Canine hip dysplasia is the most common non-traumatic orthopaedic pathology of growing dogs; it is characterized by lack of congruity between the articular surfaces of the head of femur and the acetabular cup, which inexorably leads to arthritic degeneration of variable severity.
The disorder can be diagnosed at its outset, when only the joint incongruity and capsular laxity are present, or later when the pathogenic mechanisms have already led to the development of secondary lesions and arthritic degeneration. This degeneration is not necessarily limited to adult or elderly dogs. Indeed, severe forms of dysplasia and joint alterations may also be seen in puppies. It is, therefore, mistaken to believe that dysplasia can only be diagnosed when an animal’s skeletal maturation has been completed: dysplastic features are already clear throughout the growth period. It is, however, necessary to wait for the completion of skeletal maturation in order to be able to exclude the presence of dysplasia definitively, since mild forms can pass unobserved in growing animals.
When hip dysplasia involves the two posterior limbs signs are rarely pronounced. Subjects with bilateral, posterior hip dysplasia usually learn to tolerate the chronic pain, adapting their level of activity, shifting loads onto the anterior limbs and resting frequently. Puppies with this form of dysplasia therefore often seem listless and lazy. In contrast, when the dysplasia is unilateral or presents as an acute form with severe subluxation, associated with inflammation of the joint synovium, the clinical signs are clearly evident. The biomechanical alterations resulting from joint laxity and/or malformation of the acetabulum become established as early as the second month of life, causing incongruity between the femoral head and the acetabulum; the subluxation of the head of the femur produces excessive friction between the two joint heads with erosion of joint cartilage, exposure of the subchondral bone and activation of mediators of inflammation, synovitis and osteoarthritis culminating in severe pain and difficulty with walking.
Since hip dysplasia is a progressive disorder that develops during the growth of a puppy’s skeleton, prompt evaluation of the state of the hip joints during the growth phase can enable the disease to be picked up in its initial stage and provide information in advance on whether the puppy will or will not develop dysplasia and, if so, to what degree. It is, therefore, useful to make an early or “preventive” diagnosis of canine hip dysplasia in growing dogs; this is done at different ages depending on the breed, the method used and the severity of the joint alterations present. The aims of early evaluation of canine hip dysplasia are primarily those of prophylactic medicine, with detection of early signs of the dysplasia, a prediction of its evolution and the possibility of a timely, preventive intervention to reduce or stop the expression of the disease.
An early evaluation of the hips, which can reveal the first morphological and functional changes associated with the evolving dysplasia, provides the possibility of choosing the therapeutic intervention best suited to the dog’s condition and the functional expectations. Should one wait until the time when the disease is usually diagnosed, after the onset of signs, the already established arthritis thwarts any type of treatment aimed at preventing the onset or progression of the dysplasia. Indeed, at this point the joint degeneration has already triggered a mechanism of cartilaginous fibrillation and erosion, exposure of subchondral bone and formation of osteophytes, which are irreversible.
On the other hand, when the diagnosis is made very early, by picking up the first signs of the pathogenic mechanism – joint laxity, subluxation and incongruity of the joint heads – surgical procedures can be used to prevent or limit the expression of the disease by restoring correct articular biomechanics.
The age at which an early evaluation of hip dysplasia, as indeed the standard evaluation, should be performed is not fixed, but depends on the validity of the diagnostic method used, the clinical experience, the breed of dog and the degree of dysplasia present. Although an early diagnosis can be made at any time during growth, in order to exploit any subsequent preventive strategy to the full the diagnosis must be made as soon as the investigational methods and skeletal maturation enable a reliable diagnosis. On the bases of published data and the authors’ personal experience, the youngest age at which a highly reliable early diagnosis can be made is 14-16 weeks in medium-sized and large dogs and 18-20 weeks in giant breeds. Earlier investigations would pick up only the very early and very severe cases, while most cases would be falsely negative. The disease can be diagnosed during the growth phase by careful evaluation of early radiographic and clinical signs. Joint laxity and an excessive slope of the dorsal acetabular rim are clinical and radiographic predictors related to joint morphology and congruity. Imaging techniques and palpation can be used for early evaluation of the conformation, congruence and laxity of the joint. In this early stage of the disease, the articular cartilage has undergone only minimal alterations and it is, therefore, possible to invert the pathogenic mechanism and stop the joint degeneration completely.
