Validation of Flexible Electrogoniometry as a Measure of Joint Kinematics

Summary Background and Purpose The Biometrics Flexible electrogoniometer has the potential to allow physiotherapists to record the motion of joints during dynamic functional activities. In order to make full and appropriate use of this device it is necessary to comprehend the design, attachment and measurement properties of this instrument. Methods The measurement properties of the Biometrics flexible electrogoniometer were investigated using a series of controlled experiments. The in vivo performance of the device was evaluated by comparing the results of the electrogoniometer to those from a TV motion analysis system while measuring knee movement during gait in five normal subjects. Results The results of these studies indicate that the electrogoniometers are stable, precise, accurate and repeatable in performance. Little variation exists between electrogoniometers or between the performance of an electrogoniometer at different times, on different days or in different environmental conditions. Small hysteretic effects and inaccuracies are present in the devices but these are of the order of 1 or 2 degrees. The system is not affected by environmental pollutants such as heat, electrical interference, convection currents or noise and therefore can be used in a variety of hospital settings. The device is however affected by abduction/adduction angle with angles of 40° or more giving substantial errors when associated with simultaneous flexion or extension. Conclusions The electrogoniometer should be attached firmly and securely across the joint in an essentially planar configuration. Provided care is taken to handle and mount the electrogoniometers appropriately they appear to record knee movement faithfully and accurately and the system is capable of giving valid and meaningful clinical data.