Imaging findings after fat graft interposition in an injured growth plate: an experimental study in rabbits.

RATIONALE AND

OBJECTIVES

To assess the magnetic resonance (MR) features of fat graft interposition in experimentally induced growth plate injury, to correlate these features with histologic findings, and to compare the growth disturbances of fat-grafted and nonfat-grafted growth plate injuries.

METHODS

The growth plate injury model was created in 20 skeletally immature rabbits. In 14 rabbits, a bilateral growth plate defect was made in the medial half of the proximal tibia. The defect of the right tibia was filled with autologous fat; the left tibia was left empty. In another 6 rabbits, a unilateral growth plate defect was created with (n = 3) or without (n = 3) fat graft interposition in the right tibia. MR imaging was performed at 2, 4, and 12 weeks postoperatively using a 1.5-T MR unit. T1-weighted images, T2-weighted images, gradient echo images, and contrast-enhanced T1-weighted images were obtained in the coronal plane. The authors evaluated the MR features of the growth plate defects with or without fat graft, and the remaining growth plate. The length and angulation of the grafted tibia were compared with those of the nonfat-grafted tibia. RESULTS At 2 weeks postoperatively, the grafted area showed low signal intensity mixed with high signal intensity (71%) on T1-weighted imaging. At 2 weeks, most of the growth plate defect in the control animals showed low signal intensity in all image sequences. At 4 weeks, most of the grafted area showed low signal intensity on T2-weighted imaging. A bone bridge was revealed in 15% of the grafted tibia and in 62% of the control animals at 4 weeks. On gradient echo images, high signal intensity of the remaining growth plate was preserved in grafted tibias, but in the control animals this became invisible 4 weeks postoperatively. At 12 weeks, most of growth plate defect area became isointense on all image sequences in grafted tibia and in the control animals. Histologically, the fat-grafted area was replaced by fibrous connective tissues with thin, trabecular bone formation. Growth plate defects of the control animals were filled with mature fatty marrow with trabecular bone formation. The varus angle and medial length of the tibia were significantly different between fat-grafted tibias at 4 weeks and 12 weeks postoperatively.

CONCLUSION

MR imaging was helpful for evaluating growth plate modifications and subsequent changes after fat graft interposition. Fat graft interposition had a role in reducing growth disturbance in growth plate injury.