S. Mehdi Jafari, MD & Javad Parvizi, MD, wrote an article in the American Journal of Orthopedics regarding hip arthroplasty earlier this year. The purpose of hip arthropathy is to restore function and mobility in patients with end-stage hip osteoarthritis. However, with followup, some deterioration is evident in the wearing of the bearing surface and aseptic loosening.
As the article states, “the release of wear particles, mostly from the articulating bearing surfaces, activates a complex inflammatory pathway that leads to loosening of the prosthesis and osteolysis.”
A conventional bearing surface, the metal-on polyethylene, is increasingly being replaced with newer generation bearing surfaces. According to the article, the most commonly used bearing surface is the high molecular-weight polyethylene. However, this bearing has been found to have major limitations. Wear particles are generated that engender the inflammatory process which leads to aseptic loosening and osteolysis.
Another form of a bearing surface is metal-on-metal. “By the mid-1970’s, owing to some concerns, charges against the metal-on-metal prosthesis, and the success of the Charnley prosthesis, polyethylene came to dominate the scene, and metal bearings were abandoned in favor of their polyethylene counterparts.” Metal-on-metal bearings caused irregular geometry, errors in surgical techniques, inadequate clearances, and impingement originating from inappropriate design.
The next type of bearing surfaces is the ceramic-on-ceramic. These were associated with impingement, component fracture and a high rate of implant loosening. in the late 1990s, a highly cross-linked polyethylene was introduced to try to minimize polyethylene wear debris. Also, the new generation of metal-on metal bearing surfaces were introduced and gained popularity.
“It is estimated that the number of metal particles generated annually is 13 to 500 times larger than the number of polyethylene particles produced from a traditional MOP implant.”
The article then goes on to say that patients with metal-on-metal have elevated levels of cobalt and chromium ions in their blood and urine. The particles appear in regional lymph nodes, the liver, the spleen and bone marrow. Metal hypersensitivity can occur increasingly in patients with metal-on-metal prostheses.
“Lack of scientific data precludes use of metal-on-metal prostheses in women of childbearing age and in patients with chronic renal failure or perhaps any underlying disease rendering the patient susceptible to renal dysfunction.”
The hip impant study by these two doctors showed that short and medium term clinical outcomes show third-generation alumina ceramic have shown low incidence of osteolysis, wear and failures.
Recent studies now show that patients with elevated levels of Cobalt and Chromium in their system are experiencing reactions at the surgical site. They are developing pseudo tumors and granular hemoragic masses and granular material reacting to the metalic debris or shavings resulting in lymphosites immune response that resembles the look of infection with associated necrotic tissue. This new condition is being diagnosed and called “Arthro prosthetic Cobaltism.”
“Arthro prosthetic Cobaltism” is a very serious medical condition that will likely need extensive medical treatment and follow up care with a licened provider.