Journal of Korean Society of Spine Surgery Comparison of Mechanical Property of Conventional Rods versus Growing Rods for Pediatric Early Onset Scoliosis Jin-Young Kim, M.D., Eun-Su Moon, M.D., Hyon-Su Chong, M.D., Seung-Joo Lee, M.D., Hak-Sun Kim, M.D. J Korean Soc Spine Surg 2010 Dec;17(4):177-183. Originally published online December 31, 2010; doi: 10.4184/jkss.2010.17.4.177 Korean Society of Spine Surgery Department of Orthopaedic Surgery, Ewha Womans University Collge of Medicine #911-1 Mok-dong, Yangcheon-gu, Seoul, 158-710, Korea Tel: 82-2-2646-6808 Fax: 82-2-2646-6804 Copyright 2010 Korean Society of Sping Surgery pissn 2093-4378 eissn 2093-4386 The online version of this article, along with updated information and services, is located on the World Wide Web at: http://www.krspine.org/doix.php?id=10.4184/jkss.2010.17.4.177 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. www.krspine.org
Original Article pissn 2093-4378 eissn 2093-4386 J Korean Soc Spine Surg. 2010 Dec;17(4):177-183. doi: 10.4184/jkss.2010.17.4.177 Comparison of Mechanical Property of Conventional Rods versus Growing Rods for Pediatric Early Onset Scoliosis Jin-Young Kim, M.D., Eun-Su Moon, M.D., Hyon-Su Chong, M.D., Seung-Joo Lee, M.D., Hak-Sun Kim, M.D. Department of Orthopedic Surgery, Yonsei University College of Medicine, Seoul, Korea Study Design: This is a mechanical study. Objectives: We wanted to investigate the mechanical properties of newly developed dual growing rods for obtaining approval for their clinical application. Summary of the Literature Review: The current expandable spinal implant system appears effective for controlling progressive early onset scoliosis, and it allows for spinal growth and improving lung development. Materials and Methods: We investigate the yield load and ultimate load during compression, tension and torsion of the growing rods and the conventional rods assembly using UHMWPE blocks, and the diameter of the rods was 6.0 mm and they expanded 5cm long. We also performed a fatigue test with growing rods, and the diameter of which was 6.0 mm and it expanded 2.5cm long. The guideline for the American Society for Testing Materials was followed during the entire mechanical test. With the growing rods and conventional rods, we tested for each mechanical property7 times with the new rods and blocks. Results: The yield load of the growing rods and conventional rods were 845.2±18.2 (N) and 812.9±29.9 (N), respectively, and the ultimate load of the growing rods and conventional rods were 961.9±31.1 (N) and 914.9±25.6 (N), respectively, when