行政院國家科學委員會專題研究計畫 成果報告
於正常與退化性頸椎模式探討椎間植入器植入於去椎間盤
術後之生物力學, 放射學, 與組織病理學上之長期效益
(3/3)
計畫類別： 個別型計畫
計畫編號： NSC93-2320-B-006-006-
執行期間： 93 年 08 月 01 日至 94 年 07 月 31 日
執行單位： 國立成功大學醫學系外科
計畫主持人： 李宜堅
報告類型： 完整報告
處理方式： 本計畫可公開查詢
中 華 民 國 94 年 6 月 7 日
Biomechanical evaluation of cervical spine fixation after healing in a
destabilized cervical spine model in sheep: a comparison of the
anterior plating and posterior wiring techniques
Ming-Yang Lee
1, M.D., Guan-Liang Chang
1, Ph.D., Jia-Hao Chang
1, Ph.D.,
Yu-Chang Hung
1, M.D., Ching-Hong Chang
2, M.D., E-Jian Lee
1, M.D., M.Sc.
1
Neurophysiology Laboratory, Neurosurgical Service, Department of Surgery &
Institute of Biomedical Engineering, National Cheng Kung University Medical
Center & Medical School, Tainan, Taiwan.
2
Neurosurgical Service, Department of Surgery, Chi-Mei Medical Center,
Tainan, Taiwan.
Running Title: Biomechanical Testing of Cervical Spine Fixations
Number of pages: 22
Number of figures: 4 (Figures 1 A-E, 2 A-F, 3, 4) Category: Experimental studies.
Address reprint request to:
E-Jian Lee M.D., M.Sc., Department of Surgery, National Cheng-Kung University Medical Center, No 138 Sheng-Li Road, Tainan 704, Taiwan.
Telephone: +886-6-235-3535 ext. 5186; Fax: +886-6-276-6676.
Abstract
Objective: We conducted biomechanical evaluation of the anterior plating and posterior wiring
techniques for cervical spine stabilization after a course of healing in sheep.
Methods: Seventeen sheep were included, and six of which underwent sham operations (Group A,
n=6). The other eleven received complete C2-C3 destabilization, followed by intervertebral bone grafting and cervical stabilization either with anterior plating (group B, n=5) or posterior wiring (group C, n=6) techniques. These animals were killed 6 months later. Ligamentous spines (C1-C5) were subjected to the relevantly applied loads. The load-deformation data of the C2-C3 and C3-C4 functional units were recorded and analyzed.
Results: At the C2-C3 functional unit, Group B had the least motion ranges in flexion, lateral
bending, and rotation loads than did the other two groups. Significantly smaller motion ranges of lateral bending and rotation loads were found in Group B than in Group C (P < 0.05). Compared to Group A, Group C had a decreased motion range in flexion load but showed increased motion range in rotation load. Consequently, Group B had superior intervertebral fusion and less osteophyte than did Group C. At the C3-C4 functional unit, Group B showed significantly
decreased motion ranges in extension and lateral bending loads (P < 0.05), while Group C did not.
Conclusion: The results indicated that the anterior plate-stabilized spines were more stable over
time than did the posterior-wired spines. This biomechanical advantage eventually resulted in superior intervertebral fusion masses in the former, although it also induced a slightly decreased motion range at the contiguous functional unit. In exclusively posterior wired-spines, the weakness for opposing rotation loads might contribute to the formation of osteophytes at the fusion
functional unit. These data point out that the mode and stability of implant fixation systems greatly influence the biomechanical redistribution and bone-adaptive remodeling process during healing, which are closely related to the bone graft maturation and osteophytic formations at the fusion level and the occurrence of stiffening problems at the contiguous levels.
Introduction
Cervical fusion with bone grafting and complementary implant fixation is now firmly established and widely accepted in the treatment of cervical spine instabilities arising from trauma, a tumor, and destabilizing surgical procedures such as wide laminectomy or facet destrution.1-3. For cervical disc disease, the anterior-plate fixation has also been suggested for
those patients at risk for developing soft tissue fusion, although most authors agree that the use of bone bulk intervening the discectomied interface is far enough to achieve solid bone fusion and to maintain an acceptable height of the discectomied function unit.4-6.
