行政院國家科學委員會專題研究計畫 成果報告
各式的後頸椎融合在紐西蘭白兔的生物力學分析研究
計畫類別： 個別型計畫 計畫編號： NSC91-2320-B-006-082- 執行期間： 91 年 08 月 01 日至 92 年 07 月 31 日 執行單位： 國立成功大學醫學系急診學科 計畫主持人： 李明陽 報告類型： 精簡報告 處理方式： 本計畫可公開查詢中 華 民 國 92 年 10 月 28 日
行政院國家科學委員會補助專題研究計畫
□ 成 果 報 告
□期中進度報告
各式的後頸椎融合在紐西蘭白兔的生物力學分析研究
計畫類別：□ 個別型計畫 □ 整合型計畫
計畫編號：NSC 91－2320－B－006－082－
執行期間： 91 年 08 月 01 日至 92 年 07 月 31 日
計畫主持人：李明陽
共同主持人：李宜堅, 徐阿田, 張志涵
計畫參與人員：李明陽, 李宜堅, 徐阿田, 張志涵
成果報告類型(依經費核定清單規定繳交)：□精簡報告 □完整報告
本成果報告包括以下應繳交之附件：
□赴國外出差或研習心得報告一份
□赴大陸地區出差或研習心得報告一份
□出席國際學術會議心得報告及發表之論文各一份
□國際合作研究計畫國外研究報告書一份
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□涉及專利或其他智慧財產權，□一年□二年後可公開查詢
執行單位：
國立成功大學醫學系急診學科
中 華 民 國 92 年 10 月 28 日
附件一2
研究計畫中英文摘要：
（一）計畫中文摘要。關鍵詞 ：後融合(posterior fusion) ，後鋼絲固定術 (posterior wiring fixation)，後鋼板固定 術(posterior plating fixation) ，骨移植術 (bone graft)
本研究設計為一年期模式計畫。我們將研究探討頸椎後融合 (posterior fusion) 方法中使 用骨移植術 (bone graft) 之後鋼絲固定術 (posterior wiring) 和後鋼板固定術 (posterior plating) 對於實驗兔頸椎隻生物力學在延遲性生物中隻影響及相關機轉。對於頸椎的固定， 使用後鋼絲固定術是個已被廣泛所接受的方法。有許許多多的研究資料支持著這樣的固定 方式。最近數年來，後鋼板固定術也成為頸椎固定法中一個有效的技術。雖然脊椎椎突後 鋼絲固定法為廣泛所接受用來處理頸椎不穩定的方法，然而在許多的研究報告中顯示，後 鋼板固定術仍然還是優於後鋼絲固定術。許多的生物力學實驗皆證明此一論點，然而這些 實驗都是屬於體外立即融合測試者，對於在體內晚期融合的結果至今仍付之乏如。 延續之前我們脊椎實驗室在 1999 年於 Neurosurgery 雜誌一文及最近剛投稿之頸椎椎 間盤去除術加骨移植與前未獲後位固定之延遲性生物力學之研究中，頸椎融合術所得到之 結果及經驗發現當行後鋼絲融合術而無骨移植融合術時，可得到其超出固定之節數的頸椎 融合，這有可能是後鋼絲融合術會潛在性的增加其運動單元的不穩定性，這有可能是由於 潛在性的鋼絲鬆動所造成的。所以我們準備從事有骨移植術的後鋼絲融合術。而後鋼板固 定術由於也日漸受到大家之重視，因此我們提出以兔子頸椎之生物力學實驗。對於這一方 面的研究，立即性的生物力學結果有不少的報告，但是對於比較後鋼絲融合術及後鋼板固 定術晚期經過骨移植術固定術的研究，卻沒有人做過。 本計畫預定於一年內完成。利用紐西蘭大白兔給予進行後位鋼絲融合術和後鋼板固定 術，合併有無自體骨移植術並和對照組比較而得到結論。相信以本實驗室多年來於頸椎融 合術之間的研究經驗，必可獲致相當豐碩的成果。 （二）計畫英文摘要。
Keywords ：posterior fusion ，posterior wiring fixation，posterior plating fixation ，bone graft
This study will be conducted to compare the kinematic influence of posterior cervical fusion with posterior wiring technique or posterior lateral mass plating technique in a condition involving late fusion in an animal cervical spine model.