An early evaluation of hip dysplasia should be carried out routinely in breeds more prone to developing this disease and in which it would have a strong impact on quality of life, such as the Bernese Mountain Dog, Border Collie, Boxer, Cane Corso, Dogue de Bordeaux, Labrador Retriever, Golden Retriever, Neapolitan Mastiff, Maremma Sheepdog, German Shepherd Dog, Rottweiler, St. Bernard, English Setter and Newfoundland.
In order to give reliable results, the early evaluation of canine hip dysplasia must include a meticulous orthopaedic examination and static and dynamic radiographic studies aimed at detecting prodromic signs of the disease, collecting as much information as possible and comparing the data with other findings. An incomplete evaluation, such as that based only on ventral-dorsal X-rays, can only detect the most severe cases and lead to an unreliable prognosis in all cases in which the only problem present is an increased joint laxity.
ORTHOPAEDIC TECHNIQUES FOR EARLY EVALUATION OF THE HIPS IN THE PUPPY
Deep sedation or general anaesthesia is necessary for an early evaluation of the hips in order to be able to assess joint laxity and subluxation of the hip correctly, without the interference that would otherwise be caused by the patient’s reaction and muscle contractions.
PHYSICAL EXAMINATION OF THE HIP JOINT: EVALUATION OF ORTOLANI’S SIGN AND MEASUREMENT OF THE ANGLES OF REDUCTION AND SUBLUXATION
A physical examination of the coxofemoral joint can determine the stability of the femoral head in the acetabular cup and be used to measure joint laxity when present. In the presence of joint laxity, when the femoral head is subjected to slight pressure it moves in and out of the acetabular socket, causing a distinctive “clunk” sound: this finding is called Ortolani’s sign. With the patient still sedated the angles of subluxation (AS) and reduction (AR) can be determined. These are the angles at which the joint dislocates and, conversely, when it returns into the socket, and provide a measure of the severity of the joint laxity and the changes to the dorsal acetabular rim. The AR is directly proportional to the degree of joint laxity: the greater the laxity, the more the femoral head luxates, and the louder the “clunk” of Ortolani’s sign. The AS is directly proportional to the slope of the dorsal acetabular edge and to its integrity. Ortolani’s sign is not elicited in hips with joint laxity within normal limits. Ortolani’s sign is also negative in conditions of advanced arthritis, because of the severe fibrosis of the joint capsule.
RADIOGRAPHY
Static radiographic studies include various X-ray views and are aimed at providing an objective evaluation of the arrangement and congruity of the joint heads, while dynamic radiography is aimed at showing any joint laxity present:
- Standard ventro-dorsal view
- ‘Frog-leg’ ventro-dorsal view
- Dorsal acetabular rim view
- Ventro-dorsal view with distraction to evaluate joint laxity.
Standard ventro-dorsal view
To obtain a correct evaluation of joint congruity, the patient must be placed in dorsal recumbency, resting in a V-shaped support in order to constrain the thorax and maintain it in a sagittal position which, in its turn, will keep the pelvis in a horizontal position; the pelvis should, therefore, be parallel to the X-ray table, the femora should be parallel to each other, the hips well extended and the limbs rotated such that the patellae are positioned at the centre of the femoral condyles. The following parameters must be evaluated on the X-ray: pelvic symmetry, position of the femoral head in the acetabular socket and the amount of coverage of the femoral head by the acetabular rim, the appearance of the joint line if converging or diverging and the shape and direction of the cranial acetabular margin. In order to give an objective value to the congruity of the joint and thus obtain a model applicable to all subjects, the position of the centre of the femoral head must be evaluated with respect to the dorsal acetabular rim (DAR). A circular stencil with a measuring scale is used to identify the centre of the head of the femur and then the position of this point with respect to the DAR is determined. With respect to the DAR, the position of the femoral head can be classified as medial, overlying or lateral and then, using the scale on the stencil, the amount of medial or lateral displacement can be measured in millimetres. Measurement of Norberg’s angle, which is useful in adult dogs, in not indicated in puppies because the cranio-lateral rim of the acetabulum, on which this angle is based, is still not well calcified in immature animals. Joint morphology should also be assessed in the dorso-ventral X-ray view: that is, the shape of the cranial acetabular margin, the depth of the acetabulum and the shape of the neck and head of the femur. The X-ray should also be examined carefully for any early signs of arthritis such as subchondral sclerosis, Morgan’s line, and osteophytes of the head and neck of the femur.