Treatment modalities for cervical spine stabilization, however, may include either anterior or posterior fixation, or, even further, both in one session, each of which has gained supporting rationale(s) to be used in routine neurosurgical practice. Some authors have advocated the use of the anterior-plate fixation, with an intervertebral bone graft intervened at the discectomied site, to achieve immediate stabilization and subsequent bone fusion.7-10.
Other authors recommended the use of posterior fixation with and without the complementary anterior fixation, in addition to structural bone grafting.11-14.
Sophisticated knowledge of kinematics and biomechanical data can offer a rational guide for spinal surgeons to choose the optimal operative approach in the treatment of various kinds of unstable cervical spine diseases. This information is also very helpful for predicting and avoiding of the potential complications that may occur due to
biomechanical redistribution after the treatment of spinal stabilization.5,15,16. In sheep
followed for 6 months, we previously showed that C2-C3 cervical discectomy without
intervening bone grafting resulted in an irregular and noncontinuing bony fusion as well as massive soft tissue reactions that could oppose the lateral bending but not the axial rotation loads.5. This exclusive discectomy procedure also induced an increased motion range of the
adjacent (C3-C4) functional unit in the rotation-testing mode. We reasoned that anterior
the consequence further resulted in a load-specific ligamentous laxity at the C3-C4
functional unit that became apparent in the subsequent biomechanical testing in vitro. Interestingly, the discectomy-induced hypermotility in rotation, observed either at the C2-C3 or C3-C4 functional unit, was much attenuated with the application and following
the maturation of intervertebral bone grafting.
C2-C3 cervical discectomy was, however, noted to result in an increased motion
range in flexion load at the C3-C4 functional unit, and this kinematic change could not be
reversed even with the presence of solid maturation of the intervertebral bone grafting.5. It
has been known that mechanical implants actually possess a load-sharing or -shielding biomechanical property, and, thus, have the potential to rectify the biomechanical alterations due to discectomy or the loss of functional discs.17,18. We therefore supposed
that perhaps using an implant fixation as an add-on treatment of bone grafting, this discectomy-induced unbalanced physiological load in flexion, applied by cervical musculatures, would be much attenuated and the resultant adverse kinematic changes considerably lessened.
In order to extend our original findings and in line with standard treatment modalities for unstable cervical spine disorders, we herein investigate the biomechanical influence of two different cervical fixation techniques in sheep subjected to complete cervical spine destabilization and intervertebral bone grafting following a prolonged period of the bone-adaptive remodeling processes. We attempted to determine whether anterior plating could offer superior stability over time and, consequently, resulted in superior fusion masses and a decrease in adverse kinematic changes at the adjacent functional unit than did
Materials and Methods
Animal Preparation
All procedures followed the guidelines of the National Institutes of Heath (Guide for the Care and Use of Laboratory Animals) and were approved by the University animal ethics committee. Eighteen healthy adult Barbados Black Belly sheep of either gender, aged 1-2 years old and weighing 40 to 45 kg, were used in this experiment. Anesthesia was induced by the intramuscular administration of ketalar (50 mg/kg) and was maintained by
α-chloralose (40 mg/kg). The sheep were intubated and mechanically ventilated with a respirator under full muscle paralysis induced by the intravenous administration of pancuronium bromide (8 mg/h).
Surgical Procedure and Stabilization
With the animal in the supine position and its head in normal cervical lordosis, standard anterior cervical approach was first employed. Briefly, a right oblique incision was made for exposing the C2 and the C3 vertebrae. The exposure was then widened and
deepened. The deep cervical fascia overlying the longus colli muscles and the anterior longitudinal ligament were then dissected away from the vertebral bodies and from the adherent annulus fibrosus of the disc. The levels of exposed vertebrae were verified by a lateral radiograph of cervical spine. C2-3 discectomy was then employed through incising the
annulus and removing the nucleus, the remaining cartilaginous end plates as well as the underlying posterior longitudinal ligament. The harvest and the insertion of autologous iliac crest graft (1.4x1x0.7 cm3 in size) were performed according to the Smith-Robinson
techniques.19,20.
The animals were then positioned in prone with the cranium supported on a head holder. Posterior cervical approach was performed through a midline incision. When approaching the cervical spine, subperiosteal dissections were made to detach the erector spinae muscles away from the posterior elements from the C1 to the C4. Once the spine was
exposed and self-retaining retractors were placed, the articular processes between the C2 and
the C3 levels were chiseled out bilaterally. All posterior ligamentous structures between the
C2 and the C3 levels were incised.
