frequencies of osteoarthritis, visibility of the joints and severeness of osteoarthritis are
listed in table 17 and 18 below. The gradations used were no osteoarthritis (0), mild
osteoarthritis (1) and severe osteoarthritis (2), as described in table 10.
Table 17: osteoarthritis gradation
Shoulder 1
Shoulder 2
Elbow 1
Elbow 2
Hip 1
Hip 2
Stifle 1
Stifle 2
Carpus 1
Carpus 2
Tarsus 1
Tarsus 2
Grade
0
Grade
0 (%)
Grade
1
Grade
1 (%)
Grade
2
179
187
44
25
37
38
23
11
1
0
5
0
38
39.7
9.3
5.3
7.9
8.1
4.9
2.3
0.2
0
1.1
0
51
43
36
7
14
15
5
3
1
0
2
0
10.8
9.1
7.6
1.5
3.0
3.2
1.1
0.6
0.2
0
0.4
0
8
8
9
5
6
4
6
2
0
0
0
0
Grade
2
(%)
1.7
1.7
1.9
1.1
1.3
0.8
1.3
0.4
0
0
0
0
Not
Visible:
99
233
233
382
434
414
414
437
455
469
471
464
471
Not
Visible:
99 (%)
49.5
49.5
81.1
92.1
87.9
87.9
92.8
96.6
99.6
100
98.5
100
Table 18: osteoarthritis prevalence
Shoulder 1
Shoulder 2
Elbow 1
Elbow 2
Hip 1
Hip 2
Stifle 1
Stifle 2
Carpus 1
Carpus 2
Tarsus 1
Tarsus 2
OA positive
Visible
joints
59
51
45
12
20
19
11
5
1
0
2
0
238
238
89
37
57
57
34
16
2
0
7
0
Total OA in
visible
joints(%)
24.8
21.4
50.6
32.4
35.1
33.3
32.4
31.3
50.0
0
28.6
0
Grade 1 OA in
visible joints
(%)
21.4
18.0
40.4
18.9
24.6
26.3
14.7
18.8
50.0
0
28.6
0
Grade 2 OA
in visible
joints (%)
3.4
3.4
10.1
13.5
10.5
7.0
17.6
12.5
0
0
0
0
Almost 24.8 % and 21.4 % of the visible shoulder joints had osteoarthritic changes. Even
50.6% of the visible elbow 1 joints had osteoarthritic changes, followed by 32.4% in elbow 2.
The osteoarthritic hips accounted for 35.1% and 33.3% of the visible hip joints. In Stifle 1 a
percentage of 32.4% of visible joints was osteoarthritic and 31.3% in stifle 2. The obtained
data for carpus and tarsus were not enough to draw conclusions about these joints. Therefore
these data were only summarised, but no statistical analysis were performed.
Logistic regression was performed for each joint with the six different variables listed in table
19.
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
25
Table 19: logistic regression
Breed
Gender
Age
Weight
Trauma
Diagnosis
Shoulder 1 Shoulder 2 Elbow 1
n.s.
n.s
n.s
n.s.
n.s
n.s
s.
s.
s.
s.n.s.
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s
Elbow 2 Hip 1 Hip 2 Stifle 1 Stifle 2
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s
s.
n.s
n.s
s.
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s
n.s. = not significant; s. = significant; s.n.s = significant after univariate logistic regression, but not significant
anymore after multivariate logistic regression.
As is shown in table 19 age was a significant risk factor for osteoarthritis in shoulder 1,
shoulder 2, elbow 1, elbow 2 and stifle 1. No other risk factors were found to be significantly
related to osteoarthritis. Hip 1, hip 2 and stifle 2 were not significantly related to any of the
variables.
For shoulder 1 age was a significant risk factor (P<0.001). The odds ratio for age was 1.31
after multiple logistic regression. This means that when the age of the cat advances with one
year, the odds of developing osteoarthritis in this shoulder must be multiplied with a factor of
1.31. In the univariate logistic regression model shoulder 1 at first age and weight seemed to
be risk factors. After the multivariate logistic regression model only age remained. This may
be due to the fact that there is a correlation between both variables within the shoulder 1
category, but the age variable was most important. For shoulder 2 age was a significant risk
factor (P<0.001). The odds ratio for age was 1.32. In elbow 1 age was a significant risk factor
(P<0.001). The odds ratio was 1.25. The same is true for elbow 2, in which age was a
significant factor (P=0.015). The odds ratio for elbow 2 was 1.27. For stifle 1 age was a
significant factor (P=0.002). The odds ratio was 1.43. No significant risk factors could be
distinguished for hip 1, hip 2 and stifle 2.
All of the joints that were significantly related to age were placed into tables, for a general
overview in which age categories osteoarthritis was seen most. The gradations of
osteoarthritis were regrouped into a group with osteoarthritic changes (1) and a group without
(0). This is displayed in tables 20, 21, 22, 23 and 24.
