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What is PennHIP?

PennHIP stands for the University of Pennsylvania Hip Improvement Program.

PennHIP is a multifaceted radiographic technology (x-ray) 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. Osteoarthritis, also known as degenerative joint disease (DJD), is the hallmark of canine hip dysplasia (CHD).

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. The 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 (cause), prediction and genetic basis of CHD.

PennHIP Radiographic Evaluation at a Glance

The PennHIP method is a different way to assess, measure and interpret hip joint laxity. It consists of three separate radiographs: the distraction view, the compression view and the hip-extended view (see below). The distraction view and compression view, developed by Dr. Gail Smith, 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 DJD in the hip joint.

Distraction View	Compression View	Hip-extended View
The radiographs above and to the right are of the same dog, yet the hip joint laxities (looseness) in each view look very different. Notice that the hips in the distraction view (top left) appear to be much looser than they do in the hip-extended view (right). On average the distraction view has been shown to reveal 2.5 - 11 times more hip laxity (depending on breed) than the hip-extended view. Also the PennHIP method can measure the laxity of a hip joint with greater precision than the hip-extended method.   The degree of hip joint laxity, as measured by the PennHIP method, has been shown to be the most important risk factor in determining whether a dog is prone to developing CHD.

To summarize, the PennHIP method

Canine Hip Dysplasia

Hip dysplasia was first described in 1937.  It is a disease of complex inheritance. Accordingly, 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.

What is CHD?

A Brief Anatomical Review

The hip is a ball and socket joint. The "ball" is known as the femoral head. The "socket" part of the joint is known as the acetabulum. The femoral head is attached to the inside of the acetabulum by the round ligament and to the periphery of the acetabulum by the joint capsule (see illustration). The joint capsule is a continuous envelope that surrounds the joint from the neck of the femur to pelvic bones around the acetabulum, this closed compartment is filled with a viscous, lubricating fluid called synovial fluid. Both the joint capsule and the synovial fluid play an important role in the stability of the hip joint and ultimately in the development of CHD.

The muscles that cause rotation of the hip (not shown) are also extremely important for hip stability. Each individual muscle develops a force component that pulls the femoral head into the acetabulum. For optimal function and stability of the hip, these forces require complex dynamic coordination and balance.

It is generally agreed that hip joint laxity is somehow related to the development of DJD.  CHD is a developmental disease meaning that it is not present at birth, but develops with age. The series of radiographs below illustrate how a loose hip gradually develops DJD.




At 6 months, this dog's hips exhibit extreme laxity, but no DJD.

At 15 months, laxity is accompanied by the development of "mild" to "moderate" DJD: 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 6 years, DJD has progressed into a "severe" form, marked by extreme bony remodeling of the acetabular cups and the femoral head and necks.

CHD Diagnosis

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 DJD to arrive at a definitive diagnosis.

An affected dog may have one or any combination of the following clinical signs:

• Presentation: 5 months to 12 months for the severe form of hip dysplasia; later for the chronic form
• Abnormal Gait
• Bunny-hopping When Running
• Thigh Muscle Atrophy (loss of muscle mass)
• Pain
• Low Exercise Tolerance
• Reluctance to Climb Stairs
• Audible "click" When Walking
• Increased Intertrochanteric Width ("points of hips" are wider than normal)

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.