Development of a knee telemetry data capture and feedback system

H. S. Mann, J. A. Szivek, J. B. Benjamin

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


The purpose of this study was to develop a device that will allow the wireless transmission of strain information from a prosthetic knee implant. This phase of the study consisted of the development of a digital transmitter, development of a inductively coupled power unit, and the development of real time data capture and display software. Measurements were collected with the telemetry system and compared to hard wired measurements to characterize the accuracy of the telemetry system. The experimental apparatus used to test the telemetry system against the hard wired system included a cantilever loaded aluminum bar fixed at one end. This was loaded with a servo hydraulic MTS (Materials Testing System) load control. A strain gauge was attached to the center of the aluminum bar and data collected. The software for the telemetry system was developed using Think C by Symantec on an Apple Macintosh IIcx and a C programming language. The MTS machine was set up to place a sinusoidally varying load on the aluminum bar every second. Initially the strain gauge was hardwired to the Macintosh and the data was collected by Lab View. The process was then repeated with the strain gauge connected to the telemetry system and the measurements were compared. The hardwired system produced a maximum tension of 1400 microstrains and a maximum compression of -1400 microstrains. The telemetry system produced a maximum tension of 1150 microstrains and maximum compression of -1100 microstrains. A signal attenuation of 18% was noted upon tension and signal attenuation of 21% was noted upon compression. Additionally, a zero input drift of up to 200 microstrains was noted. Upon visual inspection the graph of the telemetry data wave form was very similar to the wave form produced by the hardwired system. The similarity in the wave forms produced by the telemetry and hardwired system indicated the wireless telemetry system design is feasible. The attenuated signals produced be the telemetry systems indicate that further refinement is required to minimize or correct for noise within the system.

Original languageEnglish (US)
Pages (from-to)40A
JournalJournal of Investigative Medicine
Issue number2
StatePublished - Feb 1999

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)


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