Understanding Canine Hip Dysplasia

X-ray image of a dog with hip dysplasia. (Source: Wikimedia Commons)

Canine Hip Dysplasia (CHD) is an issue you hear about a lot, especially in the case of older dogs, and in particular in the case of larger breeds. It’s a common problem, one that can have a particular impact on the quality of the final years of your pet’s life. Dogish is taking a closer look at the ailment, to give you a better sense of what it is, how you can minimize its effects, and what you can do preventatively to keep your animals as healthy as possible for as long as possible.

What is Hip Dysplasia?

It is important to first understand that in a dog’s body—as in yours—there are generally two types of joints: hinge joints, and ball-and-socket joints. Hinges, such as at the knee and elbow, allow for movement along a two-dimensional arc. Ball and socket joints, such as at the shoulder and hip, allow for rotation through three-dimensional space. As the name suggests, the shoulder and hip maneuver using a spherical knob (called a caput) that sleeves into a concave cup-like structure. For these joints to function properly, they require a relatively close fit, but one that is protected by a healthy layer of cartilage and lubricated with a cushion of synovial fluid.

Dysplasia in the hip involves a breakdown of this complex structure. Damage to—or loss of—the protective sheath of cartilage creates a less precise fit between femur and pelvis, leading to joint pain, stiffness, or arthritis.

CHD tends to manifest later in life, but it is the result of asymmetrical bone growth during a dog’s developmental phase. If the socket and femoral head grow at different rates, the fit between ball and socket will be too loose, which over time results in a lack of stability in the joint.

Symptoms and Diagnosis

Canine and human anatomy aren’t all that different. While you might notice an increase of pain or stiffness in your own joints after an injury or as you age, your dog won’t be able to tell you what’s bothering them. Here are a few common signs of CHD that you may notice.

Among the first things to look for are signs of decreasing activity, an inability to jump or rear up on their back legs, reluctance to climb stairs or sharp inclines, or a decreasing interest in running or other vigorous play.

Secondary signs may be more easily observed, but also indicate a greater progression of the disease. These include pronounced changes in stance or gait, a sometimes visible loss of muscle mass in the hind legs, or, conversely, a sharp increase of muscle in the shoulders as the dog compensates for weakness in their hindquarters by bearing more of the load on their forelegs. In later stages, dogs may be unwilling or unable to walk for extended distances. In very advanced cases, a dog may not be able to move unassisted at all.

Clinically, the appearance of the so-called “Morgan Line”, an excessive growth of bone in the joint that is clearly visible on X-ray imaging, indicates a loss of joint stability.

Risk Factors and Causes

CHD is a complex condition with a number of contributing causes and factors. Some of these are breed-specific, and certain types of purebred dog are known to be more susceptible to the condition than others. Ongoing genetic research seeks to better understand the condition. In a 2019 study published in BMC Genomics, a team of Finnish researchers let by Lea Mikkola has documented an apparently significant link between a single nucleotide polymorphism (i.e. a single difference in nucleotide pairs) located in a single gene on a dog’s ninth chromosome points to an elevated risk for CHD. They nonetheless point out that, “The current consensus is that CHD is polygenic, and genetic contribution to the phenotype can vary from small to moderate,” and further that,“Variation between breeds is evident.”

This study also observes that a number of breeds, including “Labrador Retrievers, Bernese Mountain dogs, Golden Retrievers, and German Shepherds have been under special interest in studies of CHD, and several genetic associations with different hip phenotypes have been reported in these breeds.” These, along with a list of other larger dogs, are often cited as those who most commonly suffer from CHD, but the article’s wording suggests that the relative popularity of Labs, Retrievers, and German shepherds may have contributed to bias in our understanding of the condition.

A statistical study, by A.M. Oberbauer et al. (2017), examined over three hundred thousand records related to CHD and the related condition Elbow Dysplasia, and posits that selective breeding has led to certain breeds having higher or lower risks for the condition. Among those with elevated risk are larger breeds, including Newfoundlands, Bloodhounds, Bullmastiffs, and Rottweilers. German Shepherd’s and Golden Retrievers make the list, too, but farther down, with their total risk of developing CHD nearly twenty percent lower than those of greatest concern. Also making the top of the list are medium-sized American Staffordshire Terriers and “dwarf-sized” Pembroke Welsh corgi. The data also points to Belgian sheepdogs and their longhaired tervuren cousins, as well as gun-dogs such as the flat-coated retriever and the German short haired pointer, and even the large-sized Irish wolfhound, are less susceptible.

Prevention

It may seem as though your pet’s fate is written in their genes, but a dog’s DNA is only a part of its overall risk. It’s worth remembering that these analyses show that although breed type does have an effect on the likelihood of a dog’s susceptibility to CHD, they also demonstrate that genetics are not the only concern or consideration. According to the Texas Veterinary Medical Foundation, hip dysplasia “can occur in dogs of any size and any breed, including mixed breeds.”

Pet owners should be aware that there are some measures well within their control that can improve your pet’s overall quality of life.

Veterinarian Tiffany Tupler writes that the biggest considerations for owners are by far diet and exercise. In particular, it is imperative to ensure that you start early in your pet’s life, seeing that that they are getting the right kind of nutrition, and that they are appropriately active. This will encourage proper growth, and help the bones of the pelvis and the femoral caput to form at the same rate, and therefore maintaining a proper fit at the socket. Other sources suggest that overfeeding during this phase, or switching too soon to adult dog food may disrupt regular bone growth.

In older dogs, laxity in the joint need not progress as far as full-blown CHD. Pet owners can help their adult dogs stay mobile by following those same guidelines. Feeding your dog a healthy diet and making sure they get lots of exercise with an eye toward maintaining their ideal body weight will go a long way to preventing or delaying the onset of symptoms.

Treatment and Prognosis

If the condition does worsen, there are a number of treatment options. As in humans suffering from similar conditions, these range from pain management, to minimally invasive surgery, all the way through joint replacement. Mobility devices may also become necessary. There are a number of alternative therapies available, including acupuncture and supplements that purport to support joint health, although their value and validity as treatments remain somewhat in doubt.

Tupler explains that the surgical option, although associated with the greatest upfront cost, may be a more lasting and economical solution in the long run, given that pain management does not treat the underlying causes (although it can help get your pet up and moving again, an important aspect of any course of treatment). It is also worth considering that, according to the Texas Veterinary Medical Foundation, there is a limited window in which joint replacement is a viable option, and so while owners should consider carefully their choices, they shouldn’t delay too long.

While CHD is a relatively common condition, and although it can be debilitating for an aging dog, most experts agree that the prognosis for a dog suffering from CHD that receives proper medical treatment, and who is well cared for by their owners, will live just as long and in as good of health as those unaffected by the condition.