Biomechanical comparison of fusionless growth modulation corrective techniques in pediatric scoliosis

Abstract

Fusionless growth-sparing implants for the treatment of adolescent idiopathic scoliosis (AIS) attempt to manipulate vertebral growth to restore spinal alignment. This study critically explores different implants utilizing a human spine scoliotic finite element model (FEM). Stainless steel (SS) and shape memory alloy (SMA) staples and flexible tethers were modeled and alternatively integrated around the apex of the convexity of the scoliotic model. Stress profiles over vertebral growth plates were obtained. Two years of growth was simulated with non-instrumented and instrumented models, as curvature changes were quantified. Apical asymmetrical stresses in non-instrumented and instrumented scoliotic models with SS staple, flexible tether, and SMA staple were 0.48, 0.48, 0.23, and 0.33 MPa, respectively. Patient data and non-instrumented model progressed from 28° to 62° of thoracic Cobb angle over 2 years. Simulated projected long-term thoracic Cobb angles of instrumented models are 31° with SS staple, 31° with flexible tether, and 34° with SMA staple. Initial implant compression achieved during instrumentation provided a significant influence on initial and long-term spinal profiles. The developed FEM provides an effective platform with which to explore, critique, and enhance fusionless growth-sparing techniques.

Finite element simulation of a scoliotic spine with periodic adjustments of an attached growing rod

“…The model is composed of 17 vertebral bodies (T1-L5) and 16 intervertebral discs using linear, homogeneous and isotropic material properties, their values are presented in (Table I) [9,11]. The SFEM was developed utilizing Abaqus 6.11-1 (Dassault Systemes).…”

“…Based on the Hueter-Volkman law for bone growth modulation, recent research approaches have utilized FEA in order to simulate the progression of non-instrumented idiopathic scoliosis [8][9][10]. Mark et al has modeled the growth modulation corrective techniques in pediatric scoliosis using the finite element method [11]. However, to our knowledge, the finite element method has not been applied to simulate the spine growing rod behavior in the typical surgical procedure.…”

On the relevance of using homogeneous biphasic models to characterize the mechanical behavior of the growth plate

“…Imposing different load states might reveal that the TIBPE model identified with UC and CC is unable to fit within acceptable limits experimental data generated from other load cases. Having a reliable growth plate constitutive model is of paramount importance since the TIBPE model could be used in 3D FE simulations for the development of surgical treatment for pediatric skeletal deformities, such as fusionless techniques with growth plate stapling for the early treatment of moderate adolescent idiopathic scoliosis (Driscoll et al 2011). Finally, from a morphological point of view, the chondrocytes of the proliferative zone are arranged in columns, and the extracellular matrix might exhibit a transversely isotropic behavior.…”

Development of a Detailed Volumetric Finite Element Model of the Spine to Simulate Surgical Correction of Spinal Deformities

“…Using volumetric and rigid body models, Aubin et al have pioneered work in the understanding of the pathomechanism of scoliosis [1–5], the mechanics of spondylolisthesis [6], the correction forces offered during scoliotic brace treatment [7–9], and the performance of next generation of minimally invasive growth modulation devices [10, 11]. Using rigid body models, Aubin et al also simulated many times the surgical correction of spinal deformities via the introduction of rods and screw [12, 13] while others followed suit [14–16].…”