Camera-Based System to Track Arch Height Index and Angle of Foot Pronation during Pregnancy

Submission Type: Other Research Type: Level 5 - Case report, Expert opinion, Personal observation Introduction/Purpose: Foot structural changes and pain are some of the most common musculoskeletal conditions experienced during pregnancy [1]. Symptomatic flatfoot and pronation during pregnancy is hypothesized to result from increased body mass and circulating hormones that promote ligament laxity [2,3]. Accurately and reliably tracking foot structure is critical to understand the effects of pregnancy on the foot and to identify patients at increased risk of long-term pain and disability. This study developed a camera-based method to quantify arch height index (AHI) and angle of foot pronation (AOP) with the goal of reducing experimental time. This method offers an inexpensive, reliable, and quick technique to track and study changes in foot structure throughout pregnancy. Methods: Our camera-based foot structure measurement system captures top, side, and hind-view images of the foot simultaneously (Figure 1.). We recruited a cohort of non-pregnant control participants (n = 7, age = 27.9 ± 3.2 years) to acquire foot images in the standing position at two timepoints to test repeatability and reliability of the camera-based system. We then recruited a cohort of pregnant individuals (n = 33, age = 34.8 ± 4.2 years, gestational week = 12.2 ± 2.1 weeks) during their first trimester to acquire foot images in the standing position at 12, 24, and 36-weeks of pregnancy. We used a MATLAB script to calculate AHI and AOP (Figure 1.). We performed paired t-tests in the control group to confirm no significant differences over time. Additionally, we used paired t-tests to compare right and left foot measures as well as first and second trimester measures in the pregnant cohort. Results: Our repeated measurements of AHI and AOP in our control cohort did not change over time and was comparable to previous studies in similar patient cohorts [4,5]. We did not detect differences between first and second trimester patients (AHI: p= 0.56, AOP: p= 0.85), but our preliminary findings suggests that AHI decreased by 7% and AOP increased by 74% between the second and third trimester (Table 1.). These anticipated third trimester effects are greater than natural variations observed in the control cohort. We detected significant differences in foot structure between the right and left foot in our patients (AHI: p< 0.01, AOP: p< 0.01). Conclusion: Our novel camera-based system reliably quantifies foot structure without ionizing radiation and advanced equipment that are intrinsic to standing x-ray imaging. Our early data found that foot structure does not change between the first and second trimester but is likely to change between the second and third trimester due to increased body mass and ligament laxity that are exacerbated during this time. We expect to have a larger cohort of patients through 3 trimesters by November 2024 and will be properly powered to detect changes in foot structure similar to Segal et al. (d = 0.8) [2].