Three-Dimensional Measurements of the Sinus Tarsi and Tarsal Canal in Pediatric Flexible Flatfeet using Weightbearing CT Scans

Abstract

Category: Hindfoot; Other Introduction/Purpose: When the hindfoot is in varus the tarsal canal becomes visible on a lateral Xray (XR) and has been referred to as a 'target sign'. However, the sinus tarsi (ST) and tarsal canal (TC) are not easily visible radiographically when associated with a flatfoot. The dimensions of both the ST and TC in normal and flatfeet are unknown, but if understood, could help with the design and implantation of an arthroereisis, a commonly performed procedure for correction of pediatric flatfoot deformity. Knowing the size of the TC will also reduce postoperative complications of arthroereisis such as stiffness, resulting from too large an implant. The aim of this study was to take three-dimensional (3D) measurements of the TC in pediatric flatfeet under weightbearing (WB) conditions. Methods: This was a prospective IRB approved study in pediatric patients with flexible flatfeet and asymptomatic children without flatfeet who were reviewed and analyzed. Using 3D computer-aided design (CAD) models from weightbearing CT (WBCT) scans, the following parameters were measured: the widest diameter of the posteromedial tarsal canal (WDPTC), the narrowest supero- inferior diameter of the tarsal canal (NSDTC), the length of the tarsal sinus, (LTS), the length of the tarsal canal (LTC) and the tarsal sinus and canal volume (TSCV). Correlations between patient age, Meary's angle, foot and ankle offset (FAO), and each of the above measured parameters were investigated. Both weight bearing and non-weight bearing CT scans were used for study to investigate the effect of bearing weight on the above-mentioned parameters. (Figures 1, 2). Results: Twenty-two children with flexible flatfeet (age range 9-14) and fourteen children with no foot deformity (age 9-15) were included for study. With the WBCT the TSCV decreased by 20% in comparison with non-weightbearing evaluation. The TSCV, the widest diameter of the anterolateral tarsal sinus (WDATS) and LTC decreased in flatfeet both under WB and NWB conditions compared with the control group. A positive linear correlation was found between the TSCV and patient age (r = 0.7307, P < 0.0001), while negative linear correlations were found between the TSCV and FAO (r = -0.5188, P < 0.0001) and Meary's angle (r = -0.3132, P = 0.0019). The tarsal sinus and tarsal canal volume significantly decreased in the flatfoot group during weight bearing, while the volume of the tarsal canal remained unchanged. Older age was not associated with either a wider tarsal canal or its orientation. Conclusion: Although the tarsal sinus and canal volume was positively associated with patient age, there was a negative correlation with both the FAO and Meary's angle. These findings may be very relevant in future study of the subtalar joint in both children and adults, and clearly have an implication for treatment of the pediatric flatfoot with arthroereisis.