title: Design and evaluation of a device for measuring three-dimensional micromotions of press-fit femoral stem prostheses.
abstract: Implant micromotion is considered to be a major factor in the loosening of cementless total hip replacements. Translational micromotion at the bone-implant interface generally occurs in all three spatial directions. Under physiological loading, the interfacial micromotion consists of a cyclic amplitude and changes in the mean, which, in the cranio-caudal direction, represents subsidence of the prosthesis. Existing measurement strategies, which are based on dial gauges, extensometers, LVDTs, hall-effect transducers or strain gauge techniques provide information about only one component of the general three-dimensional micromovement. Moreover, in the majority of the studies, the data are difficult to interpret due to the measured motions being composed of interfacial micromotion and femoral strains. A new transducer was designed that allows the accurate measurement of all three isolated components of micromotion. An optoelectronic approach, based on silicon position-sensitive detectors (PSD) in combination with high precision mechanical parts, was chosen. To exclude thermodrifts during long-term testing, a thermistor was integrated in the sensor. Validation experiments on a precision positioning table indicated the high precision and resolution of the developed sensors. Furthermore, in-vitro tests on a standard press-fit prosthesis demonstrated the easy handling and reliability of the system.
authors.affiliation: M. E. Müller Institute for Biomechanics, University of Bern, Switzerland.
authors.forename: D W
authors.initials: DW
authors.lastname: Bühler
authors.forename: T R
authors.initials: TR
authors.lastname: Oxland
authors.forename: L P
authors.initials: LP
authors.lastname: Nolte
mesh_terms: D001696:Biomechanical Phenomena; D004582:Electronics, Medical / Q000295:instrumentation; D005069:Evaluation Studies as Topic; D006622:Hip Prosthesis; D006801:Humans; D066298:In Vitro Techniques; D007231:Infant, Newborn; D009038:Motion; D055095:Optics and Photonics / Q000295:instrumentation; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012815:Signal Processing, Computer-Assisted; D013696:Temperature