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 OFA Hip Dysplasia

 

 

Hip Dysplasia Radiograph Procedures

 

 

 

General Information
 

Radiographs submitted to the OFA must follow the American Veterinary Medical Association guidelines for positioning. This view is accepted world wide for detection and assessment of hip joint irregularities and secondary arthritic hip joint changes. To obtain this view, the animal must be placed on its back in dorsal recumbency with the rear limbs extended and parallel to each other. The knees (stifles) are rotated internally and the pelvis is symmetric. Chemical restraint (anesthesia) to the point of relaxation is recommended. For elbows, the animal is placed on its side and the respective elbow is placed in an extreme flexed position.

The radiograph film must be permanently identified with the animal's registration number or name, date the radiograph was taken, and the veterinarian's name or hospital name. If this required information is illegible or missing, the OFA cannot accept the film for registration purposes. The owner should complete and sign the OFA application. It is important to record on the OFA application the animal's tattoo or microchip number in order for the OFA to submit results to the AKC. Sire and dam information should also be present.

Radiography of pregnant or estrus females should be avoided due to possible increased joint laxity (subluxation) from hormonal variations. OFA recommends radiographs be taken one month after weaning pups and one month before or after a heat cycle. Physical inactivity because of illness, weather, or the owner's management practices may also result in some degree of joint laxity. The OFA recommends evaluation when the dog is in good physical condition.

Chemical restraint (anesthesia) is not required by OFA but chemical restraint to the point of muscle relaxation is recommended. With chemical restraint optimum patient positioning is easier with minimal repeat radiographs (less radiation exposure) and a truer representation of the hip status is obtained.

For large and giant breed dogs, 14" x 17" film size is recommended. Small film sizes can be used for smaller breeds if the area between the sacrum and the stifles can be included.

If a copy is necessary ask your veterinarian to insert 2 films in the cassette prior to making the exposure. This will require about a 15% increase in the kVp to make an exact duplicate of the radiograph sent to OFA. Films may be returned if a $5.00 fee and request for return are both included at time of submission.

Good contrast is desirable (high mAs, low kVp). Grid techniques are recommended for all large dogs.

OFA's Handling Procedures

When a radiograph arrives at the OFA, the information on the radiograph is checked against information on the application. The age of the dog is calculated, and the submitted fee is recorded. The board-certified veterinary radiologist on staff at the OFA screens the radiographs for diagnostic quality. If it is not suitable for diagnostic quality (poor positioning, too light, too dark or image blurring from motion), it is returned to the referring veterinarian with a written request that it be repeated. An application number is assigned.

Radiographs of animals 24 months of age or older are independently evaluated by three randomly selected, board-certified veterinary radiologists from a pool of 20 to 25 consulting radiologists throughout the USA in private practice and academia. Each radiologist evaluates the animal's hip status considering the breed, sex, and age. There are approximately 9 different anatomic areas of the hip that are evaluated (Figure 1).

  1. Craniolateral acetabular rim
  2. Cranial acetabular margin
  3. Femoral head (hip ball)
  4. Fovea capitus (normal flattened area on hip ball)
  5. Acetabular notch
  6. Caudal acetabular rim
  7. Dorsal acetabular margin
  8. Junction of femoral head and neck
  9. Trochanteric fossa

The radiologist is concerned with deviations in these structures from the breed normal. Congruency and confluence of the hip joint (degree of fit) are also considered which dictate the conformation differences within normal when there is an absence of radiographic findings consistent with HD. The radiologist will grade the hips with one of seven different physical (phenotypic) hip conformations: normal which includes excellent, good, or fair classifications, borderline or dysplastic which includes mild, moderate, or severe classifications.

Seven classifications are needed in order to establish heritability information (indexes) for a given breed of dog. Definition of these phenotypic classifications are as follows:

  1. Excellent
  2. Good
  3. Fair
  4. Borderline
  5. Mild
  6. Moderate
  7. Severe

(See What Do Hip Grades Mean for more detail on the classifications)

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 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 closed to public information.

Accuracy of Data

When results of 1.8 million radiographic evaluations by 45 radiologists were analyzed, it was found that all three radiologists agreed as to whether the dog 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 three radiologists agreed on the same hip phenotype (excellent, fair, good, borderline, mild, moderate or severe). Twenty-one percent of the time, two radiologists agreed on the same hip grade and the third radiologist was within one hip grade of the other two. Two radiologists agreed on the same hip grade and the third radiologist was within two hip grades of the other two 5.4% of the time. This percentage of agreement is high considering the subjective nature of the evaluation.

Other Radiographic Findings

In addition to assessing the dog's hip conformation, the veterinary radiologist reports other radiographic findings that could have familial, inherited causes such as transitional vertebrae or spondylosis.

