Dorsolateral Subluxation Score Research Articles

The Impact of Double Pelvic Osteotomy on Dorsolateral Subluxation in 24 Dogs.

The aim of this study was to determine the effect of double pelvic osteotomy (DPO) on dorsolateral subluxation (DLS) of the femoral head in a weight-bearing position. Retrospective observational study with treatment effect analysis. Twenty-four client-owned dogs that underwent DPO due to hip dysplasia. Computed tomography (CT) studies were performed on 24 dogs that underwent a DPO between 2015 and 2021. The patients were positioned with the femora in a weight-bearing position. The DLS score was measured pre-DPO, immediately post-DPO, and at follow-up to determine if DPO resulted in an increase in the DLS score. A total of 21 dogs underwent single-stage bilateral DPO and 3 dogs underwent unilateral DPO resulting in 45 hip joints available for analysis. Follow-up CT was available for 29 of these at a median of 51 days (range: 35-482 days). The mean DLS score was 36.1% ± 14.6 preoperatively, 71.4% ± 12.5 post-DPO, and 70.0% ± 15.3 at follow-up. The increase between the pre- and postoperative measurement was significant (p < 0.001). DPO results in reduced subluxation of the femoral head in a weight-bearing position. The in vivo results suggest that DPO will result in reduced femoral subluxation during weight-bearing.

Evaluation of hip joint laxity in crab-eating foxes (Cerdocyon thous)

ABSTRACT: Like canids, crab-eating foxes may probably be predisposed to similar orthopedic diseases of domestic dogs, such as hip dysplasia. However, for the adequate hip dysplasia diagnosis in wild animals, the normality characteristics of each species must be determined. This study aimed to estimate radiographic and computed tomographic (CT) values of hip joint laxity in healthy crab-eating foxes. Fifteen intact crab-eating foxes, eight males and seven females, ages 1 to 5 and mean body mass of 6.66kg were used. Norberg angle (NA) was calculated from ventrodorsal hip-extended radiographs. To calculate the dorsolateral subluxation (DLS) score, the center distance (CD) index, the lateral center edge angle (LCEA), and the dorsal acetabular rim angle (DARA), measurements obtained from transverse CT images were used. No statistically significant differences were observed between the right and left sides in the radiographic and tomographic parameters. The mean NA was 107.57°. The mean DLS score, the CD index, the LCEA, and the DARA were 60.79%, 0.16, 98.25° and 13.47°, respectively. The data obtained are helpful in characterizing mean values of the hip joint in healthy crab-eating foxes, and can contribute to the knowledge of the species.

The Norberg angle is not an accurate predictor of canine hip conformation based on the distraction index and the dorsolateral subluxation score

Canine hip dysplasia (CHD) is a common complex trait characterized by abnormal hip joint development. Hip joint laxity, an early characteristic of CHD, results in degeneration of the joint due to mechanical trauma, which is a clinical problem mostly in medium to large breed dogs. Clinical signs include pain, decreased activity and lameness. A retrospective, multi-center, cross sectional study of 437 dogs was performed to determine if a Norberg angle (NA) ≥105° accurately predicts a non-dysplastic hip based on a distraction index (DI) cut-off of ≤0.3 or a dorsolateral subluxation (DLS) score cut-off of ≥55%. The predictive capacity of the NA against a DI ≤0.3 or a DLS score ≥55% was assessed using area under the receiver operator characteristic (ROC) curve analysis. The ROC curve of NA for the prediction of a DI ≤0.3 was 0.59 (95% CI=0.50–0.69) and for the prediction of DLS score ≥55% was 0.69 (95% CI=0.63–0.75). Optimizing the specificity of the NA to ≥80% for prediction of a DI ≤0.3 and a DLS score ≥55% gave a cut-point for the NA of ≥112° and 108.7°, respectively. In conclusion, at the cut-point of 105°, the NA is not an accurate measurement to score normal or abnormal hips, based on the DI or DLS score. Application of screening methods for CHD based on hip laxity, such as the DI or the DLS score, would help to remove additional dysplastic dogs from the breeding pool or the NA criterion should be higher when selecting unaffected dogs for breeding.

