Femorotibial rotation and the Q-angle related to the dislocating patella

Purpose: To compare the femorotibial rotation, the patellar translation, th e hip-knee-ankle angle and the Q-angle in patients with a dislocation of th e patella with those of healthy volunteers. Further, the clinically measure d Q-angle was compared to that measured by radiography. Material and Methods: A system for measurement of patellar variables was pr eviously developed and applied to 80 healthy volunteers. In the present stu dy, 28 patients (20 women, 8 men) with dislocation of the patella were exam ined bilaterally. Fourteen patients had habitual dislocations (20 affected knees) and 14 patients traumatic dislocations (17 affected knees). In 20 pa tients the clinical Q-angle was measured bilaterally by an orthopaedic surg eon and in 9 of these patients also by a second independent orthopaedic sur geon. Results: The most striking finding was that dislocating knees in both group s showed a smaller Q-angle than the healthy knees. Further, the habitual gr oup showed greater relative rotation between the tibia and the femur and an increased patellar translation compared to the traumatic group and to the healthy volunteers. There was a poor correlation between clinical and radio graphic measurements of the Q-angle and no correlation was found between tw o independent clinical measurements. Conclusion: Surgical operations aiming at decreasing the Q-angle should be challenged.