Femorotibial rotation and the Q-angle related to the dislocating patella.
OBJECTIVE
To compare the femorotibial rotation, the patellar translation, the hip-knee-ankle angle and the Q-angle in patients with a dislocation of the patella with those of healthy volunteers. Further, the clinically measured Q-angle was compared to that measured by radiography.


METHODS
A system for measurement of patellar variables was previously developed and applied to 80 healthy volunteers. In the present study, 28 patients (20 women, 8 men) with dislocation of the patella were examined bilaterally. Fourteen patients had habitual dislocations (20 affected knees) and 14 patients traumatic dislocations (17 affected knees). In 20 patients the clinical Q-angle was measured bilaterally by an orthopaedic surgeon and in 9 of these patients also by a second independent orthopaedic surgeon.


RESULTS
The most striking finding was that dislocating knees in both groups showed a smaller Q-angle than the healthy knees. Further, the habitual group 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 radiographic measurements of the Q-angle and no correlation was found between two independent clinical measurements.


CONCLUSIONS
Surgical operations aiming at decreasing the Q-angle should be challenged.
Sanfridsson
J
J
Centre for Medical Imaging and Physiology, University Hospital, Lund, Sweden.
Arnbjörnsson
A
A
Fridén
T
T
Ryd
L
L
Svahn
G
G
Jonsson
K
K
D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D004204:Joint Dislocations / Q000503:physiopathology*; D007718:Knee Injuries / Q000503:physiopathology*; D008297:Male; D010329:Patella / Q000000981:diagnostic imaging / Q000503:physiopathology*; D011859:Radiography; D012399:Rotation; D013977:Tibia / Q000000981:diagnostic imaging / Q000503:physiopathology*