MRI Analysis of Axial Plane Rotation and Width of the Achilles Tendon: Implications for Minimally Invasive Achilles Tendon Repair
Authors: Kim Jaeyoung , Sacks Jaden , Masry Seif El , Palma Joaquin , Ellis Scott J. , Deland Jonathan T. 
Published: December 2024

Category: Sports; Other Introduction/Purpose: Minimally invasive approaches to Achilles tendon (AT) repair have garnered significant attention due to their reported effectiveness. Due to the limited visibility of the tendon, a crucial factor for the success of these approaches lies in the precise targeting and adequate capture of the tendon substance. Insufficient tendon capture can lead to re-rupture or tendon elongation, potentially leading to poor patient-outcomes. Since many of the current techniques or devices for minimally invasive AT repair rely on needle passage through a single axial plane, it is imperative to understand the axial plane orientation of the AT along its course. This study aims to elucidate the axial plane position and width of the AT from its distal insertion to a level well above its common tear site. Methods: In this retrospective study, magnetic resonance imaging (MRIs) from 82 individuals (mean age: 38.7 years) with no history of AT pathology were reviewed from the foot and ankle registry of a single institution. Any patients with evidence of foot and ankle malalignment or those with poor quality MRIs were excluded from the study. Multiplanar reconstruction of the MRI images was performed to enable synchronized viewing of both the sagittal and axial planes of each MRI scan. Measurements were made to determine the axial axis of the AT at distances of 3, 5, 7, 9, and 11 cm from its insertion. These measurements were taken in relation to both the transmalleolar (TM) axis and the axis at the AT insertion (Figure 1). The width of the AT was also measured at these corresponding levels. Results: The average rotation of the AT across all measurement levels showed an external rotation relative to the TM axis (Figure 2). The least rotation was observed at the 3cm level (2.1 degrees), while the maximum rotation was seen at both the 7cm and 9cm levels (11.2 degrees). There was a pattern where the AT showed an increasing external rotation as it extended proximally from 3cm to 9cm from its insertion. Between 5 cm and 7 cm from the insertion, there was a shift in the tendon's orientation (p<.0001), transitioning from internal to external rotation (Figure 2). Moreover, a noticeable reduction in the width of the AT was observed between the 5 cm and 7 cm measurement levels, distinct from the other levels. Conclusion: The rotational profile of the AT observed in this study indicates the need for caution regarding possible external rotation of the AT, especially when targeting its proximal portion using a minimally invasive approach, compared to its distal part. The considerable variations in AT orientations across different individuals underscore the potential benefits of using intraoperative assistive techniques such as ultrasonography to determine individual rotational profiles. Furthermore, the noted narrower width and rotational differences between the 5 cm and 7 cm levels could explain the frequent instances of AT ruptures within this specific range.