Abstract
Abstract Degenerative spine problems and spinal deformities have high socio-economic impacts. Current surgical treatment is based on bony fusion that can reduce mobility and function. Precise descriptions of the biomechanics of normal, deformed, and degenerated spinal segments under in vivo conditions are needed to develop new approaches that preserve spine function. This study developed a system that intraoperatively measures the three-dimensional segmental stiffness of patient's spine. SpineBot, a parallel kinematic robot, was developed to transmit loads to adjacent vertebrae. A force/torque load cell mounted on the SpineBot measured the moment applied to the spinal segment and calculated segmental stiffnesses. The accuracy of SpineBot was characterized ex vivo by comparing its stiffness measurement of five ovine specimens to measurements obtained with a reference spinal testing system. The SpineBot can apply torques up to 10 N·m along all anatomical axes with a total range of motion of about 11.5 deg ± 0.5 deg in lateral bending, 4.5 deg ± 0.3 deg in flexion/extension, and 2.6 deg ± 0.5 deg in axial rotation. SpineBot's measurements are noisier than the reference system, but the correlation between SpineBot and reference measurements was high (R2 > 0.8). In conclusion, SpineBot's accuracy is comparable to that of current reference systems but can take intraoperative measurements. SpineBot can improve our understanding of spinal biomechanics in patients who have the pathology of interest, and take these measurements in the natural physiological environment, giving us information essential to developing new “nonfusion” products.
Highlights
Back pain and degenerative spine problems are the main reasons people stop working and take early pensions, and the most common reason for back surgery [1,2,3]
The range of motion was calculated for each load case based on all the SpineBot measurements performed on the ovine specimens
The SpineBot accurately measured the stiffness of the three springs for measurements performed in the lateral bending direction (Fig. 3(a)); relative stiffness measurement error was under 5%
Summary
Back pain and degenerative spine problems are the main reasons people stop working and take early pensions, and the most common reason for back surgery [1,2,3]. Even in young people with scoliosis, operative treatment generally fuses the bone in deformed sections of the spinal column This method stabilizes the spine with metallic implants so motion segments can ossify. New strategies for preserving or restoring spine function include artificial discs, interspinous process spacers, posterior transpedicular dynamic stabilization, and target-oriented conservative approaches. These new technologies could be used for better advantage if we knew more about the kinematic and dynamic properties of the spine, and especially the complex force–motion relationship in normal, degenerative, and scoliotic spinal segments under in vivo conditions
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