Despite breeding selection, hip dysplasia of the dog is still a widespread congenital disorder, especially in large breeds. In hip dysplasia, the fermoral head does not lie sufficiently deep in the hip socket and is loose. During movement, this malformation of the hip joint results in a wear of the joint cartilage, and thereby inevitably to painful processes such as osteoarthritis and arthrosis. In young patients, a subluxation or full luxation of the femoral head can occur due to the excessive looseness. The looseness and potential subluxations constantly strain the joint cartilage, leading to pain and lameness. In older patients, hip dysplasia results in varying degrees of degenerative changes in the joint. Weight, overburdening, nutrition and age additionally influence the progression of the disease. Hip dysplasia is therefore a multifactorial disorder, which cannot be healed. Depending on the severity, therapy measures range from physiotherapy over gold acupuncture to surgical interventions in particularly severe cases.
In contrast to other congenital disorders, hip dysplasia is not caused by a single mutated gene but rather by several mutated genes, which have not yet been fully identified. As there still are no genetic tests available for the deliberate pairing of breeding dogs, the Fédération Cynologique Internationale (FCI) recommends conducting an x-ray in the „hip-extended position“ (radiograph with extended extremities) as a basis for the breeding evaluation of the hip joints of dogs. Veterinarians evaluate the appearance of the femoral head and the hip socket, and their fit. In addition, the so-called Norberg angle is measured, which is 105° or more in a dog with normal hips. 5 degrees of severity from A (normal hip joint) to E (severe hip dysplasia) can be differentiated. Unfortunately, after several decades of breeding using to this method, we have not seen any significant improvements in the gene pool or a reduction of hip dysplasia. Most breeding associations recommend an x-ray of the hip only after 12 months, which in many cases is too late. By that age, grave changes have occurred in the joint, which are not or only insufficiently rectifiable. This is aggravated by the fact that some breeding associations allow breeding with dogs diagnosed with hip dysplasia-B or hip dysplasia-C, despite the genetic component of hip dysplasia.
The PennHIP method (Pennyslvania Hip Improvement Program) was first developed by Prof. Dr. Gail Smith and his team at the University of Pennsylvania in the 1980s. They patented a standardized procedure, by which the looseness of the hip (laxity), the most significant indicator of an hip dysplasia, can be measured with a high degree of accuracy on the basis of x-rays conducted in certain positions and using a specifically customized distraction-device. Only veterinarians specifically trained, evaluated and certified by the University of Pennsylvania are allowed to implement the PennHIP method in Germany. The method comprises a diagnostic tool by which a predication can be made at the age of 16 weeks whether a dog or a cat will later develop an hip dysplasia and thus an osteoarthrosis. The looser the hip, the higher the likelihood that an hip dysplasia will develop. This assessment allows breeders to make early decisions regarding the choice of breeding animals, and enables veterinarians to make an early and reliable prediction regarding therapeutic and preventative measures. Suitable treatments can be implemented, and individual nutritional and training programs can be developed at a very early age for the animal. This also serves the prevention of secondary problems including overburdening and potiential disorders of the front legs, but also other parts of the locomotor system. With the insights obtained by the PennHIP method, the development of an osteoarthrosis can be slowed down or prevented at an early age.
For PennHIP, a short general examination is performed and the dog is lightly sedated. Three x-rays of the hips are performed in different positions. All x-rays are taken with the dog lying on its back.