The illustration shows mild bowing. Bowing may become extreme in certain cases.
Genu varum - the medical name for bow legs
In bow legs the knees are more widely apart than the rest of the leg. It is common in small children, who simply grow out of it, but in some people the bowing continues into adulthood.
What causes a bow leg deformity beginning in adulthood?
Bowing ('varus deformity') may develop later in life, as arthritis breaks down the inner (medial) aspect of the knee joint, often due to a meniscus having been removed some years earlier ('medial compartment' arthritis). In countries where diet and health may be poor, bow legs may also occur from such things as scurvy.
Consequences of bow legs
Bow legs may be asymptomatic or can lead to damage or aggravation of damage in the knee due to the abnormal alignment forces.
"...cartilage or meniscal injury....can be magnified in the setting of limb malalignment as a result of abnormal loading and increased contact pressures."