Total Hip Replacement

VI. Risks and Complications of Hip Replacement

Early Complications	Late Complications
Infection	Infection
Dislocation	Dislocation
Blood Clots	Failure of Bone Ingrowth into Implant
Nerve Injury	Loosening
Anesthesia	Plastic Wear (osteolysis)
Leg Length Inequality
Heterotopic Bone

All surgeries have risks, so the potential benefits must be carefully weighed. Some complications are related to the surgical procedure and some are related to the delicate balance of the body that is altered during the operation. Potential complications of any surgery include: the risks of anesthesia, bleeding, infection, blood clots, and death.

With modern techniques, the risk of anesthesia related complications is very low.

General and regional (epidural or spinal) anesthesia seem to be equally safe and effective

Epidural anesthesia has the benefit of allowing optimal pain control for the first 48 hours after surgery. Prior to the surgery, the anesthesiologist will discuss the options with you and help you to decide which type is best for you. Unless you are young and healthy, a complete preoperative medical evaluation by your family doctor or internist would be recommended to identify potential medical problems and, thereby, minimize the risks.

If a blood transfusion is required, there is a potential risk for a transfusion reaction or disease transmission (e.g. hepatitis, AIDS). The risk of contracting AIDS from a blood transfusion is now estimated at one in a million. The risk of contracting hepatitis is approximately one in two thousand. If your hemoglobin is low prior to surgery, it may be beneficial to donate autologous (your own) blood before surgery or receive a series of erythropoetin injections (Procrit) to build up your hemoglobin level. Recent studies have shown that if your preoperative hemoglobin is above 13 grams, you will be unlikely to require transfusion. For patients with a lower hemoglobin, the most effective method to avoid transfusion is a series of erythropoetin injections.

Infection has a very small chance of occurring (1 out of 100 in first time hip replacements and 4 out of 100 for revision hip replacements), but if infection occurs, it is a very difficult problem to treat. Most infections in total hip replacements occur due to contamination at the time of surgery. It is a myth that surgery can be a truly sterile procedure. Any time that people are in an operating room, there will be small numbers of bacteria that can settle in the wound. We take a number of precautions to decrease the number to a minimum. These include the use of sterile instruments and drapes as well as gowns, masks and head covers. The patient’s leg is thoroughly cleaned with an antiseptic agent and all other areas are covered with sterile drapes. In addition to these routine measures, the surgery is performed in an “ultra clean” room . In this type of operating room a uniform flow of filtered air is continually circulated over the wound. “Space helmets” (body exhaust filtration systems) are also worn by the surgical team. Another measure to decrease infection is the use of prophylactic antibiotics. This means to use antibiotics in advance to prevent an infection rather than to treat it after it occurs. Normally, we use antibiotics during surgery and for 48 hours after surgery.

If infection occurs in a total hip, every effort is made to retain the prosthesis; but this is successful only 20% of the time. If the implant is loose or if the infection continues to recur, it is usually necessary to remove the implant completely in order to cure the infection. This, of course, leaves no hip joint and, although walking is possible, usually two crutches are required. The leg is quite short and weak. At least six weeks of intravenous antibiotics are required to treat the infection. After the infection is cured, consideration can be given to reimplantation of a total hip, but statistics show that 10% of reimplantation cases develop infections again. Therefore, in some cases, the hip is not reimplanted with significant resultant disability.

Another complication that may occur is the formation of blood clots in the legs or pelvis.

Without any preventative measure, the incidence of blood clots in the legs or pelvis is approximately 50% to 60%. In and of themselves, the blood clots are not a great threat; they can be treated with blood thinners and will ultimately resolve. The patient may, however, be left with some permanent swelling of the leg due to destruction of some of the valves in the veins. The big concern, however, is that a portion of the blood clot can break off and go to the lung. This is called a “pulmonary embolism” and can be life threatening.

Four different preventative measures can be used to decrease the risk of blood clot formation. The first is the use of a blood “thinner” (anticoagulant) like Fragmin, Coumadin, aspirin, Heparin. Anticoagulation does seem to be beneficial overall, but may lead to complications of its own (e.g. excessive wound bleeding, need for transfusion or stroke).

