Biomechanics of the Scoliotic Spine

Non-fusion operative methods for the treatment of degenerative spinal diseases have tremendous potential to increase patient quality of life. In addition to the fact that motion is preserved or restored, a natural load transfer to the adjacent segments is sustained. This is important, as clinical experience shows that fusion of motion segments frequently entail adjacent level degeneration. However, non-fusion implants are challenging, particularly for the treatment of spinal deformities, in which several segments are commonly affected. A better understanding of the mechanical properties of healthy and pathological motion segments is essential.

A parallel kinematic robot – the SpineBot – has been developed to accurately measure the three-dimensional segmental stiffness of patient’s spine in-vivo. SpineBot transmits load to individual vertebra using pedicle screws implanted as part of the corrective procedure. The six DoFs of the robot allow an arbitrary motion to be applied to adjacent vertebrae and an integrated force-torque sensor measures the corresponding mechanical response. The small, compact, and lightweight parallel kinematic construction enables the device to apply moments of over 4 Nm to a FSU with a ±10° range of motion. The SpineBot will be used to quantify the stiffness at different levels of the spine of scoliosis patients as well as to compare stiffness of lumbar spinal stenosis patients before and after decompression surgery.

Numerical models of the scoliotic spine have also been developed for the design of motion preserving non-fusion treatment to correct spinal deformities. These models are unique because they consider patient-specific geometry and mechanical properties derived from intraoperative measurements. The finite element model has been used to design a new dynamic spinal anchoring system to complement a novel growing implant. In addition, these numerical simulation tools enable the optimization of the surgical procedure on a patient-specific basis.