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

Introduction: 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. Materials: Three common goniometric devices: a universal goniometer, an inclinometer, and a Smartphone app. Methods: 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. Intra-rater, inter-rater, and test-retest Intraclass Correlation Coefficients (ICC2,1) were calculated. Results: Intra-rater ICC(2,1) was excellent for the three devices ranging from 0.93-0.96, with the smartphone app yielding the best results (ICC(2,1)=0.96, [95%CI:0.89-0.95]). Inter-rater 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 intra-rater, inter-rater, and test-retest MDC95 values ranged from 1.6° to 3.5°, 3.7° to 10.4 and 2.6° to 5.4° respectively. Conclusions: The goniometer was the least reliable. The inclinometer is the recommended device due to its ease of use compared to the smartphone app.