‘Frog-leg’ ventro-dorsal view
This view enables an evaluation of the coverage of the femoral head by the acetabulum. Ideally, the acetabulum should cover more than half of the head of the femur. The development of acetabular filling by an hypertrophic round ligament and fibro-cartilaginous tissue is secondary to the lack of joint congruity and to the presence of joint laxity. Reduced acetabular coverage conditions the surgical choice. Corrective pelvic osteotomy surgery (triple or double pelvic osteotomy) will not be successful in a subject with acetabular filling (TPO and DPO).
Dorsal acetabular rim view
This X-ray view provides more information on the integrity and angulation of the DAR. The dog is placed in sternal recumbency with the posterior limbs extended and drawn forwards to the sides of the thorax. This projection enables the evaluation of the part of the acetabulum subjected to weight-bearing and its slope. This slope is measured by an angle called the “DAR angle”. The DAR angle represents the plane of inclination of the dorsal acetabular rim with respect to a line traced perpendicularly to the major axis of the pelvic girdle. In dogs with normal hips the lateral part of the DAR is clear and sharp, the femoral head is housed deeply within the acetabular cup, the joint is congruent and the DAR has a minimum slope of less than 7.5°. In puppies with early signs of hip dysplasia, the DAR slope is greater than 7.5° and can reach 20° or even more. As the disease progresses, the sharp dorsal acetabular margin becomes eroded or completely worn away.
Joint laxity, which is indicative of the development of osteoarthritic degeneration, can be objectively evaluated by measuring the distraction index on X-rays obtained with various methods of distraction:
- view with the limbs in distraction, using the PennHIP method;
- view with the limbs in distraction, using Vezzoni’s modification of the Badertscher procedure;
- view with the limbs in distraction, using Belkoff’s technique;
- view with the limbs in distraction, using Fluckiger’s technique.
The authors of this article routinely use the Badertscher technique with a personal modification and an appropriate distractor.
View with distraction
This procedure enables the degree of joint laxity to be evaluated precisely by using an appropriate distractor which, acting as a fulcrum, provides a force able to distend the joint capsule and induce subluxation of the femoral head to the extent that the laxity of the joint capsule allows.
The measurements described by G. Smith (PennHip method) are performed on the X-rays to obtain the distraction index (DI) for each joint. This index is the number obtained by dividing the distance (d) between the geometric centre of the head of the femur and that of the acetabulum by the radius (r) of the head of the femur: DI = d/r. This value is usually between 0 and 1. A hip joint with a distraction index close to 0 has a minimal physiological laxity, while a hip with a distraction index of 1 has an excessive laxity, with a severely dislocated femoral head. Intermediate values express a laxity tending towards physiological or abnormally marked values. Although there are variations in the distraction index in different breeds, in order to allow hip development without dysplasia, the value of the index should not exceed 0.3 for dolicomorphic breeds and 0.4 for mesomorphic ones. Values over 0.6 are always indicative of dysplastic joint development.
COMPARISON BETWEEN DATA COLLECTED AND PROGNOSIS
The clinician should make a thorough evaluation and careful comparison of the data obtained from the clinical examination and the X-ray screening of the hips in order to reach a diagnosis of the current state of the joint and, from this, express a prognosis based on the evolution of the disorder by completion of the dog’s skeletal development. It can then be determined whether conservative or surgical treatment is more appropriate. An early diagnosis made by evaluating the joints of puppies aged between 4 and 6 months is reliable only when all the clinical and radiographic data are collected and then studied, compared and correlated. The comparison of the data obtained makes the evaluation safer, by exposing possible incongruous findings due to errors in performing the clinical or radiographic studies. For example, a very high angle of reduction found in an animal with a low distraction index means that the distraction manoeuvre was not carried out correctly.
