Hip Dysplasia

Hip dysplasia (HD), literally defined as an abnormal development of the hip joint, was first reported in the dog in 1935 by Dr. G.B. Schnelle. Little to no further information was added to his report over the following decade, due primarily to limited availability of radiographic equipment and radiographic expertise within the veterinary profession.

Popularity of the working dog, particularly the German Shepherd Dog, increased greatly in the late 1940s and the importance of HD became evident to breeders, dog owners, and the veterinary profession. Unrelated, but concurrently, veterinary education underwent an explosion in numbers of veterinary colleges and in quality of specialized education. Rapid advances in the veterinary profession made it difficult for most general practicing veterinarians to remain current with expanding knowledge in animal diseases. To provide the best possible diagnosis and patient care, multiple specialty colleges were formed, including the discipline of radiology which became a recognized specialty in 1966 through the American College of Veterinary Radiology (ACVR).

Hip dysplasia has been reported in man and in most domestic species of animals. In some breeds of dogs and cats, it is the most common cause of osteoarthritis (degenerative joint disease). In recent years, interest in canine HD research has been at an all-time high, as evidenced by the number of conferences focusing on the subject and by the number of new publications in scientific journals and popular magazines.

We now know that HD is a more complex disease than what was first thought. The complexity of the problem is expected to, and has produced, research findings that appear to be contradictory. These research reports, and anecdotal writings that continually appear in the popular press, contribute to confusion and frustration in breeders and veterinarians not familiar with the scientific literature. Thus, few diseases in animals have resulted in such extreme emotional reactions, controversy, or monetary expense as HD.

While it is useful to summarize results from the scientific literature, in the final analysis more research is needed to find answers to the many unresolved questions about HD.

Hip dysplasia is currently accepted to be an inherited disease caused by the interaction of many genes (polygenic). In animals that are genetically predisposed, there are unknown complex interactions of genes with the environment that bring about the degree of phenotypic expression (mild, moderate, or severely hip dysplasia) of these genes within an individual.

At this time, selectively breeding for normal hips is the only means to reduce the genetic frequency of HD.

Radiography is currently the accepted means for evaluating the hip status and it is well documented that the frequency of HD can be significantly reduced using the standard hip extended view.

It is expected that future research studies will refine these currently accepted tenets. For example, advances in molecular genetics may bring about DNA tests to replace radiography as the primary diagnostic tool, or environmental factors such as medical or nutritional treatments may be identified that will overcome the genetic expression of HD in an individual animal.

There are many debates surrounding the myriad of possible factors that may influence or initiate one or more aspect of HD. While interesting to consider, the breeder and veterinarian can most successfully pursue their mutual goals by maintaining their focus on current knowledge without becoming mired in the debate. The responsible breeder attempts to produce the best possible representatives of the breed. The veterinarian assists the breeder in accomplishing this objective by encouraging breeder education, maintaining the general health of the dog and cat, and providing the best possible treatment when appropriate.

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Development of the hip joint

The embryonic hip joint and its supporting structures begin to develop from an undifferentiated mass of embryonic tissue. The differentiation of this tissue into the distinct parts of the hip joints is predetermined by a genetic code. Embryonic tissues form muscles, a specialized connective tissue that encases the joint (the joint capsule), and joint ligaments. A cartilage mold forms the unique parts of the ball and socket joint with the acetabulum functioning as the socket and the head of the femur functioning as the ball. These structures continue to grow and differentiate as the embryo matures. Ossification (bone formation) begins at approximately 49 days of pregnancy but the degree of skeletal maturity at birth appears to be breed dependent. That is, ossification in some breeds is more advanced than in others, which contributes to the continued difference in rates of skeletal growth after birth.

The surfaces of the femoral head and acetabulum are covered with smooth articular cartilage. A thin layer of fluid (synovial fluid) serves as a lubricant for the joint, carries nourishment for the articular cartilage, and separates the opposing surfaces. The head of the femur is attached to the depth of the acetabulum by a ligament (round ligament). The joint capsule encases the joint by attaching to the neck of the femur and to the rim of the acetabulum and is lined by a specialized tissue, the synovial membrane, which produces the synovial fluid. Muscles encase the entire hip structure and serve to stabilize and move the joint. The major pelvic muscles exert a forward and upward pressure on the femoral head during movement and the head of the femur is held in the acetabulum by the pelvic muscles, the joint capsule, surface tension, and the round ligament. Proper development of the joint depends upon the head of the femur being held firmly within the acetabulum.

The hip joint of the dog is reported to be normal at birth. After birth, a complex interaction of multiple genetic and environmental factors can initiate incorrect fit or function of one or more of the parts of the hip joint, although the exact pathogenesis of these interactions is not fully understood at this time. It is likely that these factors may differ between genetic lines, since HD is caused by the interaction of many genes. Currently, any attempt to define the process in an exact sequence of events is speculative.

Regardless of what the initiating interaction of factors may be, abnormal looseness (joint laxity) is generally accepted to be the most common abnormality that results in the pathologic changes of HD. However, some dogs with tight hips but shallow acetabula have also been reported to develop dysplastic changes.

Many of the early (2-14 weeks) pathologic changes are not readily detectable by clinical or radiographic examination. These include: swelling, fraying, and possible rupture of the round ligament; inflammation of the synovial membrane (synovitis) resulting in synovial fluid changes; stretching of the joint capsule; and damage to the cartilage mold of the acetabulum and femoral head. These structural alterations result in joint instability and subluxation, which are followed by erosion of the articular cartilage, changes in the bone beneath the articular cartilage, micro fractures of the dorsal acetabular rim, filling in of the acetabulum, remodeling (change in size, shape or architecture) of the femoral head, neck and acetabular rims, and production of osteophytes (bone spurs) around the joint.

Depending on the individual dog and the initiating factors of joint instability, the changes occur at varying rates and to differing degrees. Severe cases can be detected radiographically as early as 8 to 12 weeks of age, while others may not be evident until later in life (greater than two years of age).

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Clinical finding of dysplasia

While most animals with HD do not exhibit clinical signs, those that do are usually first affected between three and 15 months of age. In some, the signs may not be observed until later in life. The signs vary from decreased exercise tolerance to severe crippling. They include: a reluctance or inability to go up or down stairs, difficulty in rising from a sitting or prone position, bunny-hopping gait when running, stiffness early in the morning that improves as the animal warms up, changes in disposition due to pain, lameness after exercise, a wobbly gait, a clicking sound when walking, and many others. Many animals will shift their center of gravity forward in an effort to relieve weight and pressure on the hips, thereby developing disproportionately greater muscle mass in the front limbs as compared to the rear limbs.

The hip joint is a weakened structure in dysplastic animals and is more prone to injury from normal activities such as jumping off a couch or rough housing with a playmate. Frequently, this results in an acute lameness that appears as if it might have been caused by injury, whereas the underlying dysplasia actually made the joint more susceptible to injury. Obviously, the normal hip can be injured, but radiographic examination can usually distinguish between a hip problem due to dysplasia and one due to other causes.

HD cannot be diagnosed by observing how the animal moves, acts, lies down, etc. Clinical signs may have other causes, and therefore a complete orthopedic and radiographic examination is required before arriving at the conclusion that the signs are caused by HD.

