MR Imaging of Growth Plate Injury in Rabbit: Development of Bony Bridge and Pathologic Correlation

Seong, Chang Kyu; Kim, In One; Cheon, Jung Eun; Kim, Hyung Jin; Kim, Woo Sun; Yeon, Kyung Mo

Abstract

PURPOSE: To evaluate the MR findings of a development of bony bridge within tunnels drilled across growth plates after injury in immature rabbits, and to correlate the MR and pathological findings.
MATERIALS AND METHODS
In 19 young rabbits, a growth-plate injury model was constructed in the distal femur by longitudinal drilling with a 5-mm drill. Coronal scans with T1-weighted, T2-weighted fast spin-echo, gradient echo, and gadolinium enhanced T1-weighted sequences were obtained immediately, and at 1, 2, 3, and 4 weeks, and 3, 6 months, postoperatively. Each group underwent pathologic examination, and the signal intensity, shape, and enhancement pattern of the drill holes were assessed. All results were correlated with pathologic findings.
RESULTS
During the early period, the signal intensity of the defect site varied due to hemorrhage and inflammatory reaction in the lesion, becoming isointense to that of metaphyseal marrow on all sequences during the late period (3 and 6 months). Pathologically, it corresponded to replacement of the osseous bridge with fatty marrow. The new bone formation shown by pathologic examination to be present in the periphery of the defect during the first week corresponded to the vertical dark rim seen on MR images. It appeared during that week and became more distinct, thickening gradually until the fourth week. Enhancement was absent or faint on follow-up immediately after surgery, inhomogenous and seen in half the rabbits at week 1, and maximal and homogenous at weeks 2 and 3. In had decreased by week 4, and was absent at months 3 and 6. These findings corresponded to the changes in transphyseal vascularity across the drill hole revealed by pathologic examination.
CONCLUSION
The contrast enhancement demonstrated by defective growth plate may indicate the development of vascularity throughout the plate, a phenomenon which precedes the formation of a bony bridge after trauma.