An ankle sprain is one of the most frequent injuries, with an incidence of 1:10,000 individuals per day in amateur and high-performance sports in the United States [1]. With respect to the high prevalence of ankle ligament injuries and patients’ young age, optimizing aftercare and rehabilitation is mandatory [2]. Moreover, the economic burden of ankle sprains is enormous [3]. High medical, physiotherapeutic, and lost productivity costs burden health care systems and create the need for new, efficient diagnostic and therapeutic solutions [4].

To prevent long-term complications, complex ligament injuries and recurrent ankle sprains with progression to chronic ankle instability (CAI) have to be recognized. The development of ankle osteoarthritis (OA) as a long-term consequence of CAI was first shown by Harrington et al [5] in 1979. Following an ankle ligament injury, posttraumatic muscular insufficiency [6,7] and ankle OA were observed in 13% of the cases [8]. Therefore, the adequate and consequent treatment of an ankle sprain might prevent CAI and OA.

Nowadays, early functional treatment is considered the gold standard for the lateral ligament lesion of the ankle [2,9]. The latest national guideline published by the German Orthopedic Foot and Ankle Society (Deutsche Assoziation für Fuß und Sprunggelenk eV, DAF) also recommends a conservative approach to acute ligament tears of the lateral ankle joint [10].

In times of digitalization and emerging technologies, smartphones are regularly used to accomplish everyday tasks, such as Web-based banking and communication via messenger or email, and penetrate rapidly into more and more areas of life [11]. The portability and omnipresent accessibility of smartphones enable usage anywhere and anytime [12]. In general, the growing implementation of smartphones as a transfer media in medical context is evident [13].

It has already been shown that the patients’ acceptance is given for collecting personalized health-relevant data via software apps, to share these with their peers or the medical staff [14]. Moreover, mobile short message service text messages and apps can have a positive impact on the posttraumatic outcome by showing increased adherence to medications and protocols, improved clinic attendance, and decreased readmission rates and emergency room visits [15].

However, the implementation and use of mobile health (mHealth) in medical care, especially in the fields of orthopedics and trauma surgery, can still be regarded to be in an early stage. So far, only 13 serious medical apps in orthopedics and trauma surgery have been identified for regular use in outpatient and inpatient medical care in German-speaking countries [16]. In a survey among German orthopedic and trauma surgeons, the Ankle Joint App (Sprunggelenks-App, Mediploy GmbH, Langenfeld, Germany) was shown to be frequently chosen, although the medical usage rate was still very low at 2.3% [17].

Studies investigating mHealth-based diagnostics [18] or rehabilitation programs after lateral ankle sprains already exist, for example, in the Netherlands (app: Strengthen your Ankle) [19], where a positive influence on medical and economic aspects could be demonstrated [20-22]. To date, the application of posttraumatic mHealth solutions after ankle sprains has not been investigated in Germany.

To address this gap, this work outlines the methodology to develop and design an app for patient education as well as prevention and identification of CAI after ankle sprains (Ankle Joint App). The publication of an app development process might be the basis for future mHealth solutions to improve patient care.

The app’s content, usability, and styling were evaluated by German orthopedic or trauma surgeons and athletes who suffered from ankle sprain.

The analog (user) MARS-G was converted into a digital questionnaire on a Google Docs platform (Google LLC). Data were saved and then transferred into an Excel table (Microsoft Corp). Descriptive statistics were calculated for all items. The intraclass correlation coefficient (ICC) was calculated among the reviewers. We selected an individual absolute agreement ICC (AA-ICC) for a two-way mixed model on the basis of ICC guidelines by Shrout and Fleiss [36]. All statistical analyses were conducted using SPSS (version 25, IBM Corp).

A total of 20 foot and ankle surgeons as well as 20 athletes who suffered an ankle sprain took part in the app rating, which is equivalent to a response rate of 65% (20/31) for the surgeons and 44% (20/46) for the athletes. Excellent interrater reliabilities (two-way mixed model AA-ICC=0.92; 95% CI 0.86-0.96 for surgeons and athletes) were shown following the guidelines for ICC interpretation established by Koo et al [37]. The surgeons’ group comprised 20% (4/20) Android and 80% (16/20) iOS users, and the athletes’ group comprised 59% (10/17) Android and 41% (7/17) iOS users.

The mean overall score for the Ankle Joint App was 4.4 (SD 0.5), rated by both surgeons and athletes. It was derived from the mean scores on app functionality, engagement, esthetics, and information quality (Figure 3). The mean subjective quality scores were 3.6 (surgeons: SD 0.7) and 3.8 (athletes: SD 0.5). The section behavioral change, which included an assessment of the perceived impacts on disease-related knowledge, attitude, awareness, and behavior, had mean scores of 4.1 (surgeons: SD 0.7) and 4.3 (athletes: SD 0.7). The medical gain, rated by the surgeons only, was 3.9 (SD 0.6; Table 1, Figure 3).

Our research using the Ankle Joint App demonstrates that mHealth-based rehabilitation programs might be an adequate and innovative tool for patient education, prevention, and collection of personal data.

