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TOTAL HIP REPLACEMENT IN DOGS
Overview
The hip is a "ball and socket" joint, where the ball-shaped femoral head rests within a bony cup called an acetabulum. Ball and socket joints are very flexible, allowing dogs to run, jump, twist, and pivot. In some dogs, however, arthritis or other problems can cause such severe pain in the hip joints that the dogs have difficulty walking or even getting out of bed (Figure 1). In larger dogs, total hip replacement may be the best option for improving comfort and function.
Figure 1. Ventral-dorsal radiograph view of a canine pelvis showing severe osteoarthritis in the hip joints (arrows).
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During total hip replacement, the femoral head is removed and replaced with a metal ball, and the acetabulum (the socket part of the joint) is replaced with a plastic cup (Figure 2). The ball and stem of the artificial joint ("prosthesis") can be made from a variety of metals, including stainless steel, titanium, or cobalt-chromium. Cobalt-chromium is used most commonly in animals because of its ability to withstand stress and maintain strength for a long period of time. The socket is made of a plastic that is very resistant to friction and has an excellent longevity.
Figure 2. Picture of the components of an artificial hip. After the dog's arthritic hip joint is removed, the metal stem is inserted down the inside of the upper thigh bone (femur) and the acetabular cup is inserted into the pelvic bone (acetabulum) to make a new ball and socket joint.
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Types of Procedures
Two options are available for total hip replacement in dogs. The most common procedure uses bone cement to hold the new stem and ball joint in place. With the "cementless" technique, the stem that fits tightly into the thigh bone (femur). The stem is specially designed to encourage bone to grow around and stick to its surface, holding the stem in place. The choice of which technique is used is based on the surgeon's preference and the patient's age, physical activity level, and quality of bone.
When Should Hip Replacement be Performed?
The decision to perform a total hip replacement should be made only after consultation with your dog's veterinarian and an ACVS Veterinary Surgeon. They can best determine if your dog is a good candidate for the procedure and when it should be performed. To find an ACVS veterinary surgeon in your area, click here: Find a Surgeon.
Patient Screening
It is very important that the patient is completely examined before undergoing total hip replacement. The animal should be checked for any body infections (skin, dental, urinary, respiratory, etc.), since it cannot have surgery until all infections are cleared. It will also be evaluated for other orthopedic or neurologic condition, particularly those involving the knees or the lower back, that could be causing the lameness, discomfort, or difficulty rising. Properly positioned radiographs (x-rays) must also be taken to allow measurements in order to select the proper size artificial joint; these x-rays may require heavy sedation or anesthesia.
Description of the Procedure
The animal is given a general anesthetic and placed on its side, and the leg is prepared for surgery. A surgical approach to the hip joint is performed. The original femoral head is removed with a saw and the leg bone (femur) and pelvis (acetabulum) are cleaned out in preparation for placement of the implant. If cement is used, it is injected under pressure into the femur and acetabulum, and the implants are then placed and kept in position until cement is hardens (Figure 3).
Figure 3. Pelvic x-rays of a dog that had a cemented total hip replacement. Arrows show the components of the prosthesis.
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Postoperative Care and Prognosis
After total hip replacement, exercise is restricted to walking only for at least 1-2 months. Normal activity is then gradually reintroduced. Dogs with total hip replacements usually have normal or near normal return to function about 95% of the time, and most are pain free once they recover from the surgery.
Potential Complications Following Surgery
The most common complication after surgery is luxation (dislocation) of the prosthetic femoral head (metal ball) out of the plastic socket (Figure 4). These luxations can occur immediately after surgery because of excessive physical activity. Luxation can also occur if the acetabular cup is not positioned properly in the pelvis. Most luxations are treatable but a second surgery may be required to put the artificial joint back together.
Figure 4. Pelvic radiographs of a canine patient showing luxation (dislocation) of the implant head out of the acetabular socket (Arrow) because the dog was too active after surgery.
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Dogs that are too active after surgery of have thin bones can also fracture their femurs (Figure 5). These fractures must be surgically repaired, which sometimes requires removal of the implants.
Figure 5. Pelvic radiographs of a canine with a fractured femur shaft at the total hip replacement site (Arrow)
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Infection is a rare but serious complication of total hip replacement (Figure 6). Infections generally require removal of implants and long term use of antibiotics; if cement is present, the dog could continue to have recurrent infections even after months of treatment. Therefore, screening for infections before surgery is very important. Dental disease, open wounds, urinary tract infections and significant dermatitis (skin disease) must be eliminated before total joint replacement should be considered. Extreme care is taken during surgery to maintain sterility.
Figure 6. Pelvic radiograph of an infected total hip replacement. Note the radiolucent (black or dark grey) line (Arrows) around the acetabular socket, indicating bone destruction and loosening of the implant.
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One long-term complication that is more common in people after total hip replacement is "aseptic" (non-infectious) loosening (Figure 7). This is a chronic inflammatory reaction to the foreign material in the implants. Basically this chronic inflammation causes bone reabsorption around the implants, they become loose. This condition can occur with cemented and cementless implants. Diagnosis is based on clinical signs (lameness), radiographic changes (radiolucent lines between implant and bone indicating bone loss), and negative culture results (no evidence of infection).
Figure 7. Radiograph (x-ray) of the metal tip of a prosthetic cemented femoral stem that has aseptic loosening. The metal implant is at the left side of the picture and looks white in the x-ray. The cenment alos appears as a wavy white line just under the head of the orange arrow. The wall of the bone appears as a straight white line under the head of the read arrow. Note the radiolucent (grey) lines between the implant and the cement (Long orange arrow) and the radiolucent line between the cement and the bone (Short red arrow). These radiolucent lines indicate that there is a gap between the implant and surrounding cement, and between the cement and surrounding bone.
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—Alexander El Warrak, DMV, MS
Small Animal Resident
Editor: William Daly, DVM
Diplomate ACVS
Posted 8/13/2004
Edited 2/17/2006
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