When measuring the Q angle, the axis of the goniometer goes over what structure?

The Q angle, or quadriceps angle, is an important measurement used in assessing the alignment of the knee. When measuring the Q angle, the axis of the goniometer is placed over the center of the patella. This positioning allows for an accurate determination of the angle formed between two lines: one line extends from the anterior superior iliac spine (ASIS) to the center of the patella, and the other extends from the center of the patella to the tibial tuberosity.

Placing the goniometer's axis at the center of the patella is critical because it provides a reference point that reflects the angle created by the alignment of the quadriceps muscle and the patellar tendon. This is essential for understanding knee mechanics and can be particularly relevant in evaluating knee pathology, tracking changes in muscle function, or planning rehabilitation strategies.