Does free tendon length influence the injury risk of the Achilles tendon? A finite element study

The Achilles tendon is a common injury site, but anatomical risk factors for injury are relatively unexplored in the literature. This study aimed to evaluate whether changes in free tendon length would influence the results of a simulated rupture of the Achilles tendon.

Using a previously validated 3D finite element model of the free and aponeurotic Achilles tendon as a basis, two additional finite element models with 25% decreased and increased free tendon lengths were created. The finite element models were sequentially loaded from 2500 to 3500N in 100N increments, and the total volume of elements exhibiting a maximal principal strain above 10% was recorded. An Achilles tendon rupture was considered to have occurred when a continuous group of elements with a volume of at least 3 mm³ exhibited a maximum principal strain above 10%. Models were compared regarding the smallest load that met the rupture criterion and plots of the percentage of elements exhibiting maximum principal strains above 10% across the loading range. Sensitivity analyses assessed the influence of subtendon division variations and subtendon sliding restriction on the results.

Rupture loads and plots of the percentage of elements with maximum principal strains above 10% were similar between models, regardless of the free tendon length. No models met the rupture criterion when simulations were run without subtendon sliding. Rupture loads in the subtendon division variation models were correlated with the subtendon cross-sectional areas.

The simulated rupture results of the Achilles tendon were sensitive to variations in subtendon cross-sectional areas but not in free tendon length.

Level V.