Hip revision surgery, as opposed to a total hip arthroplasty (THA), is an intervention used to remove and replace a failing prosthetic hip unit or its components. While made to be long-lasting, there are many factors which determine whether a hip prosthetic will provide years of successful use or be the source of pain, inflammation, and ongoing suffering by the recipient.

According to a May 2011 article posted on the British Medical Journal website, conventional hip implants used to remedy failed hip replacements consist of an acetabular polyethylene cup and metal femur head.

This original combination of materials were found to wear out over time because the metal ball would break down the plastic. Because of this degradation over time—particularly if the patient was younger when the original procedure was done—hip revision surgery was often needed sooner rather than later.

In Come the MOMS

The next generation of prosthetic hips were thought to be more durable as both the acetabular cup and femur head were made of metal. They were known as metal-on-metal hip implant systems (MOMS) and were found to cause more problems than they cured with the procedure. According to an Arthritis Foundation blog, their failure rate overall was much higher than prosthetics made of other materials and many recipients have had hip revision surgery or will need it.

Chief among the MOM horror stories is that of the DePuy ASR hip system. The BMJ indicates that recall of the MOM prosthetic followed “years of denial by the company” that the implants had caused pain and disability. When finally recalled on Aug. 24, 2010, 93,000 implants had been sold, causing Johnson & Johnson—DePuy’s parent company–to face costly litigation ending in a settlement whose end date keeps being extended.

This situation and other failed MOM prosthetics spurred the U.S. Food and Drug Administration to release a communication expressing the agency’s concern with these materials. The communication indicated that particles of metal debris were often released because of the friction in MOM hip units.

These cobalt and chromium particles were found to wreak havoc in some people by embedding in surrounding tissues and causing pseudotumors to develop. These contributed to prosthetic loosening and failure. The debris was also capable of leaching metals into the bloodstream and contributing to the development of certain cancers and heart disease.

While the FDA indicated that the response was as individual as the person, the Arthritis Foundation laid out that researchers believed the debris could mesenchymal stem cells (MSCs) in bone marrow. MSCs have a key role in building new bone cells.

Bone Damage and Risks of Hip Revision Surgery

Cedars Sinai Hospital says that hip revision surgery carries more risk than the original THA. The reason behind this is because the bone is often weaker. Additional risks include fractures during the procedure or afterward for the same reason. The possibility of dislocation is also much greater, as are post-operative leg length discrepancies.

The hospital does propose that orthopedic surgical techniques for hip implant revision are always improving and, while the chance of loosening with a subsequent prosthetic is greater, technological improvements are increasing their success.