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Journal of Veterinary Medicine logoLink to Journal of Veterinary Medicine
. 2017 Mar 12;2017:5723476. doi: 10.1155/2017/5723476

The Demographics of Canine Hip Dysplasia in the United States and Canada

Randall T Loder 1,*, Rory J Todhunter 2
PMCID: PMC5366211  PMID: 28386583

Abstract

Canine hip dysplasia (CHD) is a common problem in veterinary medicine. We report the demographics of CHD using the entire hip dysplasia registry from the Orthopedic Foundation for Animals, analyzing differences by breed, sex, laterality, seasonal variation in birth, and latitude. There were 921,046 unique records. Each dog was classified using the American Kennel Club (AKC) and Fédération Cynologique Internationale (FCI) systems. Statistical analysis was performed with bivariate and logistic regression procedures. The overall CHD prevalence was 15.56%. The OR for CHD was higher in females (1.05), those born in spring (1.14) and winter (1.13), and those in more southern latitudes (OR 2.12). Within AKC groups, working dogs had the highest risk of CHD (OR 1.882) with hounds being the reference group. Within FCI groups, the pinscher/molossoid group had the highest risk of CHD (OR 4.168) with sighthounds being the reference group. The similarities between CHD and DDH are striking. Within DDH there are two different types, the typical infantile DDH and the late onset adolescent/adult acetabular dysplasia, with different demographics; the demographics of CHD are more similar to the later onset DDH group. Comparative studies of both disorders should lead to a better understanding of both CHD and DDH.

1. Introduction

Canine hip dysplasia (CHD) is a well-known disorder in veterinary medicine [14], especially amongst certain breeds. The human counterpart of CHD, developmental dysplasia of the hip (DDH), is also a well-known problem with differences in prevalence by race/ethnicity [5], analogous to breed differences in CHD. Comprehensive literature reviews of DDH have shown various demographic patterns regarding sex, laterality, latitude, and seasonal variation in birth month [5, 6]. Variation in birth month/season has been described in a few small series of CHD [712]. There has been no study of the demographics of CHD using a large data set. The purpose of this study was to investigate the demographics of CHD using a large North American data base and analyze the differences by breed, sex, laterality, seasonal variation in birth, and latitude. Comparison with the demographics of DDH may shed further light on the etiology of both conditions and specifically support the use of CHD as an animal model for DDH, as well as DDH pointing towards further comparative research areas in CHD.

2. Materials and Methods

2.1. Data Source

The data for this study was the complete hip dysplasia registry (both public and private) collected by the Orthopedic Foundation for Animals (OFA) through April 2015. There were a total of 1,430,979 records. The OFA hip score uses the American Veterinary Medical Association grading system: 1 = excellent, 2 = good, 3 = fair, 4 = borderline CHD, 5 = mild CHD, 6 = moderate CHD, and 7 = severe CHD. These scores were divided into two groups: those with CHD (scores 5–7) and those without CHD (scores 1–3); the borderline score of 4 was excluded. Duplicate records, feline cases, and those with an indeterminate score were deleted. The country of origin was known in 1,130,478 dogs; the vast majority (1,121,961–99.25%) were from the USA (1,046,249) or Canada (75,712). Dogs less than 24 or greater than 60 months of age at the time of the radiograph were next deleted, leaving 921,046 unique records which are the data for this study.

2.2. Data Groups

Each dog was classified into related breed groups using both the American Kennel Club (AKC) (http://www.akc.org) [13] and Fédération Cynologique Internationale (FCI) (http://www.fci.be/en/Nomenclature) [14] systems. Each dog was separately given an AKC and FCI group designation and analyzed separately; the two different systems were not merged. Dogs in each of these groups are relatively similar genetically [15, 16] and thus could be expected to respond to environmental triggers similarly, compared to dogs that do not share a common genetic background. The AKC categories are herding, hound, working, sporting, nonsporting, terrier, toy, native, hybrid, and miscellaneous groups. The FCI categories are (1) sheep and cattle dogs; (2) pinscher, schnauzer, molossoid, and Swiss mountain and Swiss cattle dogs; (3) terriers; (4) dachshunds; (5) spitz and primitive dogs; (6) scent hounds; (7) pointers; (8) retrievers, flushers, and water dogs; (9) companion and toy dogs; and (10) sighthounds.

The variables analyzed were sex, breed, season of birth, hip score, and latitude. Season of birth was arbitrarily defined as follows: winter, December through February, spring, March through May, summer, June through August, and autumn, September through November. Each state and province was grouped by latitude. The latitude where each dog was living at the time of the radiograph was placed into 4 groups defined as (1) <30°N, (2) 30–39°N, (3) 40–49°N, and (4) >50°N. Those <30°N were Florida, Hawaii, Louisiana, Puerto Rico, Virgin Islands, and Guam. Those 30–39°N were Alabama, Arkansas, Arizona, California, Colorado, District of Columbia, Delaware, Georgia, Indiana, Kansas, Kentucky, Maryland, Missouri, Mississippi, North Carolina, New Mexico, Nevada, Oklahoma, South Carolina, Tennessee, Texas, Virginia, and West Virginia. Those 40–49°N were the states of Connecticut, Iowa, Idaho, Illinois, Maryland, Maine, Michigan, Minnesota, Montana, Nebraska, New Hampshire, New Jersey, New York, Ohio, Oregon, Pennsylvania, Rhode Island, South Dakota, Utah, Vermont, Washington, Wisconsin, and Wyoming and the provinces of New Brunswick, Newfoundland, Nova Scotia, Ontario, Prince Edward Island, and Quebec. Those >50°N were the state of Alaska and the provinces of Alberta, British Columbia, Manitoba, Northwest Territories, Saskatchewan, and Yukon Territory. Although a few of the states and provinces straddle these latitude lines, each state/province was placed into the group corresponding to the major population areas.