The time window to correct the development of dysplasia with prophylactic surgical interventions is very limited because it is necessary to intervene before irreversible damage occurs to the joint cartilage and to the DAR and before morphological changes develop in the joint heads. Given the exuberant nature of a puppy and its weight gain, every day that passes the joint damage continues to progress until it becomes irreversible. A veterinarian who undervalues the problem loses the opportunity to treat the puppy with early surgery, which is able to prevent the development of joint degeneration.
When the values of the AR and AS are 10°-15° and 0°, respectively, the joint laxity (DI) is slightly higher than 0.3, the centres of the femoral heads in a ventro-dorsal X-ray are medial to the DAR and the slope of the DAR is less than 7°, the joint is almost normal and has only slight distension of the capsule; in these cases no corrective surgery is necessary. Simple control of physical activity and an increase in muscle mass achieved, for example, through swimming, will be sufficient to limit the joint laxity.
In puppies between 3.5 (medium-sized and large breeds) and 5 months (giant breeds) old with a tendency to hip subluxation, AR values between 15° and 35°, AS values between 0° and 15°, a DAR inclination between 7°and 10° with a conserved rim and joint laxity (DI) between 0.4 and 0.8, a juvenile pubic symphysiodesis is indicated. The prognosis of puppies with values at the limits of the indications varies depending on the lesions present and the post-operative management. Treated puppies have increased acetabular coverage, improved articular congruity and an arrest or slowing of evolving arthritis. Surgery is ineffective in puppies with values beyond those set out for the indications and when the pathology has already progressed to an advanced stage with severe subluxation. Age is an important factor which influences the outcome of the surgery. The time window indicated for the treatment remains between 12 and 20 weeks of age.
When a puppy aged between 5 and 8 months old presents with an AR between 25° and 40° and an AS between 10° and 20°, with the difference between the AR and AS values being greater than 15°, with mild involvement of the joint cartilage perceptible as a finely granular crackle (joint cartilage fibrillation), a DAR slope between 8° and 20°, without severe flattening of the rim, without acetabular filling and with subluxation of the femoral heads in the absence of arthritis or only minimal signs of arthritis, a triple or double pelvic osteotomy is indicated.
In subjects in which palpation of the hip reveals AR and AS values greater than 40° and 20°, respectively, a thickened, torn joint capsule, eburnation of the articular cartilage with severe alterations to the DAR, modifications of joint morphology and acetabular filling, the degenerative process is already underway and corrective osteotomy is not able to halt the progression of the arthritis, only a total hip replacement is able guarantee recovery of joint function.
Puppies which present between 4 and 6 months old with a high AR, but an AS that is negative or 0°, joint laxity with a DI between 0.4 and 0.6, a normal DAR slope, and with lax hip joints but without clinically significant dysplasia, as demonstrated by X-ray studies on reaching skeletal maturity, do not require surgical treatment but must undergo control X-rays after 2 months to check that the laxity has not affected the cartilaginous component and triggered joint incongruity. The laxity detected in these subjects is interpreted as “passive” laxity, induced only with a distractor, which does not occur during weight-bearing because of the correct slope of the acetabular roof and muscle contractions. In contrast, the laxity is defined “active” when the increased slope of the acetabular roof allows subluxation of the hip during weight-bearing.
When the values of AR and AS are very similar it means that the joint has undergone severe acetabular filling with erosion of the dorso-lateral acetabular rim due to a chronic dislocation of the femoral head; subsequently it will not be possible to perceive the transition between reduction and subluxation (angle of translation) clearly.
Suggested readings
- Slocum B, Slocum TM. Hip – Diagnostic Tests. In: Current techniques in small animal surgery. Ed Bojrab MJ, Ellison GW, Slocum B. Baltimore: Williams&Wilkins, 1998; pp 1127–1144.