Table 20: osteoarthritis and age in shoulder 1
Shoulder 1
0-5 years
>5-10 years >10-15 years >15 years
Total
No osteoarthritis
82 (97.6%) 59 (73.75%) 32 (53.3%)
5 (41.7%)
178 (75.4%)
Osteoarthritis
2 (2.4%)
21 (26.25%) 28 (46.7%)
7 (58.3%)
58 (24.6%)
Total
84 (100%)
80 (100%) 60 (100.0%) 12 (100%)
236 (100%)
Quite a lot of shoulder joints were evaluated. It would seem that above 5 years of age more
osteoarthritis is present than below 5 years of age. Above 10 years of age this number even
seems to increase. In the > 15 years of age category less joints were evaluated. Possibly in
cats > 15 years of age even more osteoarthritis is present, than in cats below 15 years of age.
Table 21: osteoarthritis and age in shoulder 2
No osteoarthritis
Osteoarthritis
Total
0-5 years
82 (97.6%)
2 (2.4%)
84 (100%)
Shoulder 2
>5-10 years >10-15 years
64 (80%)
35 (58.3%)
16 (20%)
25 (41.7%)
80 (100%)
60 (100%)
>15 years
5 (41.7%)
7 (58.3%)
12 (100%)
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
Total
186 (78.8%)
50 (21.2%)
236 (100%)
26
Of shoulder 2 the same number of joints were evaluated as in shoulder 1, because of the
criteria to evaluate both shoulders on the radiographs. Approximately the same distribution
can be seen in shoulder 2 as in shoulder 1.
Table 22: osteoarthritis and age in elbow 1
Elbow 1
0-5 years
>5-10 years >10-15 years >15 years
Total
No osteoarthritis
23 (82.1%)
15 (45.5%)
5 (26.3%)
0 (0%)
43 (48.9%)
Osteoarthritis
5 (17.9%)
18 (54.5%)
14 (73.7%)
8 (100%)
45 (51.1%)
Total
28 (100%)
33 (100%)
19 (100%)
8 (100%)
88 (100%)
Elbow 1 shows an increase in the number of osteoarthritic cases above 5 years of age. Above
10 years of age and above 15 years of age the prevalence seems to increase even more.
Table 23: osteoarthritis and age in elbow 2
Elbow 2
0-5 years
>5-10 years >10-15 years >15 years
Total
No osteoarthritis
9 (81.8%)
11 (84.6%)
5 (55.6%)
0 (0%)
25 (67.6%)
Osteoarthritis
2 (18.2%)
2 (15.4%)
4 (44.4%)
4 (100%)
12 (32.4%)
Total
11 (100%)
13 (100%)
9 (100%)
4 (100%)
37 (100%)
Elbow 2 shows some increase of osteoarthritic cases above 10 years of age, but only little data
is available.
Table 24: osteoarthritis and age in stifle 1
Stifle 1
0-5 years
>5-10 years >10-15 years >15 years
No osteoarthritis
16 (94.1%)
5 (55.6%)
2 (40%)
0 (0%)
Osteoarthritis
1 (5.9%)
4 (44.4%)
3 (60%)
3 (100%)
Total
17 (100%)
9 (100%)
5 (100%)
3 (100%)
Stifle 1 shows an increase of osteoarthritis above 5 years of age. Relatively
available.
Total
23 (67.7%)
11 (32.3%)
34 (100%)
little data is
Evaluation of the total prevalence of osteoarthritis in this report was done. A total number of
119 cats had osteoarthritis in at least one joint. This accounts for a prevalence of osteoarthritis
of 36.7% (119/324). A number of 147 cats were not included in this calculation, as there were
no joints present on the radiograph.
Chi-square tests revealed that osteoarthritis more often occurs bilaterally than unilaterally in
shoulders and hips (P<0.001 for both). If one of the shoulder or hip joints was positive for
osteoarthritis, in 86% (shoulders) and 95% (hips) of the cases osteoarthritic changes were also
found in the contralateral joint.
Discussion
High frequencies of osteoarthritis were seen in cats in the shoulders (c.q. 24.8 % for shoulder
1 and 21.4 % for shoulder 2) , elbows (c.q. 50.6% for elbow 1 and 32.4 % for elbow 2) and
stifles (c.q. 32.4 % for stifle 1 and 31.3 % for stifle 2). A total percentage of 36.7% was found
in this study for cats with at least one joint with signs of osteoarthritis. A significant
relationship between age and osteoarthritis status is established in this study. The odds of
having osteoarthritis increases with increasing age. Only the hips did not show a significant
correlation between the joint osteoarthritis-status and the age of the cat. Two possible
explanations can be made for this finding. At first it is possible that no significant correlation
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
27
was found, because of a too low amount of collected hip radiographs. The second explanation
consists of the possibility of osteoarthritis at younger age for the hips, because of the disease
hip dysplasia which is inherited and the osteoarthritis in these cats starts at young age. More
research on this subject is needed to draw definite conclusions.
