Q-angle--or quadriceps angle--is the angle between the quadriceps muscle (front of the thigh) and the patellar tendon (just below the kneecap). This angle can be determined using X-rays. More often, it is measured by placing the person flat on a table with the hips, knees, and feet in a neutral position. A line is drawn from the pelvic bone to the middle of the kneecap. A second line is drawn from the middle of the kneecap through the large bump on the shin (called the tibial tubercle). The angle formed by the crossing of these two lines is called the Q-angle.
Normally, the Q-angle is between 13 and 18 degrees when measured this way. Boys and men usually have smaller angles than girls and women. With a larger than normal Q-angle, the kneecap (patella) moves up and down over the knee joint in such a way that it can cause wear and tear of the cartilage. This causes crepitus, or the crunching feeling people describe when straightening the knee.
Ask your doctor about seeing a physical therapist. Using taping techniques, shoe inserts (orthotics), or muscle strengthening exercises, the therapist may be able to help your daughter learn how to keep the patella in the middle. These measures can help reduce pain, swelling, and the crepitus sensation.