Femoral Head Ostectomy (FHO) in Cats

What is a femoral head ostectomy?

A femoral head ostectomy (FHO) is a surgical procedure that removes the head and neck of the femur (the long leg bone or thighbone) to help restore pain-free mobility to a diseased or damaged hip.

How does an FHO change the hip?

The hip is a simple ball-and-socket joint. The joint consists of two parts: the acetabulum, which is a cup-shaped depression in the pelvis that forms the “socket,” and the head of the femur (thighbone), which forms the “ball.” The head of the femur fits within the acetabulum, allowing the hip to move freely in all directions.

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 limit the joint’s range of motion. In addition, poor joint fit can lead to chronic pain and inflammation.

An FHO restores mobility to the hip by removing the head of the femur (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, creating cushioning between the bones 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?

FHO is commonly recommended for cats, especially those at a healthy weight. Active cats often experience better results with FHO than less active cats. The muscle mass they have built up through activity helps to stabilize the joint, allowing them to regain pain-free mobility more quickly. Inactive cats have less muscle mass around the joint, which can make the joint less stable after surgery and lead to longer recovery times.

Why is FHO performed?

The primary goal of an 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 cost considerations, an FHO may provide the best option for pain-free mobility.

Hip luxation or dislocation (associated with trauma or severe hip dysplasia). In some cases, a hip that is out of the socket cannot be put back into place through manipulation or other medical means. Surgical repair of hip luxation can be costly and is not always successful, so many cat owners choose 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 erode, leading to painful bone-on-bone grating whenever the hip is moved. An FHO can remove this point of contact and alleviate pain.

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

What can I expect on the day of surgery?

FHO 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 your cat’s health and surgery. When you pick your cat up from the hospital, they will probably not bear any weight on the leg that had surgery.

An incision will be visible around 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 them from licking the surgical site.

What care will my cat need after an FHO?

Care varies based on the needs of the specific patient but, in general, the post-operative recovery can be divided into two phases.

Phase 1: Pain control. In the first several days after the operation, your cat will be healing from the surgical procedure. Because bones and muscles are cut during this procedure, the focus during this period is on pain control. Give all medications and treatments as prescribed by your veterinarian (e.g., warm and cold packing). Your veterinarian may also recommend laser therapy to reduce inflammation and encourage healing.

Your veterinarian will recommend activity restrictions during the first several days after surgery. Confine your cat to a crate or small room during this period and remove potential temptations to run or jump. After a few days, you can attempt passive range-of-motion (PROM) exercises, if your cat tolerates them, gently moving the hip forward and backward through its range of motion. Do not do these exercises if they cause your cat pain.

Phase 2: Rebuilding muscle mass and strength. 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 in the false joint from forming too tightly, allowing your cat to remain flexible. Good exercises during this period include:

• Walking (especially up stairs)
• Holding the front portion of your cat’s body in the air while allowing them to “walk” on their hind legs
• Walking through water

Walk slowly to encourage your cat to bear weight on the affected leg. When running, your cat will be more tempted to lift the affected leg. 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 can slow healing that is occurring within the joint and muscles.

When will my cat fully recover from surgery?

Most cats show signs of complete recovery approximately six weeks after surgery. At this point, your cat can resume regular activities. Healing may be more rapid in cats that had normal function until just before the FHO (e.g., a cat that had a sudden, traumatic injury to the hip) and may be slower in cats with longstanding, chronic issues, because these issues often lead to muscle atrophy, which takes time to resolve.

If your cat does not show significant improvement six weeks after surgery, consider a formal rehabilitation or physical therapy program. Ask your veterinarian for recommendations.

What is the prognosis after an FHO?

Most cats recover fully after an 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 affect the cat’s quality of life.