Evaluation Of Reliability And Validity Of A New Device To Measure Knee Rotation

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Rotational laxity of knee is known as the one of the intrinsic risk factors of anterior cruciate ligament (ACL) injury. However, there is no simple device to measure knee rotation. The “RotorMeter” is a newly developed, simple, non-invasive, external device that is specifically designed to measure the lower leg rotation relative to the femur in vivo. PURPOSE: To determine the reliability and validity of the RotorMeter. METHODS: Two measurements were made with the RotorMeter at 90° of knee flexion and 90° of hip flexion applying 8 Nm torque by 2 independent examiners in 14 healthy female subjects (21.1±1.2 yrs, 28 knees). Image analysis to obtain the rotation of the right lower leg was simultaneously carried out. Statistical analysis was performed using intra-class correlation coefficients (ICC, intra-examiner and inter-examiner) and Pearson’s correlation coefficient between the 2 methods. RESULTS: Total (internal + external) knee rotation ranged from 100.0° to 105.7° (standard error of measurement ranged from 2.3° to 3.7°) by the RotorMeter and was 62.2±8.24° by the image analysis. Intra-examiner ICC(1,1) results were 0.705 and 0.721, and inter-examiner ICC(2,2) was 0.828. The correlation coefficient between the results of RoterMeter and image analysis was 0.875 (significant at P < 0.05). CONCLUSIONS: The RoterMeter was found to be a reliable and valid measurement instrument concerning knee rotation. It is easy to perform and might be used in a wide field to measure knee rotation. But the deformation of soft tissue and the movement of subtalar joint should be considered. This study was supported by a Grant-in Aid Exploratory Research from NUHW (2013-A-30).