hip dysplasia

Canine hip dysplasia is a very common degenerative joint disease seen in dogs. There are many misconceptions surrounding it. There are many things that we know about hip dysplasia in dogs, there are also many things we suspect about this common cause of limping, and there are some things that we just do not know about the disease.

To understand what hip dysplasia really is we must have a basic understanding of the joint that is being affected. The hip joint forms the attachment of the hind leg to the body and is a ball and socket joint. The ball portion is the head of the femur while the socket (acetabulum) is located on the pelvis. In a normal joint the ball rotates freely within the socket. To facilitate movement the bones are shaped to perfectly match each other, with the socket surrounding the ball. To strengthen the joint, the two bones are held together by a ligament. The ligament attaches the femoral head directly to the acetabulum. Also, the joint capsule, which is a very strong band of connective, encircles the two bones adding further stability. The area where the bones actually touch each other is called the articular surface. It is perfectly smooth and cushioned with a layer of spongy cartilage. In the normal dog, all of these factors work together to cause the joint to function smoothly and with stability.
Hip dysplasia results from the abnormal development of the hip joint in the young dog. It may or may not be bilateral, affecting both right and left sides. It is brought about by the laxity of the muscles, connective tissue, and ligaments that should support the joint. Most dysplastic dogs are born with normal hips but due to genetic and possibly other factors, the soft tissues that surround the joint start to develop abnormally as the puppy grows. The most important part of these changes is that the bones are not held in place but actually move apart. The joint capsule and the ligament between the two bones stretch, adding further instability to the joint. As this happens, the articular surfaces of the two bones lose contact with each other. This separation of the two bones within a joint is called and this, and this alone, causes all of the resulting problems we associate with the disease.

What are the symptoms of hip dysplasia?

Dogs of all ages are subject to the symptoms of hip dysplasia and the resultant osteoarthritis. In severe cases, puppies as young as five months will begin to show pain and discomfort during and after vigorous exercise. The condition will worsen until even normal daily activities are painful. Without intervention, these dogs may be unable to walk at all by a couple years of age. In most cases, however, the symptoms do not begin to show until the middle or later years in the dog's life.
The symptoms are typical for those seen with other causes of osteoarthritis. Dogs may walk or run with an altered gait, often resisting movements that require full extension or flexion of the rear legs. Many times, they run with a 'bunny hopping' gait. They will show stiffness and pain in the rear legs after exercise or first thing in the morning. Most dogs will warm up out of the muscle stiffness with movement and exercise. Some dogs will limp and many will decrease their level of activity. As the condition progresses, the dogs will lose muscle tone and may even need assistance in getting up. Many owners attribute the changes to normal aging but after treatment is initiated, they are shocked to see much more normal and pain-free movement return.

All dogs wear a buoyancy jacket to help support their body weight in the water.

Damage to the spinal cord, whether it occurs spontaneously or results from an accident, can cause loss of voluntary muscle movement, changes in spinal reflexes or muscle tone, muscle shrinkage, and loss of touch and
pain sensations. This damage may be irreparable.

Paralysis
Paralysis is often caused by traumatic spinal cord injury from road traffic accidents or falls, gunshot wounds, or from intervertebral disc disease (see opposite). Partial paralysis affecting the hindquarters is more common than complete paralysis. Traumatic paralysis is treated with methylprednisolone intravenously, but, in most cases, surgery will also be necessary. Damage to a peripheral nerve, caused by a car accident or any other trauma in which a leg is jerked away from the body, can bring about loss of sensation in the muscles served by that nerve, and eventual paralysis. While in some cases it may be necessary to amputate the injured limb, a surgical procedure to transpose muscle attachments and produce a stiff, straight leg is sometimes a successful alternative.

Intervertebral Disc Dsease
The fibrous tissue that separates the intervertebral discs from the spinal cord (see above) can degenerate and rupture, causing pain and paralysis. For most dogs, corticosteroids are beneficial when given on the same day that injury occurs. After that, the most important part of treatment is rest, usually for at least two weeks.

