| BackgroundSince 1949 Harrington token the lead to use Harrington Rod to treat idiopathic scoliosis after spinal implanted thing had been studied systematically. Roy-Camille has developed the integrated pedicle steel plate to treat thoracic and lumbar vertebra fracture in1963. Pedicle fixation technology has been widely applied to vertebra fracture, dislocation, deformity and so on, now it already became in common use surgery operation, but entering pedicle screw has certain fault. Its main reason is located deviation and (or) improper operation.The gross anatomic survey and statistic analysis was carried on corpse specimens. It needs the massive materials and lots of time. Technology is relative backwardness. Results are not also precise. It is very difficult to apply to deformity and variation individual and those destruction normal osseous structure patients. The three dimensional reconstruction can return to original anatomical characteristic of objects. The widespread application of digital technology impelled powerfully the digital medical development.The computer navigation system was applied successfully to the medicine domain. The spinal navigation system has provided reliable guarantee for spinal minimally invasive surgery and precise, real-time visualization, intellectualized surgical operation. It has extremely broad applied prospect. Its essence is digitization.Based on multitudinous scientific research result and were adapted to modem digital medicine development trend. We combined human anatomy, tomography, three-dimensional reconstruction and reverse-engineering technology. To aim at the question how locate pedicle screw entering point, direction and depth. We proposed digital "pedicle screw channel (PSC)" concept and studied systematically its characteristic rule.Objectives1. To establish database of three dimensional vertebra digital model.2. To establish digital analysis method ofpedicle screw channel.3. To study the changing rule of PSC in different TSA.4. To study three dimensional relations of PSC, entering screw point and vertebra boundary in cervical, thoracic and lumbar vertebrae. The purpose is to make clear changing rule among entering screw point, size of PSC and entering screw angle.Materials and methods1. To collect CT primary data and establish database of three dimensional reconstruction model: CT scanning images of healthy adult physical examination were collected. Scanning condition is voltage 120kv, electric current 150mA, level thickness 1.25mm and 512x512 matrix. The data included 6 cases healthy adult cervical vertebrae, 5 cases healthy adult thoracic vertebrae and 6 cases healthy adult lumbar vertebrae CT scanning.We applied Mimics 8.11 to analyze CT images. Firstly we segmented the vertebra boundary to use thresholding, then applied region growing to extract different vertebra information, finally created 3D vertebra model by system default best reconstruction pattern. The models were exported by. STL format. The cervical, thoracic, lumbar vertebra 3D models were classified to save to the data.2. The analysis method of PSC: To open 3D model in UG imageware12.0, and locate 3D coordinate system. To extract pedicle on the 3D model and fix on vertical plane by revolving model. To project the pedicle to the plane along normal direction, and fit the projection object interior boundary line and its inscribed circle, ellipse and gain the ellipse offset curve. To project the interior boundary line the inscribed circle, the ellipse to centrum and lamina surface along the direction.Lofting curve surface between the interior boundary projection curve on the centrum and lamina is pedicle screw channel. Lofting curve surface between the inscribed circle projection curve on the centrum and lamina is biggest screw channel. Lofting curve surface between the fitting ellipse projection curve on the centrum and lamina is approximate pedicle screw channel. Lofting curve surface between offset curve projection curve on the centrum and lamina is approximate .axes channel. Straight line between translation inscribed circle center on