Correlation between hip joint laxity and subsequent coxarthrosis in dogs

EFFECTS OF PELVIC AND FEMORAL POSITIONING ON CANINE NORBERG ANGLE MEASUREMENTS AND TEST–RETEST RELIABILITY: A COMPUTED TOMOGRAPHY-BASED SIMULATION STUDY

Canine hip dysplasia is a common disease in dogs, often diagnosed by using the Norberg angle (NA), an index for the laxity of the hip joint. Measurement of the NA can be affected by the pelvic and femoral positioning during imaging, the effects and test–retest reliability of which have not been documented. To bridge the gap in knowledge, computed tomography data from 11 Labrador Retriever dogs were obtained and used to generate synthetic ventrodorsal radiographs of the hip for NA measurements via a perspective projection model. Twenty-five synthetic radiographs of the hips were generated at positions defined by combinations of five pelvic tilt angles (-20° to 20° at 10° intervals) and five femoral elevation angles (from full extension to 40° at 10° intervals). For each radiograph, the NA was measured three times by each of the two experienced veterinarian examiners. It was found that both the increase in caudal pelvic tilt and femoral elevation increased the measured NA, although the intra- and inter-examiner reliability was very good for a given hip position. The current results suggest that careful positioning of the pelvis and femur during radiographic imaging is critical for accurately measuring the NA, and thus the laxity of the hip, for the clinical diagnosis of hip dysplasia.

Evaluation of the relationship between Orthopedic Foundation for Animals' hip joint scores and PennHIP distraction index values in dogs

OBJECTIVE

To compare 2 screening methods for detecting evidence of hip dysplasia (Orthopedic Foundation for Animals [OFA] and PennHIP) in dogs.

DESIGN

Diagnostic test evaluation study. Animals-439 dogs >or= 24 months of age that received routine hip joint screening from June 1987 through July 2008.

PROCEDURES

Dogs were sedated, and PennHIP radiography was performed (hip joint- extended [HE], compression, and distraction radiographic views). The HE radiographic view was submitted for OFA evaluation. A copy of the HE radiographic view plus the compression and distraction radiographic views were submitted for routine PennHIP evaluation, including quantification of hip joint laxity via the distraction index (DI).

RESULTS

14% (60/439) of dogs had hip joints scored as excellent by OFA standards; however, 52% (31/60) of those had a DI >or= 0.30 (range, 0.14 to 0.61). Eighty-two percent of (183/223) dogs with OFA-rated good hip joints had a DI >or= 0.30 (range, 0.10 to 0.77), and 94% (79/84) of dogs with OFA-rated fair hip joints had a DI >or= 0.30 (range, 0.14 to 0.77). Of all dogs with fair to excellent hip joints by OFA standards, 80% (293/367) had a DI >or= 0.30. All dogs with OFA-rated borderline hip joints or mild, moderate, or severe hip dysplasia had a DI >or= 0.30 (range, 0.30 to 0.83).

CONCLUSION AND CLINICAL RELEVANCE

Dogs judged as phenotypically normal by the OFA harbored clinically important passive hip joint laxity as determined via distraction radiography. Results suggested that OFA scoring of HE radiographs underestimated susceptibility to osteoarthritis in dogs, which may impede progress in reducing or eliminating hip dysplasia through breeding.

Complex Segregation Analysis of Canine Hip Dysplasia in German Shepherd Dogs

Complex segregation analyses were carried out to clarify the mode of inheritance of canine hip dysplasia (CHD) in German shepherd dogs. Data were used from 8,567 animals examined for CHD from 20 families with three to four generations. The existence of a major gene in addition to polygenic gene effects was detected. In the present study, a mixed model with a dominant major gene effect seemed to be most probable for dichotomous encoding (0: dogs without signs of CHD; 1: dogs with borderline/slight to severe CHD). In addition, mixed major gene inheritance was shown for a binary trait where borderline was assigned to dogs scored free from CHD and for a trichotomously encoded trait (0: dogs without signs of CHD; 1: borderline CHD; 2: mild to severe CHD). Although only small frequencies were found for the unfavorable homozygotic genotype AA, the probability of the AB genotype was high in affected animals. Selection schemes to reduce the frequency of the allele A should therefore efficiently improve existing breeding programmes in German shepherd dogs.

Effect of dorsal hip loading, sedation, and general anesthesia on the dorsolateral subluxation score in dogs

OBJECTIVE

To determine whether dorsal loading of the pelvis and type of chemical restraint affected the dorsolateral subluxation (DLS) score of dog hips. STYDY DESIGN: In vivo testing of diagnostic method.