The achieved (user) MARS-G scores prove the app’s quality from a professional and user point of view, demonstrating a comparatively high overall mean (user) MARS-G value [33]. The highest scores were reached in the functionality section for both surgeons and athletes. In accordance with a recent survey among orthopedic and trauma surgeons, intuitive usability was considered the most important factor for the regular use and quality of an app. The integration of complex functions in an intuitive lean and secure user interface poses a great challenge to the development team. Moreover, the development of an intuitive frontend is complex and involves high development costs and test phases [38]. Multifunctional apps, for example, in the field of diabetes mellitus type II therapy for patients over 50 years showed limited usability with negative effects on compliance and therapy outcomes. Apps with basic functions provide enhanced usability [39], but the limitation of software features affects the app’s functionality. To address this divergence, trial runs with specific target groups and permanent reevaluation of the initial concept are mandatory during the app’s development process.

As a first step, when developing an app, the target group and the intended purpose have to be defined precisely. The Ankle Joint App was especially designed for young and active patients to optimize conservative rehabilitation following an acute ankle sprain without osseous lesions. With respect to this, the differences in evaluating the medical gain for physicians and patients, with individual requirements in their rehabilitation episode [40], can be explained.

Customization seems to be important to the target group and might be improved in our app. We believe that medical apps have to be adaptable not only to the specific users’ requirements but also to the varying hospital standards. The aspects to be considered in the development of medical apps are the limited areas of application in combination with varying standards of treatment, both national and international, and the legal and medical aspects of an app with regard to liability and data protection [21]. These aspects represent a challenge for financing the complex development and maintenance of an app, as the 10 most popular apps ranked by the number of users in Germany in 2018 were all available for free download [41].

Considering recent data scandals, which led to a fundamental distrust of apps that might be implemented in the context of Big Data, the secure and transparent collection of medical personal data can be challenging [42,43]. For this reason, we decided to store personal data exclusively on the mobile device to avoid cloud upload. In general, dichotomous scenarios about data exchange between patients and medical staff are possible. The recovery progress could be displayed analogously on the patient’s smartphone in the event of a doctor’s appointment (eg, CAIT). Alternatively, an upload of data into a secure cloud system can be taken into consideration [44]. In the event of deviations from the expected progression of the disease, patients could be informed about and provided with medical expertise more rapidly. Moreover, the collection of validated scores and surveys might be relevant for academic research.

In contrast to these positive effects, app users and providers (physicians and medical staff) should keep in mind that the collection and processing of personal data also represent cornerstones of app financing. This could lead to potential conflicts of interest as the collected data represent an immense value, for example, for the provision of personalized advertising [45]. Before downloading an app, the financing, development process, and data flow have to be completely and plausibly depicted by the publisher. Therefore, transparent and appropriate app store descriptions, data protection regulations, and terms and conditions of use are of utmost importance [46].

This study has some limitations. The evaluation of the app’s quality was carried out within a theoretical framework; thus, it only reflects its use to a limited extent in daily clinical practice. It has to be mentioned that the app was only evaluated by a relatively small number of users (patients) for a short period of 3 months. Thus, data on compliance, demographics, and usage behavior are hardly representative. Moreover, the economic aspects of the development process and app costs per user were not taken into account. In addition, the response rate was moderate, which might lead to a bias toward users with high digital affinity. Comparative randomized control trial studies are required to gain funded evidence on the app’s positive effects on patient education and treatment progress in comparison with established nondigital therapy paths to prevent CAI and reach a final scientific conclusion; this has to be addressed by future studies.

Nowadays, in many countries, an increasing number of patients visiting emergency units with minor complaints can be registered. Often, the treatment of these patients is time and staff consuming, compromising the medical attention of more severely injured individuals. This overcrowding may lead to negative consequences to the patients’ safety and their outcome [47-49]. Given the increasing workload, physicians are dissatisfied with highly time-consuming procedures, for example, electronic patient recording in the emergency department [50,51]. Apps might be used by the emergency staff to easily create and recommend digitally customized aftercare plans.

Moreover, the established discharge letter contains medical terminology, which offers very little benefit to a self-determined, competent patient. This practice does not meet the requirements of adequate patient involvement in the treatment process [52]. Improving patient education and optimizing the communication structures via apps on mobile devices have the potential to solve these issues. Individually designed and supervised aftercare treatments showed better outcomes [53]. The Ankle Joint App has a modular design and might be transferred to a wide range of aftercare treatments.

In contrast to the great potential of standardized medical app usage, there are also risks. However, medical resources and health care have to be distributed equally for everyone on the basis of moral and ethical obligations. This is why medical app usage also entails a particular risk of disadvantaging groups with low health competence and a high risk of disease [39]. In particular, the elderly patient might be disadvantaged by the use of medical apps, because in 2014, only about 17% of the individuals over 65 years regularly used a smartphone [54]. As degenerative diseases represent an important pillar of orthopedic and trauma surgery expertise, special attention has to be paid on the app development for these newcomers and their requirements in the future. Particularly in the area of app usability, the requirements of elder generations have to be addressed, for example, implementing an intuitive interface, a reading function, or a screen magnifier [55]. Self-endangerment because of incorrect app usage might occur, but the risk can be reduced by an onboarding function with an introduction of the app to new users and individual feedback mechanisms [56].

Working in a multidisciplinary team, using a backend structure to modify the app’s content and using React Native, proved to be efficient in the development process of medical apps. The success was proven by reaching high overall mean MARS-G scores for the Ankle Joint App in surgeons and athletes. Data obtained suggest that an mHealth-based rehabilitation program might be a useful tool for patient education and collection of personal data. The achieved (user) MARS-G scores prove the tested app’s high quality. Medical app development with an a priori defined target group and a precisely intended purpose, in a multidisciplinary team, is highly promising.