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Canine Hip Dysplasia-Part 1

Pathophysiology and Diagnosis

Canine hip dysplasia (CHD) is an inherited developmental disorder of the coxofemoral joint commonly affecting many of the larger breeds of dogs. Patients with clinical signs referable to CHD are regularly presented for evaluation and treatment, and selection of the most appropriate medical or surgical therapy requires a comprehensive orthopedic evaluation of each individual. The purpose of this series of articles is to describe the pathophysiology of the disease and the techniques employed for its successful diagnosis as well as the indications for the multitude of surgical procedures utilized to treat the condition.

Pathophysiology and Diagnosis

The cause and pathogenesis of canine hip dysplasia are still poorly understood; however, numerous studies over the last 15 years have indicated that CHD is a developmental disorder and that multiple factors can influence or modify the expression of the disease. No specific genetic pattern of inheritance has been demonstrated; however, the pattern of inheritance is multi-factorial. The spread of hip dysplasia is centered around the genetic transmission and heritability of a particular body size, type, confirmation, and growth pattern. The occurrence of hip dysplasia has been reduced by breeding dogs that have radiographically disease-free joints and by selecting dogs for breeding based on family performance and progeny selection. Unfortunately, many factors affect the choice of dogs used in breeding programs and breeding dogs for desirable traits (i.e., large size, temperament) may result in the inadvertent selection of dogs predisposed to CHD. Therefore, while CHD is a heritable disease, controlled breeding programs have only reduced the prevalence of hip dysplasia, but the disease has not been eliminated.

Dogs with the highest incident of hip dysplasia are large, rapidly growing and maturing breeds with a heavy body confirmation. It has been speculated that slow growth and late maturation favors the completion of ossification and development of the joint before the hips are subjected to possible injury from excessive extrinsic forces, especially excessive body weight. Rapid growth and early weight gain may result in disparities of tissue development triggering a series of events leading to subluxation, hip dysplasia, and degenerative joint disease. While the role of nutrition has been thoroughly investigated, diet has not affected the occurrence or course of CHD other than the mechanical effect of increased or decreased weight upon the hip.

Several hormones have been implicated as playing a role in causing CHD, including estrogen and relaxin. Based on the results of several studies, there is no evidence that hormonal influence (within the biologic range) is associated with the development of spontaneously developing hip dysplasia in the dog.

A causal relationship between pelvic muscle mass and/or muscle myopathies and hip dysplasia has also been advanced. The disparity between primary muscle mass and/or failure of the muscles to develop and reach maturity at the same rate as the pelvis may lead to alterations in the function of pelvic muscles and the development of CHD. There are substantial evidence that the consequence of hip joint laxity. Joint laxity is thought to precede hip joint remodeling and degenerative joint disease. The possibility that joint laxity may be associated with or influenced by pelvic muscle mass and/or maturation as well as by the anatomic structures important in maintaining hip stability (i.e., ligament of the head of the femur, joint capsule, joint confirmation) has been extensively explored. The available evidence, however, does not single out any one factor or variable, which would lead to increased joint laxity. In conclusion, the confirmation and stability of the hip is governed by a number of factors which influence the congruency of the articular surfaces between the femoral head and acetabulum, the integrity of the joint capsule and ligamentum teres, combined with the overall mass and strength of the associated pelvic musculature. The failure of one or more of the orthopedic or soft tissue supporting structures leads to joint laxity with stretching and confirmational change of the aforementioned structures, progressive subluxation, hip dysplasia, and resultant degenerative joint disease.

The clinical signs of hip dysplasia are many and varied, ranging from minimal to pronounced pain, lameness, and disability. Symptoms may be seen as early as four weeks of age, but are generally not detected until 4-6 months of age. Physical examination must include gait analysis, palpation, and precise radiography of the hip.

Observation of the gait may disclose a weight bearing lameness, which is more severe after exercise, a stilted or swaying rear limb gait, an audible “click” when walking, or walking with an arched back. There may also be pain and/or crepitation present upon manipulation of the hip and evidence of poorly developed musculature of the hind quarters.