The second is the use of spinal or epidural anesthesia (sometimes in conjunction with general anesthesia). Thirdly, mechanical pumps (compressive stockings or boots) can be used. Fourth, early mobilization of the patient is helpful. Finally, several of these may be used in combination resulting in a less than 10% chance of blood clots developing, and less than 1% chance of developing a pulmonary embolus.

Other possible complications need to be mentioned. Dislocations can occur. This is when the ball comes completely out of the socket. A normal hip is held in place by ligaments as well as muscles around the hip. The normal femoral head is quite large and difficult to dislocate. A total hip replacement has a smaller head and all of the ligaments are usually cut at the time of surgery, therefore, it is more unstable. The incidence of dislocation is 2% to 3% in first time hip replacements and 10% to 20% in revision hip replacements. If a total hip dislocates, it can usually be relocated under general anesthesia but without surgery. A cast or brace is then usually worn for six weeks, but approximately one-third of these continue to dislocate and require either a permanent brace or corrective surgery.

Often the leg shortens because the cartilage and bone wears away due to the process of arthritis. When a hip replacement is done, the leg is usually lengthened to tighten up the ligaments and reproduce the normal mechanics of the hip joint. Sometimes the leg needs to be lengthened somewhat more than the opposite side to provide adequate stability and reduce the chance of dislocating the artificial hip joint. This is because the artificial hip joint is never as stable as a normal hip. The pelvis can shift to accommodate small differences in leg length (one-quarter to one-half inch). This may take six months to one year after surgery. Occasionally, a shoe insert or lift is required to raise the other leg.

Heterotopic bone may form in the muscles around a hip joint as a reaction to the surgery. In rare cases, it leads to stiffness in the joint. Cracks or fractures of the bone may occur during insertion of (uncemented) hip implants. Usually, these can be dealt with at the time of surgery with an excellent outcome.

Causes for long term failures include loosening, wear and late infection. Loosening is the process in which the fixation between the bone and the implant breaks down. In a well functioning total hip prosthesis, the motion of the hip only occurs between the ball and the socket. When the implant loosens, motion then occur between the implant and the bone; the implant rubs on the bone resulting in pain. This usually requires “revision”; a repeat operation designed to attach a new implant to your bone.

The risk of loosening in ideal candidates is approximately 5 to 10% in 10-15 years. In non-ideal candidates, such as patients with excessive body weight and younger more active patients, as well as patients who have had a previously failed cemented implant, the chance of loosening is dramatically increased. The other end of the spectrum from the ideal candidate is illustrated by several studies reviewing the success rates of patients under 40 receiving cemented total hips. In these reports, there is a failure rate of approximately 50% within five years due to loosening.

In a cemented implant, loosening is usually caused by cracking of the cement mantle. In uncemented implants, failure of the porous surface attachment to the implant or deterioration of the bone attachment itself can occur.

Wear occurs in the artificial lining surfaces—usually metal or ceramic and plastic (polyethylene). The plastic gradually wears away, much like the rubber on a car tire. The more stress that is placed on the hip, the more it wears. The tiny particles created in this process can result in irritation and destruction of surrounding bone. This is called “osteolysis”.

Infection may also occasionally settle in an artificial joint within a matter of months to years after an operation. This may spread from a distant infection of a tooth or the skin. It may cause sudden symptoms or a gradual loosening of the implant.

Revision total hip replacements require special mention. A revision is defined as a total hip replacement done for a previousy failed implant. The chances of success in revision hips is only 80% as compared to 90% to 95% for primary procedures. A recent study has shown that this success rate deteriorates for cemented revisions such that only 60% are successful at five years. Most failures are due to loosening. Infection, as noted above, is also more common (approximately a 4% risk).

These complications have been outlined in some detail, not to frighten you intentionally, but to inform you of the possible risks of the procedure. Taken in total, the risks are usually quite low and the chances of success greatly outweigh a chance of failure.