Canine hip dysplasia (CHD) develops during postnatal skeletal growth. A definitive diagnosis can be made radiographically when secondary signs of osteoarthritis due to joint incongruity become evident. If joint incongruity is diagnosed before the start of degenerative joint changes, osteoarthritis can be prevented.
Early diagnosis and proper treatment can arrest and reverse the progression of disease and change its pathogenesis. Triple pelvic osteotomy (TPO) can be performed in puppies with femoral head subluxation due to increased dorsal acetabular rim slope. In puppies without signs of osteoarthritis, this technique modifies the direction of the forces inside the joint, leading to a redirection of the femoral head inside the acetabulum. During the residual growth period, the femoral head and the acetabulum regain their joint congruity through uniform cartilage loading, thus preventing or limiting osteoarthritis. The juvenile pubic symphysiodesis (JPS) described by Mathews and colleagues in 1996 is a technique intended to modify the slope of the acetabular roof in a more ventral direction during skeletal growth in puppies with signs that indicate early hip dysplasia. Limiting the circumferential growth of the pelvic canal by arresting growth of the pubic symphysis results in bilateral acetabular rotation, which improves femoral head coverage. In the residual growth period, joint congruity and joint biomechanics are improved, preventing or limiting osteoarthritis.
Protocol for Preoperative Evaluation and Patient Assessment
A thorough examination of the hips and several radiographic views are necessary to obtain reliable and predictive results from the selected treatments. Clinical and radiographic findings should be compared, and contrasting data scrutinised. Incomplete evaluations, such as examination of only a ventrodorsal radiographic view, lead to unreliable results.
Ortolani Sign
In the anaesthetised or deeply sedated dog, the stability of the femoral head in the acetabulum, the amount of joint laxity and the features of femoral head subluxation are evaluated. To measure these angles precisely, we use the Canine Electronic Goniometer designed by Slocum. The angle of reduction is indicative of joint capsule laxity. The angle of subluxation is indicative of the dorsal acetabular rim (DAR) slope and of acetabular filling: the DAR slope is the inclination of the weightbearing dorsal part of the acetabulum. Filling of the acetabulum with osteophytes and thickening of the round ligament can also increase the angle of subluxation.
Static Radiographic Hip Study
Using orthogonal views, lateral, ventrodorsal and anteroposterior, a three-dimensional study of the hip can be done on the anaesthetised dog to evaluate both the pelvis and femur. Joint incongruity is evaluated and signs of osteoarthritis identified by examining the craniolateral acetabular rim, the dorsal acetabular rim and the femoral head and neck. In the standard frogleg view filling of the acetabular fossa, caused by a permanently displaced femoral head or hypertrophied round ligament, will widen the articular rim. The lateral view is useful to evaluate the lumbosacral joint. To be perfectly functional, the DAR slope should be almost perpendicular to the direction of the weightbearing forces; in normal dogs the slope is <7.5 degrees from a line perpendicular to the long axis of the pelvis. As the DAR slope increases, so does the angle of subluxation. In the dysplastic dog, the lateral aspect of the DAR is blunted and rounded because of erosion and its slope is >20 degrees; the femoral head moves dorsally and laterally along the inclined plane of the sloped DAR. By combining the DAR study with passive joint laxity measurements functional joint laxity is evaluated.
Distraction View
Using a distraction device to push the femoral heads apart, a dynamic evaluation of passive joint laxity can be carried out. In a study conducted by Badertscher, the half-axial position was used to improve radiographic visualisation of subluxation; results were similar to those described later by Smith. We have used the procedure described by Badertscher (but with a modified positioner) because it is simple, rapid and provides reliable results. The dog is positioned in dorsal recumbency with the femurs slightly extended at approximately 95-105 degrees to the table surface and the tibiae parallel to the plane of the table surface. An S-shaped Teflon table device, that is 2 cm thick, 5-12 cm wide and 50 cm long with a hinged base to keep it in contact with, and parallel to, the table, is placed on the ventral surface of the pelvis. Pressure applied to the medial aspects of the proximal femurs through the handheld tibiae results in a fulcrum that subluxates the femoral heads from the acetabula. To calculate the passive joint laxity, the distraction index (DI) described by Smith and colleagues was used.
