What is the Q-Angle
A well-functioning knee joint is important for mobility, and the knee must be able to support the weight of the body. As well as a normal alignment of the knee is important for its function. The Q-angle of the knee provides useful information about the alignment of the knee joint. The Q-angle is the quadriceps angle, which is the angle between the quadriceps tendon and the patellar tendon. An increased Q angle is a risk factor for patellar subluxation.
A normal Q-angle is variable. In extension, the normal Q-angle for males is usually 14 degrees, but in female it is approximately 17 degrees. In flexion, the approximate Q-angle is 8 degrees. It is best to measure the Q-angle with the knee in extension as well as in flexion. 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. A 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, and a tight lateral retinaculum.
Measuring the Q-Angle
To measure the Q-angle, two segments are drawn in the frontal plane. The first line is drawn from the anterior superior iliac spine (ASIS) to the center of the patella. The second line is drawn from the center of the patella to the tibial tubercle. The angle that is formed by the two lines is called the Q-angle. To do this, the patella and its center and border are found, as well as the tibial tubercle. Then, a line is drawn from the ASIS to the center of the patella and a second line is drawn from the tibia tubercle through the center of the patella.
Total Knee Replacements and the Q-Angle
One of the most common complications of a total knee replacement is an abnormal patellar tracking. In these cases, preservation of a normal Q-angle is important. An increased Q-angle in the knee will lead to an increase in lateral subluxation forces on the patella, which may lead to pain, wear of the implant, and mechanical symptoms. When performing a total knee replacement, techniques that will cause an increased Q-angle, such as internal rotation of the femoral component or tibial component, should be avoided. Medialization of the femoral component and lateral placement of the patellar component should be avoided, or placing the patellar prosthesis either center or slightly center can be done if internal rotation should not be avoided. Just remember that the patella should be slightly medial, but the femoral component, opposite to that, will be slightly lateral.
Miserable Malalignment Syndrome
Miserable malalignment syndrome is a term used to describe a triad of anatomic features or findings that will increase the Q-angle. These include excessive femoral anteversion, genu valgum, and external tibial torsion or pronated feet. Symptoms of miserable malalignment syndrome include anterior knee pain, pain under the patella, and stiffness of the knee joint. When examining a patient for patellofemoral pain, alignment is important, including rotational alignment.