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Radiographic assessment of the hip joint

Modern breeds vary widely in body size, shape and pelvic conformation. Because of these differences, OFA classifications are based on comparisons among individuals of the same breed and age. Knowledge of hip phenotype can be valuable for the breeder in selection against hip dysplasia and in estimating the potential for an active working life. It is assumed that radiographs submitted to OFA are generally screened by the veterinarian and the more obvious cases of HD are probably not submitted. Therefore, the actual frequency of HD in the general population is not known, but has been approximated by Corley (1997) and Rettenmaier (2002) to be higher than reported by OFA. However, the main objective of the OFA is to identify phenotypically normal animals as potential breeding candidates. Thus, the OFA reported breed frequency of HD can be used as a benchmark for breeders to gauge their breeding program's relative position.

Historically, the diagnosis of HD has been determined by radiographic examination of the hips according to the protocol established by the American Veterinary Medical Association. In this standard hip extended position (ventrodorsal view), the animal is placed on its back with the pelvis symmetrical, both femurs extended and parallel, and with the stifles (knees) rotated internally placing the patellas (knee caps) on the midline. The radiograph should include the last two lumbar vertebra and the stifle joints. It is essential, particularly in marginal cases, to obtain proper position and radiographic technique.

The radiographic criteria of subluxation, shallow acetabula, remodeling, and/or secondary degenerative joint disease are well documented. However, interpretation and application of these criteria differ between breeds, age of evaluation and veterinarians. Figure 1 provides the nomenclature of the hip structures that are evaluated by the veterinary radiologist. The veterinary radiologist is concerned with deviations in these structures from the breed normal, and with evidence of subluxation and degenerative joint disease (also called arthritis, osteoarthritis, or osteoarthrosis).

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Multiple anatomic areas of the hip are evaluated (Fig. 1) including:

1. Craniolateral acetabular margin - Area where abnormal bone spurs (osteophytes) develop as the dysplastic joint attempts to stabilize the biomechanically unstable femoral head.

2. Cranial acetabular margin - Area visualized in conjunction with the hip ball to assess the degree of congruity and confluence of the hip joint.

3. Femoral head (hip ball) - Assessed to determine its fit into the socket and degree of congruity with the cranial acetabular margin forming the joint space.

4. Fovea capitus - Normal flattened area on ball for attachment of the round ligament; can be mistaken for degenerative changes if there is lack of familiarity or inexperience in interpretation of hip radiographs.

5. Acetabular notch - Area visualized to help assess depth of socket or "degree of fit".

6. Caudal acetabular rim - Area where bone spurs can form.

7. Dorsal acetabular margin - Area visualized to assess the depth of the hip socket (acetabulum) and percent coverage of the femoral head.

8. Junction of femoral head and neck - Area visualized to assess size, shape, and architecture of the femoral head/neck. The neck of the hip ball is usually the earliest and most commonly affected area where degenerative changes occur in a dysplastic joint. In the dysplastic joint, new bone builds up at the site of attachment of the joint capsule and muscular attachments. This is a result of abnormal stress created by incongruent articulation of the ball with the acetabulum during movement.

9. Trochanteric fossa - Area to assess for any microtrabecular bone changes or new bone proliferation.

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Unilateral hip dysplasia

Hip dysplasia may occur in only one hip (unilateral). In man, the left hip is reported to be involved more frequently than the right at a ratio of 10:1. Unilateral dysplasia in dogs follows a similar pattern, but the predominantly affected side is breed dependent. It occurs more frequently in the left hip of the Labrador Retriever, Newfoundland, Akita, and Golden Retriever, but more frequently in the right hip of the Rottweiler. The German Shepherd Dog does not appear to have a side (left or right) predilection. Frequency of unilateral HD is also independent of the frequency of HD in a breed.

The reported frequency of unilateral HD varies from 3% to more than 30% of the dysplastic dogs depending on the population studied. It appears that frequency of unilateral HD is higher in some genetic lines within a breed, than in other lines within the same breed. Furthermore, the same hip (right or left) is repeatedly involved within the line. That is, when several or influential ancestors have unilateral HD in, for example, the left hip then the progeny that are unilaterally affected will almost invariably show the abnormality in the left hip.

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Hip dysplasia database

The OFA hip dysplasia control database functions as a voluntary screening service and as a database of hip status for dogs and cats of all breeds. Information intended to aid breeders in reducing the incidence of this polygenic problem is made available from this resource. The necessity for such a central repository was recognized by the Golden Retriever Club of America and the German Shepherd Dog Club of America, which provided the impetus for formation of the OFA.

The owner or agent should notify the veterinarian, before the x-ray examination, that the purpose is for OFA evaluation. This is best done at the time of making an appointment in order to ensure that application forms are available and that the required procedures are followed. The owner also should provide the animal's registration certificate (or copy of this information) and the animal's tattoo or microchip number at the time of radiography.

General procedures

Age - Only dogs and cats that are 24 months of age or older at the time of radiography can qualify for an OFA breed registry number. The hip joint status of younger animals will be evaluated, but only a preliminary consultation report will be issued.

Restraint - Obtaining a properly positioned film may require chemical restraint. The type of restraint used - physical, sedative, tranquilizer, or general anesthesia - is best determined by the veterinarian. The dog should not be fed on the day of radiography.

Positioning - Dorsal recumbency with the rear legs extended and parallel to each other and the stifles rotated internally is the prescribed position (Fig. 2). This standard ventrodorsal view is accepted worldwide as the basis for evaluation of hip joint status with respect to hip dysplasia. Care should be exercised to be sure the patient is positioned correctly.

Film size - For large and giant breeds of dogs, 14 X 17 inch film size is recommended. Smaller film sizes can be used for smaller breeds if the area between the sacrum and stifles can be included.

Film Identification - Permanent animal identification in the film emulsion is required for radiographs to be eligible for OFA registration. Lead letters, an I.D. camera, or radio opaque tape can be used to identify the film with: a) the hospital or veterinarian's name, date taken and registered name or number of the dog, or b) the veterinarian's or hospital's identification number or case number. In this latter case (b), the radiograph must be accompanied by a signed note from the veterinarian referring to such film by its identification number, and stating the date taken, and registered name or number of the dog as in (a) above.

If the above required information is illegible or missing, the OFA cannot accept the film for registration purposes.

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Figure 2
A standard position radiograph of the pelvis that has been appropriately positioned will have symmetrical obturator foreamen (long arrow), symmetrical wings of the ilium (arrowhead) and kneecaps that are centered over the knees (short arrow) with the legs extended parallel to one another.
Figure 3
A standard position radiograph of the pelvis that has been inappropriately positioned will have asymmetrical obturator foreamen and asymmetrical wings of the ilium (long arrow). The distortion caused by poor positioning can inaccurately make one hip look worse than it actually is by creating a more shallow appearing hip socket (short arrow) and the opposite hip appear better than it actually is by creating more depth to the hip socket over the hip ball (arrowhead). The OFA will routinely mail poorly positioned films back to the referring veterinarian and request repeating the study.

Exposure - Good contrast is essential. Technique settings (low kVp and high mAs), film-screen combinations and use of grids are all considered in producing the desired contrast. Film contrast should be such that the microtrabecular pattern of the femoral head and neck are readily seen. The dorsal-lateral margin of the acetabulum must also be visible.

Radiation safety - Proper collimation and protection of attendants are the responsibility of the veterinarian. Gonadal shielding is recommended for male dogs. Radiography of females in season or pregnant should be avoided.

Application information - The owner or agent should complete and sign the OFA application form, and the information is best obtained directly from the animal's certificate or registration papers. It is also important to record the animal's tattoo or microchip number, and registration numbers of the sire and dam. Application forms are available on request from the OFA or can be downloaded from the OFA web site (www.offa.org). The radiograph, signed application form (which should include the owner's choice of open or semi-open database), and the service fee should be mailed to: Orthopedic Foundation for Animals, Inc., 2300 E. Nifong Blvd., Columbia, MO 65201-3856. All radiographic images are retained by the OFA for research and reference purposes.

