Data from 37 frontal crashes in which drivers or right-front passengers sustained lower extremity fractures at or below their femoral condyles were obtained from an ongoing study of real-world crashes in a 7-county region in central Virginia, U.S.A. Information obtained from the crash-involved vehicles included crush and intrusion measurements;​ for each injured person, injury details including the related medical records and radiographs were reviewed. Injuries were classified according to the mechanism of fracture. The most common fractures involved the ankles (36 percent), followed by the knees (33 percent). The most frequent causes of ankle fractures were axial loading and external rotation. Intrusion was common (83 percent) in below-knee fractures, though such fractures sometimes occurred in the absence of intrusion. Patella fractures typically did not involve intrusion and appeared to result from direct loading of vehicle structures in front of the knees, indicating that the risk of these fractures may be reduced with improved design of knee impact areas.