Effect of rod stiffness and screw density on correction rate of Lenke type 1 adolescent idiopathic scoliosis

Abstract

Objective To investigate the effect of rod stiffness and screw density on correction rate in Lenke type 1 adolescent idiopathic scoliosis (AIS).Methods A total of 48 patients with Lenke type 1 AIS,who had undergone surgical correction with pedicle screws from July 2008 to July 2012,were analyzed in this study.There were 10 males and 38 females,aged from 12 to 21 years (average,15.65±3.21 years).The standing anteroposterior and lateral X-rays of whole spine were obtained before surgery and at 1 week after surgery.The following parameters were measured:1) coronal Cobb angle of the major curve; 2) sagittal Cobb angle (T5-T12); 3) number of fusion segments and screws instrumented vertebrae.All cases were divided into 4 groups:low stiffness rod with low screw density (number of screws per fusion segment/2＜0.60) group (13 cases); low stiffness rod with high screw density (number of screws per fusion segment/2＞0.60) group (10 cases); high stiffness rod with high screw density group (14 cases); high stiffness rod with low screw density group (11 cases).The coronal and sagittal correction rates were compared among 4 groups.Results The correction rate of coronal and sagittal Cobb angle was respectively 79.78％±6.89％ and-53.02％±12.37％ in low stiffness rod with low screw density group,80.09％±6.28％ and-3.76％±41.58％ in low stiffness rod with high screw density group,84.48％±8.06％ and 46.25％±49.81％ in high stiffness rod with high screw density group,and 79.35％±6.80％ and-8.63％±42.69％ in high stiffness rod with low screw density group.There was no significantly statistical difference in coronal correction rate between four groups (F=1.533,P=0.219).The difference in sagittal correction rate was not significant between low stiffness rod with high screw density group and high stiffness rod with low screw density group (-3.76％±41.58％ and-8.63％±42.69％,P=0.654),but significant among other groups.Conclusion For Lenke type 1 AIS patients,rod stiffness and screw density mainly influence the sagittal correction rate rather than coronal correction rate.High stiffness rod and high screw density could significantly increase the sagittal plane correction rate. Key words: Scoliosis; Adolescent; Orthopedic procedures