Relationship between tarsal tunnel depth and weight-bearing

Objectives The tarsal tunnel is an osteofibrous canal with flexor retinaculum on calcaneus, talus, and navicular bone. The goal of this study was to explore the impact of weight-bearing on the tarsal tunnel using ultrasound.Methods Ultrasonography was performed on 21 subjects who were not obese and had no signs or symptoms referable to tarsal tunnel syndrome. The tarsal tunnel depth was measured along the malleolarcalcaneal axis, 1.5 cm above and 1.5 cm below the axis in supine and standing position by ultrasonography. Bilateral ground reaction forces and maximal plantar pressure were measured by pressure sensitivity.Results There was a decrease in bilateral tarsal tunnel depth with respect to the malleolarcalcaneal axis in the standing position compared to the supine position. However, the tarsal tunnel depth above and below the axis in standing position was increased. Right ground reaction force and maximal plantar pressure were correlated with decrease of tarsal tunnel depth at malleolarcalcaneal axis. Weight, body mass index, true leg length, and apparent leg length did not correlate with the tarsal tunnel depth at the malleolarcalcaneal axis.Conclusions The tarsal tunnel was compressed at the center of the tunnel height mainly by weight bearing. Therefore, tibial nerve compression originates from the center of the tarsal tunnel, not from the whole tarsal tunnel. Furthermore, the increase in ground reaction force and the maximal plantar pressure would be considered risk factors for tibial nerve compression.