Operational procedures

When a radiograph arrives at the OFA, the information on the radiograph is verified against information on the application form. The age of the dog in months is calculated and the submitted fee is recorded. The veterinary radiologist on staff at the OFA then evaluates the radiograph for diagnostic quality. If it is not of suitable diagnostic quality (the hip is tilted, too light or too dark, etc.) it is returned to the referring veterinarian with a written request that it be repeated (Figure 3). If the radiograph is accepted for evaluation, it is assigned an application number and given a "quality control" hip rating.

There is a pool of 20 to 25 board certified veterinary radiologists throughout the USA in private practice and academia that consult for the OFA. The radiographic images are forwarded to 3 radiologists. Each evaluation is independent -that is, no radiologist knows what interpretation was given by another. The only information they have is the radiograph, application number, breed, sex, and age. The breed, age, and sex of dog are important for the radiologists to know so that normal conformational differences among and within breeds, and differences related to degree of skeletal maturity, can be taken into consideration. Each radiologist grades the hips into one of seven phenotypic hip conformation categories: excellent, good, or fair (which are normal and receive an OFA hip number); borderline; or mild, moderate, or severe (which are abnormal). When results of over 1.5 million radiographic evaluations by 35 radiologists were analyzed, it was found that all 3 radiologists agreed as to whether the dog/cat should be classified as having a normal phenotype, borderline phenotype, or HD 94.9% of the time. In addition, 73.5% of the time, all 3 radiologists agreed on the same hip phenotype (excellent, good, fair, borderline, mild, moderate, or severe).

When the final evaluation is completed, the consensus of the three evaluations is formulated. Two evaluations of the same phenotype result in a consensus of that phenotype; 3 different evaluations (i.e., excellent, good, and fair) result in a consensus of the middle phenotype. If the consensus is phenotypically normal (excellent, good, or fair) an OFA registry number is assigned. The owner of record, referring veterinarian, AKC, and appropriate breed club are notified of the evaluation results. Dysplastic results are not in the public domain unless the owner of record gives explicit direction for the release of such information by initialing the appropriate space on the application form.

The time it takes to obtain three independent evaluations, arrive at the consensus, and type the final OFA report is dependent on a number of factors. It takes approximately a week to 10 days for the film to arrive at OFA via the mail service. Depending on the case load it takes 12 to 14 days from the time that OFA receives the film to completion of the consensus report.

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"The Use of Health Databases and Selective Breeding - Seventh Edition" ~ Download PDF from OFA  

References

1. Bennett D: Hip Dysplasia and Ascorbate Therapy: Fact or Fancy? Seminars in Vet. Med. And Surg., Vol. 2, No. 2, 1987, p. 152-157.

2. Corley EA, Carlson W: Radiographic, Genetic, and Pathologic Aspects of Elbow Dysplasia. J Am Vet Med Assoc, 1965;147:1651.

3. Corley EA, et al: Reliability of Early Radiographic Evaluation for Canine Hip Dysplasia Obtained from the Standard Ventrodorsal Radiographic Projection. JAVMA, Vol. 211, No. 9, November 1997, pp. 1142-1146.

4. Grondalen J, Grondalen T: Arthrosis in the Elbow Joint of Young, Rapidly Growing dogs. Nordish Veterinarmedicin, 1981:33:1-16.

5. Grondalen J: Arthrosis in the Elbow Joint of Young, Rapidly Growing Dogs: Interrelation between Clinical Radiological, and Pathoanatomical Findings. Nordish Veterinarmedicin, 1982; 34:65-75.

6. Kasstrom H: Nutrition, Weight Gain, and Development of Hip Dysplasia: An Experimental Investigation in Growing Dogs with Special Reference to the Effect of Feeding Intensity. Acta Radiol. Suppl.,  Vol 344: 135-179, 1975.

7. Kealy RD, et al: Effects of Limited Food Consumption on the Incidence of Hip Dysplasia in Growing Dogs. JAVMA, Vol. 201, No. 6, 1992, p.857-863.

8. Kealy RD, et al: Effect of Diet Restriction on Life Span and Age-related Changes in Dogs. JAVMA, 2002; 220: p.1315-1320.

9. Leighton EA: Genetics of Canine Hip Dysplasia. JAVMA, Vol. 210, No. 10, 1997, pp. 1474-1479.

10. Lust G et al: Joint Laxity and its Association with Hip Dysplasia in Labrador Retrievers. AJVR, Vol. 54, No. 12, 1993, p.1990-1999.

11. Lust, G et al: Comparison of Three Radiographic Methods for Diagnosis of Hip Dysplasia in Eight-month Old Dogs. JAVMA, 2001; 219: p.1242-1246.

12. Olsson SE: Osteochondrosis in Domestic Animals. ACTA Radiologic Suppl., 358, 1978, pp.299-305.

13. Olsson SE: The Early Diagnosis of Fragmented Coronoid Process and Osteochondritis Dissecans of the Canine Elbow Joint. JAAHA, 1983:19(5):616-626.

14. Padgett GA, et al: The Inheritance of Osteochondritis Dissecans and Fragmented Coronoid Process of the Elbow Joint in Labrador Re­triever. JAAHA, 1995; 31: 327-330.

15. Read RA, et al: Fragmentation of the Medical Coronoid Process of the Ulna in Dogs: A Study of 109 Cases. J. Sm. Anim. Prac., 1990; 32(7), 330-334.

16. Reed AL, et al: Effect of Dam and Sire Qualitative Hip Conformation Scores on Progeny Hip Conformation. JAVMA, 2000; 217: 675-680.

17. Rettenmaier JL, Keller GG, et al: Prevalence of Canine Hip Dysplasia in a Veterinary Teaching Hospital Population. Vet. Rad. & Ultra­sound, Vol. 43, No. 4, 2002, p. 313-318.

18. Smith, GK et al: Coxofemoral Joint Laxity from Distraction Radiography and its Contemporaneous and Prospective Correlation with Lax­ity, Subjective Score, and Evidence of Degenerative Joint Disease from Conventional Hip-Extended Radiograph in Dogs. AJVR, Vol 54: 1021-1042, No. 7, July, 1993.

19. Swenson L, Audell L, Hedhammar A: Prevalence and Inheritance of and Selection for Elbow Arthrosis in Bernese Mountain Dogs and Rottweilers in Sweden and Benefit: Cost Analysis of a Screening and Control Program. JAVMA, 1997; 210: 215 - 221.

20. Tomlinson JL: Quantification of Measurement of Femoral Head Cover­age and Norberg Angle within and among four breeds of dogs. AJVR, 2000; 61: p.1492-1498.

21. Willis MB: Practical Genetics for Dog Breeders. H. F. & G. Witherby Ltd, Great Britain, 1992.

22. Wind A: Elbow Incongruity and Development Elbow Dysplasia in the Dog (Part 1). J Amer Anim Hosp Assoc 1986:22:711-724.

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Surgical Management of Canine Hip Dysplasia - Part II

Operations: Two Viable Options - Modern technology and
an old standby method - are analyzed as CHD treatments

This is the eighth and final article in a series on canine hip dysplasia. What follows is written from the perspective that the readers of the series are conscientious breeders who are the guardians of the genetic pools that constitute their breeds. While this series of articles will not replace a stack of veterinary medical texts, it is a relatively in-depth look at the whole problem of a canine hip dysplasia. Furthermore, the series is designed to be retained as a reference. When you finish reading it you will have a sufficient background to make rational breeding choices and will be able to discuss the subject from an informed basis with your veterinarian. You may not like what you read, but you will be more competent to deal with the problem.

