The Complexity of Hip Dysplasia (HD) in Dogs
Hip dysplasia (HD) is a polygenic and multifactorial developmental condition, which basically means that multiple genes in combination with various non-genetic factors are involved in the development of the condition. This article is written with the Airedale Terrier in mind, but also the Rhodesian Ridgeback.
Studies like Mäki et al. (2002) and Leppänen et al. (2000) suggested already two decades ago that the heritability of HD was estimated to be around 30-40%. In 2012, Krontveit et al. assessed four breeds in Norway; Newfoundlands, Labrador Retrievers, Leonbergers, and Irish Wolfhounds, and reported a heritability range of 20-30% for HD.
With data from more than 700.000 HD records across 74 dog breeds in the OFA (Orthopedic Foundation for Animals) database between 1970 and 2009, Hou et al. (2013) found that heritability varied significantly among breeds, ranging from 10% to 60%. A more recent study by Oberbauer et al. (2017) that looked into 60 dog breeds from the OFA database, with a total of over one million HD evaluations from 1970 to 2015, found that the heritability rates varied from 46% to 75%, depending on breeds.
These differences in heritability indicate that HD is more influenced by genetics in some breeds than in others, suggesting that selective breeding has been more successful in breeds with higher heritability.
Selective Breeding and Estimated Breeding Values
Hou et al. (2013) found little improvement in the EBV (estimated breeding value) of Airedale terriers, suggesting that the selective breeding efforts in this period does not seem to have the same effect as in some other breeds. This suggests that the genetic heritability of HD in Airedale terriers may be lower, indicating that environmental factors play a higher role in HD development. Another aspect worth considering in this regard is the Airedales estimated overall genetic inbreeding at around 40% according to Embark. A low genetic diversity could slow the process of reducing HD prevalence due to the narrow gene pool, which would mean less variability of the genes within the breed.
For the Rhodesian Ridgeback, on the other hand, the EBV shows a clear improvement, indicating a strong reduction in genetic risk for HD over time. The breed has responded very well to selective breeding efforts, leading to a clear decrease in HD over time, which could indicate that the heritability of HD in Ridgebacks are high. The study by Oberbauer et al. (2017) suggest that the heritability of HD in ridgebacks are over 50%, which correlates to the observed increase of EBV.
A recent Swedish study by Hedhammar (2020), «Swedish Experiences From 60 Years of Screening and Breeding Programs for Hip Dysplasia” supports that selective breeding efforts significantly reduce the HD prevalence over time, especially in breeds with a higher heritability. This study highlights the challenge of further reducing the HD prevalence when the breeding population mostly consists of HD clear and unaffected dogs. In such situations the continued reduction in HD prevalence will be slower and more complex. Both Hou et al. (2013) and Hedhammar (2020) emphasise that in populations who already are largely free of severe HD, the use of EBVs to further reduce HD prevalence will be of importance in order to make continued genetic improvements and reduce the incidence of milder forms of HD.
Because the overall inheritance pattern is not straightforward, the polygenic nature of HD makes it challenging for breeders. Dogs can carry genes predisposing them to HD without showing any clinical signs, especially if their environment has been favourable and helped protect them from developing the condition. This means some dogs with a genetic predisposition may still go into breeding if they do not show HD on radiographic evaluation. This could explain why we still have HD in breeds where only HD clear dogs have been included in the breeding programmes for decades.
How Hip Dysplasia Develops
Although all puppies are born with normal hip joint structures, HD develops over time primarily due to subluxation. Subluxation occurs when the ligaments around the hip joint stretch and causing the femoral head (ball of the joint) to no longer fit snugly into the acetabulum (the hip socket). Over time, this instability leads to abnormal wear and tear on the joint structures, which in turn can cause joint deformity, arthritis and pain.
Especially in early life, dogs with HD may not always show physical symptoms. Some dogs may not show any signs of lameness or discomfort even if the joints are radiographically abnormal. This makes detecting and managing the condition even more difficult for breeders and owners, also highlighting the importance of routine screening.
The Role of Exercise, Housing and Feeding in Preventing Hip Dysplasia
In their study from Norway, Krontveit et al. (2012) found that exercise patterns and housing conditions during a dog’s early life significantly impact the risk of developing HD. Their study found the following key insights:
Early, low-impact exercise on soft, uneven surfaces, such as grass or forest trails, helps build strong muscles around the hip joint, which can stabilise it and reduce the risk of HD. These activities promote balanced muscle development, support joint stability, and decrease ligament stress.
