CT patellar cortex tilt angle: a radiological method to measure patellar tilt

ABSTRACT

The role of patellar tilt in the anterior knee pain is indisputable. Traditionally, the lateral patellofemoral angle of Laurin has been defined in both the axial view and CT images for measuring the tilt of patella. We present a new angle, which is independent of the morphology of patella and directly relates to clinical assessment of the tilt, which is appreciated from palpation of the edges of the patella. 38 patients with anterior knee pain and forty normal control subjects were examined using CT scan of patellofemoral joint in 15 degrees of knee flexion. The amount of lateral patellar tilt was quantitatively assessed using the lateral patellofemoral angle, as described by Laurin et al, and the newly defined patellar cortex tilt angle. This angle is subtended by the line drawn along the posterior femoral condyles and the one parallel to the subchondral bone of patellar cortex. The fifteen-degree tilt was taken as normal cut-off point for patellar cortex tilt angle in the control group. In patients, the average tilt of patella, using the patellar cortex tilt angle was 15.26 versus 7.05 in the control group. Using Student's t test, the difference between the two means was significant [P<0.001]. The sensitivity and specificity of patellar cortex tilt angle were 40 and 90 percent, respectively There was a moderate agreement between our presented test and the lateral tilt angle test [kappa=0.40, P<0.001]. Our results indicate that patellar tilt can also be detected using patellar cortex tilt angle. We need more specific studies to determine the validity of the test