Fixation of the posterior cervical spine with steel wire is a proven technique for stabilization of the cervical spine. There is abundant biomechanical and clinical data supporting its use. In recent years, posterior plating technique have proven to be an effective means of stabilization in the cervical spine. Although interspinous wiring remains the gold standard for most types of cervical instability, posterior plating also may provide superior fixation in cervical instability. A number of biomechanical studies attest to the superiority of internal fixation of the cervical spine using posterior plating methods compared to more commonly used wiring techniques. In spite of this, very little data exist reguarding the late fusion results about the efficacy of posterior wiring and plating methods. We therefore proposed the rabbit experimental model in biomechanical and
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radiological evaluation of posterior cervical spine stabilization.
前言:
The internal fixation of the cervical spine was introduced first in 1891 by Hadra [8], who used spinous process wires to treat a cervical spine fracture dislocation. Since that time, a gradual progression toward the use of rigid internal fixation for fusion and stabilization has culminated in the development of the new instrumentation systems available today. These cervical instrumentation systems, besides the various posterior wiring techniques, include posterior lateral mass plating and anterior plating. However, fixation of the posterior cervical spine with stainless steel wire is a proven technique for stabilization of the cervical spine. There is abundant biomechanical and clinical data supporting its use [1-4]. In recent years, the use of anterior plating has become popular because decompression, grafting and stabilization may be performed simultaneously through the same procedure.
Several biomechanical studies comparing various surgical constructs provided by anterior or posterior instrumentation of the cervical spine have been reported in the literature.[6-8,14] The major findings of these studies revealed no significant differences between implants in most cases. We previously showed the similar data in sheep model[15] and for axial rotation loads, anterior cervical discectomy without bone grafting showed an increased motion range at tested level(C2-C3), but increased range of motion was also demonstrated at adjacent level(C3-C4). From this point of view, exclusive posterior wiring may lead to excessive motion but in structural bone graft and posterior wiring not, this difference may be due to subclinical wire loosening in the late fusion period. We also found that posterior wiring with bone graft could fuse and extend to adjacent level and this phenomenon may be caused from adjacent level fusion on the facet joint area. The posterior lateral mass plating technique provides superior rotational stability at the facet joint and its use does not usually require bone grafting to ensure long term stability.[2,4,5,8,11,13] Various biomechanical studies support the superiority of internal fixation of the cervical spine using lateral mass plating than wiring technique.[6,13,16] Experimentally, the immediate kinematic changes were tested by Weis et al.[4]. Using a fresh frozen cervical calf spines, they demonstrated that the posterior cervical plate construct offered the greatest stability compared with all other constructs. This construct was the stiffest under flexion, extension and lateral bending modes before and after fatigue testing. But as the previous statement, posterior wiring technique may cause adjacent bone fusion, and bone fusion responded to the changes in load over time, which was inevitably overlooked in the biomechanical interpretation of immediate fusion results for clinical use. Undoubtedly, the influence of this clinically related bone-adaptive remodeling process only can be examined by experimental late fusion results.
Sophisticated knowledge of spinal biomechanical properties provides fundamental basis of clinical judgement when a spinal fixation is to be selected, and may also be helpful to predict final outcome following a surgical treatment. The purpose of this study was to assess relative stability provided by posterior plating with lateral mass plate, posterior wiring by Bohlman’s triple wire technique[9] with and without bone graft, and combined fixation using rabbit cervical
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spine for late fusion result. The quantitative evaluation of biomechanical properties and the fusion bone density and adjacent level bone density will be done.
研究計畫之目的
目標(Specific aims)：1. In the clinical study, posterior stabilization with posterior wiring alone (exclusive posterior wiring) allowed a relatively greater motion to occur, and thus, might need other adjunctive fixations to ensure an optimal condition of kinematic restriction.
2. In a 2 functional unit cervical spine model in New Zealand White rabbits, we plan to evaluate the kinematic data of posterior wiring technique in the rabbit cervical
spine.
3. We will also compare the kinematic differences between the posterior wiring treatment with structural bone graft, and posterior wiring with posterior lateral mass plating.