Principal component analysis of canine hip dysplasia phenotypes and their statistical power for genome-wide association mapping

The aims of this study were to undertake principal component analysis (PCA) of hip dysplasia (HD) and to examine the power of the principal components (PCs) in genome-wide association studies. A cohort of 278 dogs for PCA and that of 369 dogs for genotyping were used. The distraction index (DI), the dorsolateral subluxation (DLS) score, the Norberg angle (NA), and the extended-hip radiographic (EHR) score were used for the PCA. One thousand single-nucleotide polymorphisms (SNPs) (of 23,500) were used to simulate genetic locus sharing between the HD phenotypes and 1000 SNPs were used to calculate the genetic mapping power of the PCs. The DI and the DLS score (first group) reflected hip laxity and the NA and the EHR score (second group) reflected the congruency between the femoral head and acetabulum. The average hip measurements of the two groups reflected in the first PC captured 55% of total radiographic variation. The first four PCs captured 90% of the total variation. The PCs had higher statistical mapping power to detect pleiotropic quantitative trait loci (QTL) than the raw phenotypes. The PCA demonstrated for the first time that HD can be reduced mathematically into simpler components essential for its genetic dissection. Genes that contribute jointly to all four radiographic hip phenotypes can be detected by mapping their first four PCs, while those contributing to individual phenotypes can be mapped by association with the individual raw phenotype.

TheS‐Measurement in the Diagnosis of Canine Hip Dysplasia

To propose a direct measure of subluxation of the femoral head (S) in the assessment of hip joint laxity and evaluate it for clinical use. Method comparison study. Dogs (n = 51). Dogs were sedated or anesthetized for a dorsolateral subluxation (DLS) examination. Two sets of radiographs were acquired, 1 each by a different technologist. A calibrated measuring bar was included on the image at the height of the hip to assess magnification. The DLS was calculated for each hip and different persons unaware of these details measured the "S"-value. One person measured the S-value 3 times over 3 days. Box plots were used to determine a cut-off for the empiric (8 mm) and corrected (4 mm) S-value. Of 51 dogs, 33 were dysplastic based on a DLS score <55%. Magnification and body weight were strongly correlated (r = 0.4922, P = .0006). Both empiric and corrected S measurements showed good agreement with the DLS score (κ = 0.688 and κ = 0.681, respectively). The corrected S measurement produced more false negatives. Bland-Altman analysis showed interobserver and technician variance acceptable for clinical use (limits of agreement < ±3 mm). Intraobserver repeatability was acceptable for the right hip (95% of differences were ≤1.3 mm and 100% ≤ 1.9) but not for the left hip. Using a cut-off value of 5 mm, the empirical S measurement can be used to exclude hip dysplasia in young dogs of various body proportions.

Evaluation of a fibrillin 2 gene haplotype associated with hip dysplasia and incipient osteoarthritis in dogs

To determine whether a mutation in the fibrillin 2 gene (FBN2) is associated with canine hip dysplasia (CHD) and osteoarthritis in dogs. 1,551 dogs. Procedures-Hip conformation was measured radiographically. The FBN2 was sequenced from genomic DNA of 21 Labrador Retrievers and 2 Greyhounds, and a haplotype in intron 30 of FBN2 was sequenced in 90 additional Labrador Retrievers and 143 dogs of 6 other breeds. Steady-state values of FBN2 mRNA and control genes were measured in hip joint tissues of fourteen 8-month-old Labrador Retriever-Greyhound crossbreeds. The Labrador Retrievers homozygous for a 10-bp deletion haplotype in intron 30 of FBN2 had significantly worse CHD as measured via higher distraction index and extended-hip joint radiograph score and a lower Norberg angle and dorsolateral subluxation score. Among 143 dogs of 6 other breeds, those homozygous for the same deletion haplotype also had significantly worse radiographic CHD. Among the 14 crossbred dogs, as the dorsolateral subluxation score decreased, the capsular FBN2 mRNA increased significantly. Those dogs with incipient hip joint osteoarthritis had significantly increased capsular FBN2 mRNA, compared with those dogs without osteoarthritis. Dogs homozygous for the FBN2 deletion haplotype had significantly less FBN2 mRNA in their femoral head articular cartilage. The FBN2 deletion haplotype was associated with CHD. Capsular gene expression of FBN2 was confounded by incipient secondary osteoarthritis in dysplastic hip joints. Genes influencing complex traits in dogs can be identified by genome-wide screening, fine mapping, and candidate gene screening.

