[Computed tomography of the patellofemoral alignment after arthroscopic reconstruction following patella dislocation]

To evaluate the diagnostic impact of different CT-based measurements to analyze the patellofemoral alignment after arthroscopic reconstruction in patients with patella dislocation.

In 18 patients with dislocation of the patella, CT of the patellofemoral joint was performed after arthroscopic reconstruction. Various methods recommended in the literature were used to analyze the structure and the alignment of the patellofemoral joint with a relaxed quadriceps muscle. Axial CT scans were taken in four different knee flexion angles (15 degrees, 30 degrees, 45 degrees, 60 degrees ).

After arthroscopic stabilization in patients with patella dislocation, only the lateral patellofemoral angle (15 degrees and 30 degrees knee flexion) and the congruence angle (15 degrees knee flexion) showed significant differences between the CT-measurements in the normal and the operated group. The differences of the remaining mean values were not significant due to a high standard deviation. With increasing flexion of the knee, the differences between the normal and the dislocation group almost disappeared. Only the lateral patellofemoral angle, the patella tilt and the lateral patella shift revealed differences between the normal and the group with recurrent dislocation in every degree of knee flexion. With increasing knee flexion above 30 degrees and especially at 60 degrees, the majority of the measured values returned to the normal range.

For CT-measurements of the patellofemoral joint after arthroscopic stabilization, the patellofemoral angle and the congruence angle seemed to be most useful. The measurements of the patellofemoral joint should be taken in various degrees of knee flexion.