Conclusions from Part I:

Genetics is the foremost causative factor of canine hip dysplasia. Without the genes necessary to transmit this degenerative disease, there is no disease. Hip dysplasia is not something a dog gets; it either is dysplastic or it is not. An affected animal can exhibit a wide range of phenotypes, all the way from normal to severely dysplastic and functionally crippled. Hip dysplasia is genetically inherited.

Conclusions from Part II:

While environmental effects, to include nutrition and exercise, may play a part in mitigating or delaying the onset of clinical signs and clinical symptoms, hip dysplasia remains a genetically transmitted disease. Only by rigorous genetic selection will the incidence rate be reduced. In the meantime, it makes sense to have lean puppies and to avoid breeding animals from litters that showed signs of hip dysplasia. It is probable that even normal exercise levels may increase the phenotypic expression of CHD of a genetically predisposed dog. Stay away from calcium supplementation of any kind; all it can do is hurt. There is no conclusive evidence that vitamin C can prevent hip dysplasia, but there is some evidence that vitamin C may be useful in reducing pain and inflammation in the dysplastic dog.

Conclusions from Part III:

Canine hip dysplasia can be difficult to diagnose, as a number of other orthopedic neurological, autoimmune and metabolic problems may mimic it. Controversy surrounds the question of positioning for hip X-rays and what part joint laxity plays in hip dysplasia. Hip dysplasia may be more common in large and giant breeds and is one of the most over-diagnosed and misdiagnosed conditions.

Conclusions from Part IV:

Sadly, no breed registry in the United States requires genetic screening of parents as a prerequisite for litter registration or even offers a "fitness for breeding" certification. The current registries for hip dysplasia (and other genetically transmitted problems) cover so little of the American Kennel Club-registered dog population that their impact so far has been minimal. The tools we need are there. Joint responsibility for failing to use the tools at hand lies with the AKC, United Kennel Club, parent clubs and individual breeders.

Conclusions from Part V:

The two major methods of diagnosing canine hip dysplasia available to the fancy in the United States are those followed by OFA and those followed by PennHIP. Both are diagnostic; however, the hip-extended protocol followed by OFA may produce false-negative results. The protocol followed by PennHIP has a prognostic or predictive capacity through the use of statistics and a carefully guarded data base that allows a prediction to be made with respect to the probability of phenotypic expression of canine hip dysplasia. No one has a clear quantification of the gray area between obviously clear and obviously dysplastic hips.

Conclusions from Part VI:

For many animals, canine hip dysplasia is a manageable condition, and they can lead relatively normal and active lives given that caution is exercised. Every dog is different in its response to pain and the treatment protocol needs to be tailored specifically to the particular animal. Only aspirin and phenylbutazone ("bute") are FDA-approved drugs for use in dogs, but they are not without serious side effects. Corticosteroids are dangerous and may require experimenting to find proper dosage levels and intervals. Favorable results have been reported from chiropractic, physical drug and nutritional therapy.

Conclusions from Part VII:

Surgery is a viable option given the suitability of the candidate animal, the financial resources available, the expected activity level, longevity and the use and value of the animal. Choice of intervention, whether medical or surgical, and activity level depend upon the disease process. Problems with certain procedures may be associated with improper patient selection relative to the stage of the disease. To be fair, patient compliance, i.e., owner post-operative management, may also be a significant factor.

It is no accident that this discussion of surgical interventions should appear at the end of this series on hip dysplasia, as it is not only the viewpoint of the authors but also many veterinarians that these procedures are measures of last resort. On the other hand there are very clear indications for surgery.

Surgery is indicated when:

• medical management has resulted in unacceptable side effects;

• medical management has not been effective in restoring function and eliminating pain;

• surgery will correct current problems; or<

• surgery will preclude or ameliorate future problems.

It is important to remember from the earlier articles in this series that canine hip dysplasia, as a degenerative joint disease, is a process, and that different interventions may be required at different stages in the process.

In this final article we will explore two surgical options not previously discussed. The first is an old standby that has relieved the pain and suffering of many a dysplastic dog over the years. It is radical and invasive surgery, but under the right circumstances has produced very acceptable results. The second is modern technology in a modular form that produces exceptional, though expensive, results. The beauty of this approach is that through careful selection of components, fit to the animal's skeleton can be optimized.

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FEMORAL HEAD AND NECK EXCISION (OSTECTOMY)

Surgical options for the treatment of canine hip dysplasia have, for the most part, been adaptations of human orthopedic procedures. In 1943, a Lancet article (British medical journal) described a surgery done in 1929 to relieve the pain caused by a tubercular hip joint in a human. This was possibly one of the first complete excisions of the femoral head and neck seen-- at least it was the first example we have been able to find in the literature. Since its inception, this procedure has been modified and used extensively by veterinary surgeons. Often considered an alternative to total hip replacement, the femoral head ostectomy is sometimes the only affordable surgical option available to many dog owners. While there is significant potential for long-term complications, femoral head ostectomy should be carefully considered within its narrow recommended parameters. A prolonged recovery, muscle atrophy and "bed sore"- type ulcers are frequent problems associated with this procedure. Best results are achieved and fewer complications are encountered when the dog weighs less than 50 pounds. Some clinicians feel that the procedure is most effective for dogs less than 35 pounds.

For dogs weighing more than 50 pounds, the femoral head ostectomy has been modified to include a muscle "sling" to support and cushion the femoral shaft. The sling is formed from the biceps femoris muscle (biceps muscle of the thigh). Two other options include using a part of the gluteal muscle (buttocks muscle) to pad the area between the excised femoral shaft and the pelvis, or using the joint capsule itself to accomplish this. These "pads" are sewn into place to fix their position. Over time, the muscle pad is transformed to a fibrous mass that is better able to absorb the impact of the forces exerted by the femor. Nothing will replace the near-frictionless and hydrostatic dampening of the cartilage of the original joint when it was in good condition, but if forces are limited, the muscle pad has been shown to serve well in this function in many cases.

Once the femoral head and neck have been removed, the surgeon takes the joint through a complete range of motion. This ensures that there are no obstructions to normal articulation. The muscle pad is sewn into place so it will attach securely to the acetabulum. The clinician also checks for crepitus, which is a dry, crackly sound. Ovary crepitus may indicate that not enough of the femoral neck was removed or that bony fragments are still at the excision site. Both conditions would cause loss of function and pain after surgery. It is much better to reduce the problem at the time of surgery than to have to go back into the joint a second time.

As mentioned before, femoral head excision tends to be more effective and fewer complications are encountered when the dog weighs less than 50 pounds. A study published in 1988 evaluated the use and efficacy of the biceps femoris muscle sling. Sixteen dogs with normal hips were given the biceps femoris muscle sling surgery and six normal dogs were given the conventional excision of the femoral head and neck. While both control and treatment animals had similar post-surgical limb functions, there was marked edema and swelling of the affected limb in half of the dogs with slings and not in the control dogs. Four of the sling dogs developed post-operative infection and all of the treatment animals had elevated temperatures after the procedure. Their results indicated that the added risk of infection and complications was not justified and that further clinical trials needed to be run before the efficacy of this adjunct treatment could be established.

For those considering this type of surgery, it should be noted that this is a strictly end-stage salvage procedure. Only those animals demonstrating severe bony changes in the coxofemoral joint and clinical signs of pain should be considered for this procedure. Also, excisions without adding a prosthesis shortens the leg, which affects the gait, and the biceps sling can cause a slight adduction (drawing in toward the center line) of the affected limb during exercise. On the positive side, this procedure has worked well over the years and is still the standby short of total hip replacement.

