The cortical margin of an involved bone never completely disappears (unlike bone destruction due to disease). Similar disuse atrophy due to immobilization follows neural or muscular paralysis.
Disuse osteoporosis. (A) Severe periarticular demineralization follows prolonged immobilization of the extremity.
(B) In a patient with a fractured patella, there is pronounced subcortical demineralization in the distal femur. The cortical margin (arrows) remains intact.