The impact of intra-operative sternum vertical displacement on the sagittal curves of the spine.

Patient positioning is an important step in spinal surgeries. Many surgical frames allow for lumbar lordosis modulation due to lower limb displacement, however, they do not include a feature which can modulate thoracic kyphosis. A sternum vertical displacer (SVD) prototype has been developed which can increase a subject's thoracic kyphosis relative to the neutral prone position on a surgical frame. The kyphosis increase is obtained by lifting the subject's torso off the thoracic cushions with a dedicated sternum cushion that can be displaced vertically. The objective of this study was to evaluate the impact of SVD utilization on the sagittal curves of the spine. Experimental testing was performed on six healthy volunteers. Lateral radiographs were taken in the neutral and sternum raised positions and then analyzed in order to compare the values of sagittal curves. The displacement of volunteers and surgical frame components between positions was recorded using an optoelectronic device. Finally, interface pressures between the volunteers and surgical frame cushions were recorded using a force sensing array. Average results show that passing from the neutral to sternum raised positions caused an increase of 53% in thoracic kyphosis and 24% in lumbar lordosis; both statistically significant. Sensors showed that the sternum was raised a total of 8 cm and that interface pressures were considerably higher in the raised position. The SVD provides a novel way of increasing a patient's thoracic kyphosis intra-operatively which can be used to improve access to posterior vertebral elements and improve sagittal balance. It is recommended that its use should be limited in time due to the increase in interface pressures observed.