2.3. Statistical Analysis

Demographic variables were first analyzed using bivariate analyses (Pearson's χ2 test) to determine differences between those with and without CHD. Next, binary multivariate logistic regression analyses were performed to determine adjusted odds ratios (OR) and 95% [upper, lower] confidence intervals of a dog having CHD. While the American Veterinary Medical Association grading system is a numerical value, it is not a continuous variable such as the Norberg angle, but rather a categorical ordinal variable determined by subjective criteria (http://www.ofa.org/hd_grades.html – hip dysplasia, OFA X-ray procedures). For this reason, CHD grade was considered to be a categorical variable. All statistical analyses were performed with Systat™ 10 software (Chicago, IL, 2000), and p < 0.05 was considered statistically significant.

3. Results

3.1. Overall Results

The hip dysplasia scores were 1 in 74,931 dogs; 2 in 601,893; 3 in 95,154; 4 in 6,772; 5 in 86,321; 6 in 47,971; and 7 in 8,004, resulting in an overall CHD prevalence of 15.56%. There was significant variability in the prevalence of CHD by AKC and FCI groups, gender, latitude, and season of birth (Table 1). CHD was overall slightly more common in females, those born in spring and winter (Figure 1(a)), and those born in the more southern latitudes (Figure 1(b)). Within AKC groups, CHD was most prevalent in hybrid breeds (21.5%) and least prevalent in hounds (10.5%) (Figure 1(c)). Within FCI groups, it was most prevalent in group 2 (pinscher, schnauzer, molossoid, and Swiss mountain/Swiss cattle dogs) (20.4%) and least common in group 10 (sighthounds) (5.2%) (Figure 1(d)). Although there was a statistically significant difference in the prevalence of CHD by age at the time of radiography (Figure 1(e)), the variability was less than 2% and considered to not be clinically significant, especially since the oldest group of dogs had a lower prevalence of CHD than the youngest cohort. Age was thus deleted from all further analyses. There was significant variation by individual breeds. The prevalence of CHD by breeds in this study is very similar to that given on the OFA website http://www.ofa.org, even though dogs outside of Canada or the USA were excluded in our study. The complete CHD prevalence data set is given in Supplemental Table 1 in Supplementary Material available online at https://doi.org/10.1155/2017/5723476; the highest prevalence was in the bulldog (77.7%) and the lowest in the Italian greyhound (0.0%).

Table 1.

Prevalence of CHD by demographic variables.