the centrum and lamina is best axis. Straight line between translation ellipse center on the centrum and lamina is approximate axis.The inscribed circle center translated to the lamina is the best entering point. The ellipse center translated to the lamina is approximate entering point.3. The changing rule of C3～7, T2～12, L1～5 in different TSA: To import C3～7, T2～12, L1～5 3D model to UG Imageware12.0. Cervical vertebra: 0°SSA keep invariable, TSA from 0°～45°is evenly separated 5°and respectively studied the change rule of PSC in different TSA. Thoracic and lumbar vertebra: 0°SSA keep invariable, TSA from 0°～40°is evenly separated 5°and respectively study the change rule of PSC in different TSA.4. To study three dimensional relations of PSC, entering screw point and vertebra boundary in lumbar vertebrae: To open 3D model files from the database in UG Imagewarel2.0, and locate 3D coordinate system.The centrum were divided into 10 equal parts from front to back. Those 10 equal parts were present standard of borderline depth. From front to back 10 equal parts mark lines on the centrum were determined to 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 0% of borderline depth. To apply analysis method of PSC confirmed the radius, TSA and the length of PSC in 50%～90% borderline depth. To measure respectively perpendicularity distance from best entering point in five different borderline .depth to middle horizontal plane through pedicle and to pedicle projection lateral borderline in0TSA of L1～5.The interior borderline pedicle projection of L1～5 in 90% borderline depth was fitted ellipse and ensure its center. To measure respectively perpendicularity distance from the center to middle horizontal plane through pedicle and to pedicle projection lateral borderline in 0°TSA of L1～5.5. To study three dimensional relations of PSC, entering screw point and vertebra boundary in thoracic vertebrae: To open 3D model files from the database in UG Imageware12.0, and locate 3D coordinate system.The centrum was divided into 10 equal parts from front to back. Those 10 equal parts were token standard of borderline depth. From front to back 10 equal parts mark lines on the centrum were determined to 100%, 90%, 80%, 70%, 60%, 50%, 40%,30%, 20%, 10%, 0% of borderline depth. To apply analysis method of PSC confirmed the radius, TSA and the length of PSC in 50%～90% borderline depth. To measure respectively perpendicularity distance from best entering point in five different borderline depth to middle horizontal plane through pedicle and to pedicle projection lateral borderline in 0°TSA of T3～12.The interior borderline pedicle projection of T3～12 in 90% borderline depth was fitted ellipse and ensure its center. To measure respectively perpendicularity distance from the center to middle horizontal plane through pedicle and to pedicle projection lateral borderline in 0°TSA of T3～12.6. To study three dimensional relations of PSC, entering screw point and vertebra boundary in cervical vertebrae: To open 3D model files from the database in UG Imagewarel2.0, and locate 3D coordinate system.The centrum was divided into 10 equal parts from front to back. Those 10 equal parts were token standard of borderline depth. From front to back 10 equal parts mark lines on the centrum were determined to 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 0% of borderline depth. To apply analysis method of PSC confirmed the radius, TSA and the length of PSC in 90% borderline depth. To measure perpendicularity distance from best entering point to middle horizontal plane through pedicle and to pedicle projection lateral borderline in 0°TSA of T3～12.The interior borderline pedicle projection of C3～7 in 90% borderline depth was fitted ellipse and ensure its center. To measure respectively perpendicularity distance from the center to middle horizontal plane through pedicle and to pedicle projection lateral borderline in 0°TSA of C3～7.Results1. The database of three dimensional reconstruction model: 3D models of C3～7, T3～12, L1～5 were 30, 50, 30respectively.2. The changing rule of C3～7, T3～12, L1～5 in different TSA.. The radius mean of inscribed circle of C3～7 in different segment is 2.0～2.8mm. C5 is least. The radius mean of inscribed circle of C3～7 in different angle is 1.5～3. 