Objective—To evaluate the quantitative inheritance of secondary hip joint osteoarthritis in a canine pedigree.
Animals—137 Labrador Retrievers, Greyhounds, and mixed-breed dogs.
Procedures—Necropsy scores ranging from 0 to 4 were obtained for each hip joint. Seven unaffected Greyhounds with normal hip joint conformation were also used for genetic modeling, but were not euthanized. Sixty-six male and 71 female dogs were allocated to 2 groups (≤ 12 months of age and > 12 months of age). Statistical models were developed to establish the inheritance pattern of hip joint osteoarthritis that developed secondary to hip dysplasia.
Results—62 dogs had evidence of osteoarthritis in a hip joint, and 75 had no evidence of osteoarthritis. After sex was adjusted for, the necropsy score was found to be inherited additively but without dominance. Each Labrador Retriever allele increased the necropsy score by 0.7 to 0.9 points, compared with the Greyhound allele, and male sex increased the necropsy score 0.74 over female sex. Approximately 10% of the variation in necropsy score was attributable to the litter of puppies' origin.
Conclusions and Clinical Relevance—Because secondary hip joint osteoarthritis is inherited additively, selection pressure could be applied to reduce its incidence. Similar statistical models can be used in linkage and association mapping to detect the genes in the underlying quantitative trait loci that contribute to hip joint osteoarthritis.
Objective—To identify quantitative trait loci (QTL) associated with osteoarthritis (OA) of hip joints of dogs by use of a whole-genome microsatellite scan.
Animals—116 founder, backcross, F1, and F2 dogs from a crossbred pedigree.
Procedures—Necropsy scores and an optimized set of 342 microsatellite markers were used for interval mapping by means of a combined backcross and F2 design module from an online statistical program. Breed and sex were included in the model as fixed effects. Age of dog at necropsy and body weight at 8 months of age were also included in the model as covariates. The chromosomal location at which the highest F score was obtained was considered the best estimate of a QTL position. Chromosome-wide significance thresholds were determined empirically from 10,000 permutations of marker genotypes.
Results—4 chromosomes contained putative QTL for OA of hip joints in dogs at the 5% chromosome-wide significance threshold: chromosomes 5, 18, 23, and 31.
Conclusions and Clinical Relevance—Osteoarthritis of canine hip joints is a complex disease to which many genes and environmental factors contribute. Identification of contributing QTL is a strategy to elucidate the genetic mechanisms that underlie this disease. Refinement of the putative QTL and subsequent candidate gene studies are needed to identify the genes involved in the disease process.
Objective—To determine whether dorsolateral subluxation
(DLS) scores in young dogs could be used to
reliably predict which dogs would develop evidence of
hip osteoarthritis and whether DLS scores measured
at various ages correlated with each other.
Animals—129 Labrador Retrievers, Greyhounds, and
Labrador Retriever-Greyhound crossbreds.
Procedures—DLS scores were measured on radiographs
taken at 4, 8, and 12 months of age and at
necropsy (8 to 36 months of age). At necropsy, the
hip joints were examined macroscopically and a score
assigned for degree of cartilage degeneration.
Results—DLS scores at 4 (n = 35, rs = –0.62), 8 (n =
106, rs = –0.54), and 12 (n = 15, rs = –0.87) months of
age were significantly correlated with cartilage degeneration
scores, and DLS scores at 8 months of age
were significantly correlated with scores obtained at
the time of necropsy (n = 39, rs = 0.87). The DLS
scores at 4 months of age were significantly different
from scores at 8 months of age, but scores did not differ
significantly thereafter. Likelihood ratios for cartilage
lesions for low (< 45%), intermediate (≥ 45 but ≤
55%), and high (> 55%) DLS scores at 8 months of
age were 8.0, 2.6, and 0.2, respectively.