Selection of suitable radiographic material from the archives of the Division of Diagnostic
Imaging of the University Clinic for Companion Animals in Utrecht was done by collecting
all radiographic images from cats from May 26th 2004 until January 17th 2007, with one or
more visible joints. It may seem that these dates are randomly chosen, but this is not the case.
All radiographic images later than January 17th 2007 were not obtained, because of a change
in the archive system at the Division of Diagnostic Imaging. After this date all radiographs
were made digitally and to prevent interpretation bias due to different techniques used to
make radiographs, collection of the data was not done beyond January 17th 2007. Because of
the amount of collected radiographs (approximately 500 radiographs), collection was not done
further back than May 26th 2004.
During collection of the different variables in the cats’ patient files, several things were
noticed. The cats’ ages were not always known exactly. For example, the day of birth of a cat
presented at June 21st 2004, of which the owner did not specifically know the date of birth but
only knew the year of birth, was likely to be set at June 21st of that year. At least the year of
birth matches in these cats and it is thought not to be of great influence on the age distribution
of the cats, although it should be mentioned.
Slightly more young cats than elderly cats were radiographed at the University Clinic. It is not
known if this is representative for the age distribution in the general cat population. However,
the general prevalence of osteoarthritis in this report could be slightly lower than in the
general cat population. In most of other researches only geriatric cats were assessed, which
may have influenced the outcome of these studies. In this study, a total of 119 cats had a
positive osteoarthritis gradation in at least one joint. In the total number of evaluated cats this
accounts for a prevalence of 36.7 % (119/324 cats). A number of 147 cats were not included,
as there were no joints on the radiograph. If comparison of this research is made with the
report of Clarke et al (9) and with the report of Godfrey (12) quite similar prevalences have been
reported. Clarke et al stated a prevalence of osteoarthritis of 33.9 % (including spondylosis
deformans), which can be recalculated into a percentage of approximately 22.0% for
osteoarthritis alone in cats above 8 years of age (9). Godfrey also reported a prevalence of
osteoarthritis of 22.0%, in cats above 1 year of age (12). When comparison of this research is
made with the report of Hardie (17) a different prevalence is noted. Hardie stated a prevalence
for osteoarthritis in cats of 90.0 % (including spondylosis deformans), which can be
recalculated in 64.0% for osteoarthritis exclusively (17). The major difference between this
research and the study of Hardie is that Hardie only evaluated cats above 12 years of age. This
might be an explanation that the total prevalence found in this study is lower as the prevalence
found in the study of Hardie. The fact that increasing age increases the odds of having
osteoarthritis in elbows, shoulders and stifles supports this supposition.
With regard to the cat’s breed many cats were categorised as Domestic Shorthairs or
European Shorthairs. There is probably some confusion when it comes to the definition of
European Shorthairs and Domestic Shorthairs. European Shorthair is a pedigree and the
correct term for housecats that resemble European Shorthairs, but are of unknown descent, is
Domestic Shorthair. The assumption is made that the obtained data has too many European
Shorthairs in it, possibly caused by incorrect registering in the clinic’s database.
Compared to neutered females, more neutered males were presented at the University Clinic.
One may consider various explanations for this difference, although none can be definitively
proven with this study. Most likely, there are as many females as males in the general cat
population. The discrepancy between the amount of presented (neutered) males and females
therefore may arise from a higher amount of male cats with medical conditions that require
28
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
radiographic imaging. For instance, in this study there seem to be more males than females
with a history of trauma, possibly caused by the larger roaming space of male cats that may
contribute to a higher chance of (car or other) accidents.
No relation could be found between osteoarthritis and the weight of the cats in this study.
Bennet and Clarke also evaluated weight as a possible risk factor in their studies, but no
significant correlation was found between osteoarthritis and weight (4,9). When considering
this, it is important to distinguish that for the several breeds included in this study, each breed
has a different ideal weight. Thus, for example, a Siamese of 5 kilograms may be considered
to be obese, but a Maine Coon of 5 kilograms is not considered to be obese. Ideally, body
condition would be evaluated as a risk factor for developing osteoarthritis. There does not
seem to be a relation between age and weight (figure 3). Therefore it seems unlikely that
during the multivariate analyses the effects of weight were overruled by the effects of age.
In each of the cases the history was searched for reported trauma. 18.9% of the cases had a
report of trauma in their history. In 81.1 % of the cases no trauma was present. No significant
correlation between trauma and osteoarthritis could be made in this study. In these cases the
trauma cases were mostly cases with trauma at the date of presentation (for example a recent
car accident). It is believed that osteoarthritis can develop after trauma in a progressive way
(1,6,25,35)
, but on the day of the trauma obviously no signs of osteoarthritis are present yet.
