Abstract

BACKGROUND: Traditional anterior release followed by posterior correction and fusion is frequently used to treat severe and rigid adolescent idiopathic scoliosis, which is considered as Cobb angle of the major curve > 65° and flexibility < 34.5%; however, there are a great majority of complications. Whether isolated posterior correction using pedicle screw fixation combining with bone grafting and fusion may provide better effects on severe and rigid adolescent idiopathic scoliosis needs to be further studied.

OBJECTIVE: To evaluate isolated posterior correction using pedicle screw fixation combining with bone grafting and fusion for the treatment of severe and rigid adolescent idiopathic scoliosis.

DESIGN: Case analysis.

SETTING: Department of Orthopaedics, Renji Hospital, Medical College of Shanghai Jiao Tong University.

PARTICIPANTS: Twenty patients with severe and rigid adolescent idiopathic scoliosis, including 8 males and 12 females, were selected from Department of Orthopaedics, Renji Hospital, Medical College of Shanghai Jiaotong University from June 1999 to August 2005. They were 12-18 years old, and the mean age was 14.6 years. All patients were finally diagnosed as X-ray of whole spine. According to King-Moe criteria, patients were classified into type Ⅰ(n =4), type Ⅱ(n =6), type Ⅲ (n =5), type Ⅳ(n =3) and type Ⅴ(n =2). Before surgery, mean Cobb angle of the major curve was 82° (75°-92°), mean flexibility was 30% (20%-40%), and mean shoulder height difference was 15 mm (5-35 mm). Moreover, according to Risser syndrome, patients were classified into degree 1 (n =3), degree 2 (n =5), degree 3 (n =6), degree 4 (n =5) and degree 5 (n =1). All patients and their relatives provided the informed consents, and the experiment was approved by the local ethical committee. Artificial bone was Osteoset provided by Wright Company, USA.

METHODS: Patients underwent isolated posterior correction using pedicle screw fixation combining with bone grafting and fusion, and spinous process, lamina of vertebra, zygapophysial joints and transverse process were exposed in a preconcerted fusion area. Pedicle screw was inserted into strategy vertebra using free hand technique according to the anatomic landmark of entry point. Six patients underwent fixation with TSRH system, and the other patients with CDH M8 system. Operative time and blood loss were evaluated after surgery. At 7 days after operation, Cobb angle was measured with X-ray, and correction rate of major curve was calculated. While shoulder height difference and admission duration were evaluated simultaneously. Complications and recovery states were followed up in the next 4 years.

MAIN OUTCOME MEASURES: ① Operative time and blood loss; ② Cobb angle and correction rate of major curve; ③ shoulder height difference and admission duration; ④ follow-up results.

RESULTS: All 20 patients were included in the final analysis. ① Operative time and blood loss: Operative time lasted from 3.2 to 4.3 hours, and the mean time was 3.5 hours. Blood loss ranged from 660 to 1 070 mL, and the mean loss was 865 mL. ② Cobb angle and correction rate of major curve: Cobb angle of the major curve ranged from 82° (75°-92°) before surgery to 31° (22°-37°) after surgery, and the mean correction rate was 62%. ③ Shoulder height difference and admission duration: Mean should height difference before surgery was 15 mm (5-35 mm). Postoperative lateral film of spine indicated that thoracic and lumbar vertebra generally suffered from normal posterior and anterior convexity, and mean shoulder height difference after surgery was 7.5 mm (0-11 mm). The admission duration lasted from 8 to 11 days, and the mean duration was 9 days. ④ Follow-up results: All patients were followed up in the next 4 years after surgery. The cobb angle correction of major curve remained unchanged, and the instrumented segments were completely fused without instrumentation failure.

CONCLUSION: Isolated posterior correction using pedicle screw fixation combining with bone grafting and fusion may effectively cure severe and rigid adolescent idiopathic scoliosis, which is considered as Cobb angle of the major curve between 75° and 92° and flexibility ≥ 20%.