Evaluation of quantitative trait loci for hip dysplasia in Labrador Retrievers

To identify the quantitative trait loci (QTL) that contribute to hip dysplasia in dogs. 192 Labrador Retrievers. Hip dysplasia was measured by use of the Norberg angle (NA), dorsolateral subluxation (DLS) score, and distraction index (DI). Genome-wide screening was conducted by use of 276 unique microsatellites. Linkage analysis was performed with a variance-based linear model. Logarithm of the odds (LOD) scores were reported when values were > 2.0. Canis familiaris autosomes (CFAs) 01, 02, 10, 20, 22, and 32 harbored significant QTL at LOD scores > 2.0. Among the 6 QTL, the QTL on CFA02 had not been reported to harbor QTL for hip dysplasia. The highest LOD score of 3.32 on CFA20 contributed to the second principal component of the DLS score and NA of the right hip joint. The QTL that was mapped on CFA01 (LOD score of 3.13 at 55 centimorgans) was located on the same chromosome reported to harbor a QTL for hip dysplasia in Portuguese Water Dogs and German Shepherd Dogs. In this study, CFAs 10, 20, 22, and 32 harbored QTL for hip dysplasia that have been identified in a Labrador Retriever-Greyhound pedigree and in German Shepherd Dogs. Multiple QTL were clearly involved with hip dysplasia. Identification of these QTL will enable fine-resolution mapping and subsequent assessment of candidate genes within the refined intervals to enable researchers to develop genetic screening tests and preventative and novel therapeutic regimens.

COMPARISON OF CLINICAL, RADIOGRAPHIC, COMPUTED TOMOGRAPHIC, AND MAGNETIC RESONANCE IMAGING METHODS FOR EARLY PREDICTION OF CANINE HIP LAXITY AND DYSPLASIA

The purpose of the study was to use two palpation methods (Bardens and Ortolani), a radiographic distraction view, three computed tomography (CT) measurements (dorsolateral subluxation score, the lateral center-edge angle, and acetabular ventroversion angle) and two magnetic resonance (MR) imaging hip studies (synovial fluid and acetabular depth indices) in the early monitoring of hip morphology and laxity in 7-9 week old puppies; and in a follow-up study to compare their accuracy in predicting later hip laxity and dysplasia. The MR imaging study was performed with the dog in dorsal recumbency and the CT study with the animal in a weight-bearing position. There was no association between clinical laxity with later hip laxity or dysplasia. The dorsolateral subluxation score and the lateral center-edge angle were characterized by a weak negative correlation with later radiographic passive hip laxity (-0.26 < r < -0.38, P < 0.05) but its association with hip dysplasia was not significant. There was an association between early radiographic passive hip laxity and synovial fluid index with later passive hip laxity (0.41 < r < 0.55, P < 0.05) and this was significantly different in dysplastic vs. nondysplastic hips (P < 0.05). There was no association between the remaining variables and later hip laxity or dysplasia. The overlapping ranges of early passive hip laxity and synovial fluid index for hip dysplasia grades and the moderate correlations with the later passive hip laxity make the results of these variables unreliable for use in predicting hip laxity and dysplasia susceptibility.

Quantitative Evaluation of Hip Joint Laxity in 22 Border Collies Using Computed Tomography

The purpose of this study was to obtain the computed tomography (CT) data for the hip joints of 22 Border Collies. The dorsolateral subluxation (DLS) score, lateral center edge angle (LCEA), dorsal acetabular rim angle (DARA) and center distance (CD) index were measured on the CT images in a weight-bearing position. Radiographic Norberg angle (NA) was also measured. The mean values were 45.7 +/- 10.2% for DLS score, 85.9 degrees +/- 10.3 degrees for LCEA, 18.5 degrees +/- 7.3 degrees for DARA, 0.40 +/- 0.17 for CD index and 102.7 degrees +/- 6.9 degrees for NA. Since the DLS score and LCEA showed strong correlation, combined use of these parameters might improve diagnostic accuracy. We consider CT evaluation in a weight-bearing position to be a useful method for multidirectional evaluation of hips.

