Comparing goniometric and radiographic measurement of Q angle of the knee

Abstract

Background: The Q angle is a relevant clinical diagnostic measurement to detect various disorders of the knee. The common method used to measure the Q angle in the routine clinical practice is by radiography. An alternative to radiographic measurement is goniometry, by which exposure to x-rays can be avoided. Objectives: To compare and correlate the goniometric measurement of Q angle with radiographic measurement of the Q angle in patients with acute knee pain. Methods: We selected 45 patient participants with a mean age of 32.5 years who satisfied the inclusion criteria for this study. All the patients underwent goniometric measurement of the Q angle followed by x-ray imaging of the entire lower limb. Later the bony prominences were marked on the x-ray image and the Q angle formed was measured using a protractor. The Pearson correlation coefficient between the goniometric and radiographic measurements was determined. Results: We found a significant relationship between Q angles obtained using a goniometer and x-ray imaging in the supine position (r = 0.91, P = 0.001). The mean difference between the goniometric measurement of Q angle and the radiographic measurement was 0.1°, which is not significant. Conclusions: Goniometry can be used to measure Q angle as accurately as radiography, and can be used as an inexpensive and radiation free alternative.