INTRODUCTION

A great majority of scholars think that severe and rigid adolescent idiopathic scoliosis, which is characterized by Cobb angle of the major curve > 65° and flexibility at bending site < 34.5%, is an indication for anterior releaset followed by posterior correction and fusion [1,2]. However, there are a lot of complications. Endoscope may reduce but not completely eliminate operative complications. Therefore, with the wider and wider application of posterior internal fixation device of spine (the 4th generation), isolated posterior correction possibly becomes a new way to treat severe and rigid adolescent idiopathic scoliosis to a certain degree. This study was designed to evaluate isolated posterior correction using pedicle screw fixation combining with bone grafting and fusion for the treatment of severe and rigid adolescent idiopathic scoliosis.

SUBJECTS AND METHODS

Subjects
Twenty patients with severe and rigid adolescent idiopathic scoliosis, including 8 males and 12 females, were selected from Department of Orthopaedics, Renji Hospital, Medical College of Shanghai Jiaotong University from June 1999 to
August 2005. They were 12-18 years old, and the mean age was 14.6 years. All patients were finally diagnosed as X-ray of whole spine. According to King-Moe criteria [3], patients were classified into type Ⅰ(n = 4), type Ⅱ(n =6), type Ⅲ(n =5), type Ⅳ(n =3) and type Ⅴ(n =2). Before surgery, mean Cobb angle of the major curve was 82° (75°-92°), mean flexibility was 30% (20%-40%), and mean shoulder height difference was 15 mm (5-35 mm). Moreover, according to Risser sign syndrome, patients were classified into degree 1 (n =3), degree 2 (n =5), degree 3 (n = 6), degree 4 (n = 5) and degree 5 (n =1). All patients and their relatives provided the informed consents, and the experiment was approved by the local ethical committee.
Spain PA & LAT at standing position and left and right bending at supine position were photographed routinely before surgery, while spain PA & LAT at standing position was evaluated during postoperative follow up. Shoulder height difference was expressed as height difference of bilateral acromioclavicular joints at standing position. General baseline data before surgery are shown in Table 1. Artificial bone was Osteoset provided by Wright Company, USA.

Methods
Patients underwent isolated posterior correction of pedicle screw fixation combining with bone grafting fusion. Six patients underwent fixation with TSRH system, and the other patients with CDH M8 system.
Correction principle: Motor segments of spine were reserved as many as possible during the obtaining of equilibrium spine. Posterior-approaching median incision was performed above and below the reservation segments in a vertebral area. And then, skin, subcutaneous fascia and top cartilage cap of spinous process were incised layers by layers. Cobb dissector was used to strip paraspinal muscles to bilateral transverse process. Next, Weitlaner automatic retractor was used to expose spinous process, lamina of vertebra, zygapophysial joints and transverse process in a preconcerted fusion area. Pedicle screw was fixed at strategy vertebra by using bare-handed technique according to the anatomic landmark of approaching site [4]. Spinous process, lamina of vertebra, zygaophysial joints and transverse process in the preconcerted fused area were resected; Meanwhile, convex costatectomy or concave costa osteotomy was performed around apical vertebra of major curve in order to correct thoracic deformity. After release, a pre-contured rod was inserted into the pedicle screw anchors, leaving the set screw loose. Then, segmental distraction, compression, de-rotation and cantilever beam methods were used to correct deformity. If major curve was located at thoracic vertebra, the correction began from concave side to increase thoracic kyphosis. If major curve was located at lumbar vertebrae, the correction began from convex side to increase lumbar lordosis. Otherwise, in order to maintain balanced shoulders and balanced trunk after operation, we did not try to achieve maximum correction of the main curve. The correction should be slowly and gradually performed steps by steps to avoid spinal cord injury. Finally, set screw was tightened and locked. After correction, the decortication of lamina in the fused segments was performed, and then excised spinous process, articular process and lamina were broken with bone ribbing rongeur and mixed with artificial bone in the area of fused segments. Subcuticular suture was performed in all operations. Antibiotic was used one during the operation and applied for three times after operation.
At 7 days after operation, Cobb angle was measured with X-ray, and correction rate of major curve was calculated. While shoulder height difference and admission duration were evaluated simultaneously. Complications and recovery states were followed up in the next 4 years.

RESULTS

Quantitative analysis of the participants
All 20 patients were included in the final analysis.

Postoperative evaluation (Table 2)
The mean number of fused segments was 11 (ranged from 9 to 12). Operative time lasted from 3.2 to 4.3 hours, and the mean time was 3.5 hours. Blood loss ranged from 660 to 1 070 mL, and the mean loss was 865 mL. The admission duration lasted from 8 to 11 days, and the mean duration was 9 days. During the operation, 4 patients suffered from costatectomy and 2 from osteotomy. And they did not have postoperative infection and nervous system complication.
The mean cobb angle of major curve after surgery was corrected to 31° (22°-37°) from 82° (75°-92°) before surgery, and the mean correction rate was 62%. Postoperative X-rays in latera view indicated that thoracic kyphosis and lumbar lordosis in all the patients recovered generally, and mean shoulder height difference was 7.5 mm (0-11 mm). Typical case is shown in Figure 1.

All patients were followed up in the next 4 years after surgery. The cobb angle correction of major curve remained unchanged at the last follow-up, and the instrumented segments were completely fused without instrumentation failure.

DISCUSSION

Surgical therapy of adolescent idiopathic scoliosis includes isolated anterior correction and fusion, isolated posterior correction and fusion, and anterior release followed by posterior correction and fusion. It is generally accepted that isolated anterior or posterior correction and fusion (stage Ⅰ) is mainly applied to scoliosis which is characterized by Cobb angle < 65° and greater flexibility. However, severe and rigid scoliosis with Cobb angle more than 65° is usually treated with anterior release followed by posterior correction and fusion (stage Ⅰ or stage Ⅱ).
For severe and rigid adolescent idiopathic scoliosis, anterior release aims to increase flexibility of spine through excision of intervertebral disc and anterior longitudinal ligament and allow greater correction with posterior instrumentation[5]. Simultaneously, anterior approaching may get rid of growth center of vertebra in fused segments in order to prevent occurrence of crankshaft postoperatively in skeletally immature patients. Additionally, the defects of anterior release as compared with posterior procedure are detailed as follows: complicating approach, difficult comprehension, usually abdominothoracic incision, great operative wound, high operative risk, and more complications. With the wide application of endoscope technique, more and more anterior release are finished by using thoracoscope. Although thoracoscopic anterior release is considered to be less invasive and have less postoperative complications as compared with traditional thoracotomy [6,7], curve will not be corrected until two sequential or staged procedures are finished. While, thoracoscope is an indirect vision surgery, so its operative techniques are different from those of routine operation. Doctors who are dexterity in traditional anterior procedure still need a strict training for thoracoscopic anterior release; therefore, the development is limited to a certain degree.
Cotrel and Dubousset introduced the 4th generation posterior spinal instrumentation in 1980s. The device can correct spinal deformity in biplane and perform segmental fixation and de-rotation via pedicle screw, so it realizes three-dimensional correction and fixation of spine [8]. Because pedicle screw is anchored via anterior, middle and posterior column of vertebra, it has stronger correction ability as compared with lamina or pedicle hooks. If posterior column within fused segments is extensively released prior to the correction in the treatment for severe and rigid adolescent idiopathic scoliosis, segmental compression, distraction and derotation on deformed spine with pedicle screw can completely correct rigid curve to an acceptable degree; meanwhile, fractures of lamina or pedicle caused by strong corrective stress can be avoided [9]. With the innovation of design of pedicle screw and progress in screw placement technique, more and more scholars gradually apply posterior all pedicle screw technique, so isolated posterior correction and fusion possibly becomes a new way to treat severe and rigid adolescent idiopathic scoliosis.
In our study, according to the theory, spinous process, articular process and partial lamina of vertebra of posterior column were excised to achieve wide release, and pedicle screws were inserted in determined strategy vertebra. Finally, curve was corrected by segmental correction and de-rotation to an acceptable degree.
For skeletally immature patients, intervertebral discs and end plate within fused segments were excised by anterior procedure to inhibit growth ability of vertebra and prevent the occurrence of crankshaft after posterior correction and fusion. However, Kioschos et al [10] used pedicle screw fixation as posterior tether on dog's lumbar spine to establish mechanical epiphyseal arrest animal models. The results proved that rigid posterior pedicle screw fixation could control anterior growth center of spine and prevent the occurrence of crankshaft even without the excision of intervertebral discs and end plate. Burton and Asher et al [11] performed isolated posterior correction and fusion with Isola system in 18 patients (mean age of 12.5 years) with AIS (grade 0 of Risser syndrome). The follow-up lasted for 2 to 5 years after operation, and crankshaft occurred only in one patient, While, this patient was the earlier case in their study and sublamina wires was used as the cauda anchors of fused segments. The authors believed that for skeletally immature patients above 10 years older, isolated posterior correction and fusion with rigid posterior segmental instrumentation could effectively prevent the occurrence of crankshaft. In our study, only one patient had completely mature skeleton (grade 5 of Risser syndrome), and other patients had the ability of spinal growth to a certain degree (grades 1-4 of Risser syndrome). However, grafting bone in all patients was fused and crankshaft phenomenon did not occur in the last follow up. Our clinical outcome was coincidence with the results reported by the above scholars.
With the wider application of the 4th generation three-dimensional posterior correction and fixation system, operative correction of idiopathic scoliosis has been improved remarkably, but trunk decompensation occurs in some AIS patients. Some scholars think that trunk decompensation may be caused by vertebral rotation in non-fused segments induced by vertebral de-rotation in fused segments [12,13]. Moreover, scholars think that incorrect selection of fused segments may also cause trunk decompensation [14]. In addition, other scholars think that over correction of curve may induce trunk decompensation[15]. Vincent et al [16] report on two AIS patients to whom trunk decompensation occurred soon after posterior correction and fusion, and shoulder imbalance is the main manifestation. Both of them are treated as follows: all the screws or hooks between superior and inferior end vertebra were removed. After the revision surgery, although Cobb angle of major curve is enlarged, trunk decompensation disappears generally. The authors think that over correction is the main cause for those two cases. In our opinion, there may be many causes resulting in postoperative trunk decompensation, in particularly, over correction is an important factor based on the above two cases. The purposes of operative correction for adolescent idiopathic scoliosis are detailed as follows: ① to stop the progression of the curve by fusion; ② to save levels of fusion as many as possible; ③ to correct the curve to an acceptable degree while achieving trunk balance. If the progression of curve has not been stopped, cardiac and pulmonary functions may be damaged or even the aggravation of curve may cause death. In addition, over fusion levels may affect daily exercise. Corrective degree of curve can only affect postoperative appearance. Therefore, it is definitively not to try to maximize the correction of the Cobb angle in order to keep balance of truck due to unclear causes of discompensation of trunk.
Articles about severe and rigid AIS patients with Cobb angle of major curve from 75° to 90° undergoing anterior release followed by posterior correction and fusion were retrieved from OVID and Springerlink databases. The results demonstrated that corrective rate of major curve ranged from 47% to 60%[17-19], the operative time lasted from 4.1 to 7.8 hours, blood loss was 250 mL-4 500 mL, and admission duration lasted from 13 to 25 days. In this study, corrective rate of major curve ranged from 50% to 76%, and it was higher than that in above articles. Moreover, we did not try to maximize the correction of the cobb angle during the operation in order to prevent trunk decompensation. Therefore, we could have achieved higher corrective rate of major curve than the above articles if we had sacrifice should balance. In addition, operative time in this study lasted from 3.2 to 4.3 hours, and it was shorter than that of anterior release followed by posterior correction and fusion; blood loss was 660 mL-1 070 mL, and it was overlapped or higher than the above one. Negative pressure for drainage was not performed in this study, but patients who treated with anterior release followed by posterior correction and fusion needed thoracic closed drainage. Therefore, the blood loss was increased in the latter. The admission duration lasted from 8 to 11 days, and it was shorter than the reference report.
Isolated posterior correction using pedicle screw fixation combining with bone and grafting fusion may effectively cure severe and rigid adolescent idiopathic scoliosis, which is considered as Cobb angle of the major curve between 75° and 92° and flexibility between 20% and 40%. Moreover, Isolated posterior correction has apparent superiorities on the aspects of operative time, blood loss and admission duration as compared with anterior/posterior procedures.

