Q angle of the Knee

- Discussion:
    - 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.

Last updated by Data Trace Staff on Thursday, August 30, 2012 3:10 pm