胸腰椎骨折内固定术后椎弓根螺钉断裂及松动的原因探讨
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摘要
椎弓根是椎体后方最坚强的结构，通过它可获得脊柱三柱固定。经椎弓根螺钉内固定治疗的技术在我国已应用了十几年，它的固定效果可靠，但也出现了一些并发症，其中断钉及螺钉松动的问题更是不容忽视。几乎每一位脊柱外科医生都遇到过类似问题。本文就25例(33个椎体)胸腰椎骨折术后发生断钉、弯曲松动的病例进行分析，以探讨螺钉断裂及弯曲松动的原因。
1990年2月 — 2004年3月，我院共收治胸腰椎骨折患者867例，其中行椎弓根钉内固定的334例，有25例（33个椎体）发生椎弓根螺钉断裂或弯曲松动。本组病例均选择
后路切开复位、椎弓根螺钉系统内固定技术，有15例是在取内固定物时发现螺钉断裂或弯曲松动的,另有10例是在术前X线片中已经发现。取内固定物时间为术后3个月～2年，平均为1年3个月。多数断钉或螺钉松动的患者在取内固定物前有腰部疼痛等不适感。断钉的部位位于椎弓根与螺钉交接处，螺帽下方粗细交界处及螺纹根部；断杆的部位：1个位于左横杆中上1/4处，另1个在右下方套环处。
本组病例共发生内置物断裂或弯曲松动25例（33个椎体），分析其原因如下： ①螺钉负荷过大。用椎弓根螺钉系统治疗胸腰椎骨折，既能起到固定作用又能起到复位作用。并且通过脊柱过伸或器械撑开可以使骨折块复位或部分复位，缓解对脊髓和神经的压迫。但当骨对螺钉的把持力不够或内置物承载过大时，均会造成椎弓根螺钉松动或脱出，使内固定失效或假关节形成。椎弓根螺钉内固定系统的复位作用是利用脊柱的前、后纵韧带和椎间盘的纤维环的牵拉作用，使椎体前缘的骨块和向椎管内突出的骨块复位或部分复位，并使塌陷的椎体复位，恢复椎体的高度和形态。此时要靠起撑开作用的椎弓根螺钉内固定系统来维持复位后的椎
体。由于脊柱的前纵韧带和椎间盘前侧纤维环处于紧张状态，椎体间的间隙变宽，故脊柱上力的传导不通过患椎，而直接从患椎的上位椎体经过椎弓根螺钉内固定系统传至患椎的下位椎体，即身体负重时向下传导的力全部加载到椎弓根螺钉系统上，而螺钉受力最大。虽然椎体的外形已恢复，但椎体中松质骨压缩的部分并没有得到复位，这也给以后椎间距离的变窄和脊柱后凸畸形的复发留下了隐患。 ②椎间盘高度的丢失。本组病例中，爆裂骨折的患者在术后长期随访中均发生或多或少的伤椎与上位相邻椎体间盘退变、间隙变窄。如果椎间盘未受损，就意味着椎体的损伤是骨性的，经后路牵引即可使椎体完全复位。愈后的椎间盘仍可以维持椎间的正常高度并具有负重功能。椎间盘高度的丢失可导致椎间距离缩短和脊柱后凸畸形的复发或加重。对疑有椎间盘损伤的患者，增加椎体前、中柱的支撑是防止螺钉断裂和弯曲松动的有效方法。③内固定物取出过晚。经椎弓根内固定系统的断钉或弯曲松动大多是在取钉时发现的，我们无法总结出确切的断钉时间。本组内固定器械取出时间，最长为2年，最短为3个月，平均时间1年3个月。螺钉断裂均是在身体完全负重后发生的，椎弓根螺钉在过度负荷下的多次微
动可以在骨性融合前引起松动，特别是有骨质疏松的患者在术后因螺钉在松质骨内切割而引起复位丢失。我们认为胸腰椎骨折的椎弓根螺钉内固定系统不应固定时间过长，早取为宜。④卧床时间过短。对胸腰椎骨折的患者，我们主张术后至少卧床2～3个月，待骨折临床愈合后再逐渐下地行走。这样，既可以避免因早期活动而使胸腰椎产生持续的微动，应力分布不均，防止椎弓根螺钉过度承重；又可以尽量防止因过早活动而影响骨折愈合。⑤螺钉本身的设计或质量问题。目前应用的椎弓根螺钉，大多螺纹从钉尖向尾侧逐渐变浅、消失，而相对螺纹的根径则从下向上逐渐增粗，呈向下的锥形。这种结构克服了有螺纹与无螺纹交界处的强度突变，增强了螺钉的抗弯强度，减少了断钉的发生。骨对螺钉的握持力不够是导致螺钉松动和轴向脱出的直接原因，通过增加椎弓根钉直径，可增加固定强度和拔出力。⑥植骨融合的问题。做出一个良好的融合骨床并不容易，而融合骨面的质量是植骨融合成功与否的关键，较差的融合骨面会造成植骨融合失败。通过椎弓根向椎体内植骨仅仅填充了椎体复位后的空腔，但植骨愈合后并不能阻止椎弓根螺钉固定节段椎体间的活动，而椎体间的微动也是断钉的一个原因。此外，
有的患者在植骨未完全融合时就开始负重行走，此时骨折的愈合强度不足以抵抗负重后的椎间活动所带来的应力，这是造成部分患者椎弓根螺钉疲劳断裂或弯曲松动的一个原因。在本组334例患者中，仅有87例做了椎间或横突间植骨；在断钉或松动的25例中，有6例做了植骨。结果显示，植骨并不能有效的降低断钉或松动的发生率。因此，我们认为：只有有效的植骨融合才能有效的防止断钉的发生，而真正的做到有效的植骨融合很难，在做不到有效的植骨融合时我们不主张作脊椎骨折节段的植骨融合,以减少手术创伤。 ⑦复位不良也是螺钉松动和断裂的一个原因，复位不良会导致椎弓根螺钉承受更多的应力。
