Design of an ex-vivo experimental setup for spine surgery based on in-vivo identification of respiration-induced spine movement

In spine surgery, e.g., pedicle screw placement, patients are in the prone position, anesthetized, and breath using respirators. Respiration-induced spine movements may interfere with the operation. For evaluating spine surgery robotic systems [1] without resorting to in-vivo experi- ments, it is necessary to provide a setup that realistically reproduces the spine movement in a lab. The literature is not very rich in documenting such a movement. Most of the time, only the range of motion of one or two vertebrae is provided. Glossop et al. [2] measured this respiration-induced motion for two human lumbar vertebrae (L3 and L4) to be 1.3 mm using optical markers screwed to the spinous process. The same authors [3] measured the respiration-induced motion, using the same techniques, for three pig lumbar vertebrae (L3-L5) under ventilation that ranged from 0.8-1.1 mm. In a more recent study, Liu et al. [4] measured this motion on different levels of vertebrae – cervical (C1), thoracic (T7), and lumbar spine (L4) – using optical markers placed on the patient’s skin. Mean ± 2SD motions were 1.3 ± 0.7 mm, 2.3 ± 1.6 mm, and 1.6 ± 0.7 mm. In this study, we measure respiration-induced spine movements (T6-L5) in an open-spine surgery on a pig. A mechanical probe mounted on a force-controlled medical robotic arm is used for measurements. Then, we propose an ex-vivo experimental setup that could implement the measured motions to emulate the respiration-induced movement.