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What is PennHIP?


PennHIP is a multifaceted radiographic screening method for hip evaluation. The technique assesses the quality of the canine hip and quantitatively measures canine hip joint laxity. The PennHIP method of evaluation is more accurate than the current standard in its ability to predict the onset of osteoarthritis (OA). Osteoarthritis, also known as degenerative joint disease (DJD), is the hallmark of hip dysplasia (HD).

PennHIP is more than just a radiographic technique. It is also a network of veterinarians trained to perform the PennHIP methodology properly and, perhaps most importantly, it is a large scientific database that houses the PennHIP data. Radiographs are made by certified PennHIP members worldwide and are sent to the PennHIP Analysis Center for evaluation. The resulting data is stored in the database, which is continually monitored as it expands. As more information becomes available, the PennHIP laboratory is able to obtain more precise answers to questions about the etiology, prediction and genetic basis of hip dysplasia.

PennHIP publishes its findings in scientific journals. Published information is disseminated to all PennHIP members; it is also shared with interested breed clubs and routinely appears in publications within the dog fancy.

PennHIP is composed of three major components:

  • A diagnostic radiographic technique
  • A network of trained veterinarians
  • A medical database for scientific analysis

PennHIP at a Glance

The PennHIP method is a novel way to assess, measure and interpret hip joint laxity. It consists of three separate radiographs: the distraction view, thecompression view and the hip-extended view. The distraction view and compression view are used to obtain accurate and precise measurements of joint laxity and congruity. The hip-extended view is used to obtain supplementary information regarding the existence of osteoarthritis (OA)  of the hip joint. (The hip-extended view is the conventional radiographic view used to evaluate the integrity of the canine hip joint.) The PennHIP technique is more accurate than the current standard, and it has been shown to be a better predictor for the onset of OA.

The radiographs pictured here are of the same dog, yet the hip joint laxties in each view look very different. Notice that the hips in the distraction view appear to be much looser than they do in the hip-extended view.

Distraction View Compression View Hip-Extended View

The obvious contrast in joint laxity between the distraction and hip-extended views demonstrates the fundamental difference between the two radiographs. The looser the joint on the distraction view, the greater is the chance that the hip will develop OA. The hip-extended view tends to mask true hip joint laxity because the joint capsule iswound up into a tightened orientation when the hips are extended. This explains why measurable joint laxity on the distraction view is always greater than the measurable laxity from the hip-extended view. In fact, distraction laxity is up to 11 times greater depending on the breed of dog under study.

The compression view is used to determine the "goodness of fit" of the femoral heads into the acetabula. In a hip with OA, the remodeling that occurs in the acetabulum and/or the femoral head, will often result in an ill-fitting "ball" and "socket".

To summarize, PennHIP method:

  • Obtains OA readings from the standard hip-extended view
  • Obtains hip joint congruity readings from the compression view
  • Obtains quantitative measurements of hip joint laxity from the distraction view


Introduction to Canine Hip Dysplasia

Dysplastic Hips

The word dysplasia stems from the Greek words dys, meaning "disordered" or "abnormal", and plasseinmeaning "to form". The expression hip dysplasia can be interpreted as the abnormal or faulty development of the hip. Abnormal development of the hip causes excessive wear of the joint cartilage during weight bearing, eventually leading to the development of arthritis, often called degenerative joint disease (DJD) or osteoarthritis (OA). The terms DJD, arthritis and osteoarthritis are used interchangeably.

Canine Hip Dysplasia (CHD) was first described in 1937 by Dr. Gerry B. Schnelle.  Dr. Schnelle initially called it "bilateral congenital subluxation of the coxofemoral joint". It was originally thought to be a rare condition but is now recognized as the most common orthopedic disease in dogs. The radiograph image on the left is the first known example of CHD to be published in a scientific journal.

In 1966, Henricson, Norberg and Olsson refined the definition of CHD describing it as: "A varying degree of laxity of the hip joint permitting subluxation during early life, giving rise to varying degrees of shallow acetabulum and flattening of the femoral head, finally inevitably leading to osteoarthritis."

Today, the general veterinary consensus is that hip dysplasia is a heritable disease manifested as hip joint laxity that leads to the development of OA.

Canine Hip Dysplasia afflicts millions of dogs each year and can result in debilitating orthopedic disease of the hip. Many dogs will suffer from osteoarthritis, pain, and lameness, costing owners and breeders millions of dollars in veterinary care, shortened work longevity, and reduced performance. The occurrence of CHD is well documented in the large and giant breed dogs, but there is also evidence that CHD is prevalent in many small and toy breeds as well as in cats.

