- Q angle is the angle formed by a line drawn from the ASIS to central patella and a second line drawn from central patella to tibial tubercle;
- an increased Q angle is a risk factor for patellar subluxation
- normally Q angle is 14 deg for males and 17 deg for females;
- Agliettis et. al. Clin. Ortho 1983:
- 75 normal males: Q angle = 14 deg (+/- 3)
- 75 normal females: Q angle = 17 deg (+/- 3)
- biomechanics of patellofemoral joint are effected by patellar tendon length & the Q angle;
- q angle is increased by:
- genu valgum
- increased femoral anteversion
- external tibial torsion
- laterally positioned tibial tuberosity
- tight lateral retinaculum
- Clincal Determination:
(see examination of the patellofemoral joint
- deficiency of vastus medialis oblique is best assessed while leg is suspended in 15-20 deg of flexion;
- large convexity at superomedial corner of patella indicates vastus medialis deficiency;
- this is best measured both w/ the knee in extension as well as flexion;
- Q angle may not be accurrate in extension, since a laterally dislocated patella may give false impression that the Q angle is normal;
- in flexion, this is not a problem since the patella is well seated in the trochlear groove;
- a sitting Q angle of more than 8 deg is abnormal
A new method using computed tomographic scan to measure the rectus femoris-patellar tendon Q-angle comparison with conventional method.
Patellar tracking in primary total knee arthroplasty.
Original Text by Clifford R. Wheeless, III, MD.