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

Muller, Jacobus Hendrik (2007-04)

Thesis (MScIng) -- University of Stellenbosch, 2007.

Thesis

ENGLISH ABSTRACT: Background: A fibre optic force sensor (two transmitters and receivers, a driver circuit and the load sensing optic fibre) was designed, built and tested to be used in in vitro and in vivo patella tendon experiments. Methods: Hysteresis in the sensor output, the sensor's frequency response and its measurement repeatability were quantified through two loading tests in a hydraulic press and a cadaveric patella tendon. The sensor and loadcell measurements of the cadaveric patella tendon loading test were also used to derive five constants of a mathematical expression that models soft tissue stress relaxation. The results obtained from the sensor measurements (local stress relaxation) were compared to the results obtained from the loadcell (overall stress relaxation). The loads in the anterior third and posterior third of the right patella tendon were measured when volunteers performed a one 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 decreases when the loading frequency increases. The stress relaxation measured by the loadcell differed from the relaxation measured by the sensor (loadcell: 70%, sensor: 57%). The in vivo study results were submitted for statistical analysis and showed that posterior loads were significantly higher than anterior loads as the ratio of the peak anterior load 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 measurement repeatability and frequency response results suggest that it will be best to make use of subject and rate specific calibrations for the sensor. The sensor gives the possibility of measuring local stress relaxation, something that is not possible with the loadcell. The in vivo results provide insight into the loading patterns within the patella tendon.

AFRIKAANSE OPSOMMING: Agtergrond: 'n Veseloptiesekragsensor (twee senders en ontvangers, 'n drywerbaan en krag sensitiewe optiese vesel) is ontwerp, vervaardig en getoets wat gebruik kan word tydens in vitro en in vivo patellapees eksperimente. Metodes: Histerese in die omsetter uitreesein, die omsetter se frekwensierespons en metingherhaalbaarheid was gekwantifiseer m.b.v. twee belastingstoetse in 'n hidrouliesepers en 'n kadawer patellapees toetsopstelling in 'n trektoetsraam. Die omsetter en lassel metings van die in vitro belastingstoets is gebruik om vyf konstantes van 'n wiskundige model waarmee die ontspanningsgedrag van sagte weefsel gesimuleer word, te bepaal. Die resultate verkry deur die lassel. data (totale ontspanning) en die omsetter data (lokale ontspanning) is met mekaar vergelyk. Die kragte in die voorste en agterste derde van vrywilligers se regter patellapees is gemeet tydens 'n stel oefeninge: hurk, een-been-ekstensie, trap en spring. Resultate: Die gemiddelde histeresefout is bereken op 8.9%-vol-skaal-uitset (VSO) en metingherhaalbaarheid was 93% VSO. Die omsetter se sensitiwiteit het afgeneem vir toenemende frekwensie. Die ontspanning gemeet deur die lassel verskil van die ontspanning gemeet deur die omsetter (lassel: 70%, omsetter: 57%). Die in vivo studie resultate is ingehandig vir statistiese analise en die bevinding was dat agterste maksimum kragte in die patellapees aansienlik grater was as die voorste maksimum kragte. Die verhouding van die voorste maksimum krag oor die agterste maksimum krag· vir. die oefeninge was: hurk - konsentries = 0.56 [SD = 0.4] en eksentries 0.54 [SD = 0.41 ]; been-ekstensie - 0.33 [SD = 0.17]; trap - op = 0.28 [SD = 0.094] en af = 0.29 [SD= 0.066]; spring = 0.34 [SD= 0.14]. Bespreking: Die histeresefout was binne aanvaarbare limiete vir die studie. Die metingherhaalbaarheid en frekwensierespons resultate dui daarop dat die omsetter se kalibrasies afhanklik is van die tempo van belasting en varieer tussen optiesevesels. Die omsetter kan gebruik word om lokale ontspanning te meet, iets wat nie moontlik is met 'n lassel nie. Die in vivo resultate ondersteun die hipotese dat agterste patellapeesvesels meer belas is as die voorste patellapeesvesels.

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