High Screw Density Research Articles

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

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

Surgical treatment of Scheuermann’s kyphosis using a combined antero-posterior strategy and pedicle screw constructs: efficacy, radiographic and clinical outcomes in 111 cases

There is sparse literature on how best to correct Scheuermann's kyphosis (SK). The efficacy of a combined strategy with anterior release and posterior fusion (AR/PSF) with regard to correction rate and outcome is yet to be determined. A review of a consecutive series of SK patients treated with AR/PSF using pedicle screw-rod systems was performed. Assessment of demographics, complications, surgical parameters and radiographs including flexibility and correction measures, proximal junctional kyphosis angle (JKA+1) and spino-pelvic parameters was performed, focusing on the impact of curve flexibility on correction and clinical outcomes. 111 patients were eligible with a mean age of 23years, follow-up of 24months and an average of eight levels fused. Cobb angle at fusion level was 68° preoperatively and 37° postoperatively. Flexibility on traction films was 34% and correction rate 47%. Postoperative and follow-up Cobb angles were highly correlated with preoperative bending films (r=0.7, p<0.05). Screw density rate was 87%, with increased correction with higher screw density (p<0.001, r=0.4). Patients with an increased junctional kyphosis angle (JKA+1) were at higher risk of revision surgery (p=0.049). 22 patients sustained complication, and 21 patients had revision surgery. 42 patients with ≥24months follow-up were assessed for clinical outcomes (follow-up rate for clinical measures was 38%). This subgroup showed no significant differences regarding baseline parameters as compared to the whole group. Median approach-related morbidity (ArM) was 8.0%, SRS-sum score was 4.0, and ODI was 4%. There was a significant negative correlation between the SRS-24 self-image scores and the number of segments fused (r=-0.5, p<0.05). Patients with additional surgery had decreased clinical outcomes (SRS-24 scores, p=0.004, ArM, p=0.0008, and ODI, p=0.0004). The study highlighted that AR/PSF is an efficient strategy providing reliable results in a large single-center series. Results confirmed that flexibility was the decisive measure when comparing surgical outcomes with different treatment strategies. Findings indicated that changes at the proximal junctional level were impacted by individual spino-pelvic morphology and determined by the individually predetermined thoracolumbar curvature and sagittal balance. Results stressed that in SK correction, reconstruction of a physiologic alignment is decisive to achieving good clinical outcomes and avoiding complications.

Relationship of forces acting on implant rods and degree of scoliosis correction

BackgroundAdolescent idiopathic scoliosis is a complex spinal pathology characterized as a three-dimensional spine deformity combined with vertebral rotation. Various surgical techniques for correction of severe scoliotic deformity have evolved and became more advanced in applying the corrective forces. The objective of this study was to investigate the relationship between corrective forces acting on deformed rods and degree of scoliosis correction. MethodsImplant rod geometries of six adolescent idiopathic scoliosis patients were measured before and after surgery. An elasto-plastic finite element model of the implant rod before surgery was reconstructed for each patient. An inverse method based on Finite Element Analysis was used to apply forces to the implant rod model such that it was deformed the same after surgery. Relationship between the magnitude of corrective forces and degree of correction expressed as change of Cobb angle was evaluated. The effects of screw configuration on the corrective forces were also investigated. FindingsCorrective forces acting on rods and degree of correction were not correlated. Increase in number of implant screws tended to decrease the magnitude of corrective forces but did not provide higher degree of correction. Although greater correction was achieved with higher screw density, the forces increased at some level. InterpretationThe biomechanics of scoliosis correction is not only dependent to the corrective forces acting on implant rods but also associated with various parameters such as screw placement configuration and spine stiffness. Considering the magnitude of forces, increasing screw density is not guaranteed as the safest surgical strategy.

Does Higher Screw Density Result in Increased Curve Correction and Improved Clinical Outcomes in Adolescent Idiopathic Scoliosis (AIS)

Does Higher Screw Density Result in Increased Curve Correction and Improved Clinical Outcomes in Adolescent Idiopathic Scoliosis (AIS)