Validity and reliability of smartphone inclinometer applications for measurement of elbow range of motion in paediatric patients

Purpose: Precise measurement of elbow range of motion (ROM) post-injury or surgery forms an important part of determining prognosis and the need for further intervention. Clinicians are increasingly incorporating smartphone use in our medical practice; we sought to determine if a smartphone goniometer application is a valid and reliable tool for assessment of elbow ROM in the paediatric patient, compared to visual and goniometer assessment. Methods: In total, 20 paediatric patients (40 elbows) between six and 15 years of age with an elbow or forearm injury were included in this prospective series. Elbow flexion, extension, pronation and supination were measured independently by two orthopaedic clinicians. Measurements were taken from injured as well as unaffected side using a standardized technique, first with visual estimation and then using a universal goniometer (UG) and smartphone goniometer application Angle Meter via Google Play store (Smart Tool Factory, Istanbul, Turkey). Results: There was excellent interobserver reliability for all three modalities, with average intraclass correlation coefficient (ICC) values greater than 0.90. Visual estimation had the lowest average ICC of 0.92, compared to 0.97 for UG and smartphone. Overall, there was excellent intraobserver reliability between the smartphone application and the gold standard UG for all elbow movements with ICCs ranging between 0.98 to 0.99 and mean absolute difference ranging from 1.1 +/- 1.0 degrees to 2.6 +/- 1.9 degrees. The smartphone application showed superior agreement over visual estimation when compared to the gold standard UG with lower mean differences and 95% limits of agreement (LOA) falling within 10 degrees. Conclusions: Our study demonstrates that a smartphone application is a valid and reliable assessment tool for measurement of elbow ROM in paediatric patients, and better than visualization alone. Level of evidence: III