Therefore no correlation between trauma and osteoarthritis could be made. If these cats with
trauma would be radiographed later on in their lives, it is possible that a positive correlation
could be found between trauma and later development of osteoarthritis.
Many cats were presented with pulmonary problems, trauma, neoplasia and multiple
problems. Because of the referral status of the University Clinic it is quite logical to see these
complex cases presented at the clinic. No correlation could be made between the disease that
was diagnosed in the cats and the presence of osteoarthritis.
A point of discussion is the evaluation of the radiographs. In total 471 radiographs were
graded for osteoarthritis. Over time, the gradation became increasingly easy, because of
developed experience. Therefore it might be possible that subtle signs of osteoarthritis were
missed at the beginning of the study. However, a diagnostic imaging specialist was always
available to help with the interpretation of radiographs in case of doubt.
During the evaluation of the obtained radiographic material, it was noticed that not all of the
descriptions of radiographic signs described in the first part of this report could be evaluated
as such. Part of this can be explained by the radiographic material itself, because these
radiographs were mostly taken for non-orthopaedic assessment and not for the joints in
question. Irregularity of the joint and osteophyte formation could be seen, in most cases,
where dorsoventral and dextrosinistral images were present for comparison. Articular
cartilage destruction can not be seen on the radiographic material, but only on for example
MRI images or at necropsy. Subchondral bone sclerosis was not seen and was also often
difficult to assess, because of the abdominal or thoracic focus of the radiograph. The main
used criteria for the osteoarthritic changes graded in these data were therefore the presence of
osteophytes and irregularity of the joint surfaces.
The visible shoulder and hip joints on the obtained radiographic images consisted of 238
visible pairs of shoulders and 57 pairs of hips. Based on the assumption that osteoarthritis
more often occurs bilaterally than unilaterally in shoulders and hips, data was only included if
both shoulders or both hips were visible on the radiographs and gradable.
Because the data often had only one visible elbow, stifle, tarsus or carpus on the radiograph,
these joints were not assessed in pairs. From the 89 cases in which at least one elbow was
visible, only in 37 cases a second elbow was present. This was also the case for the stifles, in
which both stifles were present in only 16 out of 34 cases in which at least one stifle was
present. Carpi and tarsi were scarce on radiographic material. Only 2 cases with one carpus
and 7 cases with one tarsus were seen. No statistical analysis could be performed with these
29
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
low numbers. Therefore no conclusions could be made from the data of the carpi and tarsi
with regard to risk factors and prevalence. This also accounts for stifle 2, for which only 16
stifles were available.
Conclusion
In conclusion the objective in this research project was to investigate the prevalence of
osteoarthritis in the joints of the appendicular skeleton of the cat, as it is thought to be higher
as yet recognized. After this report and the retrospective evaluation of 471 radiographs it
seems that osteoarthritis is more common in cats than thought before. The significance of this
finding is unclear, because most of the cats do not show symptoms of this disease or the
symptoms aren’t recognised. More research has to be done, to find out what the clinical
relevance of osteoarthritis in cats is. A total prevalence of osteoarthritis in cats of 36.7% was
found.
Several risk factors, (c.q. breed, age, weight, gender, trauma and diagnosis) were analysed and
only age seems to be a significant factor in osteoarthritis. In both shoulder joints, the elbows
and the stifles a significant correlation was established between osteoarthritis and age.
Conclusion of this investigation is that osteoarthritis is more common in elderly cats. This is
confirmed by other researchers, for example by Bennet et al and by Clarke et al (4,9).
A remarkable finding in this report is that no significant correlation could be found between
age and osteoarthritis in the hips, which might suggest that hip osteoarthritis may be more of a
problem in younger cats because of inheritable causes. Another remarkable finding of this
report is the fact that there is a positive relation between the presence of osteoarthritis in one
shoulder and in the contralateral shoulder of the cats. The same relationship was found for the
hip joints. This report confirms that elderly cats are at greater risk of developing or having
osteoarthritic changes.
Acknowledgements
The author would like to thank the department of Diagnostic Imaging of the University Clinic
for Companion Animals in Utrecht for making the radiographic images available for use in
this report. Special thanks goes out to prof. dr. G. Voorhout and drs. E. Auriemma for
discussion of the findings and assessment of radiographic material.
The author also would like to thank dr. L.I. Slingerland for the daily supervision, critical
analysis of this report and the help with the statistical analysis. At last the author would like to
thank prof.dr. H.A.W. Hazewinkel for overall supervision and critical analysis of this report.
- “Prevalence of osteoarthritis in the joints of the appendicular skeleton of the cat” M.Verruijt, 2008
30
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