Subchondral contusion of the knee caused by axial loading from dashboard impact: detection by magnetic resonance imaging.

We studied the occurrence of "bone bruises" of the knee resulting from dashboard impaction and detected by magnetic resonance imaging (MRI). We chose 21 knees of 20 front seat occupants in head-on motor vehicle collisions. To ensure all knees had received a significant axial load, patients selected had ipsilateral posterior hip dislocations and/or posterior wall acetabular fractures. Anteroposterior and lateral knee radiographs were negative for fracture in all cases. T1-weighted axial and sagittal MRI of each knee with a 1.5-T magnetron scanner revealed signal changes consistent with subchondral microfracture or bone bruise in 8 of the 21 knees. Previous cadaveric, animal, and MRI studies have suggested that such changes may be precursors of posttraumatic osteoarthritis. With the increasing incidence of serious lower extremity injury as a result of motor vehicle accidents, these occult injuries may significantly affect individuals and society.