Femoral Head Ostectomy (FHO) in Cats

What is FHO surgery?

An FHO, or femoral head ostectomy, is a surgical procedure that aims to restore pain-free mobility to a diseased or damaged hip by removing the head and neck of the femur (the long leg bone or thighbone).

How does an FHO change the hip?

The normal hip is a ball-and-socket joint. The acetabulum, which is a part of the pelvis, composes the socket of the joint. The head of the femur, a projection from the long bone located between the hip and the knee, composes the ball that fits within the socket. The head of the femur fits within the acetabulum, allowing the hip to move freely in all directions.

However, when the hip becomes damaged or diseased, this mobility can be affected. If the acetabulum and the head of the femur do not fit together properly, this poor fit can influence the degree of movement that the joint can achieve. In addition, this poor joint fit can lead to chronic pain and inflammation.

An FHO restores mobility to the hip by removing the head of the femur. This removes the ball of the ball-and-socket joint, leaving just an empty socket. The muscles of the leg will initially hold the femur in place, and, over time, scar tissue will form between the acetabulum and the femur to provide cushioning that is referred to as a 'false joint'. Although this joint is anatomically very different from a normal hip joint, it provides pain-free mobility in most patients.

Is my cat a good candidate for FHO?

This procedure is commonly recommended for cats, especially those who are at a healthy weight. Active cats often experience better results with FHO than less-active cats. The muscle mass that has been built up through activity helps to stabilize the joint, allowing the cat to regain pain-free mobility more quickly than inactive cats. Inactive cats have less muscle mass around the joint, making the joint less stable post-operatively and leading to longer recovery times.

"Active cats often experience better results with FHO than less-active cats."

Why is FHO performed?

The primary goal of FHO is to remove bone-on-bone contact, restoring pain-free mobility. The most common reasons for FHO include:

Fractures involving the hip. When a fracture involves the hip joint and cannot be repaired surgically (either due to patient considerations or financial considerations for the owner), an FHO may provide the best option for pain-free mobility.

Hip luxation/dislocation (associated with trauma or severe hip dysplasia). In some cases, a hip that is out of the socket cannot be replaced with manipulation or other medical means. Surgical repair of hip luxations can be costly and is not always successful, so many cat owners elect FHO for cats with hip luxation. 

Severe arthritis of the hip. In chronic, end-stage arthritis, the cartilage that protects both the head of the femur and the acetabulum can become eroded away, leading to painful bone-on-bone grating whenever the hip is moved. Performing an FHO can remove this point of contact and alleviate pain.

Slipped capital physis. This is an uncommon condition that is caused by an abnormal growing center of the bone in a young cat. This causes a weakness in the femoral neck resulting in a hip fracture.

What can I expect on the day of surgery?

This surgery is performed under general anesthesia. In most situations, you will take your cat to the veterinary clinic early in the morning on the day of surgery. Your veterinarian will likely instruct you to withhold food the morning of surgery to prevent vomiting that may occur under anesthesia.

After surgery, your cat will remain in the hospital for several hours to several days depending on the specific circumstances of her health and her surgery. When you pick her up from the hospital, your cat probably will not be bearing any weight on the leg that had surgery. An incision will be visible in the area of the hip, and this incision may or may not have visible external sutures. Some veterinarians use dissolving sutures that are placed under the skin. Your cat will likely be wearing an Elizabethan collar (cone) to prevent licking at the surgical site.

What care will my cat need after FHO surgery?

Care varies based on the needs of the specific patient but, in general, the post-operative recovery can be divided into two phases. In the first several days post-operatively, your cat will be healing from the surgical procedure. Because bones and muscles are cut during this procedure, the focus during this period will be on pain control. Please give all medications as prescribed by your veterinarian. Moist heat may also be recommended during this period, to provide comfort and decrease stiffness. Your veterinarian may also recommend laser therapy to reduce inflammation and encourage healing. 

Your veterinarian may recommend activity restrictions during the first several days after surgery. If this is the case, confine your cat to a crate or small room during this period and remove potential temptations to run or jump. If your cat will tolerate it, you can attempt passive range-of-motion (PROM) exercises during this period, gently moving the hip forward and backward through its range of motion. This should not be performed, however, if it causes pain for your cat.

Your veterinarian will likely recommend introducing more physical activity approximately one week after surgery. During this phase of recovery, the focus shifts to rebuilding muscle mass and strength. Keeping your cat mobile will help keep the scar tissue within the false joint from forming too tightly, allowing your cat to remain flexible. Good exercises during this period include walking (especially up flights of stairs), holding the front portion of your cat’s body in the air while allowing her to 'walk' on her hind legs, and walking through water. Walking should be slow in order to encourage your cat to bear weight on the affected leg; when running, your cat will be more tempted to carry the affected leg.

"Keeping your cat mobile will help keep the scar tissue within the false joint from forming too tightly, allowing your cat to remain flexible."

In the first 30 days after surgery, it is important to avoid rough play or any activity that encourages sudden twists and turns. These high-impact motions will slow the healing that is occurring within the joint and muscles.

Most cats will show signs of complete recovery approximately six weeks post-operatively. At this point, your cat can resume her regular activities. Healing may be more rapid in cats that had normal function up until shortly before the procedure (for example, in the case of a cat that had a sudden, traumatic injury to the hip) and may be slower in cats with longstanding, chronic issues (because these chronic issues often lead to muscle atrophy, which takes time to resolve).

If your cat is not showing significant improvement by six weeks post-operatively, you may want to consider a formal rehabilitation or physical therapy program. Ask your veterinarian for recommendations if your cat is still having difficulties at or after six weeks.

What is the prognosis after FHO surgery?

Most cats recover fully after FHO surgery and regain essentially normal function of the affected leg. Although the leg may have a slightly decreased range of motion or decreased limb length after surgery, these impacts are typically minimal and do not impact the cat’s quality of life.