The term "Hip Dysplasia" refers to a crippling canine hip joint defect.  While often considered a "big" dog affliction, this problem may occur in any breed.  The defect is basically an abnormal formation of the hip joint.   The ball and socket of a normal hip joint come together in a snug, tight fit which allows the joint to rotate with normal movement, but in which there is no looseness or slipping.   Dogs that are affected with hip dysplasia have hip joints in which the ball and socket do not fit together correctly and in which the bones may slip and slide with the dog's movement.  Dysplastic dogs may have hip joint formation ranging from only slightly abnormal to joints that are so defective that the ball (femur) may "pop-out" of the socket and become dislocated.  

 

This disorder is genetically linked, but nutrition, exercise and environment also play key roles in the expression of clinical symptoms.  Determining the level of impact of each of the above factors, in each affected dog, is quite difficult as the percentage that each factor effects each dog can vary tremendously.  In other words, while all dysplastic dogs have some level of genetic predisposition (called genotype) for this problem, it is the total combined effects of genetics, nutrition, exercise and environment that determine the expression of the disease. 

Some affected dogs may have a high genetic factor for the disease (as much as 85%), while others can have a much lower genetic factor for disease (as little as 25%).   The genetic factor for hip dysplasia in a given dog is the result of a combination of the percentage of genetic material for hip dysplasia that is inherited from each parent.  The greater the genetic contribution for loose hips, malformed bone or abnormal muscle mass from the sire and dam, the greater the genetic risk for hip dysplasia in the resulting offspring.

As stated above, genetics play only one part in the expression of this disease, and that role varies greatly in each dog.  In addition, the effects of environment are also highly variable and how these factors all fit together with genotype to result in clinical symptoms of disease is not completely understood.  It is known that, if the nutrition, exercise and environment for the dog with a high genetic factor for hip dysplasia happen to be perfectly managed, this "high risk" dog may not show clinical signs of disease until middle or old age.  At the same time, a dog with a low genetic factor for the disease may show severe symptoms of dysplasia while still a young puppy, if the same environmental factors are improperly managed.  Further, two dogs with the same genetic makeup (genotype) will have markedly different expressions of disease if they are raised in different environmental conditions. 



Environmental factors that may affect the expression of clinical symptoms of hip dysplasia include:

• Nutrition - Growing puppies should not be allowed to become overweight.  This does NOT mean puppies should be put on a diet that restricts protein and fat.  This DOES mean that puppies should be fed a high-quality, meat-based food in appropriate proportions for their daily needs.  The goal in feeding your growing puppy is to provide adequate and proper nutrition for continuous, steady, normal growth, while preventing overly-rapid growth that could increase the potential for the dog to develop hip dysplasia.

• Exercise - A puppy with a dysplastic genotype may develop more severe arthritis and have more difficulty later in life if it is allowed to engage in strenuous physical activity as a puppy.  A puppy that may be predisposed for hip dysplasia should not be allowed to engage in EXCESSIVE climbing, running or jumping.  Jumping up and down from any raised surface (the couch, pick-up trucks, etc.) should not be allowed and going up and down stairs should be minimized.  While these activities do not "cause" hip dysplasia and are not an issue in the non-dysplastic puppy, they can subject growing hip structures of the predisposed dysplastic dog to unnecessary stress and trauma.   This impact is increased if the puppy is overweight.

• Footing - Many breeders and owners feel that the surfaces on which a dog is raised may play a role in the expression of hip dysplasia.  Slippery surfaces within the whelping box or puppy pens should be avoided.  Plastic, newspaper, concrete or any surface on which the pup/dog is unable to get or maintain its footing should be covered with a washable pad, carpet, blanket or other textured surface that will allow the puppy/dog to move without slipping.

There are many physical changes that occur in the hips of a dysplastic dog.  While these changes are generally not visible to the dog's owner, they eventually result in visible symptoms of disease.  Some of the physical changes associated with hip dysplasia are:

• Musculature - Dysplastic dogs are known to have reduced pelvic musculature around the hip joint.  It is unknown whether this decrease in musculature is a result of hip dysplasia or a contributing factor to the disease.

• Ligament of the Head of the Femur - This ligament attaches to the head of the femur from the center of the hip socket.  In a dysplastic dog, this ligament may be stretched or torn which results in a less stable hip joint. 

• Joint Capsule - The joint capsule surrounds the joint tissue, providing some support to the joint, and it produces synovial fluid to nourish and lubricate the joint cartilage.  In a dysplastic dog, the joint capsule may be irritated, stretched or scarred and these changes can result in the capsule losing elasticity, which in turn, can inhibit the range of motion in the joint. 

• Cartilage - In a dysplastic hip joint, the cartilage within the joint may thicken or thin where there is abnormal pressure applied to the cartilage surface.  In some areas, the cartilage may be eroded down to the underlying bone. 

