Hip joints deteriorate for various reasons, including, osteoarthritis and avascular necrosis. When this happens, hip replacement devices are one option for patients who still want to lead an active lifestyle.
How Does a Hip Replacement Work?
The human hip consists of a simple ball-and-socket joint connected to the femoral stem. All total hip replacement devices thus consist of the following:
- An artificial ball (femoral head)
- Stem (femoral stem)
- Cup (acetabular component)
Hip replacement devices work by securing the artificial stem inside the femur bone. The device ball then connects to the stem. The ball is also aligned and sized to fit inside an artificial cup that is implanted in the hip bone. These components together act as the artificial hip joint.
All components must be durable and sturdy and designed in a way that allows for constant movement without wear.
The History of Metal-on-Metal Hip Replacements
Artificial hip devices have been a revolutionary solution to hip failure issues. The first total hip arthroplasty performed, which involved the use of ivory products, occurred in 1891. Manufacturers went on to experiment with artificial hip product materials, using skin, pig bladders, and glass. Eventually, stainless steel hip products were used and in 1953, the first metal-on-metal prosthesis was implanted on a regular basis by an English surgeon, George McKee. While the hip prosthesis had a solid survival rate, by the 1970s, surgeons were abandoning the metal-on-metal method due to local effects of metal particles observed during revision surgeries due to hip prosthesis failures.
Sir John Charnley introduced a “low friction arthroplasty” in the 1960’s, or a non-metal-on-metal hip, in an effort to reduce metal ion release. The combination, which closely mirrors what is seen today, consisted of a metal femoral stem, a polyethylene acetabular component, and a small femoral head. The metal-on-poly hip implant combination continues to be in popular use today, but due to some poly wear observed in patients, manufacturers again returned to metal-on-metal hip parts.
Shortly after metal-on-metal hips fell out of favor in the 1970s, manufacturers reintroduced metal-on-metal hips onto the market in the 90s, claiming to have solved the previous problem of metal ion release. Unfortunately, many of those metal-on-metal designs continued to be problematic, causing metal ion release (metallosis), abnormal tissue formation (pseudotumors), and the need for revision surgery.
2000’s to Present Day
From the early 2000s to the present day, it has become apparent that certain metal-on-metal hips are defectively designed, negligently permitting continued metal on metal wear which generates dangerous metal ion release. In 2010, the United Kingdom’s Medicines and Healthcare Products Regulatory Agency issued a medical device alert that recommended blood testing and imaging for patients with painful metal on metal hips. Shortly thereafter, Canada and Australia issued alerts regarding public health concerns stemming from metal-on-metal hips. Scientific literature has also reported that there was an increasing report of early failure of metal-on-metal hips due to metal ion release, causing pain, device loosening, and tissue and muscle damage. The United States Food and Drug Administration now recommends that if patients develop any symptoms that could indicate improper functioning of their metal-on-metal hip device, that those patients undergo specific follow-up testing, including blood tests for metal ions, fluid aspirations in the hip joint to identify abnormal fluid generation and to test fluids, and soft tissue imaging to understand if there is pseudotumor formation around the hip device.
Manufacturers of hip devices have known since the 1970s that metal-on-metal hip devices if incorrectly designed, can cause devastating damage to the hip due to metal ion release. In spite of that knowledge, they continued to produce metal-on-metal hip products, claiming they were safe for patients. As a result, thousands of individuals have been implanted with defectively design metal-on-metal hip products that prematurely fail, resulting in often catastrophic damage to the muscle and bone around the artificial hip device. Types of Metal-On-Metal Hip Replacement System.