Design and evaluation of a device for measuring three-dimensional micromotions of press-fit femoral stem prostheses

• Published in: Medical engineering & physics 1997-03, Vol.19 (2), p.187-199
• Main Authors: Bühler, D.W., Oxland, T.R., Nolte, L.-P.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Biomechanical Phenomena; Electronics, Medical - instrumentation; Evaluation Studies as Topic; Hip Prosthesis; Humans; In Vitro Techniques; Infant, Newborn; interface motion; Investigative techniques, diagnostic techniques (general aspects); mechanical testing; Medical sciences; Motion; optical detectors; Optics and Photonics - instrumentation; Osteoarticular system. Muscles; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Prosthesis Design; Prosthesis Failure; Radiotherapy. Instrumental treatment. Physiotherapy. Reeducation. Rehabilitation, orthophony, crenotherapy. Diet therapy and various other treatments (general aspects); Signal Processing, Computer-Assisted; Technology. Biomaterials. Equipments. Material. Instrumentation; Temperature; Three-dimensional-displacement transducer
• ISSN: 1350-4533; 1873-4030
• DOI: 10.1016/S1350-4533(96)00060-4

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 craniocaudal 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.