On the other hand, high-impact activities, such as running on hard surfaces or excessive stair climbing, were associated with an increased risk of developing HD, particularly in those with a genetic predisposition. High-impact exercises stress growing joints, leading to ligament strain and potentially worsening the condition.
Restricted living spaces with slippery floors, like tile or hardwood, were also linked to a higher incidence of HD. Puppies raised in environments that offered more space and softer, non-slippery surfaces (e.g., carpets or rugs) had a reduced risk of developing HD. Slippery floors make it difficult for puppies to gain traction, leading to awkward movements and increased strain on their ligaments and joints.
Body Weight, Growth Rate, and Nutrition
Several studies mentioned earlier suggest that puppies with rapid weight gain and higher body fat are at a higher risk of developing HD. Excessive weight places stress on the developing hip joints, which could worsen instability and potentially lead to HD. Studies suggest that a slower, steady growth rate helps prevent joint issues like HD, and to ensure this, a properly balanced diet is essential. The ideal ratio of calcium (Ca) to phosphorus (P) is around 1.2:1 to 1.4:1, but never below 1:1 or above 2:1.
The Rhodesian Ridgeback is typically considered a large breed. Although the Airedale terrier is on the larger end of the medium scale, they often touches the large scale, which is often defined at 22-25 kg /55 pounds. Therefore, they might be placed on a large scale as a semi-large breed. If the Ca to P ratio is wrong, it can result in poor bone formation in the growing puppy and a greater likelihood of joint problems like HD and OCD (osteochondrosis dissecans) as they grow older.
Overweight puppies, especially in large breeds, are more likely to develop severe HD, as their joints bear more strain during critical periods of growth.
These studies highlight that it is important to manage the growth, especially in breeds known to be predisposed to HD, as it can reduce some of the environmental factors that contribute to the condition.
Physique and Hip Dysplasia
When evaluating for example Airedales and their physics, one could reflect on how their medium-sized (or perhaps semi-large) athletic build might influence the risk of HD. Airedales are not as heavily muscled as some larger working breeds, but would this mean that their musculature might not provide the same level of joint stability? Could this make them more susceptible to HD if not managed properly through exercise and diet? Or should it be the other way around? Because they are relatively light-weight, it shouldn’t put so much stress on their ligaments?
Public data from OFA and Nordic kennel club databases places the Rhodesian Ridgeback, with its large athletic build, as one of the breeds with the lowest incidence of HD with abnormal joints at 4,3% (OFA, US) and 2,6% (SKK, Sweden), comparable to similar athletic breeds like, for example, Siberian Husky, German Shorthaired Pointer and Dalmatian. Would this be due to their musculature providing joint stability, or is it simply a combination of favourable genetics and environment?
Data from OFA shows that Airedales have an abnormal joint prevalence of 12%, which correlates exactly with data from kennel club databases in Norway and Sweden. Are these statistics comparable to other continents and regions?
While some Airedales with radiographic signs of HD may not show any physical symptoms, others might experience discomfort, stiffness, or difficulty moving. While some Airedales with radiographic signs of HD may not display physical symptoms, others might experience discomfort, stiffness, or difficulty moving. Their active and tough nature could potentially mask early signs of HD. This highlights the necessity that not only potentially breeding animals undergo routine HD screening, but preferably all dogs in a litter (I would also stress the need to do an ED X-ray at the same time, as well as a spine X-ray).
Insights on Hip Dysplasia Screening in 22 Swedish Breeds
A recent report of HD screening in Sweden focusing on 22 breeds, like the German Pinscher and Standard Schnauzer, shows a trend where HD diagnoses have increased significantly since 2000, even though most breeding programs prioritise using HD-free parents. But most interestingly, this increase in HD diagnoses has not led to a higher prevalence of clinical symptoms, like mobility issues or insurance claims. Thus, this observation has raised concerns throughout the Nordic breed clubs, with questions about the screening accuracy and whether it’s comparable to the other HD screening programs worldwide.
