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.
Again to much of a broad question. It depends on a number of factors such as a patients age, activity level, and prognosis.