Measuring Device Aims to Boost Hip Operation Success

Researchers at the National Institute of Standards and Technology (NIST) are developing state-of-the-art measuring techniques, similar to those used in making aerospace components fit together precisely, that soon could improve success rates for hip replacement surgery.

At the request of a group of prominent orthopaedic surgeons and the American Academy of Orthopaedic Surgeons (AAOS), NIST researchers are working to improve calibrations and operating room testing of the Computer Assisted Orthopaedic Surgery (CAOS) tracking instruments surgeons use to plan the delicate, highly complex operation.

To be completely successful, CAOS hip replacement surgery must take into account tiny human skeletal differences. Imprecise measurements, which could result from conditions seemingly unrelated to the surgery, such as operation room noise or temperature, can lead to poor positioning of implants, leaving some former patients with discomfort during walking and, in rarer cases, a need to redo the operation.

The researchers have built a lightweight device called a “phantom” that resembles the artificial socket, ball and femur substitutes that surgeons use to replace the joint and bone in hip operations, based on a calibrated XY coordinate frame. They drilled tiny holes at precisely measured intervals into the phantom and made cuts at precisely measured angles, favored by surgeons for CAOS operations. Because the precise coordinates of the mechanical (magnetic) ball and socket joint center of rotation have been measured, manufacturers of CAOS tracking sensors can use the phantom to test the accuracy of their measuring instruments. Surgeons also should be able to test the accuracy of their CAOS devices, just before making their first incision, to measure ball and socket joint center of rotation coordinates, angles for cuts into the bone and places for the insertion of screws.

Currently, no standardized approach to the evaluation of CAOS technology exists, but an ASTM International committee is working on the establishment of such standards.

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