Patello-femoral tracking in the weight-bearing knee: a study of asymptomatic volunteers utilising dynamic magnetic resonance imaging: a preliminary report

Normal patello-femoral tracking is not well defined, and conventional radio logical techniques do not allow imaging in the physiological, weight-bearin g stance. A vertical-access open configuration magnetic resonance scanner a llows imaging of patello-femoral tracking during weight-bearing and through a wide range of knee flexion. We imaged 40 asymptomatic knees in this way, producing axial scans which were analysed qualitatively and quantitatively using sulcus angle, congruence angle, lateral patello-femoral angle and pa tellar centralisation, to assess patellar tilt and displacement. Mild later al tilting in hyperextension with the quadriceps relaxed was seen, but quan titative assessment of this was impeded by internal rotation of the femur i n extension. One-half of the knees were slightly laterally dis-placed in hy per-extension, becoming central during the first 30 degrees of knee flexion . During passive flexion of the knee in a seated position, fewer knees were laterally tilted or displaced, and no consistent change was seen during fl exion. These results indicate that mild lateral tilting and displacement ca n be normal phenomena in the weight-bearing knee in early flexion and shoul d not necessarily be taken as evidence of abnormal tracking in symptomatic patients. Lateral to medial movement of the patella occurs during normal kn ee flexion. In addition, imaging in the weight-bearing knee can provide val uable information not gained by imaging during passive knee flexion.