Marker-based validation of a biplane fluoroscopy system for quantifying foot kinematics.

Introduction: Radiostereometric analysis has demonstrated its capacity to track precise motion of the bones within a subject during motion. Existing devices for imaging the body in two planes are often custom built systems; we present here the design and marker-based validation of a system that has been optimized to image the foot during gait.

Methods: Mechanical modifications were made to paired BV Pulsera C-arms (Philips Medical Systems) to allow unfettered gait through the imaging area. Image quality improvements were obtained with high speed cameras and the correction of image distorting artifacts. To assess the system's accuracy, we placed beads at known locations throughout the imaging field, and used post processing software to calculate their apparent locations.

Results: Distortion correction reduced overall RMS error from 6.56 mm to 0.17 mm. When tracking beads in static images a translational accuracy of 0.094 ± 0.081 mm and rotational accuracy of 0.083 ± 0.068° was determined. In dynamic trials simulating speeds seen during walking, accuracy was 0.126 ± 0.122 mm.

Discussion: The accuracies and precisions found are within the reported ranges from other such systems. With the completion of marker-based validation, we look to model-based validation of the foot during gait.