| Background: Anterior cervical discectomy or corpectomy, interbody fusion and plate fixation have become one of the most commonly surgical procedures for treatment of the cervical disorders. To improve the effect of the primary spinal fusion, some growth factors have been attempted to utilize in this procedure. For all anterior cervical spine plates used presently in clinics, only its biomechanical characteristic was emphasized, but the biological effects required for fusion was neglected. Growth factors and their carriers can only be used by filling into the interbody devices because of their inability to bear the load between the vertebral bodies, which will sometimes result in ectopic ossification in the spinal canal or spinal cord and other complications. In this study, we developed a new cervical spine plate characterized with biological induction by fusing the biological effects and biomechanics into one. This system is made of titanium and specialized with lower profile, narrower and thinness. Importantly, a box at the ventral side of this plate can contain the growth factors and carriers and can prevent the diffusion of growth factors to adjacent areas. Due to high similarity of cervical spine between human and sheep, this cervical spine plate was designed based on the cervical spine anatomy data from sheep. To observer the effects of this new plate on spinal fusion in vivo, the plate carrying growth factors was implanted into the cervical spine of sheep. Generally, our aim of this study is to develop an anterior cervical spine system with independent intellectual property right.Objectives: (1) To obtain the reference data required for anterior cervical plate design, the related anatomy data of cervical spine were measured in sheep. (2) Develop an anterior cervical plate featured with effects of biological induction. (3) Investigate whether this new plate could display the effects of growth factors while providing rigid fixation.Methods: (1) DSH (disc space height), IA(intervertebral angle) and LA (lordosis angle) of cervical spine specimen (C0-T1) were measured from X-ray films in 12 randomly selected adult sheep, and the value of VBH (vertebral body height, VBW( vertebral body width) and VBD(vertebral body depth) of the vertebral bodyspecimen were also measured. All parameters were expressed as average value from three-time measurement. (2) A new plate was designed according to the parameters obtained from sheep cervical spine specimen and the locking mechanism between the plate and screw was referred from the LCP plate. (3) Twelve adult female sheep were used as animal models and were performed for two level anterior discectomy and fusion operation. Twelve sheep were randomly divided into two groups: group 1, discectomy with autogenous bone grafting plus anterior plate application; group 2, discectomy with autogenous bone grafting plus anterior plate contained BMP application. After operation, the fusion effects were evaluated by radiography, CT scanning and histology analyses. Results: (1) The average value of VBH, VBW, VBD and DSH of the C3-C7 vertebral body was 26.43 mm, 17.58 mm, 15.7 mm and 5.73 mm, respectively. The maximal IA (intervertebral angle) (11.7±1.5°) in the flex-extend process was observed in the space of C4-C5, the minimal IA (3.0±1.4°) in the space of C2-C3, the maximal LA (22.2±4.0°) was detected in C6-C7 space, and the minimal LA (4.1±2.5°) was in C2-C3 space. (2) The length, the width and the thickness of the plate were 35 mm, 14 mm and 2mm, respectively. The radian in the sagittal plain of the plate was 9.56 degree. There was a box carrying growth factors and their carriers at the ventral side of the plate, the volume of which was 312 cubic millimeter. When the plate was implanted in vivo, an angle between screw and plate will be formed, which enables the system more stable. (3) Results from radiographic analyses showed significant difference between group 1 and group 2 in bone fusion at three-month time point after implantation, the values of the bone formation were markedly higher in group 2 than in group 1 (3 months post-implantation: 2.40±0.58 v.s. 1.80±0.20, P<0.05). The value in group 2 was similar to group 1 at six-month time point after implantation. (6 months post-implantation:3.80±0.56 v.s. 3.60±0.40, P>0.05). The value in group 2 was similar to group 1 when the bone formation was assessed by CT scanning analyses 6 months post-implantation (3.50±0.94 v.s. 3.62±0.70, P>0.05). Results form histological analyses displayed that the structure of bone in group 2 was as good as in group 1.Conclusions: (1) The VBW and DSH values of the sheep cervical spine were relatively invariable, while the IA and LA values were comparatively variable.These detailed parameters provided important bases for designing a new cervical plate. (2) The advantages of lower profile, narrower and thinness were prominently manifested in our new anterior cervical spine plate. Importantly, a box carrying growth factors and carriers at the ventral side of the plate demonstrated its biologically induced characteristics. This box effectively prevented growth factors diffusing to the adjacent areas and prevented the resulting side-effects. (3) This new plate significantly promotes bone fusion by releasing growth factors and providing rigid fixation. |
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