My shield disappeared during the jailbreak!

As you have no doubt read from the comments on other answers and on the question itself, stolen goods are lost when you get arrested. Anything that you stole in Kingdoms of Amalur: The Reckoning is lost if it is in your possession when you are arrested. If it was stolen (little red hand beside it), your shield actually disappeared during arrest, rather than jailbreak and I believe it is unrecoverable. You can check with the NPC you stole it from and/or their lootable chests and dressers, but as NPC loot is generated on first loot and regenerates after a time, while lootables stay looted forever, I highly doubt that your exact shield will be there. In short, if you don't have a save to recover to, your shield is lost forever. The game should have auto-saved at some point around then - hopefully you didn't overwrite it.

All non-stolen items confiscated from you upon arrest are held in a treasure chest within the jail, but as you've said you recovered your equipment, you've already encountered this chest.

Deductively, barring a defect in the game whereupon your shield was accidentally destroyed, your shield must have been a stolen item and is thus unrecoverable.

Stolen Item Insurance

To avoid this problem in the future, there's an easy solution to preserving stolen items. You could not steal, but where's the fun in that? The easier solution it to make your stolen items not be stolen items. If you sell a stolen item to a fence in a Traveler camp or to any merchant if your mercantile skill is maxed and then purchase the item back from them, it will no longer be a stolen item and thus won't be lost upon arrest. I suggest you do this before socketing awesome gems so as to reduce the cost to you.