Parameter All CHD versus no CHD Bilateral versus unilateral CHD Right versus left unilateral CHD
Dogs without CHD Dogs with CHD % CHD % without CHD p value Bilateral
CHD
Unilateral CHD % bilateral % unilateral p value Left CHD Right CHD % left % right p value
All dogs 914,274 771,978 142,296 15.56 84.44 95,376 46,918 67.03 32.97 21,657 18,140 54.42 45.58
Sex
 Female 582,990 490,884 92,106 15.80 84.20 <10−6 17,079 50,189 65.97 34.03 <10−6 8,039 6,444 55.51 44.49 0.001
 Male 331,281 281,091 50,190 15.15 84.85 29,839 92,105 67.60 32.40 13,618 11,696 53.80 46.20
AKC group
 Herding 181,497 153,857 27,640 15.23 84.77 <10−6 9,770 27,639 64.65 35.35 <10−6 4,346 3,922 52.56 47.44 <10−6
 Hound 24,017 21,490 2,527 10.52 89.48 782 2,527 69.05 30.95 359 307 53.90 46.10
 Working 217,397 178,178 39,219 18.04 81.96 12,215 39,219 68.85 31.15 5,076 4,898 50.89 49.11
 Sporting 404,008 343,284 60,724 15.03 84.97 20,628 60,723 66.03 33.97 10,006 7,694 56.53 43.47
 Nonsporting 51,153 44,226 6,927 13.54 86.46 2,005 6,927 71.06 28.94 1,031 238 81.25 18.75
 Terrier 19,234 16,812 2,422 12.59 87.41 633 2,422 73.86 26.14 341 238 58.89 41.11
 Toy 11,005 9,197 1,808 16.43 83.57 497 1,808 72.51 27.49 277 194 58.81 41.19
 Native 36 32 4 11.11 88.89 2 4 50.00 50.00 1 1 50.00 50.00
 Hybrid 2,514 1,973 541 21.52 78.48 196 541 63.77 36.23 117 66 63.93 36.07
 Miscellaneous 3,413 2,929 484 14.18 85.82 190 484 60.74 39.26 103 77 57.22 42.78
FCI group
 Sheep and cattle 185,969 157,713 28,256 15.19 84.81 <10−6 18,250 10,005 64.59 35.41 <10−6 4,465 4,004 52.72 47.28 <10−6
 Pinscher Schnauzer, molossoid, and Swiss Mtn/cattle dog 176,144 140,164 35,980 20.43 79.57 24,919 11,061 69.26 30.74 4,571 4,462 50.60 49.40
 Terrier 14,542 12,374 2,168 14.91 85.09 1,623 545 74.86 25.14 291 209 58.20 41.80
 Dachshund 70 63 7 10.00 90.00 7 0 100.00 0.00 0 0
 Spitz and primitive 64,683 58,132 6,551 10.13 89.87 4,588 1,963 70.04 29.96 915 740 55.29 44.71
 Scent hounds 16,509 14,782 1,727 10.46 89.54 1,207 520 69.89 30.11 238 200 54.34 45.66
 Pointing dogs 71,170 63,403 7,767 10.91 89.09 5,045 2,721 64.96 35.04 1,293 1,073 54.65 45.35
 Retrievers, flushers, and water dogs 340,551 286,489 54,062 15.87 84.13 35,797 18,265 66.21 33.79 8,912 6,746 56.92 43.08
 Companion and toy dogs 37,085 32,071 5,014 13.52 86.48 3,484 1,530 69.49 30.51 815 586 58.17 41.83
 Sighthounds 5,129 4,860 269 5.24 94.76 148 121 55.02 44.98 48 54 47.06 52.94
Latitude
 <30°N 43,929 34,779 9,150 20.83 79.17 <10−6 6,428 2,721 70.26 29.74 <10−6 1,172 1,074 52.18 47.82 0.0037
 30–39°N 404,336 343,861 60,475 14.96 85.04 40,594 19,880 67.13 32.87 9,131 7,865 53.72 46.28
 40–49°N 425,790 357,670 68,120 16.00 84.00 45,283 22,837 66.48 33.52 10,650 8,619 55.27 44.73
 ≥50°N 37,506 33,364 4,142 11.04 88.96 2,777 1,365 67.04 32.96 655 546 54.54 45.46
Season of birth
 Autumn 215,003 182,842 32,161 14.96 85.04 <10−6 21,362 10,798 66.42 33.58 0.0016 5,020 4,099 55.05 44.95 0.10
 Winter 218,849 183,276 35,573 16.25 83.75 23,695 11,878 66.61 33.39 5,582 4,555 55.07 44.93
 Spring 255,064 213,377 41,687 16.34 83.66 28,146 13,540 67.52 32.48 6,151 5,278 53.82 46.18
 Summer 225,358 192,483 32,875 14.59 85.41 22,173 10,702 67.45 32.55 4,904 4,208 53.82 46.18

Figure 1.

Figure 1

Prevalence of CHD by various demographic parameters. (a) By season of birth. (b) By latitude. (c) By AKC groups. (d) By FCI groups. (e) By age at time of radiograph. The numbers in the boxes are the percentage within each column bar.

3.2. Results by Demographic Parameters

The overall OR for CHD was higher in females (1.05 [1.064, 1.039]; p < 10−6), those born in spring (1.143 [1.16, 1.13]; p < 0.004), and those living in more southern latitudes (<30°N) (OR 2.12; [2.21, 2.04]; p < 10−6). These results from the composite data set obviously reflect the proportion of breeds in the OFA database and could likely be different if the breed composition differed. Therefore, analyses for each AKC and FCI group, as well as individual breeds, were performed (Table 2). Due to small numbers in certain groups, those in the native, hybrid, and miscellaneous were excluded when analyzing by AKC groups and the dachshunds when analyzing by FCI groups. Within AKC groups, working dogs had the highest risk of CHD (OR 1.882) with hounds being the reference group. Within FCI groups, group 2 (pinscher, schnauzer, molossoid, and Swiss mountain/Swiss cattle dogs) had the highest risk of CHD (OR 4.168) with sighthounds being the reference group. Those born in spring had the highest risk of CHD (OR 1.14) as well as those living in latitudes < 30°N (OR 2.1), with a minimally higher risk in females (OR 1.05).

Table 2.

Odds ratios of CHD by AKC/FCI groups, sex, season of birth, and latitude.