Anterior instrumentation was performed with the Caspar anterior trapezoidal plate (37 mm in length, Aesculap, San Francisco, CA) transfixed with 2 bicortical screws (17-18 mm in length) to each vertebral body of the C2 and the C3.8-10,21. A modified Roger’s wiring
technique was used for posterior stabilization.7. Briefly, drill-holes were placed through the
base of the spinous processes of the C2 and the C3. Holes were drilled with a small diamond
burr and then enlarged by a towel clip for facilitating the passage of wires. A twisted bundle of triple 20-gauge wires were then passed through and around the spinous processes of the C2 and the C3 (including a sublaminar loop of the C3 lamina). The wires were tightened
gently to hold the vertebrae in position.
Grouping
The animals were divided into three groups. In each group, six sheep were included. In Group A, each sheep received sham anterior and posterior operations by fully exposing the anterior and posterior vertebral surfaces without disturbing the bony and ligamentous structures. In Group B, animals received C2-C3 cervical discectomy and the removal of the
anterior and posterior spinal ligaments as well as the bilateral facet joints. The insertion of autologous iliac crest graft was immediately employed under moderate retraction of
discectomied space, followed by the fixation with the anterior Caspar plate and screws at the same functional unit to achieve stabilization. Group C sheep underwent the same procedure of C2-C3 destabilization and was re-stabilized by the posterior wiring fixation in addition to
the intervertebral bone grafting. Intraoperative and postoperative antibiotics were administrated intravenously. After 24 hours of intensive observation, the animals were allowed activities and were fed a regular diet. Neurological examinations were performed weekly along with the monitoring of the animal’s eating habits, ambulatory activities and
wound healing. No attempt was made to immobilize the animals’ neck. Repeated
radiographs were required during the first 3 postoperative months to ensure that the implant did not extrude. Preliminary data indicated that, without complementary implant
stabilization, animals subjected to C2-3 destabilization rapidly developed quadriplegia and
could not survive for more than one week after the surgery, even with the presence of the intervertebral bony grafting.
Sacrifice and Specimen Preparation
Six months after surgery, a lateral radiograph was again obtained to evaluate the structural integrity of the operative level. The animals were then killed, using an injection of overdose pentobarbital, so that the cervical spine specimens (C1-C5) could be obtained. Each
specimen was sealed in double plastic bags and kept in frozen at -60°C until further
preparation for testing.
Each specimen was cleaned of ligament nuchae and all muscle tissues while taking care to preserve the other ligamentous structures. The end vertebrae (C1 and C5) were
transfixed with perpendicular pins to enhance fixation with mounting jigs. For eliminating the rotation between the C1 and the C2, one thread rod (0.25 x 1.5 in) was used to transfix
the anterior arch of the C1 to the odontoid process. The specimen was oriented in a
physiological position, with the C3-4 disc space horizontally placed. The prepared specimen
was attached to the base of a testing cage.
Biomechanical Testing
A set of three infrared light-emitting diodes (LEDs) was rigidly attached to each vertebra from the C2 to theC4 as the definable points for three-dimensional motion. Two
LEDs were screwed at the ends of the Steimann pin (0.25 x 1.5 in) drilled through each spinous process and the third LED was fixed at the inferior midportion of each vertebral body. Another set of three LEDs was attached to the base for defining an anatomically relevant Cartesian axes system. Thus, a total of 12 LEDs was used for each test. A Selspot II
system (Selcom Selective Electronic, Inc., Valdese, NC) was used for motion
monitoring.5,22-25. The LEDs were fired sequentially, and the emitted light was picked up by
four cameras, in terms of X, Y, and Z voltages, through infrared light detectors, analog amplifiers, and associated calibration.
Experimental moment exerted on the specimen was by a loading system that
contained weights, pulleys, and nylon strings, as described previously.5. Briefly, the base of
the loading frame would allow sliding toward the movement direction of the tested specimens. The loading frame was preloaded with 5 N. By gradual additions of 100- to 300-g weights on to the string, a final moment of 0.72 Nm was achieved. Load steps were repeated five times in a prescribed load type sequence: flexion and extension, left and right lateral bending, and left and right axial rotation. The weight increments were added in 30-second time intervals. With two sets of parallel loads that were simultaneously produced at both slides attached to the loading frame, a couple was obtained, which enabled one to approximate pure moments as closely as possible. The fifth cycle LED locations relative to each load type were recorded and analyzed in the study.
