Re-evaluating the functional implications of the Q-angle and its relationship to in-vivo patellofemoral kinematics |
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| Institution: | 1. Functional and Applied Biomechanics, Department of Rehabilitation Medicine, NIH, Bethesda, MD, USA;2. Physical Therapy and Rehabilitation Science, University of Maryland, College Park, MD, USA;3. Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, USA;1. Department of Physical Therapy, University of Nevada, Las Vegas, Las Vegas, NV, USA;2. Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, USA;3. Department of Radiology, University of Southern California, Los Angeles, CA, USA;4. Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA |
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| Abstract: | BackgroundThe Q-angle is widely used clinically to evaluate individuals with anterior knee pain. Recent studies have questioned the utility of this measure and have suggested that a large Q-angle may not be associated with lateral patellofemoral translation, as often assumed. The objective of this study was to determine: 1) how accurately the Q-angle represents the line-of-action of the quadriceps and 2) if adding active quadriceps contraction or a bent knee position to the measurement of the Q-angle improves its reliability, accuracy, and association with patellofemoral kinematics.MethodsThe study included individuals diagnosed with chronic idiopathic patellofemoral pain and control subjects (n = 43 and n = 30 knees). Three measures of the clinical Q-angle (straight- and bent-knee with relaxed quadriceps and straight-knee with maximum isometric quadriceps contraction) were obtained with a goniometer and compared to a fourth MR-based measure of Q-angle. Patellofemoral kinematics were derived from dynamic cine-phase contrast images, acquired while subjects extended/flexed their knee from approximately 0° and 45°.FindingsThe Q-angle did not represent the line-of-action of the quadriceps. The average difference between each clinical and the MR-based Q-angle ranged from 5° to 8°. These differences varied greatly across subjects (range: ? 28.5° to 3.9o). Adding an active quadriceps contraction or a bent knee position, did not improve the reliability of the Q-angle. An increased Q-angle correlated to medial patellar displacement and tilt (r = 0.38—0.54, P < 0.001) in the cohort with anterior knee pain.InterpretationClinicians are cautioned against using the Q-angle to infer patellofemoral kinematics. |
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