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Newer generations of hip replacement systems have not lowered the risk of revision surgery, and some may be more prone to failure than their older designs, according to the findings of a new study.
Researchers with the University of Bristol in the U.K. published a study earlier this month in The BMJ, which looked at hip replacement revision rates for modern artificial implants, including metal-on-metal, metal-on-ceramic, ceramic-on-ceramic designs and other variations.
The outcomes among individuals who received these newer designs were compared them to older metal-on-plyethylene hip implants, finding that the next generation hip systems have not actually reduced the rate of failures by a significant amount.
The study looked at randomized controlled clinical trials that compared different implant combinations, head sizes, and fixation techniques, like resurfacing. They referenced those with data on the older designs, which included metal-on-plyethylene implants with small femoral heads that were cemented in place. They compared revision rates under two years, and revision rates between two and 10 years after the implants were put in place.
Researchers looked at data on a total of 3,177 hips gleaned from 15 studies. The researchers found no evidence that the risk of revision surgery has decreased with the introduction of newer designs. In fact, they also found that metal-on-metal, small head, cemented implants, as well as resurfacing procedures, increased the risk of hip complications and revision surgery within the first two years, as well as in later years.
“Metal-on-metal, small head, cemented implants and resurfacing increased the risk of revision surgery compared with the reference implant combination,” the researchers concluded. “The results were consistent with observational evidence and were replicated in sensitivity analysis but were limited by poor reporting across studies.”
Metal-on-Metal Hip Failures
Metal-on-metal hip replacements have been sold by a number of different manufacturers in recent years, featuring a metal femoral head that rotates within a metal acetabular cup.
Unlike other artificial hip designs, which typically feature metal-on-ceramic or metal-on-plastic, the metal-on-metal hips have been found to release microscopic metallic debris as the parts rub against each other. This can lead to increased levels of metal ions in the blood, known as metallosis. This has been linked to reports of loosening and failure, often within a few years after the artificial hip is implanted.
Most of the devices were introduced in the U.S. through the controversial fast-track 510(k) approval process, which only required that the device be a “substantial equivalent” to an already existing device approved by the FDA. However, the snowball effect of the substantial equivalence test has allowed many devices now considered unreasonably dangerous and defective to be implanted in thousands of Americans.
Several manufacturers faced metal-on-metal hip lawsuits in recent years, claiming that the design was unreasonably dangerous and prone to early failure. Similar allegations led to DePuy ASR hip lawsuits, DePuy Pinnacle hip lawsuits and other cases.
More recently, a new wave of hip litigation has emerged, involving individuals who received certain large-diameter femoral heads manufactured by Stryker as part of their artificial hip replacement. The cases stem from a recent Stryker LFit V40 recall issued due to a high rate of problems experienced by individuals who received the femoral head used in various different types of hip systems, including Stryker Accolade, Stryker Meridian, Stryker Citation and other implants.