3D characterization of the triple‐bundle Achilles tendon from in vivo high‐field MRI

Abstract

The Achilles tendon consists of three subtendons that transmit force from the triceps surae muscles to the calcaneus. Individual differences have been identified in Achilles subtendon morphology and twist in cadavers, which may have implications for triceps surae mechanics and function. High‐field magnetic resonance imaging (MRI) can be used to identify boundaries within multi‐bundle tissues, which could then enable studies of subtendon structure−function relationships in humans. The objective of this study was to use high‐field MRI (7T) to image and reconstruct Achilles subtendons arising from the triceps surae muscles. We imaged the dominant lower leg of a cohort of healthy human subjects (n = 10) using a tuned musculoskeletal sequence (double echo steady state sequence, 0.4 mm isotropic voxels). We then characterized the cross‐sectional area and orientation of each subtendon between the MTJ and calcaneal insertion. Image collection and segmentation was repeated to assess repeatability. Subtendon morphometry varied across subjects, with average subtendon areas of 23.5 ± 8.9 mm2 for the medial gastrocnemius, 25.4 ± 8.9 mm2 for the lateral gastrocnemius, and 13.7 ± 5.9 mm2 for the soleus subtendons. Repeatable subject‐specific variations in size and position of each subtendon were identified over two visits, expanding on prior knowledge that high variability exists in Achilles subtendon morphology across subjects.

Estimation of the Achilles tendon twist in vivo by individual triceps surae muscle stimulation

“…Table 1 summarizes the proportions of Achilles tendon twist types in different studies highlighting a consensus in the literature that low twist has the highest prevalence among humans. Despite the growing interest, there is currently only one study that estimated this twist in vivo using high field 7-Tesla MRI (Cone et al 2023) resulting in a very limited understanding of it's in vivo structure. A possibility to give insights into the AT structure in vivo is to combine methods that distinguish the displacement of the different Achilles tendon subparts during individual force production from the triceps surae muscles.…”