Inclinometers and Apps Are Better than Goniometers, Measuring Knee Extension Range of Motion in Anterior Cruciate Ligament Patients: Reliability and Minimal Detectable Change for the Three Devices.

Knee extension range of motion (ROM) measurement is important in patients with anterior cruciate ligament (ACL) injury. The main objective is to evaluate the reliability and the minimal detectable change (MDC) of three methods of measuring knee extension ROM in ACL patients. The three common goniometric devices were a universal goniometer, an inclinometer, and a smartphone app. During a single-visit, knee extension ROM was measured in both knees of 92 ACL-injured or -reconstructed patients by two testers blinded to the other's measures. Intrarater, interrater, and test-retest intraclass correlation coefficients (ICC_2,1) were calculated. Intrarater ICC_2,1 was excellent for the three devices ranging from 0.92 to 0.94, with the inclinometer yielding the best results (ICC_2,1 = 0.94 [95% confidence interval, CI: 0.91-0.96]). Interrater ICC_2,1, however, varied from 0.36 to 0.80. The inclinometer and the smartphone app yielded similar results 0.80 (95% CI: 0.71-0.86) and 0.79 (95% CI: 0.70-0.86), respectively, whereas the universal goniometer was 0.36 (95% CI: 0.17-0.53). Test-retest ICC_2,1 for the inclinometer was 0.89 (95% CI: 0.84-0.93), 0.86 (95% CI: 0.79-0.91) for the app, and 0.83 (95% CI:0.74-0.89) for the goniometer. The intrarater, interrater, and test-retest MDC₉₅ values ranged from 2.0 to 3.5, 3.7 to 10.4, and 2.6 to 5.4 degrees, respectively. The goniometer was the least reliable. The inclinometer is the recommended device due to its highest ICC scores among the three devices and ease of use.