Estimates of prevalence of hip dysplasia in Golden Retrievers and Rottweilers and the influence of bias on published prevalence figures

Update of a retrospective cohort study of changes in hip joint phenotype of dogs evaluated by the OFA in the United States, 1989-2003

OBJECTIVE

To determine whether there has been improvement in canine hip joint phenotype classifications of dogs whelped from 1989 to 2003 by the Orthopedic Foundation for Animals (OFA), by examining results of radiographic evaluations and identifying any trends in percentages of dogs classified as having desirable hip joint phenotypes.

STUDY DESIGN

Retrospective cohort study.

SAMPLE POPULATION

OFA radiographic classifications (n=431,483) on dogs whelped between 1989 and 2003.

METHODS

Numbers and percentages of dogs classified by hip joint phenotypes were determined for 2-year cohorts. Differences between breeds and sexes were assessed using the Fisher's exact test, and odds ratios with 95% confidence intervals were calculated to express associations. The Cochran-Armitage test for trend was calculated to identify significant trends over time.

RESULTS

There were statistically significant (P<.05) increases in the proportion of all breeds of dogs evaluated as excellent and good from 1993 to 2003, controlling for gender and age at evaluation. Labrador Retrievers, Bernese Mountain Dogs, and Rottweilers had the highest proportions of excellent and good scores, and the highest rates of improvement in excellent and good scores were seen in Bernese Mountain Dogs and Rottweilers.

CONCLUSIONS

Results support the contention that there have been improvements in hip joint phenotype classifications in dogs in the United States since the previous study (1989-1992), through increases in the proportion of dogs receiving excellent and good classifications.

CLINICAL RELEVANCE

Hip joint phenotype classifications can be used by dog breeders to develop breeding programs to improve the hip joints of future generations of dogs.

Puppy line, metaphyseal sclerosis, and caudolateral curvilinear and circumferential femoral head osteophytes in early detection of canine hip dysplasia

Ventrodorsal extended hip radiographs were analyzed from Foxhounds, Irish setters, Greyhounds, and Labrador retrievers radiographed four to seven times between 8 and 110 weeks of age. Occurrence in these 91 dogs of a puppy line, an ill-defined zone of proximal femoral metaphyseal sclerosis, a femoral neck linear sclerosis, or circumferential linear femoral head osteophytosis at 15-17 weeks of age were compared with hip joint laxity, as measured by distraction index, and to later findings of caudal curvilinear femoral neck osteophytes, circumferential femoral head osteophytes, hip incongruity consistent with hip dysplasia and degenerative joint disease by 52 weeks of age. A puppy line and/or femoral metaphyseal sclerosis was common at 15-17 weeks of age for dogs at mimimal risk (Greyhounds) and high risk (Foxhounds) of developing early degenerative joint disease associated with canine hip dysplasia. Though 44% of Greyhound hips had puppy lines and 28% had femoral metaphyseal sclerosis at 15-17 weeks of age, no Greyhound had a caudolateral curvilinear osteophyte or circumferential femoral head osteophyte at 24-27 or 52 weeks of age. No significant relationship was found between occurrence of a puppy line, a circumferential femoral head osteophyte or femoral metaphyseal sclerosis at 15-17 weeks and canine hip dysplasia or degenerative joint disease incidence at 42-52 weeks. Presence of a caudolateral curvilinear osteophyte in at least one hip at 24-27 weeks was significantly related to the diagnosis of canine hip dysplasia by 42-52 weeks. When both a caudolateral curvilinear osteophyte and a circumferential femoral head osteophyte were present in a hip at 24-27 weeks, degenerative joint disease was evident in all such hips by 42-52 weeks of age.

