Hip replacement is a common orthopedic surgical procedure performed to relieve pain and restore mobility to a damaged hip joint, typically for patients with arthritis or a hip injury. Diseased or damaged portions of the hip ball and socket joint are replaced by prostheses made of metal, ceramic, plastic, or combinations of these materials. Metal-on-metal (MoM) hip replacement implants use ball and socket components that are both made of cobalt or chromium metal, or titanium. The ball fits into and glides against the surface of the socket to imitate the function of the hip joint.
Hip replacement surgery is mostly successful, and hip implants are made to last 15 or more years before replacement is required. There are risks of several complications that can occur, however; as with any type of surgery. Complications that can occur include infection, dislocation of the ball implant from the socket, and implant loosening or other wear and tear over time requiring another hip replacement surgery.
In contrast to the pain relief and durability characteristic of hip replacement treatments, recently there has been a remarkable surge in complaints of early failures of metal-on-metal hip replacements within a few years of surgery. Some patients have experienced severe ongoing pain, swelling, and difficulty walking. Others have suffered damage or death to the soft tissue surrounding the hip joint. Many of these implant failures require the patient to undergo painful and expensive revision surgery.
Metal-on-metal hip implants wear over time, resulting in deposits of metal debris in the tissues surrounding the hip joint. A chiseling effect known as edge-loading can occur when the ball of the implant presses on the socket edge as a result of poor implant design or faulty surgical technique. Large amounts of metal debris are deposited in the tissues as a result, which can lead to high levels of cobalt and chromium ions in the patient’s bloodstream, possibly leading to metal poisoning. Studies to date have not shown a greater risk of cancer or other adverse effects from the metal ions, although additional data from ongoing studies is needed before the long-term effects are known.
Current research estimates that 1 to 3 percent of patients could experience an inflammatory reaction to the metal debris, causing chronic pain, damage and death to hip tissues, and bone loss. Women appear to be affected more frequently than men. A recent Harvard Medical School study looked at the effects of edge-loading from metal hip implants. The research showed an association between resulting high cobalt and chromium blood levels and patient susceptibility to soft tissue pseudotumors. Pseudotumors are a rare complication, but nevertheless a very serious problem, causing tissue destruction and the need for revision surgery. Metal debris complications are a significant safety concern and the focus of ongoing studies.
Concerned for their patients’ safety, most orthopedic surgeons have stopped using metal-on-metal hip implants. Metal-on-metal hip implants were used in about one third of the 250,000 hip replacements performed in the United States until the past two years, when use of the implants has dropped to only about 5 percent of the market.
The Food and Drug Administration (FDA) has received over 5,000 reports of adverse events in connection with metal-on-metal hip implants since January 2011, according to a study by the New York Times. In response to the complaints, the FDA is encouraging patients who have received metal-on-metal hip replacements to contact their surgeons immediately if they experience problems, and to participate in safety surveillance studies.
The FDA has required 21 manufacturers of metal-on-metal hip implants to submit plans to conduct post-marketing surveillance studies to address safety issues related to the implants. Among these manufacturers are DePuy, a division of Johnson & Johnson, Zimmer Holdings, Wright Medical, and Biomet. The FDA has until November 2011 to decide whether the proposed plans are adequate to address safety concerns.
Of the metal-on-metal complaints received by the FDA this year, about 75 percent relate to complications with the DePuy ASR hip replacement systems. Depuy has attributed the failure of the devices to implant loosening, infection, bone fracture, dislocation, metal debris reactions, and accompanying pain. Some orthopedic surgery experts have said they believe these devices have a design flaw that makes them difficult to implant properly. DePuy refuted these statements, but announced last year that it was discontinuing the ASR systems because of declining demand.
In August 2010, Depuy voluntarily recalled its two ASR systems as a result of new data from the National Joint Registry of England and Wales showing that roughly 1 in 8 ASR patients would experience implant failure within 5 years, an unacceptably high failure rate. There have been over 90,000 DePuy metal hip implants sold; so that according to the data, over 11,000 patients are likely to experience implant failures that require painful and expensive revision surgery.
The two DePuy systems under recall are the ASR XL Acetabular System, a metal cup and ball replacing the hip joint, and the ASR Hip Resurfacing System, a metal cap that fastens onto the head of the femur. Only the ASR XL Acetabular System is FDA-approved for use in the US. Depuy has encouraged surgeons having implanted these devices to request patient evaluations and metal sensitivity testing, since not all patients with metal debris-related tissue damage would necessarily show symptoms. Depuy has stated that it will cover the costs of patient monitoring and treatment, including revision surgery costs.
DePuy is facing criticism from orthopedic experts that it should have recalled the devices much sooner considering the large number of complaints. The first of many lawsuits filed against DePuy claims the devices are defective and alleges that DePuy knew about problems with the implants early on, but did nothing to alert patients or surgeons.
Metal hip implants made by Zimmer Holdings branded “Durom” are also coming under increased scrutiny for potentially causing high blood levels of chromium and cobalt and soft tissue damage from metal debris. Studies at the University of British Columbia found that patients implanted with a Durom socket implant had 2.6 times or 10 times higher than normal blood levels of chromium and cobalt, respectively. The researchers recommended that Durom implants no longer be used in standard implants because of the metal ion levels.
The rise in the incidence of severe medical complications from metal-on-metal hip implants is a rapidly growing concern for patients and orthopedic surgeons. It is difficult to know the full extent of the problem; the use of the latest metal-on-metal devices is still relatively new, and it is estimated that only one to ten percent of all complications from medical devices are actually reported to the FDA. More information is needed from ongoing studies to determine to what extent metal debris represents a threat to patient health, and whether implants made by some manufacturers are more or less safe than others.