Optimal Design And Biomechanical Assessment Of "Artificial Cervical Joint Complex"

Cervical spine syndrome is one of common and multiple diseases. Subtotal corpectomy is used for the treatment of many kinds of cervical spine syndrome clinically, and after that, cervical spine reconstruction of stability is need. Nowadays bone graft with internal fixation and artificial vertebral replacement are the most common methods used for reconstruction, but all of the two have two deficits as following: one is the loss of the motion of surgical region which leads to decrease of the motion of cervical spine. The other is long-term acceleration of adjacent segment degeneration caused by stress concentration and motion redistribution of cervical spine. In case it occurs, it's very difficult to deal with it, and its clinical prognosis cannot give satisfaction to us. So, when do cervical spine reconstruction after subtotal corpectomy, it's very important to restore segmental motion of surgical region in order to avoid long-term acceleration of adjacent segment degeneration. Now there is no technique which can either reconstruct the stability or restore segment motion used for reconstruction following cervical subtotal corpectomy. Our group designed and manufactured ACJC and did relative biomechanical tests on cervical spines into which ACJC were implanted earlier. Results showed that ACJC can restore segmental motion of surgical region fairly, in order to avoid long-term acceleration of adjacent segment degeneration.Objective: The movement of normal cervical spine has a variable center of motion, with the shift of adjacent segment. The structure of"artificial cervical joint complex"(ACJC) can not realize the movement as normal cervical spine. To realize physiological reconstruction totally, we should improve the fixation between prosthesis and adjacent segment, the fusion between prosthesis and remnant of Centrum. Based on the geometric and movement parameters o f human'cervical spine, we optimized and manufactured"ACJC"with titanium alloy.Methods: 1) Based on the geometric and movement parameters o f human'cervical spine, we optimized"artificial cervical joint complex"(ACJC) with Solid Works and Auto CAD software. Then manufactured the prosthesis with titanium alloy by numerical controlled machine tool, assembled them to the whole one and brushed it with Ti-porosity smear layer evenly. 2)Drawing out 7 samples of 14 fresh cervical spines as intact group randomly, carried on the experiments on stability under the biomaterial experimental system of MTS 858 Mini Bionix II. Divided 14 cervical spines into two groups including plate-screw fixation group and prosthesis-implanted group averagely and randomly, then tackled them before experiment respectively: conduct anterior C5 subtotal corpectomy, bone graft fusion and internal fixation by turns for the plate-screw fixation group; conduct C5 subtotal corpectomy and prosthesis implantation by turns for the prosthesis-implanted group, carried on the same experiments as the intact group. 3)Divided 14 cervical spines into two groups including plate-screw fixation group and prosthesis-implanted group averagely and randomly, Then tackled them with the same ways mentioned above in method Measured the motion of surgical adjacent segment with the biomaterial experimental system of MTS 858 Mini Bionix II and three-dimensional shot system.Results: 1) Optimized and manufactured"ACJC", which was made up by articular head part on both sides and vertebrae part in the middle. The spherical surfaces of articular head part and vertebrae part structure the firm sphere-chute joint,with the fixation of fixed collar and locating pin. The activity of prosthesis changes from 0 to 14 degree in all directions. The shift in anteflexion and extension changes from 0 to 2㎜,and 0 to 1㎜ in Left and right axial rotation. The special structure of prosthesis not only imitates the movement of normal cervical spine, but also realize the shift of interbody. Devices on the articular head part and vertebrae part can avoid disarticulation. The prosthesis has simple structure and high mechanical stability.2) As for the lower cervical spine, there was no apparent difference between prosthesis-implanted group and intact group in the three-dimensions ROM. While in the plate-screw fixation group, ROM is smaller in the flexion, extension and tortion compared with the prosthesis implanted group and the intact group, with no difference in lateral bending. As for the surgical segment, ROM of the plate-screw fixation group is smaller in the three-dimensions ROM obviously compared with the prosthesis-implanted group and the intact group. ROM of the prosthesis-implanted group is the same in most of the activities as of the intact group while larger in the extension.3) As for the C3/4 intervertebral ROM, there is no obvious difference between the prosthesis-implanted group and the intact group. ROM of the plate-screw fixation group in flexion and extension is larger than the rest two groups without difference in lateral bending. They are the same in the C6/7 vertebra ROM.Conclusion: Using ACJC to reconstructing cervical spine following subtotal corpectomy, can either restore segmental motion or regain almost the same stability as in intact condition. Compared with the standard bone graft and palte-screw internal fixation, it fits the requirements of physiological reconstruction more and steps towards physiological reconstruction of the cervical spine technically, which offers a new option for the reconstruction of cervical spine in the future. Meanwhile, it avoids abnormal increase of intervertebral ROM in the adjacent segment, which may make sense of prevention of long-term occurences and acceleration of degeneration of adjacent segments.