Metacarpophalangeal and Metatarsophalangeal Osteoarthritis in 49 Dogs

Although osteoarthritis (OA) is a common and debilitating condition in the canine patient, few data are available on OA of the metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints. Review of medical records of 49 dogs with a radiographic diagnosis of MCP or MTP OA presented over a 7-year period demonstrated that OA was an “incidental finding” for the majority of animals (n=35), while 14 dogs were identified as clinically lame as a result of MCP or MTP OA. Dogs that were clinically lame as a result of MCP or MTP OA were significantly more likely to have visible swelling over the affected digits. Five times as many dogs were diagnosed with MCP OA than with MTP OA, and the majority of dogs had radiographic changes on multiple digits. Review and scoring of radiographs (n=44 dogs) for six radiographic signs of OA followed by logistic regression analysis demonstrated that the two lateral digits of the front limb were significantly more likely to have osteophytosis and enthesophytosis than the two medial digits. Osteoarthritis of MCP and MTP joints has unique radiographic features that are not seen in the stifle, hip, shoulder, or elbow; these features can complicate accurate diagnosis, particularly differentiation from primary bone neoplasia. These data underscore the clinical relevance of this condition and provide useful information detailing which and how many digits are most commonly affected, potentially assisting discrimination between OA and neoplasia.

Prevalence of hip dysplasia, elbow dysplasia and humeral head osteochondrosis in dog breeds in Belgium

The official screening results of the Belgian National Committee for Inherited Skeletal Disorders, an affiliate of the Belgian Kennel Club, have been used to estimate the prevalence of hip dysplasia, elbow dysplasia and humeral head osteochondrosis in the dog breeds in Belgium, and these have been compared with reported prevalence data from other countries. In some breeds, the prevalence of hip and elbow dysplasia is very high, both in Belgium and in other countries. Comparisons of the prevalence of hip dysplasia are not always feasible because different systems are used to evaluate the quality of the hips and because there is no strict consensus on what should be considered a diseased hip joint.

Hip dysplasia in Estrela mountain dogs: prevalence and genetic trends 1991-2005

Three hundred and thirteen Estrela mountain dogs were examined for hip dysplasia (HD) using the standard ventrodorsal hip extended view, and graded into five categories (A, B, C, D and E) using the Fédération Cynologique Internationale's (FCI) scoring system. The Ortolani method was performed to evaluate hip joint laxity. Pedigree information was obtained from the Portuguese Kennel Club and the genetic trend was evaluated by calculating the mean breeding values (BVs) for the last 15 years, using the threshold model. HD was found in 66% of the dogs. There was low-moderate correlation between the results of the Ortolani test and FCI hip scores (r(s)=0.386; P<0.001). Grades of hip dysplasia were equal in both males and females (P=0.14) and in the animals' right and left sides (P=0.51). The mean BVs for HD were stable in dogs born between 1991 and 2003, and showed an improvement in 2004 and 2005. The data confirm the high prevalence and severity of HD in predisposed breeds that do not have breeding programmes in place. It also confirms an initial favourable change in BVs that is a likely consequence of the voluntary radiographic hip-screening programme.

Prevalence of and risk factors for hip dysplasia and cranial cruciate ligament deficiency in dogs

OBJECTIVE-To evaluate prevalence of and risk factors for hip dysplasia (HD) and cranial cruciate ligament deficiency (CCLD) in dogs and determine change in prevalence over time. DESIGN-Cross-sectional study. ANIMALS-1,243,681 Dogs for which information was reported to the Veterinary Medical Database between 1964 and 2003. PROCEDURES-Information on breed, sex, and age was collected, and prevalences and odds ratios were calculated. RESULTS-Castrated male dogs were significantly more likely than other dogs to have HD (odds ratio [OR], 1.21), and castrated male (OR, 1.68) and spayed female (OR, 2.35) dogs were significantly more likely to have CCLD. Dogs up to 4 years old were significantly more likely to have HD (OR for dogs 2 months to 1 year old, 1.22; OR for dogs > 1 to 4 years old, 1.48), whereas dogs > 4 years old were significantly more likely to have CCLD (OR for dogs > 4 to 7 years old, 1.82; OR for dogs > 7 years old, 1.48). In general, large- and giant-breed dogs were more likely than other dogs to have HD, CCLD, or both. Prevalences of HD and CCLD increased significantly over the 4 decades for which data were examined. CONCLUSIONS AND CLINICAL RELEVANCE-Results suggested that sex, age, and breed were risk factors for HD, CCLD, or both in dogs and that prevalences of HD and CCLD have increased over time.

