MRI Evaluation of Achilles Tendon Rotation and Sural Nerve Anatomy

Abstract

Background: Limited-open and percutaneous Achilles tendon (AT) repair techniques have limited visibility, which may result in sural nerve violation and poor tendon targeting. The goal of this study was to assess the in vivo rotation of the AT and its distance to the sural nerve in ruptured and nonruptured ATs to develop guidelines to aid in limited-open and percutaneous repair techniques. Methods: A retrospective review was conducted to identify magnetic resonance imaging (MRI) studies of patients with ruptured and healthy (nonruptured) ATs. AT rotation and distance to the sural nerve in the anterior-posterior (A-P) and medial-lateral (M-L) planes were measured at the level of and proximal to the ankle. Results: The AT was externally rotated in both ruptured and nonruptured cohorts. Ruptured ATs showed greater external rotation than nonruptured ATs at the ankle (15.8 ± 16.2 degrees vs 5.9 ± 9.0 degrees, P = .008) but not at 10 cm proximal to the tendon’s insertion (10.9 ± 10.9 degrees vs 6.1 ± 8.4 degrees, P = .139). Proximal AT rotation was negatively correlated with rupture height ( r = −0.477, P = .029). At 4 cm proximal to the AT insertion, the sural nerve was closer anteriorly to and farther laterally from the AT in ruptures than in nonruptures ( P < .001). At 10 cm proximal to the AT insertion, the sural nerve was farther posteriorly and laterally from the AT in ruptures than in nonruptures ( P = .027 and P < .001, respectively). Conclusion: We found that the AT was more externally rotated in ruptured than in nonruptured tendons at the ankle and that its distance to the sural nerve differed between the 2 cohorts in the A-P and M-L planes, likely due to increased AT rotation and swelling with ruptures. To minimize sural nerve injury and improve tendon targeting, we suggest an external rotation of 11 degrees at the proximal end of the rupture and 16 degrees at the distal end when using percutaneous and limited-open AT repair devices to try to minimize sural nerve violation and increase tendon capture, which can decrease rates of complication and rerupture. Level of Evidence: Level III, retrospective comparative study.