Posttraumatic osteonecrosis in a swine model. Correlation of blood cell flux, MRI and histology.

We used a miniature swine femoral neck fracture model to demonstrate the effects of the fracture on blood flow, histologic appearance, MRI signal and the development of posttraumatic osteonecrosis. The fracture was created and internally fixed in the right hip of 11 swine, with the left hip serving as the control. Femoral head blood flow via Laser Doppler Flowmetry and MRI data was examined for the experimental hip preoperatively, postoperatively and at 1, 2, 4 and 8 weeks postfracture. At 8 weeks, the animals were killed and the femoral heads were evaluated. Femoral head blood flow decreased immediately postfracture and continued to diminish with time. MRI signal intensities in the femoral head at 4 and 8 weeks were significantly less when the fixation failed than when it was intact. Histologic grades (0-14 points) and bone densities were 7.6 and 49%, respectively, on the experimental side, compared to 1.6 and 56% on the control side. Histologic grading, bone density values and blood flow data had no relation to changes in MRI signal intensity.