- Email: [email protected]
Recent advances in internal fixation of cervical spine
Recent Advances in Internal Fixation of Cervical Spine
M. Aebi ..__ -----
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Introduction Instrumentation of the cervical spine has not been as frequently employed as instrumentation of the lumbar spine. This may be related to the frequency with which the lumbar spine has been surgically approached for degenerative disease and trauma. These disease entities are less frequently seen in the cervical spine. Secondly stabilisation has been predominantly limited to wiring techniques, and few new techniques have been developed for the cervical spine in some time. Most fusions have been performed by anterior interbody fusion or posterior laminar fusion with or without wiring. Trauma surgery of the cervical spine especially has changed significantly the options for cervical spine stabilisation. New techniques have been developed for either anterior or posterior plate and screw fixation. This instrumentation enables the surgeons to accomplish and preserve correction and reduction of a diseased or traumatised cervical spine region while stabilising one or more unstable or dysfunctional spinal segments. However, not only instrumentation techniques have changed the principles and contributed to recent advances in cervical spine surgery. The development of more advanced diagnostic tools has contributed significantly to treatment modalities. CT and MRI, as well as functional neurophysiological and pain screening methods, offer new insights into spinal anatomy and disease processes. With the introduction of new instrumentations for the cervical spine, a more intensive study of the biomechanics of
M. Aebi, MD, Department of Orthopaedic Bern. Inselspital, 3010 Bern. Switzerland.
Surgery,
University
of
__
the spine with and without instrumentation was initiated. The discussion of what instability exactly means and how much surgically obtained stability is necessary for treatment is still one of the most controversial topics. However, we have to accept that injury induced instability cannot be compared necessarily with disease induced instability of dysmobility as in degenerativecervical spine disease. Furthermore, the results obtained from biomechanical analyses of different instrumentation systems for the cervical spine do not correlate necessarily with the clinical experience established over the last few years. Decompressive techniques of the cervical spine have taken advantage of microsurgical techniques. However, for orthopaedic surgeons, the indications for direct decompression have changed recently, especially in spinal trauma. It has become apparent, that direct posterior decompression, through a Iaminotomy or laminectomy, is almost never indicated, but anatomic reduction and stabilisation in the reduced positions offers the best decompression indirectly. When there is residual compression of the neural elements following reduction, it is usually produced from anterior vertebral body fragments, and anterior decompression is needed. Consequently, anterior decompression creates a defect in the mechanically important anterior spinal column. Following anterior decompression, the anterior column needs to be replaced by bone and secured by a stabilising method. Direct decompression of neural elements maybe indicated in degenerative disease and tumors. In these disease entities microscopic surgery is of great help. Working with optimal illumination and atrauit offers optimal hemostasis. matic techniques, Whether stabilisation is needed or not depends on the
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amount of stabilising elements removed and, therefore, on iatrogenically created instability. The need for stabilisation also relates to the demands imposed by the postoperative treatment. This depends on whether the patient and the surgeon accept a more or less rigid external post-operative fixation and whether the nursing and aftercare can be simplified by an optimal surgical stabilisation. The risk and benefits of more invasive surgery need to be balanced carefully against well established and simpler techniques (e.g., with wires). One must recognise, however, that simpler wiring techniques may not offer as much correction and stabilisation as newer techniques. A systematic training in the newer techniques, a profound knowledge of the anatomical relationships, and atraumatic surgical techniques are prerequisites for good results. This implies, that this kind of spinal surgery more and more becomes reserved for surgeons who are specialised in spinal surgery. Because posterior wiring techniques of the Cl/C2 segments and the lower cervical spine as well as the simple anterior bone grafting techniques are well standardised, only alternative techniques will be described (Fig. 1).
Instrumentation of the Upper Cervical Spine Atlanta-axial stabilisation. This may be indicated in certain traumatic lesions of the first two cervical vertebrae, in degenerative, tumoral or inflammatory diseases of the Cl/C2 joint, and in some forms of congenital malformations. In very special cases the fixation needs to be extended to the occiput. Most of the stabilisation techniques are performed through a median posterior approach. However, both the lateral and combined anterior and posterior techniques require two approaches. Anterior transoral techniques
carry well-known risks, particularly infection and have very rare indications. Anteriorfixation of an odontoidfracture. This stabilises only the fracture itself and avoids a fusion of the Cl/ C2 segment. a) Transarticular screw fixation of Cl/C2 segment according to Magerl This technique consists basically of two 35AO/ASIF cortical screws which are introduced in the lateral mass of C2 from posteriorly with an obliquity of about 60” to the vertical axis of the spine, traversing the Cl/ C2 joint and ending in the anterior arch of Cl. The fixation is then augmented by a posterior bone graft between Cl/C2 (Fig. 2). The indications include acute and chronic atlanto-axial instability of the Cl/C2 joint in degenerative, inflammatory or tumoral disease. The main advantage of this technique is its biomechanical superiority to wiring techniques since the fixation is positioned in the center of the C l/C2 segment, where axial compression forces act. l*2 All wiring techniques are applied eccentrically in the motion segment at the posterior tension banding site. With the screw technique, the integrity of the posterior arch of Cl is not needed and it is consistently possible to maintain the reduction without significant external immobilisation. The technique, however, is technically demanding, and the proximity of the vertebral artery lateral and the spinal cord medial to the screw position are reported to be risky. In a recent multi-center study, in which our center also participated, over 163 cases of Cl/C2 transarticular screw fixation were performed and data demonstrated that neither a lesion of the vertebral artery nor of the spinal cord occurred, and the fusion rate was higher than most of the described wiring techniques.3 When the screw technique is combined with a wiring technique according to Brooks or others, the postoperative care is free of any external immobilisation. The bone graft between the arch of Cl and spinous process of C2, may be held by a nonabsorbable suture. In these cases an external immobilisation with a collar is advised for 6-12 weeks, however, the collar could be removed while resting or for daily care. b) Plating of CO-C2 or further
Fig. l--Implants used for internal fixation of the cervical spine. (A) Cannulated self-cutting screw for the anterioyfixation of an odontoidfracture or the posterior transarticu$% Cl/$2-fixation or the posterior screw fixation of the traumatrc sp’bhdylolysis of C2 according to Judet. (B) One-third-tubular 3.5-AO/ASIF plate for the posterior plate fixation. Alternative: 3.5 AO/ASIF reconstruction plate. (C) AO/ASIF H-plate for anterior plate fixation. Alternative: Titanium-locking-screw-plate. (D) Posterior hook plates according to Magerl. (E) 3.5 mm standard cortical screws. (F) Titanium covered 3.5 mm screws.