Comparison of two canine registry databases on the prevalence of hip dysplasia by breed and the relationship of dysplasia with body weight and height

OBJECTIVE

To compare the results of 2 canine registries for classification of the hip joints for dysplasia by breed, and to relate the percentage of dysplastic dogs with body metric characteristics.

SAMPLE POPULATION

Data on the ranking order of hip dysplasia by breed from 2 registries for 156 dog breeds.

PROCEDURES

The prevalence of hip dysplasia listed by the Orthopedic Foundation for Animals (OFA) and the breed mean score according to the list of the British Veterinary Association (BVA) Kennel Club Hip Dysplasia scheme were related to weight and height as well as the body mass index (BMI; kg/m(2)) by breed.

RESULTS

The OFA ranking order and the percentage of dysplastic dogs were highly correlated with the BVA mean score (rho = 0.74). A significant correlation was found between the prevalence of hip dysplasia and the BMI (r = 0.63). Receiver operating characteristic curve analysis revealed that the highest area under the curve, corresponding to the best discrimination, was at a BMI of 110 kg/m(2) with a criterion value of 15% dysplastic dogs (area under the curve, 0.89). Because the ratio of dogs in the positive and negative groups reflected the prevalence of the condition among breeds in the OFA database, the positive likelihood ratio was 9.32 and the negative likelihood ratio was 0.24.

CONCLUSION AND CLINICAL RELEVANCE

The OFA statistics and the BVA mean scores reflected the prevalence of hip dysplasia among dog breeds. Body mass index accurately discriminated between breeds with high or low prevalence of hip dysplasia.

Interobserver agreement in the diagnosis of canine hip dysplasia using the standard ventrodorsal hip-extended radiographic method

OBJECTIVES

To determine the agreement between observers and to investigate the effect of observer experience in diagnosing canine hip dysplasia and providing final scoring of hips using the standard ventrodorsal hip-extended radiographic method. The agreement of the final scoring, with a presumed correct assessment based on the Norberg angle, is also investigated.

METHODS

Thirty observers were requested to read 50 ventrodorsal hip-extended radiographs of 25 dogs according to Federation Cynologique International criteria. Groups of experienced (nine members) and inexperienced (21 members) observers were used.

RESULTS

For providing the distinction between dysplastic versus non-dysplastic dogs, the average interobserver agreement was 72 per cent and was significantly higher (P<0.0001) than the score that could be expected by chance without any agreement between observers. For providing the final score (A, B, C, D or E), an average interobserver agreement of 43.6 per cent was found. In the experienced group, an agreement score of 76 per cent was found for the distinction between AB versus non-AB and an agreement score of 81 per cent was found for the distinction between C versus non-C. The agreement score was significantly higher (P<0.0001) for the experienced group than for the inexperienced group in all cases. Agreement between the presumed correct assessment based on the Norberg angle and the observer's evaluation was low (P=0.35), irrespective of whether the observers were experienced (71.8 per cent correct assessments) or inexperienced (69 per cent correct assessments).

CLINICAL SIGNIFICANCE

Although interobserver agreement is low, observer experience increases agreement.

Expression stability of commonly used reference genes in canine articular connective tissues

Background

The quantification of gene expression in tissue samples requires the use of reference genes to normalise transcript numbers between different samples. Reference gene stability may vary between different tissues, and between the same tissue in different disease states. We evaluated the stability of 9 reference genes commonly used in human gene expression studies. Real-time reverse transcription PCR and a mathematical algorithm were used to establish which reference genes were most stably expressed in normal and diseased canine articular tissues and two canine cell lines stimulated with lipolysaccaride (LPS).