compression force was applied. The yield load and ultimate load of the growing rods were statistically higher than those of the conventional rods (p<0.05). The ultimate load of the growing rods and conventional rods were 3281.7±41.5 (N) and 3678.5±447.9 (N), respectively when tension force was applied. The ultimate load was similar for both types of rods (p>0.05). The yield loads of the growing rods and conventional rods were 11.56±0.59 (Nm) and 12.46±0.71 (Nm), respectively, the ultimate loads of the growing rods and conventional rods were 16.97±0.94 (Nm) and 17.42±2.66 (Nm) during the torsion, respectively. The yield load and ultimate load of the growing rods were statistically lower than that of the conventional rods (p<0.05). Conclusions: The newly developed growing rods have a higher yield load and ultimate load under compression, a similar ultimate load under tension and a lower yield load and ultimate load under torsion. The differences of the yield load and ultimate load under torsion were minimal, and so the growing rods and conventional rods have similar mechanical properties. Key Words: Early onset scoliosis, Growing rod, Mechanical study 서론 척추가성장이완료되지않은어린소아에서발생한진행성고도척추측만증은환자자신에게도심각한문제가발생할뿐만아니라이를치료하는의사도고민을하지않을수없다. 1,2) 어린소아에서발생한척추측만증의치료에있어서전통적인치료방법으로는캐스트, 보조기치료와이둘을동시에사용하는방법이있다. 3) 할로견인 (Halo traction) 도사용할수있지만이는수술과동시에사용될때에도움이될수있다. 그러나아주어린나이에척추의변형이진행하는경우이러한보존적방법은변형의정도를조절하기에는어려움이많고, 흉곽의성장과폐기능의발달을방해할가능성과더불어욕창 (pressure sore) Received: December 1, 2009 Revised: December 16, 2010 Accepted: December 16, 2010 Published Online: December 31, 2010 Corresponding author: Hak Sun Kim, M.D. Department of Orthopaedic Surgery, Gangnam Severance Hospital, 712 Eunjuro, Gangnam-gu, Seoul 135-720, Korea TEL: 82-2-2019-3411, FAX : 82-2-573-5393 E-mail: HAKSUNKIM@yuhs.ac This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 본연구는연세대학교의과대학 - 일반교수연구비 ( 과제번호 : 6-2010-0039) 의지원하에진행되었습니다. Copyright 2010 Korean Society of Spine Surgery www.krspine.org 177
Jin-Young Kim et al Volume 17 Number 4 December 2010 과같은피부문제를일으킬가능성이많다. 4) 따라서보존적인치료에반응하지않고만곡의정도가계속 진행하여 50 도이상으로진행되면수술을시행해야한다. 5) 수술 적방법으로원주상유합술 (circumferential fusion) 은변형의진 행을조절하는데에는효과적이지만척추가더자랄수있는성 장잠재력을잃게되어결국에는폐기능저하와복부장기성장 의문제를야기할소지가많다. 이러한문제를해결하기위하여척추를유합하지않는척추 기기고정술이소개되었다. 6,7) 그뒤에 Luque Trolley 라불리는 척추를유합하지않는 Luque 기기고정술이소개되었다. 8) 이후 수술기법이발전하여외국에서는성장형금속봉이소개되어이 를이용한다양한기기가선보이고있는상태이다. 그러나, 우리 나라에는여러가지이유로이의보급이활발하지않은상황이 며, 현재까지국내에서개발된기기는저자들이알기에는없는 것으로알고있다. 이에저자들은국내에서사용가능한성장형 금속봉을개발하게되었다. 