The report suggests that new digital imaging techniques and equipment, as well as variations in sedation during X-rays, may lead to an increase in diagnoses of minor abnormalities that were previously undetected. One important note in this matter is that the hip joints do not seem to have become more dysplastic, but the external factors discover more abnormalities than before.
The figures below provide an overview of HD evaluations for Airedale Terriers (first figure) and Rhodesian Ridgebacks (second figure) in Sweden and Norway from 2000 to 2023. The columns on the left show the percentage of dogs examined and their respective HD scores. On the right, the solid lines represent the number of dogs born or registered in each country, as well as the total number of dogs evaluated.
The graphs include a third-order polynomial trendline (dotted line) for each HD grade to illustrate overall development over time. These trendlines provide a visual indication of general patterns but should be interpreted with caution, as they may be influenced by random fluctuations in the data.
Notable trends, similar to those observed in other breeds, include a slight decline in HD A and B scores on average, while HD C scores have increased. However, HD D and HD E scores have shown a decline overall.
The table below from SRRS (Specialklubben Rhodesian Ridgeback Sverige) illustrates the prevalence of HD (C-D-E) in Rhodesian Ridgeback from 2000 to 2020. The yellow line represents dogs diagnosed with mild HD (HD C). According to Hedhammar (2020), the prevalence of HD C has risen since around 2010, while the rate of HD A+B (mainly HD B) has decreased slightly. Still, the prevalence of moderate and severe HD (HD D+E) has remained fairly unchanged, and even decreased slightly.
In my own experience, I have seen similar variations in HD grading across countries. For example, a dog evaluated as HD B/C in the Nordics was graded A2/B1 in Germany and further given a score of 2/4 in Australia and evaluated as Good by OFA (US), highlighting the variability in evaluation systems internationally. According to the CHD scoring table below, these evaluations from Germany, Australia and the US are inconsistent with the Nordic (FCI) standard. This means that an HD C evaluated, especially the Nordics, in some cases would not directly compare to OFA borderline/mild or even HD C in Germany as one has thought earlier. This inconsistency underscores the need for a standardised approach to HD evaluations, as it directly impacts breeding decisions and outcomes worldwide. In breeds with already limited gene pools, excluding dogs based on potentially mismatched grading systems may do more harm than good. On the other hand, when we see that the risk of HD in Airedale terriers is not decreasing as in other breeds, it raises the question of whether this breed has a higher genetic predisposition to HD, or if it is a matter of physical attributes or other environmental factors contributing to the development of HD.
Especially for the Nordic countries, we should use this information wisely. Based on this understanding, several Nordic breed clubs have updated their breeding recommendations to allow dogs with HD grade C (without secondary osteoarthritis) to be used in breeding, provided they are paired with a dog graded HD A – preferably radiographed in a Nordic country.
Hip Dysplasia vs. Other Orthopaedic Concerns
While hip dysplasia is a significant concern in many breeds, other orthopaedic conditions, such as elbow dysplasia (ED) and lumbosacral transitional vertebrae (LTV), may present more immediate challenges in some dogs.
LTV Grading
Lumbosacral transitional vertebrae (LTV) is a spinal malformation where the junction between the lumbar and sacral vertebrae develops abnormally. According to Anu Lappalainen’s research in Finland, LTV is classified into different grades based on the severity of the malformation:
LTV0: No abnormal findings
LTV1: Divided sacral crest (S1–S3) or some other mild abnormal structure
LTV2: Symmetrical lumbosacral vertebra
LTV3: Asymmetrical lumbosacral vertebra
LTV4: 6 or 8 lumbar vertebrae
An important question arises regarding whether Lumbosacral Transitional Vertebrae (LTV), a condition that affects the spinal structure, could be a contributing factor to HD. Berg et al. (2024) suggest that LTV may induce HD by altering the body´s biomechanics, increasing the load on the hips and potentially leading to joint damage. Even though there are substantial differences among breeds, this study indicates that LTV type 2 and type 3 are associated with the development of mild and severe HD. This raises an important question: could some of the cases of HD thought being attributed to genetics result from LTV? The above mentioned study by Berg et al. (2024) identified Ridgebacks as one of the breeds with the highest LTV prevalence among 14 breeds, at above 40% incidence of LTV 1-3. In Airedale Terrier however, LTV is not widely screened, and only a few individuals have been evaluated for LTV in Finland and Norway, with results registered in Koiranet and INCOC.fi.