1mm. The radius mean of left and fight inscribed circle of C3～7 from 25°to 45°is respectively 2.6mm～2.7mm and 2.9mm～3.1mm. The length mean of PSC of C3～7 in different segment is 18.5mm～24.9mm. The length mean of PSC of C3～7 in different angle is 17.8mm～29.5mm. The length mean of left and right PSC of C3～7 from 25°to 45°isrespectively 22.1～29.5mm and 20.9mm～29.4mm.The radius mean of inscribed circle of T3～12 in different segment is 2.3mm～4.5mm. T7 is least. The radius mean of inscribed circle of T3～12 in different angle is 2.3mm～3.5mm. The radius mean of left and right inscribed circle of T3～12 from 0°to 20°is respectively 3.4～3.5mm and 3.3mm～3.5mm. The length mean of PSC of T3～12 in different segment is 26.9mm～47.8mm. The length mean of PSC of T3～12 in different angle is 23.1mm～53.2mm. The length mean of left and right PSC of T3～12 from 0°to 20°is respectively 23.1～39.7mm and 24.8mm～41.6mm.The radius mean of inscribed circle of L1～5 in different segment is 2.6mm～5.7mm. L1 is least. L5 is most. The radius mean of inscribed circle of L1-5 in different.angle is 3.8mm～4.8mm. The radius mean of left and right inscribed circle of L1～5 from 0°to 35°is respectively 4.0mm～4.5mm and 4.2mm～4.8mm. The length mean of PSC of L1～5 in different segment is 28.mm2～46.9mm. The length mean of PSC of L1-5 in different angle is 24.8mm～50.5mm. The length mean of left and right PSC of L1～5 from 0°to 10°is respectively 30.5mm～37.9mm and 24.8mm～35.0mm. The length mean of left and right PSC of L1～5 from 15°to 40°is respectively 39.1mm～47.4mm and 39.0mm～47.5mm.3. To study three dimensional relations of PSC, entering screw point and vertebra boundary in lumbar vertebrae: The inscribed circle radius scope of L1～5 in 50～90% different boundary depth respectively is following.Left and right of L1 is 3.4～3.7mm, 3.6mm～3.8mm. Left and right of L2 is 4.0mm～4.3mm, 4.1～4.4mm. Left and right of L3 is 4.8mm～5.1mm, 4.7～5.1mm. Left and right of L4 is 5.8mm～5.8mm, 5.6mm～5.8mm. Left and right of L5 is 6.0mm～6.1mm, 6.0mm～6.2mm. The transverse diameter scope of L1～5 in different boundary depth is 6.8mm～14.4mm. The mean difference value of L1～L5 between the biggest and the smallest inscribed circle radius is (0.0±0.17)mm～(0.4±0.13)mm in 50%～90% boundary depth. The difference of inscribed circle diameter of L1～5 is smaller than 1mm in the centrum 50%～90%boundary depth.The scope of L1～5 PSC length in 50%～90% different boundary depth respectively is following.Left and fight of L1 is 35.4mm～49.3mm, 36.7mm～50.5mm. Left and right of L2 is 36.6mm～48.8mm, 36.6mm～47.7mm. Left and right of L3 is 36.7mm～51.7mm, 36.8mm～50.7mm. Left and right of L4 is 36.0mm～48.7mm, 35.7mm～47.8mm. Left and right of L5 is 36.0mm～43.6mm, 38.9mm～44.5mm. The greatest depth and the smallest depth mean difference value is (11.3±2.46)mm～(17.0±3.77)mm. L(1～4) depth scope changes within (11.3±2.46)mm～(14.2±2.18)mm. L5 depth scope changes within (16.6±2.70)mm～(17.0±3.77)mm. The length scope in 90% boundary depth is 43.61mm～51.71mm. L3 is the longest.The TSA scope of L1～5 in 50%～90% boundary depth respectively is following.Left and right of L1 is -1.5°～15.7°, -2.1°～13.6°. Left and right of L2 is 0.02°～14.8°, -1.5°～13.9°. Left and right of L3 is 1.2°～18.3°, 1.83°～18.8°. Left right of L4 is 0.33°～22.6°, 9.7°～22.7°. Left and right of L5 is 35.2°～39.8°, 36.17°～39.0°. With depth changing, the mean different value of the maximum TSA and the minimum TSA of L1～4 is (12.3±2.19)°～(17.2±4.14)°, and L5 is (3.2±1.65)°～(4.2±1.65)°. The scope of TSA of L1～5 in 90% boundary depth is 13.6°～15.7°, 13.9°～14.8°, 18.3°～18.8°, 22.6°～22.7°, 39.0°～39.8°respectively.Perpendicularity distance from best screw point in 50%～90% borderline depth to pedicle projection lateral borderline in 0°TSA of L(1～5) respectively is following.Left and right of L1 is -0.6mm～4. 