The details concerning the last minute alteration of the Chris Houston trade has come out. Initially we heard that the terms of the deal involved the Falcons receiving Detroit's sixth-round pick in the 2010 draft, along with a swap of fifth-round selections. Then the terms were altered with Atlanta only receiving Detroit's sixth-rounder this year and a conditional seventh-round pick next year.
According to PFT
"...the Lions contacted the Falcons and said that Houston could not pass the physical imposed by Lions' doctors. We're told that the Lions also said that perhaps Houston could pass the physical if the terms of the deal were adjusted.
And so the terms of the deal were adjusted, and Houston passed the physical.
Though the Falcons could have scrapped the trade and kept Chris Houston, they opted to process, and they probably will be reluctant to do a deal with Detroit the next time an opportunity to do so arises."