Hip Dysplasia in Dogs

What is hip dysplasia?

Hip dysplasia is one of the most common developmental orthopaedic diseases affecting companion animals. Canine hip dysplasia (CHD) refers to the abnormal development of the hip joints in dogs. It primarily affects medium-sized and large-breed dogs. CHD is d

escribed as a developmental

condition because the hip joints of dogs that

become dysplastic (malformed/malaligned) later in life, are initially

normal and congruent at the time of birth.

CHD has a multifactorial mode of inheritence, meaning that although the disease can be passed from one generation to another, environmental effects can also influence the development of the condition (see more below).

The disease is characterised by hip joint instability, causing pain which is manifests as lameness and/or stiffness. Over time, there will be a progressive decline in joint function as osteoarthritis develops and progresses.

How does hip dysplasia develop?

At birth, the puppy's original anatomical conformation of the hip joint and its surrounding structures are genetically pre-determined by its parents. But, the continued growth and development of the puppy's hip joint are synchronised and dependent on the joint congruency, the movement and balance of forces occuring across the hip joint. An alteration in any or all of these factors may affect or interfere with development of the hip joint.

Prior to 6 months of age, the dorsal acetabular rim (upper rim of the hip socket) in dogs is is mostly made up of cartilage and is very susceptible to deformation. Normally, the hip joint is stabilised by its joint capsule and the muscles surrounding the hip. In dogs with CHD, hip laxity is present - this means that the stabilising structures fail to restrain the femoral head (ball of the hip) within the acetabulum (hip socket). Therefore, when the puppy is moving around and weight-bearing, the femoral head moves out of the acetabulum, causing an abnormal concentration of forces on the dorsal acetabular rim. Over time, this causes the joint cartilage to wear out and alters the composition of the joint fluid such that osteoarthritis eventually develops. These changes further destabilise the hip joint, sometimes even causing subluxation (partial dislocation) or complete luxation (full dislocation) of the affected hip joint.

Several factors that have been implicated in predisposing or causing a genetically-susceptible puppy to develop CHD in adulthood. These include, but are not limited to:-

Abnormal pelvic muscle mass
Spasms or contracture of the pectineus muscle (a muscle in the thigh)
Hormonal influence (e.g. relaxin and/or oestrogen)
Synovial fluid volume and osmolality (composition of the joint fluid)
Nutrition
Rate of weight gain
Overexercise in the skeletally-immature animal

Diagnosis of hip dysplasia

As CHD has a multifactorial mode of inheritance (see above), it is unlikely that a simple genetic screening test will be developed in the near future to identify susceptible dogs. Therefore, in order to objectively quantify CHD, several radiological (x-ray) scoring/grading methods have been developed in an attempt to identify dogs affected with this condition.

One of the most accurate methods of evaluating the congruence of the hip joints is using distraction radiography (PennHIP), a method of x-rays whereby a special device is placed between the thighs of the anaesthetised canine patient and then gently distracted apart. The patient is x-rayed lying on their backs with their hindlimbs extended in a relaxed fashion, and also x-rayed with their hindlimbs extended in a distracted fashion. Put simply, the congruency between the "relaxed" hip and "distracted" hip is compared and a distraction index is calculated. Dogs with distraction index of more than 0.3 is thought to be at risk for hip dysplasia. PennHIP radiograph should only be carried out by a PennHIP vet. Find out more about PennHIP xrays here. You can locate your nearest PennHIP veterinarian here.

Another way of evaluating the hip joints for evidence of dysplasia, or osteoarthritis secondary to CHD, is by performing a more "traditional" ventrodorsal extended-hip radiograph. In this method, the anaesthetised patient is placed on their backs, with their hindlimbs fully extended, and then a hip x-ray is performed and evaluated for signs of arthritis or incongruency.

Worried your dog may have hip dysplasia?

If you are concerned that your pet may have hip dysplasia, please phone us on (06) 3588675 to book them in for an appointment with our team of experienced veterinarians.

The above information is provided for educational purposes only and not intended or implied to be a substitute for professional veterinary medical advice, diagnosis or treatment; and should not be relied on solely as veterinary advice.

Parts of this pet health article is based on Soo M & Worth AJ (2015). Canine hip dysplasia: Phenotypic scoring and the role of estimated breeding value analysis. New Zealand Veterinary Journal 63(2), 69-78. Read the full article here.

Updated by Cahill Animal Hospital on 19 September 2016

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