The Q angle is the difference between the direction of pull of the quadriceps along the shaft of the femur and the direction of pull of the patellar tendon, which is almost vertical.

The knee is the largest synovial joint in the body, consisting of the articulation between the femur and tibia (tibiofemoral joint), and that between the femur and patella (patellofemoral joint). The tibiofemoral joint is weightbearing, and consists of two articulations. The patellofemoral joint helps give a mechanical advantage to the pull of the quadriceps as it acts over the knee. In addition to these two main joints, a third – the superior tibiofibular joint – is formed between the lateral tibial condyle and the head of the fibula.