Mechanical Growth Modulation for Scoliosis Correction

Problems Associated with Scoliosis Assessment and Treatment

Spontaneously arising adolescent scoliosis is a complex structural 3D spinal deformity. Severe scoliosis can lead to symptoms such as pain accompanied by cardiopulmonary compromise. Currently, there are no pediatric spinal implants that can correct scoliosis in children without a fusion surgery. Additionally, 3D morphological analyses are rarely available, even though scoliosis has long been recognized as a three-dimensional deformity. The third dimension is critically important, but currently scoliosis is characterized using two-dimensional X-rays.

This study introduces growth modulation by applying anterolateral spinal tethers in a growing mini-pig model. This technique redirects growth, slowing growth at the outer (concave) side of the curve while allowing for further growth at the inner (convex) side. This procedure leads to natural straightening of the spine with growth. Advanced 3D imaging techniques were used to better understand mechanical spinal growth modulation and its efficacy. No previous research thoroughly or systematically describes these 3D alterations using 3D CT studies for vertebra reconstruction, 3D micro-CT studies for growth and end plate evaluation and MRI studies for disc assessment.

3D Reconstructions for a Full Description of Spinal Deformity

Surface reconstructions of individual vertebra and disc space assessment from CT scans, disc evaluation from MRI, and growth and end plate characterization from micro-CT were created using the Mimics Innovation Suite. Once complete, the team exported and loaded STL models of each vertebra, disc, and end plate to a custom MATLAB application. The 3D reconstruction enabled them to collect an entire range of critical data for the spinal deformations. This included calculations about principal axes and points of interest for the vertebra, angles for vertebral body wedging, metrics for spinal deformation, and more.

Micro-CT reconstruction of the growth plate

“The Mimics Innovation Suite proved invaluable for getting us the 3D spinal representations needed for our study. 3D models were quickly and reliably generated and moreover, we were able to import data from a number of different modalities: MRI, CT, and micro-CT. Manual adjustments and measurements were easy to carry out and the variety of export options allowed us to use the models for further data processing.” 
(Diana Glaser, Orthopedics Biomechanics Research Center/ Rady Children’s Hospital, USA)

Improved Data Can Lead to Improved Treatment

In ANSYS the muscle was modeled using the two-parameter Mooney-Rivlin material model because of its computational efficiency. The aim was to compute the pressure of the socket on the stump and, ideally, to achieve a homogenous pressure distribution. The team came up with a clever alternative to this computationally hard task, which provided them with a simpler model with nearly the same results. Optimizing this, however, is still part of their future work.