CONCLUSION

The goal of scoliosis surgery aims not to try to maximize the correction of the cobb angle, but achieve a balance of trunk as well as correct the minimum angle. Extensive posterior releaset, pedicle screw correction and fixation combining with bone grafting and fusion may completely achieve the above therapeutic requests for treating severe and rigid adolescent idiopathic scoliosis, which is considered as Cobb angle of major curve between 75° and 92° and flexibility ≥ 20%.

REFERENCES

1 Bradford DS, Tribus CB. Vertebral column resection for the treatment of rigid coronal decompensation. Spine 1997;22(14):1590-1599
2 Byrd JA 3rd, Scoles PV, Winter RB,et al. Adult idiopathic scoliosis treated by anterior and posterior spinal fusion.J Bone Joint Surg Am 1987;69(6):843-850
3 King HA, Moe JH, Bradford DS, et al. The selection of fusion levels in thoracic idiopathic scoliosis. J Bone Joint Surg Am 1983;65(9):1302-1313
4 Kim YJ, Lenke LG, Bridwell KH, et al. Free hand pedicle screw placement in the thoracic spine: is it safe? Spine 2004;29(3): 333-342
5 Mack MJ, Regan JJ, McAfee PC, et al. Video-assisted thoracic surgery for the anterior approach to the thoracic spine. Ann thorac Surg 1995;59(5):1102-1106
6 B?hm H, el Saghir H. Minimally invasive ventral release and endoscopic ventral instrumentation in scoliosis. Orthopade 2000; 29(6):535-542
7 Newton PO, Shea KG, Granlund KF, et al. Defining the pediatric spinal thoracoscopy learning curve: sixty-five consecutive cases. Spine 2000;25(8):1028-35
8 Cotrel Y, Dubousset J, Guillaumat M, et al. New Universal instrumentation in idiopathic scoliosis. Clin Orthop 1988;227:10-23
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10 Kioschos HC, Asher MA, Lark RG, et al. Overpowering the crankshaft Mechanism:The effect of posterior spinal fusion with and without stiff transpedicular fixation on anterior spinal column growth in immature canines.Spine 1996;21(10):1168-1173
11 Burton DC, Asher MA, Lai SM, et al. Scoliosis correction maintenance in skeletally immature patients with idiopathic Scoliosis: Is anterior fusion really necessary? Spine 2000;25(1):61-68
12 Bridwell KH, McAllister JW, Betz RR,et al.Coronal decompensation produced by Cotrel-Dubousset "derotation"maneuver for idiopathic right thoracic scoliosis. Spine 1991:16(7):769-777
13 Moore MR, Baynham GC, Brown CW,et al.Analysis of factors related to truncal decompensation following Cotrel-Dubousset instrumentation. J Spinal Disord 1991;4(2):188-192
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15 Benli IT, Tuzuner M, Akalin S, et al. Spinal imbalance and decompensation problems in patients treated with Cotrel-Dubousset instrumentation. Eur Spine J 1996;5(6):380-386
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椎弓根螺钉内固定材料置入并植骨融合后路矫正治疗重度僵硬性青少年特发性脊柱侧凸20例★

