Effectiveness of foot orthoses in controlling the posture of medial longitudinal arch: A pilot study

INTRODUCTION: Foot orthoses are frequently used in the management foot pain and dysfunction caused by excessive foot mobility. Previous research has shown that the midfoot region exhibits the greatest amount of mobility during dynamic activity.1,2 The longitudinal arch angle (LAA) has been used in numerous studies to measure the change in the posture of the medial longitudinal arch associated with midfoot mobility as well as assess the effectiveness of foot orthoses.3,4 Prior studies using the LAA to assess foot orthoses' effectiveness have been forced to alter footwear in order to permit the use of reflective markers required for video-based motion capture.3 Thus, the effect of footwear in modifying the LAA in contrast to foot orthoses is unknown. We have developed a high-speed stereo radiography (HSSR) system, an advancement of bi-plane fluoroscopy, that utilizes two views to capture 3D x-ray images of radiopaque beads allowing researchers to measure dynamic foot motion inside footwear on the sub-mm level.5 The purpose of this study was to assess the effect of footwear and foot orthoses on the LAA during walking. It was hypothesized that the LAA would demonstrate the greatest increase, indicating reduced midfoot pronation, in the shod + orthosis condition in comparison to the shod and barefoot conditions. METHODS: Three males (26 ± 2 years, BMI: 27 ± 5), with no history of traumatic or overuse injury to either lower extremity six months prior to study, no congenital defect to either lower extremity, and no visible signs of foot pathology, signed informed consents and participated in the IRB-approved study. Both feet of each subject were assessed using the Bony Arch Index (BAI) and Navicular Drop (ND). Based on previous research, the criteria used to classify a foot as pronated was a BAI of less than 0.200 and a ND of greater than 7.81 mm.6 The mean BAI for the six feet was 0.162 ± 0.020 and the mean ND was 13.2 ± 4.0 mm, classifying all six feet as pronated. 3 mm metal beads were placed on bony landmarks, including the medial malleolus, navicular tuberosity, and the medial aspect of the first metatarsal head. Static barefoot loaded HSSR images of each foot were collected, and subjects walked at a self-selected pace along a raised walkway while HSSR images of each foot during stance phase were captured at a rate of 100 Hz during stance for three conditions: barefoot, shod, and shod + orthosis. Subjects wore their own athletic shoes and standardized prefabricated foot orthoses (Vasyli Medical, San Rafael, CA). XMALab (Brown University, Rochester, NY) was used to undistort the images and export the 3D positions of the metal beads. The LAA was calculated by projecting the angle between the medial malleolus, navicular tuberosity, and the medial aspect of the first metatarsal head onto the sagittal plane of the foot (Figure 1). Multiple paired t-tests (p<0.05) were used to compare LAA measurements at end of loading response (19% stance phase), end of midstance (50% stance phase), the minimum LAA during terminal stance (50-80% stance phase), and LAA excursions (difference between maximum and minimum LAA) between the end of loading response to the end of terminal stance (19-80% stance phase) using Matlab (MathWorks, Natick, MA). RESULTS: Mean LAA in the static loaded position for the barefoot condition was 128.5° ± 3.9°. Mean LAAs of the end of loading response and the end of terminal stance for all three conditions were between 121.9° and 133.7°. LAA excursions between end of loading response and end of terminal stance for barefoot, shod, and shod + orthosis conditions were 8.8° ± 4.0°, 6.4° ± 2.1°, and 7.9° ± 2.3°, respectively, but none were significantly different. Compared to the barefoot condition, the shod condition resulted in significantly increased LAAs during the end of midstance while the shod + orthosis condition showed significantly increased LAAs during end of midstance and end of loading response (Figure 2). Compared to the shod condition, LAAs were significantly increased in the shod + orthosis condition during end of midstance and terminal stance by 1.5° and 1.1°, respectively. The static loaded LAA measurement was closest to the LAA at end of midstance of the shod dynamic gait trial (Figure 3). DISCUSSION: The findings of this pilot study support our hypothesis that footwear with foot orthoses can effectively change the position of the midfoot by increasing the LAA throughout the midstance and terminal stance periods of walking in comparison to barefoot walking. The effectiveness of any foot orthosis is dependent on the footwear used with the device, because the shoe provides the base of support for the orthosis. In contrast to previous studies, this study was able to examine the effect of the orthosis on the LAA while preserving the full effect of the footwear design. Our findings also validate that footwear alone can influence the posture of the midfoot by increasing the LAA. In contrast to previous research 3, the results of this pilot study validate that foot orthoses when used in unmodified footwear effectively control the position of the midfoot during walking, resulting in reduced midfoot pronation. While the small sample size (n=6 feet) and skin artifact are limitations, the HSSR protocol used in this study allowed for the assessment of midfoot movement without the modification of footwear. (Figure Presented).