DOES THE Q-ANGLE REFLECT THE FORCE ON THE PATELLA IN THE FRONTAL PLANE

Background and Purpose. The quadriceps femoris muscle angle (Q angle) is used to reflect the quadriceps femoris muscle's force on the patell a in the frontal plane. We found no studies, however, that validate th is assumption. The purpose of this study was to determine whether the Q angle can be used to represent the force on the patella in the front al plane. Subjects. Seven lower extremities from four male cadavers we re dissected and investigated. Methods. We devised a model in which th e line of action of quadriceps femoris muscle's resultant force was ca lculated in the frontal plane on the seven lower-extremity specimens. We then compared these calculations with the Q angles from the same ca daver specimens. The differences between the measured and calculated Q angles were tested for significance using a paired t test. In additio n, we calculated a simple linear regression to test the relationship b etween the calculated and measured Q angles. Results. Our data showed that the angle for the average resultant force of the quadriceps femor is muscle was 3.90 degrees greater (P = .0003) than the measured Q ang les. A significant relationship (r = .919, P = .0035), however, was fo und between the measured and calculated Q angles. Conclusion and Discu ssion. The Q angle, as measured in clinical practice, appears to refle ct the angle of the resultant quadriceps femoris muscle force. We beli eve, however, that this measurement is significantly less than the act ual quadriceps femoris muscle force vector and underestimates the late ral force on the patella.