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TOTAL HIP REPLACEMENT / TOTAL HIP ARTHROPLASTY

The first human total hip replacement was performed in 1891 using an ivory ball-and-socket joint that was attached to the bone with nickel-plated screws. After this pioneering effort, replacement of just the femoral head or the acetabulum (unipolar) was the accepted practice until the 1950's. Later, the bipolar procedure (replacing both the femoral head and the acetabulum) was adopted as the preferred way to achieve long-term success. Better results were obtained, too, after the advent of polymethylmethacrylate (PMMA, or bone cement, which was approved by the FDA in 1967. Not only was the prosthesis stabilized by the cement, but its use was effective in preventing bone resporption where metal contacted bone. Orthopedic surgery has never been the same since.

In 1953, the first unipolar arthroplasty performed on a canine was described by R.E. Brown. His procedure replaced just the femoral head with a stainless-steel prosthesis. It was not until 1957, though, that H.A. Gorman did the first total bipolar hip replacements on 53 military working dogs. Much of the work done today is based on Gorman's truly pioneering efforts.

Besides the secondary osteoarthritis associated with canine hip dysplasia, total hip replacement is indicated for failed femoral neck and head excisions, irreparable femoral head and neck fractures, non-reducible chronic hip luxations, avascular necrosis of the femoral head and repair of a failed total hip arthroplasty. Major surgical failure lead directly to a requirement for total hip replacement. In a nutshell, when all else has failed, especially surgical procedures, total hip replacement may be the solution to restoring function and a pain-free quality of life.

The ideal candidate must have obtained adult growth, usually between 9 to 12 months of age, and must have obtained at least 30 pounds lean weight (no fat little dogs need apply). Other contraindications include infection anywhere in the body, anemia, neurological disease and concurrent orthopedic problems. A dog with arthritic hips and pain-free normal function is not a candidate for total hip replacement.

The most recent innovation developed for this type of surgery is the use of modular components in a sort of "mix and match" attempt to optimize the fit of the prosthesis. In June 1990, a canine modular hip prosthesis and instrument system was introduced at Ohio State University and marketed under the name of BioMedtrix. This system has the obvious advantage of being able to customize the fit of the various prosthesis components to better match the dog's original skeletal conformation. Thus femoral neck lengthening can be accomplished through choosing a particular femoral head and a particular femoral shaft. Note from Figure 1 that there is a set of prosthetic hip components for virtually any dog; specifically there are five-stem sizes, four standard and one nonstandard, acetabular cup sizes and three neck lengths\ offsets. Figure 2 shows an example of the prosthetic acetabulum, femoral head and neck. Figure 3 shows a "junk" hip on a 1 and a half year old Labrador Retriever. Figure 4 shows the same animal eight years and one month post-surgery. This ought to dispel doubts as to the length of benefit to be derived from total hip replacement. Look at the X-rays for a while. This is a good result, and it shows what can be expected from the technology.

Although expensive (our quick, non-statistical survey revealed $1,300 to $1,600 per hip was common), replacement of the arthritic hip with the appropriately sized mix of prosthesis components allows early if not immediate post-operative use of the limb. Most dogs are able to resume their normal level of activity within two months after surgery. Where there is clear indication that conditions will only worsen with time, a total hip replacement may make social and economic sense consistent with the age, purpose and value of the animal and the financial condition of the owner. We found that though results are not guaranteed, they tend to be consistently good to excellent, as supported by reports in the medical literature.

Complication due to infection is the most common occurrence associated with hip replacement and is directly related to the number of surgeries and the duration of the procedure. In dogs, blood-borne infections have been reported at 22 to 28 weeks after surgery. Infection rates in the 1970s ranged from 7.7 to 11 percent. More recently, infection rates of 1.5 to 3 percent have been reported.

Another complication that occurs with this surgery is a condition called "cement disease" or aseptic loosening. A fibrous membrane normally develops between the bone and the cement. With cement disease, however, a synovial like membrane containing particulate debris develops that produces large amounts of bone resorbing factors such as prostaglandin E2, collagenase, interleukin-1 and tumor necrosis factor. Newer techniques using a cement gun to introduce PMMA under pressure have decreased the incidence rate of cement disease. Mixing gentamyacin and the cephalosporins in the cement has also reduced the rates of infection. Another complication due to the use of cement is sciatic neuropraxia (the inability of the nerve to conduct impulses). Nerve contact with PMMA during its exothermic or heat-generating reaction has been implicated.

How well does a total hip replacement work? Very well, indeed. Olmstead, Hohn and Turner (1983) did follow-ups on 221 total hip replacements done between 1976 and 1981. After a four-week convalescent period, 216 cases (91.2 percent) had satisfactory function. A follow-up study of 174 THRs was done with 95.2 percent of the cases being restored to satisfactory function. We conclude that the total hip replacement, in suitable candidates, provides exceptional results. Olmstead boasts, as well he should, that one of his THRs won an international field trial. Total hip replacement restores function and relieves pain. Be aware that surgery cannot undo generations of genetic makeup, or prevent that which is predisposed. Total hip replacement is not prophalaxis to the problem; it is but a band-aid to the underlying genetic problems.

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Conclusions:

Femoral head and neck ostectomy and total hip arthroplasty are two of the major surgical options available to the owner of a dysplastic animal. If economically feasible, the THA/THR option is the more viable in terms of predictable outcome in larger animals. In smaller animals, favorable results have been reported with the femoral head and neck ostectomy, though obviously, somewhat less than total function is restored. With the advent of the use of PMMA and adjunct of antibiotic therapy, infection and "cement disease" rates have dropped remarkably during the past decade to the extent that they should be viewed as manageable concerns.

There is no substitute for genetic screening and refraining from breeding, no matter how attractive a particular breeding might be unless there is a clear indication that the parents, their siblings and get are free of hip dysplasia. To that end, we support the concept of open registries and place the blame for much of the genetic disease we find in the fancy today squarely on the shoulders of the various registries that have the power to make a difference. Until the time that the genetic disease aspect is recognized and successfully handled, there will a continued necessity for the surgical option.

We, the authors, wish to thank those professionals and caring veterinarians and researchers who have provided much of the information, without which this series would have been impossible. They not only gave generously of their time, but even shared unpublished manuscripts and unpublished manuscripts and unpublished insights to the various procedures. The result has been a survey of the recent literature with comments extracted from those at the very forefront of technology. Controversy has raged throughout the research process as the many professional opinions struggle for primacy. We have attempted to present not only the mainstream but also the fringe where there was adequate documentation of beneficial results.

Special acknowledgment goes to Doctors of Veterinary Medicine Marvin Olmstead, Gail Smith, Barclay Slocum, William Inman, Daniel Richardson and Terry Braden, all of whom we found to be genuinely concerned with the welfare of their animal charges. They are truly pioneers in the treatment of canine hip dysplasia.

Special thanks go to Doctors of Veterinary Medicine Rachel St. Vincent and Veronika Kiklevich of the Washington State Veterinary School.

For more information about PennHIP contact International Canine Genetics Inc., 271 Great Valley Parkway, Malvery, Pa. 19355; (800) 248-8099.

Special dedication goes to author Susan Thorpe-Vargas' dog-- call name "Smash," or if we're being more formal, Belaya Sobaka's Simply Smashing-- a Samoyed who touched our hearts as we wrote this series.

Last, but not least, we thank the readers who steered us in the right directions to those important researchers mentioned above and sincerely appreciate how DOG WORLD Editor Donna Marcel and her staff went out on a limb to approve and schedule this long series of eight articles.

