Cone SG, Kim H, Thelen DG, Franz JR. 3D characterization of the triple-bundle Achilles tendon from in vivo high-field MRI. Journal of Orthopaedic Research.
The Achilles tendon consists of three subtendons that transmit force from the triceps surae muscles to the calcaneus. Potentially meaningful individual differences have been identified in subtendon morphology, with potential implications in triceps surae mechanics and function. Recently, advances in high-field magnetic resonance imaging (MRI) have previously been used to delineate boundaries within multi-bundle tendons and ligaments, including those between bundles of the anterior cruciate ligament. 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, 0.4mm 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 tendon morphology across subjects.