Implant Distribution Versus Implant Density in Lenke Type 1 Adolescent Idiopathic Scoliosis: Does the Position of the Screw Matter?

Abstract

Study Design: Retrospective study. Objective: Previous studies have demonstrated that increased implant density (ID) results in improved coronal deformity correction. However, low-density constructs with strategically placed fixation points may achieve similar coronal correction. The purpose of this study was to identify key zones along the spinal fusion where high ID statistically correlated to improved coronal deformity correction. Our hypothesis was that high ID within the periapical zone would not be associated with increased percent Cobb correction. Methods: We identified patients with Lenke type 1 curves with a minimum 2-year follow up. The instrumented vertebral levels were divided into 4 zones: (1) cephalad zone, (2) caudal zone, (3) apical zone, and (4) periapical zone. High and low percent Cobb correction groups were compared, high percent Cobb group was defined as percent correction >67%. Total ID, total concave ID, total convex ID, and ID within each zone of the curve were compared between the groups. A multivariable analysis was performed to identify independent predictors for coronal correction. Subsequently increased and decreased thoracic kyphosis (TK) groups were compared, increased TK was defined as post-operative TK being larger than preoperative TK and decreased TK was defined as post-operative TK being less than preoperative TK. Results: The cohort included 68 patients. The high percent Cobb group compared with the low percent Cobb group had significantly greater ID for the entire construct, the total concave side, the total convex side, the apical convex zone, the periapical zone, and the cephalad concave zone. The high percent Cobb group had greater pedicle screw density for the total construct, total convex side, and total concave side. In the multivariate model ID and pedicle screw density remained significant for percent Cobb correction. Ability to achieve coronal balance was not statistically correlated to ID ( P = .78). Conclusions: Increased ID for the entire construct, the entire convex side, the entire concave side, and within each spinal zone was associated with improved percent Cobb correction. The ability to achieve coronal balance was not statistically influence by ID. The results of this study support that increasing ID along the entire length of the construct improves percent Cobb correction.

Post-marketing surveillance on safety and efficacy of posterior spinal correction and fusion with the CD Horizon Solera instrumentation for adolescent idiopathic scoliosis. A retrospective cohort study

“…Some find a significantly higher curve correction in high-density constructs, while other studies contradict this [ 21 , 24 , [33] , [34] , [35] , [36] , [37] , [38] , [39] , [40] ]. This may be caused by the flexibility of the curves and screw position [38] , [39] , [40] , [41] . However, in high-density constructs there is an increased risk of screw misplacement which can lead to neurological, vascular or visceral injury.…”

“…In all-screw constructs, literature describes different results on curve correction. Some find a significantly higher curve correction in high-density constructs, while other studies contradict this [21,24,[33][34][35][36][37][38][39][40]. This may be caused by the flexibility of the curves and screw position [38][39][40][41].…”

Perioperative outcome and complications following single-staged Posterior Spinal Fusion (PSF) using pedicle screw instrumentation in Adolescent Idiopathic Scoliosis (AIS): a review of 1057 cases from a single centre

“…Our first postoperative lateral view radiograph will be taken at 8–12 weeks follow up. Previous studies have been inconsistent in demonstrating effect of screw density (low-density versus high-density) on postoperative kyphosis [ 58 , 59 ]. Future studies are warranted to further explore these issues.…”

Letter to the Editor Regarding “Outcome of Posterior-Only Approach for Severe Rigid Scoliosis: A Retrospective Report” by Mirzashahi et al

“…Several strategies have been described to afford similar correction while cutting down on the number of pedicle screws used: interval fixation, skipped fixation, periapical-dropout fixation, and ''key'' pedicle screw placement. 9 The general consensus is to deploy a high implant density at the apex and juxta-apical zones and skipping some points of fixation as one moves cephalad or caudad. However, when correction is being attempted through multilevel Ponte's osteotomies, I feel that a high implant density should be deployed through the entirety of at least the concave side to effectively harness the forces of correction that are going to be distributed at multiple levels.…”