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Serious complications and patient harm related to the use of cobalt chrome hip implants are well documented. Just ask orthopedic surgeon Stephen Tower, M.D. Dr. Tower published the first two reported cases of systemic cobalt poisoning caused by metal-on-metal implants. He also happened to be patient zero.
Dr. Tower, an avid endurance athlete, underwent a total hip replacement in 2006. He chose to have a metal-on-metal device implanted to reduce the risk of dislocation during intense physical exertion. The operating surgeon, who knew about Dr. Tower’s active lifestyle, positioned the implant in a way that offered protection against posterior dislocation. However, this positioning made the implant susceptible to runaway wear, especially given its minimal clearances and truncated hemisphere on the acetabular side.
Months after the procedure, Dr. Tower began to experience severe pain in the artificial joint and developed neurological toxicity and mild heart failure. Clearly, he thought, systemic issues were impacting his cardiovascular and nervous systems. His blood cobalt levels had peaked at 120 parts per billion (ppb), compared to the reference of 0.1 ppb.
Although Dr. Tower endured the symptoms for a while, the pain in his hip became too severe to ignore and the implant’s functioning deteriorated significantly — he could hear creaking and grating every time he bent down.
One of Dr. Tower’s colleagues performed revision surgery, which revealed extensive implant damage. The hip capsule was compromised, and the direct header by the rectus femoris muscle was lost.
Dr. Tower realized the significance of his experience given that at the time approximately 2 million metal-on-metal implants were implanted worldwide. “I felt compelled to write and publish my own case report,” he said.
Ultimately, after facing challenges in the publication process, the report was published in 2010 in the Journal of Bone and Joint Surgery. His story was also told in the Netflix documentary “The Bleeding Edge,” which details how innovative medical devices can lead to patient harm.
Dr. Tower’s efforts to expose the dangers of cobalt chrome played a role in the declining favor and subsequent market removal of certain metal-on-metal hip implants. “It quickly became apparent that the cobalt in the hip implants was not different from the cobalt in other orthopedic devices,” he said.
In a research letter published in JAMA Network Open, Dr. Tower noted that 20 million North Americans have received cobalt chrome implant components, and 1 million have undergone metal-on-metal hip replacements. He wrote that millions of joint replacement patients implanted with non-recalled risky implants are not monitored for dangerous levels of cobalt and are likely experiencing cobalturia — concerning cobalt levels in the urine of 1 ppb or above.
The bioinert nature and strength of cobalt chrome make it well-suited to produce orthopedic implants and all the risks of systemic complications, allergic reactions and implant failure caused by the material are largely low and mostly unknown. Still, some experts wonder, why not eliminate the potential of adverse outcomes altogether through innovative implant designs?
Durability Leads to Longevity
Issues associated with the use of cobalt chrome in hip replacement surgery should raise red flags about the use of the material in all implants. “Why is cobalt chrome still utilized in knees when the implants do not have metal-on-metal articulation,” said Andrew Morris, Chief Commercial Officer at TJO. “Although corrosion is not occurring in the knee, there is evidence of cobalt-ion leaching, which raises concerns about potential issues and allergies.”
Total Joint Orthopedics (TJO) launched its Klassic Knee System with Aurum Technology in March 2022 as part of a multi-year effort to reduce the use of cobalt chrome in orthopedic implants. Aurum bonds a titanium nitride coating to the titanium substrate, creating a hardened surface with strong wear characteristics without the use of cobalt chrome.
“Strength and scratch resistance are key considerations in the design of implants,” Morris said. “Our goal was to achieve mechanical properties equivalent to cobalt chrome while addressing potential material issues.”
The 5-micron thickness of Aurum Technology’s coating adds to its durability. “Previous implant technologies often had a thin one-micron layer that could peel off with wear,” Morris said. “Our thicker layer, combined with the interdigitated bonding, prevents such issues. While we can’t claim absolute certainty without long-term data, the testing conducted so far supports the durability of our solution.”
Morris said third-party testing has shown that Aurum’s mechanical properties — strength, scratch hardness and surface hardness — are better than cobalt chrome. “Scratches on cobalt chrome implants can lead to long-term wear and reduced survivorship,” he said. “Our material remains smooth even after millions of wear testing cycles. The real question is how this translates to durability and longevity inside the patient’s body.”
TJO is focused on improving implant longevity by reducing polyethylene wear and metal-on-metal contact. “Increasing scratch resistance is beneficial, especially for younger patients undergoing knee replacement surgery,” Morris said.
Morris acknowledged that the incidence and extent of metal allergy in patients are not precisely known, but said the literature suggests that it is the fifth most common cause of revision surgeries — albeit with a low occurrence rate.
“The challenge lies in the uncertainty of identifying patients who may experience poor outcomes due to metal allergies,” Morris said. “Various methods, such as patch testing and lymphocyte transformation tests, are being explored to address this issue. However, it remains difficult to accurately predict which patients may have adverse reactions to cobalt chrome. And although there is no definitive link to cancer, some sources suggest a potential association.”
To tackle this problem, TJO sought to develop a material that surpasses cobalt chrome in terms of efficacy, eliminating the need for discussions around patient selection and potential adverse reactions. “We aimed to avoid these concerns by creating a material that is superior to cobalt chrome, considering its known negative aspects such as toxicity and allergic reactions,” Morris said.
TJO is focused on finding ways to replace or minimize the use of cobalt chrome in other devices, such as dual mobility hip implants with a cobalt interface. The company expects the Aurum Technology to be compatible with its Platform Acetabular System, which received FDA 510(k) clearance in September 2022.
The revision space also poses challenges for metal-on-metal implants, and TJO is actively exploring how Aurum can address this issue. “From the very beginning, our goal has been to completely remove cobalt chrome from the joint replacement equation,” Morris said. “That remains our primary objective.”
Cost is a significant concern that can impede the adoption of new implant materials. It took time for the use of ceramic heads in hip implants to catch on because of the initial high cost of the material. However, as time went on, the drawbacks of metal-on-metal implants became apparent, and the price of premium ceramic heads became less of a concern.
“We see a similar trend in knee replacements with respect to the use of cobalt chrome,” Morris said. “Our aim is to eliminate the limitations and concerns associated with the material by providing a superior option. We recognize the importance of lowering the cost of care and believe that the long-term benefits of our solution will outweigh any initial price considerations.”
A ‘No Brainer’ Approach
It’s been a decade since Dr. Tower implanted a cobalt chrome component in a patient. He called moving away from using the material in orthopedic devices a “no-brainer.”
Limiting the use of cobalt chrome hip implants has been a relatively easy shift because ceramic heads have a long history of successful use, according to Dr. Tower. He said companies have introduced advanced non-cobalt chromium implant materials that reduce wear and improve the corrosion resistance of hip and knee implants. He also said there have been significant advancements in the processes of hardening titanium to make it a more suitable bearing surface.
Still, he said, improving implant designs to make joint replacement surgery safer for all patients is a complicated and layered process.
“Industry receives substantial input from design surgeons who may be the most reluctant to accept this problem due to their involvement with the problematic implants,” Dr. Tower said. “I’ve tried to emphasize to industry members that the sooner they recognize that cobalt chrome might be a problem, the better. Tens of millions of individuals worldwide are at-risk for arthroprosthetic cobaltism because cobalt chrome has been — and remains — a common implant material.”
