Experimental study on the model of steroid-induced femoral head osteonecrosis by measuring the MR transverse relaxation parameters

Abstract

Objective To evaluate the marrow composition and microstructurechangesin animal model of steroid-induced avascular osteonecrosis of femoral head(SANFH) by estimating MR transverse relaxation. Methods Sixty pure-bred New Zealand rabbits were divided randomly into 5 groups, including a control group(n=8) and 4(M2w, M4w, M6w, M8w) experimental groups(n=13×4). Animal model was established according to the methods mentioned by Yamamoto. At the end of each experiment, MR was performed by GE Signa EXICITE scanner and the original transverse relaxation images were transferred to GE AW4.2 workstations for the further data analysis using functool software. T2, T2*values of the region of interest in the femoral head, metaphysis and marrow cavity were calculated, and the color-coded maps were created. Experimental animals were sacrificed and the femoral heads were collected for the followed histomorphological investigation. Results The actual sample size of the control group and the groups of M2w, M4w, M6w, M8w was 8 (16 hips), 10 (20 hips), 9 (18 hips), 9 (18 hips), 10 (20 hips). Statistical differences in T2 values(F=51.601, P<0.01), T2* values(F=36.889, P<0.01) were observed between the groups of M2w, M4w, M6w, M8w and control group in all anatomic femoral regions. The T2 and T2* values of the experimental groups were lower than the control group. This decreasing began at the initial stage of the modeling(M2w), reached the lowest point at M4w, and then rebounded in group of M6w and M8w. The T2(F=86.274, P<0.01), T2*(F=53.172, P<0.01) values were statistically different between the different anatomical regions. The T2 and T2*values of the femoral head area were higher than the metaphyseal and marrow cavity area. It was distinguished that both the amount and the size of fat cells increased in marrow and trabeculae, whereas the hematopoietic tissues decreased. Microthrombi in the arterioles and extravasation of erythrocytes were observed in the femora metaphysic at the earlier stage of the modeling. Such pathologic changes showed particular significance in group M4w. Then trabecular bone necrosis, inflammatory reaction and fibrosiswereobserved obviously in group of M6w and M8w. Conclusions Determination of MR transverse relaxation can sensitively reflect the bone marrow composition and microstructure changes in the SANFH models. This technique may have potential applications in the early diagnosis and monitoring the disease progression of SANFH. Key words: Femur head necrosis; Adrenal cortex hormones; Magnetic resonance; Relaxation; Models, animal; New Zealand rabbits