The spatial locations of LEDs were defined with relevance to the Cartesian axes system located at the base plate. The spatial data were compiled and then transformed into three Bryant/Euler angles as the relative rotations between two contiguous vertebrae. These angles represented three primary vertebral 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.
Quantification of Bony Fusion
To determine the quality of intervertebral fusion and the coupling resorption of the bone graft, a semi-automated computerized imaging analysis system (MCID Elite, Imaging Research Inc., Ontario, Canada) was used to measure the integrated optical density
regions of interest in the lateral views of the cervical spine. In addition, the dimension (mm2)
of the discectomied space was measured. The density values obtained were further expressed as a ratio relative to the density value of the C1 in each animal so as to correct the light
source-induced error and to compensate for the variations in radiographic exposure as well as the differences in tissue mineralized density from animal to animal.26. The dimension data
were expressed as a percentage of the mean value obtained in the sham-operated group. Moreover, the length of posterior extension of bone margins (mm) was measured with adjustments for the magnification of lateral radiographs. Finally, gross pathological sections were undertaken and photographed, followed by the processing of the specimens for further histological sections. Longitudinal sections (10 µm) across the region of interest, at where discectomy and bony grafting had been performed, were made and stained with traditional hematoxylin and eosin (H&E) staining. Histological sections were then examined under a light microscope (Zeiss Axioskop 2 Mot) equipped with a digital CoolSnap-Pro cf camera (Media Cybernetics, Inc., Carlsbad, CA). Bony fusion was defined as a solid consolidation if the interface had the formation of continuous solid osteoids and clearly crossing bone trabecullae between the cortical walls of the C2 and C3 vertebral bodies.
All data presented in this study are expressed as the mean ± standard error of the
mean (SEM). Differences among groups were analyzed using the Kruskal-Wallis test at each variable. The Mann-Whitney U test was conducted when indicated. A P value of less than 0.05 was selected for statistical significance.
Results
Mortality was 5.6%. One Group B animal had implant extrusion during early postoperative period, obviously as a consequence of technical failure. This animal, which eventually developed quadriplegia and died before completing the recovery protocol, was excluded for further data analysis. The other cervical spine-stabilized animals either with the anterior plate or the posterior wiring techniques did not have notable implant extrusion or wire loosening during the whole observation period.
Animals received implant stabilization showed various degrees of bony fusion, but there was no spontaneous fusion for the sham-operated animals (Fig. 1, A & Fig. 2 A, D). The fusion masses were more consolidated in Group B (Fig. 1, B & Fig. 2 B, E) than in Group C (Fig. 1, C & Fig. 2 C, F), although the latter actually had a higher radiographic density of fusion than did the former. Group B demonstrated a dense bony response with continuous osteoid tissue formations and calcifications across the fusion interface (Fig. 2, B
and E ), and had minimal osteophytic outgrows from the adjacent cortical walls of the C2 and
C3 vertebral bodies. However, coupling bony resorption was noted in the central part of the
bone graft (Fig. 1, D). In contrast, Group C animals had fusion masses which were
constituted with a clearly fewer amount of crossing bony ridges admixed with massive soft tissue formations (Fig. 2, C and F). Radiographically, intense optical concentrations were also observed at the interface of fusion in lateral views of the posterior-wired spines, in consistent with soft tissue reactions. Additionally, these animals had obviously more osteophytic growths extending beyond the margins of the anterior and posterior cortical walls of the C2 and C3 vertebral bodies (Fig. 1, E). Our results indicated that Group C had a
significantly higher ratio of the IOD(c) than did Group B (0.95 ± 0.03 versus 0.35 ± 0.01, P
< 0.01). Group C also had more osteophytes extending beyond the posterior margins of the C2 and C3 vertebral bodies than did Group B (4.1 mm ± 0.2 versus 1.1 mm ± 0.1, P < 0.01).
Group B (106.7% ± 4.5 versus 85.4% ± 4.4, P < 0.01).
