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Use of a life-size three-dimensional-printed spine model for pedicle screw instrumentation training

Use of a life-size three-dimensional-printed spine model for pedicle screw instrumentation training Background: Training beginners of the pedicle screw instrumentation technique in the operating room is limited because of issues related to patient safety and surgical efficiency. Three-dimensional (3D) printing enables training or simulation surgery on a real-size replica of deformed spine, which is difficult to perform in the usual cadaver or surrogate plastic models. The purpose of this study was to evaluate the educational effect of using a real-size 3D-printed spine model for training beginners of the free-hand pedicle screw instrumentation technique. We asked whether the use of a 3D spine model can improve (1) screw instrumentation accuracy and (2) length of procedure. Methods: Twenty life-size 3D-printed lumbar spine models were made from 10 volunteers (two models for each volunteer). Two novice surgeons who had no experience of free-hand pedicle screw instrumentation technique were instructed by an experienced surgeon, and each surgeon inserted 10 pedicle screws for each lumbar spine model. Computed tomography scans of the spine models were obtained to evaluate screw instrumentation accuracy. The length of time in completing the procedure was recorded. The results of the latter 10 spine models were compared with those of the former 10 models to evaluate learning effect. Results: A total of 37/200 screws (18.5%) perforated the pedicle cortex with a mean of 1.7 mm (range, 1.2–3.3 mm). However, the latter half of the models had significantly less violation than the former half (10/100 vs. 27/100, p <0.001). The mean length of time to complete 10 pedicle screw instrumentations in a spine model was 42.8 ± 5.3 min for the former 10 spine models and 35.6 ± 2.9 min for the latter 10 spine models. The latter 10 spine models had significantly less time than the former 10 models (p <0.001). Conclusion: A life-size 3D-printed spine model can be an excellent tool for training beginners of the free-hand pedicle screw instrumentation. Keywords: 3D-printed spine model, Pedicle screw instrumentation, Beginners, Training Background of pedicle screw malpositioning ranges from 0 to 25%, Pedicle screws are frequently used in spine surgeries, depending on the case’s degree of complexity and the and their use is expected to increase as the number of surgeon’s level of experience [8–12]. Safe and accurate spinal fusion surgeries is rapidly increasing [1–4]. Ped- instrumentation of pedicle screws is important, and this icle screw fixation is beneficial in achieving mechanical technique is one of the major skills that a trainee in stabilization during bony fusion. However, inadvertent spine surgery has to learn and acquire. perforation of pedicle screws into the spinal canal can Training beginners of this technique through surgical sometimes be fatal [5]. It can lead to neurologic injury procedures of patients in the operating room is limited or unsatisfactory degrees of stabilization [6, 7]. The rate because of issues related to patient safety and surgical efficiency [13]. Training on cadaver spines can be an ap- propriate alternative, but due to high costs and lack of * Correspondence: hyongnyun@naver.com available cadavers for all trainees, trainers seek for other Department of Orthopaedic Surgery, Kangnam Sacred Heart Hospital, Hallym surrogate spine models [14–16]. We believe that a life- University College of Medicine, 948-1, Dalim-1dong, Youngdeungpo-gu, Seoul 150-950, South Korea © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Park et al. Journal of Orthopaedic Surgery and Research (2018) 13:86 Page 2 of 8 size 3D-printed model can be an excellent solution. Ac- tual osseous spine anatomy can be reproduced into a life-size 3D-printed model allowing surgeons a firsthand look at what they will be operating on before the real surgery. This allows simulation surgery before the real surgery, increasing the learner’s ability to retain surgical skills and building learner confidence in a low-stress environment [17, 18]. Furthermore, 3D printing enables training on a life-size replica of deformed spine or young-aged spine, which is difficult to perform in the usual cadaver or surrogate plastic models. 3D printing technologies are common in product de- sign industries, and their use is increasing in all fields [19, 20]. Recent technical developments and their popu- larity within the general public are leading the world to an era of personalized 3D printing, similar to what has become of a personalized computer or printer. As the popularity of 3D printing is increasing, it is becoming fi- nancially feasible and accessible to use the practice of medicine [20]. As this technology enables replication of actual osseous anatomy, it can be most beneficial to sur- geons who operate on bony structures, including the spine [21]. We believe this technology can be useful in educating residents of their surgical skills. To our knowledge, no reports have described surgical skill training of the pedicle screw instrumentation tech- nique using a life-size 3D-printed spine model. The pur- pose of this study was to evaluate the educational effect of using a life-size 3D-printed spine model for training beginners of the free-hand pedicle screw instrumenta- tion technique in improving screw instrumentation ac- curacy and procedure time. Fig. 1 A CT scan was taken from the lower endplate of 12th thoracic vertebra (T12) and below the 1st sacral vertebra (S1) with a Methods 1-mm thickness slice 3D printing of life-size spinal models CT scan Ten adult patients (5 male, 5 female) with low back pain were enrolled. The mean age of patients was 35.2 years by the 3D printing machine (Objet30Pro®, Stratasys, (range, 24–52 years). They were confirmed not to have Valencia, CA, USA) to produce a life-size lumbar spine any congenital abnormalities, other deformities, and in- model with polypropylene (Fig. 2). Twenty life-size 3D- stability on the lumbosacral spine by using plain radio- printed lumbar spine models were made for the study. graphs and CT scan. Patients underwent CT scan from the lower endplate of the 12th thoracic vertebra (T12) Pedicle screw fixation in life-size 3D-printed lumbar spine and below the 1st sacral vertebra (S1) with a 1-mm models thickness slice (Fig. 1). Institutional review board ap- Two residents who had no experience of pedicle screw in- proval was obtained for the study. strumentation were selected to participate in this study. First, the residents were instructed by an experienced 3D printing spine surgeon (KJC) on the instrumentation technique of The data acquired from the CT scan were stored in the pedicle localization and the method of pedicle screw Digital Imaging and Communications in Medicine for- fixation. Subsequently, each 3D-printed spine model was mat and converted to a standard triangulation language mounted on the lumbar spine holder (Sawbones®, Vashon file format by using a specialized software (MIMICS: Island, WA, USA) to secure each vertebral body with the Materialise Interactive Medical Image Control System L3 vertebra placed most ventrally (Fig. 3a). Synthetic poly- Software, Materialise, Leuven, Belgium) that can be used mer clay was placed surrounding the pedicle; thus, only Park et al. Journal of Orthopaedic Surgery and Research (2018) 13:86 Page 3 of 8 Fig. 2 A real-sized lumbar spinal model was produced using the 3D printing machine (Objet30Pro®, Stratasys, Valencia, CA, USA). Five lumbar models were produced for one spine model. In total, 20 spine models (100 lumbar models) were produced the posterior surface anatomy could be seen, but the ped- icle size or orientation could not be seen (Fig. 3b). Two novice orthopedic residents were provided with plain ra- diographs and CT scan images on each patient’s lumbar spine, then each inserted 10 pedicle screws (two screws for one vertebra) for one spine model (5 lumbar verte- brae). The residents first inserted a K-wire on the entry point of the pedicle screw, which was at the junction of the midline of the transverse process and the lateral mar- Fig. 3 a Each 3D-printed spine model was mounted on the lumbar gin of the facet joint. A small pilot hole was made with an spine holder (Sawbones®, Vashon Island, WA, USA) to secure each vertebral body. b Synthetic polymer clay was placed surrounding the awl. After determining the ideal pathway for the screw by pedicle; thus, only the posterior surface anatomy could be seen, but the using a guide wire, a hole was made with a small-diameter pedicle size or orientation could not be seen. c Two novice surgeons drill. The opening for the entrance of the pedicle screw who had no experience of free-hand pedicle screw insertion technique was checked with a small ball tip probe. The safety of the were instructed of the technique by an experienced surgeon, and each pathway for the pedicle screw was determined when an inserted 10 pedicle screws for each lumbar spinal model intraosseous resistance was noted in all (medial, lateral, superior, and inferior) directions. Drilling was further carried out using tappers with larger diameters up to 5 mm. Finally, the pedicle screw was gently inserted pedicle: category A, fully contained within the pedicle; (Fig. 3b). Each resident inserted pedicle screws into 10 category B, breach less than 2 mm; category C, breach of 3D-printed spine models (100 pedicle screws for one resi- 2 to 4 mm; and category D, breach greater than 4 mm. dent) (Fig. 3c). The residents examined each specimen A critical violation was defined as > 2 mm. Perforation after instrumentation to identify their errors to improve of the pedicle wall > 2 mm is reported to increase the their accuracy on the next one (Fig. 4a). potential for neurologic complications. These results were interpreted and recorded by expert musculoskeletal Radiologic analysis of pedicle screw instrumentation radiologists blinded to this study. In addition, the length The spinal models underwent CT scan immediately after of time to complete the procedure was recorded. The the pedicle screws were inserted to evaluate their instru- results of the latter 10 spinal models were compared mentation accuracy (Fig. 4b). Screw malposition and with those of the former 10 models to evaluate learn- breach of medial and lateral wall of the pedicles were re- ing effect. The resident, who has done the screw in- corded. Position of the screws were classified into one of strumentation just after their procedure and before four categories based on their position relative to the the new specimen, was informed of the pedicle screw Park et al. Journal of Orthopaedic Surgery and Research (2018) 13:86 Page 4 of 8 Spearman’s correlation analysis. Statistical significance was accepted for p values < 0.05. Results Pedicle screw violations Two-hundred pedicles in 100 vertebral bodies were inserted with 5-mm cylindrical pedicle screws. A total of 37/200 screws (18.5%) perforated the outer cortex of the pedicles with a mean of 1.7-mm violation (range, 1.2–3. 3 mm). Of the 37 perforating screws, 36 (97%) violated the medial side of the pedicle. The first and second resi- dents made 18 (49%) and 19 (51%) violations, respect- ively, and no significant difference was found between the two (p > 0.05). No screw was classified in category D (> 4-mm cortical breach). However, blinded CT evaluations of screw placement indicated that 5.5% (11/200), 13% (26/200), and 81.5% (163/200) of screws were in categories C (2- to 4-mm breach), B, and A, respectively. When 20 spine models were divided into two groups (the former and latter 10 spine models), the former 10 spine models had 11% (11/100), 16% (16/100), and 73% (73/100) of screws in categories C, B, and A, respectively. The latter 10 spine models had 0% (0/100), 10% (10/100), and 90% (90/100) of screws in categories C, B, and A, respectively (Table 1). Less percent total violations were seen in the latter 10 spine models (10/100 pedicle screws) compared with the former 10 spine models (27/100 pedicle screws) (p <0. 05; odds ratio, 0.30; 95% CI, 0.137–0.661) (Fig. 1). No critical violation of the pedicle screws (> 2 mm) were seen in the latter 10 spine models (0/100 pedicle screws) Fig. 4 a The spinal models underwent b CT scan immediately after the pedicle screws were inserted to evaluate their instrumentation compared with the former 10 spine models (11/100 ped- accuracy icle screws). instrumentation result on each spine model (10 ped- Incidence and degree of violation based on vertebral icle screws inserted in 5 vertebrae); hence, their ex- level perience can help with the next procedure. Violations occurred in all levels of the lumbar spine ex- cept at L5 (Table 2). The most common level of viola- Statistical analysis tion occurred at L1 with 32.5% (13/40). L2, L3, and L4 Statistical analysis was performed using SPSS version 23. had 25% (10/40), 22.5% (9/40), and 12.5% (5/40), 0 (SPSS, SPSS Inc., Chicago, IL, USA) software. Data normality was assessed by the Kolmogorov–Smirnov Table 1 Screw placement accuracy test. Chi-square test was used to compare the inci- dence of screw violation of the pedicle between the Screw placement category Percentage of screws former 10 (100 pedicles) and latter 10 spine models Former group Latter group (n = 100 screws) (n = 100 screws) (100 pedicles). Mann–Whitney U test was used to compare the length of time to complete the screw in- A (fully contained) 73 90 strumentation between the former and latter 10 spine B (breach < 2 mm) 16 10 models. Logistic regression analysis was performed to C (breach of 2–4 mm) 11 0 evaluate improvement in error rates through the 20 D (breach > 2 mm) 0 0 spinal models with respect to the total error rates. Bi- Former group: 10 3D-printed spinal models that residents instrumented pedicle variate associations between the vertebral level and screws earlier to the 10 latter group. Latter group: 10 3D-printed spinal models the pedicle screw violation were examined by using that residents instrumented pedicle screws later to the 10 former group Park et al. Journal of Orthopaedic Surgery and Research (2018) 13:86 Page 5 of 8 Table 2 Results of 20 spinal models with 200 lumbar pedicles instrumented No. pedicles instrumented No. violations % violation Avg. violation (mm) Range of violation (mm) No. critical violation % critical violation L1 40 13 32.5 1.85 1.3–2.5 5 12.5 L2 40 10 25 1.87 1.2–3.1 4 10 L3 40 9 22.5 1.74 1.2–3.3 2 5 L4 40 5 12.5 1.44 1.3–1.8 0 0 L5 40 0 0 0 0 0 0 respectively, with L4 having the least number of viola- Discussion tions (Table 2). Pedicles in the lower vertebral level had Pedicle screw is a penetrating type of fixation device and less percent violation compared with higher vertebra offers a secure vertebral grip that enhances control of level (Spearman’s correlation coefficient, − 0.28; p <0. the inserted segments and firm fixation [11, 22]. After it 01). Based on the lumbar spine level, violations has gained popularity, the number of spinal fusion has above and below L3 were 86% (32/37) and 14% (5/ exceedingly increased for the last few decades. Spinal fu- 37), respectively, and a significant difference was sion using pedicle screw fixation became a gold standard found (p <0.05). technique, but pedicle screw instrumentation has its Critical violation (> 2 mm) did not occur in L4 and L5. own risk. Complications such as neurological injury, The most common level of critical violation occurred at spinal construct failure, and deep wound infection have L1 with 12.5% (5/40). L2 and L3 had 10% (4/40) and 5% been reported by researchers [6, 7]. Moreover, great (2/40) violations, respectively. Pedicles in the lower vessel injury caused by malposition of the pedicle vertebral level had less percent violation compared with screw may cause fatal results in the thoracic spine in higher vertebral level (Spearman’s correlation coefficient, patients undergoing deformity correction [5]Safeand − 0.22; p < 0.01). Violations more than 4 mm of the efficient technique for pedicle screw instrumentation pedicles did not occur. is essential [23, 24]. Many techniques have been reported during several Length of procedure for pedicle screw placement decades [22, 25, 26]. Parker et al. reported the accuracy The mean length of time to complete 10 pedicle and safety of free-hand technique for pedicle screw in- screw instrumentations in a spine model was 42.8 ± strumentation in thoracic and lumbar spine [10]. Cur- 5.3 min for the former 10 spine models and 35.6 ± rently, more accurate pedicle screw instrumentation is 2.9 min for the latter 10 spine models (Table 3). possible with the aid of computer-assisted navigation The latter 10 spine models required significantly systems [8, 9, 12, 26]. Although advanced scientific de- less time than the former 10 spine models (p <0. vices are beneficial, having surgeons well accustomed to 001). Later instrumentation of the pedicle screws anatomy and the applied technique is essential [27, 28]. required less time compared with earlier instrumen- This is more important to residents who are not familiar tation (Spearman’s correlation coefficient, − 0.71; p with surgical skills and when mistakes can cause fatal < 0.001) (Fig. 5). results, such that can occur during pedicle screw instru- mentation [20, 21]. Table 3 Procedure time required for fixation of 10 pedicle However, learning the technique is technically de- screws for each model manding even for clinical fellow surgeons. For this No. Resident 1 Resident 2 reason, Bergeson et al. insisted that surgeons who do 1 51.19 44.48 not have enough experience in pedicle screw instrumen- 2 51.21 39.13 tation should practice the technique with cadavers 3 43.26 37.36 before the real surgery [23]. Training can be safely per- formed in a low-stress environment using cadavers and 4 42.50 41.14 synthetic bone. However, getting enough cadavers for 5 40.38 35.28 teaching and training of pedicle screw instrumentation is 6 35.06 34.49 difficult. Even when surgical simulation training on ca- 7 36.18 31.44 davers or synthetic bone is over, the opportunity to 8 42.53 36.21 visualize and handle a replica of the spine before surgery 9 35.11 34.52 can be enormously helpful in building confidence. A life- size 3D-printed spine model can be an excellent solution. 10 35.41 33.06 Our study has shown that the use of the life-size 3D- Numbers presented as minutes No. numbers of the real-sized 3D-printed spinal models printed spine model improves accuracy and length of Park et al. Journal of Orthopaedic Surgery and Research (2018) 13:86 Page 6 of 8 Fig. 5 Total pedicle violation percentage, critical (breach of >2mm) pedicle violation percentage are shown for resident 1 (b), resident 2 (c), and combined (a). (a) The mean total violation percentage decreased from 30% with the first spine model to 10% after completing five spine models (50 pedicle screws). This violation percentage became stable at 10% from the sixth to tenth models. The mean critical violation (>2-mm breach) percentage also decreased as residents continued practicing and became stable at 0% after completing five models. (d) The length of time required to complete screw instrumentation decreased as residents continued to practice the skills on the 3D-printed models. A strong negative correlation was observed between the repetitive time of screw instrumentation and length of procedure (Spearman’s correlation coefficient, −0.71; p <0.001) time to complete pedicle screw instrumentation. Prac- and length of procedure (Spearman’s correlation coeffi- ticing instrumentation of pedicle screws on the 3D- cient, − 0.71; p <0.001). printed spine model has shown a learning effect (Fig. 5). In the study, L5 did not show any screw violation Less violation of the screws was seen as residents contin- compare with 32.5% of total violation in L1. Pedicles in ued practicing the technique on the model. The mean the lower vertebral level showed less percent violation total violation percentage for a resident decreased from compared with the higher vertebral level (Spearman’s 30% with the first spine model to 10% after completing correlation coefficient, − 0.28; p < 0.01). Pedicles of the five spine models (50 pedicle screws). This violation lower vertebral level are known to be wider than the percentage became stable at 10% from the sixth to tenth higher vertebral level, and this can be the reason for the models. The mean critical violation (> 2-mm breach) lower rate of screw violation in the lower vertebral level percentage also decreased as residents continued pedicles. Furthermore, total violation rate (18.5%) in this practicing and became stable at 0% after completing five study on the lumbar vertebra was lower than that (29%) models. The earlier and later performed 10 spine models on the thoracic vertebra in different cadaveric studies showed less percent total violations in the latter 10 [8]. This may have a similar reason, as pedicles in spine models (10/100 pedicle screws) compared with lumbar vertebra are wider than those in the thoracic ver- the former 10 spine models (27/100 pedicle screws) tebra. It can be inferred that narrower pedicles have a (p < 0.05; odds ratio, 0.30; 95% CI, 0.137–0.661). More- higher possibility of screw violation than wider pedicles. over, the length of time required to complete screw instru- Therefore, pedicle instrumentation on a young patient mentation decreased as residents continued to practice with congenital deformity may have higher risk for screw the skills on the 3D-printed models. The mean length of violation. However, practicing the skills on young ca- time to complete 10 pedicle screw instrumentations in davers with spine deformity is almost impossible because one spine model was 42.8 ± 5.3 min and 35.6 ± 2.9 min for most cadavers are old aged. 3D printing enables training the former (100 pedicle screws) and latter 10 spine models on a life-size replica of deformed spine or young-aged (100 pedicle screws), respectively. The latter 10 spine spine, which is a great advantage over using cadavers for models required significantly less time than the former 10 skills training. models (p < 0.001). A strong negative relationship was ob- 3D printing has a number of applications in medicine, served between repetitive time of screw instrumentation and we propose that this technique can be used for Park et al. Journal of Orthopaedic Surgery and Research (2018) 13:86 Page 7 of 8 training of pedicle screw instrumentation [19, 20]. Wu Received: 19 December 2017 Accepted: 28 March 2018 et al. provided a protocol for replication of accurate 3D spine models and reported that the models can be suit- References able for spinal fixation research [21]. For an in-office 1. Yoshii T, Hirai T, Yamada T, Sumiya S, Mastumoto R, Kato T, Enomoto M, production of 3D models, Schwartz et al. reported it Inose H, Kawabata S, Shinomiya K, Okawa A. Lumbosacral pedicle screw took an initial investment of $52,000 to $56,000, which placement using a fluoroscopic pedicle axis view and a cannulated tapping device. J Orthop Surg Res. 2015;10:79. covers the printer, printer base cabinet, installation, 2. Chen C, Cao X, Zou L, Hao G, Zhou Z, Zhang G. Minimally invasive unilateral training, and printer software, plus a 1-year warranty versus bilateral technique in performing single-segment pedicle screw [29]. To lower the cost, open-source software for the fixation and lumbar interbody fusion. J Orthop Surg Res. 2015;10:112. 3. 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Various materials can be used for Belg. 2013;79:361–7. 3D printing, and further evaluation to mimic the osseous 6. Blumentahl S, Gill. Complications of the Wiltse pedicle screw fixation feel of the real pedicle may enable replication of the real system. Spine 1993; 18: 1867–1871. 7. Faraj AA, Webb JK. Early complications of spinal pedicle screw. Eur Spine J. osseous feeling replicas in the near future. 1997;6:324–6. 8. Laine T, Lund T, Ylikoski M, Lohikoski J, Schlenzka D. Accuracy of pedicle screw insertion with and without computer assistance: a randomized Conclusion controlled clinical study in 100 consecutive patients. Eur Spine J. 2000;9: A life-size 3D-printed spine model can be an excellent 235–40. tool for training beginners of the free-hand pedicle screw 9. Lieberman IH, Hardenbrook MA, Wang JC, Guyer RD. Assessment of pedicle screw placement accuracy, procedure time, and radiation exposure using a instrumentation. miniature robotic guidance system. J Spinal Disord Tech. 2012;25:241–8. 10. Parker SL, McGirt MJ, Farber SH, Amin AG, Rick AM, Suk I, Bydon A, Sciubba Abbreviations DM, Wolinsky JP, Gokaslan ZL, Witham TF. Accuracy of free-hand pedicle 3D printing: Three-dimensional printing; CT: Computed tomography screws in the thoracic and lumbar spine: analysis of 6816 consecutive screws. Neurosurgery. 2011;68:170–8. Acknowledgements 11. Suk SI, Kim WJ, Lee SM, Kim JH, Chung ER. Thoracic pedicle screw fixation in Not applicable spinal deformities: are they really safe? Spine. 2001;26:2049–57. 12. van Dijk JD, can den Ende RP, Stramigioli S, Köchling M, Höss N. Clinical Funding pedicle screw accuracy and deviation from planning in robot-guided spine This work was supported by the National Research Foundation of Korea surgery: robot-guided pedicle screw accuracy. Spine (Phila Pa 1976). 2015; (NRF) grant funded by the Korea government (MSIP; Ministry of Science, ICT 50:E986–91. and Future Planning) (2017R1C1B5075653). 13. 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Use of a life-size three-dimensional-printed spine model for pedicle screw instrumentation training

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10.1186/s13018-018-0788-z
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Abstract

Background: Training beginners of the pedicle screw instrumentation technique in the operating room is limited because of issues related to patient safety and surgical efficiency. Three-dimensional (3D) printing enables training or simulation surgery on a real-size replica of deformed spine, which is difficult to perform in the usual cadaver or surrogate plastic models. The purpose of this study was to evaluate the educational effect of using a real-size 3D-printed spine model for training beginners of the free-hand pedicle screw instrumentation technique. We asked whether the use of a 3D spine model can improve (1) screw instrumentation accuracy and (2) length of procedure. Methods: Twenty life-size 3D-printed lumbar spine models were made from 10 volunteers (two models for each volunteer). Two novice surgeons who had no experience of free-hand pedicle screw instrumentation technique were instructed by an experienced surgeon, and each surgeon inserted 10 pedicle screws for each lumbar spine model. Computed tomography scans of the spine models were obtained to evaluate screw instrumentation accuracy. The length of time in completing the procedure was recorded. The results of the latter 10 spine models were compared with those of the former 10 models to evaluate learning effect. Results: A total of 37/200 screws (18.5%) perforated the pedicle cortex with a mean of 1.7 mm (range, 1.2–3.3 mm). However, the latter half of the models had significantly less violation than the former half (10/100 vs. 27/100, p <0.001). The mean length of time to complete 10 pedicle screw instrumentations in a spine model was 42.8 ± 5.3 min for the former 10 spine models and 35.6 ± 2.9 min for the latter 10 spine models. The latter 10 spine models had significantly less time than the former 10 models (p <0.001). Conclusion: A life-size 3D-printed spine model can be an excellent tool for training beginners of the free-hand pedicle screw instrumentation. Keywords: 3D-printed spine model, Pedicle screw instrumentation, Beginners, Training Background of pedicle screw malpositioning ranges from 0 to 25%, Pedicle screws are frequently used in spine surgeries, depending on the case’s degree of complexity and the and their use is expected to increase as the number of surgeon’s level of experience [8–12]. Safe and accurate spinal fusion surgeries is rapidly increasing [1–4]. Ped- instrumentation of pedicle screws is important, and this icle screw fixation is beneficial in achieving mechanical technique is one of the major skills that a trainee in stabilization during bony fusion. However, inadvertent spine surgery has to learn and acquire. perforation of pedicle screws into the spinal canal can Training beginners of this technique through surgical sometimes be fatal [5]. It can lead to neurologic injury procedures of patients in the operating room is limited or unsatisfactory degrees of stabilization [6, 7]. The rate because of issues related to patient safety and surgical efficiency [13]. Training on cadaver spines can be an ap- propriate alternative, but due to high costs and lack of * Correspondence: hyongnyun@naver.com available cadavers for all trainees, trainers seek for other Department of Orthopaedic Surgery, Kangnam Sacred Heart Hospital, Hallym surrogate spine models [14–16]. We believe that a life- University College of Medicine, 948-1, Dalim-1dong, Youngdeungpo-gu, Seoul 150-950, South Korea © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Park et al. Journal of Orthopaedic Surgery and Research (2018) 13:86 Page 2 of 8 size 3D-printed model can be an excellent solution. Ac- tual osseous spine anatomy can be reproduced into a life-size 3D-printed model allowing surgeons a firsthand look at what they will be operating on before the real surgery. This allows simulation surgery before the real surgery, increasing the learner’s ability to retain surgical skills and building learner confidence in a low-stress environment [17, 18]. Furthermore, 3D printing enables training on a life-size replica of deformed spine or young-aged spine, which is difficult to perform in the usual cadaver or surrogate plastic models. 3D printing technologies are common in product de- sign industries, and their use is increasing in all fields [19, 20]. Recent technical developments and their popu- larity within the general public are leading the world to an era of personalized 3D printing, similar to what has become of a personalized computer or printer. As the popularity of 3D printing is increasing, it is becoming fi- nancially feasible and accessible to use the practice of medicine [20]. As this technology enables replication of actual osseous anatomy, it can be most beneficial to sur- geons who operate on bony structures, including the spine [21]. We believe this technology can be useful in educating residents of their surgical skills. To our knowledge, no reports have described surgical skill training of the pedicle screw instrumentation tech- nique using a life-size 3D-printed spine model. The pur- pose of this study was to evaluate the educational effect of using a life-size 3D-printed spine model for training beginners of the free-hand pedicle screw instrumenta- tion technique in improving screw instrumentation ac- curacy and procedure time. Fig. 1 A CT scan was taken from the lower endplate of 12th thoracic vertebra (T12) and below the 1st sacral vertebra (S1) with a Methods 1-mm thickness slice 3D printing of life-size spinal models CT scan Ten adult patients (5 male, 5 female) with low back pain were enrolled. The mean age of patients was 35.2 years by the 3D printing machine (Objet30Pro®, Stratasys, (range, 24–52 years). They were confirmed not to have Valencia, CA, USA) to produce a life-size lumbar spine any congenital abnormalities, other deformities, and in- model with polypropylene (Fig. 2). Twenty life-size 3D- stability on the lumbosacral spine by using plain radio- printed lumbar spine models were made for the study. graphs and CT scan. Patients underwent CT scan from the lower endplate of the 12th thoracic vertebra (T12) Pedicle screw fixation in life-size 3D-printed lumbar spine and below the 1st sacral vertebra (S1) with a 1-mm models thickness slice (Fig. 1). Institutional review board ap- Two residents who had no experience of pedicle screw in- proval was obtained for the study. strumentation were selected to participate in this study. First, the residents were instructed by an experienced 3D printing spine surgeon (KJC) on the instrumentation technique of The data acquired from the CT scan were stored in the pedicle localization and the method of pedicle screw Digital Imaging and Communications in Medicine for- fixation. Subsequently, each 3D-printed spine model was mat and converted to a standard triangulation language mounted on the lumbar spine holder (Sawbones®, Vashon file format by using a specialized software (MIMICS: Island, WA, USA) to secure each vertebral body with the Materialise Interactive Medical Image Control System L3 vertebra placed most ventrally (Fig. 3a). Synthetic poly- Software, Materialise, Leuven, Belgium) that can be used mer clay was placed surrounding the pedicle; thus, only Park et al. Journal of Orthopaedic Surgery and Research (2018) 13:86 Page 3 of 8 Fig. 2 A real-sized lumbar spinal model was produced using the 3D printing machine (Objet30Pro®, Stratasys, Valencia, CA, USA). Five lumbar models were produced for one spine model. In total, 20 spine models (100 lumbar models) were produced the posterior surface anatomy could be seen, but the ped- icle size or orientation could not be seen (Fig. 3b). Two novice orthopedic residents were provided with plain ra- diographs and CT scan images on each patient’s lumbar spine, then each inserted 10 pedicle screws (two screws for one vertebra) for one spine model (5 lumbar verte- brae). The residents first inserted a K-wire on the entry point of the pedicle screw, which was at the junction of the midline of the transverse process and the lateral mar- Fig. 3 a Each 3D-printed spine model was mounted on the lumbar gin of the facet joint. A small pilot hole was made with an spine holder (Sawbones®, Vashon Island, WA, USA) to secure each vertebral body. b Synthetic polymer clay was placed surrounding the awl. After determining the ideal pathway for the screw by pedicle; thus, only the posterior surface anatomy could be seen, but the using a guide wire, a hole was made with a small-diameter pedicle size or orientation could not be seen. c Two novice surgeons drill. The opening for the entrance of the pedicle screw who had no experience of free-hand pedicle screw insertion technique was checked with a small ball tip probe. The safety of the were instructed of the technique by an experienced surgeon, and each pathway for the pedicle screw was determined when an inserted 10 pedicle screws for each lumbar spinal model intraosseous resistance was noted in all (medial, lateral, superior, and inferior) directions. Drilling was further carried out using tappers with larger diameters up to 5 mm. Finally, the pedicle screw was gently inserted pedicle: category A, fully contained within the pedicle; (Fig. 3b). Each resident inserted pedicle screws into 10 category B, breach less than 2 mm; category C, breach of 3D-printed spine models (100 pedicle screws for one resi- 2 to 4 mm; and category D, breach greater than 4 mm. dent) (Fig. 3c). The residents examined each specimen A critical violation was defined as > 2 mm. Perforation after instrumentation to identify their errors to improve of the pedicle wall > 2 mm is reported to increase the their accuracy on the next one (Fig. 4a). potential for neurologic complications. These results were interpreted and recorded by expert musculoskeletal Radiologic analysis of pedicle screw instrumentation radiologists blinded to this study. In addition, the length The spinal models underwent CT scan immediately after of time to complete the procedure was recorded. The the pedicle screws were inserted to evaluate their instru- results of the latter 10 spinal models were compared mentation accuracy (Fig. 4b). Screw malposition and with those of the former 10 models to evaluate learn- breach of medial and lateral wall of the pedicles were re- ing effect. The resident, who has done the screw in- corded. Position of the screws were classified into one of strumentation just after their procedure and before four categories based on their position relative to the the new specimen, was informed of the pedicle screw Park et al. Journal of Orthopaedic Surgery and Research (2018) 13:86 Page 4 of 8 Spearman’s correlation analysis. Statistical significance was accepted for p values < 0.05. Results Pedicle screw violations Two-hundred pedicles in 100 vertebral bodies were inserted with 5-mm cylindrical pedicle screws. A total of 37/200 screws (18.5%) perforated the outer cortex of the pedicles with a mean of 1.7-mm violation (range, 1.2–3. 3 mm). Of the 37 perforating screws, 36 (97%) violated the medial side of the pedicle. The first and second resi- dents made 18 (49%) and 19 (51%) violations, respect- ively, and no significant difference was found between the two (p > 0.05). No screw was classified in category D (> 4-mm cortical breach). However, blinded CT evaluations of screw placement indicated that 5.5% (11/200), 13% (26/200), and 81.5% (163/200) of screws were in categories C (2- to 4-mm breach), B, and A, respectively. When 20 spine models were divided into two groups (the former and latter 10 spine models), the former 10 spine models had 11% (11/100), 16% (16/100), and 73% (73/100) of screws in categories C, B, and A, respectively. The latter 10 spine models had 0% (0/100), 10% (10/100), and 90% (90/100) of screws in categories C, B, and A, respectively (Table 1). Less percent total violations were seen in the latter 10 spine models (10/100 pedicle screws) compared with the former 10 spine models (27/100 pedicle screws) (p <0. 05; odds ratio, 0.30; 95% CI, 0.137–0.661) (Fig. 1). No critical violation of the pedicle screws (> 2 mm) were seen in the latter 10 spine models (0/100 pedicle screws) Fig. 4 a The spinal models underwent b CT scan immediately after the pedicle screws were inserted to evaluate their instrumentation compared with the former 10 spine models (11/100 ped- accuracy icle screws). instrumentation result on each spine model (10 ped- Incidence and degree of violation based on vertebral icle screws inserted in 5 vertebrae); hence, their ex- level perience can help with the next procedure. Violations occurred in all levels of the lumbar spine ex- cept at L5 (Table 2). The most common level of viola- Statistical analysis tion occurred at L1 with 32.5% (13/40). L2, L3, and L4 Statistical analysis was performed using SPSS version 23. had 25% (10/40), 22.5% (9/40), and 12.5% (5/40), 0 (SPSS, SPSS Inc., Chicago, IL, USA) software. Data normality was assessed by the Kolmogorov–Smirnov Table 1 Screw placement accuracy test. Chi-square test was used to compare the inci- dence of screw violation of the pedicle between the Screw placement category Percentage of screws former 10 (100 pedicles) and latter 10 spine models Former group Latter group (n = 100 screws) (n = 100 screws) (100 pedicles). Mann–Whitney U test was used to compare the length of time to complete the screw in- A (fully contained) 73 90 strumentation between the former and latter 10 spine B (breach < 2 mm) 16 10 models. Logistic regression analysis was performed to C (breach of 2–4 mm) 11 0 evaluate improvement in error rates through the 20 D (breach > 2 mm) 0 0 spinal models with respect to the total error rates. Bi- Former group: 10 3D-printed spinal models that residents instrumented pedicle variate associations between the vertebral level and screws earlier to the 10 latter group. Latter group: 10 3D-printed spinal models the pedicle screw violation were examined by using that residents instrumented pedicle screws later to the 10 former group Park et al. Journal of Orthopaedic Surgery and Research (2018) 13:86 Page 5 of 8 Table 2 Results of 20 spinal models with 200 lumbar pedicles instrumented No. pedicles instrumented No. violations % violation Avg. violation (mm) Range of violation (mm) No. critical violation % critical violation L1 40 13 32.5 1.85 1.3–2.5 5 12.5 L2 40 10 25 1.87 1.2–3.1 4 10 L3 40 9 22.5 1.74 1.2–3.3 2 5 L4 40 5 12.5 1.44 1.3–1.8 0 0 L5 40 0 0 0 0 0 0 respectively, with L4 having the least number of viola- Discussion tions (Table 2). Pedicles in the lower vertebral level had Pedicle screw is a penetrating type of fixation device and less percent violation compared with higher vertebra offers a secure vertebral grip that enhances control of level (Spearman’s correlation coefficient, − 0.28; p <0. the inserted segments and firm fixation [11, 22]. After it 01). Based on the lumbar spine level, violations has gained popularity, the number of spinal fusion has above and below L3 were 86% (32/37) and 14% (5/ exceedingly increased for the last few decades. Spinal fu- 37), respectively, and a significant difference was sion using pedicle screw fixation became a gold standard found (p <0.05). technique, but pedicle screw instrumentation has its Critical violation (> 2 mm) did not occur in L4 and L5. own risk. Complications such as neurological injury, The most common level of critical violation occurred at spinal construct failure, and deep wound infection have L1 with 12.5% (5/40). L2 and L3 had 10% (4/40) and 5% been reported by researchers [6, 7]. Moreover, great (2/40) violations, respectively. Pedicles in the lower vessel injury caused by malposition of the pedicle vertebral level had less percent violation compared with screw may cause fatal results in the thoracic spine in higher vertebral level (Spearman’s correlation coefficient, patients undergoing deformity correction [5]Safeand − 0.22; p < 0.01). Violations more than 4 mm of the efficient technique for pedicle screw instrumentation pedicles did not occur. is essential [23, 24]. Many techniques have been reported during several Length of procedure for pedicle screw placement decades [22, 25, 26]. Parker et al. reported the accuracy The mean length of time to complete 10 pedicle and safety of free-hand technique for pedicle screw in- screw instrumentations in a spine model was 42.8 ± strumentation in thoracic and lumbar spine [10]. Cur- 5.3 min for the former 10 spine models and 35.6 ± rently, more accurate pedicle screw instrumentation is 2.9 min for the latter 10 spine models (Table 3). possible with the aid of computer-assisted navigation The latter 10 spine models required significantly systems [8, 9, 12, 26]. Although advanced scientific de- less time than the former 10 spine models (p <0. vices are beneficial, having surgeons well accustomed to 001). Later instrumentation of the pedicle screws anatomy and the applied technique is essential [27, 28]. required less time compared with earlier instrumen- This is more important to residents who are not familiar tation (Spearman’s correlation coefficient, − 0.71; p with surgical skills and when mistakes can cause fatal < 0.001) (Fig. 5). results, such that can occur during pedicle screw instru- mentation [20, 21]. Table 3 Procedure time required for fixation of 10 pedicle However, learning the technique is technically de- screws for each model manding even for clinical fellow surgeons. For this No. Resident 1 Resident 2 reason, Bergeson et al. insisted that surgeons who do 1 51.19 44.48 not have enough experience in pedicle screw instrumen- 2 51.21 39.13 tation should practice the technique with cadavers 3 43.26 37.36 before the real surgery [23]. Training can be safely per- formed in a low-stress environment using cadavers and 4 42.50 41.14 synthetic bone. However, getting enough cadavers for 5 40.38 35.28 teaching and training of pedicle screw instrumentation is 6 35.06 34.49 difficult. Even when surgical simulation training on ca- 7 36.18 31.44 davers or synthetic bone is over, the opportunity to 8 42.53 36.21 visualize and handle a replica of the spine before surgery 9 35.11 34.52 can be enormously helpful in building confidence. A life- size 3D-printed spine model can be an excellent solution. 10 35.41 33.06 Our study has shown that the use of the life-size 3D- Numbers presented as minutes No. numbers of the real-sized 3D-printed spinal models printed spine model improves accuracy and length of Park et al. Journal of Orthopaedic Surgery and Research (2018) 13:86 Page 6 of 8 Fig. 5 Total pedicle violation percentage, critical (breach of >2mm) pedicle violation percentage are shown for resident 1 (b), resident 2 (c), and combined (a). (a) The mean total violation percentage decreased from 30% with the first spine model to 10% after completing five spine models (50 pedicle screws). This violation percentage became stable at 10% from the sixth to tenth models. The mean critical violation (>2-mm breach) percentage also decreased as residents continued practicing and became stable at 0% after completing five models. (d) The length of time required to complete screw instrumentation decreased as residents continued to practice the skills on the 3D-printed models. A strong negative correlation was observed between the repetitive time of screw instrumentation and length of procedure (Spearman’s correlation coefficient, −0.71; p <0.001) time to complete pedicle screw instrumentation. Prac- and length of procedure (Spearman’s correlation coeffi- ticing instrumentation of pedicle screws on the 3D- cient, − 0.71; p <0.001). printed spine model has shown a learning effect (Fig. 5). In the study, L5 did not show any screw violation Less violation of the screws was seen as residents contin- compare with 32.5% of total violation in L1. Pedicles in ued practicing the technique on the model. The mean the lower vertebral level showed less percent violation total violation percentage for a resident decreased from compared with the higher vertebral level (Spearman’s 30% with the first spine model to 10% after completing correlation coefficient, − 0.28; p < 0.01). Pedicles of the five spine models (50 pedicle screws). This violation lower vertebral level are known to be wider than the percentage became stable at 10% from the sixth to tenth higher vertebral level, and this can be the reason for the models. The mean critical violation (> 2-mm breach) lower rate of screw violation in the lower vertebral level percentage also decreased as residents continued pedicles. Furthermore, total violation rate (18.5%) in this practicing and became stable at 0% after completing five study on the lumbar vertebra was lower than that (29%) models. The earlier and later performed 10 spine models on the thoracic vertebra in different cadaveric studies showed less percent total violations in the latter 10 [8]. This may have a similar reason, as pedicles in spine models (10/100 pedicle screws) compared with lumbar vertebra are wider than those in the thoracic ver- the former 10 spine models (27/100 pedicle screws) tebra. It can be inferred that narrower pedicles have a (p < 0.05; odds ratio, 0.30; 95% CI, 0.137–0.661). More- higher possibility of screw violation than wider pedicles. over, the length of time required to complete screw instru- Therefore, pedicle instrumentation on a young patient mentation decreased as residents continued to practice with congenital deformity may have higher risk for screw the skills on the 3D-printed models. The mean length of violation. However, practicing the skills on young ca- time to complete 10 pedicle screw instrumentations in davers with spine deformity is almost impossible because one spine model was 42.8 ± 5.3 min and 35.6 ± 2.9 min for most cadavers are old aged. 3D printing enables training the former (100 pedicle screws) and latter 10 spine models on a life-size replica of deformed spine or young-aged (100 pedicle screws), respectively. The latter 10 spine spine, which is a great advantage over using cadavers for models required significantly less time than the former 10 skills training. models (p < 0.001). A strong negative relationship was ob- 3D printing has a number of applications in medicine, served between repetitive time of screw instrumentation and we propose that this technique can be used for Park et al. Journal of Orthopaedic Surgery and Research (2018) 13:86 Page 7 of 8 training of pedicle screw instrumentation [19, 20]. 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Journal of Orthopaedic Surgery and Research – Springer Journals

Published: Apr 16, 2018

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