Patellar tilt: the physical examination correlates with MR imaging.

Patella malalignment is a recognized cause of knee pain, tilt being one of its more common forms. Although patellar tilt has been described both on the physical examination and on computerized imaging, to date the correlation between the two has not been established. A strong correlation would strengthen the value of each. Moreover, in situations where tilt cannot be clinically assessed (e.g. obesity), CT or MR imaging could be an adequate substitute for the clinical determination of tilt. We propose to correlate the physical examination with the magnetic resonance examination by way of an MR Tilt Angle. This angle is measured in a manner similar to the assessment of tilt on the physical examination, in that a line is drawn across the medial and lateral borders of the patella and referenced off the posterior femoral condyles. Most tilt angles use the slope of the lateral facet as a measure of tilt. These tilt angles paradoxically diminish as patellar tilt increases, a potential source of confusion. In this study, we use an MRI tilt angle that increases in the same direction as the actual tilt, which is more intuitive. We examined 30 patients with tilt and 51 patients without tilt. Patients with significant tilt on the physical examination can be expected to have an MRI Tilt Angle that is 10 degrees or greater whereas an angle of less than 10 degrees is associated with the absence of significant tilt on the physical examination. This MRI Tilt Angle fills the need for an easy, objective, intuitive measure of tilt and is an excellent adjunct to the physical examination.