When it comes to health testing for hip dysplasia in North America there are two options available. Pennhip and OFA (Orthopedic Foundation for Animals). What does this mean? Are they the same? Are they both good indicators in determining whether a dog should be bred? I’m going to break this down in simple terms to help explain.
First and foremost, Pennhip and OFA do not test all the same indicators. Pennhip is objective meaning the results are QUANTITATIVE. This means the result is numbers based, a measurable value. OFA is subjective meaning the results are QUALITATIVE. This means it is interpretation based.
Pennhip provides a Distraction Index (DI) number value based on 3 submitted radiology films. Each film is a different view. One distraction view, one compression view and one extended view. It also evaluates the current presence of any osteoarthritis (OA) which would be indicative of dysplasia. The higher the numerical PennHip value, the more likely the patient will develop osteoarthritis at a later date due to hip looseness/instability. This is broken down on the Pennhip report into Mild, Moderate or High risk categories. The lower the DI, the more unlikely OA will form. The DI is measuring the joint laxity. Laxity is how loose the hip joint is (ball in socket). Each breed has an average value based on all dogs within that breed that have been tested. The goal is to have a result less than your breed average but just because you have a result less than your breed average DOES NOT MEAN your dog does not already have joint changes or predisposing indicators of dysplasia. This is where OFA comes into play.
OFA is based on one radiology view (extended hip). It can be submitted for preliminary results over the age of 4 months and under the age of 2 years but you cannot submit for official results until the dog is 2 years old. Preliminary results are read and reported by one veterinary radiologist. Official results are read and reported by three veterinary radiologists. These are BOARD CERTIFIED RADIOLOGISTS. Meaning that they have completed further schooling and passed board exams to become certified in reading diagnostic images. OFA is not objectively measuring the degree of laxity in the joint but instead looking at multiple aspects of the hip joint itself. Aspects they look at are as follows:
SUBLUXATION: How much dislocation/space is there between the ball (head of femur) and the socket. The higher the degree of subluxation, the worse the rating.
REMODELING OF FEMORAL HEAD/NECK: Abnormal changes of structure/form of the head of the femur. Femoral head should be smooth, not jagged or rough.
OSTEOARTHRITIS / DEGENERATIVE JOINT DISEASE: Bony changes within one or both hip joints indicating osteoarthritis/degenerative joint disease. This is progressive and worsens over time. If present, it won’t go away.
SHALLOW ACETABULA: The socket that the head of the femur sits in has poor coverage over the head of the femur. Imagine an egg on a saucer vs an egg in a shot glass. Over time there will be excess strain on the femoral head when it’s not seated well within the pelvic acetabulum (socket). This excess strain can cause degenerative changes to form over time.
ACETABULAR RIM/EDGE CHANGE: Indicates bony changes within the actual socket itself. Along the edges you may find osteophytes (bone spurs) which cause excess pain. Usually this is seen with other arthritic changes in moderate/severe hip ratings.
OFA will take the radiographic findings as well as the breed and breed history into consideration before rating them as passing (Excellent Hips, Good Hips, Fair Hips), Borderline (undetermined, recheck in 6 months), or failing (Mild Hip Dysplasia, Moderate Hip Dysplasia or Severe Hip Dysplasia). OFA will also comment on failing reports on the reason behind why they have failed. They will also comment on whether it is one or both hips.
In summary, Pennhip is measuring the looseness of the hip joint and OFA is grading the degree of dysplasia seen (if any). You can have a dog with lower than average PennHip ratings that has Mild Dysplasia. You can have a dog with very high Pennhip ratings that will still pass with no dysplasia for OFA.
PENNHIP
• Uses 3 x-ray film views
• Objective numerical measurement as compared to breed average
• Measures hip joint laxity
• No pass or fail
• Always completed under heavy sedation or IV anesthesia
• Only veterinarians who are certified for Pennhip are allowed to provide this service.
• No public database available to research specific dogs.
OFA
• Uses 1 x-ray film view
• Subjective opinion from 3 board-certified radiologists
• Looks at 5 indicators of hip dysplasia and gives rating accordingly
• Pass or Fail
• Can be completed awake with no sedation
• Any veterinarian can submit OFA radiographs
• Records available for public viewing. Failing dogs do need to approve being added to this database.
EXAMPLE
12 month old Female Presa Canario
PennHip average for the Presa Canario breed is 0.54.
Patient comes back with a Distraction Index on the Right Hip of 0.46 and a Distraction Index on the Left Hip of 0.39. Both hips are below breed average. There is no evidence of Osteoarthritis in either hip and no cavitation present in the joints. Cavitation means excess space within the joint.
The same extended view x-ray that Pennhip analyzed was sent to OFA for preliminary ratings since this dog is only 12 months old. The results came back with Unilateral (one sided) Mild Hip Dysplasia. The reasoning selected was Subluxation.
The conclusion is that this dog is still dysplastic. Period. This dog has hip dysplasia even though her Pennhip results do not specify or show that. Whether the dysplasia is genetic or environmental we cannot ever know. Multiple factors need to be considered here. Is it one side or both? What is the reason for the rating? Breed history and comparibles can be considered in whether this dog is still sound for breeding. What this means without knowing OFA results is that you can possibly take two dogs with less than average PennHip scores and breed them together despite them both having dysplasia. In a study titled Emerging insights into the genetic basis of canine hip dysplasia, it states:
For the PennHIP method, there are no reports of its effectiveness in reducing the prevalence of Canine Hip Dysplasia in different dog populations.
In another study titled “Effectiveness of PennHIP and Orthopedic Foundation for Animals measurements of hip joint quality for breeding selection to reduce hip dysplasia in a population of purpose-bred detection dogs”, it stated hip joint quality scores were unchanged by use of OFA measurements only. When both PennHIP and OFA measurements were used for the selection of breeding stock, hip joint quality scores improved significantly.
Gold standard across breeds that are predisposed to hip dysplasia would be completing BOTH OFA and PennHip. This will give you a full comprehensive look with both qualitative and quantitative data on the hips.
Hip Dysplasia is not cut and dry by any means. Its multi-factorial and can be genetic, environmental or a combination of both. It is said that the first 60 days of a puppy’s life is the most critical period as the hip joint is developing. Ensuring proper whelping box traction and avoiding high impact activities such as jumping, stairs etc during growth may help reduce instances. Below is a chart outlining Progeny Results of matings between parents with known hip scores.
You can see breeding OFA Excellent to Excellent still yields a 3.6% chance of hip dysplasia. Hip dysplasia can also skip generations. A breeder can only do their best with what is available. Testing stock being most important. This does NOT mean that there will never be puppies with dysplasia in a litter. It's nature and absolutely there still may be.
Clinical signs of hip dysplasia may include slight to moderate lameness, gait and running abnormalities such as bunny hopping, reluctance to rise or climb stairs. Dogs may also be asymptomatic meaning there are no obvious signs or symptoms. Any reputable breeder of large / XL breed dogs should be testing all of their breeding stock and making educated decisions on whether their dogs should reproduce based on the findings. It's important to also note that some breeds with smaller gene pools may be breeding failing scores in order to gradually improve results over generations. It's important to speak with your breeder about results and reasonings behind their pairings.