(a).
By AKC group
OR 95% CI p value
Sex
 Female 1.056 (1.069, 1.044) <10−6
 Male 1.0 R
Season of birth
 Autumn 1.025 (1.042, 1.008) <10−6
 Winter 1.131 (1.149, 1.112) 0.081
 Spring 1.146 (1.165, 1.128) <10−6
 Summer 1.0 R
Latitude
 <30°N 2.116 (2.203, 2.034) <10−6
 30–39°N 1.428 (1.477, 1.381) <10−6
 40–49°N 1.552 (1.605, 1.501) <10−6
 ≥50°N 1.0 R
AKC group
 Herding 1.535 (1.602, 1.470) <10−6
 Toy 1.675 (1.788, 1.570) <10−6
 Working 1.882 (1.965, 1.804) <10−6
 Sporting 1.504 (1.569, 1.442) <10−6
 Nonsporting 1.348 (1.415, 1.284) <10−6
 Terrier 1.236 (1.311, 1.164) <10−6
 Hound 1.0 R
(b).
By FCI group
OR 95% CI p value
Sex
 Female 1.053 (1.065, 1.040) <10−6
 Male 1.0 R
Season of birth
 Autumn 1.021 (1.038, 1.004) 0.016
 Winter 1.124 (1.142, 1.105) <10−6
 Spring 1.143 (1.161, 1.125) <10−6
 Summer 1.0 R
Latitude
 <30°N 2.047 (2.13, 1.967) <10−6
 30–39°N 1.410 (1.458, 1.363) <10−6
 40–49°N 1.546 (1.599, 1.496) <10−6
 ≥50°N 1.0 R
FCI group
 Sheep and cattle 3.229 (3.653, 2.854) <10−6
 Pinscher schnauzer, molossoid, and Swiss Mtn/cattle dog 4.618 (5.224, 4.082) <10−6
 Terrier 3.163 (3.605, 2.774) <10−6
 Spitz and primitive 2.059 (2.334, 1.816) <10−6
 Scent hounds 2.096 (2.393, 1.836) <10−6
 Pointing dogs 2.184 (2.473, 1.927) <10−6
 Retrievers, flushers, and water dogs 3.386 (3.830, 2.994) <10−6
 Companion and toy dogs 2.824 (3.204, 2.489) <10−6
 Sighthounds 1.0 R

3.3. Results by AKC and FCI Groups

Analyses by each of the AKC and FCI groups were next performed (Table 3). Again, many of the groups showed an increase in CHD in those living in latitudes <30°N, except for toy dogs (where the opposite was noted with a higher risk in the most northern latitudes >50°N); hounds had no variation in CHD by latitude. When there was an increased OR by season of birth, winter and spring seasons most commonly demonstrated the increased risk with a few demonstrating an autumn increase; no group demonstrated a summer increase. A few groups demonstrated an increased CHD risk in females (AKC herding, working and sporting groups and FCI sheep/cattle and pinscher groups); sighthounds had an increased risk in male dogs.

Table 3.

Odds ratios of CHD for each AKC/FCI group by sex, season of birth, and latitude.

Sex Latitude Season of birth
n Female p value (<30°N) p value (30–39°N) p value (40–49°N) p value Autumn p value Winter p value Spring p value
OR (95% CI) OR (95% CI) OR (95% CI) OR (95% CI) OR (95% CI) OR (95% CI) OR (95% CI)
By AKC group
 Herding 180,911 1.14 (1.171, 1.110) <10 6 2.129 (2.323, 1.052) <10 6 1.383 (1.489, 1.285) <10 6 1.531 (1.648, 1.422) <10 6 0.996 (1.035, 0.958) 0.83 1.148 (1.191, 1.107) <10 6 1.102 (1.141, 1.063) <10 6
 Toy 11,011 0.948 (1.052, 0.853) 0.31 0.457 (0.620, 0.339) <10 6 0.54 (0.678, 0.430) <10 6 0.499 (0.628, 0.397) <10 6 0.918 (1.062, 0.794) 0.25 1.073 (1.239, 0.930) 0.34 1.041 (1.200, 0.903) 0.58
