Q-Angle

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.