The Role Of Growth Plate In Correction Of Scoliosis Using Staple And Relative Quantitative Study

Objective:To investigate the role of vertebral growth plates in correction of scoliosis using Staple by quantifying the effect of Staple on growth rate and histomorphology of vertebral growth plates in scoliosis and the correlation between the change of growth plate and correction of scoliosis,and to provide experimental date for the clinical application of Staple in correction of scoliosis.Background:Biomechanical factors play a significant role in the development and progression of scoliosis,and asymmetrical loading can cause progression of deformity in a "vicious cycle".Human vertebrae grow by endochondral ossification,similar to long bones."Hueter-Volkmann" law states that growth is retarded by mechanical compression of the growth plate and stimulated by distraction or reduced compression,which is the theoretical basis of the Staple technique.Implanted Staples inhibit the vertebrae growth by imposing sustained compression on the growth plates.In this way,Staple can modulate the spine growth in short segments form.Animal experiments and clinical research about Staple have indicated that Staple may have certain curative effect in correcting scoliosis.However,quantitative analysis about the effect of Staple on abnormal vertebral growth plate is till lacking during the correction of scoliosis.In addition, the correlation between the change in growth plate and the degrees of scoliosis correction also needs further study.Methods:Experimental scoliosis was created in 10 juvenile female goats using unilateral pedicle screws asymmetric tethering.After a period of 8-10weeks,goats were randomized into Staple treated(n=5)and untreated(n=5)groups.All tethers were removed in both groups and Staple group underwent anterior vertebral stapling with 4-5 shape memory alloy Staples along the convexity of the maximal curvature after posterior tether being removed.All goats were observed for an additional 8-13 weeks and serial radiographs were used to document Cobb angles of the maximal curvature.The fluorochromes Oxytetracycline and Calcein were administered systemically 18 and 3 days prior to death to label the ossifying front under the growth plates.Superior intervertebral disc of apical vertebra and two adjacent growth plates were completely harvested in all goats.All specimens were embedded with polymethyl methacrylate(PMMA)and sliced undecalcified. Growth rates of the vertebral growth plates were calculated by measuring the distance between the two fluorescent markers with fluorescence microscope.And then the correction angles of stapled vertebrae were estimated according to the difference of growth rates between two sides.The proliferative zonal height,the hypertrophic zonal height,the amount of increase in chondrocyte height and the final height of hypertrophic chondrocytes were also measured in slides stained with toluidine blue.Results:9 of 10 tethered goats had progressive scoliotic curves of significant magnitude during 8-10weeks of tethering.In the additional 8-13weeks for treatment,the scoliosis in Staple treated group(n=5)measured 34.8±12.4°at the beginning and 15.6±11.7°at the end(P＜0.05),whereas Cobb angles in untreated group(n=4)almost had no change.The correction angle of stapled apical vertebra was 0.017±0.006°per day on average,which had significant correlation with correction degree of main curvature(r=0.970,P=0.006). Correction of apical vertebra contributed 13.18±3.04%to the total correction. Providing the capacity of every Staple for correction was equal,all the stapled vertebrae contributed 61.54±19.91%to the total.In Staple treated group,the growth rate,the hypertrophic zonal height,the amount of increase in chondrocyte height and the final height of hypertrophic chondrocytes of the concavity were all higher than those of stapled side,while there was no difference in the proliferative zonal height of two sides.In untreated group,all these measurements of the concavity did not differ significantly from those of the convexity.For all the date, the proliferative zonal height,the hypertrophic zonal height,the amount of increase in chondrocyte height and the final height of hypertrophic chondrocytes correlated with the growth rate significantly(correlation coefficients were 0.626[P=0.009],0.654[P=0.006],0.880[P＜0.001],0.848[P＜0.001]respectively). According to multiple linear regression of the growth rate,coefficients for the proliferative zonal height and the final height of hypertrophic chondrocytes were 0.023 and 0.247 respectively,and the regression model and coefficients all had statistical significance.Conclusions:1.Staple can significantly alter the growth rates of two sides of vertebrae in scoliosis with the growth rate of concavity exceeding the one of convexity,which results in correction of deformity.According to the difference between the growth rates of both sides,the correction angle of stapled apical vertebra can be calculated,which is 0.017°per day and contributes 13.18%to the total correction.And contribution of all the stapled vertebrae to the whole may probably be 61.54%at least.2.Staple can diminish the hypertrophic zonal height and the degree of enlargement of hypertrophic chondrocyte of the convexity,and reverse the intrinsical difference in the hypertrophic zone.The vertebral growth rate may probably be expressed as follows:R_growth=0.023~* Prolif-Z_ht+0.247~* H_final-2.670,in which R_growth represents growth rate,and Prolif-Z_ht represents the proliferative zonal height,and H_final represents the final height of hypertrophic chondrocytes.