In Vitro Biomechanical Validation of a Self-Adaptive Ratchet Growing Rod Construct for Fusionless Scoliosis Correction. Issue 21 (1st November 2019)

• Record Type: Journal Article
• Authors: Chen, Zong-Xing; Kaliya-Perumal, Arun-Kumar; Niu, Chi-Chien; Wang, Jaw-Lin; Lai, Po-Liang
• Is Part Of: Spine. Volume 44:Issue 21(2019)
• Publication Date: 2019-11-01
• Subjects: growth and development -- in vitro techniques -- laboratory animal science -- scoliosis -- spinal curvatures; Spine -- Abnormalities -- Periodicals; Spine -- Diseases -- Periodicals; Spine -- Surgery -- Periodicals; 616.73005
• DOI: 10.1097/BRS.0000000000003119
• Languages: English
• ISSNs: 0362-2436

Abstract

Abstract : Study Design: In vitro biomechanical evaluation of a novel self-adaptive unidirectional ratchet growing rod (RGR) system. Objective: The aim of this study was to propose and biomechanically validate a novel RGR construct in vitro using porcine thoracic spines and calculate the tensile force required to elongate the RGR with springs, without springs, and with soft tissue encapsulation (induced in vivo in rabbits). Summary of Background Data: Literature lacks clear consensus regarding the implant of choice for early-onset scoliosis. Multiple systems are currently available, and each has its own advantages and disadvantages. Therefore, studying novel designs that can credibly accommodate growth and curb deformity progression is of principle importance. Methods: In vitro biomechanical motion tests were done using six porcine thoracic spines with pedicle screws at T3 and T8. A pure moment of ±5 Nm was loaded in lateral bending (LB) and flexion-extension. Range of motion (ROM) and neutral zone (NZ) of each specimen was determined after connecting the free movable growing rods (FGRs), RGRs, and standard rods (SRs). Tensile tests were done to measure the force required to elongate the RGR with springs, without springs, and with soft tissue encapsulation (induced in vivo in rabbits). Results: Global ROM, implanted T3-T8 ROM, and the NZ of specimens with FGRs and RGRs were significantly higher than that with SRs. The RGRs favored unidirectional elongation in both LB and flexion. The tensile forces required for elongating the RGR without springs, with springs, and with soft tissue capsulation (by a scaled unit of 3 mm) were 3 ± 1.3 N, 10.5 ± 0.4 N, and 48.4 ± 14.4 N, respectively. Conclusion: The RGR could stabilize and favor unidirectional elongation of the implanted spinal column when appropriate forces were present. There was no device failure as far as we have studied and it is anticipated that, with further safety and feasibility assessment, RGRs could be adapted for clinical use. Level of Evidence: N/A Abstract : A self-adaptive ratchet growing rod was designed and in vitro biomechanical tests were conducted using porcine spines. We noted that the ratchet growing rods favored unidirectional elongation when appropriate forces were present. Therefore, it is perceived that, if normal growth provides adequate forces, ratchet growing rods can self-elongate and lengthening procedures can be avoided.