We have assessed the effect of a variety of implants commonly used in fracture fixation and joint replacement on the activation of metal detectors at airport security gates. A volunteer with metal implants strapped on and patients with implants in situ walked through the device. Implants used in fixation do not activate it, except for Richards cannulated screws. An Austin-Moore prosthesis does set off the detector, but a single joint replacement does not. Three or four joint replacements activate the alarm and patients with these implants should be warned of this possibility.
We studied the detection of joint replacements at airport security checks in relation to their weight, using two types of detector arch. A single-source, unilateral detector showed different sensitivities for implants on different sides of a test subject. All implants weighing more than 145 g were detected by one of the arches. The degree of detection was directly related to the logarithm of the weight of the prosthesis in patients, with a linear correlation (r2 = 0.61). A bilateral arch detected all prostheses weighing over 195 g. With their usual sensitivity settings many joint replacements were detectable; an identification pass containing the site and weight of such prostheses would help to avoid the need for body-search procedures.
The effect of storage at sub-zero temperatures and subsequent thawing was investigated in dissected muscles, tendons, limbs and spines. Freezing caused a noticeable shortening of muscles which when thawed could easily be elongated; the same effects, though less pronounced, were observed with tendons. During freezing, myotomy or tenotomy led to the development of a striking deformity owing to unopposed shortening of the opposing muscles. After thawing, all frozen specimens containing muscles and joints showed an increased range of passive movements, easily demonstrable by mild tensile forces.