ANIMALS

Labrador retrievers, Greyhounds, and crosses between both breeds (n = 119 dogs).

METHODS

Dorsal load was applied to the hips through a strap that was placed over the hips, and the peak vertical and steady-state vertical, ground-reaction forces exerted on the stifles were measured in the DLS position. The DLS score was measured with their hips under dorsal load and compared with the DLS score without load. For 24 dogs, the DLS score was measured both under chemical restraint (medetomidine) and under general anesthesia. Wilcoxon-signed rank test and paired t test was used to compare effects of dorsal load and restraint method on the left and right DLS hip score, and P <.05 was considered significant.

RESULTS

Both stifles together accepted median 15% body weight in the vertical plane in the unloaded steady state. Loading the hips increased the steady-state, vertical ground-reaction force to 34% body weight. At 8 months of age, loading significantly decreased the DLS score from 65% +/- 11% (mean +/- SD) to 60% +/- 12% for left hips and 66% +/- 11% to 63% +/- 13% for right hips. The left hip DLS score was affected by load more consistently than the right hip. In general, loading the hips decreased the DLS score in all breeds by 4% to 6% except for the greyhounds, in which the DLS score was unchanged by dorsal loading. When grouped by their DLS scores, load significantly decreased DLS scores in dogs with unloaded scores greater than 55% (nondysplastic), whereas DLS scores of dogs with unloaded scores between 55% and 45% (dysplastic) and less than 45% did not change significantly with load. Unloaded scores did not change significantly when compared under sedation versus general anesthesia. However, load significantly decreased the DLS score under general anesthesia for the left hip but not for the right hip.

CONCLUSIONS

Less than half of the vertical ground-reaction force normally exerted by the hindlegs of a standing dog was sufficient to induce hip subluxation in the DLS position. Although dorsal loading approximately doubled the steady-state, vertical ground-reaction force, the decrease in the DLS score under load was never greater than 6%. Furthermore, the DLS scores of dogs most likely to be dysplastic (based on DLS scores <45%) were not affected by load, whereas load slightly decreased DLS cores of dogs with DLS scores greater than 55%.

CLINICAL RELEVANCE

External influences can change the DLS score significantly, but the magnitude of change is unlikely to be of clinical importance, making the method useful as a field screening test for both dysplastic and nondysplastic hips in young dogs.

Hip dysplasia in labrador retrievers: the effects of age at scoring

Selective breeding policies for preventing or controlling hip dysplasia require accurate estimates of parameters in offspring/parental relationships and estimates of heritability. Recent literature includes some major studies of pedigree breeds of dog, using data derived from the hip dysplasia screening scheme set up by the British Veterinary Association. These publications have not taken into account the age of the animals when they were screened. This study analyses the data from 29,213 labrador retrievers whose ages were known when they screened. The mean hip score of the dogs was positively and significantly correlated with their age. If this relationship with age is ignored, various offspring/parental relationships and the estimates of heritability are likely to be distorted.

Heritability and epidemiology of canine hip-dysplasia score and its components in Labrador retrievers in the United Kingdom

Hip-dysplasia (malformation of the coxofemoral joint) in dogs is a major health problem. Under the British Veterinary Association/Kennel Club's voluntary hip-dysplasia scheme, dog-owners/breeders submit radiographs from animals >1-year-old, to ensure adequate skeletal maturity. An overall hip score quantifies the degree of malformation in the hip joints of these animals, by summing the scores for nine components of the radiographs of both the left and right joints. The hip score data for 29,610 Labrador retrievers (registered with The Kennel Club, UK) were merged with the Kennel Club pedigree database for 472,435 Labrador retrievers. The merged data included the animal's identity, date of birth, sex and hip score and similar records for the dog's relatives, including the hip score if the relative had been tested. In recent years, breeding had been increasingly from tested parents. The mean hip score for male Labradors was significantly higher than that for females. Regression modelling showed a significant, positive dependence of the hip score of the offspring upon the hip scores of its sire, dam and grandparents. Genetic heritability (using data from 13,382 Labrador retrievers comprising 718 litters) was highly significant: 0.34 from the two parents, 0.41 from sire alone and 0.30 from dam alone. Using components data from 2038 offspring Labrador retrievers comprising 1248 litters, three similar estimates of heritability were significant for three major components (Norberg angle, cranial acetabular edge and subluxation); for other components, heritability was significant from the sire but not from the dam. Offspring hip score could be reduced substantially by using only parents with zero hip score.

Comparison of three radiographic methods for diagnosis of hip dysplasia in eight-month-old dogs

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.

DESIGN

Cohort study

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.