 Working 216,599 1.069 (1.903, 1.045) <10 6 2.345 (2.519, 2.182) <10 6 1.489 (1.584, 1.401) <10 6 1.558 (1.657, 1.465) <10 6 0.979 (1.011, 0.948) 0.19 1.075 (1.109, 1.041) 0.000008 1.146 (1.182, 1.111) <10 6
 Sporting 402,911 1.027 (1.046, 1.009) 0.0038 2.179 (2.328, 2.038) <10 6 1.523 (1.609, 1.441) <10 6 1.7 (1.796, 1.609) <10 6 1.082 (1.111, 1.056) <10 6 1.189 (1.219, 1.159) <10 6 1.195 (1.224, 1.167) <10 6
 Nonsporting 51,045 0.988 (1.042, 0.938) 0.94 1.588 (1.881, 1.341) <10 6 1.258 (1.443, 1.096) 0.0011 1.266 (1.454, 1.103) 0.0008 0.975 (1.046, 0.938) 0.19 1.004 (1.081, 0.932) 0.000008 1.067 (1.146, 0.994) <10 6
 Terriers 19,156 0.978 (1.071, 0.894) 0.63 2.489 (3.281, 1.887) <10 6 1.414 (1.776, 1.126) 0.0028 1.492 (1.870, 1.190) 0.0005 0.987 (1.118, 0.872) 0.84 1.102 (1.245, 0.975) 0.12 1.082 (1.216, 0.963) 0.19
 Hounds 23,974 1.024 (1.114, 0.941) 0.58 1.31 (1.748, 0.980) 0.067 1.044 (1.336, 0.815) 0.74 1.165 (1.493, 0.909) 0.23 0.99 (1.115, 0.879) 0.87 0.933 (1.046, 0.832) 0.23 0.92 (1.031, 0.820) 0.15
By FCI group
 Sheep and cattle 185,366 1.138 (1.169, 1.109) <10 6 2.105 (1.295, 1.931) <10 6 1.371 (1.475, 1.274) <10 6 1.512 (1.623, 1.405) <10 6 0.987 (1.026, 0.951) 0.51 1.145 (1.187, 1.105) <10 6 1.098 (1.137, 1.060) <10 6
 Pinscher schnauzer, molossoid, and Swiss Mtn/cattle dog 175,562 1.078 (1.104, 1.053) <10 6 2.227 (2.409, 2.059) <10 6 1.52 (1.628, 1.419) <10 6 1.626 (1.743, 1.518) <10 6 1.006 (1.041, 0.972) 0.74 1.076 (1.113, 1.041) 0.00002 1.168 (1.207, 1.131) <10 6
 Terrier 14,507 1.013 (1.115, 0.921) 0.79 2.131 (2.864, 1.585) 0.000001 1.287 (1.651, 1.003) 0.047 1.412 (1.810, 1.102) 0.0064 0.999 (1.142, 0.875) 0.99 1.125 (1.281, 0.988) 0.076 1.089 (1.233, 0.961) 0.18
 Spitz and primitive 64,393 1.014 (1.069, 0.961) 0.62 1.709 (2.022, 1.444) <10 6 1.121 (1.263, 0.995) 0.06 1.164 (1.311, 1.033) 0.012 1.007 (1.081, 0.938) 0.85 1.008 (1.084, 0.937) 0.84 0.92 (0.992, 0.853) 0.031
 Scent hounds 16,490 1.095 (1.215, 0.987) 0.085 1.15 (1.573, 0.841) 0.38 0.911 (1.192, 0.700) 0.50 0.922 (1.212, 0.702) 0.56 0.97 (1.121, 0.839) 0.68 1.09 (1.254, 0.947) 0.23 0.939 (1.074, 0.820) 0.36
 Pointing dogs 70,962 0.998 (1.048, 0.951) 0.93 1.412 (1.722, 1.164) 0.0005 1.179 (1.384, 1.004) 0.045 1.288 (1.509, 1.098) 0.0018 1.124 (1.207, 1.046) 0.0014 1.257 (1.346, 1.173) <10 6 1.184 (1.260, 1.112) <10 6
 Retrievers, flushers, and water dogs 339,651 1.015 (1.035, 0.995) 0.14 2.305 (2.471, 2.149) <10 6 1.578 (1.672, 1.488) <10 6 1.781 (1.886, 1.681) <10 6 1.044 (1.073, 1.016) 0.0021 1.15 (1.182, 1.120) <10 6 1.188 (1.213, 1.158) <10 6
 Companion and toy dogs 37,025 0.99 (1.054, 0.930) 0.75 1.02 (1.234, 0.850) 0.83 0.958 (1.102, 0.832) 0.55 0.97 (1.117, 0.842) 0.67 0.938 (1.054, 0.930) 0.14 1.031 (1.123, 0.946) 0.49 1.113 (1.207, 1.026) 0.001
 Sighthounds 5,111 0.739 (0.945, 0.578) 0.016 2.607 (6.622, 1.027) 0.044 1.482 (3.421, 0.642) 0.36 2.122 (4.872, 0.924) 0.076 1.45 (2.073, 1.014) 0.042 1.24 (1.784, 0.860) 0.25 1.177 (1.661, 0.834) 0.35

