A reliability study of a new back strain monitor based on clinical trials

Movements of the lower back are a contributing factor for developing low back pain. Various techniques have been developed and tested for the measurement of lower back movement but most have been too expensive, too cumbersome and have been unable to measure movements over a prolonged period. The thesis investigates the development, the reliability and the validity of a new device (the Back Strain Monitor) to be used to measure lower back movement during a day’s activity.

After a review of potential devices, three transducers to measure back movement were selected for laboratory testing. The first transducer, the conductive silicone polymer, performed poorly displaying an electrical drift as the polymer underwent repeated stretching. The second, the inductive coil technique, performed well in the laboratory trials with a CV of 0.54% for maximum linear stretch measurements. However, issues relating to electrical drift and electrical lag led to large variation of the baseline readings (CV = 82%). The third transducer, the accelerometer method, performed very well during the laboratory trials displaying a CV of 0.12% for the range of movement.

Two of the three sensors (the inductive coil and the accelerometer method) were developed to the level of stand-alone prototypes, capable of being tested within a clinical trial setting. The first clinical trial involved three testers applying the inductive coil prototype to 15 subjects to assess its measurement properties. The inductive coil performed with moderate inter tester reliability (ICC (2,1) = 0.65). There was limited evidence of validity for the inductive coil technique as it showed poor to average correlation with the three comparator techniques (ICC (2,1) values from 0.47 to 0.75).

The second clinical trial applied the accelerometer method to 23 subjects with three testers. There was very good inter tester reliability (ICC (2,1) ≥ 0.86) and test re-test reliability (ICC (2,1) ≥ 0.89). The accelerometer method also displayed a high level of agreement (ICC (2,1) ≥ 0.88) with the main recognized comparator technique (the double inclinometer) providing evidence of criterion validity.

The accelerometer method provided a reliable option for measuring movements of the lower back. There was evidence of criterion validity and a preliminary case study demonstrated that the movement data collected over 8 hours was able to alter back postures via biofeedback. The accelerometer method displays advantages over other methods in that there is the potential to measure three dimensional movement at a high sampling rate and for extended periods of time. The device may provide a new management tool to assist health practitioners in the treatment of low back pain.