## 3 Results  
Table 1 shows the comparison of the range of intersegmental joint angular motion during the stance phase and the maximum and minimum values for each range measured using optical motion capture and fluoroscopic RSA. The motions reported are for hindfoot supination/pronation, hindfoot internal/external rotation, forefoot supination/pronation, and the height-to-length ratio of the MLA. These are reported in degrees, except for the MLA height-to-length ratio, and averaged over all subjects. The values for the MLA height-to-length ratio values have been normalized to quiet standing, which is 0. Positive means a higher arch, negative means a lower arch. Figure 3: The calcaneus (blue bone), navicular (purple bone) and first metatarsal (red bone) were each tracked individually. The height-to-length ratio of the medial longitudinal arch was calculated as the ratio of the right-angle distance of the navicular tuberosity (NT) to the vector connecting the medial posterior border of the calcaneus (MP) and the head of the first metatarsal (MH) in the sagittal plane, as shown. The greatest difference in angular motion between the two datasets was for forefoot supination/pronation. The range of forefoot segment motion in the frontal plane with respect to the midfoot was \(18.27^{\circ}\) and \(10.18^{\circ}\) for optical motion capture and fluoroscopy, respectively. Overall, the optical motion capture values for the range of intersegmental joint motion tended to overestimate the motion when compared to fluoroscopic RSA. Table 2 compares the average angle value for heel strike, midstance, and toe off measured with optical motion capture and fluoroscopic RSA as an average of all trials for each foot joint motion examined. Angle values during mid-stance were the most similar when comparing motion capture and fluoroscopy. An asterisk indicates there is a significant difference between optical motion capture and fluoroscopic RSA values. The level of significance was set to \(p<0.05\). From this table, the only significant difference between motion capture and fluoroscopy was found at the level of the MLA height-to-length ratio for mid-stance and toe off. Table 3 displays the difference in angles between optical motion capture and fluoroscopic RSA for all foot joint motions. For supination/pronation of the hindfoot, the smallest difference between both motion capture techniques was seen at heel strike. For internal/external rotation of the hindfoot, the smallest difference was seen at midstance. For forefoot motion, the smallest difference was also seen at midstance. For the MLA height-to-length ratio at heel strike, there was no difference seen between the value obtained from motion capture and fluoroscopy. There is no consistent trend in the joint angles of the optical motion capture over-estimating or under-estimating fluoroscopic RSA. The largest limits of agreement were for the supination/pronation of the forefoot, with values of 3.6 to \(11.8^{\circ}\), suggesting that 95% of the differences between the two methods fall within this range. The standard deviation of the differences for forefoot supination/pronation was smaller than the standard deviation for the study population. There was no evidence of a proportional bias, and the difference between the two measurement methods did not increase with the magnitude of the angles.