Morphological Changes One Year After Achilles Tendon Rupture Repair: A Comparison of Loading Strategies

<b>Purpose:</b> This study investigated effects of delayed initial loading in comparison to a standard regime following an Achilles tendon rupture (ATR) on tendon cross-sectional area (CSA) and fat infiltration by using 3D magnetic resonance imaging (MRI) and ultrasound (US) measurements. <b>Methods:</b> Secondary analysis of a randomized controlled trial. Forty-eight patients with an ATR were randomized to a Standard regime with weight-bearing after 6 weeks or a Delayed regime with weight-bearing after 12 weeks postsurgery. Achilles tendon CSA, fat fraction, and vascularization were measured on both the injured and the uninjured side using MRI and US at 12 and 52 weeks. <b>Results:</b> The injured tendon was significantly larger (> 300%) than the uninjured tendon for both the distal and proximal parts (<i>p</i> < 0.0001). The CSA of the distal part was smaller in the Delayed group at 3 months (<i>p</i>=0.038), but not at 12 months. Fat fraction in the tendon increased in both groups. The Delayed group had significantly less vascularization compared with the Standard group at 3 months, and the vascularization decreased in both groups from 3 to 12 months. <b>Conclusion:</b> In comparison to the Standard treatment, the Delayed group had reduced CSA and vascularization for the distal part of the tendon after 3 months. After a year, these differences had become insignificant. From 3 to 12 months, the distal parts of the injured tendon showed an accumulation of fat in both groups. Not only the rupture site but also the entire tendon was affected by the inflammatory repair response. <b>Trial Registration:</b> ClinicalTrials.gov identifier: NCT04263493.