Whenever it is necessary to include the occiput within the fixation, a plate is used. Buttressing is the principle of this technique. Indications are rarely seen in spinal trauma, but are occasionally seen in tumor surgery and in rheumatoid arthritis. The rare traumatic lesions which require occipito-cervical fixation include occipital condylar fractures and atlanto-occipital dislocation. The surgical technique utilises two l/3 tubular AO-plates4 or 3.5 A0 reconstruction plates.4,5 One plate on each side spans from the occiput to C2 or C3, depending on the length of fixation needed. The plates are bent to accommodate the posterior angle of the
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Fig. Z-Transarticular screw fixation of C 1/C2. (A) Landmark for the screw insertion. The inner border of the C2 pedicle can be identified by a dissector. (B) Screw holes drilled with a 2.0 mm drill. The interlaminar space between C t/C2 can be increased by pulling the two arches apart through wire loops. (C) The transarticular screw fixation can be combined with a Brooks-type wiring and bone grafting which enhances stability significantly. (D) Clinical example.
occipito-cervical junction. With this angle the position of the head in relation to the cervical spine can be determined. A 1.2 mm K-wire is then inserted into the lateral mass of C2 and occasionally into the lateral mass of C3. The direction and placement technique of these K-wires is either the same as in direct screwing of the C2 pedicle according to Jude@ or as in Cl/C2 transarticular screwing according to Magerl.‘***’ The position of the K-wire is checked by an image intensifier in lateral projection. The pre-bent plate is inserted over the K-wires on each side and placed on the occiput, determining the insertion point for the occipital screws. The fixation oftheocciput is achieved by two 3.5 cortical screws on each side, usually 810 mm long. A 2.0 mm drill is carefully used for the outer and inner tables of the occipital bone. The best position for screw insertion is the midline of the occiput. The screw holes need to be tapped. To avoid perforation of the dura mater a drill guide is used with a stopper at the intended depth. The depth can be adjusted gradually until perforation of the inner table
is achieved. In most instances the screws in theocciput have a very good hold. The K-wires at the C2 (and C3) lateral masses are then either removed or canulated self-tapping screws are used over the K-wires. In case of removal, the screw-holes have to be drilled in the same direction as the removed K-wires. Additional fixation to the arch of Cl is obtained by a sublaminar wire which is tightened through a free screw hole of the plate or through an additional screw within the arch of Cl when the size of the arch is suitable for a screw (Fig. 3). A midline fusion is then performed using a firm cortical cancellous graft between the occiput and the spinous process of C2 as well as additional cancellous bone chips around the plates. Alternatively a 3.5 mm Y-reconstruction plate can be used instead of two 3.5 mm straight plates. The Yplate is placed with the single branch against the occiput and the two branches are fixed against Cl/C2 with transarticular screws. The graft is put below the plate in a sandwich position with the underlying bone of the occiput and the cervical spine.’
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A
B
C
Fig. 4-(A. B) Typical indication for the direct screw fixation of odontoid fractures: Type II of the Anderson d’Alonzo classification (neck fracture). The screws can be used as compression screws. (C) Contraindication for the direct screw fixation: oblique fracture line imitating approximately the screw direction within the odontoid.
Fig. 3-Occiput-C2 (-C3 and more) fixation. (A) K-wires within the articular mass of C3 and transarticular C l/C2 on both sides. 3.5 mm contoured AO/ASIF reconstruction plate inserted over the K-wires. (B) The plates in position indicate the location for the drill holes at the occiput. (C) K-wires replaced by screws and plate fixed at the occiput with 3.5 mm cortical screws and at the C 1-arch with a wire loop. (D) Cortico-cancellous bone grafting. (E) Clinical example.
The post-operative treatment consists of a firm collar for 612 weeks post-operatively, or until X-rays have proven that the fusion has taken. An isometric training program of the neck muscle for self stabilising the cervical spine is mandatory.
c) Anterior screwfixation of odontoidfractures The principle of this operation consists of a compression osteosynthesis by screw fixation and avoidance of a segmental fusion.* The indication for this technique is limited to the type II and the swallow type III odontoid fracture according to Anderson and d’Alonzo8y9 (Fig. 4A). This technique preserves the Cl/C2 motion segment, simplifies post-operative care and immobilisation and is performed through an atraumatic anteromedian approach. The contraindications, however, are important to know. Oblique flexion fractures of the neck of the odontoid process should not be treated with this technique as the superior fragment of the C2-vertebral body is too small for adequate screw fixation and the fracture line is relatively parallel to the screw direction preventing the screw from imparting compression across the fracture (Fig. 4B). Tech-
nically it is difficult or impossible to perform this procedure in short-necked patients and obese patients, in patients with limited motion of the cervical spine and in patients with pronounced kyphosis of the upper thoracic spine. Furthermore, the technique is dependent on high resolution two plane imaging and corresponding technical equipment. Also the technique is contraindicated in cervical spinal stenosis because of the danger of cord injury associated with hyperextension of the neck. However, it is absolutely necessary to place the head in an extended position to reduce the fracture and to facilitate the insertion of the screws. The approach to the anterior inferior border of the body of the axis can be facilitated, when the placement of the antero-median incision is determined by placing a long Kirschner-wire along the side of the neck in the intended direction of the screw and viewing on the image intensifier. There are two different techniques available for the screw insertion. The first technique utilises two standard lag screws. Screw holes are drilled with a 2.5 mm drill perforating the posterior half of the tip of the odontoid process. The body fragment is then overdrilled with a 3.5 mm drill and after tapping both holes the appropriate length 3.5 mm cortical screws are inserted (Fig. 5A).8 The second technique utilises two canulated screws. Initially two 20 cm long 1.2 mm K-wires are inserted in the appropriate position on the image intensifier. The appropriate length of self-tapping canulated 3.5 mm cancellous bone screws are then inserted over the well positioned K-wires. The progress of the screw must be observed with the image intensifier to avoid migration of the K-wire proximally9 (Fig. 5B). The post-operative care consists of a soft collar in co-operative patients and of a firm collar in less reliable patients for 6-12 weeks. The collar can be removed for daily care and when resting. There is another possibility in upper cervical spine fractures to use direct screw fixation and compression osteosynthesis. Traumatic spondylolysis of C2 with persistent instability but no relevant dislocation and disc disruption of C2/C3 may rarely be an indication for a direct screw fixation according to the technique of Judet4 (Fig. 6).