The reference groups were male, latitude ≥50°N, and summer.

The p values for statistically significant variables are in bold type.

Analyses within subgroups of AKC and FCI groups (Supplemental Table 2) as well as the most common 25 breeds in the data set (Supplemental Table 3) were also performed. Here again, similar findings are as seen for individual AKC and FCI groups. The detailed ORs of CHD for all dogs with n > 1000 as well as all dogs with n > 100 and a CHD prevalence of >15% (the median value) are given in Supplemental Table 4.

3.4. Severity and Laterality of CHD

For those dogs with CHD, severity of the CHD was analyzed (Table 4). Severe CHD (score of 7) was more common in those with bilateral involvement, AKC groups of herding and working dogs, FCI groups of pinscher and sheep/cattle dogs, those living in the most southern latitudes (<30°N), and those born in spring. Males had a slightly higher proportion of severe CHD. Regarding unilateral or bilateral involvement, bilateral disease was most prevalent in terriers and least prevalent in hybrid dogs within AKC groups (Figure 2(a)); bilateral disease was most prevalent in terriers and least prevalent in sighthounds within FCI groups (Figure 2(b)).

Table 4.

Severity of CHD by demographic parameters.

Parameter CHD severity % severity p value
Mild Moderate Severe Mild Moderate Severe
Age (mos ± 1 sd) 31.4 ± 8.4 32.0 ± 8.9 32.5 ± 9.3 <10−6
Sex
 Male 55,390 31,452 5,264 60.14 34.15 5.72 <10−6
 Female 30,931 16,519 2,740 61.63 32.91 5.46
Laterality
 Bilateral 51,085 36,754 7,537 53.56 38.54 7.90 <10−6
 Unilateral 35,236 11,217 465 75.10 23.91 0.99
AKC group
 Herding 17,011 8,906 1,723 61.54 32.22 6.23 <10−6
 Hound 1,329 427 52 73.51 23.62 2.88
 Working 22,469 14,379 2,371 57.29 36.66 6.05
 Sporting 36,994 20,498 3,232 60.92 33.76 5.32
 Nonsporting 4,452 2,062 413 64.27 29.77 5.96
 Terrier 1,757 605 60 72.54 24.98 2.48
 Toy 1,622 800 105 64.19 31.66 4.16
FCI group
 Sheep and cattle 17,387 9,106 1,763 61.53 32.23 6.24 <10−6
 Pinscher schnauzer, molossoid, and Swiss Mtn/cattle dog 20,179 13,430 2,371 56.08 37.33 6.59
 Terrier 1,563 552 53 72.09 25.46 2.44
 Spitz and primitive 4,106 2,120 325 62.68 32.36 4.96
 Scent hounds 1,142 511 74 66.13 29.59 4.28
 Pointing dogs 4,981 2,496 290 64.13 32.14 3.73
 Retrievers, flushers, and water dogs 32,742 18,344 2,976 60.56 33.93 5.50
 Companion and toy dogs 3,710 1,178 126 73.99 23.49 2.51
 Sighthounds 181 85 3 67.29 31.60 1.12
Geographic group
 <30°N 2,760 1,183 199 66.63 28.56 4.80 <10−6
 30–39°N 41,628 22,781 3,711 61.11 33.44 5.45
 40–49°N 36,358 20,619 3,498 60.12 34.10 5.78
 ≥50°N 5,335 3,235 580 58.31 35.36 6.34
Season of birth
 Autumn 19,795 10,644 1,722 61.55 33.10 5.35 <10−6
 Winter 21,512 12,101 1,960 60.47 34.02 5.51
 Spring 24,728 14,456 2,503 59.32 34.68 6.00
 Summer 20,286 10,770 1,819 61.71 32.76 5.53

Figure 2.

Figure 2

Unilateral and bilateral involvement in CHD. (a) By AKC group. (b) By FCI group.

4. Discussion

Limitations of this study need to be acknowledged. Although we used a very large data set, it may not give the true prevalence of CHD, since it only represents the data on those dogs whose radiographs were submitted to the OFA. This predisposes to selection bias as it is not a truly random sample of the canine population [17]. Determination of the “true” prevalence would require a prospective radiographic exam between 2 and 5 years of age of every dog consecutively born, with a population of at least 1 million. Obviously such a study is impossible to perform. The OFA data set is therefore likely the best that can be presently obtained in the North America with the possible exception of the PennHIP™.

With these limitations in mind, there are several important findings. CHD is slightly more common in females, but with a large variation, ranging from 3.36 times more frequent in female Polish Tatra Sheepdogs to 1.63 times more frequent in male Afghan Hounds (Supplemental Table 1). CHD prevalence varies by breed, which was again demonstrated in this study, ranging from 77.7% in the bulldog to 0% in the Italian Greyhound. Many breeds demonstrated a mild increase in risk for CHD when born in winter and spring. CHD was unilateral in 33% of all dogs with CHC. Unilateral involvement was more common in herding/sporting dogs and they had lower hip dysplasia scores. Finally, a new finding is that the prevalence of CHD is more common in dogs living in more southern latitudes.

This study confirms the marked variability in CHD prevalence by breed. In France, the highest prevalence of CHD was in the Cane Corso (59.7%) and the lowest in the Siberian Husky (3.9%) [18]. In a national Veterinary Medical Database from the entire USA [19], the OR of CHD was 10.2 in the Kuvasz with mixed breed dogs being the reference group. In a more recent study using the Veterinary Medical Database [20] the highest prevalence of CHD was 17.16% in the Newfoundland and 0.12% in the Scottish Terrier. In USA veterinary teaching hospitals, the prevalence of CHD was highest in the Rottweiler (35.4%) and lowest in the miniature schnauzer dogs (1.5%) [21]. In a Norwegian study comprised of Newfoundland, Leonberger, Labrador Retriever, and Irish Wolfhounds (n = 501), the highest prevalence of CHD was in the Newfoundland and the lowest in the Irish Wolfhound (OR 0.22 that of the Newfoundland) [22]. In Turkey, a study of 484 dogs from 7 different breeds revealed the highest prevalence in Doberman Pinschers (70.6%) and the lowest in Golden Retrievers (50%); the prevalence in Doberman Pinschers in this study in North America was low at 5.1%. It must be remembered that many of these studies used a different grading system than the OFA scores; however, it still confirms marked variability within breeds within each study.

The quoted prevalence of CHD is frequently different between different studies for a particular breed. When comparing the data of Witsberger et al. [20] to ours, the prevalence of CHD for the Newfoundland was 17.2% versus 20.0%, Saint Bernard 14.7% versus 36.8%, Rottweiler 10.3% versus 12.5%, German Shepherd 10.3% versus 16.3%, Golden Retriever 8.5% versus 14.9%, Labrador Retriever 7.4% versus 9.2%, Bulldog 4.4% versus 68.9%, Doberman Pinscher 1.3% versus 5.1%, and Greyhound 0.4% versus 2.1%, respectively. This demonstrates that the sampling technique/composition of the data set markedly impacts the prevalence value as previously mentioned. Prevalence amongst each breed within a country, or region, is likely a result of gene flow, bottle necks, popular sire effects, and the efforts of individuals and breed clubs to impact the prevalence and severity of CHD in a particular breed.