4. We will compare the late results of intervertebral fusion among different groups following a prolonged recovery period.
研究方法、進行步驟及執行進度 (Research design and methods)
1. Thirty-two adult New Zealand White rabbits of either gender, each weighing about 3-4 kg, will be used in the experiment, including the eight as the control group.
2. Anesthesia will be induced by ketamine (15mg/kg) and pentobarbital intramuscular injection and then intubated with 3.0 cuffed endotracheal tube. Inhalation anesthesia was induced by 4% halothane and be maintained by N2O/O2 (70:30), mechanical ventilation was also used with a
respirator under full muscle paralysis induced by the intravenous administration of pancuronium bromide (8-10 mg/kg).[17,18]
3. With the animals in the prone position and its head in cervical flexion, a midline longitudinal incision will be made and down into the spinal process. Dissect the paraspinal muscles and expose the bilateral facet joint.
4. The levels of exposed vertebrae will be verified by a lateral radiograph of cervical spine. The posterior stabilization was accomplished using a modification of the sublaminar wiring technique construct described by Coe, Sutterlin & McAfee. Specifically, the spinous processes of C-2, bilateral sublaminar wires passing through C-3, and C-4 were synchronously tightened to obtain adequate bilateral compression posteriorly. Bone graft from the iliac crest will be packed along the decorticated posterior elements in and around the wires to obtain a bony fusion at these levels. All wires were made of No. 24 stainless steel. The entire sequence of
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tests were repeated.[1,3,4]
5. Insertion of lateral mass screws will be started at the point 1mm medial to the center of the lateral mass with its direction kept consistently 25。laterally and 15。cephalad with bicortical purchase. Loosening of the implants will be checked by hand immediately after testing each construct to ensure the fixation at bone-screw and screw-plate interfaces.
6. The animals will be divided into four groups. In each group, eight rabbits will be included. In Group A, each rabbit receive a sham operation that served as intact controls. In Group B, animals will only receive C2-C4 posterior wiring without structural bone graft. Group C animals will receive the insertions of bone graft with two iliac crest strut grafts secured to these spinous processes with twisted wires. For Group D animals, posterior wiring with iliac bone strut graft and bilateral posterior lateral ass plate will be performed.
7. Intraoperative and postoperative antibiotics will be administrated intramuscularly. After 24 hours of intensive observation, the animals were allowed activity and were freely fed a regular diet. Neurological examinations were performed weekly along with monitoring of the animals’ eating habits, ambulatory activities, and wound healing. No attempt was made to immobilize the animals’ neck. Repeated radiographs will be required during the initial three postoperative months to ensure that the graft and/or the implant do not be broken.
8. Six months after surgery, a lateral radiograph will be obtained again to evaluate the structural integrity of the operative level. The animals will then be sacrificed, using the inhalation of 100% CO2, so that the cervical spine specimens(C1-C7) can be obtained. Each specimen will
be sealed in double plastic bags and kept in frozen at -60 ℃ until further preparation for testing.
9. Each specimen will be cleaned of ligament nuchae and all muscle tissue while taking care to preserve the other ligamentous structures. The end vertebrae (C2 and C6) will be transfixed with perpendicular pins to enhance fixation with mounting jigs. The specimens will be oriented in physiological position and the prepared ones will be attached to the base of a testing cage. 10. A set of three infrared light-emitting diodes (LEDs) will be rigidly attached to each vertebrae
of C2-C4 (2 functional units) as the definable points for three-dimensional motion.[15]
11. Two LEDs will be screwed at the ends of Steimann pin (0.25 x 1.5 in) drill through the spinous process and the third LED will be fixed at the inferior midportion of each vertebrae body. Another set of three LEDs will be attached to the base for defining an anatomically relevant Cartesian axes system. Thus, a total of 12 LEDs will be used for each test.[15]
12. A Selspot II system (selcom Selective Electronic, Inc., Valdese, NC) will be used for motion monitoring. The LEDs will fire sequentially, and the emitted light will be picked up by four cameras, in terms of X, Y, and Z voltages, through infrared light detectors, analog amplifiers and associated calibration.[15]
13. Experimental moment exerted on the specimen will be exerted by a loading system, as described previously. Briefly, the base of loading frame will allow sliding toward the moment direction of tested specimens. With two sets of parallel loads applying simultaneously onto two slides, each of which will be attached laterally to one side of the loading frame, a couple can be obtained, which enable one to approximate pure moments as closely as possible.[15]
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14. The loading frame will be preloaded with 5 N. By gradual additions of 100- to 300-g weights, a final moment of 0.72Nm can be achieved. Load steps will be repeated five times in a prescribed load type sequence, and the weight increments were added in 30-second time intervals. The fifth cycle LED locations relative to each load type will be recorded and analyzed in the study.