1mm, -1.0mm～3.5mm. Left and right of L2 is -0.6mm～3.9mm, 0.3mm～4.7mm. Left and right of L3 is -0.3mm～4.5mm, -1.4mm～3.8mm. Left and right of L4 is -2.2mm～1.6mm, -1.6mm～2.1mm. Left and right of L5 is -4.2mm～-5.8mm, -4.6mm～-6.00mm. The mean different value of perpendicularity distance of L1～4 between the interior and the lateral screw point in 50%～90% different boundary depth is (3.7±1.70)mm～(5.4±0.97)mm, and L5 is (1.5±2.74)mm～(1.7±1.40)mm.4. To study three dimensional relations of PSC, entering screw point and vertebra boundary in thoracic vertebrae: 50%～90% different boundary depth, the mean different value of the greatest depth and the smallest depth inscribed circle radius of T3～12 is (0.0±0.19)mm～(0.5±0.19)mm. The T12 difference value is biggest, about 0.5mm, other sections mostly are between 0mm～0.2mm.The mean different value of the biggest and the smallest PSC length of T3～12 in 50%～90% boundary depth is (9.1±2.21)mm～(14.9±3.36)mm. From 50% to 90% boundary depth difference value is consistent, maximum value is 14.9mm, mostly concentrates between 10～12mm. Various segments in 90% boundary depth the PSC length scope is following. T3 is 33.5mm～37.3mm. T4 is 36.5mm～37.3mm. T5 is 38.2mm～40.0mm. T6 is 41.7mm～42.1mm. T7 is 41.9mm～42.3mm. T8 is 42.9mm～45.6mm. T9 is 43.6mm～44.1mm. T10 is 41.9mm～42.9mm. T11 is 42.6mm～46.7mm. T12 is 51.3mm～51.5mm.The mean different value of the biggest and the smallest angle of T3～12 in 50%～90% boundary depth is (7.9±1.87)°～(12.5±1.97)°. The boundary depth from 50% to 90%, the angle difference value is consistent, mostly between 9°～11°. 80%～90% boundary depth angle scope is following. Left and right of T3 is 15.0°～18.8°, 16.6°～20.7°. Left and right of T4 is 11.7°～14.1°, 14.2°～16.9°. Left of right of T5 is 11.3°～13.7°, 10.1°～13.6°. Left and right of T6 is 11.5°～15.0°, 9.9°～13.4°. Left and right of T7 is 10.4°～13.3°, 7.5°～10.7°. Left and right of T8 is 10.0°～14.2°, 7.3°～11.4°. Left and right of T9 is 9.9°～14.5°, 6.7°～11.0°. Left and right of T10 is 10.8°～15.1°, 7.4°～11.1°. Left and right of T11 is 12.7°～17.0°, 10.4°～14.0°. Left and right of T12 is 14.0°～18.0°, 11.8°～15.0°.～The S SA of T3～12 respectively is - 14.94°, - 14.64°, - 16.52°, - 10.18°, - 13.2°, -6.76°, -3.2°, -5.46°, 0°, 0°, 0°.The mean different value of T3～12between the interior and the lateral screw point in 50%～90% boundary depth is (1.5±1.66)mm～(3.7±1.51)mm. With increasing depth, entering screw point position move outside. Motion scope is 2mm～4mm.The range of best screw point distance to horizontal plane of T3～12 in 80%～90% boundary depth is mostlyl～2mm position above the symbol plane.5. To study three dimensional relations of PSC, entering screw point and vertebra boundary in cervical vertebrae: The radius of inscribed circle of C3～7 PSC respectively is following. Left is 2.63mm, 2.71mm, 2.91mm, 3.08mm, 3.35mm. Right is 2.52mm, 3.04mm, 3.12mm, 3.14mm, 3.79mm. It increases gradually, the scope is 2.63mm～3.79mm. C7 is biggest, C3 is smallest.The length 0f C3～7 PSC respectively is following. Left is 23.9mm, 23.9mm, 24.5mm, 27.92m, 27.8mm. Right is 23.4mm, 23.8mm, 24.5mm, 26.7mm, 28.2mm. It increases gradually, scope is 23.8mm～28.2mm. C7 is biggest, C3 is smallest.The TSA of C3～7 PSC respectively is following. Left is 33.2°, 33.1°, 35.0°, 35.3°, 33.5°. Right is 33.2°, 37.9°, 37.0°, 36.3°, 34.3°. The scope is 33.2°～37.9°.Perpendicularity distance from best screw point corresponding on the lamina surface to middle horizontal plane through pedicle and pedicle projection lateral borderline in 0°TSA and SSA of C3～7The perpendicularity distance from best screw point corresponding on the lamina surface to middle horizontal plane through pedicle of C3～7 respectively is following. Left is-0.47mm, 0.78mm, -0.33mm, -0.43 mm, -0.53mm. Right is -0.12mm, 0.50mm, 0.10mm, -0.32mm, -0.13mm.The perpendicularity distance from best screw point corresponding on the lamina surface to pedicle projection lateral borderline in 0°TSA and SSA of C3～7 respectively is following. Left is -5.83mm, -5.33mm, -6.85mm, -5.67mm, -2.67mm. Right is -5.42mm, -6.25mm, -6.50mm, -5.88mm, -3.00mm.The perpendicularity distance from best screw point corresponding on the lamina surface to Lamina lateral borderline of C3～7 respectively is