Palpation of the hip has been utilized to determine the presence or absence of joint laxity and early CHD, especially in immature dogs. The ability to accurately quantitate hip joint laxity should provide key diagnostic and prognostic information for affected dogs. There are, however, a number of concerns, which must be addressed relating to the accuracy of palpation as a method of diagnosis. Palpation is at best a subjective evaluation and is influenced by practitioner experience, positioning of the dogs, amount of forced applied, and whether or not the dog is anesthetized. As of yet, an objective method of determining the amount of joint laxity of subluxation in dogs manifesting symptoms of CHD prior to the development of detectable radiographic changes. The two most common procedures employed are the Bardens’ method and the test for the Ortolani sign, both of which are described extremely well in the article authored by Chalman and Butler. The Bardens’ test detects movement of the femoral head in and out of the acetabulum as the femur is lifted horizontally. Elicitation of an Ortolani sign may be performed with the patient in either dorsal or lateral recumbancy. During testing, the application of pressure along the femoral shaft will subluxate the femoral head dorsally. As the limb is abducted, the femoral head will reseat within the acetablulum. The resulting sound and vibrations or “clicks” produced by this reseating is a positive Ortolani sign. The degree of grading residence of “click” gives an appreciation of the severity of the existing pathology. Dogs with extensive pathology, however, may have a negative Ortolani sign because distortion of the acetabular rim combined with a thickened joint capsule and osteophyte production may lead to an extremely limited range of motion. In these cases, however, radiographic evidence of joint distortion exists and diagnosis should be straightforward.

Although observation of the gait and palpation of the hip can indicate the possibility of CHD, radiographic examination is used to establish the diagnosis in the majority of cases. Historically, radiographic evaluation consists of a symmetric ventrodorsal radiograph of the pelvis and femors with the hind limbs extended and parallel to each other. Lateral pelvic views contribute minimally in the assessment of possible CHD. A major deficiency in this standard radiographic view is the failure to adequately delineate the weight bearing portion of the acetabulum. In addition, this hip extended position may mask the true potential hip joint laxity because in this position, the joint capsule tightens and may act to drive the femoral head into the acetabulum. The dorsal acetabular rim radiographic view has been recommended to evaluate the dorsal rim of the acetabulum for damage and secondary changes to show acetabular filling and congruency of the hip and to correlate palpation of joint laxity and crepitation with radiographic appearance.

The primary radiographic signs of CHD are a shallow acetabulum and a small flattened femoral head. The dorsal acetabular rim recedes and becomes less concave, and increased joint space and subluxation or luxation of the femoral head is observed. As dysplasia progresses, joint instability, synovitis, and cartilage degeneration increase as evidenced by radiographic indication of osteoarthritic changes including femoral neck and acetabular osteophyte development, sclerosis of subchondral bone, subcondral cysts of the femoral head, and ossification of the joint capsule.

While one study reports excellent success in obtaining pelvic radiographs of dogs for hip dysplasia without sedation or anesthesia, chemical restraint is usually employed to achieve proper positioning. Once again, while anesthesia allows for proper positioning, the effects of anesthesia on the relaxation of tissues in the hip joint region and how this may affect the radiographic diagnosis of CHD needs to be taken into consideration.

In conclusion, CHD is a developmental disorder, the expression of which is influenced by a multitude of factors. Gait analysis, palpation, and radiography are indicated to establish a correct diagnosis, but the incipient disease may be difficult to identify because interpretation of the aforementioned diagnostic procedures can be subjective and requires a great deal of skill and expertise for accuracy.

In the next article, we will discuss the treatment of the young growing dog with hip dysplasia. The third article will address the treatment of the mature dog with secondary osteoarthritic changes and degenerative joint disease.

Canine Hip Dysplasia


Canine Hip Dysplasia-Part 2

Surgical Treatment for the Immature Patient

A number of different surgical techniques have been employed to treat canine hip dysplasia. The procedure, which is ultimately selected, should be based upon careful observation and evaluation of the individual patient. Criteria, which must be addressed, include the age of the patient; the severity of subluxation (i.e., the angle of Wiberg); the angle of inclination and anteversion; the depth of the acetabulum; and the presence or absence of femoral head deformity and associated changes indicative of osteoarthritis.

Canine Hip Dysplasia

The surgical procedures most commonly recommended for treatment include triple pelvic osteotomy; intertrochanteric de-rotational femoral osteotomy; excision arthroplasty with or without a bicep sling; and total hip replacement.

The advantages, as well as the indication for each of these procedures, will be discussed in this and in a future article.

The primary goal of surgical intervention for the treatment of canine hip dysplasia in the majority of immature patients is re-direction of the acetabulum. The restoration of hip stability promotes a more normal development of the hip and results in a decrease or halt of the osteoarthritic changes typically associated with a degerenative joint disease.

