The word ‘dysplasia’ just means badly formed. This means that the joint is normal at birth and then becomes abnormal over a period of time. In other words dogs are not born with Hip Dysplasia, but they are born with a variable genetic tendency or predisposition to the hip developing abnormally over the period of skeletal development (up to 9-10 months). Some dogs may have no predisposition to developing Hip Dysplasia whilst others may have a significant predisposition.

This likelihood of developing Hip Dysplasia is based on the Genetic make up of the dog and this is obviously governed by the “Family Tree” of the dog and the transmission of genetic material between generations. There is however no single Gene for Hip Dysplasia. Instead it is termed polygenic. The genes involved in Hip Dysplasia relate to the genetic influences on Growth Rate and so forth. In particular it is felt that rapid skeletal growth results in the skeleton outgrowing the supporting soft tissues leading to hip laxity (loose hips). Depending on the degree of laxity and the activity of the individual this leads to a braod spectrum of pathologies of the hip joint itself.

In the early stages of Hip Dysplasia, there may be little to see in the way of overt lameness. Instead in this stage it is things like difficulty to rise from sitting or lying or a tendency to “Bunny-Hop” when moving at a trot or faster. Bunny Hopping means running with both hindlimbs close together. Dogs with symmetric bilateral clinical Hip Dysplasia may appear completely normal apart from these signs. This is because dogs can transfer their body weight forward onto the forelimbs without there being any obviously visible change in their appearance.

Of course some patients at this early phase may appear subdued and even vocalise in discomfort occasionally. They may prefer to eat whilst lying down and may pull themselves along the floor to reach a distant toy for example. If the signs progress from here owners may begin to see stiffness after rest affecting one limb more than another. Stiffness is a “poverty of action” with reduced flexibility and an appearance similar to that seen in an aged animal.

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The knee of a dog is just like a human knee in that it consists of three main bones: The thigh bone or femur, the shin bone or tibia and the knee cap or patella. The patella nestles within a groove in the end of the thigh bone and is attached to the shin bone by the patellar tendon. The knee cap is also attached to the thigh bone and the pelvis by the large and powerful group of muscles at the front of the thigh called the quadriceps. This combination of quadriceps-patella-tendon-tibia creates a pulley system that produces and maintains extension of the knee. Without this mechanism neither humans nor dogs or cats would be able to maintain a standing position. This would be very disabling.

In the most severe forms of patellar luxation (slipping or dislocating knee cap), this is exactly what happens with dogs unable to maintain an upright hindlimb stance and instead they walk with very crouched hindquarters. The patella can slip towards the inner side of the thigh bone as shown in the image or to the outside. Slipping towards the inside is most common and is called Medial Patellar Luxation (MPL). Whilst most of the information on this page relates to Medial Patellar Luxation, it is relevant to dogs with Lateral or outward patellar luxation.

The signs associated with patellar luxation can vary depending on the grade of patellar luxation. Generally we grade this problem on a four point scale. The higher the grade the more permanent the luxation is. In dogs with Grade 1 patellar luxation, the patella may quickly jump in and out of the groove. This may cause a skipping lameness of varying frequency. In between skips, your dog may walk perfectly normally. Most dogs will not squeak or yelp when the skip occurs and they will not seem to notice that it has happened. In Grade 2, the patella may jump out of the groove and stick in this position for a number of steps before popping back into the groove. Again the frquency of this can vary as can the duration of non weight bearing lameness.

Also, the steps between these episodes will likely appear normal. In Grade 3 patients, the patella is almost permanently positioned outside of the groove and there is often no skipping. Instead, the dog will walk with a crouched gait and often be seen to shuffle. The shape of the leg is usually abnormal in appearance with a bowing of the limb. In Grade 4 patents, an upright stance cannot be achieved, a poor shuffling gait and limb deformity are seen. Some dogs (especially Bull type dogs) may show little skipping but appear lame at all times and stiff on rising. These dogs have a patella that sits permanently on the inner ridge of the groove and have rubbed away the cartilage on the back of the patella and on the ridge. This problem will be covered separately.

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This problem affects dogs (and some cats) of all shapes and sizes but is mostly a problem of medium and large breeds of dog. Our commonest patient with this condition is the Labrador and they can be affected from 8 months of age unfortunately. On a positive note we do have a good solution for this problem in the form of Tibial Tuberosity Advancement (TTA) procedure and we will discuss this in more detail down this page. TTA was devised by Slobodan Tepic (Kyon) and Pierre Montavon and Torrington Orthopaedics have been at the forefront of its use and development since 2008.

Click here for more in-depth information about cruciate disease.