Cobalt-chromium and titanium lower extremity implants top the list of “most liketly to trigger a metal detector.”
Increased security measures in U.S. commercial airports have found passengers shedding belts, change purses, shoes and jewelry as they walk through metal detectors before proceeding to the gate. With the increased security, orthopaedic patients are increasingly concerned that their implants will set off alarms.
According to researchers from the orthopaedic surgery department at Beth Israel Deaconess Medical Center (Harvard Medical School) in Boston, that concern may be well-founded. Their report, which appeared in the April 2007 issue of the Journal of Bone and Joint Surgery, lists the implants that are most likely to trigger detectors with new security sensitivities.
The study results showed that more than half of all orthopaedic implants triggered metal detectors. Although plates, screws, intramedullary nails, and wires were rarely detected, all total hip replacements and 90 percent of total knee replacements were detected, whether they were unilateral or bilateral. Lower-extremity implants were detected 10 times more often than upper-extremity implants, and 11 times more often than spine implants.
In additon, cobalt-chromium and titanium implants were much more likely to be detected than stainless-steel implants. Upper-extremity prostheses—total shoulder replacements, total wrist replacements, and radial head replacements—were not detected.
“Our results will aid surgeons in counseling patients regarding their implants and security agencies by identifying which medical devices commonly set off metal detectors,” said co-author Edward K. Rodriguez, MD.
During the one-month study, 129 volunteers with a total of 149 implants walked through an M-Scope three-zone metal detector used at commercial airports. It was programmed at both low and high levels, with sensitivities equivalent to U.S. Transportation Security Administration settings. The low-sensitivity setting detected 57 of the 149 implants; the high-sensitivity level detected 77 implants. The type of implant, material composition, and the location of the implant in the body were all independent predictors of detection.
Although older studies found a general insensitivity of airport detectors to metal implants, “no trials have been performed in the United States to analyze the detection of orthopaedic implants under the new security guidelines,” said Dr. Rodriguez. In addition, the study found that increasing the sensitivity setting of the detector—as might occur when the security level is raised, such as during holidays or terrorism alerts—substantially increased the rate of implant detection as a whole.
As a result of the study, orthopaedic surgeons can warn their patients who have total hip and/or total knee prosthesis—particularly those with a cobalt-chromium implant—that the implant may trigger a delay when traveling.
To reduce this delay, the Transporta-tion Safety Administration’s Web site offers the following suggestions:
- Patients with an implanted medical device or metal implant should advise the Security Officer of this fact and where that implant is located (recommendation, not required). This will enable the patient to receive a private screening rather than walk through the metal detector.
- Patients whose devices might be affected by walking through the metal detector or being hand-wanded can ask the Security Officer for a pat-down inspection instead.
- If the patient walks through the metal detector and sets off an alarm, a Security Officer will need to conduct a “pat-down,” as an extra screening process.