Computed tomographic evaluation of growth-related changes in the hip joints of young dogs

To evaluate changes in canine hip joint characteristics during growth via computed tomography (CT) and compare CT features of hip joints with and without laxity in young dogs placed in 2 imaging positions. 21 dogs (42 hip joints). From 2 to 12 months after birth, CT examinations of the acetabulum of each hip joint in simulated normal standing and simulated weight-bearing positions were performed monthly for all dogs. Acetabular angle, dorsal acetabular rim angle (DARA), and femoral head diameter (FHd) were analyzed as skeletal variables; the lateral center edge angle (LCEA), dorsolateral subluxation (DLS) score, and center distance (CD) index were analyzed as joint laxity variables. At 12 months, all dogs underwent the Ortolani test to as-sess hip joint laxity. Hip joint laxity was detected in 5 dogs (10 joints) at 12 months of age; from 2 months, the acetabular angle and FHd increased and DARA decreased significantly until 5 months and the LCEA and DLS score increased significantly until 6 months. In nonlax hip joints in both positions, the CD index decreased significantly until 4 months of age and be-came stable thereafter. In lax hip joints, the CD index increased from 4 through 12 months; between 8 and 12 months, these changes were significantly greater in the weight-bearing position than in the standing position. Results suggest that CT-detected abnormalities in the DARA and CD index during body weight loading might be useful indicators of hip dysplasia in 2- to 6-month-old dogs.

Quantitative trait loci for hip dysplasia in a crossbreed canine pedigree

Canine hip dysplasia is a common developmental inherited trait characterized by hip laxity, subluxation or incongruity of the femoral head and acetabulum in affected hips. The inheritance pattern is complex and the mutations contributing to trait expression are unknown. In the study reported here, 240 microsatellite markers distributed in 38 autosomes and the X chromosome were genotyped on 152 dogs from three generations of a crossbred pedigree based on trait-free Greyhound and dysplastic Labrador Retriever founders. Interval mapping was undertaken to map the QTL underlying the quantitative dysplastic traits of maximum passive hip laxity (the distraction index), the dorsolateral subluxation score, and the Norberg angle. Permutation testing was used to derive the chromosome-wide level of significance at p<0.05 for each QTL. Chromosomes 4, 9, 10, 11 (p<0.01), 16, 20, 22, 25, 29 (p<0.01), 30, 35, and 37 harbor putative QTL for one or more traits. Successful detection of QTL was due to the cross-breed pedigree, multiple-trait measurements, control of environmental background, and marked advancement in canine mapping tools.

Laxity of canine hip joint in two positions with computed tomography.

Computed tomographic (CT) examination of 20 canine hip joints was carried out in two positions, normal-standing and weight-bearing. In normal (dorsal acetabular rim angle: DARA < 15 degrees ) or slightly abnormal (DARA, 15 degrees to 20 degrees ) hip joints, the values of parameters to laxity were evaluated as more severe in the weight-bearing position. Comparisons of results using various indicators, including the center distance (CD) index, dorsolateral subluxation score, and lateral center edge angle, revealed that the CD index may be a useful marker of functional laxity in the canine hip joint under CT scanning. Further, CT scanning in the weight-bearing position was more sensitive than in the normal-standing position for the detection of laxity in hips with normal or only slightly abnormal DARA.

Power of a Labrador Retriever-Greyhound pedigree for linkage analysis of hip dysplasia and osteoarthritis.

To estimate the number of dogs required to find linkage to heritable traits of hip dysplasia in dogs from an experimental pedigree. 147 Labrador Retrievers, Greyhounds, and their crossbreed offspring. 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. 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.

Genetic structure of susceptibility traits for hip dysplasia and microsatellite informativeness of an outcrossed canine pedigree.

