Defining the load bearing axis of the lower extremity obtained from anterior-posterior digital radiographs of the whole limb in stance

SummaryObjectiveThe purpose of this study was to evaluate the reliability of inter-and intra-observer assessments of the mechanical alignment of the lower extremities with digitally computed radiographs of an anterior-posterior view of the whole leg using a new computer-assisted method.MethodLoad bearing axis deviation of the lower extremities was quantitatively measured by three examiners in 105 knees of 73 subjects who had osteoarthritis of the knee with a Kellgren–Lawrence grade of 1 or more. A line representing the load bearing axis was drawn from the center of the femoral head to the center of the ankle and the alignment of the leg was assessed by measuring the width of the proximal tibia and the perpendicular distance from the middle of the proximal tibial condyle to the load bearing axis (Fujifilm OP-A). A ratio of the values was calculated and expressed as a percentage.ResultsThe inter-observer mean difference was 2.9 % (SD, 2.7), and the intra-observer mean difference was 2.1% (SD, 2.2). The mean intraclass correlation coefficient (ICC) for inter-observer trials was 0.96; that for intra-observer trials was 0.99.ConclusionOur computer-assisted method was reproducible, and should be considered an alternative method for the measurement of the alignment of the whole leg.