Results

The optimal reference genes for comparing gene expression data between normal and diseased infrapatella fat pad were RPL13A and YWHAZ (M = 0.56). The ideal reference genes for comparing normal and osteoarthritic (OA) cartilage were RPL13A and SDHA (M = 0.57). The best reference genes for comparing normal and ruptured canine cranial cruciate ligament were B2M and TBP (M = 0.59). The best reference genes for normalising gene expression data from normal and LPS stimulated cell lines were SDHA and YWHAZ (K6) or SDHA and HMBS (DH82), which had expression stability (M) values of 0.05 (K6) and 0.07 (DH82) respectively. The number of reference genes required to reduce pairwise variation (V) to <0.20 was 4 for cell lines, 5 for cartilage, 7 for cranial cruciate ligament and 8 for fat tissue. Reference gene stability was not related to the level of gene expression.

Conclusion

The reference genes demonstrating the most stable expression within each different canine articular tissue were identified, but no single reference gene was identified as having stable expression in all different tissue types. This study underlines the necessity to select reference genes on the basis of tissue and disease specific expression profile evaluation and highlights the requirement for the identification of new reference genes with greater expression stability for use in canine articular tissue gene expression studies.

Effects of pelvic positioning and simulated dorsal acetabular rim remodeling on the radiographic shape of the dorsal acetabular edge

A radiographic study was conducted to evaluate the effect of pelvic rotation and of simulated dorsal acetabular rim (DAR) remodeling on the radiographic appearance of the dorsal acetabular edge (DAE). The DAE is the line connecting the cranial and caudal rims of the acetabulum when viewing a pelvic radiograph made with the dog in the ventrodorsal position with the hind limbs extended. In this study, it was hypothesized that the DAE would change with pelvic rotation and simulated DAR damage. Ventrodorsal radiographs of eight canine pelves were made at 0 degrees, 5 degrees, and 10 degrees of left and right pelvic rotation over its longitudinal axis. These radiographs were repeated following removal of 2, 4, and then 6 mm of bone from the right DAR of each pelvis. The ratio of acetabular width to maximum depth of the DAE was calculated. The area between the DAE and a straight line connecting the cranial and caudal acetabular rims was measured digitally. The DAE depth and area changed with pelvic rotation, and with increasing simulated DAR damage. A linear relationship between the obturator foramina width ratio and pelvic rotation allowed estimation of the degree and direction of pelvic rotation. Equations were developed from the data to assist with the estimation of the amount of DAR remodeling on a clinical radiograph.

Lifelong diet restriction and radiographic evidence of osteoarthritis of the hip joint in dogs

OBJECTIVE

To evaluate the effects of diet restriction on development of radiographic evidence of hip joint osteoarthritis in dogs.

DESIGN

Longitudinal cohort study.

ANIMALS

48 Labrador Retrievers from 7 litters.

PROCEDURES

Forty-eight 6-week-old puppies from 7 litters were paired with littermates by sex and weight, and each pairmate was randomly assigned to 1 of 2 groups of 24 dogs each. Starting at 8 weeks of age, 1 group was fed ad libitum (control fed) and the other was fed 25% less (restricted fed) of the same diet for life on a pairwise basis. The dogs' hip joints were radiographed in the standard ventrodorsal hip-extended view at multiple intervals prior to 1 year of age and at annual intervals thereafter on the basis of birth anniversary. A board-certified radiologist unaware of group assignment scored the radiographs for evidence of osteoarthritis.

RESULTS

Prevalence of radiographic evidence of hip joint osteoarthritis in all dogs increased linearly throughout the study, from an overall prevalence of 15% at 2 years to 67% by 14 years. Restricted-fed dogs had lower prevalence and later onset of hip joint osteoarthritis. Median age at first identification of radiographic evidence of hip joint osteoarthritis was significantly lower in the control-fed group (6 years), compared with the restricted-fed group (12 years).

CONCLUSIONS AND CLINICAL RELEVANCE

Restricted feeding delayed or prevented development of radiographic signs of hip joint osteoarthritis in this cohort of Labrador Retrievers. Lifetime maintenance of 25% diet restriction delayed onset and reduced severity of hip joint osteoarthritis, thus favorably affecting both duration and quality of life. In addition, the data indicated that development of hip joint osteoarthritis was not bimodal in these dogs but occurred as a continuum throughout life.