Dogs with hip dysplasia generally fall into one of two categories. The first population is the young dogs (5-10 months old) and the second are older animals that have chronic degenerative joint disease (arthritis). Animals with hip dysplasia will generally present with clinical signs of lameness, pain when rising, worsening of lameness after exercise and "bunny hopping " when running (bringing both rear legs forward at the same time). In the young dogs, the underlying abnormality is laxity of the hip joint. Normally the femoral head (ball) and the acetabulum (socket) should fit closely and congruently with most of the femoral head covered by the acetabulum and the femoral head remains within the acetabulum during weight bearing. Dogs with early dysplastic changes (shallow acetabulum, poor seating and coverage of the femoral head) experience laxity or subluxation of the joint during weight bearing. The laxity of the joint leads to abnormal wear on the dorsal rim of the acetabulum, increased joint fluid and inflammation within the joint. With time the joint capsule stretches and the developing bone of the acetabulum is deformed by continual subluxation of the joint, which leads to an abnormally shallow acetabulum. This concentrates the weight-bearing surface to a small area which results in microfractures of the cartilage and acetabular bone. The body's response to laxity and subluxation is to thicken the joint capsule and bony proliferation. This temporarily eases the associated pain and lameness but as the dog ages, further degenerative changes develop.

Young dogs with clinical signs of hip dysplasia may benefit from surgery to reduce laxity and subluxation and prevent the development of degenerative arthritis in the future. The goal of the triple pelvic osteotomy (TPO) is to provide increased coverage of the femoral head by the acetabulum to prevent subluxation and to improve the congruity of the hip joint. Dogs are screened prior to surgery to determine whether or not they are good candidates for surgery based on standard view hip radiographs, palpation of the hips under sedation and physical exam. In general the surgery is performed on young dogs (5-15 months of age). This allows for growth and remodeling of the hip joint in the improved position. Dogs should have minimal to no arthritic changes in the hip joints on radiographs. Radiographs and hip palpation also evaluate the depth of the acetabulum. An ideal candidate has a good acetabular rim and a deep cup that will provide good coverage and seating of the femoral head. Recently we have begun evaluating the hip joints immediately prior to surgery with arthroscopy to look directly into the joint to determine the condition of the bone and cartilage damage. In the future this may allow for better screening of TPO candidates.

The TPO surgery involves three cuts in the pelvis, which free the acetabulum to be rotated laterally into a more horizontal position to increase femoral head coverage. See figure 1. Once the acetabulum is rotated it is held in place with a special bone plate and screws so the bone can heal in the new position. The TPO can be performed on both hips during the same surgery if needed. See figures 2 and 3.

After surgery the patient is restricted in activity to controlled leash walks until the osteotomies have healed (about 6 weeks). Unrestricted activity can lead to implant bending or breaking and the need for a second surgery. Long term function is generally very good. While some arthritic changes may develop in the joint, they are minimized by the TPO and much less than without surgery.