Reliability, Concurrent Validity, and Minimal Detectable Change for iPhone Goniometer App in Assessing Knee Range of...

Area of Science:

• Orthopedics
• Biomedical Engineering
• Rehabilitation Science

Background:

• Previous studies on smartphone goniometer apps (SG) often lack generalizability due to testing in healthy populations.
• Standard error of measurement (SEM) and minimal detectable change (MDC) values, crucial for clinical utility in range of motion (ROM) assessment, have not been established for SGs.
• This study addresses the need for reliability and validity data of SGs in patient populations, specifically for knee ROM.

Purpose of the Study:

• To evaluate the test-retest reproducibility and concurrent validity of the iPhone goniometer app (i-Goni) for assessing knee ROM.
• To determine the standard error of measurement (SEM) and minimal detectable change (MDC) values for the i-Goni in patients with knee osteoarthritis or following total knee replacement.
• To compare the performance of the i-Goni against a universal goniometer (UG) in this patient cohort.

Main Methods:

• Sixty participants with knee osteoarthritis or post-total knee replacement underwent assessment of active knee ROM using the i-Goni and a universal goniometer (UG).
• Knee muscle strength, pain (quadruple numeric pain rating scale - Q-NPRS), and lower extremity disability (lower extremity functional scale - LEFS) were also measured.
• Intraclass correlation coefficients (ICCs) and Bland-Altman analysis were used for reproducibility and agreement; Pearson correlation assessed concurrent validity.

Main Results:

• The i-Goni demonstrated superior test-retest reproducibility for knee flexion/extension ROM (ICC: 0.97/0.94) compared to the UG (ICC: 0.95/0.87).
• The i-Goni yielded smaller SEM (2.72°/1.18°) and MDC (6.3°/2.72°) values for knee flexion/extension, indicating lower measurement error and a smaller true change threshold.
• Concurrent validity was supported by expected relationships between i-Goni ROM and UG, knee strength, Q-NPRS, and LEFS scores.

Conclusions:

• The iPhone goniometer app (i-Goni) exhibits superior reproducibility and reduced measurement error compared to the universal goniometer for knee ROM assessment in patients.
• The established SEM and MDC values for the i-Goni provide clinically relevant metrics for interpreting knee ROM changes in patient populations.
• The i-Goni presents a reliable and valid tool for assessing knee ROM, with potential for application to other joints in future research.