Background While numerous clinical studies have compared the surgical and non-surgical treatment of acute Achilles tendon rupture (ATR), there are no studies that have performed a non-inferiority analysis between treatments. Methods Data from patients who were included in five randomised controlled trials from two different centres in Sweden were used. Outcomes at 1 year after ATR consisted of the patient-reported Achilles tendon Total Rupture Score (ATRS) and the functional heel-rise tests reported as the limb symmetry index (LSI). The non-inferiority statistical 10% margin was calculated as a reflection of a clinically acceptable disadvantage in ATRS and heel-rise outcome when comparing treatments. Results A total of 422 patients (350 males and 72 females) aged between 18 and 71 years, with a mean age of 40.6 (standard deviation 8.6), were included. A total of 363 (86%) patients were treated surgically. The ATRS (difference (Δ) = − 0.253 [95% confidence interval (CI); − 5.673;5.785] p = 0.36) and LSI of heel-rise height (difference = 1.43 [95% CI; − 2.43;5.59] p = 0.81), total work (difference = 0.686 [95% CI; − 4.520;6.253] p = 0.67), concentric power (difference = 2.93 [95% CI; − 6.38;11.90] p = 0.063) and repetitions (difference = − 1.30 [95% CI; − 6.32;4.13] p = 0.24) resulted in non-inferiority within a Δ − 10% margin for patients treated non-surgically. Conclusion The non-surgical treatment of Achilles tendon ruptures is not inferior compared with that of surgery in terms of 1-year patient-reported and functional outcomes.

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