The relative primary rotation data responding to the final load step of 0.72 N-m at the C2-C3 functional unit are illustrated in Fig.3. The results indicate that Group B had the least
motion ranges responding to the flexion, lateral bending and rotation loads than did the other two groups. Significantly smaller motion ranges in the lateral bending- and rotation-testing modes were found in Group B than in Group C (P < 0.05). Compared to Group A, Group B exhibited significantly smaller motion ranges in the flexion-, lateral bending- and axial rotation-testing modes (P < 0.05). Group C also had decreased motion ranges in response to the flexion and lateral bending loads than did Group A, but showed a modest increase in the motion range in the rotation-testing mode. The motion range responding to the extension load was not significantly different among the 3 study groups.
The relative primary rotation data responding to the final load step of 0.72 N-m at the C3-C4 functional unit are illustrated in Fig. 4. Both the 2 stabilization groups showed
significantly smaller motion ranges in response to the extension and lateral bending loads than did Group A, but had a modest increase in the motion range in the rotation-testing mode. Compared to Group A, Group B exhibited a significantly smaller motion range responding to the extension and right lateral bending loads (P < 0.05), while Group C did not. In addition, Group B showed a decreased motion range responding to the flexion loads, whereas Group C had a modest increase in this motion range.
Discussion
Our previous work ascertained that anterior cervical fusion did not completely eliminate intervertebral motion of the fusion functional unit, presumably as a result of movements at the facet joints.5,27. In this experiment, we used a 3-column cervical spine
injury model to enhance residual movements after anterior fusion. With 2 functional units that were simultaneously measured in the pure-moment biomechanical testing, the stability of the destabilized/fusion functional unit and the kinematic influence, applied by cervical musculatures under physiological loads over time, onto the adjacent functional units could be evaluated. Additionally, the fusion quality of intervertebral bone grafting could be used to decipher the net effects of biomechanical redistribution over time relevant to an implant fixation.
For the C2-C3 functional unit, our results showed that the anterior plate-stabilized
spine provided superior stiffness over time in response to the flexion and lateral bending loads than did the posterior-wired spines. The posterior-wired spines were more stable in the flexion-testing mode than did the sham-operated specimens. These findings are compatible with the observation reported in human cadaveric spines.25. One changed finding of our
results was that, relative to the sham-operated specimens, the posterior-wired spines had nearly equal stability for the extension and lateral bending loads, indicating that the
bone-adaptive remodeling process had already occurred to effect these 2 forms of stability in these animals.5.
The other changed finding for the C2-C3 functional unit of our results was that the
posterior-wired spines were not as stable as the anterior plate-stabilized spines in the rotation-testing mode.25. Curiously, a modest increase in the motion range in response to the
rotation loads was also seen at the C3-C4 functional unit in these posterior-wired spines.
Thus, a decrease in stress absorption for the rotation loads at the C2-C3 functional unit might
eventually resulted in a load-specific ligamentous laxity at the C3-C4 functional unit in these
animals.5,28. Conversely, the anterior plate-stabilized spines had a more rigid C2-C3
functional unit for opposing the rotation loads than did the posterior-wired spines and the intact control specimens. Fixation with an anterior-plating and -screwing system, therefore, appears to be an effective treatment modality for postinjury rotational hypermotility.
For the fusionfunctional unit, our results, combined with other observations previously discussed,5,29. also indicated that the anterior-plate fixation provided strong stability over time
in response to all modes of testing loads. These anterior plate-stabilized spines, however, showed a slight increase in the stiffness responding to the extension and lateral bending loads at the adjacent functional unit. Actually, the posterior-wired spines also had a modest
decrease in the motion range of the C3-C4 functional unit in the extension- and lateral
bending-testing modes. Thus, both the 2 fixation methods might have provided a load-sharing action for the extension and lateral bending loads during healing, and, consequently, resulted in a stiffening adjacent functional unit in response to the 2 testing modes.
Our results further indicated that Group C animals might have experienced a late-onset event of subtle wire loosening that allowed some movements to occur at the fusion function unit.27. A similar event of wire loosening has been observed in human
cadaveric spines in previous work of Ulrich, et al. 30. They demonstrated that exclusive
posterior wiring techniques were weak for opposing persistent translatory displacement and, eventually, resulted in permanent subluxation of the fusion functional unit. In clinical practice, a significantly higher incidence of prolonged postoperative neck pain have also been observed in patients treated with posterior wiring fixations without in situ structural bone fusion, as compared to those patients who received an anterior-plate stabilization.31.
