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This article covers Hip dysplasia, a condition affecting the hip joint, which occurs in humans but is more commonly associated with animals, especially dogs (Canine hip dysplasia). For Dysplasia itself, a different condition related to pre-cancerous changes in cellular structures, please see the article Dysplasia.

Hip dysplasia is a congenital disease that, in its more severe form, can eventually cause crippling lameness and painful arthritis of the joints. It is caused by a combination of genetic and environmental factors. It can be found in many animals and occasionally in humans, but is most commonly associated with dogs, and is not uncommon in many dog breeds, particularly the larger breeds.

Hip dysplasia is one of the most studied veterinary conditions in dogs, and the most common single cause of arthritis of the hips. In humans it occurs at a rate of about 4 births per thousand (0.4%)

Overview

Normal hip anatomy

In the normal anatomy of the hip joint, the thigh bone (femur) is connected to the pelvis at the hip joint. The almost spherical end of the femur (the caput, or caput ossis femoris) fits into the socket of the hip joint (the acetabulum), to form a smooth joint with a wide range of leg movement, and the force of movement and walking is buffered by the joint itself, a mold made partly of cartilage into which the caput neatly fits.

It is important that the weight of the body is carried on the bony part of the acetabulum, not on the cartilage part, because otherwise the caput can glide out of the acetabulum, which is very painful. Such a condition also may lead to maladaptation of the respective bones and poor articulation (movement) of the joint.

Dysplastic hip anatomy

In a hip sufferring from dysplasia, two things are commonly abnormal. First, the caput is not deeply and tightly held by the acetabulum. Instead of being a snug fit, it is a loose fit, or a partial fit. Secondly, the caput or acetabulum are not smooth and round, but are mis-shapen, causing abnormal wear and tear or friction within the joint as it moves.

The body reacts to this in several ways. First, the joint itself is continually repairing itself and laying down new cartilage. However cartilage repair is a relatively slow process (the most rapid bodily repairs are often in systems with a blood flow, which cartilage lacks).

So the joint may suffer degradation due to the abnormal wear and tear, or may not support the body weight as intended. The joint becomes inflammed and a cycle of cartilage damage, inflammation and pain commences. This is a self-fueling process, in that the more the joint becomes damaged, the less able it is to resist further damage. The inflammation causes further damage. The bones of the joint may also develop osteoarthritis, visible on an X-ray as small outcrops of bone, which further degrade the joint.

To reduce pain, the animal or person will typically reduce their movement of that hip. In animals this may be visible as "bunny hopping", where both legs move together, or less dynamic movement (running, jumping), or stiffness. Since the hip cannot move fully, the body compensates by adapting its use of the spine, often causing spinal, stifle (a dog's knee joint), or soft tissue problems to arise.

The underlying deformity of the joint may get worse over time, or may remain static. A dog may have good X-rays and yet be in pain, or may have very poor X-rays and apparently almost no problems. The hip condition is only one factor to determine the extent to which dysplasia is causing pain or affecting the quality of life. In mild to moderate dysplasia it is often the secondary effects of abnormal wear and tear or arthritis, rather than dysplasia itself, which is the direct causes of visible problems.

Causes and effects

In dogs, there is considerable evidence that genetics plays a large role in the development of this defect. There might be several contributing genetic factors, including a femur that does not fit correctly into the pelvic socket, or poorly developed muscles in the pelvic area. Large and giant breeds are susceptible to hip dysplasia, and Cocker spaniels and Shetland sheepdogs are also known to suffer from it. Cats are also known to have this condition, especially Siamese.

In dogs, the problem almost always appears by the time the dog is 18 months old. The defect can be anywhere from mild to severely crippling. It can cause severe osteoarthritis eventually.

It is most common in medium-large pure bred dogs, such as German Shepherd Dogs, Labrador or Golden retrievers, Rottweilers and Mastiffs, but also occurs in some smaller breeds such as spaniels and occasionally (usually with minor symptoms) in cats.

Hip dysplasia in humans

In humans, hip dysplasia manifests in early life at a rate of about 4 per thousand. It usually manifests from birth, and is associated in part with conditions such as breech birth and other conditions. It can be detected by a "click" in the hip (although not all clicks indicate hip dysplasia), and confirmed by ultrasound.

Early hip dysplasia can usually be corrected using a Pavlik harness in the first year of life with usually normal results. Hip dysplasia that develops later can be more problematic.