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insertion within the articular mass. Roy-Camille and others propose placing screws perpendicular into the center of the lateral mass (Fig. 7A).‘O In contrast, Magerl emphasises placing the screws parallel to the joint line in an oblique direction from just medial to the vertical midline of the lateral mass and just below the horizontal intersection line. Thereby the distance of the screws within the bone is increased and avoiding the vertebral artery, which is directly in front of the articular mass (Fig. 7B).’ l, l2 This second screw direction is not possible in combination with simple round hole plates, as the screw cannot be inclined sufficiently in the sagittal as well as in the frontal plane within the plate hole. Magerl’s proposed screw direction is best applied when using the hook plate for fixation. This special plate (developed by the same author) l l- ’ z is not placed in the sagittal plane along the facet joint, but in the frontal plane, as it is fixed with a hook at the lamina and with one or two screws in the articular masses (Fig. 8). This plate acts exclusively as a tension banding system against a bone graft which is placed between the adjacent spinous processes. The straight plates, either one-third-tubular 3.5 mm AO/ASIF plates4 or 3.5 mm reconstruction AO/ASIF platess, are placed over the facet joints and can be used as buttressing or neutralising systems as well as tension banding systems. In the latter case the distal holes should be placed eccentrically within the plate hole therefore producing dynamic compression (Fig. 9). With this plate a solid midline corticocancellous bone graft can be placed under compression through the tension banding effect of the plate. However, it may be sufficient to place bone chips along the plate over the freshened up articular masses and laminae. 6) Anterior plating
Fig. S-Anterior screw fixation of the odontoid fracture. (A) Drilling of the holes for the use of lag screws (right side). (B) Use of cannulated self cutting screws (right side) after having inserted 1.2 mm K-wires which perforate the posterior apical area of the odontoid process (left side). (C) Clinical example.
Plate Fixation Techniques of the Lower Cervical Spine There are plating techniques for anterior and posterior fixation as well. All of these techniques are usually combined with a fusion extended over the fixation area. a) Posterior plating
Posterior plate fixation is accomplished using screws which are anchored within the articular mass of the cervical vertebrae. There are different types of plates available, and there are at least two methods of screw
In traumatic as well as in reconstructive surgery of the cervical spine a fixation system which can be used in combination with anterior surgery is of great importance. Several authors have presented their systems in the last 15 years. 13-17 Such internal fixation systems allow the creation of such stable fusion constructs that the patient’s post-operative care becomes very simple, with no need for significant external immobilisation. To place and secure an anterior graft under axial compression encourages early integration with a very high healing rate. Many of the graft and postoperative complications can be avoided by using an adequate internal fixation. Most anterior fixation systems of the cervical spine consist of a plate with screws positioned within the vertebral body. One of the controversial points is the length of the screws. There are authors who propose screw penetration of the posterior cortex of the vertebral body, l 3, l 6 to provide a better screw fixation. However, Titanium 3.5 mm cortical screws provide sufficient holding strength without including the posterior cortex.18 The interface between the screw
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Fig. 6-Screw fixation of traumatic spondylolysis of the axis according to Judet. (A) Screw with about 25’ inclination cranially. (B) Screws in the horizontal plane converging by about 25” each. (C) Clinical example.
Fig. 7-(A) Landmark for the screw insertion into the lateral mass according to Roy-Camille: exactly in the center of the articular mass and perpendicular to the posterior surface of the facet. (B) Landmark for the screw insertion into the lateral mass according to Magerl. Starting about 2 mm medial to the vertical midline of the lateral mass and below the horizontal intersection line. The screw is inserted about 30” laterally and parallel to the facet joint.
Fig. g-(A) Hook-plate according to Magerl acts as a tension banding system and creates compression to an interspinous Hgraft. (B) Lateral view of an unisegmental fixation with bone graft. (C) Posterior view of the same construct. (D) Clinical example.
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Fig. S-Posterior plate fixation with a one-tubular plate. (A) Insertion of the K-wires at the end vertebrae. (B) Insertion of the plate over the K-wires, after having contoured and hammered fiat the plate. (C) Plate in position. (D) K-wires replaced by 3.5 mm cortical screws which are inserted at the landmarks described above. (E) Clinical example.
surface and the bone provides a better interlocking of these two elements (Fig. 10). The screw length can be determined by measuring the sagittal diameter of the vertebral body on the X-ray or through the evacuated disc space. This measured value can be preset on a special drill guide with a stopper at the appropriate depth. This allows anterior screw insertion without imparting danger to the spinal cord. Also the Titanium hollow screw system of Morscher” can do it without screw penetration of the posterior wall. However, the construct is a buttressing system, due to the fixed angle between the screws and the plates (Fig. 11). The screw head locks to the plate by small threads around the screw head. There may be some difficulties in directing the screws correctly within the vertebral body due to the fixed screw/plate relationship. However, the highly sophisticated instrumentation facilitates standardised screw insertion.
c) Anterior or posterior$xation ?
