Knee replacement surgery is currently considered to be the gold standard for people suffering from severe symptomatic osteoarthritis of the knee. However, a large proportion of patients experience functional problems, to the point that the knee often can give way, and these persons are at risk of falls. Stepping has demonstrated to be one of the main strategies to avoid falling once balance control is lost. With the Four Square Step Test (FSST) or, better, the modified version (mFSST), it is possible to discriminate fallers from non-fallers.