HD: Hip Dysplasia
Canine HD is a developmental trait primarily affecting medium and large sized dogs, and it is also known in Cardigans. However, many Cardi's with affected hips do not seem to suffer a lot and manage to live their lives as any other dog.
Canine hip dysplasia is a developmental malformation of the hip joints resulting in secondary joint disease (arthrosis, arthritis) and corresponding clinical symptoms such as pain and lameness. The major cause of CHD is an excessive laxity of the hip joint, characterized by subluxation of the femoral head out of the acetabulum. The aetiology of CHD is not fully understood. Poor quality connective tissue of the joint capsule may play a crucial role. The disease is hereditary, and current data suggest a major gene theory. Heritability may be up to 95 % (!) depending on breed and population studied. Many breed clubs have established a program to control CHD.
Diagnosis of CHD is commonly based on radiographic findings in large-scale screening of dogs. Radiographic technique has been standardized worldwide. The dog is deeply sedated or anesthetized to guarantee adequate muscle relaxation. Then it is positioned in dorsal recumbence with the hind limbs extended caudally and the femora parallel to the spine, to the table top and to each other. The patellae are centered over the femoral shafts.
The severity of CHD is judged based on the degree of subluxation and to a lesser degree on the presence and severity of secondary joint disease. It must be noted though that radiographs do not precisely reflect the genetic make up of a dog itself nor the risk for passing CHD to the offspring.
Internationally 3 somewhat differing scoring modes are in use:
- the FCI (Fédération Cynologique Internationale)
- the OFA (Orthopedic Foundation for Animals)
- the BVA/KC (British Veterinary Association/The Kennel Club)
FCI is the umbrella organisation of more than 80 national kennel authorities located in most European countries, in Russia, South America, and Asia. The scientiﬁc committe of FCI proposes a 5 grades scoring system from A (reﬂecting a normal hip joint) to E (indicating severe hip dysplasia). Grades are deﬁned descriptively based on the size of Norberg angle (NA), degree of subluxation, shape and depth of the acetabulum and signs of secondary joint disease. Radiographic evaluation of the hip joints has been implemented as mandatory prerequisite for breeding dogs in many western countries in the last 40 years. Dogs must be at least 1 year of age for ofﬁcial scoring. Hips are usually scored by a single scrutineer per breed club or within a country with some exceptions. Dogs scoring moderate or severe are banned from breeding in most countries. For mildly dysplastic dogs speciﬁc breeding restrictions may apply.The following FCI classiﬁcation is based on radiological features noted on a radiograph taken with the hind limbs extended of dogs between 1 and 2 years of age. It is as objective as possible. It may be adopted for older dogs, but secondary arthrotic changes have then to be judged according to the age of the dog. Final grading is based on the worst hip joint. The mode of publication of the results depends on the bye-laws established by the individual breed clubs.
A: No signs of Hip Dysplasia
The femoral head and the acetabulum are congruent. The craniolateral acetabular rim appears sharp and slightly rounded. The joint space is narrow and even. The Norberg angle is about 105°. In excellent hip joints the craniolateral rim encircles the femoral head somewhat more in caudolateral direction.
B: Near normal hip joints
The femoral head and the acetabulum are slightly incongruent and the Norberg angle is about 105° or The femoral head and the acetabulum are congruent and the Norberg angle is less than 105°.
C: Mild hip dysplasia
The femoral head and the acetabulum are incongruent, the Norberg angle is about 100° and/or there is slight ﬂattening of the craniolateral acetabular rim. No more than slight signs of osteoarthrosis on the cranial, caudal, or dorsal acetabular edge or on the femoral head and neck may be present.
D: Moderate hip dysplasia
There is obvious incongruity between the femoral head and the acetabulum with subluxation. The Norberg angle is more than 90° (only as a reference). Flattening of the craniolateral rim and/or osteoarthrotic signs are present.
E: Severe Hip Dysplasia
Marked dysplastic changes of the hip joints, such as luxation or distinct subluxation are present. The Norberg angle is less than 90°. Obvious ﬂ attenting of the cranial acetabular edge, deformation of the femoral head (mushroom shaped, ﬂ attening) or other signs of osteoarthrosis are noted.
The phenotypic evaluation of hips done by the OFA (Orthopedic Foundation for Animals, USA) falls into seven different categories. Those categories are Normal (Excellent, Good, Fair), Borderline, and Dysplastic (Mild, Moderate, Severe).
