Histological and MR quantitative analysis of repaired tissue following microfracture treatment for knee joint osteochondritis dissecans in rabbit models

Abstract

Objective To quantitatively analyze the histological and MR images of repaired tissue (RT) following microfracture for knee joint osteochondritis dissecans (OCD) in rabbit models at different time points,make comparisons with the RT performances of joint debribement,explore the efficiency of the microfracture treatment for OCD. Methods Twenty-seven New Zealand rabbits were randomly assigned into 3 groups (sacrificed at the end of 3,5 and 7 weeks post-operation respectively),with 9 in each group.For each rabbit,one knee joint was made into an OCD model.In each group,6 were for microfracture treatment,and the other 3 were for joint debridement as control.MR scan,which mainly included sequences of 3D double echo steady state sequence (3DDESS) and T2-mapping,was taken at 3,5 and 7 weeks post-operation.The thickness index and T2value index of RT were calculated and T 2-mapping of repaired region was drafted.Then the operation sites were removed to make histological sections of HE and Masson staining.The modified O'Driscoll score system was employed to make semi-quantitative evaluation for the histological performance of RT.Comparisons were made with respect to MR and histological findings between two treatments at each time point using unpaired Student t test.Effects of two treatments were evaluated longitudinally by comparing the results of three time points using one-way ANOVA. Results The post-operation thickness indexes of two groups increased gradually (F=33.940,28.841,P<0.05),T 2value indexes decreased (F=80.183,206.206,P<0.05),and O'driscoll scores increased gradually (F=29.867,17.167,P<0.05).At each time point,the thickness index of microfracture was higher than that of debridement group (3-week:0.743±0.048 vs 0.624±0.013,t=4.077;5-week:0.813±0.031 vs 0.734±0.015,t=4.107;7-week:0.972±0.064 vs 0.777±0.039,t=4.782;P<0.05),and the defects of microfracture in 7-week group were almost fully recovered while the defects of the debridement in 7-week group were not.The T 2value index of microfracture group was lower than that of debridement group at 3-week point (1.338±0.043 vs 1.510±0.009,t=6.583,P<0.05),but it was higher than that of debridement group at 5-week and 7-week points (5-week:1.284±0.097 vs 1.116±0.068,t=2.663;7-week:0.916±0.036 vs 0.843±0.016,t=3.283;P<0.05).The O' Driscoll score of microfracture group was higher than that of joint debridement at every time point (3-week:7.167±0.753 vs 4.667±0.577,t=5.000;5-week:9.833±1.169 vs 7.667±0.577,t=2.960; 7-week:11.167±0.753 vs 8.333±1.155,t=4.520;P<0.05).For microfracture group,the RT was mainly repaired by fibrocartilage and got matured gradually with more production of well-distributed collagen fibrils; while for joint debridement group,the RT was mainly repaired by fibrous and scar tissue. Conclusions The post-operation repairing thickness and tissue composition of microfracture for OCD are superior to that of joint debridement.MR 3D-DESS and T2-mapping can show the thickness and tissue composition of the RT after OCD treatments,provide effective evaluation of repairing conditions,and they are of great importance on the OCD post-op follow-up. Key words: Osteochondritis dissecans; Magnetic resonance imaging; Histology