Steven D Voinier1, Michael J Agnew2, Jonathan J Carmouche3. 1. Virginia Polytechnic Institute and State University, Department of Mechanical Engineering, Durham Hall, 1145 Perry St, Blacksburg, VA 24061, USA. Electronic address: voinier3@vt.edu. 2. Department of Industrial Systems Engineering, Virginia Polytechnic Institute and State University, Durham Hall, 1145 Perry St, Blacksburg, VA 24061, USA. Electronic address: mjagnew@vt.edu. 3. Carilion Clinic, Department of Orthopaedic Surgery, 3 Riverside Circle, Roanoke, VA 24016, USA. Electronic address: jjcarmouche@carilionclinic.org.
Abstract
BACKGROUND: The 1-10% prevalence rate of adult scoliosis frequently requires expensive therapy and surgical treatments and demands further research into the disease, especially with an aging population. Most studies examining the mechanics of scoliosis have focused on in vitro testing or computer simulations. This study quantitatively defined the passive stiffness properties of the in vivo scoliotic spine in three principle anatomical motions and identified differences relative to healthy controls. METHODS: Adult scoliosis (n = 14) and control (n = 17) participants with no history of spondylolisthesis, spinal fracture, or spinal surgery participated in three different tests (torso lateral side bending, torso axial rotation, and torso flexion/extension) that isolated mobility to the in vivo lumbar spine. The spinal stiffnesses and spinal neutral zone width were calculated. These parameters were statistically compared between factor of population and within factor of direction. FINDINGS: Torque-rotational displacement data were fit using a double sigmoid function, resulting an in excellent overall fit (Avg. R2 = 0.95). There was a significant interaction effect between populations when comparing axial twist neutral zone width vs. lateral bend neutral zone width and axial twist stiffness vs. lateral bend stiffness. The axial twist neutral zone width magnitude was significantly larger in scoliosis patients. INTERPRETATION: The present study is the first investigation to quantify the whole trunk neutral zone of the scoliotic lumbar spine. Future research is needed to determine if lumbar spine mechanical characteristics can help explain progression of scoliosis and complement scoliosis classification systems.
BACKGROUND: The 1-10% prevalence rate of adult scoliosis frequently requires expensive therapy and surgical treatments and demands further research into the disease, especially with an aging population. Most studies examining the mechanics of scoliosis have focused on in vitro testing or computer simulations. This study quantitatively defined the passive stiffness properties of the in vivo scoliotic spine in three principle anatomical motions and identified differences relative to healthy controls. METHODS: Adult scoliosis (n = 14) and control (n = 17) participants with no history of spondylolisthesis, spinal fracture, or spinal surgery participated in three different tests (torso lateral side bending, torso axial rotation, and torso flexion/extension) that isolated mobility to the in vivo lumbar spine. The spinal stiffnesses and spinal neutral zone width were calculated. These parameters were statistically compared between factor of population and within factor of direction. FINDINGS: Torque-rotational displacement data were fit using a double sigmoid function, resulting an in excellent overall fit (Avg. R2 = 0.95). There was a significant interaction effect between populations when comparing axial twist neutral zone width vs. lateral bend neutral zone width and axial twist stiffness vs. lateral bend stiffness. The axial twist neutral zone width magnitude was significantly larger in scoliosispatients. INTERPRETATION: The present study is the first investigation to quantify the whole trunk neutral zone of the scoliotic lumbar spine. Future research is needed to determine if lumbar spine mechanical characteristics can help explain progression of scoliosis and complement scoliosis classification systems.