Reliability and validity of first metatarsophalangeal joint orientation measured with an electromagnetic tracking device

Objective. To establish the reliability and validity of measurements of sagittal plane orientation of the first metatarsophalangeal joint using the Flock of Birds™ electromagnetic tracking device. Design. Different joint orientations were reproduced on cadaver specimens in a specially designed jig with skin and skeletal application of the sensors. Background. The Flock of Birds™ provides a means for quantifying first metatarsophalangeal joint motion, however, the reliability and validity of such an application has not been determined. Methods. Joint orientation was measured in five cadaver feet with skin and skeletal sensor application. A specially designed jig allowed simulation of clinical tests of range of motion. Sagittal plane orientation was determined from 3-D, anatomically-based, reference frames embedded in the first metatarsal and proximal hallux. Results. Reliability of all measurements was high for skin and skeletal sensor application. There were no significant differences in joint orientation between either technique for any of the simulated motion tests. Conclusions. The Flock of Birds™ provides reliable and valid measures of first metatarsophalangeal joint orientation with the sensors applied to the skin over the first metatarsal and proximal hallux.