There is an ongoing controversy whether anterior or posterior fixation is better in terms of stability and fusion rate. In vitro testing with cadaveric spines by Ulrich et al and others*9y 20,21 have demonstrated more rigid fixation of a cervical spine segment when posterior fixation was performed. While this may be true for simulated trauma, with total anterior and posterior disruption or isolated posterior disruption this may not be true when the anterior intervertebral defect has been replaced by bone or by a mechanical
support against which the vertebral bodies can put under compression. The anterior plate is exposed to maximal flexion load and shear, whereas the posterior tension banding plate replaces the posterior ligamentous structures and provides better stability. An earlier work 22 states that one increases an already existing instability (mostly traumatic) by excising the annulus of the disc and the anterior longitudinal ligament. This may be true, as long as an unfixed bone graft is inserted anteriorly following decompression. However, if the graft is placed in compression in combination with a plate, the anterior longitudinal ligament and the annulus may be imitated (Fig. 12). There are some substantial reasons to favour anterior surgery in the cervical spine : 1) The anterior approach is relatively atraumatic, which contrasts to the posterior approach, where muscle stripping may partially denervate surrounding muscles. 2) Many of the spinal pathologies have their etiology from the vertebral body column and threaten the spinal cord from the front. Therefore, a direct decompression of the spinal cord is better done by an anterior approach. 3) An anteriorly inserted graft is placed under compression which enhances the interface healing, whereas a posterior graft is on the tension banding side. 4) Specifically in traumatology, the patient can be operated in the supine position and does not need to be turned over to a prone position. 5) Based on extensive clinical experience the stability and stiffness in anterior plate fixation seems to be sufficient even though biomechanical in vitro tests showed it inferior to posterior instrumentation. l*
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Fig. 1 l-Modification
of the graft technique together with an anterior plating. (A) Trapezoid shaped graft. When the plate is contoured and the screws drilled eccentrically an important anterior tension banding effect is created, however, with compression of the posterior joints. (B) In a rectangular graft the posterior joints open themselves through the tension banding effect.
C Fig. 12-Titanium locking screw plate system. (A) The angle between screw head and plate is stable due to the locked head through a small spreading screw. (B) Special instrumentation facilitates the right placement of the screws and plate. (C) The screws do not penetrate the posterior wall.
Fig. lo-Anterior plating with the AO/ASIF H-plate according to Orozco. (A) There is a special drill guide with a stopper at the intended length. This length can be measured either preoperatively on the X-ray or through an evacuated disc space. (6) Hole drilled with the special guide. (C) Screws inserted either the posterior wall included with the standard cortical screws or not included with the Titanium covered screws. (D) Clinical example of an unisegmental lesion. (E) Clinical example of a segmental fixation due to a complete vertebral body fracture.
techniques for the spine, and who have the opportunity to constantly perform these techniques. These more sophisticated technical demands in the treatment of spinal disorders together with complex diagnostic procedures necessitates a new generation of surgeons who specialise entirely in spinal surgery. Acknowledgement The author gratefully acknowledges the help of Mark Gillespy, MD, Department of Orthopaedics, College of Medicine, University of Florida, Gainesville, USA, in the preparation of the English manuscript.
References Conclusions The last decade has seen an array of new spinal instrumentation in general and has seen standardised fixation systems for the cervical spine in particular. The armentarium has been extended from simple wire cerclages to effective plate or isolated screw fixation with better immediate stability and higher fusion rates. This allows earlier mobilisation without heavy external fixation. However, this sort of surgery should only be practised by surgeons who are familiar with the principles of internal fixation and with special
1. Magerl F, Seemann P. Stable posterior fusion of the atlas and axis by transarticular screw fixation. In: Kehr P, Weidner A (Eds) Cervical Spine I. Springer Verlag, Wien New York 1986; pp. 322-327 2. Grob D, Magerl F. Operative Stabilisierung bei Frakturen von Cl und C2. Orthopgde 1987; 16: 46-54 3. Grob D, Jeanneret B, Aebi M, Markwalder T. Atlanto-axial fusion with transarticular screw-fixation. J Bone Joint Surg (Br) 1991; accepted for publication 4. Aebi M. Surgical Treatment of Cervical Spine Fractures by A0 Techniques. In : Bridwell K Hand DeWald R L (Eds) Textbook of Spinal Surgery. J B Lippincott Philadelphia 1991 5. Anderson P A, Henley M B, Grady M S, Montesano P X, Winn H R. Posterior cervical arthrodesis with A0 reconstruction plates and bone graft. Spine 1991; 16 (3s): 7279
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Grob D, Dvorak J, Panjabi M, Froehhch M, Hayek J. Posterior occipito-cervical fusion. Spine 1991; 16 (3s): 17-24 Biihler J. Anterior screw fixation for acute fractures and nonunions of the dens. J Bone Joint Surg 1982; 64-A: 18-27 Aebi M, Etter Chr, Coscia M. Fractures of the Odontoid Process: Treatment with Anterior Screw Fixation. Spine 1989; 14: 106551070 Roy-Camille R. Arguments en faveur de la voie posterieure dans la chirurgie du rachis cervical. Revue de Chirurgie Orthopedique 1984; 70: 55&557 Magerl F, Grob D, Seemann P. Stable dorsal fusion of the cervical spine (C2-Thl) using hook plates. In: Kehr P, Weidner A (Eds) Cervical Spine 1. Springer Verlag pp. l-1 8, 1987 Jeanneret B, Magerl F, Ward E H, Ward J-Ch. Posterior stabilization of the cervical spine (C2C7) with hook plates. Spine 1991; 16 (3s): 5663 Orozco Delclos R, Llovet Topes J. Osteosintesis en las fracturas de raquis cervical. Nota de technica. Revista Orthop Traumatoll970; 14: 285-288 Senegas J, Gauzere J M. Plaidoyer pour la chirurgie anterieure dans le traitement des traumatismes graves des 5 demieres vertibres cervicales. Revue de Chirurgie Orthoptdique 1976; 62 (Suppl II): 1233128