Wobbler syndrome
This serious condition, also known as cervical spondylomyelopathy, occurs most frequently in young Great Danes and young to middle-aged Dobermans. It causes progressive loss of coordination in the hind legs, caused by instability of the vertebrae in the neck that results in compression and damage to the spinal cord. If untreated, partial paralysis may spread to the front legs. Wobbler syndrome responds best to early surgical correction.

Chronic Myelopathy
Primarily affecting German Shepherd dogs, although it does occur in other large breeds, chronic degenerative radiculomyelopathy (CDRM) is a debilitating disease that causes partial paralysis. Starting as early as six years of age, an affected dog slowly develops a painless lack of coordination of the hind legs. Over the following years, weakness evolves into partial paralysis, but pain perception and voluntary control over urinating and defecating remain intact. Unfortunately, while many treatments have been attempted, none have been discovered yet that slow down or reverse CDRM. Weight control and routine daily exercise are valuable, however, to ensure the best possible muscle tone.

All dogs wear a buoyancy jacket to help support their body weight in the water.

 

What is the cruciate ligament?

There are two cruciate ligaments in the knee joint, the cranial (or anterior) cruciate ligament and the caudal (or posterior) cruciate ligament. The cranial cruciate ligament is very commonly injured in dogs and this causes instability of the knee and may lead to other problems such as meniscal (cartilage) injury and osteoarthritis. It is rare for the caudal cruciate ligament to be injured.

What sort of dogs are affected?

Although in people, cruciate ligament rupture usually occurs during sports injuries incurred, for example, by skiers, soccer and rugby players, the situation in dogs is quite different. The cruciate ligament seems to weaken gradually in dogs, particularly in some larger breeds, and this means that the cruciate ligament may eventually rupture even during normal activity. Some large breed dogs can suffer cruciate ligament rupture from quite an early age (1-3 years) and often in both knees. Epidemiological evidence does indicate that certain breeds are at increased risk for cruciate rupture and these breeds include:

Labrador Retriever, Golden Retriever, Rottweiler, Mastiffs, Boxer, Newfoundland, West Highland White Terrier. However, many dog breeds can suffer from cruciate ligament rupture.

There is a suggestion that obesity also increases the risk of cruciate ligament rupture. This may be so, although further scientific information on this is required. Certainly avoiding obesity has been shown to reduce the severity of arthritis in other joints, so it seems to be sensible.

What causes cruciate ligament rupture?

The cause of the gradual degeneration of the cruciate ligament is not known. However, recent research indicates that even "normal" ligaments from dogs at risk of cruciate rupture are weaker compared to those breeds at low risk. It appears that the ligament structure is altered such that it is unable to function as it should and is prone to failure. Research continues to elucidate the reasons for ligament degeneration. This department currently has a research programme addressing this issue. Our recent finding will be published shortly and we have ongoing funding for further studies. In addition, we are also investigating the genetic basis for this disease through the UK Companion Animal DNA archive, in collaboration with other UK veterinary schools and the Animal Health Trust.

What are the signs of this condition?

Rupture of the cruciate ligament may occur suddenly or gradually and this can be reflected in the appearance of the signs of the condition which include lameness and stiffness of the knee. Full rupture of the cruciate ligament causes instability of the knee and this may lead to joint swelling and wasting (atrophy) of the muscles of the hindlimb, particularly the quardiceps muscle group. Dogs with cruciate ligament rupture often prefer to sit with the affected limb straightened out in front of them rather than tucked up; this is because they do not like to flex the knee.

How are these conditions diagnosed?

A clinical examination by a veterinary surgeon is the first step in diagnosis. If cruciate ligament rupture is suspected, further tests may be required, including x-rays, joint fluid analysis, arthroscopy, MRI, or exploratory surgery. Once the cruciate ligament is ruptured, about 40-60% of knees will also develop injury to one of the cartilages of the knee. Osteoarthritis will develop in all knees with cruciate rupture, but may not cause problems for many months or years.

All dogs wear a buoyancy jacket to help support their body weight in the water.