Transitional vertebrae are a congenital malformation of the spine that occur at the junctions of major divisions of the spine (usually between the thoracic and lumbar vertebral junction and the lumbar and sacral vertebral junction). Transitional vertebrae take on anatomic characteristics of both divisions of the spine it occurs between. The most common type of transitional vertebrae in dogs is in the lumbo-sacral area where the last lumbar vertebral body takes on anatomic characteristics of the sacrum. Transitional vertebrae are usually not associated with clinical signs and the dog can be used in a breeding program. The OFA recommends breeding the dog to another dog that does not have transitional vertebrae.

Spondylosis is another incidental radiographic finding where smooth new bone production is visualized between vertebral bodies at the intervertebral disc spaces. The new bone production can vary in extent from formation of small bone spurs to complete bridging of adjacent vertebral bodies. Spondylosis may occur secondary to spinal instability but often it is of unknown cause and clinically insignificant. A familial basis for its development has been reported. Like transitional vertebrae, dogs with spondylosis can be used in a breeding program.

OFA's Handling Procedures

When a radiograph arrives at the OFA, the information on the radiograph is checked against information on the application. The age of the dog is calculated, and the submitted fee is recorded. The board-certified veterinary radiologist on staff at the OFA screens the radiographs for diagnostic quality. If it is not suitable for diagnostic quality (poor positioning, too light, too dark or image blurring from motion), it is returned to the referring veterinarian with a written request that it be repeated. An application number is assigned.

Radiographs of animals 24 months of age or older are independently evaluated by three randomly selected, board-certified veterinary radiologists from a pool of 20 to 25 consulting radiologists throughout the USA in private practice and academia. Each radiologist evaluates the animal's hip status considering the breed, sex, and age. There are approximately 9 different anatomic areas of the hip that are evaluated (Figure 1).

  1. Craniolateral acetabular rim
  2. Cranial acetabular margin
  3. Femoral head (hip ball)
  4. Fovea capitus (normal flattened area on hip ball)
  5. Acetabular notch
  6. Caudal acetabular rim
  7. Dorsal acetabular margin
  8. Junction of femoral head and neck
  9. Trochanteric fossa

The radiologist is concerned with deviations in these structures from the breed normal. Congruency and confluence of the hip joint (degree of fit) are also considered which dictate the conformation differences within normal when there is an absence of radiographic findings consistent with HD. The radiologist will grade the hips with one of seven different physical (phenotypic) hip conformations: normal which includes excellent, good, or fair classifications, borderline or dysplastic which includes mild, moderate, or severe classifications.

Seven classifications are needed in order to establish heritability information (indexes) for a given breed of dog. Definition of these phenotypic classifications are as follows:

  1. Excellent
  2. Good
  3. Fair
  4. Borderline
  5. Mild
  6. Moderate
  7. Severe

(See What Do Hip Grades Mean for more detail on the classifications)

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 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 closed to public information.

Accuracy of Data

When results of 1.8 million radiographic evaluations by 45 radiologists were analyzed, it was found that all three radiologists agreed as to whether the dog 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 three radiologists agreed on the same hip phenotype (excellent, fair, good, borderline, mild, moderate or severe). Twenty-one percent of the time, two radiologists agreed on the same hip grade and the third radiologist was within one hip grade of the other two. Two radiologists agreed on the same hip grade and the third radiologist was within two hip grades of the other two 5.4% of the time. This percentage of agreement is high considering the subjective nature of the evaluation.

Other Radiographic Findings

In addition to assessing the dog's hip conformation, the veterinary radiologist reports other radiographic findings that could have familial, inherited causes such as transitional vertebrae or spondylosis.

Transitional vertebrae are a congenital malformation of the spine that occur at the junctions of major divisions of the spine (usually between the thoracic and lumbar vertebral junction and the lumbar and sacral vertebral junction). Transitional vertebrae take on anatomic characteristics of both divisions of the spine it occurs between. The most common type of transitional vertebrae in dogs is in the lumbo-sacral area where the last lumbar vertebral body takes on anatomic characteristics of the sacrum. Transitional vertebrae are usually not associated with clinical signs and the dog can be used in a breeding program. The OFA recommends breeding the dog to another dog that does not have transitional vertebrae.

Spondylosis is another incidental radiographic finding where smooth new bone production is visualized between vertebral bodies at the intervertebral disc spaces. The new bone production can vary in extent from formation of small bone spurs to complete bridging of adjacent vertebral bodies. Spondylosis may occur secondary to spinal instability but often it is of unknown cause and clinically insignificant. A familial basis for its development has been reported. Like transitional vertebrae, dogs with spondylosis can be used in a breeding program.

 

 

 

 

 

 

 

 

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