Why hip replacements fail

Jan 5 2009

Each year thousands of patients undergo total hip replacement surgery in order to help alleviate pain associated with debilitating hip disease and other related hip problems.

According to a new study published in the January 2009 issue of The Journal of Bone and Joint Surgery, while many successful, long-term results have been documented, limited information currently exists regarding why hip replacements fail in the United States population.

"This is the first study in which we were able to look at the entire country and gain a better understanding of why total hip replacement surgeries can fail," said Dr. Kevin Bozic, lead investigator of the study and assistant professor of orthopaedics at the University of California, San Francisco. Researchers analyzed data from about fifty thousand patients who had to have their hip replacements revised in the U.S. between October 1, 2005 and December 31, 2006. Based on new diagnosis and procedure codes specifically for hip replacement revision, they were able to identify certain trends.

Researchers found the most common reasons for patients needing subsequent hip replacement surgery include:

• Dislocation of the implant
• Loosening of the implant
• Infection -- such as staph infections either around the time of surgery or later through the bloodstream    

"The reason why this study is important is because up until now it has been believed that the most common reason why hip replacements fail is because the bearing surface wears out. Although our study confirmed that problems related to bearing surface wear do cause hip replacements to fail, we found that other problems -- including dislocation, implant loosening, and infection -- may be even more common causes of hip replacement failure," explains Bozic. "This suggests that in addition to research aimed at developing better implants, we also need to direct new research efforts to improve care in those three areas."

Bozic also noted that there are other benefits to having this type of information. "One of our goals is to use these new diagnoses and procedure codes related to hip replacement to help create a national joint replacement registry which is what has been done in many other developed countries. Every patient who has a joint replacement gets entered into a national database and is tracked over time. It allows us to know specifically what happened to their hip replacement and when."

Results from the study indicate there are things within the surgeon's control such as surgical technique and the way the implant is installed that physicians should be thinking about as potential causes for failure as opposed to just design factors related to the implants. "Although we now have a better understanding as to why hip replacements fail, we need to do more detailed studies to find out the reasons why dislocation and infection are common causes of hip replacement failure," said Bozic.