Conclusions and Clinical Relevance—Results suggest
that DLS score at 8 months of age was a reasonable,
albeit imperfect, predictor of the condition of the
hip joint cartilage at necropsy. Thus, the DLS method
might be useful for early identification of dogs with hip
dysplasia. (Am J Vet Res 2001;62:1711–1715)
Objective—To compare the accuracy of the extended-
hip radiographic (EHR) score, the distraction index
(DI), and the dorsolateral subluxation (DLS) score for
identifying hip dysplasia in dogs at 8 months of age.
Animals—129 Labrador Retrievers, Greyhounds, and
Labrador Retriever-Greyhound crossbreds.
Procedure—Radiography was performed when dogs
were 8 months of age. Dogs were euthanatized at 8
to 36 months of age; hip dysplasia was diagnosed at
the time of necropsy on the basis of results of a gross
examination of the articular cartilage of the hip joints
for signs of osteoarthritis.
Results—The EHR score, DI, and DLS score at 8
months of age were all significantly correlated with
degree of cartilage degeneration at necropsy.
Sensitivity and specificity of using EHR score at 8
months of age to diagnose hip dysplasia (scores > 3
were considered abnormal) were 38 and 96%, respectively;
sensitivity and specificity of using DI (values >
0.7 were considered abnormal) were 50 and 89%; and
sensitivity and specificity of using DLS score (scores ≤
55% were considered abnormal) were 83 and 84%.
Conclusions and Clinical Relevance—Results suggested
that specificities of the 3 methods for diagnosing
hip dysplasia in dogs at 8 months of age were
similar. However, the DLS score had higher sensitivity,
indicating that there were fewer false-negative
results. (J Am Vet Med Assoc 2001;219:1242–1246)
Procedure—Computed tomography (CT) of the pelvis, including a bone-density phantom, was performed for each dog. Centrally located transverse CT slices and a computer workstation were used to identify 16 regions of interest (ROIs) in the proximal portion of the femur. For each ROI, the mean Hounsfield unit value was recorded; by use of the bone-density phantom and linear regression analysis, those values were converted to equivalent BMD (eBMD). Mean eBMD values for the subchondral and nonsubchondral ROIs in dogs with and without osteoarthritis (determined at necropsy) were compared. A mixed-model ANOVA and post hoc linear contrasts were used to evaluate the effects of osteoarthritis, breed, and sex on the BMD value.
Results—At necropsy, osteoarthritis was detected in 14 hip joints in 9 dogs; all lesions included early cartilage fibrillation. After adjusting for breed and sex, eBMD in subchondral ROIs 8 and 12 (adjacent to the fovea) were 8% and 6% higher, respectively, in osteoarthritis-affected dogs, compared with unaffected dogs; in the nonsubchondral ROIs, eBMD was 10% higher in osteoarthritis-affected dogs.
Conclusions and Clinical Relevance—Compared with findings in unaffected dogs, increased eBMD in hip joints of dogs with early osteoarthritis supports a strong relationship between the subchondral and epiphyseal regions and articular cartilage in the pathogenesis and progression of osteoarthritis.
Objective—To determine the radiographic methods
that best predict the development of osteoarthritis in
the hip joints of a cohort of dogs with hip dysplasia
and unaffected dogs.
Animals—205 Labrador Retrievers, Greyhounds, and
Labrador Retriever-Greyhound crossbred dogs.
Procedure—Pelvic radiography was performed when
the dogs were 8 months old. Ventrodorsal extendedhip,
distraction, and dorsolateral subluxation (DLS)
radiographs were obtained. An Orthopedic
Foundation for Animals-like hip score, distraction
index, dorsolateral subluxation score, and Norberg
angle were derived from examination of radiographs.