Source and further information: orthoseek.com

Clinical detection and testing

Symptoms

Dogs might exhibit signs of stiffness or soreness after rising from rest, reluctance to exercise, bunny-hopping or other abnormal gait (legs move more together when running rather than swinging alternately), lameness, pain, reluctance to stand on rear legs, jump up, or climb stairs, subluxation or dislocation of the hip joint, or wasting away of the muscle mass in the hip area. Radiographs (X-rays) often confirm the presence of hip dysplasia, but radiographic features may not be present until two years of age in some dogs. Moreover, many affected dogs do not show clinical signs, but some dogs manifest the problem before seven months of age, while others do not show it until well into adulthood.

In part this is because the underlying hip problem may be mild or severe, may be worsening or stable, and the body may be more or less able to keep the joint in repair well enough to cope. Also, different animals have different pain tolerances and different weights, and use their bodies differently, so a light dog who only walks, will have a different joint use than a more heavy or very active dog. Some dogs will have a problem early on, others may never have a real problem at all.

Each case must be treated on its own merits, and a range of treatment options exist.

Diagnosis

The classic diagnostic technique is with appropriate X-Rays and hip scoring tests. These should be done at an appropriate age, and perhaps repeated at adulthood - if done too young they will not show anything. Since the condition is to a large degree inherited, the hip scores of parents should be professionally checked before buying a pup, and the hip scores of dogs should be checked before relying upon them for breeding. Despite the fact that the condition is inherited, it can occasionally arise even to animals with impeccable hip scored parents.

In diagnosing suspected dysplasia, the X-ray to diagnose and confirm the internal state of the joints, is usually combined with a study of the animal and how it moves, to confirm whether it is being affected in its quality of life. Evidence of lameness or abnormal hip or spine use, difficulty or reduced movement when running or navigating steps, are all evidence of a problem. Both aspects have to be taken into account since there can be serious pain with little X-ray evidence.

It is also common to X-ray the spine and legs, as well as the hips, where dysplasia is suspected, since soft tissues can be affected by the extra strain of a dysplastic hip, or there may be other undetected factors such as neurological issues (eg nerve damage) involved.

There are several standardized systems for categorising dysplasia, set out by respective reputable bodies (Orthopedic Foundation for Animals/OFA, PennHIP, British Veterinary Association/BVA). Some of these tests require manipulation of the hip joint into standard positions, in order to reveal their condition on an X-ray, and since this is very painful and must be held still for a clear image, often the animal will be anaesthetised or sedated to achieve clear diagnostic results.

Long term pain

It is important to note that a dysplastic animal has probably lived with the condition since it was very few months old, and has therefore grown up taking the chronic pain for granted and have learned to live with it. Dogs suffering such pain do not usually cry out or show it. Sometimes, they will suddenly and abnormally sit down when walking, or suddenly refuse to walk or climb objects which they usually would, but this can equally be a symptom of many other things, including a thorn in the paw, or a temporary muscle pain. So pain recognition is less common a means of detection than the visible gait and other abnormalities described above.

Treatment

Overview

There is no complete cure, although there are many options to alleviate the clinical signs. The aim of treatment is to enhance quality of life. Crucially, this is a congenital condition and so will change during the life of an animal, so any treatment is subject to regular review or re-assessment if the symtoms appear to get worse or anything significantly changes.

If the problem is relatively mild, then sometimes all that is needed to bring the symptoms under control are suitable medications to help the body deal better with inflammation, pain and joint wear. In many cases this is all that is needed for a long time.

If the problem cannot be controlled with medications, then often surgery is considered. There are traditionally two types of surgery - those which reshape the joint to reduce pain or help movement, and hip replacement for animals which completely replaces the damaged hip with an artificial joint, similar to human hip replacements.

Non surgical interventions

Non surgical intervention is typically a combination of an anti-inflammatory painkiller, such as carprofen (often sold as Rimadyl and used to treat arthritis), and a glucosamine based nutritional supplement to give the body additional raw materials used in joint repair.

Glucosamine can take 3-4 weeks to start showing its effects, since it can take up to 6 weeks to reach full therapeutic effect in the body, so the trial period for medication is usually around 3-5 weeks minimum before assuming it isn't working. It's important to remember that glucosamine is not a medication, it's a raw material, so the body still takes considerable time to build more cartilage once it has access to this raw material.

It is also common, if necessary, to try multiple anti-inflammatories over a further 4-6 week period. This is since an animal will often respond to one type, but will fail to respond to another. If one anti-inflammatory does not work, a vet will often try one or two other brands for 2-3 weeks each, also in conjunction with ongoing glucosamine, before necessarily concluding that the condition does not seem responsive to medication. Typical alternatives include tepoxalin (Zubrin) or other NSAIDs suitable for animals.

