MR imaging of changes of the growth plate after partial physeal removal and fat graft interposition in rabbits

RATIONALE AND OBJECTIVES. The most important complication of skeletal injur ies involving the growth plate is growth disturbance. The purpose of this s tudy was to evaluate MR features of growth plate modification after fat gra ft interposition in growth plate injury and to correlate these findings wit h pathological findings. METHODS. A growth plate injury model was used in 12 skeletally immature rab bits. A longitudinal drip hole 5 mm in diameter was created in the central part of the growth plate in the distal femur, bilaterally. One side was fil led with autologous fat, and the contralateral defect was left empty as a c ontrol, Magnetic resonance imaging was obtained 1, 3, and 6 months after su rgery, and routine histological study was performed, The authors evaluated sequential changes in MR images and the histological basis of MR findings. RESULTS. In grafted femur, the signal intensity of the grafted area was low er than that of the surrounding bone on T2-weighted images at 1 month. The growth plate defect at 3 to 6 months was modified and had a proximally tape ring appearance. The ratio of the growth plate defect was smaller in the gr afted femur than in the control femur after surgery. Histologically, the fa t-grafted area was replaced by fibrous connective tissue. In the control fe mur, a bony bridge was rectangular in the longitudinal direction and showed isosignal intensity with a rim of low signal intensity on T1-weighted imag ing, Histologically, the defect was filled with mature fatty marrow with ne w bone formation in the control femur. CONCLUSIONS. The proximally pointing appearance and the low signal intensit y of the grafted area on MR suggested fibrous degeneration of grafted fat t hat prevented solid bony bridge formation in experimentally induced growth plate injury.