We noted a slight increase in CHD in females with marked differences by breed. Several studies noted no sex difference in the prevalence of CHD. In Norway, Turkey, and the United Kingdom no sex differences were noted for the various breeds studied [2225]. In Sweden, CHD was 1.14 times more common in female German Shepherds compared to males [26]. In the United States, sex differences were noted in Golden Retrievers [27]; the prevalence of CHD was 5.1% in intact males, 10.3% in males neutered early, 0% in males neutered late, 39% in intact females, 4.5% in females neutered early, and 0% in females neutered late. The status of neutering in the OFA registry is not given, so we cannot compare our findings to those of Torres de la Riva [27].

The prevalence of unilateral CHD was 33% in this study. The prevalence of unilateral CHD was 35% in a New York study of 1022 dogs consisting of Labrador Retrievers, Golden Retrievers, German Shepherds, and crossbreeds [2]. In Pennsylvania, it was 6% in 133 Greyhounds. A recent study of multiple breeds from Italy noted an overall percentage of unilateral CHD of 31.5% [28], strikingly similar to the 33% in this study and the 35% of Lust et al. [2]. This is the first study to investigate the proportion of unilateral CHD by AKC/FCI groups; for AKC groups it was highest in herding dogs (35.4%) and lowest in terriers (27.5%); for FCI groups it was highest in sheep/cattle dogs (35.4%) and lowest in terriers (25.1%) (Table 1).

Few studies discuss season of birth and CHD. In Norway [29], the OR for CHD (Newfoundland, Leonberger, Labrador Retriever, and Irish Wolfhounds) was 3.94 times higher in autumn and 1.85 times higher in winter compared to spring. In another Norwegian study [9], pointers had an increase in CHD in those born in August to February, Labrador Retrievers September to February, with no seasonal effect on CHD in German Shepherds or Golden Retrievers. In Finland [7], German Shepherds born in spring or summer had less CHD. In England [10], Labrador Retrievers and Gordon Setters had less CHD when born in July through October. In New Zealand [8], Labrador Retrievers and Rottweilers had less CHD when born in autumn, but no seasonal variation was observed for German Shepherds or Golden Retrievers. In aggregate, the previous studies in the Northern Hemisphere noted that dogs born in autumn and/or winter months demonstrate a higher prevalence of CHD. In this study we noted an increase of CHD primarily in winter and spring months. When reviewing the data from Supplemental Table 3, 563,403 of the 619,825 dogs (81.4%) showed a seasonal variation. Of these 536,403, 313,202 (55.6%) had the highest percentage in winter, 229,925 (40.8%) in spring, and 20,276 (3.6%) in autumn.

There are several postulated reasons for seasonal differences in CHD. One is the relationship between hip muscle development and season. The most critical time for canine hip joint development is between 3 and 9 months of age [8, 30]; cage confinement during this crucial period has a protective effect on the hip [30]. The proposed explanation is that puppies born in winter spend more time in cages/indoors than in free activities, and indoor confinement may keep the hips in flexion and abduction lessening the development of CHD [29]. The same has been noted in human DDH, where carrying the infant in positions of hip abduction and flexion reduces the incidence of DDH [3135] while swaddling in extension increases the incidence of DDH [5, 36, 37]. Our results refute a winter protective effect in CHD. A second explanation is that puppies born in late autumn or early winter, compared to those born in spring or early summer, do not get as much physical exercise. Puppies getting less physical exercise may develop weaker hip musculature than those with a lot of outdoor activity, which when combined with rapid skeletal growth results in weakened constraints on the hip, subsequent subluxation, and CHD [8, 22, 29, 30]. This can explain the increase in CHD in dogs born in late autumn/early winter and corroborates the findings from New Zealand, England, and our study, while conflicting with the data from Norway, Finland, and Sweden.

Another postulated mechanism for CHD seasonal variation is diet and weight gain in puppies. Dogs with limited weight gain in early life have a lower prevalence of CHD [2, 22, 29, 38, 39]. In cold winter months dogs have increased food intake [40, 41], and if not accompanied by an increase in energy consumption (e.g., activity), the dog will gain weight. Increased body weight increases the stress across the developing hip joint leading to subluxation [17, 42, 43]. Vitamin D plays a role in DDH, as humans with homozygosity for the mutant Taq1 vitamin D receptor t allele demonstrate increased acetabular dysplasia [44]. Vitamin D levels may vary by season due to seasonal variation in vitamin D dietary content in both humans and animals [4552]. Low vitamin D levels and increased body fat in winter may result in more CHD. Finally, various dietary factors differ by season and could result in seasonal differences in hormones in milk (vitamin D, relaxin, and vitamin C) and secondarily influence hip development [5257].

This is the first description of an increased prevalence of CHD in more southern latitudes. This was true even when multivariate regression logistic analysis was performed adjusting for breed group, gender, and season of birth. One potential explanation is that the generally warmer climate in more southern latitudes may result in a general increase in physical activity at all times, with the hips being less abducted and flexed, resulting in more CHD. Another potential explanation is that the gene pools may be different in different latitudes. Finally, other environmental factors such as diet as discussed above may be involved, resulting in increased CHD. Perhaps the dogs in the more southern latitudes are heavier and place more stress across the hip. It could also be that the dogs in the warmer more southern latitudes grow more rapidly early in life, which is a well-known contributing factor to CHD [38, 39]. This finding and potential explanations will require further study.

