June 20, 2024

Q Angle of the knee is defined as the Mean vector angle of quadriceps pull on the patella.

Q angle measurement

Normal alignment of the knee is important for functioning properly and maintaining the kinematics of the knee joint.

Q-angle (Quardiceps angle)

Provides useful information about the alignment of knee joint

It is the angle between the quadriceps tendon and patella tendon (Represent the dynamic instability of patella=> Greater it is more unstable it is)

Measurement methods for Q angle

It is measured in the frontal planes

1st line is drawn from ASIS to the center of the patella

2nd line is drawn from the center of the patella to the tibial tubercle

Q angle of the knee is measured in extension as well as 30 degrees of flexion

In extension

Normal value represents

  • Male: 11-14 degrees
  • Female: 14-17 degrees

In flexion normal value is 8 degrees

Pre-requisites of measurement

Patella should be centered on the trochlea otherwise in an already dislocated patella, the angle will be falsely reduced (So, measured in 15-20 degrees of flexion of the knee with relocated patella)

Alignment of the patellofemoral joint is determined by the Patella tendon and Q-angle

Larger Q-angles are seen in

  • Genu valgum
  • External tibial torsion
  • Femoral anteversion


  • Lateral positioned tibial tuberosity
  • Tight lateral retinaculum

Abnormal Q-angle after TKA: Abnormal patella tracking (So, should avoid it)

Patella prosthesis should be kept either in the center or in slight medial

J-Sign in patella

  • One of the forms of dynamic (abnormal ) patella tracking
  • Normally patella glides in a straight line with a minimal sideways shift at the end of extension in the trochlear groove but due to various regions patella may have an excessive lateral shift at the end describing an inverted ‘J’ trajectory

Other forms of mal-tracking include:

  1. Subluxation ( +ve congruence angle even after 10-degree flexion)
  2. Tilt angle < 80 degree
  3. Combination of both

See also: Knee Biomechanics

See also: Recurrent dislocation of Patella