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Q-Angle

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Updated December 31, 2007

Definition: The Q-angle is often measured when examining the knee, especially when kneecap problems are being evaluated.

Three landmarks are needed to determine the Q-angle:

  • Anterior Superior Iliac Spine (ASIS)
    The ASIS is the front of the pelvic bone that is felt in front of the hip at the level of your waist.

  • Center of the Patella (Kneecap)
    The center of the kneecap is best identified by locating the top, bottom and each side of the kneecap, and then drawing intersecting lines.

  • Tibial Tubercle
    The tibial tubercle is the bump about 5 centimeters below the kneecap on the front of the shin bone (tibia).
The Q-angle is formed from a line drawn from the ASIS to the center of the kneecap, and from the center of the kneecap to the tibial tubercle. To find the Q-angle, measure that angle, and subtract from 180 degrees.

A normal Q-angle in men is 14 degrees and in women is 17 degrees. An increase in Q-angle can mean a higher risk of kneecap problems including patellar subluxation and patellar dislocation.

Sources:

Conley S, "The Female Knee: Anatomic Variations" J. Am. Acad. Ortho. Surg., September 2007; 15: S31 - S36.

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  5. Finding The Cause
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  7. Q-Angle of the Knee Measurement of the Q-Angle

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