There are marked differences and similarities between DDH and CHD (Table 5). The most striking is the difference in incidence/prevalence by race/breed. Prevalence/incidence variation in humans is higher (950-fold difference in Native Americans compared to Africans in Africa) than canines (96-fold difference in the bulldog compared to the whippet) (Supplemental Table 1). DDH occurs predominantly in females (75%) for all races [5], while for CHD the prevalence was only slightly higher in females compared to males (Table 1). However there are large sex variations in CHD which ranged from 3.4 times more frequent in female Polish Tatra Sheepdogs to 1.6 times more frequent in male Afghan Hounds. DDH is usually unilateral (63.4%) [5] compared to CHD which is usually bilateral (67%). DDH demonstrates a seasonal variation in ~91.0% of cases [6], and 81.4% in CHD, which is remarkably similar. DDH was most prevalent when the baby was born in winter months (70.3%); CHD was most prevalent when the puppy was born in winter and spring. DDH is more common in northern latitudes, while CHD is more common in southern latitudes [5, 6]. This latitudinal difference has also been noted in children with Perthes' disease [58]. Within DDH there are two different types, the typical infantile DDH and the late onset adolescent/adult acetabular dysplasia [59]. The older group, when compared to the infantile group, demonstrated a lower female predominance (88.0 versus 98.0%) with more bilateral involvement (61.2% versus 45.1%). Our findings in CHD more closely mirror the demographics of DDH in the late onset group.

Table 5.

Comparisons between DDH and CHD.

(a).

Human DDH Canine CHD
Race Incidence per 1000 births % M % F % bilateral % unilateral AKC groups Prevalence % bilateral % unilateral FCI groups Prevalence % bilateral % unilateral
Indigenous peoples Sporting dogs 15.03 66.03 33.87 Sheep and cattle 15.19 64.6 35.4
Native American 95.0 30 70 50 50 Retrievers 16.52 65.68 34.32 Pinscher schnauzer, molossoid, and Swiss mountain/cattle dog 20.43 69.3 30.7
Sami 40.0 Movers/flushers 12.71 68.7 31.3 Terrier 14.91 74.9 25.1
Aboriginal 3.7 Pointers/setters 12.13 65.96 34.04 Spitz and primitive 10.00 70.0 30.0
Versatile sporting 8.42 60.16 39.84 Scent hounds 10.13 69.9 30.7
Caucasian Herding 15.23 64.65 35.35 Pointing dogs 10.46 65.0 35.0
Eastern Europe 44.2 21 79 19 81 Working 18.04 68.85 31.15 Retrievers, flushers, and water dogs 10.91 66.2 33.8
Mediterranean Islands 14.3 Nonsporting 13.54 71.06 28.94 Companion and toy dogs 15.87 69.5 30.5
Australia/New Zealand 12.0 16 84 43 57 Terrier 12.59 73.86 66.14 Sighthounds 13.52 55.0 45.0
Western Europe 8.1 21 79 19 81 Toy 16.43 72.51 27.49
United Kingdom 8.0 Hound 10.52 69.05 30.95
Scandinavia 7.3 21 79 41 59 Scent hounds 12.97 71.0 29.0
South America 4.6 24 76 Sighthounds 4.64 54.2 45.8
North America 0.8 19 81 13 87
Indo-Mediterranean 5.5 21 79 50 50
Indo-Malay 0.4
Africans
North America 0.5
Africa 0.1

(b).

Seasonal variation n % Seasonal variation n %
Single winter peak 16,425 70.3 Autumn (Sept-Nov) 20,276 2.93
Single summer peak 1,280 5.5 Winter (Dec–Feb) 312,202 45.27
Spring and autumn peaks 3,450 14.8 Spring (March–May) 229,925 33.23
No variation 2,205 9.4 Summer (June–Aug) 0 0
No variation 128422 18.56

Data extracted from [5].

Data extracted from [6].

Present study.

In conclusion, the prevalence of CHD differed markedly by breed, having a slight female predominance but with significant variability by breed, was unilateral in about one-third of cases, and often demonstrated a seasonal variation with a mild increase when the dog was born in spring and winter months. Most interestingly, CHD was more prevalent in the more southern latitudes. This information is important to owners/breeders, suggesting that monitoring of puppies for signs of CHD should be undertaken during the birth months when there is an increased OR of CHD for those affected breeds and/or AKC groups, especially in more southern latitudes. The similarities between CHD and DDH are striking, especially late onset DDH, and suggest that comparative studies of both disorders should lead to a better understanding of a problem that leads to debilitating hip osteoarthritis in both canines and humans.

Supplementary Material

The supplementary material in these gives detailed results of many of the analyses done, such as detailed prevalence or odds ratios for many specific breeds and groups. This is for the reader interested in more information.

5723476.f1.doc (546KB, doc)

Acknowledgments

The authors wish to thank Mr. Eddi Dzuik and Jon Curby, Orthopaedic Foundation for Animals, for granting the authors access to the entire hip dysplasia registry. This research was supported in part by the Garceau Professorship Endowment, Indiana University, School of Medicine, Department of Orthopaedic Surgery, and the Rapp Pediatric Orthopaedic Research Endowment, Riley Children's Foundation, Indianapolis, Indiana.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

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Supplementary Materials

The supplementary material in these gives detailed results of many of the analyses done, such as detailed prevalence or odds ratios for many specific breeds and groups. This is for the reader interested in more information.

5723476.f1.doc (546KB, doc)

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