Detection of orthopaedic implants in vivo by enhanced-sensitivity, walk-through metal detectors

Since the September 11, 2001, World Trade Center terrorist attack, airports worldwide have heightened their security standards in efforts to discourage terrorist attacks. Patients have become increasingly concerned about whether their metallic implants will set off airport metal detectors. The purpose of this study was to assess rates of detection of various orthopaedic implants by airport detectors with the new security sensitivities.

One hundred and twenty-nine volunteers with a total of 149 implants were asked to walk through an M-Scope three-zone metal detector at two sensitivity settings. Low sensitivity was equivalent to the United States Transportation Security Administration setting for regular security, and high sensitivity was equivalent to its standard for high security.

Of the 149 implants in 129 patients who were screened, eighty-four (56%) were trauma hardware, including intramedullary nails, plates, screws, and Kirschner wires, and sixty-five (44%) were arthroplasty implants. Seventy-seven (52%) of the 149 implants were detected by the metal detector at one or both settings. Multivariate analysis revealed that the type (p < 0.001), material (p < 0.001), and location (p < 0.001) of the implant were independent predictors of detection. The overall rate of detection was 88% for prosthetic replacements compared with 32% for plates, with the likelihood of detection being fifteen times greater (odds ratio = 15.0, 95% confidence interval = 5.9 to 39.1) for the prosthetic replacements. All total hip replacements and 90% of the total knee replacements were detected at the low-sensitivity setting. Intramedullary nails and Kirschner wires were not detected. The overall detection rate was 67% for implants in the lower extremity, 17% for those in the upper extremity, and 14% for those in the spine. The detection rate for implants in the lower extremity was ten times higher than that for implants in the upper extremity and eleven times higher than that for implants in the spine.

More than half of all orthopaedic implants may be detected by metal detectors used at commercial airports. Total joint prostheses will routinely set off the detector, whereas nails, plates, screws, and wires are rarely detected. Cobalt-chromium and titanium implants are more likely to be detected than stainless-steel implants.