15. The spatial locations LEDs will be defined with relevance to the anatomically Cartesian axes system located at the base plate. The spatial data will be compiled and then transformed into three Bryant/Eular angles as the relative rotations between any two contiguous vertebrae. These angles represent three primary vertebrae rotations: rotation in the sagittal plane for flexion and extension, rotation in the transverse plane for axial rotation, and rotation in the frontal plane for lateral bending.
16. Bony union was defined as a solid consolidation if the interface showed continuous bone density and had clearly crossing bone trabecullae.
17. To determine the quality of intervertebrae fusion and the coupling resorpition of bone grafting, a semi-automated computerized imaging analysis system (MCID, imaging Research Inc., Ontario, Canada) will be used to measure the integrated optical density concentration (IOD(c)=sum of pixel concentration values/numbers of pixels) and the dimension (mm2) of the bone fusion.
18. To avoid a light source-induced error and to compensate for the variations in radiographic exposure as well as tissue mineralized density from animal to animal, the formal data were further expressed as a ratio relative to the density concentration of the C2. The dimension data will be expressed as a percentage of the mean value of the sham operated group.
19. Partitioning color images into red, blue, and green components can improve visualization of normal trabecular anatomy (orange component image) and greatly enhanced the definition of the bone resorption (black component image), the mineralized bone (blue/green components), and the solid osseointegrated (white component image) areas. In addition, posterior extension of bone margin (mm) will be measured with adjustments for magnification of lateral radiographs.
20. Pathological section will also be done for further verifying the quality of intervertebral bony fusion.
21. All data presented in this study will be expressed as mean ± standard error of the mean (SEM). Differences among groups were analyzed using the Mann-Whitney test. A p value of less than 0.05 will be selected for statistical significance.
Results
More than forty rabbit were included in this experiment. Posterior cervical fixation by sublaminar wiring with or without bone graft was done after several times of practice and experiment. However, sublaminar wiring combined with lateral mass plates and screws were hard to be completed in the last year, animals death after several days of operation. According to the autopsy results showed that the possible causes of death may be related to the potential neurological injuries in bicortical screws purchasing period, wound infection, and unable to eat
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due to cervical spine over-rigidity after operation. It may be resulted from smaller rabbit posterior elements and unsuitable instruments sizes. After animals sacrificed and cervical spine specimens were obtained, posterior cervical fixation with combined sublaminar and interspinous process wiring with or without structural iliac bone graft showed restricted range of motions than control group.
The radiographs of posterior wiring fixation with structural bone graft group showed solid posterior bone fusion between the C2-C4 spinous processes (Fig.1) and we also found that posterior wiring with bone graft could fuse and extend to adjacent level as we previously mentioned. This phenomenon may be caused from adjacent level fusion on the facet joint area due to stress concentration effect. The group of posterior wiring without structural bone graft showed posterior fusion in situ by the instrument but no obvious bone fusion was found (Fig.2). The posterior lateral mass screwing was done and the result was satisfactory, however no suitable plate could be available in the rabbit model and we looked for the craniofacial miniplate for another substitute (Fig.3).
Biomechanical analyses were subjective to execute with Selspot system in original planning,
but due to software failure, so we changed to the Vicron 370 motion analysis system in these recent time and the parameters setting were under constructed.
Discussion
In 1942, Rogers firstly introduced his technique for interspinous wiring of the posterior cervical spine, with excellent clinical results. Bohlman modified this simple wiring technique to improve biomechanical stability with two construct iliac bone grafts anchoring to the base of the spinous process.
