Q Angle Measurement and Significance

By Arun Pal Singh

Q angle is the angle formed by a line drawn from the anterosuperior iliac spine to the central patella and a second line drawn from central patella to tibial tubercle

Patellofemoral joint biomechanics is influenced by the direction and magnitude of force exerted by quadriceps muscle. In a normal knee, the line of force exerted by the quadriceps is lateral to the joint line, probably due to a larger force of vastus lateralis.

Normally angle is 14 deg for males and 17 deg for females.

Measurement of Q angle — Measurement of Q-angle, Image credit: Physiopedia

Increase in Q angle is associated with increased risk of lateral subluxation of the patella.

Therefore assessment of this angle is a measure of the pull of the quadriceps relative to the patella.

Q angle was described by Brattstrom.

Measurement of Q Angle

The angle is traditionally be measured in the supine position with the knee in full extension. [Standing position is considered more suitable as it mimics the joint biomechanics during daily activity.]

It is measured with the knee at or near full extension.

The normal value is 13.5 ± 4.5°.

Women have a greater value greater than that for men. This is due to the wider pelvis, increased femoral anteversion, and a relative knee valgus angle.

Method

Patient supine with knee extended with the hip in neutral position and foot also in neutral position. Ensure that the lower extremity is at a right angle to the line joining both anterosuperior iliac spine.
Draw a line from anterosuperior iliac spine to the midpoint of the patella.
Draw another line from the midpoint of the patella to the tibial tubercle.
The resultant angle formed by the crossing of these two lines is called the Q angle.

Factors Affecting Value

Q angle is only an estimate of the line of pull of the quadriceps and can be affected by

The significant imbalance between the vastus medialis and vastus lateralis muscles
An abnormally sitting patella
Q angle may not be accurate in extension, since a laterally dislocated patella may give a 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

Q angle is increased by

Genu valgum More obliquity of the femur and concomitantly, the obliquity of the pull of the quadriceps
Increased femoral anteversion
External tibial torsion
Laterally positioned tibial tuberosity
Tight lateral retinaculum

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About Arun Pal Singh

Arun Pal Singh is an orthopedic and trauma surgeon, founder and chief editor of this website. He works in Kanwar Bone and Spine Clinic, Dasuya, Hoshiarpur, Punjab.

This website is an effort to educate and support people and medical personnel on orthopedic issues and musculoskeletal health.

You can follow him on Facebook, Linkedin and Twitter

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Q Angle Measurement and Significance