In this study, the posterior-wired spines were also noted to have more osteophytic growths at the fusion functional unit than did the anterior plate-stabilized spines.
Interestingly, this pattern of osteophytic growths has previously been linked with increased motion ranges in response to the rotation loads at both the fusion and adjacent functional units in animals subjected to discectomy without bone grafting.5. Thus, the biomechanical
weakness for opposing the rotation loads might have contributed to the formation of
osteophytes at the fusion functional unit in these posterior-wired animals. It has been known that the formation of solid intervertebral bone fusion provides strong stability against the rotational hypermotility induced by anterior cervical discectomy.5. Relative to the
sham-operated specimens, the posterior-wired spines exhibited modest increases in the motion ranges responding to the rotation loads at both the fusion and adjacent functional units, in accompanying with massive soft tissue reactions formed at the fusion interface. Accordingly, it is very likely that the formation of osteophytes in these posterior-wired spines may actually reflect a bone-adaptive remodeling process in response to the in vivo biomechanical weakness for opposing the rotation loads. Further studies are, however, needed to determine whether these osteophytes observed in the posterior-wired spines will subsequently absorb or turn out to be more enhanced after a longer period of healing.
An ideal stabilization method should include dual biomechanical properties, for providing a rigid stability and for effecting a load-sharing action, so as to achieve immediate stabilization for the fusion functional unit and to allow an appropriate amount of
physiological loads, applied by the cervical musculature responding to gravity and normal daily activities, transferring onto the bone graft and the adjacent functional unit.12,32. Thus,
solid maturation of the bone graft can be obtained without deleterious biomechanical effects onto the adjacent functional units. In this study, the finding that Group B animals had a superior consolidation of the fusion masses further justified tough stability coupling with a load-sharing action offered by the anterior-plate fixation system.33,34. On the other hand, the
posterior-wired animals were noted to have massive soft tissue reactions formed at the interface of fusion. Thus, exclusive posterior-wire fixation appeared to be not strong enough
in the management of completely disrupted cervical spines.1.
Our data further suggest that radiographic examinations should be carefully interpreted for patients who have undergone a cervical fusion, because an increase in
radiographic density may not necessarily represent a consolidation of bone fusion, especially in those cases with the concomitant formations of severe osteophytes at the fusion level. Moreover, these results indicate that a rigid implant fixation such as an anterior-plating and -screwing system may also increase the possibility for developing stiffening neck after cervical fusion, although the reasons underlying these changes are not currently clear. It, however, needs to be stressed that the numbers of animals per group in the present study are low, and that there may be some limitations for applying the current findings from an animal model directly to the clinical application in human beings.
Our results indirectly support anterior cervical fixation as an effective treatment modality for repairing symptomatic pseudarthrosis in those cases with a failed posterior cervical fusion.33,35. Our results also support the use of other fixation methods (e.g., in situ
structural bone grafting, facet fusion or a rigid postoperative orthosis) as adjuvant for posterior wiring techniques in the management of complete discoligamentous cervical spine injuries, thus enhancing the stability against rotational hypermotility during healing and decreasing the potential risk for developing osteophytes and wire loosening. Additionally, we suggest that intervertebral bone grafting may need to be centrally strengthened in the application of the anterior-plate fixation so as to improve full maturation of bone fusion. During a course of the bone-adaptive remodeling process, these anterior plate-stabilized patients should also receive early rehabilitation programs to strengthen their cervical musculatures, thereby allowing an appropriate amount of physiological loads onto the bone graft and decreasing the potential risk for developing adverse stiffness at the adjacent levels.
Conclusion
Our results indicated that the anterior-plate fixation was more stable over time than did the posterior wiring fixation in the management of complete discoligamentous spinal injuries, because the former had superior biomechanical advantages for the maturation of fusion masses. Exclusive posterior wiring techniques were weak for opposing the rotation loads, and this biomechanical defect might be closely related to the formation of soft tissue responses and osteophytes during a course of the bone-adaptive remodeling process. Our data also indicated that cervical stabilization, regardless of the use of the anterior-plate or posterior wiring techniques, would decrease the motion ranges in extension and lateral bending at the contiguous functional unit. These data point out that the mode and stability of fixation systems carries a significant impact on the biomechanical redistribution and
bone-adaptive remodeling process during healing. These complex interactions may be closely related to the bone graft maturation and the formations of osteophytes at the fusion functional unit as well as the occurrence of stiffening problems at the adjacent functional unit following the treatment of unstable cervical spine diseases.
