IN-VITRO MEASURED STRAINS IN THE LOADED FEMUR - QUANTIFICATION OF EXPERIMENTAL ERROR

The application of strain gauges to bone surfaces has been extensively employed as a method of determining strain fields in response to impl anted devices in orthopaedics. The aim of this study was to determine some of the experimental errors associated with the use of strain gaug es in in vitro experimental investigations of the loaded femur. An exp erimental protocol was devised to obtain strain data at 20 strain gaug ed locations on the proximal femur. These data were interpolated using a parametric model. The parametric model was then used to estimate th e errors associated with mispositioning of the gauges and deviations i n their direction of application to the bone. This sensitivity analysi s was also supported by a finite element analysis for the purposes of comparison and cross-validation. The results indicated that the nature of the loading normally employed in the literature can contribute to making the readings for some of the gauges (anterior and posterior) un reliable and redundant, even for small positioning errors. The greates t predicted errors for the lateral and medial gauges were due to misal ignment of the gauge as opposed to mispositioning. The size of the gau ge had a negligible effect on the errors predicted relative to those c aused by misalignment.