对行经椎弓根内固定的胸腰椎骨折患者，应根据其具体情况选择设计合理的椎弓根内固定器械，对合并有间盘损伤及伴有脱位的病例应行植骨融合术，术后应至少卧床2 ～3个月，在6～8
Pedicle of vertebral arch is the most powerful structure of the rear vertebral body. Through the pedicle of vertebral arch, we can get the three-column immobilization. Having been used over ten years in our country, transpedicular fixation has a reliable outcome, but there were some complications. The breakage and loosing of screws were not neglected indeed. Almost every spinal surgery doctor have met problems like this. To investigate the causes of breakage, bending and loosening of pedicle screw
systems in fixation of fractures of the thoracic and lumbar spine, 25 cases（33 bodies of vertebra）of fractures of the thoracic and lumbar spine were studied.
From February 1990 to March 2004, 867 cases of fractures of the thoracic and lumbar spine were treated in our hospital, 334 cases were treated with pedicle screws. The breaking, bending and loosing were found in 25 cases (33 bodies of vertebra). This group cases were treated with route of retreat open reduction and pedicle screws in fixation of fractures of the thoracic and lumbar spine. In these cases, the breakage, bending and loosing were founded when the screws were removed, the others were found by taking X rays before operation. The screws were removed from three months to two years after operation, average fifteen months. Before the screws were removed, most patients with breakage or loosing of pedicle screws feel pain or malaise in lumbar part. The breakage part of screws are most on
the cross point between pedicle of vertebral arch and screws, the point between thick and thin below the nut or the radical part in the screw thread. One of the break rod part occurred in the upper level 1/4 of the left cross bar and another in the collar.