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15. Aebi M, Mohler J, Zlch G, Morscher E. Indication, surgical technique and results of 100 surgically treated fractures and fracture dislocations of the cervical spine. Clin Orthop 1986; 203 : 244257 16. Caspar W. Advances in cervical spine surgery. First experiences with the trapezia1 osteosynthetic plate and a new surgical instrumentation for anterior interbody stabilization. Orthopaedic News, USA 1982; 4 (6) 17. Morscher E, Sutter F, Jenny H, Olerud S. Die vordere Verplattung der Halswirbelsaule mit dem HohlschraubenPlattensystem aus Titanium. Chirurg 1986; 57: 702-707 18. Aebi M, Zuber K, Marchesi D. The treatment of cervical spine injuries by anterior plating. Spine 1991; 16 (3s): 3845 19. Ulrich Chr, Worsdorfer 0, Kalff R, Claes L, Wilke H J. Biomechanics of fixation systems to the cervical spine. Spine 1991; 16(3S):49 20. Sutterlin C E, McAfee P C, Warden K C, Rey R M, Farey I D. A biomechanical evaluation of cervical spinal stabilization methods in a bovine model. Spine 1988; 13 : 795-802 21. Coe J D, Warden K E, Sutterlin C E, McAfee P C. Biomechanical evaluation of cervical spinal stabilization methods in a human cadaveric model. Spine 1989; 14. 11221131 22. Stauffer E S, Kelly E G. Fracture-dislocations of the cervical spine. J Bone Joint Surg 1977; 59-A: 4548
M. Aebi ..__ -----
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_-_.~__~____ _. _~
Introduction Instrumentation of the cervical spine has not been as frequently employed as instrumentation of the lumbar spine. This may be related to the frequency with which the lumbar spine has been surgically approached for degenerative disease and trauma. These disease entities are less frequently seen in the cervical spine. Secondly stabilisation has been predominantly limited to wiring techniques, and few new techniques have been developed for the cervical spine in some time. Most fusions have been performed by anterior interbody fusion or posterior laminar fusion with or without wiring. Trauma surgery of the cervical spine especially has changed significantly the options for cervical spine stabilisation. New techniques have been developed for either anterior or posterior plate and screw fixation. This instrumentation enables the surgeons to accomplish and preserve correction and reduction of a diseased or traumatised cervical spine region while stabilising one or more unstable or dysfunctional spinal segments. However, not only instrumentation techniques have changed the principles and contributed to recent advances in cervical spine surgery. The development of more advanced diagnostic tools has contributed significantly to treatment modalities. CT and MRI, as well as functional neurophysiological and pain screening methods, offer new insights into spinal anatomy and disease processes. With the introduction of new instrumentations for the cervical spine, a more intensive study of the biomechanics of
M. Aebi, MD, Department of Orthopaedic Bern. Inselspital, 3010 Bern. Switzerland.
Surgery,
University
of
__
the spine with and without instrumentation was initiated. The discussion of what instability exactly means and how much surgically obtained stability is necessary for treatment is still one of the most controversial topics. However, we have to accept that injury induced instability cannot be compared necessarily with disease induced instability of dysmobility as in degenerativecervical spine disease. Furthermore, the results obtained from biomechanical analyses of different instrumentation systems for the cervical spine do not correlate necessarily with the clinical experience established over the last few years. Decompressive techniques of the cervical spine have taken advantage of microsurgical techniques. However, for orthopaedic surgeons, the indications for direct decompression have changed recently, especially in spinal trauma. It has become apparent, that direct posterior decompression, through a Iaminotomy or laminectomy, is almost never indicated, but anatomic reduction and stabilisation in the reduced positions offers the best decompression indirectly. When there is residual compression of the neural elements following reduction, it is usually produced from anterior vertebral body fragments, and anterior decompression is needed. Consequently, anterior decompression creates a defect in the mechanically important anterior spinal column. Following anterior decompression, the anterior column needs to be replaced by bone and secured by a stabilising method. Direct decompression of neural elements maybe indicated in degenerative disease and tumors. In these disease entities microscopic surgery is of great help. Working with optimal illumination and atrauit offers optimal hemostasis. matic techniques, Whether stabilisation is needed or not depends on the
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amount of stabilising elements removed and, therefore, on iatrogenically created instability. The need for stabilisation also relates to the demands imposed by the postoperative treatment. This depends on whether the patient and the surgeon accept a more or less rigid external post-operative fixation and whether the nursing and aftercare can be simplified by an optimal surgical stabilisation. The risk and benefits of more invasive surgery need to be balanced carefully against well established and simpler techniques (e.g., with wires). One must recognise, however, that simpler wiring techniques may not offer as much correction and stabilisation as newer techniques. A systematic training in the newer techniques, a profound knowledge of the anatomical relationships, and atraumatic surgical techniques are prerequisites for good results. This implies, that this kind of spinal surgery more and more becomes reserved for surgeons who are specialised in spinal surgery. Because posterior wiring techniques of the Cl/C2 segments and the lower cervical spine as well as the simple anterior bone grafting techniques are well standardised, only alternative techniques will be described (Fig. 1).