Comparison of two palpation, four radiographic and three ultrasound methods for early detection of mild to moderate canine hip dysplasia

Hip joint laxity was evaluated in Golden Retriever (n = 60), Labrador Retriever (n = 23), and Labrador/Golden Retriever mix (n = 24) puppies. Ortolani and Bardens maneuvers, four radiographic measurement indices and three dynamic ultrasonographic measurements were used. Each puppy was evaluated twice; at 6.5 to 9 and 43 to 79 weeks of age. These nine methods were compared for accuracy in predicting the development of canine hip dysplasia with or without degenerative joint disease by a median age of 16 months. The Bardens maneuver was a significant predictor of canine hip dysplasia/+/-degenerative joint disease for Golden Retriever puppies, however, it was not a reliable predictor for the other two breeds. Norberg angle measurements taken with femurs in a neutral position with hips distracted (PennHip position) was a significant predictor of degenerative joint disease in two breeds, but not in Golden Retriever puppies. Ultrasound measurement was a reliable predictor of hip canine hip dysplasia/+/-degenerative joint disease for Labrador/Golden Retriever mix puppies, but was not reliable for the other two breeds. Palpation, radiographic, and ultrasonographic methods of evaluating hip joint laxity in puppies at 6.5 to 9 weeks of age were not consistently reliable for all three breeds in predicting hip dysplasia with or without degenerative joint disease at one year of age. A strong association was found between Norberg angle and degenerative joint disease occurrence, as well as between distraction index (PennHip) and degenerative joint disease occurrence when measured at 52 to 79 weeks of age, but not when measured at 6.5 to 9 weeks of age in these breeds. These results emphasize the difficulty of early detection of mild hip dysplasia in the dog.

Heritability of canine hip-dysplasia score and its components in Gordon setters

Hip dysplasia (malformation of the hip joint) is an important health problem in dogs. The condition and the control scheme for Gordon Setters was organised by the British Veterinary Association (BVA) and the Kennel Club before 1976 and use hip scores. Our analyses of hip dysplasia in Gordon Setters used both hip scores and the scores for the nine components (which collectively defined the hip score). The scores for all nine components were available for 732 females and 420 males. These clinical data were merged with the Kennel Club pedigree database (animal's identity, date of birth, and also similar data for its parents, including hip scores if the parent had been tested). Regression models showed strong positive relationships between offspring and parental hip scores as well as for some component scores. The heritability of hip dysplasia (assessed using both hip scores and the major components) was significant, particularly from dams. Our research emphasizes the need for both sires and dams--particularly dams, to have zero or small hip scores. Tested parents have been used increasingly in recent years, but greater reduction in offspring hip score will require stricter selection of potential breeding stock. The models reported here provide quantitative predictions of likely health benefits from selective breeding.

Heritability and epidemiology of canine hip-dysplasia score in flat-coated retrievers and Newfoundlands in the United Kingdom

Hip dysplasia (malformation of the coxofemoral joint) in dogs is a major health problem for which the British Veterinary Association (BVA) had set up a control scheme in 1965. Based on scoring nine components of the radiographs of both the left and right joints, the degree of hip joint malformation is now quantified by an overall hip score (a measure of the condition of the hip joint). The hip scores of 1258 flat-coated retrievers and 1566 Newfoundlands (registered with The Kennel Club in the United Kingdom) were analysed after merging with Kennel Club pedigree data for 19036 flat-coated retrievers registered by 1995 and 14336 Newfoundlands registered by 1997. The merged data included the animal's identity, date of birth, sex and hip scores and also similar records for the dog's relatives including the hip score if the relative had been tested. In recent years, breeding has been increasingly from tested parents. There has been some reduction in offspring hip scores - presumably because breeders avoided breeding from males with very high scores. However, a much greater reduction in offspring hip score would be achieved by stricter science-based selection of potential sires and dams. Regression modelling quantified the positive relationship between offspring and parental hip scores. The genetic heritability of hip scores was large and significant in both breeds (particularly from dams). The breeders in UK tended to use healthy sires for breeding but they have taken less care in selecting dams. Our regression models emphasise the need for both sires and dams, particularly dams, to be healthy with very small hip scores.

Recent information about hip dysplasia

Dogs suffering from HD have a genetic background, but the releasing factors are many. Two of the most important are overnutrition and overexercising, especially in the young puppy. Radiography can give an estimate of the degree of secondary OA, and by evaluating the laxity in the hip joints at an early age, it seems to be possible to predict the chances for later development of OA. The eradication program has to be instituted in such a way that only the best dogs are accepted into breeding programs. It seems to be more efficient to eradicate the genetic part of the etiology by creating a breeding index by means of evaluating the offspring of the male dogs.