Hip dysplasia is a disease of complex inheritance, that is it is caused by many genes. Veterinarians and dog breeders have attempted to eliminate CHD through selective breeding strategies. However, the reduction of CHD frequency in pure-breed dogs has been disappointing.

Fast facts about Canine Hip Dysplasia

  • Canine hip dysplasia (CHD) is the most commonly inherited orthopaedic disease in dogs.
  • CHD is a degenerative, developmental condition, leading to painful hip osteoarthritis, stiffness, and diminished quality of life.
  • All dog breeds are affected by the disease, in some breeds more than 50% of dogs are afflicted.
  • The disease is polygenic and multifactorial.
  • The development of CHD is affected by environmental factors such as weight and age.
  • There is no medical or surgical cure for CHD.
  • CHD is a major concern for working dogs, pet owners, breeders and veterinarians.

Clinical Signs of Hip Dysplasia

There is an acute and a severe form of CHD. An affected dog may have one or any combination of the following clinical signs:Canine hip dysplasia (CHD) in its severest form can be diagnosed by clinical signs, but it usually requires radiographic evidence of hip joint laxity and/or the appearance of osteoarthritis (OA) to arrive at a definitive diagnosis.


Severe (Acute) Phase

  • Presentation at five to 12 months of age,
  • Overt pain, lameness, and functional deficits (low exercise tolerance, reluctance to climb stairs) and
  • Other signs: audible "click" when walking, increased intertrochanteric width ("points of hips" are wider than normal), thigh muscle atrophy.


Mild (Chronic) Form

  • Clinical signs ranging from none to mild,
  • Mild discomfort and stiffness in geriatric years and
  • Possible pain and crepitus on range of motion.

Clinical signs by themselves do not necessarily mean that a dog has hip dysplasia, other conditions of the hip can mimic CHD. A radiograph is essential for a more accurate assessment of the dog's hip joint integrity.

Defining Hip Laxity

Hip joint laxity is the most important risk factor for the development of osteoarthritis. In other words, the amount of laxity or looseness in a hip joint is related to the chance that a hip will develop OA: the looser the hip, the greater the risk. For this reason, it is important to understand the difference between passive and functional hip laxity.

  • Passive hip laxity is subjectively scored or measured on a hip radiograph of a dog while it is under heavy sedation or anesthesia. The PennHIP method measures passive laxity.
  • Functional hip laxity is the pathologic form of laxity occurring during normal weightbearing in dogs with dysplastic hips. Current hip screening methods cannot assess functional hip laxity.

To see how PennHIP measures passive hip laxity, go to the Distraction Index - Measuring Laxity section.

For an in-depth discussion of the association between laxity and OA, go to the Laxity and Osteoarthritis section.

Osteoarthritis (OA): The Big Picture

  • OA causes pain and disability.
  • OA affects all components of the synovial joint.
  • There is no cure for OA.
  • There are treatment options for OA.
    • Non-surgical treatments include use of NSAIDS and nutraceuticals, the modification of nutrition, increase exercise, and physical therapy.
    • Surgery is also an option for end stage disease (ex., FHO, THR).
  • Prevention is key in the fight against canine hip dysplasia (CHD) and OA:
    • Accurate prediction of OA requires a reliable screening method implemented early in life.
    • Genetic control and selective breeding are substantiated effective means of reducing the severity of CHD and the development of OA in subsequent generations of animals.
  • Environmental factors such as diet, activity level, and pharmaceuticals can influence the onset of OA.
  • Surgery is also an option (ex., TPO, JPS). However, the safety and efficacy of preventative surgical procedures have not yet been studied adequately.

The Development of Canine Hip Dysplasia

Canine hip dysplasia (CHD) is a developmental disease. A developmental disease is not present at birth but arises with age. The series of radiographs below illustrate how a loose hip gradually develops osteoarthritis (OA).

At six months, this dog's hips exhibit extreme laxity, but no OA.

At 15 months, laxity is accompanied by the development of "mild" to "moderate" OA: the femoral heads appear slightly "flattened", the femoral necks are beginning to thicken and the acetabular rims are in the early stages of remodeling.

At six years, OA has progressed into a "severe" form, marked by extreme bony remodeling of the acetabular cups and the femoral head and necks.


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