ACKNOWLEDGEMENTS:
This study was supported by the grants from the National Science Council of Taiwan (NSC 91-2320-B-006-086, NSC 92-2218-E-006-010 and NSC 92-2320-B-006-030).
References
1. Fielding JW: The status of arthrodesis of the cervical spine. J Bone Joint Surg Am. 1988; 70:1571-1574.
2. Moskovich R: Cervical instability: Rheumatoid, Dwarfism, Degenerative, Others, in Bridwell KH, Dewald RL (eds): The Textbook of Spinal Surgery, Vol 2. Philadelphia: J.B. Lippincott, 1991, pp 813-854.
3. Stillerman CB, Roy RS, Weiss MH: Cervical Spine Injuries: Diagnosis and management, in Wilkins RH, Rengachary SS (eds): Neurosurgery, Vol 2. New York: McGraw-Hill, 1996, pp 2875-2904.
4. Grob D, Peyer JV, Dvorak J The use of plate fixation in anterior surgery of the degenerative cervical spine: a comparative prospective clinical study. Eur Spine J 2001; 10:408-413. 5. Lee EJ, Hung YC, Lee MY, et al. Kinematics of cervical spine discectomy with and without
bone grafting: quantitative evaluation of late fusion in a sheep model. Neurosurgery 1999; 44:139-147.
6. Wang JC, McDonough PW, Endow K, et al. The effect of cervical plating on single-level anterior cervical discectomy and fusion. J Spinal Disord. 1999; 12:467-471.
7. Coe JD, Warden KE, Sutterlin CE III, McAfee PC. Biomechanical evaluation of cervical spinal stabilization methods in a human cadaveric model. Spine 1989; 14:1122-1131. 8. Goffin J, Plets C, Van den Bergh R Anterior cervical fusion and osteosynthetic stabilization
according to Caspar: a prospective study of 41 patients with fractures and/or dislocations of the cervical spine. Neurosurgery 1989; 25:865-871.
9. Herrmann HD Metal plate fixation after anterior fusion of unstable fracture dislocations of the cervical spine. Acta Neurochir 1975; 32:101-111.
10.Tippets RH, Apfelbaum RI Anterior cervical fusion with the Caspar instrumentation system. Neurosurgery 1988; 22:1008-1013.
overview. Orthopedics 1992; 15:287-295.
12.Capen DA, Garland DE, Waters RL Surgical stabilization of the cervical spine. A comparative analysis of anterior and posterior spine fusions. Clin Orthop 1985; 196:229-237.
13.Lovely TJ, Carl A Posterior cervical spine fusion with tension-band wiring. J Neurosurg 1995; 83:631-635.
14.Schultz KD Jr, McLaughlin MR, Haid RW Jr, et al. Single-stage anterior-posterior decompression and stabilization for complex cervical spine disorders. J Neurosurg. 2000; 93:214-221.
15.Goel VK, Pope MH Biomechanics of fusion and stabilization. Spine 1995; 20 (Suppl):85S-99S.
16.Sanan A, Rengachary SS The history of spinal biomechanics. Neurosurgery 1996; 39:657-669.
17.DiAngelo DJ, Foley KT, Vossel KA, et al. Anterior cervical plating reverses load transfer through multilevel strut-grafts. Spine 2000; 25:783-795.
18.Rapoff AJ, O'Brien TJ, Ghanayem AJ, et al. Anterior cervical graft and plate load sharing.
J Spinal Disord. 1999; 12:45-49.
19.Fielding JW: Disc excision and anterior fusion using the Smith-Robinson or Cloward technique, in Sherk HH (ed): The Cervical Spine: An Atlas of Surgical Procedures. Philadelphia: J.B. Lippincott, 1994, pp 189-192.
20.Robinson RA, Smith GW Anterolateral cervical disc removal and interbody fusion for cervical disc syndrome. Johns Hopkins Hosp Bull 1955; 96:223-224.