• Bone Changes - Bone is alive and constantly responds to the stress and pressure applied to it.   As a dog's posture and movement are changed by the pain and discomfort of disease progression, abnormal stress is applied to the dog's hip joints.  In response to this abnormal pressure, the dog's bone will grow in a manner that helps distribute weight more evenly.  Unfortunately, these abnormal changes in the bone produce more abnormal stress and a vicious cycle ensues. 

The changes in bone structure in dysplastic hip joints is known as Degenerative Joint Disease.  As the changes within dysplastic hip joints continues and the dog's pain and discomfort increase, he will exhibit more noticeable symptoms of Canine Hip Dysplasia.  These symptoms may be somewhat different depending on the age of the dog, but most will be a similar unwillingness to perform certain physical activities.

• Signs of Dysplasia in Young Dogs - Many dysplastic pups will begin to show disease symptoms in the rapid growth period between four and nine months of age.  (Remember that some dogs may show no symptoms till middle or old age!)  One of the first indications that there is a problem may be a decreased range of motion in the rear legs (inability or reluctance to extend the legs very far backward).  This may make a dysplastic pup reluctant to jump up or stand on their hind legs.   They also will not be likely to lay on their bellies with their legs in a frog-like position with knees extended out to either side.  (Many pups rest or sleep this way and this is a good sign in relation to hips.)  Young dysplastic dogs will often "bunny hop" also.  This is when the dog runs with both back legs close together and the motion will look similar to the way a rabbit runs.

A dysplastic pup may be sore after exercise and may be reluctant to engage in further activity.  A dysplastic pup may have difficulty climbing stairs or inclines and may appear unsteady in the rear.  You may also notice that a dysplastic pup has an underdeveloped look in the rear with a bony appearance to the pelvic area.   In some severe cases of dysplasia, the dog may tend to rock its weight forward onto the front legs.  This can make it appear that the dog is tip-toeing on the rear legs.

As a puppy matures, symptoms may improve or disappear entirely.  However, a dysplastic dog is likely to develop arthritis later in life. 

• Signs of Dysplasia in Older Dogs - In dogs that have a late on-set of Degenerative Joint Disease, the dog may have learned to minimize or live with a certain amount of pain and discomfort, so the owner is unaware of the impending problem until much later in the dog's life.   However, as DJD begins to alter the older dysplastic dog's hip structure, an owner may notice their adult dog is not as active or involved with normal activities.  An affected dog may sit more often, may have difficulty getting up, may run with the rear legs together and may not be able to keep up when asked to perform normal physical activities such as going for walks or playing fetch.

The most common diagnostic tool for diagnosing Hip Dysplasia is a pelvic x-ray.  Most often this must be taken while the dog is under anesthesia to assure the dog is totally relaxed, the hips are properly positioned and that the dog doesn't move.  (It is possible to do the x-rays without anesthesia, but most vets are able to get the job done quicker and more accurately if the dog is not able to tense or shift position.)

There are 2 database programs set up within the United States that are used by breeders to help identify dogs and/or bloodlines with Canine Hip Dysplasia.  These programs offer veterinary evaluations of a particular dog's hips and then the dog receives a "rating" certifying whether the examining veterinarian(s) believe the dog to have normal or abnormal hips for its age and breed.  These databases compile information on each breed to help owners and breeders try to improve the health of their dogs.   

• OFA - The Orthopedic Foundation for Animals - This program has expanded its database to a number of health issues besides Hip Dysplasia.  Breeders and owners can search the database for information on animal health issues and specific health information on their dog's ancestors. 

• PennHIP - (University of Pennsylvania Hip Improvement Program) - "PennHIP is a multifaceted radiographic technology (x-ray) for hip evaluation. The technique assesses the quality of the canine hip and quantitatively measures canine hip joint laxity."¹  This procedure became available in 1993 and was developed as an alternative to OFA evaluation.   In this procedure, the hips of the dog being examined are x-rayed, but the comparison, evaluation and rating are based on a comparison of the hips of the tested dog to the hips of other dogs of the same breed.  (OFA evaluations rate all breeds on the same criteria.)  Many consider the PennHIP exam to be a more accurate evaluation as different breeds may have different susceptibility to osteoarthritis.  Additionally, since the PennHIP exam has set parameters that are not open to personal interpretation and since only PennHIP certified veterinarians can do the PennHIP evaluation, it is felt that the subjectivity that sometimes exists in evaluation and certification of dogs by the OFA is removed. 

For breeding and training purposes, OFA evaluations or a PennHIP exam can be done with a reasonable level of accuracy any time after the dog is 4 months of age.  However, for OFA certification purposes, any x-rays done before the dog is 2 years of age are considered preliminary exams.  The Orthopedic Foundation for Animals, which issues OFA hip certifications, will not issue a permanent certification number to dogs under 2 years of age. 

