title: Knee pain, swelling, and instability.
abstract: A 20-year-old man who was playing recreational football caught a pass and turned to his left with his left foot planted, just as he was tackled from the right side. He heard a popping sound and felt immediate pain in his left knee. The patient developed swelling within 2 hours and was unable to walk because of pain, instability, and stiffness in his left knee. He reported to the emergency department, where routine x-rays were obtained (figure 1).
authors.affiliation: Department of Orthopedics, Kaiser Permanente, Sacramento, CA, 95821, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Shea
authors.forename: Gregory W
authors.initials: GW
authors.lastname: Coppola