Recognising the needs of various breeds and establishing a global standard for LTV screening could highlight this issue and improve our understanding of the true causes of HD. This knowledge can transform our perspective on HD, encouraging us to rethink the idea that it’s mainly linked to genetics and instead highlight the importance of LTV screening as an essential aspect of evaluating HD risk in breeding programs.
Final Thoughts for Breeders
Managing hip dysplasia (HD) in Airedales and other breeds requires carefully balancing genetic and environmental factors. A probably polygenetic inheritance makes it difficult to predict whether a dog will develop HD based solely on its genetics and lineage, especially when many dogs with radiographic evidence of HD show no clinical symptoms. However, controlled, low-impact exercise during puppyhood, along with maintaining strong muscles in adulthood, can help support joint health and reduce the risk of HD-related issues.
Additionally, it’s important to consider the impact that HD has on the dog’s quality of life. Many dogs diagnosed with HD through X-rays remain clinically healthy, showing no pain or mobility issues. We must weigh this against the genetic diversity crisis already affecting breeds like the Airedale and others. Disqualifying dogs from breeding solely based on radiographic findings without considering their overall health and contribution to genetic diversity could exacerbate the issue. As the breed’s gene pool shrinks, breeders may face even more challenges related to other inherited conditions. We cannot afford to “throw the baby out with the bathwater.”
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Note: This text was initiated and written by the author, with AI tools used to enhance language and readability.
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References:
- Krontveit et al. (2012). Housing- and exercise-related risk factors associated with the development of hip dysplasia as determined by radiographic evaluation in a prospective cohort of Newfoundlands, Labrador Retrievers, Leonbergers, and Irish Wolfhounds in Norway. https://doi.org/10.2460/ajvr.73.6.838
- Mäki et al. (2002). Estimates of genetic parameters for hip and elbow dysplasia in Finnish Rottweilers. https://doi.org/10.2527/2000.7851141x
- Leppänen et al. (2000). Factors affecting hip dysplasia in German shepherd dogs in Finland: efficacy of the current improvement programme. https://doi.org/10.1111/j.1748-5827.2000.tb03130.x
- Oberbauer et al. (2017). Long-term genetic selection reduced prevalence of hip and elbow dysplasia in 60 dog breeds. https://doi.org/10.1371/journal.pone.0172918
- Hou et al. (2013). Monitoring Hip and Elbow Dysplasia Achieved Modest Genetic Improvement of 74 Dog Breeds over 40 Years in USA. https://doi.org/10.1371/journal.pone.0076390.
- Hedhammar (2020). Swedish Experiences From 60 Years of Screening and Breeding Programs for Hip Dysplasia – Research, Success, and Challenges. https://doi.org/10.3389%2Ffvets.2020.00228
- Calcium and phosphorus – getting the balance right. https://vetfocus.royalcanin.com/en/scientific/calcium-and-phosphorus-getting-the-balance-right.
- Bodo Bäckamo (2017). Observations regarding hip status and screening procedure in 22 dog breeds in Sweden. Report to the Swedish Schnauzer- Pinscher Club
- Berg, L. (2024). Lumbosacral Transitional Vertebrae and its Relationship with Hip Dysplasia in Dogs. https://doi.org/10.1016/j.tvjl.2023.106056
- Lappalainen (2014). Radiographic Screening for Hereditary Skeletal Disorders in Dogs. https://helda.helsinki.fi/server/api/core/bitstreams/c946aaf3-8f25-4408-ae27-884990a80c63/content
- Flückiger et al. (2017). Asymmetrical lumbosacral transitional vertebrae in dogs may promote asymmetrical hip joint development. https://www.thieme-connect.de/products/ejournals/abstract/10.3415/VCOT-16-05-0072
- Lappalainen et al. (2012). Alternative classification and screening protocol for transitional lumbosacral vertebra in German shepherd dogs. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3403972/
- Nina Lindquist. Lumbosacral transitional vertebra (LTV) in Rhodesian Ridgebacks. https://lumottu.net/?page_id=5874
- INCOC. Basis for LTV grading (lumbosacral transitional vertebra). https://www.incoc.fi/asiat/uploads/2024/02/Basis-for-LTV-grading.pdf