To understand hip surgery, it is helpful to have a brief description of the structure of the human hip. The femur, or thigh bone, is connected to the knee at its lower end and forms part of the hip joint at its upper end. The femur ends in a ball-shaped piece of bone called the femoral head. The short, slanted segment of the femur that lies between the femoral head and the long vertical femoral shaft is called the neck of the femur. In a normal hip, the femoral head fits snugly into a socket called the acetabulum. The hip joint thus consists of two parts, the pelvic socket or acetabulum, and the femoral head.
The hip is susceptible to damage from a number of diseases and disorders, including arthritis, traumatic injury, avascular necrosis, cerebral palsy, or Legg-Calve-Perthes (LCP) disease in young patients. The hip socket may be too shallow, too large, or too small, or the femoral head may lose its proper round contour. Problems related to the shape of the bones in the hip joint are usually referred to as hip dysplasia. Hip replacement surgery is often the preferred treatment for disorders of the hip in older patients. Adolescents and young adults, however, are rarely considered for this type of surgery due to their active lifestyle; they have few good options for alleviating their pain and improving joint function if they are stricken by a hip disorder. Osteotomies are performed in these patients, using the patient's own tissue in order to restore joint function in the hip and eliminate pain. An osteotomy corrects a hip deformity by cutting and repositioning the bone, most commonly in patients with misalignment of certain joints or mild osteoarthritis. The procedure is also useful for people with osteoarthritis in only one hip who are too young for a total joint replacement.
The incidence of hip dysplasia is four per 1,000 live births in the general world population, although it occurs much more frequently in Lapps and Native Americans. In addition, the condition tends to run in families and is more common among girls and firstborns. Acetabular dysplasia patients are usually in their late teens to early thirties, with the female: male ratio in the United States being 5:1.
A hip osteotomy is performed under general anesthesia. Once the patient has been anesthetized, the surgeon makes an incision to expose the hip joint. The surgeon then proceeds to cut away portions of damaged bone and tissue to change the way they fit together in the hip joint. This part of the procedure may involve removing bone from the femoral head or from the acetabulum, allowing the bone to be moved slightly within the joint. By changing the position of these bones, the surgeon tries to shift the brunt of the patient's weight from damaged joint surfaces to healthier cartilage. He or she then inserts a metal plate or pin to keep the bone in its new place and closes the incision.
There are different hip osteotomy procedures, depending on the type of bone correction required. Two common procedures are:
- Varus rotational osteotomy (VRO), also called a varus derotational osteotomy (VDO). In some patients, the femoral neck is too straight and is not angled far enough toward the acetabulum. This condition is called femoral neck valgus or just plain valgus. The VRO procedure corrects the shape of the femoral neck. In other patients, the femoral neck is not straight enough, in which case the condition is referred to as a femoral neck varus.
- Pelvic osteotomy. Many hip disorders are caused by a deformed acetabulum that cannot accommodate the femoral head. In this procedure, the surgeon redirects the acetabular cartilage or augments a deficient acetabulum with bone taken from outside the joint.
A physical examination performed by a pediatrician or an orthopaedic surgeon is the best method for diagnosing developmental dysplasia of the hip. Other aids to diagnosis include ultrasound examination of the hips during the first six months of life. An ultrasound study is better than an x ray for evaluating hip dysplasia in an infant because much of the hip is made of cartilage at this age and does not show up clearly on x rays. Ultrasound imaging can accurately determine the location of the femoral head in the acetabulum, as well as the depth of the baby's hip socket. An x-ray examination of the pelvis can be performed after six months of age when the child's bones are better developed. Diagnosis in adults also relies on x ray studies.
To prepare for a hip osteotomy, the patient should come to the clinic or hospital one to seven days prior to surgery. The physician will review the proposed surgery with the patient and answer any questions. He or she will also review the patient's medical evaluation, laboratory test results, and x-ray findings, and schedule any other tests that are required. Patients are instructed not to eat or drink anything after midnight the night before surgery to prevent nausea and vomiting during the operation.
Immediately following a hip osteotomy, patients are taken to the recovery room where they are kept for one to two hours. The patient's blood pressure, circulation, respiration, temperature, and wound drainage are carefully monitored. Antibiotics and fluids are given through the IV line that was placed in the arm vein during surgery. After a few days the IV is disconnected; if antibiotics are still needed, they are given by mouth for a few more days. If the patient feels some discomfort, pain medication is given every three to four hours as needed.
Patients usually remain in the hospital for several days after a hip osteotomy. Most VRO patients also require a body cast that includes the legs, which is known as a spica cast. Because of the extent of the surgery that must be done and healing that must occur to restore the pelvis to full strength, the patient's hip may be kept from bearing the full weight of the upper body for about eight to 10 weeks. A second operation may be performed after the patient's pelvis has healed to remove some of the hardware that the surgeon had inserted. Full recovery following an osteotomy usually takes longer than with a total hip replacement; it may be about four to six months before the patient can walk without assistive devices.
Although complications following hip osteotomy are rare, there is a small chance of infection or blood clot formation. There is also a very low risk of the bone not healing properly, surgical damage to a nerve or artery, or poor skin healing.
Full recovery from an osteotomy takes six to 12 months. Most patients, however, have good outcomes following the procedure.
One alternative is to postpone surgery, if the patient's pain can be sufficiently controlled with medication to allow reasonable comfort, and if the patient is willing to accept a lower range of motion in the affected hip.
Surgical alternatives to a hip osteotomy include:
- Total hip replacement. Total hip replacement is an operation designed to replace the entire damaged hip joint. Various prosthetic designs and types of procedures are available. The procedure involves surgical removal of the damaged parts of the hip joint and replacing them with artificial components made from ceramic or metal alloys. The bearing surface is usually made from a durable type of polyethylene, but other materials including ceramics, newer plastics, or metals may be used.
- Arthrodesis. This procedure is rarely performed as of 2003, but is considered particularly effective for younger patients who are short in stature and otherwise healthy. Arthrodesis relieves pain by fusing the femoral head to the acetabulum. It has none of the limitations that a joint replacement or other procedure imposes on the patient's activity level. An arthrodesis is especially suited for patients with strong backs and no other symptoms. The procedure generally requires internal fixation with a plate and screws. The patient may be immobilized in a cast while healing takes place. An arthrodesis can be converted to a total hip replacement at a later date.
- Pseudarthrosis. This procedure is also called a Girdlestone operation. A pseudarthrosis involves removing the femoral head without replacing it with an artificial part. It is performed in patients with hip infections and those whose bones cannot tolerate a reconstructive procedure. Pseudarthrosis leaves the patient with one leg shorter and usually less stable than the other. After this procedure, the patient almost always needs at least one crutch, especially for long-distance walking.
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