Biomechanical Analysis of a Growing Rod with Sliding Pedicle Screw System for Early-Onset Scoliosis

Abstract

Early-onset scoliosis (EOS) remains a challenging condition for which current nonfusion surgeries require iterative lengthening surgeries. A growing rod with sliding pedicle screw system (GRSPSS) was developed to treat spinal deformities without repeated operative lengthening. This study was performed to evaluate whether GRSPSS had similar stability as a conventional pedicle screw system to maintain deformity correction. A serial-linkage robotic manipulator with a six-axis load cell positioned on the end-effector was utilized to evaluate the mechanical stability of the GRSPSS versus conventional fixed scoliosis instrumentation. Ten skeletally mature thoracic female Katahdin sheep spines (T4-L1) were subjected to 2.5 Nm of flexion-extension (FE), lateral bending (LB), and axial rotation (AR) in 2° increments for each state. The overall range of motion (ROM), apical segment ROM, and stiffness were calculated and reported. A two-tailed paired t-test was used to detect significant differences (p<0.05) between the fixed group and GRSPSS fixation. There were no significant differences in overall range of motion (ROM), apical segment ROM, or stiffness for FE or LB between the GRSPSS group and fixed group. In AR, the GRSPSS group showed increased ROM compared to the fixed group for the overall spine (36.0° versus 19.2°, p<0.01) and for the instrumented T8-T10 segments (7.0° versus 2.9°, p=0.02). Similarly, the fixed rod elastic zone (EZ) stiffness was significantly greater than the GRSPSS EZ stiffness (0.29 N/m versus 0.17 N/m, p<0.001). The space around the rod allows for the increased AR observed with the GRSPSS fusion technique and is necessary for axial growth. The GRSPSS fusion model shows equivalent flexion and LB stability to current fusion models and represents a stable fusion technique and may allow for longitudinal growth during childhood.

Kyphectomy and Sliding Growing Rod Technique in patients with congenital lumbar kyphosis deformity with myelomeningocele

“…In a study by Ouyand et al, the stability of the sliding growing rod technique was evaluated on sheep spine, the technique protected the stability as much as a totally xated system also in movements like exion, extension, and lateral bending along with posterior instrumentation and fusion performance. In the literature, the outcomes of sliding growing double rod technique is more successful with less complication rates when compared to the single growing rod system in patients with early onset scoliosis and congenital scoliosis [17].…”

Biomechanical Comparison of Different Numbers and Configurations of Cross-Links in Long-Segment Spinal Fixation—An Experimental Study in a Porcine Model

“…From a physical perspective, the sagittal and coronal planes can be controlled by segmental screws with rigid rods; however, only fixed orthogonal devices prevent rod rotation. 23,24 In a short-segment fusion study, Peltier et al showed that constructs with one cross-link were 31% stiffer and those with 2 cross-links were 43% stiffer in torsion compared with constructs without cross-links. 9 In our results, axial stiffness was significantly higher in Group D than Group C, and similar results were observed between Groups D and E. Our results demonstrated that in a long-segment spinal construct, greater rotational rigidity may be achieved in a position-dependent manner by increasing the separation distance for the 2 crosslink configuration (Group C compared with Group D).…”

“…From a physical perspective, the sagittal and coronal planes can be controlled by segmental screws with rigid rods; however, only fixed orthogonal devices prevent rod rotation. 23,24…”

Clinical and radiological results of kyphectomy and sliding growing rod surgery technique performed in children with myelomeningocele

“…Ouyang et al compared this technique with a posteriorly fused sheep spine to evaluate the stability of the SGR technique in a study conducted in sheep spine. These researchers showed that the SGR technique has stability with respect to flexion, extension, and lateral bending movements in addition to the performance of posterior instrumentation and fusion to the spine [ 20 ].…”