Measurement Error Between a Goniometer and the NIH ImageJ Program for Measuring Quadriceps Angle

Purpose: Measurement error when determining the size of an angle is always an issue for clinicians. Computer assistance may help to decrease that error. The purpose of this study is to determine the amount of error when measuring Q-angles using a goniometer and the IMAGEJ program, a public domain program developed at the U.S. National Institutes of Health. Methods: Two investigators participated in data collection; one who is a licensed physical therapist who has over 25 years of clinical practice in orthopedic physical therapy and a second who is familiar and experienced with analyzing data using the National Institute of Health (NIH) IMAGEJ computer program. Quadriceps angles measured bilaterally for 30 subjects between the ages of 21 and 50 years were recorded. Interrater and intrarater reliability with standard error of the measurements were calculated. Results: The ICC (2,1) for measuring Q-angle with a goniometer was .96 (SEM =1.02°), while the ICC (2,1) for measuring Q-angle with the IMAGEJ program was .98 (SEM = 1.05°). The ICC (3,2) between measures obtained with a goniometer versus the IMAGEJ program was .89 (SEM = 2.06°). Conclusions: There is a high association between measures of Q-angle obtained with a goniometer compared to those obtained with computer-assistance using the IMAGEJ program. There may be a bias on the part of raters when measuring higher values of Q-angle. Further investigations should be conducted to examine the feasibility of increased use of IMAGEJ in measuring angles