Functional evaluation of patello-femoral incongruence by computer tomography

Background. The purpose of this study was to specify the types of incongruence detected in the patellofemoral joint by computer tomography. The joints were examined in both internal and external rotation of the lower leg. Material and methods. We examined 16 patients with pain in the anterior compartment of the knee joint (12 women, 4 men, average age 34.2 years). CT scans of the patellofemoral joint were performed in two positions: with the knee flexed 20 degrees and 30 degrees . The measurements were taken at rest and during contracture of the quadriceps, and in both internal and external rotation of the lower leg. The results were used to calculate the lateral angle of the patella, the congruence angle, and the angle of the intercondylar sulcus. Results. Contracture of the quadriceps causes an increase in the lateral angle of the patella, both in the patient group and in the controls. In 12 cases, internal rotation of the lower leg caused increased values for the lateral angle of the patella, while external rotation reduced this angle. In the control group, in 20 degrees and 30 degrees flexion of the knee, tension in the quadriceps increased the lateral angle of the patella. Rotation in either direction did not affect the congruence angle. In 12 patients we diagnosed incongruence of the lateralization type and deviation of the patella. In 4 cases we observed reduction of the congruence angle. External rotation diminished this angle. In these patients we diagnosed incongruence of the medialization type. Conclusions. Our research confirms the suitability of computer tomography in examining the patello-femoral joint in flexion from 0 to 30 degrees. The functional examination method described here using rotation of the lower leg dives now possibilities for the exact specification of the type of incongruence in the knee joint.