Once each of the radiologists classifies the hip into one of the 7 phenotypes above, the final hip grade is decided by a consensus of the 3 independent outside evaluations. Examples would be:
Two radiologists reported Excellent, one Good - the final grade would be Excellent
One radiologist reported Excellent, one Good, one Fair - the final grade would be Good
One radiologist reported Fair, two radiologists reported Mild - the final grade would be Mild
The hip grades of Excellent, Good and Fair are within normal limits and are given OFA numbers. This information is accepted by AKC on dogs with permanent identification (tattoo, microchip) and is in the public domain. Radiographs of Borderline, Mild, Moderate and Severely dysplastic hip grades are reviewed by the OFA radiologist and a radiographic report is generated documenting the abnormal radiographic findings. Unless the owner has chosen the open database, dysplastic hip grades are not in the public domain.
Excellent: this classification is assigned for superior conformation in comparison to other animals of the same age and breed. There is a deep seated ball (femoral head) which fits tightly into a well-formed socket (acetabulum) with minimal joint space. There is almost complete coverage of the socket over the ball.
Good: slightly less than superior but a well-formed congruent hip joint is visualized. The ball fits well into the socket and good coverage is present.
Fair: Assigned where minor irregularities in the hip joint exist. The hip joint is wider than a good hip phenotype. This is due to the ball slightly slipping out of the socket causing a minor degree of joint incongruency. There may also be slight inward deviation of the weight-bearing surface of the socket (dorsal acetabular rim) causing the socket to appear slightly shallow.
Borderline: there is no clear cut consensus between the radiologists to place the hip into a given category of normal or dysplastic. There is usually more incongruency present than what occurs in the minor amount found in a fair but there are no arthritic changes present that definitively diagnose the hip joint being dysplastic. There also may be a bony projection present on any of the areas of the hip anatomy illustrated above that can not accurately be assessed as being an abnormal arthritic change or as a normal anatomic variant for that individual dog. To increase the accuracy of a correct diagnosis, it is recommended to repeat the radiographs at a later date (usually 6 months). This allows the radiologist to compare the initial film with the most recent film over a given time period and assess for progressive arthritic changes that would be expected if the dog was truly dysplastic. Most dogs with this grade (over 50%) show no change in hip conformation over time and receive a normal hip rating; usually a fair hip phenotype.
Mild Hip Dysplasia: there is significant subluxation present where the ball is partially out of the socket causing an incongruent increased joint space. The socket is usually shallow only partially covering the ball. There are usually no arthritic changes present with this classification and if the dog is young (24 to 30 months of age), there is an option to resubmit an radiograph when the dog is older so it can be reevaluated a second time. Most dogs will remain dysplastic showing progression of the disease with early arthritic changes. Since HD is a chronic, progressive disease, the older the dog, the more accurate the diagnosis of HD (or lack of HD).
Moderate Hip Dysplasia: there is significant subluxation present where the ball is barely seated into a shallow socket causing joint incongruency. There are secondary arthritic bone changes usually along the femoral neck and head (termed remodeling), acetabular rim changes (termed osteophytes or bone spurs) and various degrees of trabecular bone pattern changes called sclerosis. Once arthritis is reported, there is only continued progression of arthritis over time.
Severe Hip Dysplasia: assigned where radiographic evidence of marked dysplasia exists. There is significant subluxation present where the ball is partly or completely out of a shallow socket. Like moderate HD, there are also large amounts of secondary arthritic bone changes along the femoral neck and head, acetabular rim changes and large amounts of abnormal bone pattern changes.
|OFA||FCI (European)||BVA (UK/Australia)||SV (Germany)|
|Excellent||A-1||0-4 (no > 3/hip)||Normal|
|Good||A-2||5-10 (no > 6/hip)||Normal|
BVA/KC reports the pooled consensus brought up by 3 highly experienced and skilled scrutineers who guarantee a correct reading. Final hipscore reaches a heritability of up to 70%, which is high for a system based on standard radiographs in a non-stressed position. Final score is given as a ﬁgure from 0 for an excellent to 106 for a highly dysplastic and severely arthrotic hip joint. No translation of the numerical score into a dysplasia grade is provided. BVA recommends breeding dogs with a score of 5 or less (total score for both joints < 10) or clearly below breed mean score.
Breed mean score is listed and regularly updated for each breed on the BVA’s website (www.bva.co.uk/public/chs/bms2006.pdf). Breeding from dogs scoring more than 15 (total score for both joints > 30) is undesirable. Additional information regarding health and diseases of selected breeds is available from www.thekennelclub.org.uk