The following quote from the OFA web-site (http://www.offa.org/hipprelim.html) is in regards to the reliability of preliminary OFA hip evaluations:

"A recent publication compared the reliability of the preliminary evaluation hip grade phenotype with the 2 year old evaluation in dogs and there was 100% reliability for a preliminary grade of excellent being normal at 2 years of age (excellent, good, or fair). There was 97.9% reliability for a preliminary grade of good being normal at 2 years of age, and 76.9% reliability for a preliminary grade of fair being normal at 2 years of age. Reliability of preliminary evaluations increased as age at the time of preliminary evaluation increased, regardless of whether dogs received a preliminary evaluation of normal hip conformation or HD. For normal hip conformations, the reliability was 89.6% at 3-6 months, 93.8% at 7-12 months, and 95.2% at 13-18 months. These results suggest that preliminary evaluations of hip joint status in dogs are generally reliable."

Early PennHIP evaluation is considered more accurate than OFA exams and is considered permanent on any dog over 16 weeks of age.

Approximately 10% of dogs evaluated by OFA as Dysplastic are diagnosed due to only one affected hip.  There is some conjecture that it is possible that these dogs may actually have suffered an injury that resulted in changes to the hip joint and that these dogs are not actually Dysplastic.

While many breeders swear by OFA and PennHIP exams and maintain that all breeding stock must be tested to assure that genetic defects are not passed to future generations, it must be noted that this testing and certification DO NOT guarantee that any particular dog will produce 100% healthy, non-Dysplastic puppies.   Two dogs that have been rated "Excellent" by OFA and which have acceptable PennHIP evaluations can still produce severely Dysplastic puppies.  Tested, certified clear parents may have as much as a 25% chance of producing Dysplastic puppies in a given litter. 

Testing of two particular dogs that are bred to each other is not a sure-fire method of preventing Hip Dysplasia due to the fact that tested dogs may carry the genetic material for Hip Dysplasia and yet be unaffected themselves.   Testing results for any given dog can be misleading since even if one dog's hips test as "normal", 1 or 2 or 3 of that dog's littermates could be Dysplastic.  If the littermates of a dog that tests "normal" are Dysplastic, then the "normal" dog is almost certain to carry some genetic material for the defect and may well produce Dysplastic puppies.   Since it is extremely rare that all puppies from a litter are OFA or PennHIP evaluated (at least in Cockers!), it can be difficult for even the most responsible breeders to entirely eliminate the risk of producing Dysplastic puppies. 

To obtain a reasonable assessment of the risk of Hip Dysplasia for puppies from a particular breeding, a breeder would need to obtain AT LEAST the results of hip evaluations for the parents and grand-parents of the litter AND testing results for ALL of the siblings of the parents and grandparents of the litter.    Only when the test results of all of the dogs listed above had been compiled into a genetic family tree, would a breeder have a reasonable amount of information to evaluate the potential of whether a particular puppy might or might not have inherited Hip Dysplasia.  (This scenario is assuming that the parents and grandparents have a reasonable number of siblings to test and compare results from - approximately 6 pups per litter.  Without sufficient animals for comparison, testing might need to include another entire generation or two behind the grandparents.)

Due to the complexity of this health issue, there are no absolute guarantees that a purchased puppy, whether from tested or untested parents, will or will not be affected with Hip Dysplasia.  Your best bet for protecting your investment in a purchased dog (whether for pet or show) is to buy from a breeder that will guarantee their puppies to pass an OFA and/or PennHIP exam. 

Hip Dysplasia is not considered a major health risk within the breed, but it is known to occur regularly.  The following table shows the OFA statistics for Cocker Spaniels based on tested dogs from January 1974 through December 2004.*²

Breed	Rank	Number of Evaluations	Percent "Excellent"	Percent "Dysplastic"
COCKER SPANIEL	103	9201	10.3	6.2

In the  table above, "Rank" identifies the order in which the breed falls for frequency of occurrence according to OFA testing.  In other words, there are 102 breeds within the OFA database that show a higher incidence of Hip Dysplasia than Cocker Spaniels.  The percentage listed as "Excellent" shows the percentage of tested Cocker Spaniels that were evaluated as having the best hips.  There are 2 other ratings, "Good" and "Fair", which are considered "Normal" ratings.    The "Dysplastic" percentage shown includes all dogs considered to be Dysplastic, regardless of actual rating.

While I do believe that testing for genetic diseases and defects has a place in improving the health of future generations of Cocker Spaniels, I also feel that we must be realistic and cautious in how we use and interpret the data we collect from such tests.  OFA Hip Dysplasia evaluations and the automatic removal of breeding stock from the gene pool based on this one exam is one area in which I have a rather high level of concern.   My concern is based on the subjectivity of OFA exams.  I think the quote below adequately illustrates my concerns!

"A study conducted at the University of Pennsylvannia revealed a startling amount of variability for hip interpretations among non-OFA and OFA board certified radiologists. When these radiologists were asked to grade hips based on the OFA rating system (excellent, good, fair, borderline CHD, mild CHD, moderate CHD or severe CHD), non-OFA readers agreed with an OFA reader in fewer than 50% of the cases. The most disturbing revelation was that when each radiologist was asked to rate certain cases a second time, each radiologist gave the same rating that he had given the first time on less than half the radiographs."^*3

1* From the PennHIP website.

2* From the OFA website.

3* From Wing and Wave Labradors website.

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