Because the ultimate goal in a young dog is to help reshape the acetabulum so as to create more depth to accommodate the femoral head and save the hip joint, the technique of choice is the triple pelvic osteotomy (TPO). This procedure presupposes that the femoral component of the hip is normal. Triple pelvic osteotomy is not designed to correct the subluxation problems associated with coxa valga, i.e., increased angle of inclination or increased anteversion of the proximal femur. Such problems need to be addressed by performing a varus osteotomy and demonstrated, however, that if the acetabular component is repositioned such that normal congruency of the joint is maintained, the femoral changes will revert toward normal with time.

Fortunately, in my experience, a femoral osteotomy is usually not necessary, although several studies have indicated that functional results tend to be less satisfactory in dogs having the largest angles of anteversion. Varus and/or intertrochanteric osteotomy is most appropriate in the young dog with subluxation and femoral dysplasia without acetabular dysplasia. As acetabular dysplasia is frequently present, these techniques are seldom employed as a sole means of surgical correction. As previously mentioned, the overwhelming majority of patients exhibit acetabular dysplasia, and the resulting new position obtained by a TPO produces adequate acetabular depth to provide hip stability. However, femoral osteotomy needs to be considered as an ancillary procedure in some cases.

The ideal candidates for a TPO are immature dogs with pain and/or lameness associated with hip subluxation. Since the purpose of the TPO is to prevent the development of degenerative joint disease, only those joints with minimal or no preexisting degenerative joint disease should be considered as candidates for the procedure. When radiographic changes of osteoarthritis are present, excision arthroplasty or total hip replacement may be indicated as the likelihood of success with a TPO is minimized.

The dog’s age is also an important consideration, as rapid breakdown of the dorsal acetabular rim occurs from 4 to 8 months of age in dysplastic puppies. For these reasons, the surgery should be performed prior to nine to ten months of age to achieve best results. However, if the other criteria mentioned previously have been met, good clinical results can still be achieved in older dogs.

Another prerequisite of surgery is the ability to reduce the hip while the patient is under general anesthesia. If the hip cannot be reduced and stabilized by the femoral abduction and internal rotation, there is a diminished chance of success that a TPO would produce good hip stability. Dogs with complete luxation of the hip (grade IV hip dysplasia) however, have been successfully treated with this procedure.

As with any other surgical procedure, numerous techniques and variations of TPO have been developed and used over the last several years to enhance success and minimize complications. The earlier techniques advocated a stair-step osteotomy of the ilium and internal stabilization consisting of screw and wire fixation with or without trochanteric osteotomy. More recently, techniques have employed straight osteotomy of the ilium and rigid internal fixation utilizing bone plates with or without ischial wiring. My own personal preference is to use an oscillating saw to perform the pubic, ischial, and ilial osteotomies through three separate skin incisions. The freely movable acetabular segment is then rotated and tilted into its new position, and rigid stability is achieved and maintained by application of a special pre-contoured bone plate.

Canine Hip Dysplasia

Routine post-operative care consists of confinement and restriction of exercise throughout the immediate post-operative period. Strict rest and confinement should eliminate the potential complication of loss of fixation. Other complications include constipation, urethral impingement, and sciatic nerve injury. Constipation is usually easily alleviated with the administration of stool softener. The proper surgical technique should prevent complication related to urethral and/or sciatic injury. The overwhelming majority of animals will begin bearing weight on the operated limb within 24 to 48 hours, although significant additional time is required for complete healing.

All in all, a triple pelvic osteotomy is an extremely successful treatment of choice for hip dysplasia in the immature dog. This high degree of success, however, depends upon the careful selection of surgical candidates and familiarity with the surgical techniques available.

Canine Hip Dysplasia


Canine Hip Dysplasia-Part 3

Surgical Treatment for the Mature Patient

Although it is highly preferable to diagnose and treat canine hip dysplasia (CHD) in the immature patient, numerous dogs are presented with initial clinical signs of pain and lameness associated with hip subluxation once they have achieved maturity. While triple pelvic osteotomies are routinely performed on mature dogs with no or minimal pre-existing degenerative joint disease with a great degree of success, when moderate to severe radiographic changes of osteoarthritis are present, excision arthroplasty with or without a biceps sling or total hip replacement (THR) is indicated as the likelihood of success with a triple pelvic osteotomy is minimized. The purpose of this article is to discuss the advantages and disadvantages as well as the indication for each of these procedures.

Any discussion about the operative procedures utilized for degenerative disease of the canine coxofemoral joint must be preceded by mention of the fact that the procedure ultimately performed depends upon the surgeon’s experience and training. While this seems intuitively obvious, surgeons are extremely adamant in their views (also intuitively obvious) about which procedure is beset for management of degenerative hip dysplasia in the canine. While some surgeons consider a femoral head and neck excision, a salvage procedure one step short of an amputation, others feel that the inherent risks involved in a THR do not warrant its utilization as a form of treatment. In light of this fact, the discussion of the operative procedures available will proceed from the least aggressive to the most aggressive options rather than from worst to best or visa versa.