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CREDITS

References

1. Girdlestone, G.R. "Acute pyrogenic arthritis of the hip: Operation giving free access and effective drainage." Lancet. 1:419-421. 1943

2. Personal communication with Daniel Richardson, D.V.M., diplomat ACVS, director, Department of Advanced Research, Hills Pet Nutrition, Topeka, KS. 66601. Sept. 15, 1995.

3. Lippincott, C.L. "Improvement of excision arthroplasty of the femoral head and neck utilizing a biceps femoris muscle sling." J Am Animal Hospital Assoc. 17:668-673. 1981

4. Lewis, D.L.; Bellah, J.R.; McGavin, M.D., et. Al. "Postoperative examination of the biceps femoris muscle sling used in excision of the femoral head and neck in dogs." Vet Surg. 17:269-277. 1988.

5. Newman, P.H. "Development of total hip replacement." Total Hip Replacement. Jayson, M. (Editor). J.B. Lippincott, pp.13-25. 1971.

6. Brown, R.E. "The experimental use of stainless steel femoral head prosthesis in normal dogs and cats." North Am. Vet. 34:423-428. 1953.

7. Gorman, H.A. "A new prosthesis hip joint." Military Med.121:91-93. 1957.

8. Personal Communication with Marvin Olmstead, D.V.M., M.S., Diplomate of the American College of Veterinary Surgeons, Professor of Small Animal Orthopedics, Ohio State University, College of Veterinary Medicine, Columbus, Ohio 43210; (614)292-0950

9. Olmstead, M.L.; Hohn, R.B.; Turner, T.M. "A five year study of 221 total hip replacements in the dog." J Am Vet Med Assoc. 183:191-194. 1983.

10. Goldring, S.R.; Jasty, M.; Roelke, M.S., et. al. "Formation of a synovial-like membrane at the bone-cement interface: Its role in bone resorption and implant loosening after total hip replacement." Arthritis Rheum. 29:836-841. 1986.

11. Olmstead, M.L.; et. al.

Surgical Management of Canine Hip Dysplasia

Surgery may be recommended for suitable candidates, taking into account
expected activity level, longevity and use and value of the dog.

This is the seventh part in a series on canine hip dysplasia. What follows is written from the perspective that the readers of the series are conscientious breeders who are the guardians of the genetic pools that constitute their breeds. While this series of articles will not replace a stack of veterinary medical texts, it is a relatively in-depth look at the whole problem of a canine hip dysplasia. Furthermore, the series is designed to be retained as a reference. When you finish reading it you will have a sufficient background to make rational breeding choices and will be able to discuss the subject from an informed basis with your veterinarian. You may not like what you read, but you will be more competent to deal with the problem.

Conclusions from Part I:

Genetics is the foremost causative factor of canine hip dysplasia. Without the genes necessary to transmit this degenerative disease, there is no disease. Hip dysplasia is not something a dog gets; it either is dysplastic or it is not. An affected animal can exhibit a wide range of phenotypes, all the way from normal to severely dysplastic and functionally crippled. Hip dysplasia is genetically inherited.

Conclusions from Part II:

While environmental effects, to include nutrition and exercise, may play a part in mitigating or delaying the onset of clinical signs and clinical symptoms, hip dysplasia remains a genetically transmitted disease. Only by rigorous genetic selection will the incidence rate be reduced. In the meantime, it makes sense to have lean puppies and to avoid breeding animals from litters that showed signs of hip dysplasia. It is probable that even normal exercise levels may increase the phenotypic expression of CHD of a genetically predisposed dog. Stay away from calcium supplementation of any kind; all it can do is hurt. There is no conclusive evidence that vitamin C can prevent hip dysplasia, but there is some evidence that vitamin C may be useful in reducing pain and inflammation in the dysplastic dog.

Conclusions from Part III:

Canine hip dysplasia can be difficult to diagnose, as a number of other orthopedic neurological, autoimmune and metabolic problems may mimic it. Controversy surrounds the question of positioning for hip X-rays and what part joint laxity plays in hip dysplasia. Hip dysplasia may be more common in large and giant breeds and is one of the most over-diagnosed and misdiagnosed conditions.

Conclusions from Part IV:

Sadly, no breed registry in the United States requires genetic screening of parents as a prerequisite for litter registration or even offers a "fitness for breeding" certification. The current registries for hip dysplasia (and other genetically transmitted problems) cover so little of the American Kennel Club-registered dog population that their impact so far has been minimal. The tools we need are there. Joint responsibility for failing to use the tools at hand lies with the AKC, United Kennel Club, parent clubs and individual breeders.

Conclusions from Part V:

The two major methods of diagnosing canine hip dysplasia available to the fancy in the United States are those followed by OFA and those followed by PennHIP. Both are diagnostic; however, the hip-extended protocol followed by OFA may produce false-negative results. The protocol followed by PennHIP has a prognostic or predictive capacity through the use of statistics and a carefully guarded data base that allows a prediction to be made with respect to the probability of phenotypic expression of canine hip dysplasia. No one has a clear quantification of the gray area between obviously clear and obviously dysplastic hips.

Conclusions from Part VI:

For many animals, canine hip dysplasia is a manageable condition, and they can lead relatively normal and active lives given that caution is exercised. Every dog is different in its response to pain and the treatment protocol needs to be tailored specifically to the particular animal. Only aspirin and phenylbutazone ("bute") are FDA-approved drugs for use in dogs, but they are not without serious side effects. Corticosteroids are dangerous and may require experimenting to find proper dosage levels and intervals. Favorable results have been reported from chiropractic, physical drug and nutritional therapy.

It is no accident that this discussion of surgical interventions should appear at the end of this series on hip dysplasia, as it is not only the viewpoint of the authors but also many veterinarians that these procedures are measures of last resort. On the other hand there are very clear indications for surgery.

Surgery is indicated when:

• medical management has resulted in unacceptable side effects;

• medical management has not been effective in restoring function and eliminating pain;

• surgery will correct current problems;

• surgery will preclude or ameliorate future problems.

It is important to remember from the earlier articles in this series that canine hip dysplasia, as a degenerative joint disease, is a process, and that different interventions may be required at different stages in the process.

Many animals lead a non-working pet life and have a level of activity that would not be expected to accelerate the degenerative process. Thus they might not require surgery in order to sustain that level of activity for their remaining life spans. Working and other high-activity-level dogs are another issue entirely, as are dogs used for special purposes. Some of these procedures are also recommended when there exists a genetic or traumatic orthopedic condition that must be corrected in order to begin long-term medical treatment modalities.

We should also note that surgery is used jointly with adjunct therapies.¹ Weight control, or where indicated weight loss, along with appropriate exercise restrictions, also apply. Careful consideration must be taken to limit the post-surgical canine patient to those exercises and exercise levels that do not accelerate the degenerative process. Water exercise is ideal as a non-weight-bearing activity that prevents atrophy of those muscle masses that support the hip, burns calories and maintains cardiovascular fitness. For those dogs for whom water activities are not available, or who do not enjoy the water or retrieving, the choice of exercise surface should be considered. Hard-packed sand along the water's edge, soft grass or dirt roads and trails are much preferred over concrete or asphalt. Appropriate drug and nutritional support are also indicated.²

Surgical procedures for the management of canine hip dysplasia tend to be controversial. Each procedure has its pros and cons, and therefore, not surprisingly, there are veterinary orthopedic surgeons who for a given patient would choose different procedures, much as in human medicine. This leads the authors to conclude that there is no one ideal procedure that is suitable for all stages of the disease process. Each dog presenting with hip dysplasia may be more or less a candidate for one or more of the procedures described here. There are, however, clear indications for the type of procedures that might be most beneficial at different stages of the disease process.

