Measurement of Elbow Flexion and Pronation with Angular Rate Sensors

Increases in upper extremity injuries as a result of air bag deployment have spurred research on upper extremity response kinematics. During airbag deployment, forearm angular rates can exceed 150 rad/sec, requiring a sensor scheme that demonstrates durability for repeated use, high frequency response to capture the dynamic event, and small mass to minimize artifacts due to inertial effects. In this study an instrumentation scheme for the measurement of cadaveric elbow flexion and elbow pronation resulting from airbag deployment is developed. The instrumentation scheme involves mounting a three-axis magnetohydrodynamic angular rate sensor (MHD ARS) on the humerus, a single axis MHD ARS on the ulna and a single axis MHD ARS on the radius. Elbow flexion validation was performed with a Hybrid III instrumented arm and yielded an error in peak flexion angle of 6.5 ± 3.3 % and error in flexion rate of 6.3 ± 4.8 %. Elbow pronation of cadaveric specimens was verified qualitatively with film analysis. The results suggest that this instrumentation scheme is an acceptable means for measuring upper extremity kinematics during rapid motion tests.