Instrumentation of the Upper Cervical Spine Atlanta-axial stabilisation. This may be indicated in certain traumatic lesions of the first two cervical vertebrae, in degenerative, tumoral or inflammatory diseases of the Cl/C2 joint, and in some forms of congenital malformations. In very special cases the fixation needs to be extended to the occiput. Most of the stabilisation techniques are performed through a median posterior approach. However, both the lateral and combined anterior and posterior techniques require two approaches. Anterior transoral techniques
carry well-known risks, particularly infection and have very rare indications. Anteriorfixation of an odontoidfracture. This stabilises only the fracture itself and avoids a fusion of the Cl/ C2 segment. a) Transarticular screw fixation of Cl/C2 segment according to Magerl This technique consists basically of two 35AO/ASIF cortical screws which are introduced in the lateral mass of C2 from posteriorly with an obliquity of about 60” to the vertical axis of the spine, traversing the Cl/ C2 joint and ending in the anterior arch of Cl. The fixation is then augmented by a posterior bone graft between Cl/C2 (Fig. 2). The indications include acute and chronic atlanto-axial instability of the Cl/C2 joint in degenerative, inflammatory or tumoral disease. The main advantage of this technique is its biomechanical superiority to wiring techniques since the fixation is positioned in the center of the C l/C2 segment, where axial compression forces act. l*2 All wiring techniques are applied eccentrically in the motion segment at the posterior tension banding site. With the screw technique, the integrity of the posterior arch of Cl is not needed and it is consistently possible to maintain the reduction without significant external immobilisation. The technique, however, is technically demanding, and the proximity of the vertebral artery lateral and the spinal cord medial to the screw position are reported to be risky. In a recent multi-center study, in which our center also participated, over 163 cases of Cl/C2 transarticular screw fixation were performed and data demonstrated that neither a lesion of the vertebral artery nor of the spinal cord occurred, and the fusion rate was higher than most of the described wiring techniques.3 When the screw technique is combined with a wiring technique according to Brooks or others, the postoperative care is free of any external immobilisation. The bone graft between the arch of Cl and spinous process of C2, may be held by a nonabsorbable suture. In these cases an external immobilisation with a collar is advised for 6-12 weeks, however, the collar could be removed while resting or for daily care. b) Plating of CO-C2 or further
Fig. l--Implants used for internal fixation of the cervical spine. (A) Cannulated self-cutting screw for the anterioyfixation of an odontoidfracture or the posterior transarticu$% Cl/$2-fixation or the posterior screw fixation of the traumatrc sp’bhdylolysis of C2 according to Judet. (B) One-third-tubular 3.5-AO/ASIF plate for the posterior plate fixation. Alternative: 3.5 AO/ASIF reconstruction plate. (C) AO/ASIF H-plate for anterior plate fixation. Alternative: Titanium-locking-screw-plate. (D) Posterior hook plates according to Magerl. (E) 3.5 mm standard cortical screws. (F) Titanium covered 3.5 mm screws.
Whenever it is necessary to include the occiput within the fixation, a plate is used. Buttressing is the principle of this technique. Indications are rarely seen in spinal trauma, but are occasionally seen in tumor surgery and in rheumatoid arthritis. The rare traumatic lesions which require occipito-cervical fixation include occipital condylar fractures and atlanto-occipital dislocation. The surgical technique utilises two l/3 tubular AO-plates4 or 3.5 A0 reconstruction plates.4,5 One plate on each side spans from the occiput to C2 or C3, depending on the length of fixation needed. The plates are bent to accommodate the posterior angle of the
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Fig. Z-Transarticular screw fixation of C 1/C2. (A) Landmark for the screw insertion. The inner border of the C2 pedicle can be identified by a dissector. (B) Screw holes drilled with a 2.0 mm drill. The interlaminar space between C t/C2 can be increased by pulling the two arches apart through wire loops. (C) The transarticular screw fixation can be combined with a Brooks-type wiring and bone grafting which enhances stability significantly. (D) Clinical example.
occipito-cervical junction. With this angle the position of the head in relation to the cervical spine can be determined. A 1.2 mm K-wire is then inserted into the lateral mass of C2 and occasionally into the lateral mass of C3. The direction and placement technique of these K-wires is either the same as in direct screwing of the C2 pedicle according to Jude@ or as in Cl/C2 transarticular screwing according to Magerl.‘***’ The position of the K-wire is checked by an image intensifier in lateral projection. The pre-bent plate is inserted over the K-wires on each side and placed on the occiput, determining the insertion point for the occipital screws. The fixation oftheocciput is achieved by two 3.5 cortical screws on each side, usually 810 mm long. A 2.0 mm drill is carefully used for the outer and inner tables of the occipital bone. The best position for screw insertion is the midline of the occiput. The screw holes need to be tapped. To avoid perforation of the dura mater a drill guide is used with a stopper at the intended depth. The depth can be adjusted gradually until perforation of the inner table
is achieved. In most instances the screws in theocciput have a very good hold. The K-wires at the C2 (and C3) lateral masses are then either removed or canulated self-tapping screws are used over the K-wires. In case of removal, the screw-holes have to be drilled in the same direction as the removed K-wires. Additional fixation to the arch of Cl is obtained by a sublaminar wire which is tightened through a free screw hole of the plate or through an additional screw within the arch of Cl when the size of the arch is suitable for a screw (Fig. 3). A midline fusion is then performed using a firm cortical cancellous graft between the occiput and the spinous process of C2 as well as additional cancellous bone chips around the plates. Alternatively a 3.5 mm Y-reconstruction plate can be used instead of two 3.5 mm straight plates. The Yplate is placed with the single branch against the occiput and the two branches are fixed against Cl/C2 with transarticular screws. The graft is put below the plate in a sandwich position with the underlying bone of the occiput and the cervical spine.’
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Fig. 4-(A. B) Typical indication for the direct screw fixation of odontoid fractures: Type II of the Anderson d’Alonzo classification (neck fracture). The screws can be used as compression screws. (C) Contraindication for the direct screw fixation: oblique fracture line imitating approximately the screw direction within the odontoid.
Fig. 3-Occiput-C2 (-C3 and more) fixation. (A) K-wires within the articular mass of C3 and transarticular C l/C2 on both sides. 3.5 mm contoured AO/ASIF reconstruction plate inserted over the K-wires. (B) The plates in position indicate the location for the drill holes at the occiput. (C) K-wires replaced by screws and plate fixed at the occiput with 3.5 mm cortical screws and at the C 1-arch with a wire loop. (D) Cortico-cancellous bone grafting. (E) Clinical example.
The post-operative treatment consists of a firm collar for 612 weeks post-operatively, or until X-rays have proven that the fusion has taken. An isometric training program of the neck muscle for self stabilising the cervical spine is mandatory.
