Health Issues Canine Hip Dysplasia

    Canine Hip Dysplasia

Canine Hip Dysplasia (CHD) afflicts millions of dogs each year and can result in debilitating
orthopaedic 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 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 or ligamentum teres 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.

  CHD Definitions

Dysplasia comes from the Greek words dys, meaning "disordered" or "abnormal", and plassein meaning
"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. The terms DJD, arthritis and osteoarthritis are used interchangeably.
CHD was first described in 1937 by Dr. Gerry B. Schnelle. In a paper entitled Bilateral
Congenital Subluxation of the Coxofemoral Joints of a Dog Schnelle writes: "The condition
described herein, rare though it may be, should be recognized as being congenital and potentially
hereditary, and the dog or bitch in which it occurs should be destroyed or sterilized in the eugenic
interests of the breed."
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 hip joint laxity resulting in
osteoarthritis.

  The Development of CHD

It is generally agreed that hip joint laxity is somehow related to the development of DJD. However,
prior to the research conducted at the University of Pennsylvania, there existed little or no scientific
evidence to bolster this empirical association. The magnitude of hip laxity had not been correlated
with the presence or the extent of DJD. The above definitions of CHD are vague as to the amount
of laxity required to bring about arthritic change. The science behind the PennHIP method has shown
unequivocally that hip joint laxity is the most important risk factor for the development of DJD.
As described above, 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.