본논문에서는저자들이개발한성장형금속봉을어린나이에 발생한척추측만증환자에게기존에사용가능하였던일반적인 금속봉과역학적강도를비교함으로써동일한역학적특성을가 지고있는지를파악하여향후저자들이개발한성장형금속봉이 실제환자의수술에서적용가능한것인지를알아보고자하였 다. Fig.1. This picture show the standard dimension of test block follows the standards of The American Society for Testing Materials (ASTM) F1717-04. 연구대상및방법 저자들이새로이개발한성장형금속봉의재질은 titanium alloy 이며직경은 6mm이고구성은크게세개의부분으로구성되어있다. 가장윈위부부분은일반적인금속봉으로써요추부의만곡에따라구부릴수있는부분이며, 가장근위부부분은성장형금속봉으로써흉요추부의만곡에따라구부린후척추경나사못에부착하게되며이후성장형원통안에서톱니의조작에따라길이성장이이루어지는부분이고, 중간부분은성장형원통으로써근위부와원위부금속봉을서로연결하고이후내부의톱니를조작함으로써근위부의성장형금속봉이점차근위부로이동을가능하게하여길이성장을이루어지게하는부분이며, 성장형금속봉의이동을가능하게하는톱니부위가기존의다른성장형금속봉기기들과비교하였을때비교적작은크기로부피가작아특히체구가작은소아의요추후방에기기를삽입하는데있어서유리하다는특징이있다. 본실험에서저자들은일반적인금속봉과새로개발한성장형금속봉의역학적인특성의비교를위하여국제인정기준의역학적검사 (The American Society for Testing Materials = ASTM F1717-04) 에따라성장형금속봉과일반금속봉각각에대하여정적시험 (static test) 과피로시험 (fatigue test) 을시행하였다. ASTM 규격에따라제작된초고분자량폴리에틸렌블록 (Ultra-High Molecular Weight Polyethylene block = UHMWPE) 을근위부와원위부에위치시키고각각 2개의척추경나사못 (GS mono screw, Φ5.5.x30mm) 를삽입한다음성장형금속봉과일반적인금속봉을척추경나사못의양쪽으로연결하고 20N m 의토크 (touque) 로조여자유도 (degree of freedom) 을제거하고역학시험기계 (MTS 858 Bionix, MTS system Corp., MN, USA) 장착하여실험을진행하였다 (Fig. 1, 2, 3). 역학시험동안 ASTM 규격에따라온도는섭씨 25 를유지하였으며습도는 30% 로유지하였다. 피로시험에서는 ASTM 규격에따라근위부와원위부에삽입된척추경나사의거리를 75mm 로하였으며, 연장이가능한성장형금속봉의연결부위는 40mm 를사용하였고성장형금속봉을 10mm 연장후 10mm 는연결부위에중첩되게한후정적시험중압박의항복하중 (yield load) 를먼저측정하였으며, 확인된압박시항복하중의 25%, 50% 의강도로 5Hz 주기의힘을가하여 5,000,000 회반복하여시료의상태를확인하였다. 정적시험에서는실제임상에서사용시두척추경나사의거리가 75mm보다는길것으로생각되어피로시험과는달리두척추경나사의거리를 150mm로연장하고, 성장형금속봉의연결부위는 80mm를사용하였으며, 성장형금속봉을 178 www.krspine.org
Journal of Korean Society of Spine Surgery Growing Rods for Pediatric Early Onset Scoliosis 45mm 연장한후 25mm 는연결부위에서중첩되게한후압박 (compression), 신전 (tension) 및염전 (torsion) 의항복하중, 최종하중 (ultimate load) 를조사하였다. 압박은최대 25mm/min 의속도로가하였고이때압력변위곡선 (load displacement curve) 를기록하였다. 신전에서도마찬가지로최대 25mm/ min 의속도로신전을시켰으며이때에도신전변위곡선 (load displacement curve) 을기록하였다. 염전을시행할때는최대 60 /min 의각속도로휘어지는힘을가하였고이때축성압박과신전력은작용하지않도록유지하면서실험을진행하였다 (Fig. 4). 피로시험과정적시험에서사용된일반금속봉의재질은 titanium alloy 이며직경은 6mm로성장형금속봉과동일한직경의금속봉을사용하였고금속봉의길이는초고분자량폴리에틸렌블록에장착후성장형금속봉과의길이가동일하게하였다. 나머지자세한순서와장비의조절은 F1717-04 기준에따라시행하였다. 역학적시험은각각 7회를시행하였으며각기다른금속봉과초고분자량폴리에틸렌블록으로실시하여그평균과표준편차를구하여결과를비교하였다. 통계처리과정은 SPSS(Statistical Package for Social Science, ver 12.0, Chicago, USA) 를사용하였고군간의비교에있어최종하중은모수검정방법인 two sample t-test 를사용하였으며항복하중은비모수검정방법인 Wilcoxon rank sum test 를이용하였고유의수준 5% 로통계적검정을하였다. Fig. 2. These pictures show the basic assembly of the growing rods for static test (A), the growing rods for fatigue test (B) and the conventional rods for static test (C) with UHMWPE(Ultra-High Molecular Weight Polyethylene) blocks through the mechanical testing and this setup follows the standards of The American Society for Testing Materials (ASTM) F1717-04. Fig. 3. These pictures show the bilateral construct test setup for screws and rods. www.krspine.org 179
Jin-Young Kim et al Volume 17 Number 4 December 2010 결과 1. 압박시험결과항복하중은일반형금속봉에서 812.9±29.9(N), 성장형금속봉에서 845.2±18.2(N) 였으며이는일반형금속봉에비해성장형금속봉에서 3.97% 높게측정되었다 (fig. 5). 최종하중에서도일반형금속봉에서는 914.9±25.6(N), 성장형금속봉에는961.9±31.1(N) 로성장형금속봉에서 5.14% 높게측정되었다. 통계분석결과에서압박에대한항복하중은성장형금속봉이일반형금속봉에비해통계적으로의미있게높았고 (p-value = 0.011), 최종하중도성장형금속봉이일반형금속봉에비해통계적으로의미있게높은값을보였다 (p-value = 0.009). 2. 신전시험결과에서최종하중은일반형 3678.5±447.9(N), 성장형 3281.7±41.5(N) 이었으며이는성장형에비해일반형이 12.1% 높게측정되었다 (fig. 6). 하지만통계분석결과신전에대한최종하중은성장형금속봉과일반형금속봉사이에통계적으로의미있는차이를보이지않았다 (p-value = 0.209). 3. 염전시험결과에서항복하중은일반형이 12.46±0.71(Nm), 성장형이 11.56±0.59(Nm) 였으며이는성장형에비해일반형에서 7.8% 높게측정되었다 (fig 7). 최종하중에서도일반형이 17.42± 2.66(Nm), 성장형이 16.97±0.94(Nm) 이었으며이는성장형에비해일반형에서 2.7% 높게측정되었다. 통계분석결과염전에대한항복하중은성장형금속봉에비해일반형금속봉에서통계적으로의미있게높았고 (p-value = 0.017), 최종하중도성장형금속봉에비해일반형금속봉에서통계적으로의미있게높은값을보였다 (p-value = 0.011). 4. 피로시험정적시험을먼저시행후확인된압박시항복하중의 25%, 50% 의강도로시험을진행한결과 25% 에서는기기의손상이없었으나, 50% 에서는금속봉의균열이관찰되었다. Fig. 4. These pictures show the test results of growing rods construct during the extension test (A), the compression test (B), and the torsion test(c). Fig. 5. These diagrams show load displacement curve of the growing rods (A) and the conventional rods (B) during compression test. 180 www.krspine.org
Journal of Korean Society of Spine Surgery Growing Rods for Pediatric Early Onset Scoliosis 고찰 성장이많이남아있는어린소아에서발생한척추측만증에서비수술적인방법으로만곡의진행을막지못하고 50도이상의만곡이있는경우에수술적인치료법을사용하게된다. 5,9) 수술적방법은크게척추를유합하는경우와유합하지않는경우로나눌수있다. 유함술을시행함에있어척추의성장잠재력이남은환아에게후방척추만을유합할때발생하는크랭크샤프트현상 (crank shaft phenomenon) 10,11) 을방지하기위하여, 원주상척추유합술을시행할수있으나결과적으로는척추와흉곽의성장도함께막는단점이있다. 이러한단점을해결하기위하여유함을하지않는여러가지수술방법이소개되었다. Harrington 에의해척추의유합시키지않으면서척추에기기를고정하는방법이소개되었고 6), Moe 등의피하금속봉테크닉, Marchetti 등에의한말단유합 (end fusion) 개념이등장하면서근위부와원위부의금속봉과척추경나사가연결되는부위에안정성이증가되었다. 12) 그후에추궁하강선결박술 (sublaminar wiring) 기법을이용한 Luque Trolley 라불리는척추를유합하지않는 Luque 기기고정술이소개되었다 7). 그러나이수술방법은골막하박리 (subperiosteal dissection) 를하기때문에예상하지않았던척추자연유합이발생하였다. 8,13,14) 이후수술기법이발전하여현재소아에서조기발현된척추측만증에대해성장형금속봉과 vertically expandable prosthetic titanium rib (VEPTR) 15) 등다양한기기가소개되었으며외국에서는이를이용한수술이다양하게임상적으로적용되고있다. 특히 VEPTER 는주로흉과부족증후군이발생한측만증환자에게사용하고있고흉곽의기형을직접적으로교정할수있으며기기를삽입하여도척추의유합이일어나지않는장점은있으나기기의부피가상대적으로크며시상면상의불균형은교정할수없고흉과의강직을초래하게된다는단점을가지고있다. 반면성장형금속봉은 VEPTER 와동일하게척추와흉곽의성장을유지할수있다는본래의기능과함께관상면과시상면의불균형을함께교정할수있으며흉과의강직을초래하지않는다는장점이있으나경우에따라척추의자연유합이발생하기도하고금속봉의파손이발생할수있다는단점이있다. 하지만, 우리나라에는여러가지이유로이의보급이활발하지않은상황이며, 특히국내에서현재임상에사용할수있는성장형금속봉이없어저자들은국내실정에맞는성장형금속봉을개발하게되었다. 본실험에서저자들은피로시험과함께정적시험을시행하였다. 피로시험은 ASTM 규격에맞추어진행하였으며정적시험을먼저시행하여확인한항복하중의 25% 로진행한피로강도시험에서는기기의파손이없었으나 50% 로시행한시험에서 Fig. 6. These diagrams show load displacement curve of the growing rods (A) and the conventional rods (B) during extension test. Fig. 7. These diagrams show torque angular curve of the growing rods (A) and the conventional rods (B) during torsion test. www.krspine.org 181
Jin-Young Kim et al Volume 17 Number 4 December 2010 는기기의파손이관찰되었고이는 ASTM 기준의척추삽입용 금속봉의기준을충족하는결과이었다. 정적시험에서는금속봉의길이를피로시험에서시행한것보 다두배로연장하여시행하였는데, 이러한긴길이는금속봉에 가해지는하중이길이가짧은 ASTM 규격보다는크게작용한다 는것과실제임상에서성장형금속봉을사용할경우 ASTM 시 험규격보다는긴길이의금속봉을사용하게되는데일반형금 속봉과의역학적특성을비교한데있어서좀더임상에사용하 게될환경과유사한상황에서비교하기위해서였다. 정적시험 결과는압박에서는일반형금속봉보다우위를, 신전에서는같은 정도의강도를보였다. 염전에서는일반형금속봉보다낮은강 도를보였다. 하지만차이가적어서성장형금속봉이일반형금 속봉과비교하여역학적성질의측면에서는큰차이가없는것 으로생각된다. 그러나본연구는역학적성질만을시험하기위한모형화된 실험이라는한계점을가지고있다. 역학적인강도의측정에서 초고분자량폴리에틸렌블록에척추경나사를고정하였기때문 에실제척추와척추경나사못사이의관계를정확하게반영하 지못해실제로환자에게적용하기위해서는척추골과척추경 나사못의관계를알수있는시험이필요하고실제수술을할때 는금속봉을구부리게되는데이렇게굽어진정도에따라성장 형금속봉이일반금속봉과비교하여역학적강도에있어통계 학적으로의미있는차이가있을지에대하여서도추가적인시 험이필요할것이다. 그러므로본연구와같은결과를환자의치 료에적용해나가기위해서는추가적인역학적인성질의검사가 필요할것이고, 동물을이용한실험이나연구용시신을이용한 역학적인실험이진행되어야할것으로판단된다. 결론 저자들이새로개발한성장형금속봉은피로시험에서척추 삽입용금속봉으로서의기준을충족하였으며실제임상사용과 유사한환경에서시행한정적시험결과에서도기존의일반형금 속봉과비교하였을때유사한역학적강도를확인하였다. REFERENCES 1. Branthwaite MA. Cardiorespiratory consequences of unfused idiopathic scoliosis. Br J Dis Chest. 1986;80:360 9. 2. Campbell RM, Smith MD, Mayes TC, et al. The characteristics of thoracic insufficiency syndrome associated with fused ribs and congenital scoliosis. J Bone Joint Surg Am. 2003;85:399 408. 3. Mehta M, Morel G, orab Zorab P, Siezler D. The Non- per- Non-Operative Treatment of Infantile Idiopathic Scoliosis. London, Academic Press: 1979. 4. Kennedy JD, Robertson CF, Olinsky A, Dickens DR, Phelan PD. Pulmonary restrictive effect of bracing in mild idiopathic scoliosis. Thorax. 1987;42:959 61. 5. Klemme WR, Denis F, Winter RB, Lonstein JW, Koop SE. Spinal instrumentation without fusion for progressive scoliosis in young children. J Pediatr Orthop. 1997;17:734 42. 6. Harrington PR. Treatment of scoliosis. Correction and internal fixation by spine instrumentation. J Bone Joint Surg Am. 1962;44:591 610. 7. Moe JH, Kharrat K, Winter RB, Cummine JL. Harrington instrumentation without fusion plus external orthotic support for the treatment of difficult curvature problems in young children. Clin Orthop Relat Res. 1984;185:35 45. 8. Sengupta D, Freeman B, Grevitt M, et al. Long term followup of Luque trolley growing-rod construct in the surgical treatment of early onset idiopathic scoliosis. Scoliosis Research Society Annual Meeting. Seattle. 2002. 9. Tello C, Bersusky E, Francheri A, et al. Severe infantile scoliosis treated with repetitive distractions followed by definitive arthrodesis. Scoliosis Research Society Annual Meeting. Seattle. 2002. 10. Dubousset J, Herring JA, Shufflebarger H. The crankshaft phenomenon. J Pediatr Orthop. 1989;9:541 50. 11. 1. Roberto RF, Lonstein JE, Winter RB, Denis F. Curve progression in Risser stage 0 or 1 patients after posterior spinal fusion for idiopathic scoliosis. J Pediatr Orthop. 1997;17:718 25. 12. Marchetti PG, Faldini A. End fusions in the treatment of some progressing or severe scoliosis in childhood or early adolescence. Scoliosis Research Society, 1977. Orthop Trans. 1978;2:271. 13. Mardjetko SM, Hammerberg KW, Lubicky JP, Fister JS. The Luque trolley revisited: review of nine cases requiring revision. Spine. 1992;17:582 9. 14. Rinsky LA, Gamble JG, Bleck EE. Segmental instrumentation without fusion in children with progressive scoliosis. J Pediatr Orthop. 1985;5:687 90. 15. Campbell RM, Smith M, Hell-Vocke A. Expansion thoracoplasty: the surgical technique of opening-wedge thoracostomy. surgical technique. J Bone Joint Surg Am. 2004;86:51 64. 182 www.krspine.org
Journal of Korean Society of Spine Surgery Growing Rods for Pediatric Early Onset Scoliosis 조기발현형소아측만증치료를위한성장형금속봉과일반금속봉의역학적강도비교 김진영 문은수 정현수 이승주 김학선연세대학교의과대학정형외과학교실 연구계획 : 역학적연구연구목적 : 본연구는새로이개발된성장형금속봉의임상적적용을위해역학적인성질을시험하고자한다. 선행문헌의요약 : 본연구는조기발현형소아척추측만증환자의치료를위해새로이개발된성장형금속봉의임상적적용을앞서역학적인성질을시험하고자한것으로서일반금속봉에대하여성장형금속봉의압박시항복하중과최종하중은높았으며, 신전시최종하중도비슷하였고, 염전시항복하중과최종하중에서는일반형보다강도가작았으나그차이가적어결과적으로두금속봉간의역학적강도에는큰차이가없는것으로생각된다. 대상및방법 : 수술로고정한후신장이가능하도록고안된지름 6.0 mm의성장형금속봉과일반금속봉을국제인정기준의역학적검사 (The American Society for Testing Materials = ASTM, F1717-04) 에알맞게제작된폴리에틸렌블록에근위부, 원위부에각 2개의척추경나사못으로고정하였다. 성장형금속봉을 5cm 신장시킨후일반금속봉과같은길이로하여정적시험을통하여압박, 신전및염전의항복하중, 최종하중을조사하였고, 성장형금속봉을 2.5cm 신장후압박시험후항복하중의 25% 로피로시험을진행하였다. 역학적시험은각기다른금속봉과폴리에틸렌블록으로각 7회실시하여그평균과표준편차를구하였다. 결과 : 정적시험에서압박시항복하중은성장형이 845.2±18.2(N), 일반형이 812.9±29.9(N), 최종하중은성장형이 961.9±31.1(N), 일반형이 914.9± 25.6(N) 이었다. 압박에대한항복하중과최종하중은성장형이일반형에비해통계적으로의미있게높은값을보였다 (p<0.05). 신전시최종하중은성장형이 3281.7±41.5(N), 일반형이 3678.5±447.9(N) 이었다. 최종하중은성장형과일반형사이에통계적으로의미있는차이를보이지않았다 (p>0.05). 염전시항복하중은성장형이 11.56±0.59(Nm), 일반형이 12.46±0.71(Nm) 이고최종하중은성장형이 16.97±0.94(Nm), 일반형이 17.42±2.66(Nm) 이었다. 항복하중과최종하중은성장형에비해일반형에서통계적으로의미있게높은값을보였다 (p<0.05). 피로시험에서는기기의손상이없었다. 결론 : 일반금속봉에대하여성장형금속봉의압박시항복하중과최종하중은높았으며, 신전시최종하중도비슷하였고, 염전시항복하중과최종하중에서는일반형보다강도가작았으나그차이가적어결과적으로두금속봉간의역학적강도에는큰차이가없는것으로생각된다. 색인단어 : 소아조기발현형척추측만증, 성장형금속봉, 역학적연구 약칭제목 : 소아척추측만증을위한성장형금속봉 www.krspine.org 183