Omni Apex K2 Modular Hip Problems Lead Researchers to Cancel Study

Australian researchers warn that problems with the Omni Apex K2 modular hip implant system may include a risk of fretting and corrosion, which could contribute to a high hip replacement failure rate. 

In a study published recently in the The Journal of Arthroplasty, researchers from the Perth Orthopedic Institute were forced to end research involving the modular hip replacement system, after they discovered that nearly 10% of Apex K2 hips were subject to revision surgery within just three years.

Researchers conducted a prospective, randomized study to evaluate stem stability and clinical outcomes for the modular neck and stem hip system, which has been on the market for over 10 years. The study was inspired by a number of recent modular hip problems, involving fretting and corrosion of the neck and stem, including the Stryker Rejuvenate hip, Wright Profemur hip and other similar modular systems.

Unlike traditional hip replacements, modular hips involve two femoral pieces that fit inside each other to allow the surgeon to adjust the length of the component to match the specific patient. However, modular hip problems plaguing other implants have been linked to corrosion as the pieces rub against each other during normal daily activities.

With the Omni Apex K2 hip, researchers found that the study had to be halted prematurely due to an “unfavorably high early revision rate” of 9.3% at just three years. The corrosion resulted in metal-related pathology, often referred to as metallosis or metal blood poisoning. To confirm their findings, researchers analyzed seven other Apex K2 stems that were not part of the study and found similar evidence of corrosion.

“The study shows potentially concerning subsidence of both stems and is the first to describe corrosion at the neck-stem interface, and a relationship to metal-related pathology,” the researchers warned.

The Apex K2, manufactured by OMNI, was approved for sale in the U.S. in 2004

Modular Hip Lawsuits

One of the first modular hip implant designs was the Wright ProFemur Total Hip System, which has been linked to problems where the femoral neck stem may fracture and fail.

Several hundred Wright Profemur hip lawsuits were filed by individuals who had their device fail within a few years, alleging that the system featured an unreasonably dangerous design, making the femoral stem likely to fracture, break, degrade, fret and ultimately fail.

In July 2012, a Stryker Rejuvenate hip recall was issued for a similar modular design, after the manufacturer acknowledged that the components were prone to fail after the components rub against each other during normal use. The recall came only two years after the design was introduced, and has resulted in thousands of Stryker Rejuvenate lawsuits alleging that the manufacturer failed to adequately research the design. An estimated 20,000 of the implants were sold before the problems were discovered, according to allegations raised in the complaints.

Last year, a $1 billion global Stryker Rejuvenate settlement was reached by the manufacturer to resolve all cases where plaintiffs underwent revision surgery on or before November 2, 2014. However, as the defective modular systems remain in the bodies of thousands of patients, Stryker Rejuvenate failures continue to result in the need for revision surgery.