MRI Analysis of the Axial Plane Orientation of the Achilles Tendon: Implications for Level-Specific Percutaneous Repair Trajectories

Abstract

Background:

Percutaneous Achilles tendon repair has become increasingly favored because of its lower rate of wound complications compared with open techniques. However, its success rates are limited and rely on precise tendon capture, which can be challenging because of limited intraoperative visualization. Previous clinical and cadaveric studies have reported frequent cases of incomplete or eccentric suture placement with this approach. Although not the only factor in improving the results of percutaneous Achilles repair, understanding the positional anatomy of the Achilles could be helpful in improving capture of the tendon. This study aimed to characterize the level-dependent axial orientation of the distal Achilles tendon using magnetic resonance imaging (MRI), focusing on levels relevant to percutaneous needle passage to improve the accuracy of repair.

Methods:

A retrospective review of MRI scans from 82 individuals without Achilles pathology was performed. The axial orientation of the tendon was measured at 3, 5, 7, 9, and 11 cm proximal to its calcaneal insertion, relative to both the transmalleolar (TM) axis and the insertional tendon axis. Tendon width was also measured at each level. All measurements were performed using multiplanar reconstructed images, and differences across levels were analyzed using a linear mixed effects model with Bonferroni correction for multiple comparisons. A separate age-matched cohort of patients with acute Achilles rupture (n = 82) was also analyzed to compare orientation patterns between normal and ruptured tendons.

Results:

The Achilles tendon orientation exhibited level-dependent variation in external rotation proximally when measured relative to the TM axis, increasing from 2.1 degrees (95% CI, 0.8-3.4) at 3 cm to a peak of 11.2 degrees at 7 cm (95% CI, 9.3-13.1) and 9 cm (95% CI, 9.6-12.8), with a slight decrease at 11 cm. When referenced to the insertional axis, a transition from internal to external rotation was observed between 5 and 7 cm (Δ = +6.6 degrees, P < .001). The narrowest tendon width was also noted at 5 cm (13.3 mm), with greater width observed both proximally and distally. In the ruptured cohort, the tendon demonstrated a more externally rotated configuration at the rupture zone compared with normal tendons.

Conclusion:

The Achilles tendon demonstrates level-dependent variation in axial orientation along its length, with a general tendency toward external rotation at more proximal levels. Although there are currently no established guidelines regarding needle trajectory during percutaneous repair, these findings suggest that a uniform axial needle path may not align with native tendon anatomy at all levels. Adjusting the direction of suture passage based on the specific level of repair may enhance procedural accuracy during percutaneous Achilles repair. Notably, these MRI-based recommendations have not been validated with cadaveric or other biomechanical testing.

Level of Evidence:

Level III, diagnostic retrospective study.