| BackgroundIn recent years, cervical kyphosis has become a hot spot in the spine surgery research.. There are some reports about the relationships between the clinical manifestations and the spine morphology or spinal cord morphology in patients with myelopathy. In most of these reports about cervical kyphosis , the cross-sectional area, compression ratio, and anteroposterior diameter are used as morphologic parameters of the spinal cord, but no reports have been published on the use of vertebral canal available volume.ObjectivesTo research the relationships between the degenerative cervical kyphosis and the available volume of vertebral canal and to establish the mathematic model by the measurement of X-ray and MRI .To calculate the available volume of vertebral canal and to evaluate cervical kyphosis correction or not to the effects of surgical efficacy.MethodsThere are 94 outpatients or inpatients from july 2004 to december 2006 in this study. two groups :lordosis group(57 patients) and kyphosis group(37 patients); Cervical lordosis group: All of outpatients, the total of 57 cases, of which 36 are male and 21 female. The average age is 51.2 (42-72). kyphosis groups: in the X-ray and MRI films cervical lordosis disappears and shows the kyphosis deformities. 16 cases of outpatients, of which 9 are men and 7 women with a mean age 53.6 (43-71);a total of 21 inpatients,are diagnosed with cervical spondylotic myelopathy and the average age of 54 (42-70), including 13 males and 8 females. Patients in kyphosis group are ruled out other causes.Using photoshop and autoCAD software, we measure the vertebral number N of the kyphosis segment, Featuring distance M, the Cobb angle of the kyphosis segment, integrity cervical Cobb angle and the anterior margin line and posterior margin line length of cervical vertebrae (P is the ratio of the two) in the X-ray films.We also measure: layer spacing e(mm); MRI sagittal dimensions of the dural sac area; Sa is the area from foramen magnum to the lower edge of the C2 ,Sb is the area from foramen magnum to the lower edge of the C7; Sc is the area of kyphotic vertebrae invading the vertebral canal in the MRI films. All layers of the Sa, Sb and Sc are integrated to get the Va,Vb,Vc by using the mathematical model. In addition ,the cervical vertebral canal volume ratio is evaluated (R=Vb/Va).All the inpatients are treated with anterior decompression and kyphosis correction,and were applied with plate fixation in addition .the patients were permitted to leave bed at 3 days after operation. post-operative nerve function is evaluated as follows according to JOA scoring system.All values are dealt with statistic analysis with SPSS11.0 and at last we come to a conclusion.ResultThe average integrity cervical Cobb angle is 27±8.1°in lordosis group and—18±7.8°in kyphosis group. The average value of Va is 6.30±0.62 (cm~3) in lordosis group and 6.22±0.41 (cm~3) in kyphosis group. There is no statistical differences in the average value of Va in two groups (P>0.05 ) . The average value of Vb is 17.28±1.42 (cm~3) in lordosis group and 13.63±1.30 (cm~3) in kyphosis group; The average value of R is 3.1±0.3 in lordosis group and 2.4±0.4 in kyphosis group; The average value of P is 3.1±0.3 in lordosis group and 2.4±0.4 in kyphosis group; Statistical analysis showed that there are significant differences in the average value of Vb,R,P in two groups (P<0.05) . There is a positive correlation between Vc and MN(P<0.05).In this study, postoperative recovery rate > 50% as excellent efficacy and postoperative recovery rate <50% as poor efficacy. There are significant differences between kyphosis correction or not and postoperative recovery rate(chi-square test, P<0.05). ConclusionsIn our study we firstly calculate the available volume of vertebral canal and the available volume of kyphotic vertebrae invading the vertebral canal through the mathematic model that we established.However, the effectiveness of this mathematical models has yet to be verified.Cervical kyphosis will lead to the available volume of cervical vertebral canal reduction. Cervical kyphosis correction to patients is advantageous to the recovery of neurological function ,so we consider that the reason is possibly the expansion of the available volume of cervical vertebral canal.
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