On October 5, 2016, at about 1725 MDT, Southwest Airlines flight 3663, Boeing B737-800, N8324A, after arrival into Denver International Airport (KDEN), Denver, Colorado, the "B" position flight attendant lost her balance while retrieving her carryon bag from an overhead bin. The flight attendant fell against a seat arm rest near her right rib area. She was examined by paramedics and later escorted to a local hospital for further evaluation. An X-ray identified the flight attendant had sustained a fractured rib. The flight was operated as a 14 Code of Federal Regulations Part 121 domestic passenger flight from Salt Lake City International Airport (KSLC) , Salt Lake City, Utah, with 2 pilots, 4 flight attendants and 173 passengers on board. After the event, the injured flight attendant stated they had finished their day in Denver and while retrieving her bag from the overhead bin she stepped back and lost her balance. She thought her foot may have caught on the bar underneath a seat. She fell onto a row of seats making contact with an arm rest. She heard a crack in her rib area and it was difficult to breathe. The "C" flight attendant got help, the crew came back and paramedics were called.