Mathematic Requirement Of Fusion Instrument For Shape Of Vertebral And Plate

BackgroundEveryone’s life pattern is changing with the development and progress of the times. Unhealthy lifestyles and work habits induce a significant rising of cervical spondylosis incidence, and more professional and younger people are suffering from this disease. Neck injury has also become a common injury in traffic accidents. Among the treatment approaches for cervical spondylotic myelopathy(CSM), anterior cervical decompression and fusion becomes a universal surgical treatment of curing cervical myelopathy due to its advantages including immediate stabilizing, pressure relieving, symptoms alleviation, maintaining and distraction of disc height, integration promotion and so on. However, as time goes on, the postoperative complications such as the shift, sink, and infusion of the fusion device have also raised concern. It is critical to utilize a fusion device which can fit the anatomy of the human as well as avoid all the postoperative complications. The cervical interbody fusion cage newly designed based on the shape of cervical vertebral body endplate can fit more with the vertebral body endplate; a further promotion of surgical treatment efficacy and reduction of complication incidence can be realized through applying this device. ObjectiveIn this article, the 3D reconstruction was performed for the morphology of the cervical spine based upon the medical images of human head and neck and then the required data was measured in accordance with the established 3D model. The shape curve of the upper vertebral endplate of intervertebral space was designed according to the measured data and then cervical fusion cages with higher integration degree to the vertebral endplate were designed accordingly. MethodA total of 100 cases of cervical CT samples photographed from Jul. 2012 to Jul. 2014 were randomly selected from the image library of the First Affiliated Hospital of Zhengzhou University. Among those samples, patients too old(over 60 years), too young(below 20 years) or those with significant morphological abnormalities(obvious abnormalities induced by vertebral missing, congenital malformations, tumors and other factors) were ruled out, and a total of 48 samples(27 males with average age of 38.2 years and 21 females with average age of 37.9 years) meeting the requirements were screened out as subjects. Mimics software was utilized for 3D restoration of all CT photos, and the 3D models of all cervical vertebras were built. Thereby intervertebral coronal diameters, sagittal diameters and heights of C34, C45, C56, and C67 were measured, and all the measured values were statistically analyzed with SPSS 19.0 statistical software. Founded on the measured values, the shape of the upper vertebral endplate of intervertebral space was calculated and the fusion device was designed. The 3D model of the designed cervical interbody fusion cage was then produced as well. Results① Intervertebral sagittal diameters of C34, C45, C56, and C67 were 17.79±2.72 mm, 17.93±2.87 mm, 18.41±2.66 mm and 18.84±2.58 mm, respectively. Differences among various intervertebral spaces were significant(P=0.008), and the sagittal diameters of males and females were significantly different(P=0.000). Intervertebral sagittal diameters increased gradually from the upper to the lower segments. ② Intervertebral coronal diameters of C34, C45, C56, and C67 were 15.79±2.68 mm, 15.91±2.72 mm, 16.12±2.56 mm and 16.44±2.60 mm, respectively. There was no significant difference between various intervertebral spaces(P=0.006), and the sagittal diameters of males and females were significantly different(P=0.000). Intervertebral coronal diameters increased gradually from the upper to the lower segments. ③ The intervertebral space heights of C34, C45, C56, and C67 presented significant differences(P=0.000) because of the differences of intervertebral spaces and subject gender variations. There are significant interactions between positions and intervertebral spaces, as well as between genders and intervertebral spaces(P=0.000). The comparison result between the adjacent positions of the same intervertebral space indicated significant difference(P=0.000) and the maximum height was at the H10 position. ④ The cervical fusion cage was designed and the 3D model of the cervical fusion cage was produced according to the measured data. Conclusion① The 3D model of cervical spine is built according to the CT image samples of human cervical spine.② In accordance with the shape curve of vertebral endplate, the curve of the upper surface of the fusion device should be a curved edge attaching to the curved surface of the device; the lower surface of the fusion device is also a curved surface, but it can be abstracted into a flat surface.③ Pre-operative 3D printing can make the fusion device fit more with individual requirements.