Main thoracic curve adolescent idiopathic scoliosis: association of higher rod stiffness and concave-side pedicle screw density with improvement in sagittal thoracic kyphosis restoration

Abstract

<jats:sec> <jats:title>OBJECT</jats:title> <jats:p>The aim of this study was to evaluate the effects of rod stiffness and implant density on coronal and sagittal plane correction in patients with main thoracic curve adolescent idiopathic scoliosis (AIS).</jats:p></jats:sec> <jats:sec> <jats:title>METHODS</jats:title> <jats:p>The authors conducted a retrospective study of 77 consecutive cases involving 56 female and 21 male patients with Lenke Type 1 main thoracic curve AIS who underwent single-stage posterior correction and instrumented spinal fusion with pedicle screw fixation between July 2009 and July 2012. The patients' mean age at surgery was 15.79 ± 3.21 years. All patients had at least 1 year of follow-up. Radiological parameters in the coronal and sagittal planes, including Cobb angle of the major curve, side-bending Cobb angle of the major curve, thoracic kyphosis (TK), correction rates, and screw density, were measured and analyzed. Screw densities (calculated as number of screws per fusion segment × 2) of &lt; 0.60 and ≥ 0.60 were defined as low and high density, respectively. Titanium rods of 5.5 mm and 6.35 mm diameter were defined as low and high stiffness, respectively. Patients were divided into 4 groups based on the type of rod and density of screw placement that had been used: Group A, low-stiffness rod with low density of screw placement; Group B, low-stiffness rod with high density of screw placement; Group C, high-stiffness rod with low density of screw placement; Group D, high-stiffness rod with high density of screw placement.</jats:p></jats:sec> <jats:sec> <jats:title>RESULTS</jats:title> <jats:p>The mean coronal correction rate of the major curve, for all 77 patients, was (81.45% ± 7.51%), and no significant difference was found among the 4 groups (p &gt; 0.05). Regarding sagittal plane correction, Group A showed a significant decrease in TK after surgery (p &lt; 0.05), while Group D showed a significant increase (p &lt; 0.05); Group B and C showed no significant postoperative changes in TK (p &gt; 0.05). The TK restoration rate was highest in Group D and lowest in Group A (A, −39.32% ± 7.65%; B, −0.37% ± 8.25%; C, −4.04% ± 6.77%; D, 37.59% ± 8.53%). Screw density on the concave side was significantly higher than that on the convex side in all the groups (p &lt; 0.05).</jats:p></jats:sec> <jats:sec> <jats:title>CONCLUSIONS</jats:title> <jats:p>For flexible main thoracic curve AIS, both rods with high stiffness and those with low stiffness combined with high or low screw density could provide effective correction in the coronal plane; rods with high stiffness along with high screw density on the concave side could provide better outcome with respect to sagittal TK restoration.</jats:p></jats:sec>

Effects of Multilevel Facetectomy and Screw Density on Postoperative Changes in Spinal Rod Contour in Thoracic Adolescent Idiopathic Scoliosis Surgery

“…However, the effect of implant density on sagittal plane correction and TK restoration has been reported in only a few studies, and the results have been controversial [12,14,19]. Larson et al [12] demonstrated that decreased TK was correlated with increased screw density for Lenke type 1 and 2 curves.…”

“…Larson et al [12] demonstrated that decreased TK was correlated with increased screw density for Lenke type 1 and 2 curves. Conversely, Liu et al [14] documented that higher screw density provided better TK restoration than low screw density. Recently, Sudo et al [9] also documented that in patients with preoperative TK < 15°, a significant positive correlation was found between the change in TK and screw density, whereas no correlation was found in patients with TK ≥15°, suggesting that screw density had a positive effect on TK restoration in patients with hypokyphotic thoracic spines.…”

“…Some studies have investigated the correlation between AIS curve correction and destabilization procedures such as multilevel facetectomy [10] or the number of fixation anchors, such as PS density [11–14]. Implant rod curvature will also influence the postoperative TK.…”

Does higher screw density improve radiographic and clinical outcomes in adolescent idiopathic scoliosis? A systematic review and pooled analysis

“…Bharucha et al explained that most of the cases in the LD group were their earlier cases, with the latter cases having an HD screw pattern, and increasing experience with implanting pedicle screws led to a decreased operative time. Finally, the data from the study by Liu et al 20 were divided into 2 subgroups according to the diameter of the titanium rods: low stiffness (5.5 mm) and high stiffness (6.35 mm).…”

“…In addition, high-density (HD) screw constructs have been shown to result in better restoration of thoracic kyphosis and better spinal appearance questionnaire (SAQ) scores. 12,20,28 However, a large body of research has shown that low-density (LD) screw constructs can provide similar radiographic or clinical outcomes. 3,7,[22][23][24][25]30,33 Furthermore, the number of pedicle screws placed has been shown to be an independent predictor of increased total cost for patients undergoing AIS correction procedures.…”