21.Caspar W, Barbier DD, Klara PM Anterior cervical fusion and Caspar plate stabilization for cervical trauma. Neurosurgery 1989; 25:491-502.
22.Roozmon P, Gracovetsky SA, Gouw GJ, et al. Examining motion in the cervical spine II: Characterization of coupled joint motion using an opto-electronic device to track skin
markers. J Biomed Eng 1993; 15:13-22.
23.Schendel MJ, Dekutoski MB, Ogilvie JW, et al. Kinematics of the canine lumbar
intervertebral joints: An in vivo study before and after adjacent instrumentation. Spine 1995; 20:2555-2564.
24.Schulte K, Clark CR, Goel VK Kinematics of the cervical spine following discectomy and stabilization. Spine 1989; 14:1116-1121.
25.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; 79:96-103.
26.Stutz FA, Hefti AF, Gibbs CH Light source-induced error in computer-assisted image analysis with a video-based system. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 1996; 81:491-497.
27.Neuwirth MG, Margulies JY: Spinal stabilization: Is fusion the right way, in Holtzman RNN, McCormick PC, Farcy JPC (eds): Spinal instability. New York: Spinger-Verlag, 1993, pp 79-86.
28.Panjabi MM Biomechanical evaluation of spinal fixation devices: I. A conceptual framework. Spine 1988; 13:1129-34.
29.Zdeblick TA, Cooke ME, Wilson D, et al. Anterior cervical discectomy, fusion, and plating: A comparative animal study. Spine 1993; 18:1974-1983.
30.Ulrich C, Woersdoerfer O, Kalff R, et al. Biomechanics of fixation systems to the cervical spine. Spine 1991; 16(Suppl):S4-S9.
31.Feldborg Nielsen C, Annertz M, Persson L, et al. Fusion or stabilization alone for acute distractive flexion injuries in the mid to lower cervical spine? Eur Spine J 1997; 6:197-202. 32.Kaufman HH, Jones E The principles of bony spinal fusion. Neurosurgery 1989;
24:264-270.
anterior corpectomy and fusion with and without plate instrumentation: etiology and corrective management. Surg Neurol. 2001; 56:73-81.
34.Lowery GL, McDonough RF: The significance of hardware failure in anterior cervical plate fixation. Patients with 2- to 7-year follow-up. Spine 1998; 23:181-187.
35.Brodsky AE, Khalil MA, Sassard WR, Newman BP Repair of symptomatic
pseudoarthrosis of anterior cervical fusion. Posterior versus anterior repair. Spine 1992; 17:1137-1143.
Legends of Figures
Figure 1. Saggital sections of the specimens and the graphs of imaging analysis in the study: There
is no spontaneous fusion in the sham-operated group (A). The anterior plate-stabilized spine (B) has continuing bony responses along with minimal posterior osteophytes, whereas high-density fusion masses and severe posterior osteophytic growths are seen in the posterior-wired spine (C). The graphs of imaging analysis further show (D) continuing trabecular fusion masses bridging the discectomied interface and evidences of central resorption of the bone graft in the anterior
plate-stabilized spines. Conversely, (E) the posterior-wired spines have dense tissue reactions within the discectomied interface along with massive formations of posterior osteophytes (arrows). The discectomied/bone fusion interface is outlined by the dotted lines.
Figure 2. The histopathology of the specimens in the study: There is no spontaneous fusion in the
sham-operated group (A and D). The anterior plate-stabilized spines (B and E) show osteoid tissue formations crossing the intervertebral interface (arrows), indicating the formation of solid bony fusion. On the other hand, the posterior-wired spines had extensive soft tissue responses and some posterior osteophytic outgrowths, in consistent with the radiographic findings. (A-C), scale bar=2 mm; (D-F), scale bar=500 µm.
Figure 3. The changes in relative motion ranges of the C2-C3 functional unit responding to the
relevantly testing loads for the sham-operated specimens (Group A), the anterior plate-stabilized spines (group B) and the posterior-wired spines (Group C).
The results corresponded to a
0.72-N-m load step.
Figure 4. The changes in relative motion ranges of the C3-C4 functional unit responding to the
relevantly testing loads for the sham-operated specimens (Group A), the anterior plate-stabilized spines (group B) and the posterior-wired spines (Group C). The results corresponded to a 0.72-N-m load step.