Osteoarthritis was diagnosed at the time of necropsy
in dogs ≥ 8 months of age on the basis of detection
of articular cartilage lesions. Multiple logistic regression
was used to determine the radiographic technique
or techniques that best predicted development
Results—A combination of 2 radiographic methods
was better than any single method in predicting a cartilage
lesion or a normal joint, but adding a third radiographic
method did not improve that prediction. A
combination of the DLS score and Norberg angle best
predicted osteoarthritis of the hip joint or an unaffected
hip joint. All models that excluded the DLS score
were inferior to those that included it.
Conclusions and Clinical Relevance—A combination
of the DLS score and Norberg angle was the best
predictor of radiographic measures in 8-month-old
dogs to determine whether a dog would have normal
or osteoarthritic hip joints. (Am J Vet Res 2003;64:1472–1478)
Objective—To estimate the number of dogs required
to find linkage to heritable traits of hip dysplasia in
dogs from an experimental pedigree.
Animals—147 Labrador Retrievers, Greyhounds, and
their crossbreed offspring.
Procedure—Labrador Retrievers with hip dysplasia
were crossed with unaffected Greyhounds. Age at
detection of femoral capital ossification, distraction
index (DI), hip joint dorsolateral subluxation (DLS) score,
and hip joint osteoarthritis (OA) were recorded. Power
to find linkage of a single marker to a quantitative trait
locus (QTL) controlling 100% of the variation in a dysplastic
trait in the backcross dogs was determined.
Results—For the DI at the observed effect size,
recombination fraction of 0.05, and heterozygosity of
0.75, 35 dogs in the backcross of the F1 to the
Greyhound generation would yield linkage at a power
of 0.8. For the DLS score, 35 dogs in the backcross to
the Labrador Retriever generation would be required
for linkage at the same power. For OSS, 45 dogs in
the backcross to the founding Labrador Retrievers
would yield linkage at the same power. Fewer dogs
were projected to be necessary to find linkage to hip
OA. Testing for linkage to the DLS at 4 loci simultaneously,
each controlling 25% of the phenotypic variation,
yielded an overall power of 0.7.
Conclusions and Clinical Significance—Based on
this conservative single-marker estimate, this pedigree
has the requisite power to find microsatellites
linked to susceptibility loci for hip dysplasia and hip
OA by breeding a reasonable number of backcross
dogs. (Am J Vet Res 2003;222:418–424)
Objective—To determine the genetic influence on
expression of traits associated with canine hip dysplasia.
Animals—193 dogs from an experimental canine
Procedure—An experimental canine pedigree was
developed for linkage analysis of hip dysplasia by mating
dysplastic Labrador Retrievers with nondysplastic
Greyhounds. A statistical model was designed to test
the effects of Labrador Retriever and Greyhound alleles
on age at detection of femoral capital epiphyseal
ossification, 8-month distraction index, and 8-month
dorsolateral subluxation score.
Results—The additive effect was significant for age
at detection of femoral capital epiphyseal ossification.
Restricted maximum likelihood estimates (± SD)
for this trait were 6.4 ± 1.95, 10.2 ± 2.0, 10.8 ± 3.1,
11.4 ± 2.1, and 13.6 ± 4.6 days of age for
Greyhounds, Greyhound backcross dogs, F1 dogs,
Labrador Retriever backcross dogs, and Labrador
Retrievers, respectively. The additive effect was also
significant for the distraction index. Estimates for this
trait were 0.21 ± 0.07, 0.29 ± 0.15, 0.44 ± 0.12, 0.52
± 0.18, and 0.6 ± 0.17 for the same groups, respectively.
For the dorsolateral subluxation score, additive
and dominance effects were significant. Estimates
for this trait were 73.5 ± 4.1, 71.3 ± 6.5, 69.1 ± 6.0,
50.6 ± 12.9, and 48.4 ± 7.7%, respectively, for the
Conclusions—In this canine pedigree, traits associated
with canine hip dysplasia are heritable. Phenotypic
differences exist among founder dogs of each breed
and their crosses. This pedigree should be useful for
identification of quantitative trait loci underlying the
dysplastic phenotype. (Am J Vet Res 2002;63: