Cell Biochem Biophys (2015) 71:1243–1248 DOI 10.1007/s12013-014-0335-4
ORIGINAL PAPER
Anatomical Measurement and Finite Element Study on Screw Channel Parameter in Percutaneous Fixation of Canulated Screw for Symphyseolysis Kehe Yu • Jianjun Hong • Yuefei Sun • Chengdi Shi • Xiaoshan Guo • Dongsheng Zhou
Published online: 12 November 2014 Ó Springer Science+Business Media New York 2014
Abstract To provide anatomical basement for symphyseolysis treatment with percutaneous fixation of canulated screw, through anatomical measurement on pubic symphysis and the surrounding tissues, and conduct the finite element studies on screw channel parameters. 20 cases of normal pelvic specimens from embalmed adult cadavers were taken to measure the anatomical parameter of bony remark of pubic symphysis and the space between spermatic cord (round ligament of the uterus) and pubic tubercle. Anatomical measurement results showed that the narrowest diameter of the superior ramus of pubis was 9.127 ± 1.189 mm, distance between two pubic tubercles was 55.656 ± 3.780 mm, thickness of the upper pubic symphysis was 10.510 ± 0.814 mm, and distance between upper and lower pubic symphysis was 40.872 ± 1.211 mm; the distance between round ligament of the uterus and pubic tubercle was 4.408 ± 0.304 mm, and the distance between spermatic cord and pubic tubercle was 5.196 ± 0.251 mm. The angle between canulated screw guide pin and horizontal plane was 8.342 ± 2.152°, the one between guide pin and coronal plane was
K. Yu D. Zhou (&) Department of Traumatic Orthopedics, Shandong Provincial Hospital Affiliated to Shandong University, No. 324 Jin Wu Wei Seventh Road, Jinan 250021, Shandong, China e-mail: [email protected] K. Yu J. Hong C. Shi X. Guo (&) Department of Orthopedic Surgery, The Second Affiliated Hospital of Wenzhou, Medical University, No. 109 Xueyuan West Road, Wenzhou 325000, Zhejiang, China e-mail: [email protected] Y. Sun Wenzhou Medical University, Chashan University Town, Wenzhou 325000, Zhejiang, China
5.236 ± 1.612°, and the distance from entry point to the outer edge of pubic tubercle was 10.023 ± 1.245 mm, which was measured by Mimics software. Percutaneous surgery at horizontal position was simulated on cadaver. And the screw was correctly placed in postoperative imaging examination. According to the anatomical data and finite element studies of screw channel parameter in percutaneous fixation of canulated screw for symphyseolysis, the method can improve the accuracy of screw placement and reduce complications. Keywords Symphyseolysis Percutaneous Canulated screw Anatomy Finite element
Introduction Clinically, most of the pelvic fractures are caused by the high falling and traffic accident. Pelvic fractures caused by these high-impact forces often accompanied with urethral disruption, rectal damage, and even angiorrhexis, thus resulting in a critical condition. Literature reports that unstable pelvic fracture had a morbidity of as high as 4–8 % after treatment [1]. Open reduction and internal fixation (ORIF) has been used from 1980s in the treatment of pelvic fractures [2], which has obtained a good curative effect. Early research, however, also found that the ORIF had disadvantages such as more bleeding and injury, and easy to cause blood vessels and nerve damage [3–5]. Symphyseolysis is a common injury in pelvic fracture, accounting for about 24 % of the pelvic fractures [6]. Most of symphyseolysis is caused by extorsion force. Study has shown that if the pubic symphysis was more than 2.5 cm and there existed stable rotation, surgeries like external or internal fixation should be used for treatment [7].
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Fig. 1 a Cervical-thoracic-lumbar-pelvic-upper femoral composite; b Fifth lumbar vertebra-pelvic-upper femoral composite
Percutaneous internal pelvic fixation has the advantages of less bleeding and injury. But since the anatomical structure of the pelvic ring is complicated and closed reduction is relatively difficult [8], serious complications may appear in case of careless operation. This research attempts to obtain accurate anatomical data through measurement of normal pelvic specimens from embalmed adult cadavers combined with finite element analysis, so as to help canulated screw placement for percutaneous treatment of symphyseolysis, improve the accuracy of screw placement and reduce operation complications.
Materials and Methods Specimens’ Collection and Preparation 20 cases of adult cadavers (13 cases = male, 7 cases = female) were provided by Department of Anatomy of Wenzhou Medical University. The cadavers were transected on the cervical vertebra and upper 1/3 of the thighs. Soft tissues (i.e., muscle) that attached to the cervical and lumbar spines and femoral shaft were stripped. 10 composites were obtained (cervical-thoracic-lumbar-pelvicupper femoral composite) (Fig. 1a). The cadavers were transected on the fifth lumbar vertebra and upper 1/3 of the thighs. Soft tissues (i.e., muscle and ligament) that attached to the lumbar vertebra, pelvis, and femoral shaft were stripped. Hip articular capsule and ligaments were carefully removed. 10 fifth lumbar vertebra-pelvic-upper femoral composites were obtained (Fig. 1b).
Equipment and Software Operating equipments and measurement tools were (1) electric drill, kirschner wire (2.5 mm), hacksaw and canulated screw (6.5 mm, Stryker company); (2) vernier
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caliper, straight ruler, set square, protractor; and (3) C-arm machine (Fig. 2a). 10 adult patients with whole pelvic CT (64 slice spiral CT, Brilliance) scan were selected randomly, and those having cancer and malformation were excluded. Softwares used for the finite element analysis were ABAQUS 6.11, MIMICS14.11, and CATIAV5R19, which required Windows XP operating system.
Measurement of Pelvic Specimens Transverse incision was given on the upper ledge of the pubic symphysis. Spermatic cord or round ligament of the uterus was exposed. And the distance between the pubic tubercle with spermatic cord or round ligament of the uterus was measured (Fig. 2b). Soft tissue around the pubic symphysis was removed to measure the following indexes: the narrowest diameter of the superior ramus of pubis (Fig. 3a), distance between two pubic tubercles (Fig. 3b), the thickness of the upper pubic symphysis (Fig. 3c), and distance between upper and lower pubic symphysis (Fig. 3d).
Finite Element Analysis 3D finite element model of pelvis was established and observed using fluoroscopy. Cylinder was set by function ‘‘cylinder’’ of MEDCAD. The pubic symphysis was reset by virtual operation function of MIMICS, and model of canulated screw fixation for symphyseolysis was established (Fig. 4a). The 2D horizontal plane which canulated screw located on was found, and 2D distance measuring tool was used to determine the length of canulated screw that could fit in (Fig. 4b). Combining with the 2D sagittal position and coronal position, whether the screw could pierce through the cortex was estimated via fluoroscopy
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Fig. 2 a Operating equipment and measurement tools; b Distance between the pubic tubercle with spermatic cord
Fig. 3 a Narrowest diameter of the superior ramus of pubis; b Distance between two pubic tubercles; c Thickness of the upper pubic symphysis; d Distance between upper and lower pubic symphysis
(Fig. 4c). Canulated screw was selected, and 3D distance measuring tool was used to determine the distance between needle entry point and pubic tubercle (Fig. 4d). The pubic symphysis screw was selected, which 3D coordinates could be found under the option of ‘‘characteristics’’ (Fig. 4e). Since the quadratic sums of 3D coordinates were all 1, the angels of the screw with horizontal plane, coronal, and sagittal planes namely the entry directions of the canulated screw could be calculated directly with the formula (Fig. 4f).
Results Measurement Results of Pelvic Specimens The distance between round ligament of the uterus and pubic tubercle was 4.408 ± 0.304 mm, and the distance between spermatic cord and pubic tubercle was 5.196 ± 0.251 mm. Both the spermatic cord and round ligament of the uterus have a certain degree of mobility. Narrowest diameter of the superior ramus of pubis was
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Fig. 4 a Model was in horizontal position. Pubic symphysis screw was placed via fluoroscopy; b 2D distance measuring tool was used to determine screw length; c Whether the screw was through the bone cortex was observed on the coronal and sagittal planes; d The radium of the screw was decreased to reduce error. The pubic tubercle was marked and the distance between canulated screw and pubic tubercle was measured; e Properties were clicked to indicate the entry direction of the canulated screw; f Function formula was used for experiment
Fig. 5 a The model was in horizontal position, and parameters of screw channel was used for closed reduction and internal fixation; b Postoperative X-ray indicated that the screw position was good
9.127 ± 1.189 mm, distance between two pubic tubercles was 55.656 ± 3.780 mm, thickness of the upper pubic symphysis was 10.510 ± 0.814 mm, and distance between upper and lower pubic symphysis was 40.872 ± 1.211 mm (Data not shown).
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Anatomical Parameters of Screw Channel Measured by Finite Element The angle between canulated screw guide pin and horizontal plane was 8.342 ± 2.152°, the one between guide pin and
Cell Biochem Biophys (2015) 71:1243–1248
coronal plane was 5.236 ± 1.612°, and the distance from entry point to the outer edge of pubic tubercle was 10.023 ± 1.245 mm (Data not shown). Percutaneous Surgery at Horizontal Position was Simulated on Cadaver Percutaneous surgery was performed on cadaver at horizontal position, and the screw was placed correctly in postoperative imaging examination (Fig. 5).
Discussion During percutaneous pelvic fixation, entry point and direction of screw are not easy to master, so there often appears deviation. Repeat intraoperative adjustment and nailing not only makes the patients and doctors exposed to excessive X-ray radiation, but also easily causes damage to adjacent neurovascular and other related organizations. Therefore, the development of such minimally invasive operation requires the doctor to have excellent operative skill, and also needs the support of good fluoroscopic equipment and imaging system [9]. Certain numbers of hospitals that conduct percutaneous pelvic fixation do not have 3D positioning system but are based on the repeat intraoperative fluoroscopy with single bulb X-ray fluoroscopic machine. Considering the above facts, this study aims to obtain accurate anatomical data of canulated screw channel through measurement of normal pelvic specimens from embalmed adult cadavers combined with finite element analysis, which can help the canulated screw placement for percutaneous treatment of symphyseolysis by improving the accuracy of screw placement. Pubic symphysis is a hemi-joint structure, which is closely connected with the aid of the fibrous cartilage. There are four ligaments (superior pubic ligament, lower pubic ligament, anterior pubic ligament, and posterior pubic ligament) around that closely connected bilateral pubes. According to the thickness of the upper pubic symphysis, distance between upper and lower pubic symphysis, and the narrowest diameter of the superior ramus of pubis measured in the experiment, all could accommodate the canulated screw of 6.5 mm. So, canulated screw replacement was feasible on anatomy. Spermatic cord or round ligament of the uterus was near the pubic tubercle and required special protection during operation. Through the anatomical study, patient accepting percutaneous canulated screws for treating symphyseolysis is in the supine position. A small incision was given on the lateral-superior area of pubic tubercle, and separated to the pubic tubercle bluntly. The pelvic reduction clamp, which reached the basement of the pubic tubercle through the lateral channel
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of the spermatic cord (round ligament of the uterus), was used to clamp and reset pubic symphysis. Pelvic clamp could reset pubic symphysis and protect the spermatic cord (round ligament of the uterus). In addition, it could be the reference for nailing under X-ray fluoroscopic machine. There are large errors in angel and direction of canulated screw using traditional manual measurement. This study adopted 3D finite element analysis to measure its 3D angle so as to improve the reliability and authenticity of the measured results. Finite element software applied in the field of orthopedic biomechanics firstly reported in 1972 [10]. It is widely applied in the field of biomechanics in recent years. Using Mimic software, entry angle of canulated screw guide pin could be calculated by its 3D coordinates. And the anatomic relationship between entry point of canulated screw guide pin and pubic tubercle could also be measured by 3D measuring tool. Compared with the traditional cadaver anatomy method, the finite element analysis on parameters of canulated screw channel for symphyseolysis was of high precision and repeatability [11, 12], and was not limited by the specimen of cadaver; At the same time, the entry angle of screw was calculated from the finite element model reconstructed on the data of pelvic CT scan, which had a better simulation, and could provide patients with a more personalized treatment option. Study on parameters of screw channel in percutaneous fixation of canulated screw for symphyseolysis can improve the accuracy of the screw placement, avoid the damage of peripheral spermatic cord (round ligament of the uterus) around, also reduce the fluoroscopy number of C-arm machine intraoperatively, and reduce the risk of infection in operative field. In addition, the significance of the research results is also reflected indirectly in the following aspects: (1) canulated screw with appropriate length was selected. Canulated tension screw produced pressure between the pubic symphysis, because its thread could only be embedded in contralateral cortex of the pubic symphysis. Cortex of the nailing side formed into a sliding hole due to the self-drilling effect of the canulated screw. Therefore, the selected intraoperative canulated screw must be ensured to be embedded in the contralateral cortex of pubic symphysis, and yet not too long so that the surrounding tissue would not be damaged. (2) The best operation time was attempted to be adopted. Routt et al. believed that the best operation time for patients with symphyseolysis was within 5 days after injury [13]. Delayed treatment would reduce the success of closed reduction. Research on screw parameters could provide better clinical reference for surgeon. Early anatomical repositioning of pelvis could effectively control bleeding, which was conducive to treatment and postoperative nursing for patients with combined injury. (3) Personalized
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treatment can be provided through the preoperative CT scan and postoperative 3D finite element analysis, which can better prevent the missed diagnosis of fractures at pelvic posterior ring. Swiss scholar Scheyerer found that the missed diagnosis rate of fractures at pelvic posterior ring was very high in patients with simple pubic ramus fracture [14]. And Simonian et al. suggested that single used of anterior ring fixation could not stabilize posterior pelvic ring [15]. Therefore, research on parameters of screw channel can improve diagnosis, and provide personalized treatment options. Limited by the number of pelvis specimens, and the influence factors such as race, height, gender, etc., the sampling error is unavoidable. Moreover, part of the pelvic fractures of symphyseolysis was caused by high-impact force. As the fracture displacement is complicated, there may be differences between the fixation methods. Acknowledgments This research was supported by the Zhejiang Provincial Natural Science Foundation of china under Grant No. LQ12H06002. The work was also supported by Zhejiang province health department funding under Grant No. 2013KYB176 and Zhejiang Province University Students’ Science and Technology Innovation Program (XinMiao plan) under Grant No. 2012R413006. Conflict of interest interest.
The authors have not declared any conflicts of
References 1. Chong, K., DeCoster, T., Osler, T., & Robinson, B. (1997). Pelvic fractures and mortality. The Iowa orthopaedic journal, 17, 110. 2. Failinger, M., & McGanity, P. (1992). Unstable fractures of the pelvic ring. The Journal of Bone and Joint Surgery, 74, 781–791. 3. Routt, C, Jr, Simonian, P. T., & Swiontkowski, M. F. (1997). Stabilization of pelvic ring disruptions. Orthopedic Clinics of North America, 28, 369–388.
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4. Giannoudis, P. V., Chalidis, B. E., & Roberts, C. S. (2008). Internal fixation of traumatic diastasis of pubic symphysis: is plate removal essential? Archives of Orthopaedic and Trauma Surgery, 128, 325–331. 5. Sagi, H. C., & Papp, S. (2008). Comparative radiographic and clinical outcome of two-hole and multi-hole symphyseal plating. Journal of Orthopaedic Trauma, 22, 373–378. 6. Pohlemann, T., Bosch, U., Ga¨nsslen, A., & Tscherne, H. (1994). The Hannover experience in management of pelvic fractures. Clinical Orthopaedics and Related Research, 305, 69–80. 7. Tile, M., & Helfet, D. (2003). Kellam J. Fractures of the pelvis and acetabulum: Lippincott Williams & Wilkins. 8. Matta, J. M., & Yerasimides, J. G. (2007). Table-skeletal fixation as an adjunct to pelvic ring reduction. Journal of Orthopaedic Trauma, 21, 647–656. 9. Lefaivre, K., Starr, A., Barker, B., Overturf, S., & Reinert, C. (2009). Early experience with reduction of displaced disruption of the pelvic ring using a pelvic reduction frame. Journal of Bone & Joint Surgery, British, 91, 1201–1207. 10. Brekelmans, W., Poort, H., & Slooff, T. (1972). A new method to analyse the mechanical behaviour of skeletal parts. Acta Orthopaedica, 43, 301–317. 11. Chen, H., Wu, L., Zheng, R., Liu, Y., Li, Y., & Ding, Z. (2013). Parallel analysis of finite element model controlled trial and retrospective case control study on percutaneous internal fixation for vertical sacral fractures. BMC musculoskeletal disorders, 14, 217. 12. Zhang, S., Su, W., Luo, Q., Leung, F., Chen, B. (2014). Measurement of the ‘‘safe zone’’ and the ‘‘dangerous zone’’ for the screw placement on the quadrilateral surface in the treatment of pelvic and acetabular fractures with stoppa approach by computational 3D technology. BioMed Research International, 2014. doi:10.1155/2014/386950. 13. Routt, M. C, Jr, Nork, S. E., & Mills, W. J. (2000). Percutaneous fixation of pelvic ring disruptions. Clinical Orthopaedics and Related Research, 375, 15–29. 14. Scheyerer, M. J., Osterhoff, G., Wehrle, S., Wanner, G. A., Simmen, H.-P., & Werner, C. M. (2012). Detection of posterior pelvic injuries in fractures of the pubic rami. Injury, 43, 1326–1329. 15. Simoniun PT, Routt Jr MC, Harrington RM, Tencer AF. 1995. Anterior versus posterior provisional fixation in the unstable pelvis: a biomechanical comparison. Clinical Orthopaedics and Related Research, 310, 245–251.
ORIGINAL PAPER
Anatomical Measurement and Finite Element Study on Screw Channel Parameter in Percutaneous Fixation of Canulated Screw for Symphyseolysis Kehe Yu • Jianjun Hong • Yuefei Sun • Chengdi Shi • Xiaoshan Guo • Dongsheng Zhou
Published online: 12 November 2014 Ó Springer Science+Business Media New York 2014
Abstract To provide anatomical basement for symphyseolysis treatment with percutaneous fixation of canulated screw, through anatomical measurement on pubic symphysis and the surrounding tissues, and conduct the finite element studies on screw channel parameters. 20 cases of normal pelvic specimens from embalmed adult cadavers were taken to measure the anatomical parameter of bony remark of pubic symphysis and the space between spermatic cord (round ligament of the uterus) and pubic tubercle. Anatomical measurement results showed that the narrowest diameter of the superior ramus of pubis was 9.127 ± 1.189 mm, distance between two pubic tubercles was 55.656 ± 3.780 mm, thickness of the upper pubic symphysis was 10.510 ± 0.814 mm, and distance between upper and lower pubic symphysis was 40.872 ± 1.211 mm; the distance between round ligament of the uterus and pubic tubercle was 4.408 ± 0.304 mm, and the distance between spermatic cord and pubic tubercle was 5.196 ± 0.251 mm. The angle between canulated screw guide pin and horizontal plane was 8.342 ± 2.152°, the one between guide pin and coronal plane was
K. Yu D. Zhou (&) Department of Traumatic Orthopedics, Shandong Provincial Hospital Affiliated to Shandong University, No. 324 Jin Wu Wei Seventh Road, Jinan 250021, Shandong, China e-mail: [email protected] K. Yu J. Hong C. Shi X. Guo (&) Department of Orthopedic Surgery, The Second Affiliated Hospital of Wenzhou, Medical University, No. 109 Xueyuan West Road, Wenzhou 325000, Zhejiang, China e-mail: [email protected] Y. Sun Wenzhou Medical University, Chashan University Town, Wenzhou 325000, Zhejiang, China
5.236 ± 1.612°, and the distance from entry point to the outer edge of pubic tubercle was 10.023 ± 1.245 mm, which was measured by Mimics software. Percutaneous surgery at horizontal position was simulated on cadaver. And the screw was correctly placed in postoperative imaging examination. According to the anatomical data and finite element studies of screw channel parameter in percutaneous fixation of canulated screw for symphyseolysis, the method can improve the accuracy of screw placement and reduce complications. Keywords Symphyseolysis Percutaneous Canulated screw Anatomy Finite element
Introduction Clinically, most of the pelvic fractures are caused by the high falling and traffic accident. Pelvic fractures caused by these high-impact forces often accompanied with urethral disruption, rectal damage, and even angiorrhexis, thus resulting in a critical condition. Literature reports that unstable pelvic fracture had a morbidity of as high as 4–8 % after treatment [1]. Open reduction and internal fixation (ORIF) has been used from 1980s in the treatment of pelvic fractures [2], which has obtained a good curative effect. Early research, however, also found that the ORIF had disadvantages such as more bleeding and injury, and easy to cause blood vessels and nerve damage [3–5]. Symphyseolysis is a common injury in pelvic fracture, accounting for about 24 % of the pelvic fractures [6]. Most of symphyseolysis is caused by extorsion force. Study has shown that if the pubic symphysis was more than 2.5 cm and there existed stable rotation, surgeries like external or internal fixation should be used for treatment [7].
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Fig. 1 a Cervical-thoracic-lumbar-pelvic-upper femoral composite; b Fifth lumbar vertebra-pelvic-upper femoral composite
Percutaneous internal pelvic fixation has the advantages of less bleeding and injury. But since the anatomical structure of the pelvic ring is complicated and closed reduction is relatively difficult [8], serious complications may appear in case of careless operation. This research attempts to obtain accurate anatomical data through measurement of normal pelvic specimens from embalmed adult cadavers combined with finite element analysis, so as to help canulated screw placement for percutaneous treatment of symphyseolysis, improve the accuracy of screw placement and reduce operation complications.
Materials and Methods Specimens’ Collection and Preparation 20 cases of adult cadavers (13 cases = male, 7 cases = female) were provided by Department of Anatomy of Wenzhou Medical University. The cadavers were transected on the cervical vertebra and upper 1/3 of the thighs. Soft tissues (i.e., muscle) that attached to the cervical and lumbar spines and femoral shaft were stripped. 10 composites were obtained (cervical-thoracic-lumbar-pelvicupper femoral composite) (Fig. 1a). The cadavers were transected on the fifth lumbar vertebra and upper 1/3 of the thighs. Soft tissues (i.e., muscle and ligament) that attached to the lumbar vertebra, pelvis, and femoral shaft were stripped. Hip articular capsule and ligaments were carefully removed. 10 fifth lumbar vertebra-pelvic-upper femoral composites were obtained (Fig. 1b).
Equipment and Software Operating equipments and measurement tools were (1) electric drill, kirschner wire (2.5 mm), hacksaw and canulated screw (6.5 mm, Stryker company); (2) vernier
123
caliper, straight ruler, set square, protractor; and (3) C-arm machine (Fig. 2a). 10 adult patients with whole pelvic CT (64 slice spiral CT, Brilliance) scan were selected randomly, and those having cancer and malformation were excluded. Softwares used for the finite element analysis were ABAQUS 6.11, MIMICS14.11, and CATIAV5R19, which required Windows XP operating system.
Measurement of Pelvic Specimens Transverse incision was given on the upper ledge of the pubic symphysis. Spermatic cord or round ligament of the uterus was exposed. And the distance between the pubic tubercle with spermatic cord or round ligament of the uterus was measured (Fig. 2b). Soft tissue around the pubic symphysis was removed to measure the following indexes: the narrowest diameter of the superior ramus of pubis (Fig. 3a), distance between two pubic tubercles (Fig. 3b), the thickness of the upper pubic symphysis (Fig. 3c), and distance between upper and lower pubic symphysis (Fig. 3d).
Finite Element Analysis 3D finite element model of pelvis was established and observed using fluoroscopy. Cylinder was set by function ‘‘cylinder’’ of MEDCAD. The pubic symphysis was reset by virtual operation function of MIMICS, and model of canulated screw fixation for symphyseolysis was established (Fig. 4a). The 2D horizontal plane which canulated screw located on was found, and 2D distance measuring tool was used to determine the length of canulated screw that could fit in (Fig. 4b). Combining with the 2D sagittal position and coronal position, whether the screw could pierce through the cortex was estimated via fluoroscopy
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Fig. 2 a Operating equipment and measurement tools; b Distance between the pubic tubercle with spermatic cord
Fig. 3 a Narrowest diameter of the superior ramus of pubis; b Distance between two pubic tubercles; c Thickness of the upper pubic symphysis; d Distance between upper and lower pubic symphysis
(Fig. 4c). Canulated screw was selected, and 3D distance measuring tool was used to determine the distance between needle entry point and pubic tubercle (Fig. 4d). The pubic symphysis screw was selected, which 3D coordinates could be found under the option of ‘‘characteristics’’ (Fig. 4e). Since the quadratic sums of 3D coordinates were all 1, the angels of the screw with horizontal plane, coronal, and sagittal planes namely the entry directions of the canulated screw could be calculated directly with the formula (Fig. 4f).
Results Measurement Results of Pelvic Specimens The distance between round ligament of the uterus and pubic tubercle was 4.408 ± 0.304 mm, and the distance between spermatic cord and pubic tubercle was 5.196 ± 0.251 mm. Both the spermatic cord and round ligament of the uterus have a certain degree of mobility. Narrowest diameter of the superior ramus of pubis was
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Fig. 4 a Model was in horizontal position. Pubic symphysis screw was placed via fluoroscopy; b 2D distance measuring tool was used to determine screw length; c Whether the screw was through the bone cortex was observed on the coronal and sagittal planes; d The radium of the screw was decreased to reduce error. The pubic tubercle was marked and the distance between canulated screw and pubic tubercle was measured; e Properties were clicked to indicate the entry direction of the canulated screw; f Function formula was used for experiment
Fig. 5 a The model was in horizontal position, and parameters of screw channel was used for closed reduction and internal fixation; b Postoperative X-ray indicated that the screw position was good
9.127 ± 1.189 mm, distance between two pubic tubercles was 55.656 ± 3.780 mm, thickness of the upper pubic symphysis was 10.510 ± 0.814 mm, and distance between upper and lower pubic symphysis was 40.872 ± 1.211 mm (Data not shown).
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Anatomical Parameters of Screw Channel Measured by Finite Element The angle between canulated screw guide pin and horizontal plane was 8.342 ± 2.152°, the one between guide pin and
Cell Biochem Biophys (2015) 71:1243–1248
coronal plane was 5.236 ± 1.612°, and the distance from entry point to the outer edge of pubic tubercle was 10.023 ± 1.245 mm (Data not shown). Percutaneous Surgery at Horizontal Position was Simulated on Cadaver Percutaneous surgery was performed on cadaver at horizontal position, and the screw was placed correctly in postoperative imaging examination (Fig. 5).
Discussion During percutaneous pelvic fixation, entry point and direction of screw are not easy to master, so there often appears deviation. Repeat intraoperative adjustment and nailing not only makes the patients and doctors exposed to excessive X-ray radiation, but also easily causes damage to adjacent neurovascular and other related organizations. Therefore, the development of such minimally invasive operation requires the doctor to have excellent operative skill, and also needs the support of good fluoroscopic equipment and imaging system [9]. Certain numbers of hospitals that conduct percutaneous pelvic fixation do not have 3D positioning system but are based on the repeat intraoperative fluoroscopy with single bulb X-ray fluoroscopic machine. Considering the above facts, this study aims to obtain accurate anatomical data of canulated screw channel through measurement of normal pelvic specimens from embalmed adult cadavers combined with finite element analysis, which can help the canulated screw placement for percutaneous treatment of symphyseolysis by improving the accuracy of screw placement. Pubic symphysis is a hemi-joint structure, which is closely connected with the aid of the fibrous cartilage. There are four ligaments (superior pubic ligament, lower pubic ligament, anterior pubic ligament, and posterior pubic ligament) around that closely connected bilateral pubes. According to the thickness of the upper pubic symphysis, distance between upper and lower pubic symphysis, and the narrowest diameter of the superior ramus of pubis measured in the experiment, all could accommodate the canulated screw of 6.5 mm. So, canulated screw replacement was feasible on anatomy. Spermatic cord or round ligament of the uterus was near the pubic tubercle and required special protection during operation. Through the anatomical study, patient accepting percutaneous canulated screws for treating symphyseolysis is in the supine position. A small incision was given on the lateral-superior area of pubic tubercle, and separated to the pubic tubercle bluntly. The pelvic reduction clamp, which reached the basement of the pubic tubercle through the lateral channel
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of the spermatic cord (round ligament of the uterus), was used to clamp and reset pubic symphysis. Pelvic clamp could reset pubic symphysis and protect the spermatic cord (round ligament of the uterus). In addition, it could be the reference for nailing under X-ray fluoroscopic machine. There are large errors in angel and direction of canulated screw using traditional manual measurement. This study adopted 3D finite element analysis to measure its 3D angle so as to improve the reliability and authenticity of the measured results. Finite element software applied in the field of orthopedic biomechanics firstly reported in 1972 [10]. It is widely applied in the field of biomechanics in recent years. Using Mimic software, entry angle of canulated screw guide pin could be calculated by its 3D coordinates. And the anatomic relationship between entry point of canulated screw guide pin and pubic tubercle could also be measured by 3D measuring tool. Compared with the traditional cadaver anatomy method, the finite element analysis on parameters of canulated screw channel for symphyseolysis was of high precision and repeatability [11, 12], and was not limited by the specimen of cadaver; At the same time, the entry angle of screw was calculated from the finite element model reconstructed on the data of pelvic CT scan, which had a better simulation, and could provide patients with a more personalized treatment option. Study on parameters of screw channel in percutaneous fixation of canulated screw for symphyseolysis can improve the accuracy of the screw placement, avoid the damage of peripheral spermatic cord (round ligament of the uterus) around, also reduce the fluoroscopy number of C-arm machine intraoperatively, and reduce the risk of infection in operative field. In addition, the significance of the research results is also reflected indirectly in the following aspects: (1) canulated screw with appropriate length was selected. Canulated tension screw produced pressure between the pubic symphysis, because its thread could only be embedded in contralateral cortex of the pubic symphysis. Cortex of the nailing side formed into a sliding hole due to the self-drilling effect of the canulated screw. Therefore, the selected intraoperative canulated screw must be ensured to be embedded in the contralateral cortex of pubic symphysis, and yet not too long so that the surrounding tissue would not be damaged. (2) The best operation time was attempted to be adopted. Routt et al. believed that the best operation time for patients with symphyseolysis was within 5 days after injury [13]. Delayed treatment would reduce the success of closed reduction. Research on screw parameters could provide better clinical reference for surgeon. Early anatomical repositioning of pelvis could effectively control bleeding, which was conducive to treatment and postoperative nursing for patients with combined injury. (3) Personalized
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treatment can be provided through the preoperative CT scan and postoperative 3D finite element analysis, which can better prevent the missed diagnosis of fractures at pelvic posterior ring. Swiss scholar Scheyerer found that the missed diagnosis rate of fractures at pelvic posterior ring was very high in patients with simple pubic ramus fracture [14]. And Simonian et al. suggested that single used of anterior ring fixation could not stabilize posterior pelvic ring [15]. Therefore, research on parameters of screw channel can improve diagnosis, and provide personalized treatment options. Limited by the number of pelvis specimens, and the influence factors such as race, height, gender, etc., the sampling error is unavoidable. Moreover, part of the pelvic fractures of symphyseolysis was caused by high-impact force. As the fracture displacement is complicated, there may be differences between the fixation methods. Acknowledgments This research was supported by the Zhejiang Provincial Natural Science Foundation of china under Grant No. LQ12H06002. The work was also supported by Zhejiang province health department funding under Grant No. 2013KYB176 and Zhejiang Province University Students’ Science and Technology Innovation Program (XinMiao plan) under Grant No. 2012R413006. Conflict of interest interest.
The authors have not declared any conflicts of
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