title: "Back on Track": A Mobile App Observational Study Using Apple's ResearchKit Framework.
abstract: BACKGROUND
  In March 2015, Apple Inc announced ResearchKit, a novel open-source framework intended to help medical researchers to easily create apps for medical studies. With the announcement of this framework, Apple presented 5 apps built in a beta phase based on this framework.
  
  
  OBJECTIVE
  The objective of this study was to better understand decision making in patients with acute anterior cruciate ligament (ACL) ruptures. Here, we describe the development of a ResearchKit app for this study.
  
  
  METHODS
  A multilanguage observatory study was conducted. At first a suitable research topic, target groups, participating territories, and programming method were carefully identified. The ResearchKit framework was used to program the app. A secure server connection was realized via Secure Sockets Layer. A data storage and security concept separating personal information and study data was proposed. Furthermore, an efficient method to allow multilanguage support and distribute the app in many territories was presented. Ethical implications were considered and taken into account regarding privacy policies.
  
  
  RESULTS
  An app study based on ResearchKit was developed without comprehensive iPhone Operating System (iOS) development experience. The Apple App Store is a major distribution channel causing significant download rates (>1.200/y) without active recruitment. Preliminary data analysis showed moderate dropout rates and a good quality of data. A total of 180 participants were currently enrolled with 107 actively participating and producing 424 completed surveys in 9 out of 24 months.
  
  
  CONCLUSIONS
  ResearchKit is an easy-to-use framework and powerful tool to create medical studies. Advantages are the modular built, the extensive reach of iOS devices, and the convenient programming environment.
authors.affiliation: Department of Orthopedic Surgery and Traumatology, University Medical Center Freiburg, University of Freiburg, Freiburg, Germany.
authors.forename: Martin
authors.identifier: http://orcid.org/0000-0002-5102-979X
authors.initials: M
authors.lastname: Zens
authors.affiliation: Design of Microsystems, Department of Microsystems Engineering (IMTEK), University of Freiburg, Freiburg, Germany.
authors.forename: Peter
authors.identifier: http://orcid.org/0000-0002-4715-6032
authors.initials: P
authors.lastname: Woias
authors.affiliation: Department of Orthopedic Surgery and Traumatology, University Medical Center Freiburg, University of Freiburg, Freiburg, Germany.
authors.forename: Norbert P
authors.identifier: http://orcid.org/0000-0002-5913-624X
authors.initials: NP
authors.lastname: Suedkamp
authors.affiliation: Department of Orthopedic Surgery and Traumatology, University Medical Center Freiburg, University of Freiburg, Freiburg, Germany.
authors.forename: Philipp
authors.identifier: http://orcid.org/0000-0001-8433-0872
authors.initials: P
authors.lastname: Niemeyer
keywords: anterior cruciate ligament injury; mHealth; mobile health