c) Anterior screwfixation of odontoidfractures The principle of this operation consists of a compression osteosynthesis by screw fixation and avoidance of a segmental fusion.* The indication for this technique is limited to the type II and the swallow type III odontoid fracture according to Anderson and d’Alonzo8y9 (Fig. 4A). This technique preserves the Cl/C2 motion segment, simplifies post-operative care and immobilisation and is performed through an atraumatic anteromedian approach. The contraindications, however, are important to know. Oblique flexion fractures of the neck of the odontoid process should not be treated with this technique as the superior fragment of the C2-vertebral body is too small for adequate screw fixation and the fracture line is relatively parallel to the screw direction preventing the screw from imparting compression across the fracture (Fig. 4B). Tech-
nically it is difficult or impossible to perform this procedure in short-necked patients and obese patients, in patients with limited motion of the cervical spine and in patients with pronounced kyphosis of the upper thoracic spine. Furthermore, the technique is dependent on high resolution two plane imaging and corresponding technical equipment. Also the technique is contraindicated in cervical spinal stenosis because of the danger of cord injury associated with hyperextension of the neck. However, it is absolutely necessary to place the head in an extended position to reduce the fracture and to facilitate the insertion of the screws. The approach to the anterior inferior border of the body of the axis can be facilitated, when the placement of the antero-median incision is determined by placing a long Kirschner-wire along the side of the neck in the intended direction of the screw and viewing on the image intensifier. There are two different techniques available for the screw insertion. The first technique utilises two standard lag screws. Screw holes are drilled with a 2.5 mm drill perforating the posterior half of the tip of the odontoid process. The body fragment is then overdrilled with a 3.5 mm drill and after tapping both holes the appropriate length 3.5 mm cortical screws are inserted (Fig. 5A).8 The second technique utilises two canulated screws. Initially two 20 cm long 1.2 mm K-wires are inserted in the appropriate position on the image intensifier. The appropriate length of self-tapping canulated 3.5 mm cancellous bone screws are then inserted over the well positioned K-wires. The progress of the screw must be observed with the image intensifier to avoid migration of the K-wire proximally9 (Fig. 5B). The post-operative care consists of a soft collar in co-operative patients and of a firm collar in less reliable patients for 6-12 weeks. The collar can be removed for daily care and when resting. There is another possibility in upper cervical spine fractures to use direct screw fixation and compression osteosynthesis. Traumatic spondylolysis of C2 with persistent instability but no relevant dislocation and disc disruption of C2/C3 may rarely be an indication for a direct screw fixation according to the technique of Judet4 (Fig. 6).
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insertion within the articular mass. Roy-Camille and others propose placing screws perpendicular into the center of the lateral mass (Fig. 7A).‘O In contrast, Magerl emphasises placing the screws parallel to the joint line in an oblique direction from just medial to the vertical midline of the lateral mass and just below the horizontal intersection line. Thereby the distance of the screws within the bone is increased and avoiding the vertebral artery, which is directly in front of the articular mass (Fig. 7B).’ l, l2 This second screw direction is not possible in combination with simple round hole plates, as the screw cannot be inclined sufficiently in the sagittal as well as in the frontal plane within the plate hole. Magerl’s proposed screw direction is best applied when using the hook plate for fixation. This special plate (developed by the same author) l l- ’ z is not placed in the sagittal plane along the facet joint, but in the frontal plane, as it is fixed with a hook at the lamina and with one or two screws in the articular masses (Fig. 8). This plate acts exclusively as a tension banding system against a bone graft which is placed between the adjacent spinous processes. The straight plates, either one-third-tubular 3.5 mm AO/ASIF plates4 or 3.5 mm reconstruction AO/ASIF platess, are placed over the facet joints and can be used as buttressing or neutralising systems as well as tension banding systems. In the latter case the distal holes should be placed eccentrically within the plate hole therefore producing dynamic compression (Fig. 9). With this plate a solid midline corticocancellous bone graft can be placed under compression through the tension banding effect of the plate. However, it may be sufficient to place bone chips along the plate over the freshened up articular masses and laminae. 6) Anterior plating
Fig. S-Anterior screw fixation of the odontoid fracture. (A) Drilling of the holes for the use of lag screws (right side). (B) Use of cannulated self cutting screws (right side) after having inserted 1.2 mm K-wires which perforate the posterior apical area of the odontoid process (left side). (C) Clinical example.
Plate Fixation Techniques of the Lower Cervical Spine There are plating techniques for anterior and posterior fixation as well. All of these techniques are usually combined with a fusion extended over the fixation area. a) Posterior plating
Posterior plate fixation is accomplished using screws which are anchored within the articular mass of the cervical vertebrae. There are different types of plates available, and there are at least two methods of screw
In traumatic as well as in reconstructive surgery of the cervical spine a fixation system which can be used in combination with anterior surgery is of great importance. Several authors have presented their systems in the last 15 years. 13-17 Such internal fixation systems allow the creation of such stable fusion constructs that the patient’s post-operative care becomes very simple, with no need for significant external immobilisation. To place and secure an anterior graft under axial compression encourages early integration with a very high healing rate. Many of the graft and postoperative complications can be avoided by using an adequate internal fixation. Most anterior fixation systems of the cervical spine consist of a plate with screws positioned within the vertebral body. One of the controversial points is the length of the screws. There are authors who propose screw penetration of the posterior cortex of the vertebral body, l 3, l 6 to provide a better screw fixation. However, Titanium 3.5 mm cortical screws provide sufficient holding strength without including the posterior cortex.18 The interface between the screw
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Fig. 6-Screw fixation of traumatic spondylolysis of the axis according to Judet. (A) Screw with about 25’ inclination cranially. (B) Screws in the horizontal plane converging by about 25” each. (C) Clinical example.
Fig. 7-(A) Landmark for the screw insertion into the lateral mass according to Roy-Camille: exactly in the center of the articular mass and perpendicular to the posterior surface of the facet. (B) Landmark for the screw insertion into the lateral mass according to Magerl. Starting about 2 mm medial to the vertical midline of the lateral mass and below the horizontal intersection line. The screw is inserted about 30” laterally and parallel to the facet joint.
Fig. g-(A) Hook-plate according to Magerl acts as a tension banding system and creates compression to an interspinous Hgraft. (B) Lateral view of an unisegmental fixation with bone graft. (C) Posterior view of the same construct. (D) Clinical example.
