Zimmer Hip Failure: the Implants Involved
A total hip replacement is an invasive procedure that surgically removes the entire “ball and socket” hip joint. The “ball” is the head of the femur or thigh bone and the “socket” is the cup shaped surface of the pelvic bone called the acetabulum. The joint is replaced with prosthesis that consists of a metal head and stem that is inserted into the femur and an artificial acetabular cup. The prosthesis can be attached to the surrounding bone either with cement or through a cementless process. In cementless fixation the metal of the prosthesis and/or acetabular cup has special microscopic pores that allow the natural bone to form ingrowths into the implant which hold it in place. The Durom Cup utilizes cementless fixation.
Zimmer Durom Cup failure is growing global worry
Zimmer Holdings, Inc. is a medical device company headquartered in Warsaw, Indiana and established in 1927. The company is an innovator of medical devices including orthopaedic implants and other related orthopaedic surgical materials. Recently they have come under fire in the United States and Europe over the greater then expected failure rate of their Durom Acetabular Component system or “Durom Cup”. The Durom Cup is a monoblock cup, meaning single piece, made of a cobalt chromium alloy with a pure titanium plasma-sprayed coating for fixation. The cup has been on the market in Europe, Canada, and Australia since 2003, in India and Korea since 2005, and in Argentina since 2006. It was also marketed in the US starting in 2006 but was withdrawn from the market by the company in 2008 because of the increased reports by US surgeons of a higher than expected rates of cup loosening.
Hip revision surgery required for many Zimmer hip failure patients
In the US, Dr. Lawrence Dorr, a former Zimmer consultant was the first surgeon to make public the problem with the Durom Cup. In April of 2008 he sent a letter to the members of the American Association of Hip and Knee Surgeons (AAHKS) and stating that out of 165 hip replacements using the Durom Cup he had about ten to fourteen patients that needed revision surgery. On July 22, 2008 Zimmer initiated a voluntary suspension of Durom Cup sales while it investigated the claims.
A study published in the Journal of Arthroplasty September 2010 edition compared the Durom Cup with another Zimmer product, Trilogy. They found that the failure rate was significantly higher in Durom patients, about 11%, than for Trilogy patients, which was 0%. They also noted that there were no in-bone growths in Durom patients requiring revision surgery, and stated that further study to determine the basis for their observed results was needed.
Another study published in the Clinical Orthopedics and Related Research February 2010 edition compared large-diameter metal-on-metal, Durom Cup, failure rates with a historical control that had a small-diameter, Metasul also another Zimmer product. They followed 181 Durom patients and 54 Metasul patients and determined that the revision rate and quality of clinical results were unacceptable in Durom patients when compared to the historic controls. The authors did not recommend the use of Durom Implants.
Zimmer investigates Durom Cup problems
According to the Zimmer website relating to the Durom Cup the company states that they investigated the 2008 US surgeon reports by visiting 12 clinics and reviewing 3,100 cases and concluded that the more successful users, or surgeons, where those that “consistently executed crucial technique steps for Durom Cups in a specific manner”. It was concluded that additional surgical technique instructions and training were needed in the United States.
In 2009, in response to Durom/Metasul LDH system revisions in Europe another investigation was launched. This time the company investigated 52 users who collectively implanted 8,654 Durom Cups and it was again decided that the root cause for the reported revisions from loosening was surgical technique. Though the defective Zimmer Durom Cup is no longer available in the US the company has updated and distributed new surgical technique instructions and surgeons wishing to use this product must participate in a mandatory DVD training module.