Using a mobile application to assess knee valgus in healthy and post-anterior cruciate ligament reconstruction participants.

CONTEXT:: Popularity of using handheld devices in clinical settings has increased, especially the use of motion analysis applications (MAA). Video-based measurement tools have been found reliable in measuring knee valgus in subjects without anterior cruciate ligament (ACL) injury. However, there is a need for validation of using a MAA to measure knee valgus in an injured population given that they may exhibit higher degrees of knee valgus.

OBJECTIVE:: To examine the reliability and validity of using a MAA to measure knee valgus during functional activities used to assess return-to-sport after ACL reconstruction (ACLR).

DESIGN:: Reliability and validity study.

SETTING:: University laboratory.

PARTICIPANTS:: Twelve ACLR participants and 20 healthy individuals.

INTERVENTIONS:: Each subject performed single-leg drop landing, single-leg hop, and 90º cut with simultaneous 3-dimensional (3D) motion capture and video recording on an iPad.

MAIN OUTCOME MEASURES:: Peak knee valgus during the landing phase was measured using MAA and 3D analysis. To obtain reliability, peak knee valgus was measured on 2 separate days. Reliability was determined using intra-class correlation coefficients (ICCs) and standard errors of measurement (SEMs). Validity was assessed using Pearson correlation coefficients by comparing peak knee valgus between the MAA and 3D analysis. T tests were used to compare knee valgus obtained between raters, within raters, and between the MAA and 3D analysis.

RESULTS:: Our data revealed excellent intra- and inter-rater reliability with low SEMs of using a MAA for both groups. Significant, moderate to large associations were found in comparing peak knee valgus between the MAA and 3D analysis. However, knee valgus was significantly different between the MAA and 3D analysis across all tasks in both groups.

CONCLUSIONS:: While a MAA is reliable for measuring peak knee valgus in individuals with ACLR and healthy controls, the actual values obtained by a MAA should be viewed with caution.