In the fourth great ninja war, when Obito makes the ten tails transformed into God Tree that devoured the chakra of all the shinobi it touched(or its branches), where you will see Sarutobi Hiruzen cutting/destroying the branches of the Ten-Tails' tree form, and he does that with the help of Enma's transformation - Adamantine Staff.
When Sandaime Hokage is summoned using "Impure World Reincarnation", you aren't supposed to have any blood in you to summon Enma.
So, now if you check the naruto wiki, to summon a contract animal, first of all we would need to have a blood contract with the summoning animal, Afterwards they only need to offer an additional donation of blood on the hand they signed the contract with, mould their chakra with hand seals and then plant the hand they signed the contract with at the location they wish to summon the creature.
So, was it a flaw to show Sandaime Hokage with Adamantine Staff or is there any other technique this is used to summon a contract animal. Or was this explained in Manga..