Hip Dislocation

normal hip close1

luxated hip close

normal hip - femoral head fits
snugly inside acetabulum
(original graphic by marvistavet.com)

Dislocated hip
(original graphic by marvistavet.com)

The hip joint is a “ball and socket” type joint attaching the rear leg to the trunk of the body. The "ball” part is the head of the first long bone of the rear leg, called the "femur", and the socket is the part of the pelvis known as the “acetabulum.” The femoral head is held in place by a thick ligament called the “capital” ligament or simply the “round ligament of the femoral head.” 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.

THE PATIENT

Limping Dog brown

(original graphic by marvistavet.com)

A radiograph is necessary to confirm the luxation but it will be clear simply from looking at the patient (assuming he or she is walking) that a major orthopedic problem exists. The patient will not be bearing weight on the affected leg and the leg may actually seem shorter than the other three.

If the luxation is not corrected, a false joint, consisting of scarring and fibrous attachment, may form and the patient may begin to bear some weight again but not in a normal way. False joints of this sort are not very strong and do not afford normal range of motion but may be adequate for a very small patient such as an indoor cat or sedentary toy breed dog. Surgical correction should provide a better result, however.

hip displasia xray

(original graphic by marvistavet.com)

THE RADIOGRAPHS

Sometimes it is possible to tell by feeling the joint whether or not it is luxated. Radiographs are still necessary in patient evaluation. This is because there is additional information to be obtained beyond simply whether the joint is luxated. Sometimes when the capital ligament tears, a chip of bone from is femoral attachment comes off as well. If the luxated hip were simply popped back into place with the chip in the joint, the chip would forever be trapped to grind painfully inside the joint. Instead, it should be surgically trimmed.

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 know whether or not it is luxated is important in selecting therapy.

CLOSED REDUCTION

“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.

Dog with Ehmer sling 2

Ehmer slings are usually fashioned
out of bandage tape but can be purchased pre-made (original graphic by marvistavet.com)

To reduce the luxated hip, the patient must be anesthetized to relax the local muscles. The femoral head is manipulated back into place (often with a satisfying “pop”). Radiographs confirm the reduction and a special sling is placed to keep the hip bones together while the joint capsule around them heals.

The sling, called an “Ehmer” sling, involves flexing up the knee and taping the foot to the thigh. The sling stays on approximately 1-2 weeks, while the patient leads a confined lifestyle indoors at home. The bandages must stay clean and dry. After the sling has been on an appropriate time the sling is removed and confinement continues another 2-4 weeks.

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.

SURGERY

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.

There are numerous methods and the surgeon will choose the most appropriate. Expect a sling as described 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

normal hip close1

femoral head cut off

normal hip
(original graphic by marvistavet.com)

femoral head cut off after FHO
(original graphic by marvistavet.com)

This surgery is commonly referred to as the “FHO” and is best used for smaller dogs (50 lbs or less), very active dogs, or 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 other procedures.

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: 9/22/2013