A well-functioning knee joint is important for mobility. The knee must be able to support the weight of the body during activities such as walking or running. The Q-angle refers to the quadriceps angle. The Q-angle is the angle between the quadriceps tendon and the patellar tendon. An increased Q-angle is a risk factor for patellar subluxation. In order to measure the Q-angle, you will first find the patella and its border, the center of the patella, and the tibial tubercle. Then, the physician will draw a line from the ASIS to the center of the patella and a second line from the tibial tubercle through the center of the patella. The Q-angle (quadriceps angle) is formed in the frontal plane by the two line segments. The Q-angle is the angle formed by a line drawn from the Anterior Superior Iliac Spine (ASIS) to the center of the patella. A second line is drawn from the center of the patella to the tibial tubercle. The angle formed by the two lines is called the Q-angle. The normal Q-angle is variable. The normal Q-angle for males is usually 14 degrees and 17 degrees in females. A wider pelvis and an increased Q-angle in females is linked to knee pain, patellofemoral pain, and ACL injury. The alignment of the patellofemoral joint is effected by the patellar tendon length and the Q-angle. It is best to measure the Q-angle with the knee in extension as well as flexion. Larger Q-angle plus a strong quadriceps contraction can dislocate the patella.
The Q-angle is increased by:
Genu valgum
External tibial torsion
Femoral anteversion
Lateral positioned tibial tuberosity
Tight lateral retinaculum
A CT scan study of the patellofemoral articulation is found to be very helpful.