An outcrossed canine pedigree was developed for quantitative trait locus (QTL) mapping of hip dysplasia by breeding dysplastic Labrador retrievers to trait-free greyhounds. Measured susceptibility traits included age at onset of femoral capital chondroepiphyseal ossification (OSS), maximum hip distraction (laxity) index (DI), and the dorsolateral subluxation (DLS) score. The pedigrees consisted of 147 dogs representing four generations. For 59 dogs genotyped with 65 microsatellites, the median heterozygosity and polymorphic information content (PIC) values of the F(1) generation were 0.82 and 0.68, respectively. Seventy-seven percent of microsatellites had a PIC greater than 0.59 in the F(1)s. Ninety-six percent of alleles showed Mendelian inheritance. Based on marker informativeness, approximately 350 randomly selected markers would be required for genome-wide screening to obtain an average interval between informative markers of 10 cM. Heritability was estimated as 0.43, 0.5, and 0.61 for OSS, DI, and the DLS score, respectively. Biometric estimates of the mean (+/- variance) effective number of segregating QTLs was 1.2 (+/- 0.05), 0.8 (+/- 0.02), and 1.0 (+/- 0.03) for OSS, DI, and the DLS score, respectively. The distributions of simulated backcross trait data suggested that the loci controlling these traits acted additively and that the DI may be controlled by a major locus. When combined with previous power and quantitative genetic analyses, these estimates indicate that this pedigree is informative for QTL mapping of hip dysplasia traits.

Quantitative genetics of traits associated with hip dysplasia in a canine pedigree constructed by mating dysplastic Labrador Retrievers with unaffected Greyhounds.

To determine the genetic influence on expression of traits associated with canine hip dysplasia. 193 dogs from an experimental canine pedigree. 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. 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 same groups. 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.

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

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. Cohort study 129 Labrador Retrievers, Greyhounds, and Labrador Retriever-Greyhound crossbreds. 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. 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%. 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.

Repeatability of dorsolateral subluxation scores in dogs and correlation with macroscopic appearance of hip osteoarthritis

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. 129 Labrador Retrievers, Greyhounds, and Labrador Retriever-Greyhound crossbreds. 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. DLS scores at 4 (n = 35, r(s) = -0.62), 8 (n = 106, r(s) = -0.54), and 12 (n = 15, r(s) = -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, r(s) = 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 (> or = 45 but < or = 55%), and high (> 55%) DLS scores at 8 months of age were 8.0, 2.6, and 0.2, respectively. 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.

Comparison of measurements of dorsolateral subluxation of the femoral head and maximal passive laxity for evaluation of the coxofemoral joint in dogs

Abstract Objective To determine whether dorsolateral subluxation (DLS) of the femoral head reflects osseous conformation of the coxofemoral (hip) joint and represents a property distinct from maximum passive laxity of the hip joint in dogs. Animals 14 Labrador Retrievers, 16 Greyhounds, 58 Greyhound-Labrador Retriever mixed-breed dogs, and 1 Rottweiler. Procedures DLS of the femoral head (DLS score) and passive laxity of the hip joint (distraction index) were determined radiographically in 3 groups of dogs: not treated (167 joints of 84 dogs); before and after injecting 2 ml of hyaluronan into 25 hip joints of 13 dogs; and before and after unilateral triple pelvic osteotomy in 5 dogs. Results of the 2 methods were compared for each group. Results In untreated dogs, the correlation coefficient (r) of DLS score versus distraction index was −0.73 and −0.69 for 84 left and 83 right hip joints, respectively. Mean coefficient of determination (r2) for both hips was 0.5. Mean DLS score did not differ before and after intra-articular injection of hyaluronan into either hip joint, whereas mean distraction index increased significantly after intra-articular injection. Unilateral triple pelvic osteotomy resulted in a significant increase in DLS score, compared with values obtained before surgery. However, distraction index before and after surgery did not differ significantly. Conclusions and Clinical Relevance The DLS test assesses the congruity of the acetabulum and the femoral head in a canine hip joint and thus represents a characteristic distinct from maximum passive laxity. The DLS score and the distraction index evaluate different components of hip joint stability. (Am J Vet Res 1999;60:1571–1576)

An outcrossed canine pedigree for linkage analysis of hip dysplasia.