During the 1990s, use of posterior cervical plates was developed in European centers. Many surgeons believe that posterior plating with screws will provide excellent immediate fixation than wiring technique. Several authors have compared posterior cervical fixation techniques in animal models in vitro, however, less in vivo, late fusion results were known. As we mentioned previously, bone fusion responded to the changes in load over time, which was inevitably overlooked in the biomechanical interpretation of immediate fusion results for clinical use. Undoubtedly, the influence of this clinically related bone-adaptive remodeling process only can be examined by experimental late fusion results. But in the past one year, no long enough time were obtained to wait for the matured bone fusion (at least six months) and some animals were under holding in the cages to wait for the matured bone fusion.
In this experiment, many difficulties were encountered during proceeding the posterior fixation techniques. Authors have tried the posterior wiring fixation with Roger’s or Bohlman’s technique, however, smaller C3 and C4 spinous processes noted in rabbit model and unable to obtain satisfying fusion results. Sublaminar wiring technique was an alternative procedure for smaller animal models to obtain posterior fixation with wires. However, potential neurological injuries when passed the steel wire under the small lamina and higher animal mortality rate in the beginning may need more practice to overcome. We have ever tried to find some mini-plates which used in craniofacial surgery to be an alternative instrumentation in the posterolateral
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fixation with plates and screws, however, unsuitable size of posterior plate and screws system were also waiting to solve.
Biomechanical tests were important for the comparisons in several methods of posterior fixation technique. However, we planned to test the specimens with Selspot system, software fail was noted due to harddisk broken. So the biomechanical tests will wait for another experimental model setup with another motion analysis system (Vicron 370) in the following time.
Sophisticated knowledge of spinal biomechanical properties provides fundamental basis of clinical judgement when a spinal fixation is to be selected, and may also be helpful to predict final outcome following a surgical treatment. We will keep this experiment ongoing and the final consequence will be reported.
Conclusions
Posterior wiring with structural bone graft show solid bone fusion and may extend to the adjacent level. Although, the sublaminar wiring for posterior fixation in New Zealand White rabbits are difficult, but passage of the wires through the narrow epidural space can be achieved under the aid of operative microscope and more meticulous surgical technique. Posterior lateral mass screws and plates need time to overcome the small lateral mass area and technique difficulty. Alternatively, more rigid craniofacial mini-plates may be another choice for posterior plating technique in rabbit model.
References
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2. Gill K, Paschal S, Corin J, Ashman R, Bucholz RW. Posterior plating of the cervical spine. Spine 1988;13:813-6.
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4. Weis JC, Cunningham BW, Masahiro Kanayama, Larry Parker, McAfee PC. In vitro biomechanical comparison of multistrand cables with conventional cervical stabilization. Spine 1996; 21(18): 2108-2114.
5. Richman JD, Daniel TE, Anderson DD, Miller PL, Douglas RA. Biomechanical evaluation of cervical spine stabilization methods using a porcine model. Spine 1995;20(20):2192-7.
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8. Young Do Koh, Tae-Hong Lim, Jae Won You, et al. A biomechanical comparison of modern anterior and posterior plate fixation of the cervical spine. Spine 2001;26(1):15-21
9. Traynelis VC, Donaher PA, Roach RM, et al. Biomechanical comparison of anterior Caspar plate and three-level posterior fixation techniques in a human cadaveric model. J Neurosurg 1993; 79(1): 96-103.
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10. Kotani Y, Cunningham BW, Abumi K, McAfee PC. Biomechanical analysis of cervical stabilization systems: an assessment of transpedicular screw fixation in the cervical spine. Spine 1994;7:222-9
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atlantoaxial posterior fixation techniques. Spine 2000; 25(22): 2877 - 2883.
13. Errico T, Uhl R, Cooper P, et al. Pullout strength comparison of two methods of orienting screw insertion in the lateral masses of the bovine cervical spine. J Spinal Dis 1992;5: 459-463
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Legends
Fig.1
The figure showed solid bone fusion over posterior aspect of C2-C4 in posterior wiring with structural bone graft group
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Fig.2
Fig.3
The figure showed no obvious bone fusion at posterior aspect of C2-C4 in posterior wiring without bone graft group
Posterior lateral mass screws were inserted in the bilateral C3 lateral mass without neurovascular injury