- Slocum TD, Slocum B. Radiographic characteristics of hip displasia. In: Current techniques in small animal surgery. Bojrab MJ, Ellison GW, Slo- cum B (eds). Williams&Wilkins, Baltimore, 1998, pp 1145–1150.
- Dueland RT, Patricelli AJ, Adams WM, Linn KA, Crump PM. Canine hip dysplasia treated by juvenile pubic symphysiodesis. Part II: two year clinical results. Vet Comp Orthop Traumatol. 2010; 23(5): 318-25. Epub 2010 Aug 25. Erratum in: Vet Comp Orthop Traumatol.2010; 23(6): 472
- Dueland RT, Adams WM, Patricelli AJ, Linn KA, Crump PM. Canine hip dysplasia treated by juvenile pubic symphysiodesis. Part I: two year results of computed tomography and distraction index. Vet Comp Orthop Traumatol. 2010; 23(5): 306-17. Epub 2010 Aug 25. Erratum in: Vet Comp Orthop Traumatol. 2010; 23(6): 472.
- Bernardé A. Juvenile pubic symphysiodesis and juvenile pubic symphysiodesis associated with pectineus myotomy: short-term outcome in 56 dysplastic puppies. Vet Surg. 2010 Feb; 39(2): 158-64.
- Vezzoni A, Dravelli G, Vezzoni L, De Lorenzi M, Corbari A, Cirla A, Nassuato C, Tranquillo V. Comparison of conservative management and juvenile pubic symphysiodesis in the early treatment of canine hip dysplasia. Vet Comp Orthop Traumatol. 2008; 21(3): 267-79.
- Manley PA, Adams WM, Danielson KC, Dueland RT, Linn KA. Long-term outcome of juvenile pubic symphysiodesis and triple pelvic osteotomy in dogs with hip dysplasia. J Am Vet Med Assoc. 2007 Jan 15; 230(2): 206-10.
- Patricelli AJ, Dueland RT, Adams WM, Fialkowski JP, Linn KA, Nordheim EV. Juvenile pubic symphysiodesis in dysplastic puppies at 15 and 20 weeks of age. Vet Surg. 2002 Sep-Oct; 31(5): 435-44.
- Dueland RT, Adams WM, Fialkowski JP, Patricelli AJ, Mathews KG, Nordheim EV. Effects of pubic symphysiodesis in dysplastic puppies. Vet Surg. 2001 May-Jun; 30(3): 201-17.
- Risler A, Klauer JM, Keuler NS, Adams WM. Puppy line, metaphyseal sclerosis, and caudolateral curvilinear and circumferential femoral head osteophytes in early detection of canine hip dysplasia. Vet Radiol Ultrasound. 2009 Mar-Apr; 50(2): 157-66.
- Ginja MM, Gonzalo-Orden JM, Melo-Pinto P, Bulas-Cruz J, Orden MA, San Roman F, Llorens-Pena MP, Ferreira AJ. Early hip laxity examination in predicting moderate and severe hip dysplasia in Estrela mountain dog. J Small Anim Pract. 2008 Dec; 49(12): 641-6. Epub 2008 Aug 5.
- Adams WM. Radiographic diagnosis of hip dysplasia in the young dog. Vet Clin North Am Small Anim Pract 2000; 30: 267–280
- Slocum B, Devine TM. Dorsal acetabular rim radiographic view for evaluation of the canine hip. J Am Anim Hosp Assoc 1990; 26: 289–296.
- Smith GK, Mayhew PD, Kapatkin AS et al. Evaluation of risk factors for degenerative joint disease associated with hip dysplasia in German Shepherd Dogs, Golden Retrievers, Labrador Retrievers, and Rottweilers. J Am Vet Med Assoc 2001; 219: 1719–1724.
- Smith GK, Popovitch CA, Gregor TP. Evaluation of risk factors for degenerative joint disease associated with hip dysplasia in dogs. J Am Vet Med Assoc 1995; 206: 642–647.
- Fluckiger MA, Friedrich GA, Binder H. A radiographic stress technique for evaluation of coxofemoral joint laxity in dogs. Vet Surg 1999; 28: 1–9.