Characterization and application of thin film pressure sensors

Data regarding intra-joint loads during range of motion is essential to understanding normal joint mechanics and pathology. The investigators configured and characterized the response of a 440 N range, 0.076 mm thick commercial thin film sensor to monitor joint loads through a range of motion. Following preconditioning, static and dynamic tests were performed to evaluate the sensor response under varied environmental conditions. Both tests utilized a fixture to align the sensor and applied load. Under conditions that included dry, wet, folded and kinked configurations, a static load of 100 N was applied and the sensor output monitored up to thirty minutes from the time of loading. A load of 400 N at 50 N/s was applied to the sensor to determine dynamic characteristics and calibration curves under the conditions described for static tests in addition to curved, hard and soft contact surfaces and sensor overload. Static kinked data was significantly different from the dry, wet and folded conditions. Dynamic data showed that inter-package variability was not significant but that differences between sensor packages and sensor configuration conditions were significant. To investigate applicability of these sensors to the field of orthopaedics, a cadaveric knee was instrumented with sensors to examine the role of the meniscus in load transmission and distribution across the knee. The sensors were placed bilaterally below each meniscus on the anterior, posterior and center of the tibial plateau. Sensor data were obtained at these locations during manually flexed range of motion for the intact, re-attached and lateral menisectomized conditions of the knee specimen.