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Femoral neck lengthening
The goal of this article is to acquaint the reader with the options available, and to provide a depth of understanding sufficient that the reader may participate in the choice of techniques chosen or rejected by the attending veterinary orthopedic surgeon. Caveat: Many orthopedic surgeons become so skilled in one method that their success is greater with that procedure than with another that theoretically might be better suited for the candidate animal. The authors suggest finding a surgeon comfortable with a particular procedure that would seem to fit the case, and whose patients have done well. Be aware that no one procedure is suitable for all candidates for surgery and that some level of argument may be made for and against any given procedure for any given candidate. The best choice, when factoring cost, age value of the animal, use of the animal, stage in the disease process, etc., may not always be clear.

Before the development of advanced degenerative joint disease, surgical options include:

• pectineal myotomy-cutting or dissection of the pectineous muscles;

• pectineal myectomy-excision of a portion of the pectineous muscles;

• three-plane intertrochanteric osteotomy-changing the angle of the femoral head;

• triple pelvic osteotomy-cutting the pelvis into three pieces then putting it back together with more favorable acetabular angles.

After the development of advanced degenerative joint disease, surgical options include:

• excision of the femoral head and neck;

• shelf arthroplasty;

• total hip replacement.

The excision of the femoral head and neck is often selected for those animals in the end stage of the disease. For advanced cases, where the value of the animal warrants the expense, often the procedure of choice is total hip replacement. For those dogs that are too far advanced into degenerative joint disease for a reconstructive procedure such as triple pelvic osteotomy to be effective, and yet not bad enough to warrant total hip replacement, there is a new "shelf" procedure in development that uses a bone graft technique to extend the acetabular rim and improve femoral head coverage. Due to their complexity and cost, we will reserve our treatment of femoral neck and head excision and THA (total hip arthroplasty) to the eighth and final part of this series.

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PECTINEAL MYOTOMY/MYECTOMY

Originally developed by J. Barden, Larry J. Wallace, D.V.M., M.S., modified the procedure in 1967 to include the tenectomy (cutting out a portion of the tendon) or tenotomy (cutting of the tendon) of the pectineus tendon of insertion (that part of the muscle that goes into and attaches to the bone). Pectineal myotomy/myectomy was first used to treat canine hip dysplasia in clinically affected dogs.³ Wallace's procedure is by no means a cure for CHD, but has been described as somewhat effective in temporarily relieving pain and restoring function. One of the adductors of the hip, the pectineal muscle brings the hind leg in toward the mid-line of the dog. The rationale for this procedure is to relieve the tension on the joint capsule, caused by the upward force on the coxofemoral joint from a contracted pectineus muscle. It is also thought that improved weight loading of the femoral head within the acetabulum may result from the increased range of abduction. Note the difference between "adduction" (moving toward the center line) and "abduction" (moving away from the center line). This type of surgery should be considered strictly therapeutic in nature and does little or nothing to stabilize the dysplastic hip. Therefore, the owner of an affected animal can expect the degenerative changes due to osteoarthritis to continue.

Figure 3 (below left) shows before and Figure 4 (below right) shows after triple pelvic osteotomy and femoral neck lengthening. Figures 1-4 courtesy of Dr. Barclay Slocum, Slocum Veterinary Clinic.

Complications attributed to this surgical option include fibrotic reattachment of the muscle or tendon and seroma formation. Seroma are tumor-like collections of blood and serum in the muscle tissue. A modification of the earlier procedure, which allows suturing the tendon of insertion to the "belly" of the pectineus muscle, has been suggested to address both of these post-surgical consequences.

Published data showing the efficacy of this surgical treatment include several studies where dogs that had had pectineus surgery at 4 to 12 weeks of age demonstrated no beneficial effects from this procedure when evaluated again at 12 to 47 months.^4,5 However, this surgery is used in clinical practice when an owner cannot afford one of the more sophisticated surgical procedures, or to restore function to a working animal when the dog needs to be used in the near future. Activity is restricted for only two weeks after this type of surgery.

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SHELF ARTHROPLASTY

The purpose of shelf arthroplasty is to form an extension over a shallow acetabulum to improve joint stability. Diminished depth of the acetabulum is most often the result of osteophyte formation. This procedure is supposed to improve coverage of the femoral head, prevent stretching of the joint capsule and thus eliminate and reduce pain. But as yet, there is no evidence that this surgery alters the progression of CHD in young dogs.

Because of the controversy surrounding the BOP (biocompatible osteoconductive polymer) shelf arthroplasty, which questions both the efficacy of the procedure itself and the safety of the material used, the authors choose not to recommend this surgical option. "I have reservations about the procedure," says Dr. Marvin Olmstead, professor of small animal orthopedics at the Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Ohio State University. "When one critically looks at the postoperative radiographs provided by the BOP manufacturer, it is apparent that the arthritis continues. I know of several cases in which there was development of foreign body reactions and draining tracts from this substance." [Authors' emphasis.]⁶ Dr. Barclay Slocum of the Slocum Clinic (Eugene, OR) also concurs with this opinion and adds, " It just doesn't do what it claims to do."⁷ Minor complications can include broken screws and seroma formation. There are a number of researchers developing bone graft shelf arthroplasty techniques to extend the acetabular rim to provide greater coverage of the femoral head. Shelf arthroplasty is not a true arthroplasty as it does not change the existing joint surfaces, it only extends their rim.

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INTERTROCHANTERIC OSTEOTOMY

Prior to improvements in the method for performing triple pelvic osteotomy, the intertrochanteric osteotomy was commonly used if there was adequate depth in the acetabulum socket, and if the dorsal rim was normal, i.e., osteophyte formation had not begun.⁸ This surgery reduces the angle of the femoral neck, which improves congruity between the femoral head and the acetabulum, resulting in an improved fit. Because it corrects conformational and structural problems of the femoral head, this procedure must be performed before any major remodeling of the acetabulum has occurred. Nevertheless, pain and radiographic subluxation must be clinically evident prior to any reconstructive surgery in order to justify the pain, effort and expense. The average angle of inclination of the femoral neck in the dog is 149 degrees(normal range 141 to 157 degrees). The intertrochanteric osteotomy over-corrects this angle to approximately 135 degrees by removing a wedge of bone. See Figure 5 and Figure 6 for before and after images. This is thought to increase the surface area over which the pressure or "load" is spread. The greater the surface area, the less the pressure per unit of area there is on the coxofemoral joint in any one place.

Figure 5 (below left) shows before and Figure 6 (below right) shows after double intertrochanteric osteotomy. Note the improved congruity between the femoral head and acetabulum. Photos courtesy of Braden, T.D.; Prieur, W.D. "Three plane intertrochanteric osteotomy for treatment of early stage hip dysplasia." Vet Cl N Am Sm Anim Prac. Vol.22 No.3 May 1992. pp.624-643.

Two studies have been done to evaluate the effectiveness of this surgical procedure. The first one was published in 1987 and assessed 183 dogs from one to seven years after the surgery was performed. ⁹The results of this study demonstrated an 89.6 percent "excellent" or "good" return to motor activity. "Excellent" was reserved for those dogs that exhibited a normal gait and no pain when exercised over long distances. "Good" was defined as a slight limp appearing after exercise, but exhibiting a normal gait while walking or running. Better results were attained if the dogs were operated on prior to the appearance of degenerative joint disease. Only 12.1 percent of the dogs with severe osteoarthritis had excellent results as opposed to 51.4 percent of those dogs without any osteoarthritis before surgery and 45 percent of those dogs with mild degenerative joint disease. A later study covered the seven-year period between 1980 and 1987. Published in 1990, this article evaluated 37 dogs with a total of 43 hip surgeries.¹⁰ The evaluation procedure consisted of a questionnaire and/or an orthopedic examination. Also included was a report from the owners via telephone. A rating of "excellent" in this second study was defined as normal function, whereas "good" was characterized as normal weight-bearing with joint stiffness after strenuous exercise or a long rest.

