Fig. 2

Z-axis alignment errors between reconstructions for 24 native scans of the femorotibial joint. Errors along the x axis represent rotations about the y axis, and vice versa. Angular errors have been derived from the axis cosines and corrected by subtraction of 90°. The 95% error ellipse is shown overlying the data points, rotated clockwise by the ellipse angle 4.4°. There is increased variability in rotation about the y axis (equivalent to femoral abduction/adduction) compared to the x axis (equivalent to femoral extension/flexion), as evidenced by flattening of the ellipse and the underlying data spread