Spinal shape modulation in a porcine model by a highly flexible and extendable non-fusion implant system

Purpose: In vivo evaluation of scoliosis treatment using a novel approach in which two posterior implants are implanted: XSLAT (eXtendable implant correcting Scoliosis in LAT bending) and XSTOR (eXtendable implant correcting Scoliosis in TORsion). The highly flexible and extendable implants use only small, but continuous lateral forces (XSLAT) and torques (XSTOR), thereby allowing growth and preventing fusion. Methods: Since (idiopathic) scoliosis does not occur spontaneously in animals, the device was used to induce a spinal deformity rather than correct it. Six of each implants were tested for their ability to induce scoliotic deformations in 12 growing pigs. Each implant spanned six segments and was attached to three vertebrae using sliding anchors. Radiological and histological assessments were done throughout the 8-week study. Results: In all animals, the intended deformation was accomplished. Average Cobb angles were 19° for XSLAT and 6° for XSTOR. Average apical spinal torsion was 0° for XSLAT and 9° for XSTOR. All instrumented segments remained mobile and showed 20 % growth. Moderate degeneration of the facet joints was observed and some debris was found in the surrounding tissue. Conclusions: The approach accomplished the intended spinal deformation while allowing growth and preventing fusion.