Case Selection for Prophylactic Treatment
When hip dysplasia is detected at an early age, it is possible to alter the progression of the disease with appropriate treatment before the onset of osteoarthritis. The success of preventive treatment is measured by its ability to prevent osteoarthritis in clinical cases with pathological joint conditions. The timeframe to correct developing hip dysplasia by surgical treatment is limited and is lost once cartilage damage, DAR microfractures and acetabular filling have occurred. With the most commonly used techniques aimed at altering the course of developing hip dysplasia in the growing dog, the best results are obtained before lameness and other signs of disease have occurred. Case selection for prophylactic treatment is accomplished according to the following criteria:
Triple Pelvic Osteotomy
Triple pelvic osteotomy (TPO) is indicated in dogs 5-12 months old with no or minimal signs of osteoarthritis and joint subluxation, an angle of reduction between 20 and 40 degrees, an angle of subluxation between 10 and 30 degrees and a DAR slope between 10 and 20 degrees with its lateral border preserved. The degree of acetabular rotation, i.e., the degree of torsion of the canine pelvic osteotomy plate, is determined according to the DAR slope, whereby excessive correction that would limit abduction of the leg must be avoided. After correction, the DAR slope should be 0 to -5 degrees and the angle of subluxation 0 to 5 degrees. With the indications described above, the most successful degree of correction is 20 degrees; with this correction, the DAR does not impinge upon the femoral neck and the gait is not altered. When the angles of reduction and subluxation are very close (less than 15 degrees), acetabular filling and blunting of the dorsolateral acetabular rim are present, indicating loss of dorsal coverage; in these cases, TPO is contraindicated. When the distraction index is very high (i.e., over 0.9), capsulorrhaphy should be performed in addition to TPO. When properly performed and with the right indications, TPO can reverse CHD, prevent the development of osteoarthritis and provide full joint function. When performed in less than ideal candidates with mild osteoarthritis, TPO will not prevent further development of osteoarthritis and for that reason it is not indicated.
Juvenile Pubic Symphysiodesis
JPS is performed at an early age and the most favourable results are achieved in 3.5-4-month-old puppies. Indications for JPS are signs that predict the future development of CHD: a positive Ortolani sign with an angle of reduction of 20-40 degrees, an angle of subluxation of 0-15 degrees, DI from 0.4 to 0.8 and DAR angles of 7-12 degrees. The procedure is not effective in puppies with more severe signs or with established osteoarthritis and clinical signs; the degenerative process cannot be stopped by a slow-effect procedure such as JPS. While the acetabular roofs are slowly moving ventrally, the femoral heads slip laterally along the sloped and rounded lateral acetabular border, leading to further erosion of this area. In contrast, when performed in selected cases with the appropriate indications and postoperative restriction of physical activity (limiting playing and jumping, promoting swimming), JPS is effective in improving joint congruity and preventing or limiting the development of osteoarthritis.
Contraindications for Prophylactic Treatment
The disadvantages of preventive surgeries are related to incorrect case selection, such as performing TPO or JPS in dogs with osteoarthritis. These techniques are contraindicated in such cases because they will not prevent the progression of osteoarthritis. In these cases, palliative surgeries such as dorsal acetabular rim plasty (DARthroplasty) or elective surgeries such as total hip replacement should be suggested instead. In severe early CHD, cementless total hip replacement like the 'Zurich' model can be applied successfully in patients as young as 5 months. JPS is a surgical procedure that modifies the canine phenotype without leaving radiographic evidence of the operation. For this reason, JPS has a strong ethical implication that must be discussed thoroughly with puppy owners to gain their understanding and compliance. We strongly recommended that puppies undergoing JPS be neutered at the same time. We believe that the lifelong benefits provided by successful JPS would justify this procedure, provided that the ethical aspects are well understood.
Conclusions
The predictive value of early diagnosis and treatment of CHD can be substantiated by monitoring cases that receive conservative treatment. Early and reliable diagnosis of CHD allows timely surgery that is intended to modify joint morphology, restore joint congruity and prevent or limit osteoarthritis.
References
1. Badertscher RR. The half-axial position: improved radiographic visualization of subluxation in canine hip dysplasia. MS Thesis, Athens, Georgia, 1977.
2. Dueland RT, Adams WM, et al. Effect of pubic symphysiodesis in dysplastic puppies. Veterinary Surgery 2001; 30: 201-217.
3. Mathews KG, Stover SM, Kass PH. Effect of pubic symphysiodesis on acetebular rotation and pelvic development in guinea pigs. American Journal of Veterinary Research 1996; S7: 1427-1433.
4. Slocum B, Devine Slocum T. Pelvic osteotomy. In: Bojrab, MJ; Ellison, GW; Slocum, B. eds. Current Techniques in Small Animal Surgery (fourth edition). Baltimore: Williams & Wilkins, 1998; 1159-1165
5. Smith GK, Biery DN, Gregor TP. New concepts of coxofemoral joint stability and the development of a clinical stress-radiographic method for quantitating hip joint laxity in the dog. Journal of the American Veterinary Medical Association 1990; 196: 59-70.