Design, building and testing of a fibre optic force sensor and its application in an in vitro and in vivo study investigating the biomechanical properties of the patella tendon

[摘要] ENGLISH ABSTRACT: Background: A fibre optic force sensor (two transmitters and receivers, a drivercircuit and the load sensing optic fibre) was designed, built and tested to be used in invitro and in vivo patella tendon experiments.Methods: Hysteresis in the sensor output, the sensor's frequency response andits measurement repeatability were quantified through two loading tests in a hydraulicpress and a cadaveric patella tendon. The sensor and loadcell measurements of thecadaveric patella tendon loading test were also used to derive five constants of amathematical expression that models soft tissue stress relaxation. The results obtainedfrom the sensor measurements (local stress relaxation) were compared to the resultsobtained from the loadcell (overall stress relaxation). The loads in the anterior third andposterior third of the right patella tendon were measured when volunteers performed aone leg squat and a leg extension as well as a step and jump exercise.Results: The sensor has an average hysteresis error of 20% full scale output(FSO), its measurement repeatability is 93% FSO and its measurement sensitivity decreaseswhen the loading frequency increases. The stress relaxation measured by theloadcell differed from the relaxation measured by the sensor (loadcell: 70%, sensor:57%). The in vivo study results were submitted for statistical analysis and showed thatposterior loads were significantly higher than anterior loads as the ratio of the peak anteriorload over the peak posterior load indicates (squat: concentric = 0.56 [SD = 0.4]and eccentric 0.54 [SD = 0.41], leg extension: 0.33 [SD = 0.17], step: up = 0.28 [SD =0.094] and down= 0.29 [SD= 0.066], jump: 0.34 [SD= 0.14]).Discussion: The hysteresis was within acceptable limits for the study. The measurementrepeatability and frequency response results suggest that it will be best tomake use of subject and rate specific calibrations for the sensor. The sensor gives thepossibility of measuring local stress relaxation, something that is not possible with theloadcell. The in vivo results provide insight into the loading patterns within the patellatendon.

[发布机构] Stellenbosch University