Author Affiliations: Department of Medicine, Mount Sinai Hospital and University Health Network, Toronto,
Ontario, Canada; and Departments of Health Policy Management and Evaluation and Medicine, University of Toronto, Toronto.
On August 1, 2007, a bridge on interstate 35W collapsed during rush-hour traffic near Minneapolis, Minnesota, with tragic consequences.
Engineers commissioned by the National Transportation Safety Board are still investigating the cause of this structural failure, and the final report is expected by fall 2008. The bridge buckled because its load exceeded the strength of its structure. Was the bridge collapse caused by an external force such as extra weight on the bridge, or was it due to structural deficiencies such as corrosion and deterioration of the truss gusset plates joining the beams? Although current evidence suggests that the collapse was due to a design flaw (the gusset plates were too thin) coupled with the 300 tons of extra construction equipment and gravel, the collapse could have been caused by one of many elements.
These general principles and possible explanations for structural failure apply not only to the collapse of bridges, but also to the fracture of bones.
Cheung AM, Detsky AS. Osteoporosis and FracturesMissing the Bridge?. JAMA. 2008;299(12):1468-1470. doi:10.1001/jama.299.12.1468