Background: Ankle-foot conditions are ubiquitous in the US Military. The objective of this study was to evaluate the burden and associated factors of Achilles tendinopathy (AT). Methods: The Defense Medical Epidemiology Database was used to identify all diagnosed AT in military personnel from 2006 to 2015. Prevalence of AT was calculated and compared by year, service branch, and military rank. Unadjusted and adjusted assessment of injury risk were calculated. Results: Officers incurred 37,939 episodes at a prevalence of 17.65 per 1000 (male officers: 18.20 per 1000; female officers: 14.80 per 1000). Among enlisted personnel, there were 116,122 episodes of AT that occurred in 12.22 per 1000 (male enlisted: 12.07 per 1000; female enlisted: 13.22 per 1000). All officer specialties had significantly higher risk of AT episodes compared to the ground and naval gunfire officers (PR: 1.04-1.43), with aviation demonstrating a significant protective effect (PR: 0.65). Among enlisted specialties, maritime/naval specialties had reduced risk (PR: 0.82), with all specialties (except aviation) having increased risk of AT compared to infantry (PR: 1.07-1.71). There were multiple associated factors identified, to include sex, age, rank, military occupation, and service branch. Conclusions: AT was ubiquitous in the US military, with a progressive increase in prevalence during the study epoch. There were multiple associated factors identified, to include sex, age, rank, military occupation, and service branch. These findings highlight both the need for prophylactic interventions and identification of the populations with the greatest need.

Dr Fraser reports grants from Congressionally Directed Medical Research Programs and the Office of Naval Research, outside of the submitted work. In addition, Dr Fraser has a patent pending for an Adaptive and Variable Stiffness Ankle Brace, U.S. Provisional Patent Application No. 63254,474.

The authors are military service members or employees of the U.S. Government. This work was prepared as part of our official duties. Title 17, U.S.C. SS105 provides that copyright protection under this title is not available for any work of the U.S. Government. Title 17, U.S.C. SS101 defines a U.S. Government work as work prepared by a military service member or employee of the U.S. Government as part of that person's official duties. The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, nor the U.S. Government.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The study protocol was approved by the Naval Health Research Center Institutional Review Board in compliance with all applicable Federal regulations governing the protection of human subjects. Research data were derived from an approved Naval Health Research Center Institutional Review Board protocol, number NHRC.2020.0207-NHSR.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

All data produced in the present work are contained in the manuscript.