Total Hip Replacement

Mature dogs with hip dysplasia suffer from chronic, painful, degenerative joint disease (arthritis). The clinical signs occur in one or both rear limbs but are usually bilateral (occurring in both legs). Lameness often appears suddenly after prolonged exercise or after a brisk walk. This is the result of tears or injuries to the abnormal joint tissue. The dog may be slow upon rising and may take a few minutes to warm out of joint stiffness. Occasionally, stifle (knee) ligaments are injured when the dog tries to protect the hip by overextending the stifle joint.

In the chronically affected hip, the joint capsule (which is normally paper thin) is markedly thickened. Subsequently, extension of the hip becomes difficult. This results in shorter, choppy steps when running. Due to discomfort and pain, the dog sits rather than stands when he or she stops. When rising, he or she does so slowly and with some degree of difficulty. The dog may be reluctant to chase, jump, or run a long distance. Finally, when pain has restricted limb use for weeks to months, muscle atrophy and loss of muscular support in the rear limbs becomes severe. At the same time, weight is shifted to the forelimbs and the shoulder muscles enlarge.

Once the patient has radiographic (x-ray) evidence of degenerative arthritis, it is no longer a candidate for a triple pelvic osteotomy. Over time, many of these dogs will become less responsive to analgesic medications and surgical therapy should be considered.

There are two procedures available:

• Removal of the femoral head and neck (excision arthroplasty, femoral head ostectomy, FHO).

• Total hip replacement.

Femoral head excision works well for dogs under thirty pounds and those with unilateral hip dysplasia. It is less satisfactory for dogs over fifty pounds particularly when performed bilaterally. This is a salvage procedure for those owners who cannot afford the cost of a total hip replacement but need an alternative to constant medication and debilitating pain.

Introduced in 1976, the total hip replacement has become the only treatment available that provides normal hip joint function once advanced arthritis is present. With this technique, the femoral head and neck (ball portion of the hip joint) are replaced with a stainless steel or titanium component and the acetabulum (hip socket) is replaced with a plastic cup prosthesis. A five year followup study of 221 total hip replacements revealed an overall success rate of 91%. Total hip replacement can be done on both hips although many dogs (80-90%) do very well with only one side replaced.

Common problems which mimic hip dysplasia:

• Cauda equina syndrome (i.e. lower back problems)

• Cranial (anterior) cruciate ligament tears

• Other rear limb arthritic conditions

Traditionally, the signs of hip dysplasia are rarely extreme. Usually, only mild to moderate lameness is noted which may suddenly worsen. Dogs with a cranial (anterior) cruciate ligament tear typically hold the affected leg up (which is unusual with hip dysplasia). Patients with back (spinal) problems often scuff their toenails when walking, have an uncoordinated gait, and are weak in the rear limbs. They may be very painful if they have a disc rupture (sciatica) or show no spinal pain in certain degenerative spinal cord conditions (German Shepherd myelopathy). In any case, the complete evaluation of a total hip replacement candidate will include an examination for these problems.