Answer: Chronic lymphedema.
The image shows the typical foot of chronic lymphoedema. Lymphoedema characteristically involves the foot, and several signs appear together:
The submalleolar depressions fill in, so the ankle contour is lost.
A 'buffalo hump' of swelling forms on the dorsum of the foot.
The toes look 'square' because footwear confines them.
The skin on the dorsum of the toes cannot be pinched up because of subcutaneous fibrosis. This is a positive Stemmer's sign and is a hallmark of lymphoedema.
Why not the others: Cushing syndrome and osteoporosis do not produce this localized foot picture. Ref: Bailey & Love, Short Practice of Surgery, 27th ed, p. 998