Q-angle and J-sign: indicative of maltracking subgroups in patellofemoral pain.

Mechanical factors related to patellofemoral pain syndrome and maltracking are poorly understood. Clinically, the Q-angle, J-sign, and lateral hypermobility commonly are used to evaluate patellar maltracking. However, these measures have yet to be correlated to specific three-dimensional patellofemoral displacements and rotations. Thus, we tested the hypotheses that increased Q-angle, lateral hypermobility, and J-sign correlate with three-dimensional patellofemoral displacements and rotations. We also determined whether multiple maltracking patterns can be discriminated, based on patellofemoral displacements and rotations. Three-dimensional patellofemoral motion data were acquired during active extension-flexion using dynamic MRI in 30 knees diagnosed with patellofemoral pain and at least one clinical sign of patellar maltracking (Q-angle, lateral hypermobility, or J-sign) and in 37 asymptomatic knees. Although the Q-angle is assumed to indicate lateral patellar subluxation, our data supported a correlation between the Q-angle and medial, not lateral, patellar displacement. We identified two distinct maltracking groups based on patellofemoral lateral-medial displacement, but the same groups could not be discriminated based on standard clinical measures (eg, Q-angle, lateral hypermobility, and J-sign). A more precise definition of abnormal three-dimensional patellofemoral motion, including identifying subgroups in the patellofemoral pain population, may allow more targeted and effective treatments.