Literally translated, osteomalacia means “soft bones”, and in modern times very rarely leads to such extreme deformities as these.
There are many diseases and situations that lead to osteomalacia, but ultimately only one cause - defective bone mineralization leading to decreased or ceased deposition of new calcium or phosphorus in the bones. The condition itself is usually treated by administering high doses of vitamin D, while attempting to treat the underlying cause.
In children, osteomalacia is often called rickets. The adult form of the condition is often much milder than in children, but can still lead to bone weakness and bowing. In all ages, the most common cause is vitamin D deficiency, due to malabsorption by the intestines (as in Coeliac disease) , lack of sunlight, or very poor diet.
Deformities, Including Diseases of the Joints and Bones. A. H. Tubby, 1912.