臧危平，刘祖德，李展春，冯 宇，张 磊
上海交通大学医学院附属仁济医院骨科，上海市 200127
臧危平★，男，1973年生，汉族，安徽省阜南县人，1996年上海医科大学毕业，硕士，主治医师，主要从事脊柱外科专业研究。
通讯作者：刘祖德， 教授，主任医师，上海交通大学医学院附属仁济医院骨科，上海市 200127
摘要
背景：主弯Cobb角大于65°、柔韧性小于34.5%的重度僵硬性青少年特发性脊柱侧凸多以传统的前后联合入路手术矫正，但并发症较多。应用使单纯后路手术对矫正置入椎弓根螺钉固定材料植入并植骨融合是否会有更好的效果?
目的：评价单纯后路矫正椎弓根螺钉固定材料并植骨融合术矫正治疗重度僵硬性青少年特发性脊柱侧凸的效果。
设计：病例分析。
单位：上海交通大学医学院附属仁济医院骨科。
对象：选择1999-06/2005-08在上海交通大学医学院附属仁济医院骨科收治的20例重度僵硬性青少年特发性脊柱侧凸患者，男8例，女12例，年龄12~18岁，平均15岁。均经全脊柱X片确诊。King-Moe分型Ⅰ型4例，Ⅱ型6例，Ⅲ型5例，Ⅳ型3例，Ⅴ型2例。术前侧凸主弯平均Cobb角82°(75o~92o),平均柔韧性为30%(20%~40%),术前平均双肩高度差为15 mm（5~35 mm）。 患者中Risser征1度3例，2度5例，3度6例,4度5例，5度1例。患者及家属均对治疗知情同意，实验经过医院伦理委员会批准许可。本组患者所用的人工骨为美国Wright公司的产品Osteoset。
方法：患者均行单纯后路矫正椎弓根螺钉固定植骨融合手术，暴露预定融合范围内椎体的棘突、椎板、关节突关节及横突。暴露完成后先根据进钉点的解剖标志以徒手技术在术前确定的“关键性椎体”上置入椎弓根螺钉。其中6例手术以TSRH系统进行固定，其余手术均以CDH M8系统固定。术后评估手术时间及失血量。术后7 d 采用X线测量患者Cobb角，计算主弯矫正率，同时评估双肩高度差及住院时间。术后4年随访患者并发症及恢复情况。
主要观察指标：①手术时间及失血量。②Cobb角及主弯矫正率。③双肩高度差及住院时间。④随访结果。
结果：患者20例均进入结果分析。①手术时间及失血量：手术时间为3.2~4.3 h，平均3.5 h；失血量为660~1 070 mL，平均865 mL。②Cobb角及主弯矫正率：术后主弯平均Cobb角从术前的82°(75o~ 92o)矫正到31°(22°~37°),平均矫正率为62%。③双肩高度差及住院时间：术后脊柱侧位片均显示患者胸腰椎基本恢复正常后凸及前凸，平均双肩高度差为7.5 mm（0~11 mm），患者住院日为8~11 d, 平均9 d。④随访结果：所有患者均获术后4年随访，所有侧凸主弯矫正角度未发生丢失，固定节段全部融合，无断钉、断棒发生。
结论：单纯后路椎弓根螺钉内固定材料置入并植骨融合术能有效治疗主弯在75o~92o，柔韧性≥ 20％的重度僵硬性青少年特发性脊柱侧凸。
关键词：特发性脊柱侧凸；后路矫正；椎弓根螺钉；融合术；骨科植入体
中图分类号: R617 文献标识码: A 文章编号: 1673-8225(2008)04-00755-05
臧危平，刘祖德，李展春，冯宇，张磊.椎弓根螺钉内固定材料置入并植骨融合后路矫正治疗重度僵硬性青少年特发性脊柱侧凸20例[J].中国组织工程研究与临床康复，2008，12(4):755-759
[www.zglckf.com/zglckf/ejournal/upfiles/07-4/4k-755(ps).pdf]
（Edited by Seok-Jung Kim/Ji H/Wang L）