Contact measurements in the cadaveric human hip using optical fiber sensors

Date

2012-08-29

Authors

Bouchard, Devan

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Abstract

The overarching goal of this study was to develop a method to measure solid matrix stress, ex vivo, in the articular cartilage of three cadaveric human hip joints. The primary objectives were to establish the day to day repeatability of the method over three sequential days of testing before resecting the labrum on the fourth day to observe changes in joint behavior. Three to six fiber optic contact stress sensors were inserted within the middle zone of the acetabular cartilage to measure solid matrix stress in three hemipelvis hip specimens. A fiber optic hydrostatic fluid pressure sensor was used to simultaneously measure the synovial fluid pressure in the fossa while a representative physiological load was applied using a materials testing machine. Once inserted, the location of all sensors was quantified using a radio-stereometric analysis technique showing good repeatability of sensor location. The target radial positions of contact stress sensors were 0º, 25º, and 50º anterior of the AIIS and the observed positions were -1º ± 5º, 27º ± 3º and 56º ± 14º. Measurements of 0.26 ± 0.13 MPa and 0.440 ± 0.14 MPa for peak hydrostatic synovial fluid pressure show poor repeatability and no consistent change was observed after labral resection. Two contact stress sensors measured positive solid matrix stress values of 0.21 MPa and 0.69 MPa which agree with the findings of a similar experiment, however, poor day to day repeatability was observed. The difference between maximum and minimum stress values tended to be lower, and the nominal maximum solid matrix stress value higher, on the final day of testing after labral resection. No clear, consistent difference in the mean value of the solid matrix stress at the end of the test was found between tests with the intact labrum and after labral resection. Significant cross-sensitivity artifact is suspected in the solid matrix stress measurements significantly limiting the results. Several recommendations to improve upon these limitations in future work have been identified. Despite challenges during the experimental work and poor repeatability of measurements from the fiber optic sensors, incremental advances were made toward achieving the goal of developing a measurement system for cartilage solid matrix stress in the hip.

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Keywords

Hip, Sensor, Fiber optic, Contact stress, Human, Cadaveric

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