Follow-up consisted of:

• owners' phone reports-68 percent "excellent" or "good" at 11 months;

• a questionnaire that evaluated dogs at one year-70 percent "excellent" or "good"

• an orthopedic exam at 15 months-80 percent "excellent" or "good."

The stated goal of this procedure is to relieve pain. In humans, the surgery provides relief for an average of five to six years.¹¹ It has been assumed that the results are somewhat similar in dogs, but the actual expected duration of improvement has not yet been determined.

Triple Pelvic Osteotomy

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TRIPLE PELVIC OSTEOTOMY

The TPO may be considered the exception to the view that these surgeries are "salvage" in nature. For this procedure to be effective, this surgery must be performed before major remodeling of the femoral head and the acetabular rim has occurred. That means that the primary abnormality should be radiographic indications of subluxation of the affected hip.

Slocum believes there are two forms of canine hip dysplasia.¹² One condition exhibits either a shortened femoral neck or an improper angle between the femoral head and the long axis of the femur. This problem can be corrected by lengthening the femoral neck (Figure 1). The femur is split down the long axis and a polymer wedge is placed proximal (toward the center) to the femoral head. The bone is then wired together and the new bone fills in the gap. Some controversy exists with this procedure, however. "I view the femoral neck lengthening procedure with extreme caution," says Dr. Gail Smith of Penn State. "Although I have not performed mechanical testing on femurs treated with this method I estimate the reduction in femoral torsional strength [resistance to twisting] to be at least 70 percent, leaving the femur susceptible to fracture. This procedure has a theoretical basis only, and I am unaware of scientific proof supporting its clinical efficacy. "¹³ In answer to this criticism, Slocum adds, "Although drilling a hole or cutting a bone as in any surgical technique will make a bone weak to torsional stresses, the healed bone is strong, durable and functional. After healing has been completed in the femoral head lengthening, no clinical experiences of this bone fracturing has been reported by other doctors using this technique or experienced by me in my clinical practice."¹⁴

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By far the most common form of CHD that Slocum sees in his clinical practice is acetabular hip dysplasia.¹⁵ This type is characterized by having an excessive slope to the dorsal rim of the acetabulum. When the dog is standing, it is this portion of the pelvis that supports the animal's weight. Slocum believes excessive slope of the acetabulum is the primary cause of the sideways displacement or subluxation of the femoral head. This leads to stretching of the round ligament, which in turn can cause the joint capsule to stretch, thus producing the hip laxity that commonly characterizes CHD.

Slocum believes that the best candidate for this type of surgery should have a combined dorsal acetabular rim (DAR) slope of more than 15 degrees. The determining factors for suitability of triple pelvic osteotomy are: DAR angle, angle of reduction and angle of subluxation. His past candidates have been from 4 months to 8 years of age. The surgical procedure consists of cutting the pelvis at three different points (Figure 2). This allows the acetabulum to be tilted until it is perpendicular to the femoral head. With the force generated at a 90-degree angle the femoral head is kept within the socket by the weight of the animal. This procedure also relies on muscular contraction to keep the femoral head seated within the socket, so any neurological deficit or muscular problems would necessarily disqualify a dog for this type of surgery. Various methods are used by the surgeons to determine the angle at which to tilt the pelvis. Slocum uses the DAR projection and draws a line parallel to the top of the femur. This indicates the required angle when this line intersects the dorsal slope.

Note that the intertrochanteric osteotomy and the triple pelvic osteotomy are in essence two approaches to the same overall goal: that of aligning the acetabulum and the femoral head for the greatest congruity. The intertrochanteric osteotomy attacks the problem from the pelvis. If done well, indications are that the results are beneficial and similar. Indications for a triple pelvic osteotomy combined with a femoral neck lengthening are: the dorsal acetabular rim is damaged, the acetabulum is not filled with osteophytes and the joint capsule is stretched. Figure 3 and Figure 4 show before and after imaging of femoral neck lengthening and pelvic osteotomy procedures done on the same animal. Note the great improvement in the femoral head to acetabular cup fit in the after view.

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Conclusions:

Surgery is a viable option given the suitability of the candidate animal, the financial resources available, the expected activity level, longevity and the use and value of the animal. Choice of intervention, medical, surgical or activity level is process-dependent. Problems with certain procedures may be associated with improper patient selection relative to the stage of the disease. To be fair, patient compliance, i.e., owner post-operative management, may also be a significant factor.

The next and final article in this eight-part series will cover total hip replacement. Exciting new advances have been made and are currently supported by manufacturers. The costs remain high, but then so are the benefits to be gained in a suitable candidate.

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CREDITS

References

1. Goring, Robert. "Surgical and medical management of canine hip dysplasia." Hoffman-LaRoche Symposium on Degenerative Joint Disease. Orlando, FL January 12, 1992. Pp.7-15.

2. Cargill, J.C.; Thorpe-Vargas, S. "Medical management of canine hip dysplasia." Dog World. October 1995. Pp.24-28.

3. Wallace, L.J. "Pectineous tenectomy or tenotomy for treating clinical canine hip dysplasia." Vet Clin N Am. 1971. Vol. 1. Pp.455-465.

4. Bowen, J.M.; Luis, R.E.; Kneller, S.K., et al. "Progression of hip dysplasia in German Shepherd Dogs after unilateral pectineal myotomy." J Am Vet Med Assoc. 1972. 161:899-904.

5. Lust, G.; Craig, P.H.; Ross, G.E.; et al. "Studies on pectineous muscles in canine hip dysplasia." Cornell Vet. 1972. Vol. 62. Pp. 628-645.

6. Smith, Carin. "Treatments for hip dysplasia spark controversy." J Am Vet Med Assoc. Vol. 201. No. 2. July 15, 1992.

7. Personal communication with Dr. Barclay Slocum, Slocum Clinic, (503) 689-9393. August 17, 1995.

8. Prieur, W.D. "Intertrochanteric osteotomy in the dog: Theoretical considerations and operative techniques." J Sm Anim Pract. 28:3-20, 1987.

9. Walker, T.; Prieur, W.D. "Intertrochanteric femoral osteotomy." Seminar Vet Med Surg (Small Animal). 2:117-130, 1987.

10. Braden, T.D.; Prieur, W.D.; Kaneene, J.B. "Clinical evaluation of intertrochanteric osteotomy for treatment of dogs with early-stage hip dysplasia: 37 cases (1987-1989)." J Am Vet Med Assoc. 196:337-341, 1990.

11. Reigstad, A.; Gronmark, T. "Osteoarthritis of the hip treated by intertrochanteric osteotomy." J Bone Joint Surg Am. Vol. 66. Pp. 1-6. 1984.

12. Slocum, B.; Slocum, T.D. "Pelvic osteotomy for axial rotation of the actabular segment." Vet Clin N Am. Vol. 22. No. 3. Pp. 645-682. May 1992.

13. Smith.

14. Personal communication with Dr. Barclay Slocum, Slocum Clinic, (503)689-9393. August 22, 1995.

15. Slocum, B; Slocum, T.D.