In order to understand how hips dislocate and how they can be put back in place, some knowledge of the anatomy is needed. The normal hip joint can be described as a "ball and socket." The thigh bone, called the "femur" possesses a head that constitutes the "ball" part of the hip joint while the socket is a special area of the pelvic bone called the "acetabulum." In other words, the femoral head and acetabulum form the ball and socket of the hip joint. The femoral head is held in place by a thick ligament called the “capital” ligament or simply the “round ligament of the femoral head” which spans across the center of the joint. Also keeping the bones in their proper location are the muscles of the hip, the upper rim of the acetabulum which acts as a protective ledge, and the fact that the whole joint is enclosed in fibrous capsule.
Hip dislocation is the common term for the separation of the femoral head from the pelvic acetabulum. The more medical term is “hip luxation” and you will probably hear your veterinarian use this term.
In order for the hip to luxate/dislocate, trauma must be severe enough to break the capital ligament and tear the joint capsule. The femur almost always luxates the same way: up and forward.
Radiographs are also important to assess hip dysplasia (the shallow acetabula of this condition may impede manual joint placement or may determine “off the bat” that a surgical correction is needed. If the patient is a puppy or kitten, there is a growth plate (an area where the bone is growing) that may have been damaged in the trauma and this must be assessed. In short, the status of the hip beyond simply knowing whether or not it is luxated is going tobe important in selecting therapy.
“Reduction” is the act of putting the bones of the luxated joint back where they belong. “Closed” reduction means that the bones are put back without surgically opening the joint. If the hip appears to be normal other than the luxation, it is probably worth at least attempting closed reduction; although, after 3 days, local muscle contraction makes successful reduction very difficult. In cats, closed reduction is problematic no matter how old the luxation is as the reduced hip frequently pops out again. Still, as mentioned, closed reduction is a non-invasive procedure and is worth a try if the hip is otherwise normal.
This may sound simple enough but it is not always successful. Large dogs are difficult to manipulate. Cats tend to promptly reluxate their hips. Do not be surprised if closed reduction does not work and surgery is recommended.
There are many techniques of surgical treatment that might be employed in keeping the bones where they are supposed to be. In a perfect situation, the hip is reduced and only a small tear in the joint capsule is present. Sewing the joint capsule back together hold the femoral head where it belongs in the acetabulum.
In a less perfect situation, the joint capsule is too damaged to simply sew back together. In this situation, screws can be placed around the acetabulum and a hole drilled through the neck of the femur. A stiff suture can run around the screws and through the femoral neck holding the femoral head in place.
Another technique uses a pin passing from the femur, out the femoral head and into the bone of the acetabulum like an axle (effectively re-creating the torn capital ligament).
There are numerous methods and the surgeon will choose the most appropriate. Expect some type of bandaging to be necessary for at least a week and confinement for at least a couple of weeks after that to be necessary.
THE FEMORAL HEAD OSTECTOMY
This surgery is commonly referred to as the “FHO” and is best used for smaller dogs (50 lbs or less), for very active dogs, or for cats. Here, the femoral head is cut off and removed, allowing the joint to heal as a “false joint” (just a capsule connecting the two bones but no actual bone to bone contact.) If the pet is not carrying too much weight, a false joint is strong enough. If the dog is very active, a false joint will form quickly. The pet typically does not want to use the leg for the first 2 weeks but should at least be partially using the leg after 4-6 weeks. The leg should be used nearly normally after a couple of months. Many veterinarians are well experienced with this surgery and often a specialist is not needed. This surgery is typically substantially less expensive than the other procedures. For more details, click here.
If the patient has significant hip dysplasia, this may be a good time to address the dysplasia surgically. For more information on hip dysplasia, click here.
Page last updated: 5/13/2022