"Ottowa rules" for when to do an x-ray to r/o fx; based on a retrospective study of 707 pts with knee injuries & x-rays: No pts with none of these had fx on x-ray.
- Age >55yo
- Tender at head of fibula
- Isolated patellar tenderness
- Inability to flex knee to 90 degrees
- Inability to bear weight (4 steps) both immediately after injury & in ED
(Ann. Emerg. Med 26:405, 1995)
In a meta-analysis of validation studies, the Ottawa Knee Rules were 98.5% sensitive and 49% specific for knee fractures (Ann. Int. med. 140:121, 2004--JW)
In a study comparing the Ottawa rules with the "Pittsburgh Rule" (x-ray if (< 12yo or > 50yo) + injury involving direct blow, OR if 12-50yo + can't walk 4 weight-bearing steps in ER), Ottawa rule had sens 97% and specificity of 27% for knee fx but Pittsburgh Rule had sensitivity of 99% and specificity of 60% for fx!