Thorn manacles are a form of manacles used to prevent the cuffed person from using magic. They're first seen in Dead Beat.
According to Quintus Cassius, formerly of the Order of the Blackened Denarius, Nicodemus Archleone himself designed the manacles he put on Dresden. They had been used on witches and wizards for centuries. Dresden himself suspected the Red Court designed them for their war with the White Council.
According to Lash, however, the manacles were made by troll smiths of the Unseelie Court, and to overcome the bindings of the manacles one needs to seek the bane to those who made them. Dresden did it with iron and sunlight, the bane to trolls.
In the series
In Proven Guilty, Darby Crane and his assistant Lucius Glau abducted Dresden and Henry Rawlins. He woke up in a pair of thorn manacles as well as a gag and hood at the Full Moon Garage, all to keep him from using his magic. When he attempted to reach for his magic, he felt the manacles become a frozen agony so strong they wiped out all thought. After a brief discussion with Lasciel to plot an escape, Dresden dislocates all the joints in his bad left hand and painfully squeezes it out of the manacle.