It should be noted that carprofen, and other anti-inflammatories in general, whilst very safe for most animals, can sometimes cause problems for some animals, and (in a few rare cases) sudden death through liver toxicity. This is most commonly discussed with carprofen but may be equally relevant with other anti-inflammatories too. As a result it is often recommended to have monthly (or at least, twice-annually) blood tests performed, to confirm that the animal is not reacting badly to the medications, if these are being used. Such side effects are rare but worth being aware of, especially if long term use is anticipated. (Main article: Rimadyl)

This regime can usually be maintained long term, for as long as it is effective in keeping the symptoms of dysplasia at bay.

Surgical interventions

If medications fail to maintain an adequate quality of life, surgical options may need to be considered. These may attempt to modify or repair the hip joint, in order to allow pain free usage, or may in some cases completely replace it.

Hip modification surgeries include excision arthroplasty, in which the head of the femur is removed and reshaped or replaced, and pelvic rotation (also known as triple pelvic osteotomy, or pubic symphodesis) in which the hip socket is realigned, may be appropriate if done early enough. These treatments can be very effective, but as a rule tend to become less effective for heavier animals - their ability to treat the problem becomes reduced if the joint has to handle more pressure in daily life. Pelvic rotation is also not as effective if arthritis has developed to the point of being visible on X-rays . Hip modification surgeries usually accept some reduction in hip function, in return for improved quality of life, pain control, and a reduction in future risk.

Hip replacement is expensive but (since it completely replaces the faulty joint) has the highest percentage of success especially in severe cases, usually restores complete mobility if no other joint is affected, and also completely prevents recurrence. Hip replacement for dogs, can sometimes also be a preferred clinical option for serious dysplasia in animals over about 40 - 60 lbs (20-30 kg), a weight that excludes certain other surgical treatments. For additional information and considerations for canine hip replacement and other surgeries, see main article: Hip replacement (animal).

Other options under exploration include:

• DARthroplasty (Dorsal Acetabular Rim arthroplasty) is a technique developed by Dr. Barclay Slocum and Theresa Devine Slocum whereby cortico-cancellous bone strips, taken from the iliac crest, are contoured over the femoral head and sutured to the dorsal hip joint capsule and packed with additional cancellous bone graft dorsally to eventually anchor to drill holes in the original dorsal acetabulum. The new "shelf" eventually becomes an extension of the original acetabulum, thereby providing support and eliminating subluxation of the hip joint. The joint capsule becomes the new joint surface.

• Pubic symphysiodesis (also known as juvenile pubic symphysiodesis, or JPS), is a procedure for very young dogs that manipulates the way the pelvis grows to create a tighter hip. It involves cauterizing the growth plates of the pelvis, in other words, the part of the pelvis which would usually grow and spread in puppyhood, no longer does so. To compensate, the rest of the pelvis grows outward, in a manner which enhances the "socket" of the hip and provides better support than that dog would have had naturally. Since it relies on growth in puppyhood, it has a very tight window for surgery -- currently no sooner than about 4 months and no later than about 5 months. This is compatible with hip scoring of puppies at 4 months.

Prevention

Overfeeding puppies and young dogs, particularly in the giant breeds, might aggravate the problem or bring it on earlier, because pups tend to be more active, less aware of their physical limitations, and have immature bones and supporting structures carrying their weight. Dogs from breeds which are known to be prone to dysplasia, can be kept slightly leaner than normal until around 2 years old, by which time the bones are full strength and the animal can be easily brought up to its normal adult weight. Overexercising young dogs whose bones and muscles have not yet fully developed might also be a contributing factor.

Responsible breeders who track the incidence of hip dysplasia have been able to reduce the incidence in some breeds but not to eliminate it altogether.

References

• Ettinger, Stephen J.;Feldman, Edward C. (1995). Textbook of Veterinary Internal Medicine (4th ed. ed.). W.B. Saunders Company. ISBN 0-7216-6795-3. {{cite book}}: |edition= has extra text (help)CS1 maint: multiple names: authors list (link)
• Siegal, Mordecai (editor); UC Davis School of Veterinary Medicine Book of Dogs, 1995. Harper Collins. ISBN 0-06-270136-3.
• Slocum, B. & Slocum, T.D. DARthroplasty. In: Bojrab, M.J., ed. Current Techniques in Small Animal Surgery, 4th Ed. Baltimore: Williams & Wilkins 1998: 1168 - 1170.

External links

• Orthopedic Foundation for Animals
• workingdogs.com
• Columbia Animal Hospital, detailed discussion of condition, prognosis and different surgeries

• Dog health
• Cat health