Occult posttraumatic bone injury.

Knee injury evaluation with magnetic resonance imaging (MRI) has enabled a high percentage of associated diagnoses of occult bone injuries. An experimental occult bone injury was produced in the rabbit knee with a controlled impact in the range of approximately half the fracture force. An MR image of the occult bone injury was obtained after killing the animals at 1, 3 and 9 weeks after impact. Histological study of the area under optical microscopy showed a benign, self-resolving injury pattern in the subchondral cancellous bone. The samples were compared with 11 human biopsy samples obtained during knee surgery. The same benign pattern was observed except for one case. The healing response of this injury at the subfracture level appears rather benign, and a permanent scar will probably not develop.