Ultrasonographic evaluation of patellar tracking in children.

Patellar positions with the knee in extension and in 10 degrees and 20 degrees flexion were measured by ultrasonography in both knees of 20 children with patellar dislocation and in both knees of 30 healthy children for controls. Ultrasonography proved to be applicable to measuring the distance between the most anterior point of lateral femoral condyle and patellar apex, the sulcus angle and the vertical position of the patella. Compared with normal knees, the sulcus angle was wider and the patellar position more lateral and cranial in both the dislocated and asymptomatic knees of the patients. These results suggest that false tracking of the patella in early flexion is a predisposing factor to patellar dislocation.