The surgical application of metal-on-metal hip replacement systems has become the subject of intense criticism. An increasing number of adverse reactions, associated with metal debris, have been reported in those who have undergone total metal-on-metal hip arthroplasty. In response to the increasing reports of defective hip replacement systems, researchers in Norfolk, UK have conducted a study to determine the adverse reactions in a series of patients who have received a metal-on-metal hip replacement system.
Metal-on-metal hip replacement systems are comprised of a series of metallic components (cobalt and chromium) in order to promote longevity and dexterity. Unfortunately, recent evidence suggests that metallic components consisting of cobalt and chromium may coincide with catastrophic complications in defective hip replacements. More specifically, the wear and tear that ball and socket components generate may lead to significant deterioration over a seemingly short period of time. This degeneration has a tendency to create minute metal shavings that have the potential to cause significant damage to an individual. As a result, these metal pieces may lead to a concentration of hazardous metal shards in the fluid of the joint and surrounding muscles that can cause extreme pain an swelling when leached into the recipient.
Concern regarding defective hip replacement systems has grown exponentially in the healthcare community. Recent evidence lends weight to the long-suspected link between defective metal-on-metal hip replacement systems and catastrophic complications. In a recent report issued by the Australian National Joint Replacement Registry (NJRR), a popular metal-on-metal prosthetic displayed a 6.4% failure rate after three years and a 10.9% failure rate after five years. The frequency in which these devices required revision surgery was unprecedented, considering an acceptable upper rate of failure of hip prostheses is considered to be below 1% per year.
According to the UK study, DePuy’s ASR acetabular hip component has been regarded as one of the most frequent hip replacement systems to display signs of high failure rates. The design of the ASR acetabular component utilizes between 148 and 160 degrees of a sphere. As a result, more of the ASR head is uncovered, regardless of where the cup is situated. This may lead to increased edge loading and wear of the ASR cup. Chromium and cobalt concentrations from the ASR prostheses are significantly increased due to the orientation of these components. Therefore, there is an increase in metal ions at inclinations that are greater than 45° with the ASR hip replacement device. Researchers concluded that the ASR Corail THR has a high rate of early revision due to metal-on-metal related soft tissue problems.
In response to significantly high failure rates, researchers studied the early clinical results in a series of 79 metal-on-metal hip arthroplasties, totaling 68 patients in all. MRI scans were implemented at an average of 3 months after the initial surgery took place. MRI results discovered that 27 out of 75 hips displayed a significant concentration of MRI-detected metal debris-related abnormalities. Of the anomalies found, five were considered mild and 18 displayed symptoms of moderate level. However, four of the hips that showed concentrated levels of metal debris were considered to display severe systemic symptoms.
Of the hips displaying signs of metallic debris-related abnormalities, eight required total revision surgery. However, six of the eight abnormalities required revisions due to the presence of adverse reactions to the metal debris that leached into the recipients system. Studies indicated a significantly high frequency in the revision rate of modern, large-head metal-on-metal hip arthroplasty. More specifically, MRI scans detected metal debris-related abnormalities in about one-third of the patients who had received a metal-on-metal hip replacement. The detrimental complications that the deposits of metal have on soft tissue can be seen in a number of side effects. Patients may experience complications ranging from severe pain and swelling to the development of cobalt toxicity.