Femoral head and neck ostectomy (FHO) is a relatively simple procedure that has been used frequently to eliminate the pain experienced by dysplastic patients. Because the procedure does not reconstruct an intact coxofemoral joint, normal function of the joint is not restored. While the formation of a false joint often alleviates pain and produces increased weight bearing ability on the affected limb, post-operative sequellae including shortening of the affected limb, muscle atrophy, decreased range of motion of the pseudoarthrosis and continued pain, and/or lameness is not uncommon after simple excision of the femoral head and neck. Although these residual clinical signs may result from the biomechanical alterations associated with the formation of a false joint, they may also be attributable to persistent abnormal contact of the proximal femur with the pelvis. For these reasons, various modifications of the standard technique for excision arthroplasty have been developed to prevent bone on bone contact between the cut surface of the femoral neck and the acetabulum.

My own clinical observation has been that in dogs receiving excision, arthroplasty of the femoral head and neck alone increased morbidity, and generally overall, poorer results are achieved than if an ancillary, interpositional procedure is concurrently performed. It is therefore my own personal preference to discourage utilization of a simple FHO for treatment of degenerative joint disease of the canine hip and to rely instead on an ancillary interpositional procedure in combination with an FHO or total hip replacement. While a variety of tissues including the joint capsule and the deep gluteal and biceps femoris muscles have been mobilized to prevent bone on bone contact between the pelvis and the cut surface of the femoral neck, utilization of the biceps femoris allows for a wider and thicker flap of muscle to be mobilized easily for translocation.

The advantages and disadvantages of performance of a biceps sling compared to a simple FHO have been debated for a number of years. Surgeons that discourage its utilization argue that the increased operative time and potential morbidity (i.e., increased swelling or edema of the operated limb, wound infection, sciatic nerve entrapment), outweigh any potential benefits including excellent coverage of the ostectomy site, to decreased bone on bone contact, and the promotion of early post-surgical use of the limb.

Over the course of the last nine years, I have had considerable exposure to and experience with the biceps sling, and my clinical impression is that these patients, while perhaps not being restored to a totally normal state, fare far better than if a simple FHO had been performed. In fact, the overwhelming majority return to at least good, if not excellent, function over a relatively short period of time, free from pain, discomfort, and crepitation at the ostectomy site. Excision arthroplasty of the femoral head and neck utilizing a biceps femoris muscle sling is certainly an effective alternative to total hip replacement.

Total hip replacement is a rewarding method of treatment for canine hip dysplasia as the best approach to restoring normal hip function is to reestablish as closely as possible normal joint configuration. While standard operative procedures have been in use for more than 15 years, recent advances in surgical technique and modifications of the implants themselves have led to greater acceptance of the procedure as complication rates have decreased and long term success has been documented. The hesitancy to recommend THR as the primary means of treatment of canine hip dysplasia outside of limited availability and cost has been the potential for complications including prosthesis dislocation, deep infection, loosening of the implants, femoral fracture, and sciatic neuropraxia. Once again, by paying strict attention to detail, the potential for complications following THR is minimized and excellent long-term success rates can be achieved, clearly demonstrating the THR is an effective method of treating canine hip dysplasia.

In conclusion, it should be mentioned that patient selection for any of the aforementioned procedures is of the utmost importance. A dog that has hip dysplasia but has clinically sound ambulatory function is not a candidate for surgery. Many dogs function with minimal pain or impairment on medical management alone, despite tremendous bony changes. Others, with what appear to be minimal lesions, are severely hindered. It follows then that a reasonable effort at medical management must have been tried and failed. The point of medical failure must be clearly recognized, however, because continuing medical therapy after these treatments have become ineffective decreases the chances for surgical success. In addition, an accurate neurologic examination is mandatory, as many myelopathies co-exist in dysplastic dogs. If there is the presence of neurologic degeneration, the dog should not be considered a surgical candidate.

In response to the poor results consistently obtained with excision arthroplasty in large dogs, my recommendation is to avoid this procedure as a treatment for hip dysplasia and to rely instead on a biceps sling surgery or a total hip replacement. The determination of which of these two procedures to use depends upon the client’s expectations for return to function and the degree to which they are willing to accept the potential limitations and/or complications associated with each procedure.

canine hip-dysplasia