This study aims at investigating the validity and reliability of a smartphone application "MyAnkle: in assessing the balance component of postural control in patients with chronic ankle instability (CAI).

Lateral ankle sprain (LAS) is a common injury in athletic and regular activities; with an incidence of 7 per 1000 exposure. After LAS, residual symptoms may persist leading to chronic ankle instability (CAI). This instability is believed to arise from dysfunctional postural control, defective proprioception, weak muscles, or reduced ankle range of motion (ROM).Thus, assessment of postural control is essential for proper clinical decision-making and treatment selection.

With advances in technology, smartphone has been introduced as an assessment tool for the musculoskeletal system. For example, it was used in assessment of ROM and mobility in stroke patients and frail elderly conditions. Further, it was used to assess balance and falling risk in those population. In addition, it was used to assess balance in healthy and participants with chronic ankle sprain. These studies proved that smartphone is a valid and reliable tool that is light in weight and inexpensive. Yet, these studies have some methodological concerns. For example, the application was not validated against gold standard or was validated only in healthy volunteers rather than in patients with musculoskeletal dysfunction. Further, a few of these studies did not establish the application discriminative validity between patients and healthy controls. Thus, this study will try to answer the following question: "Is smartphone application a valid and reliable tool to assess balance in patients with CAI compared to gold standards?

Inclusion Criteria:

1. Adult males and females aging from 18 to 35 years old.
2. Referred with a confirmed diagnosis of CAI, with a Cumberland Ankle Instability tool score lower than 27 points.
3. Had a recurrent sprain within the previous year.

Exclusion Criteria:

1. History of major surgery of lower limb or spine.
2. History of ankle fracture or any other lower limb fracture in the past 2 years.
3. History of lower limb injury 3 months prior to study.
4. Presence of problems that affect balance performance as visual or vestibular deficits, neurologic disease, or cerebral concussions during the past 3 months.
5. Being currently enrolled in a balance training rehabilitation program.
6. Weakness of lower limb musculatures or trunk upon screening muscle testing by the investigator.

Fifty patients with CAI and 50 gender-, BMI and age-matched healthy volunteers will be enrolled in this study.

Healthy participants will be recruited from undergraduate and graduate students of the faculty of Physical Therapy, Cairo University, Egypt. All healthy subjects will be asymptomatic with no neuromusculoskeletal signs or symptoms.

Male and female adult patients with CAI will be recruited from the outpatient clinic of the faculties of Physical Therapy and Medicine, Cairo University, Egypt.

Individual participant data for all primary and secondary outcome measures will be made available.

Data will be available within 6 months of study completion.

Data access requests will be reviewed by an external independent review panel. Requestors will be required to sign a data access agreement.