Canine hip dysplasia (CHD) is a prevalent, debilitating, polygenic disease characterized by hip subluxation and laxity which results in osteoarthritis. We are developing an informative pedigree for linkage analysis of CHD. The seven greyhound founders had excellent hip conformation with high dorsolateral subluxation scores (percentage of femoral head covered by the dorsal acetabulum in a weight-bearing position) of 66 +/- 4% (mean +/- SD averaged over both hips) and low hip distraction (laxity) indices of 0.14 +/- 0.08. Nine greyhounds bred on site had radiographic evidence of ossification in the capital femoral chondroepiphysis at 7.7 +/- 0.9 days of age. At 8 months of age they had a mean distraction index of 0.24 +/- 0.08 and dorsolateral subluxation score of 76 +/- 1%. Of the four dysplastic Labrador retriever founders, three had mean age at onset of capital femoral chondroeplphyseal ossification of 20 +/- 7 days of age n = 3) and a mean distraction index of 0.46 +/- 0.1 accompanied by hip osteoarthritis. Thirty-four F1s had mean onset of capital femoral ossification (10.7 +/- 4.0 days of age) and mean dorsolateral subluxation scores (61 +/- 12%) similar to the greyhound founders, but distraction indices (0.42 +/- 0.2) more similar to the Labrador retriever founders. One F1 had CHD radiographically but none of 20 F1s had osteoarthritis at necropsy at 10 months of age. These data suggested that maximum passive laxity (as measured by the distraction index) and normal osseous conformation (as indicated by a high dorsolateral subluxation score) were both dominant traits and were controlled by separate quantitative trait loci (QTL). Forty-three back-crosses between F1s with the highest hip laxity and greyhound founders had mean onset of capital femoral ossification at 9.9 +/- 2.6 days of age. Of 10 dogs in the backcross generation that have reached 8 months of age, 2 had palpable subluxation without marked CHD radiographically. The mean distraction index of these dogs was 0.36 +/- 0.16 and the dorsolateral subluxation score was 65 +/- 5%. Although dogs in the backcross generation that were three-quarter greyhound had a broad range of hip laxity, a protective effect of the greyhound QTLs for good osseous conformation has mitigated thus far against subluxation and CHD.

Dorsolateral subluxation of hip joints in dogs measured in a weight-bearing position with radiography and computed tomography.

develop a radiographic procedure to measure dorsolateral subluxation (DLS) of the femoral head in canine coxofemoral (hip) joints in a weight-bearing position. DLS measured on a radiographic projection was compared with DLS measured on computed tomography (CT) images of hip joints in a weight-bearing position. A total of 24 dogs of varying ages were examined including Labrador retrievers, greyhounds, and Labrador-greyhound crossbreeds. Anesthetized dogs were placed in sternal recumbency in a kneeling position in a foam rubber mold. The stifles were flexed and adducted with the femora perpendicular to, and in contact with, the table. To test for DLS, dogs were imaged in this weight-bearing position (DLS test) with routine radiography and CT. For each hip, the DLS score was determined by measuring the percentage of the femoral head medial to the lateralmost point of the cranial acetabular rim on the dorsoventral radiographic projection and the lateralmost point of the central, dorsal acetabular rim on the CT image. Higher DLS scores indicated better coverage of the femoral head by the acetabulum. DLS scores were compared with the distraction index (DI) by grouping joints according to their probability of developing osteoarthritis (OA) as predicted by the DI. The DLS score in the new position ranged from 29% to 71% for radiography and 15% to 59% for CT. Joints classified as OA unsusceptible had a mean score of 64% +/- 1.5% for radiography and 55% +/- 0.8% for CT (n = 10); hip joints having a high probability of developing OA had a score of 39% +/- 2.6% for radiography and 26% +/- 1.9% for CT (n = 8). When the DLS test was repeated on the same dogs at a different time, the intraclass correlation coefficient for the DLS score on the radiographs was 0.85 (left hip) and 0.89 (right hip). There was a strong correlation (r = .89 for both hips) between the DLS score measured on the weight-bearing radiograph and the CT image. A strong correlation also was observed between the DLS score and the DI (r = -.87). The DLS scores for OA unsusceptible joints and joints with a high probability of developing OA were significantly different (P < .05). The DLS test can be performed with CT or routine radiography to measure variable amounts of DLS in weight-bearing hip joints oriented similarly to those of a standing dog. After additional long-term follow-up studies evaluating the development of OA and breed effects are performed, the DLS method may prove useful in studies of normal and abnormal hip joint development related to canine hip dysplasia.