A Minimally Invasive Surgical Device Inspired By The Biomechanical Characteristics Of Crocodile Skull

Minimally invasive surgery has a few limitations in the treatment of the B-type lumbar burst fracture with posterior wall fracture and bone fragments retropulsed into the spinal canal.Due to the small operating space in the vertebral body,the clamp size of the minimally invasive instrument is limited,which leads to the difficulty to meet the requirements in mechanical properties and the clamping reliability.Therefore,based on the characteristics of crocodile skull,this paper presents a minimally invasive vertebral reduction clamp which can be used with an endoscope to remove the bone fragments retropulsed into the spinal canal,achieve decompression and reconstruct the posterior wall.In order to make the vertebral reduction clamp with small volume and high structural rigidity,Siamensis crocodile skull is treated as a bionic target.The crocodile skull was reconstructed by Mimics,Geomagic and Solid Works.The biomechanical analysis of skull features was carried out by ANSYS to obtain bionic characteristics of the skull.Design the structure of the vertebral reduction clamp according to the bionic principle,and then use ANSYS to optimize its structure.In order to improve the gripping firmness of bone pieces,a series of bionic microstructures was fabricated on the occlusal surfaces of the vertebral reduction clamp according to the crocodile molariform teeth distribution and dental shapes.To analyze the mechanical performance of the bio-inspired vertebral reduction clamp,the device's maximum gripping force was measured and the stiffness of the vertebral resetting clamp and its contrast model were tested by using the digital image correlation method.The results show that stiffness of the vertebral resetting clamp with bionic structures is bigger and the mechanical performance is obviously improved.In order to validate the gripping performance of the designed vertebral resetting clamp,we measured the friction coefficient and the sliding coefficient of the bio-inspired microstructures,the triangular serratures and the wavelike serratures to the vertebral bone piece,respectively.The results showed that,compared with the other two kinds of tooth,the crocodile-tooth-like microstructure possesses higher clamping reliability,which has greater friction coefficient and smaller slip coefficient.In order to evaluate the performance of the MIS device,a burst fracture was made in a bovine vertebra by using compression as well as a human vertebra by artificial destruction method.Vitro simulation experiments were performed with an endoscope as an intraoperative lighting and imaging equipment.The results show that the MIS device has the reliability and flexibility for the reduction of vertebral burst fractures.The bionic MIS device mimics the biomechanical characteristics of a crocodile rostrum to improve the mechanical performance in gripping and moving bone pieces in the confined space of a vertebral body.This study may be capable of converting the posterior open surgeries to the MIS procedures,and expands the use of the MIS techniques in the treatment of lumbar burst fractures.