What deformity of the knee is this? 

Valgus is a force that is applied to the knee, not the physical condition itself. The condition is better known as genu valgum or knock knees when there is a bend inward at the apex of the knee. If you put valgus on a test, you will get it wrong. The correct answer is genu valgum.

In this photograph the patient's knee bone segment distal to the joint is angled outward. This is called a vagus and may be congenital. A knee that is perfectly aligned has its load-bearing axis on a line that runs down the middle of the leg, through the hip, knee, and ankle. When the knee is malaligned, it naturally causes mobility problems and walking is clumsy and awkward for the patient.