Functional assessment of the spring ligament using ultrasonography in the Japanese population

Spring ligament (SL) insufficiency is observed commonly in association with adult-acquired flatfoot deformity. Evaluation of the SL using ultrasonography (US) has not been fully investigated, and the functional characteristics of the spring ligament have not been clarified. The purpose of this study was to perform a functional evaluation of the SL using US.

Fifty-one healthy young volunteers (31 males, 20 females; 102 feet) participated in this study. The thickness of the SL in both non-weight bearing (NSL) and 90% weight bearing (WSL) conditions was measured using US. The correlation between assessment of foot alignment (Navicular Drop test (NDT), Arch height Index (AHI), and Arch height flexibility (AHF)) and the thickness of the SL was investigated.

The thickness of the SL in NSL and WSL conditions was 2.28 ± 0.38 mm and 2.13 ± 0.34 mm, respectively. The thickness was 2.42 ± 0.38 mm (NSL)/2.26 ± 0.31 mm (WSL) in males, and 2.07 ± 0.28 mm (NSL)/1.93 ± 0.29 mm (WSL) in females. The standard values of the thickness of the SL were 2.0-2.8 mm in males and 1.8-2.4 mm in females. The thickness of the SL was significantly different between males and females (p < 0.01), but was within the margin of error between NSL and WSL. The relationship between NSL and foot alignment only showed a weak correlation with AHI (r = 0.23, p < 0.05).

Our results indicate that the SL is a hardy structure that shows little change in thickness on weight bearing in vivo.