The reasons that the breakage, bending or loosing of pedicle screws were as follows:
1. Overloading of the pedicle screw. We can get a satisfactory effect on fixation or restoration when the fractures of the thoracic and lumbar spine were treated with pedicle screws. The pieces of fracture may be restored wholly or partially through over-extension of spine or propped open by instrument, this can release the compression of spinal cord or nerves. But when there are no enough hold power of bone to the pedicle screws or overloading of the implant, the loosing or escaping of pedicle screws appeared. This may lead to the invalid fixation or pseudoarticulation formation. The restoration role of pedicle screws is
getted through utilizing the dragging effect of anterior longitudinal ligament, the posterior longitudinal ligament and fibrous rings of intervertebral disc. This can restore the fracture pieces of anterior border of vertebra or protruded to the vertebral canal, replace the sinking vertebral body, restore the height and form of vertebra. At this time, the maintenance of restoring certebral body can be getted by the propping open role of pedicular screws. Because the anterior longitudinal ligament and the anterior fibrous rings of disc are stressful, the interspace of intervertebral are wide, so the force conduction on the spinal column are passing from the superior vertebral body to the inferior through the pedicular screws, but not through the trouble vertebra, the force loaded wholly on the pedicular screws, this can make the screws overloaded. At the same time, although the vertebral body form were restored, the compressed cancellous bone were not restored, and this
may contribute to intervertebral narrow and hunchback afterward.
2. The loss of the intravertebral disc heights. In this group, the intervertebral narrow or retrograde disc between wounded and superior vertebral body were found more or less in bursting fracture patients. If the intervertebral disc was not wounded, this mean the injury just take place on the vertebral body, the form of the vertebral body can be restored wholly by posterior traction. The intervertebral disc after healing can maintain the normal function of weight loading. Height loss of intervertebral disc may lead to the narrowing of intervertebra
1990年2月 — 2004年3月，我院共收治胸腰椎骨折患者867例，其中行椎弓根钉内固定的334例，有25例（33个椎体）发生椎弓根螺钉断裂或弯曲松动。本组病例均选择
后路切开复位、椎弓根螺钉系统内固定技术，有15例是在取内固定物时发现螺钉断裂或弯曲松动的,另有10例是在术前X线片中已经发现。取内固定物时间为术后3个月～2年，平均为1年3个月。多数断钉或螺钉松动的患者在取内固定物前有腰部疼痛等不适感。断钉的部位位于椎弓根与螺钉交接处，螺帽下方粗细交界处及螺纹根部；断杆的部位：1个位于左横杆中上1/4处，另1个在右下方套环处。
本组病例共发生内置物断裂或弯曲松动25例（33个椎体），分析其原因如下： ①螺钉负荷过大。用椎弓根螺钉系统治疗胸腰椎骨折，既能起到固定作用又能起到复位作用。并且通过脊柱过伸或器械撑开可以使骨折块复位或部分复位，缓解对脊髓和神经的压迫。但当骨对螺钉的把持力不够或内置物承载过大时，均会造成椎弓根螺钉松动或脱出，使内固定失效或假关节形成。椎弓根螺钉内固定系统的复位作用是利用脊柱的前、后纵韧带和椎间盘的纤维环的牵拉作用，使椎体前缘的骨块和向椎管内突出的骨块复位或部分复位，并使塌陷的椎体复位，恢复椎体的高度和形态。此时要靠起撑开作用的椎弓根螺钉内固定系统来维持复位后的椎
体。由于脊柱的前纵韧带和椎间盘前侧纤维环处于紧张状态，椎体间的间隙变宽，故脊柱上力的传导不通过患椎，而直接从患椎的上位椎体经过椎弓根螺钉内固定系统传至患椎的下位椎体，即身体负重时向下传导的力全部加载到椎弓根螺钉系统上，而螺钉受力最大。虽然椎体的外形已恢复，但椎体中松质骨压缩的部分并没有得到复位，这也给以后椎间距离的变窄和脊柱后凸畸形的复发留下了隐患。 ②椎间盘高度的丢失。本组病例中，爆裂骨折的患者在术后长期随访中均发生或多或少的伤椎与上位相邻椎体间盘退变、间隙变窄。如果椎间盘未受损，就意味着椎体的损伤是骨性的，经后路牵引即可使椎体完全复位。愈后的椎间盘仍可以维持椎间的正常高度并具有负重功能。椎间盘高度的丢失可导致椎间距离缩短和脊柱后凸畸形的复发或加重。对疑有椎间盘损伤的患者，增加椎体前、中柱的支撑是防止螺钉断裂和弯曲松动的有效方法。③内固定物取出过晚。经椎弓根内固定系统的断钉或弯曲松动大多是在取钉时发现的，我们无法总结出确切的断钉时间。本组内固定器械取出时间，最长为2年，最短为3个月，平均时间1年3个月。螺钉断裂均是在身体完全负重后发生的，椎弓根螺钉在过度负荷下的多次微
动可以在骨性融合前引起松动，特别是有骨质疏松的患者在术后因螺钉在松质骨内切割而引起复位丢失。我们认为胸腰椎骨折的椎弓根螺钉内固定系统不应固定时间过长，早取为宜。④卧床时间过短。对胸腰椎骨折的患者，我们主张术后至少卧床2～3个月，待骨折临床愈合后再逐渐下地行走。这样，既可以避免因早期活动而使胸腰椎产生持续的微动，应力分布不均，防止椎弓根螺钉过度承重；又可以尽量防止因过早活动而影响骨折愈合。⑤螺钉本身的设计或质量问题。目前应用的椎弓根螺钉，大多螺纹从钉尖向尾侧逐渐变浅、消失，而相对螺纹的根径则从下向上逐渐增粗，呈向下的锥形。这种结构克服了有螺纹与无螺纹交界处的强度突变，增强了螺钉的抗弯强度，减少了断钉的发生。骨对螺钉的握持力不够是导致螺钉松动和轴向脱出的直接原因，通过增加椎弓根钉直径，可增加固定强度和拔出力。⑥植骨融合的问题。做出一个良好的融合骨床并不容易，而融合骨面的质量是植骨融合成功与否的关键，较差的融合骨面会造成植骨融合失败。通过椎弓根向椎体内植骨仅仅填充了椎体复位后的空腔，但植骨愈合后并不能阻止椎弓根螺钉固定节段椎体间的活动，而椎体间的微动也是断钉的一个原因。此外，
有的患者在植骨未完全融合时就开始负重行走，此时骨折的愈合强度不足以抵抗负重后的椎间活动所带来的应力，这是造成部分患者椎弓根螺钉疲劳断裂或弯曲松动的一个原因。在本组334例患者中，仅有87例做了椎间或横突间植骨；在断钉或松动的25例中，有6例做了植骨。结果显示，植骨并不能有效的降低断钉或松动的发生率。因此，我们认为：只有有效的植骨融合才能有效的防止断钉的发生，而真正的做到有效的植骨融合很难，在做不到有效的植骨融合时我们不主张作脊椎骨折节段的植骨融合,以减少手术创伤。 ⑦复位不良也是螺钉松动和断裂的一个原因，复位不良会导致椎弓根螺钉承受更多的应力。
对行经椎弓根内固定的胸腰椎骨折患者，应根据其具体情况选择设计合理的椎弓根内固定器械，对合并有间盘损伤及伴有脱位的病例应行植骨融合术，术后应至少卧床2 ～3个月，在6～8
Pedicle of vertebral arch is the most powerful structure of the rear vertebral body. Through the pedicle of vertebral arch, we can get the three-column immobilization. Having been used over ten years in our country, transpedicular fixation has a reliable outcome, but there were some complications. The breakage and loosing of screws were not neglected indeed. Almost every spinal surgery doctor have met problems like this. To investigate the causes of breakage, bending and loosening of pedicle screw
systems in fixation of fractures of the thoracic and lumbar spine, 25 cases（33 bodies of vertebra）of fractures of the thoracic and lumbar spine were studied.
From February 1990 to March 2004, 867 cases of fractures of the thoracic and lumbar spine were treated in our hospital, 334 cases were treated with pedicle screws. The breaking, bending and loosing were found in 25 cases (33 bodies of vertebra). This group cases were treated with route of retreat open reduction and pedicle screws in fixation of fractures of the thoracic and lumbar spine. In these cases, the breakage, bending and loosing were founded when the screws were removed, the others were found by taking X rays before operation. The screws were removed from three months to two years after operation, average fifteen months. Before the screws were removed, most patients with breakage or loosing of pedicle screws feel pain or malaise in lumbar part. The breakage part of screws are most on
the cross point between pedicle of vertebral arch and screws, the point between thick and thin below the nut or the radical part in the screw thread. One of the break rod part occurred in the upper level 1/4 of the left cross bar and another in the collar.
The reasons that the breakage, bending or loosing of pedicle screws were as follows:
1. Overloading of the pedicle screw. We can get a satisfactory effect on fixation or restoration when the fractures of the thoracic and lumbar spine were treated with pedicle screws. The pieces of fracture may be restored wholly or partially through over-extension of spine or propped open by instrument, this can release the compression of spinal cord or nerves. But when there are no enough hold power of bone to the pedicle screws or overloading of the implant, the loosing or escaping of pedicle screws appeared. This may lead to the invalid fixation or pseudoarticulation formation. The restoration role of pedicle screws is
getted through utilizing the dragging effect of anterior longitudinal ligament, the posterior longitudinal ligament and fibrous rings of intervertebral disc. This can restore the fracture pieces of anterior border of vertebra or protruded to the vertebral canal, replace the sinking vertebral body, restore the height and form of vertebra. At this time, the maintenance of restoring certebral body can be getted by the propping open role of pedicular screws. Because the anterior longitudinal ligament and the anterior fibrous rings of disc are stressful, the interspace of intervertebral are wide, so the force conduction on the spinal column are passing from the superior vertebral body to the inferior through the pedicular screws, but not through the trouble vertebra, the force loaded wholly on the pedicular screws, this can make the screws overloaded. At the same time, although the vertebral body form were restored, the compressed cancellous bone were not restored, and this
may contribute to intervertebral narrow and hunchback afterward.
2. The loss of the intravertebral disc heights. In this group, the intervertebral narrow or retrograde disc between wounded and superior vertebral body were found more or less in bursting fracture patients. If the intervertebral disc was not wounded, this mean the injury just take place on the vertebral body, the form of the vertebral body can be restored wholly by posterior traction. The intervertebral disc after healing can maintain the normal function of weight loading. Height loss of intervertebral disc may lead to the narrowing of intervertebra
引文
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洪天禄，徐耀增，孙俊英，等. 腰椎滑脱症和胸腰椎骨折的内固定器研制及其临床应用. 中华骨科杂志，1998，8：456～459.
李书纲，邱贵兴，翁习生，等. 通用型脊柱内固定系统椎弓根螺钉的生物力学测试. 中华骨科杂志，2002，4：
229～232.
Mclain RF, Fry MF, Moseley TA, et al. Lumbar pedicle screw salvage: pullout testing of three different pedicle screw designs. J Spinal Discord, 1995, 8: 62～68.
Weidenbaux M, Farcy JPC. Surgical management of thoracic and lumbar burst fractures. In: Bridwell KH. Dewald RL. Eds. The text book of spinal surgery. 2nd ed. Philadelphia (NY): Lippincott–Raven Publishers, 1997, 1839～1880.
徐宝山，唐天四，杨惠林. 经后路短节段椎弓根内固定治疗胸腰椎爆裂性骨折的远期疗效. 中华骨科杂志，2002，11：641～647.
McCormack T, Karaikovic E, Gaines RW. The load sharing classification of spine fracture. Spine, 1994, 19：1741～1744。
Knop C, Fabian HF, Bastian L, et al. Late results of thoracolumbar fractures after posterior instrumentation and transpedicular bone grafting.
Spine, 2001, 26: 88～99.
Alanay A, Acaroglu E, Yazici M, et al.Short – segment pedicle instrumentation of thoracolumbar burst fractures:does transpedicular intracorpore- al grafting prevent early failure? Spine, 2001, 26: 213～217.
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