Risks and Possible Complications

The two major complications that can cause failure of a total hip replacement are infection and loosening. Infection has a very small chance of occurring (less than 1 out of 100 in first time hip replacements and less than 2 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.

Anytime that people are in an operating room there will be small numbers of bacteria in the air 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, gloves and "Space helmets" for breathing filtration. In addition to these routine measures, the surgery is performed in an "ultra clean room" (also called a "Laminar Airflow Room"). 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 an infection occurs in a total hip, every effort is made to retain the prosthesis but only 20% of the time is this successful. 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 the patient with no hip joint, and although walking is possible, usually two crutches are required and 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 infection again. Therefore, in some cases the hip is not reimplanted with significant resultant disability.

The second major complication is that of loosening. The key to success for total hip replacement is that all motion should occur between inert materials (i.e. at the ball and socket joint). If any movement occurs between the implants and their respective bones (i.e. loosening), this will cause pain, bone resorption and ultimate failure. Loosening usually takes one to two years to develop and can occur as late as 10 to 15 years for a cemented implant. Sir John Charnley in the late '50's and early '60's developed the current concepts of cemented total hip replacements. His major contributions were the bearing material of high density polyethylene for the socket and the use of polymethacrylate, which is an acrylic cement used frequently by dentists. This cement is mixed at the time of surgery as a powder and a liquid which turns into a slurry which is then injected into the bone. Its role is to get into all the "nooks and crannies" of the bone, solidify in approximately 15 minutes, and provide a rigid fixation of the implant to the bone. This major contribution of Charnley's allowed a previously unsuccessful operation to become very successful. Despite this accomplishment, loosening of the implant can still occur as noted above. The current theory is that loosening is caused by a failure (i.e. cracking) of the cement. It is felt that this occurs by a fatigue process which is caused by excessive repetitive heavy loading.

The risk of loosening in ideal candidates is approximately 3% to 5% in 10 to 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 increases dramatically. The other end of the spectrum from the ideal candidate is illustrated in a study done several years ago which reviewed the success rates in patients under 40 receiving cemented total hips. In this report there was approximately a 40% failure rate within five years due to loosening. Other studies have been done that are not -quite so bleak but certainly in these higher risk individuals, the risk of loosening is at least three to five times the incidence than that in ideal candidates. Newer developments in cementing techniques may improve these results in even high risk candidates.

Revision total hip replacements require special mention. A revision is defined as a total hip replacement done for a previously failed implant. The chances of success in revision hip is only 80% as compared to 95% for primary procedures and this is for a very short term. A recent study has shown that this success rate deteriorates for cemented revisions such that only 60% are successful at five years. Most of the cause for failure has been loosening. Infection, however, as noted above is also increased up to approximately 2%.

Other possible complications need to be mentioned. Dislocation 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 excised at the time of surgery, therefore it is more unstable. The incidence of dislocation is 1% to 3% in first time hip replacements and 5% to 15% in revision hip replacements. If a total hip dislocates it can usually be relocated under sedation or 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.

Another complication that should be discussed is blood clots that can form 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 threat; they can be treated with blood thinners and will ultimately resolve. The big concern, however, is that a portion of the blood clot can break off and go to the lung. If that occurs it can be life threatening. While some degree of pulmonary embolism may occur in as many as 17% of cases, they are symptomatic and clinically significant in only 2% of patients, and fatal complications are much rarer.

Heterotopic ossification is a late postoperative complication of total hip replacement. This is when varying amounts of bone form in the soft tissues and muscles surrounding the hip joint. Most cases are mild with the patient being unaware of any problems, and can only be identified by x-ray examination of the hip. this mild form does not have any long term adverse consequences. In more severe cases, large amounts of bone may bridge across the hip Joint causing pain and stiffness. When this occurs, a second surgical procedure may be required to remove the abnormal bone in an attempt to improve function. Some degree of heterotopic ossification has been reported to occur between 1% and 20% of total hip replacements. The more serious forms occur only rarely. Some patients are at increased risk for this complication including patients with another active disease- ankylosing spondylitis, as well as patients with a past history of heterotopic ossification after a previous surgery, and in males with a severe form of osteoarthritis characterized by large bone spur formation. When there is a high window of suspicion that heterotopic ossification may develop, preventative measures may be taken to help avoid this. Within two to three days of surgery, the patient is given a single dose of radiation therapy carefully limited to the region at risk. This has been very successful in preventing heterotopic ossification.

Various preventative measures are used to decrease the risk of blood clots forming You are normally given a blood thinner, Coumadin, during your hospital stay. This helps to prevent clot formation. Pneumatic compression stockings are also used, but early mobilization beginning on the first or second day after surgery and active in-bed exercises such as ankle "pumps" are most helpful. All of these measures decrease the chance of blood clots forming to less than 10% and a chance of a pulmonary embolus to less than 3% and a fatal pulmonary embolus to less than 1 in 5000.

Other risks that you should be aware of are anesthetic risks, the strain of surgery on the heart and lungs, and possible damage to nerves, arteries and veins which can affect the circulation, as well as, the function of the leg. All of these occur less than 1% of the time.
These complications have been outlined in some detail not to frighten you, 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 outweighs the chance of failure.