following. Left is 4.08mm, 4.83mm, 3.58mm, 2.67mm, 3.75mm. Right is 4.08mm, 3.33mm, 3.33mm, 3.42mm, 3.33mm.Conclusions1. PSC is the channel between interior boundary of positive projection of pedicle three-dimensional space corresponding on the centrum and lamina in the random orientation. In certain scope a three-dimensional direction corresponds a PSC, this PSC corresponds the biggest screw channel, the channel corresponds best axis and entering screw point, also corresponds safe area of certain size screw.2. The PSC of cervical, thoracic and lumbar vertebrae have common characteristic. The length of PSC increases with angle increasing. The radius of inscribed circle increases gradually at first, and then decreased subsequently with the increased TSA. The difference of length and radius of inscribed circle is remarkable to segment of cervical, thoracic and lumbar vertebrae. The difference of length and radius of inscribed circle are remarkable to different TSA. The difference between left and right of length and radius of inscribed circle are remarkable to the part segment. It prompts the clinical practice to notice the difference.3. The radius of inscribed circle and length were synthetized. The radius of inscribed circle and length of C3～7 left and right PSC are relative more big in 25°～45°TSA. It is the best region. The radius of inscribed circle and length of T2～12 left and right PSC are relative more big in 0°～20°TSA. 25°～40°TSA is opposite. The length of L1～5 left and right PSC are relative longer in the 15°～35°TSA. The length of L1～5 left and right PSC are relative shorter in the 0°～10°TSA. The mean different value of diameter of inscribed circle is about lmm in 0°～35°TSA.4. The mean difference value of the biggest and the smallest radius inscribed circle of L1～5 and T3～12 in 50%～90% boundary depth is smaller than 0.5mm. With changing depth, the radius of inscribed circle is a relatively stable range of variation.5. The perpendicularity distance of best entering point of L1～4 in 50%～90% boundary depth is about±1mm range to pedicle projection lateral borderline. It is about±2mm to middle horizontal plane through pedicle. L5 has differently compared with L1～4, the perpendicularity distance to middle horizontal plane through pedicle is also about±2mm, but the perpendicularity distance to pedicle projection lateral borderline range is -5mm～-6mm.6. Pedicle projection lateral borderline was taken as reference mark line ofdifferent entering screw point in 50%～90% boundary depth. The boundary depth of T3 is relative shorter. The boundary depth of T9～11 is relative longer. Comparison analyzed value, entering screw point of T3 was supposed to move outside 1mm～2mm, but entering screw point of T9～11 was supposed to move inside 1mm～2mm, other segments entering screw point may on the projection boundary.7. The perpendicularity distance of best entering screw point T3～12 to middle horizontal plane through pedicle is above the symbol plane 1～2mm in 80%～90% boundary depth.8. The position of approximate entering screw point of L1～5 and T3～12 approached to best entering screw point in 90% boundary depth. It may consider the localization reference point. This reference point is relatively easier and is also accurate.9. Pedicle projection lateral borderline and lamina lateral boundary were taken as reference mark line of entering screw point of C3～7. The position of best entering screw point of C3～6 is outside of median line between two references marks line. C7 is inside of median line between two references marks line.10. In 90% boundary depth, the radius of inscribed circle cervical, thoracic and lumbar vertebrae in the transition part upper segment is bigger than lower segment. The radius of inscribed circle assumed the wave shape characteristic rule and was consistent with the adult spinal column physiology bend. The change rule of TSA is big of the beginnings and ends, middle is small, and assumes the concave glyph linear characteristic. The length of PSC assumed the increasing tendency of straight line.
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