Bruce woke up from having his spine 'put back,' which involved a single punch from the prison doctor. Soon he was able to walk normally, and after a pair of failed attempts to make the climb, he realized the other prisoners were doing things all wrong.
Bruce walked up to his bed, and started kicking at the metal bedframe. One of the puzzled prisoners asked him, "What are you doing?" Bruce replied, "Getting out of here." Soon, Bruce had succeeded in breaking off a long section of metal, which he then carefully bent. He then asked for the rope that the other prisoners used as a safety rope when attempting the climb. He then securely tied the rope to the bent piece of metal. The doctor objected, "This can't possibly work. It's ridiculous." Bruce countered with, "Is it more or less ridiculous than one-punch spinal surgery?" The doctor shrugged and muttered, "Touché"
The curious prisoners watched as Bruce then walked to the bottom of the exit, and coiled the rope, placing it around his shoulders. He climbed up as far as he could on his own, then looked up. He was approximately twenty feet from the lip of the chasm. Bruce uncoiled the rope, and let approximately five feet of rope dangle down. He then swung the metal end and threw it as hard as he could. With the weight of the metal at the end of the rope, it sailed up and over the lip of the chasm. Bruce then carefully pulled the rope. Outside, the piece of metal met the brick lip of the chasm, where it dug in, acting perfectly as a grappling hook.
Bruce tugged on the rope, satisfied that it was secure, and easily climbed the remaining 20 feet, and was out of the chasm in no time. Bruce stood on the ground, savoring the sunlight, then peered back in to the chasm, at the prisoners below. "All those years in there, and none of you considered this option? Dumbasses." Nevertheless, he tossed the rope down to them, leaving the makeshift grappling hook in place. He then walked toward the nearest city with an airport.
Just illustrating one of the glaring plot holes in "The Dark Knight Rises." I like the movie overall, but this plot hole bothered me from the first day I saw the movie. The prisoners had rope, they had metal bed frames, and they had nothing but time on their hands. Hello?! Anyone home, McFly?!