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Fig. S-Posterior plate fixation with a one-tubular plate. (A) Insertion of the K-wires at the end vertebrae. (B) Insertion of the plate over the K-wires, after having contoured and hammered fiat the plate. (C) Plate in position. (D) K-wires replaced by 3.5 mm cortical screws which are inserted at the landmarks described above. (E) Clinical example.
surface and the bone provides a better interlocking of these two elements (Fig. 10). The screw length can be determined by measuring the sagittal diameter of the vertebral body on the X-ray or through the evacuated disc space. This measured value can be preset on a special drill guide with a stopper at the appropriate depth. This allows anterior screw insertion without imparting danger to the spinal cord. Also the Titanium hollow screw system of Morscher” can do it without screw penetration of the posterior wall. However, the construct is a buttressing system, due to the fixed angle between the screws and the plates (Fig. 11). The screw head locks to the plate by small threads around the screw head. There may be some difficulties in directing the screws correctly within the vertebral body due to the fixed screw/plate relationship. However, the highly sophisticated instrumentation facilitates standardised screw insertion.
c) Anterior or posterior$xation ?
There is an ongoing controversy whether anterior or posterior fixation is better in terms of stability and fusion rate. In vitro testing with cadaveric spines by Ulrich et al and others*9y 20,21 have demonstrated more rigid fixation of a cervical spine segment when posterior fixation was performed. While this may be true for simulated trauma, with total anterior and posterior disruption or isolated posterior disruption this may not be true when the anterior intervertebral defect has been replaced by bone or by a mechanical
support against which the vertebral bodies can put under compression. The anterior plate is exposed to maximal flexion load and shear, whereas the posterior tension banding plate replaces the posterior ligamentous structures and provides better stability. An earlier work 22 states that one increases an already existing instability (mostly traumatic) by excising the annulus of the disc and the anterior longitudinal ligament. This may be true, as long as an unfixed bone graft is inserted anteriorly following decompression. However, if the graft is placed in compression in combination with a plate, the anterior longitudinal ligament and the annulus may be imitated (Fig. 12). There are some substantial reasons to favour anterior surgery in the cervical spine : 1) The anterior approach is relatively atraumatic, which contrasts to the posterior approach, where muscle stripping may partially denervate surrounding muscles. 2) Many of the spinal pathologies have their etiology from the vertebral body column and threaten the spinal cord from the front. Therefore, a direct decompression of the spinal cord is better done by an anterior approach. 3) An anteriorly inserted graft is placed under compression which enhances the interface healing, whereas a posterior graft is on the tension banding side. 4) Specifically in traumatology, the patient can be operated in the supine position and does not need to be turned over to a prone position. 5) Based on extensive clinical experience the stability and stiffness in anterior plate fixation seems to be sufficient even though biomechanical in vitro tests showed it inferior to posterior instrumentation. l*
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Fig. 1 l-Modification
of the graft technique together with an anterior plating. (A) Trapezoid shaped graft. When the plate is contoured and the screws drilled eccentrically an important anterior tension banding effect is created, however, with compression of the posterior joints. (B) In a rectangular graft the posterior joints open themselves through the tension banding effect.
C Fig. 12-Titanium locking screw plate system. (A) The angle between screw head and plate is stable due to the locked head through a small spreading screw. (B) Special instrumentation facilitates the right placement of the screws and plate. (C) The screws do not penetrate the posterior wall.
Fig. lo-Anterior plating with the AO/ASIF H-plate according to Orozco. (A) There is a special drill guide with a stopper at the intended length. This length can be measured either preoperatively on the X-ray or through an evacuated disc space. (6) Hole drilled with the special guide. (C) Screws inserted either the posterior wall included with the standard cortical screws or not included with the Titanium covered screws. (D) Clinical example of an unisegmental lesion. (E) Clinical example of a segmental fixation due to a complete vertebral body fracture.
techniques for the spine, and who have the opportunity to constantly perform these techniques. These more sophisticated technical demands in the treatment of spinal disorders together with complex diagnostic procedures necessitates a new generation of surgeons who specialise entirely in spinal surgery. Acknowledgement The author gratefully acknowledges the help of Mark Gillespy, MD, Department of Orthopaedics, College of Medicine, University of Florida, Gainesville, USA, in the preparation of the English manuscript.
References Conclusions The last decade has seen an array of new spinal instrumentation in general and has seen standardised fixation systems for the cervical spine in particular. The armentarium has been extended from simple wire cerclages to effective plate or isolated screw fixation with better immediate stability and higher fusion rates. This allows earlier mobilisation without heavy external fixation. However, this sort of surgery should only be practised by surgeons who are familiar with the principles of internal fixation and with special
1. Magerl F, Seemann P. Stable posterior fusion of the atlas and axis by transarticular screw fixation. In: Kehr P, Weidner A (Eds) Cervical Spine I. Springer Verlag, Wien New York 1986; pp. 322-327 2. Grob D, Magerl F. Operative Stabilisierung bei Frakturen von Cl und C2. Orthopgde 1987; 16: 46-54 3. Grob D, Jeanneret B, Aebi M, Markwalder T. Atlanto-axial fusion with transarticular screw-fixation. J Bone Joint Surg (Br) 1991; accepted for publication 4. Aebi M. Surgical Treatment of Cervical Spine Fractures by A0 Techniques. In : Bridwell K Hand DeWald R L (Eds) Textbook of Spinal Surgery. J B Lippincott Philadelphia 1991 5. Anderson P A, Henley M B, Grady M S, Montesano P X, Winn H R. Posterior cervical arthrodesis with A0 reconstruction plates and bone graft. Spine 1991; 16 (3s): 7279
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Grob D, Dvorak J, Panjabi M, Froehhch M, Hayek J. Posterior occipito-cervical fusion. Spine 1991; 16 (3s): 17-24 Biihler J. Anterior screw fixation for acute fractures and nonunions of the dens. J Bone Joint Surg 1982; 64-A: 18-27 Aebi M, Etter Chr, Coscia M. Fractures of the Odontoid Process: Treatment with Anterior Screw Fixation. Spine 1989; 14: 106551070 Roy-Camille R. Arguments en faveur de la voie posterieure dans la chirurgie du rachis cervical. Revue de Chirurgie Orthopedique 1984; 70: 55&557 Magerl F, Grob D, Seemann P. Stable dorsal fusion of the cervical spine (C2-Thl) using hook plates. In: Kehr P, Weidner A (Eds) Cervical Spine 1. Springer Verlag pp. l-1 8, 1987 Jeanneret B, Magerl F, Ward E H, Ward J-Ch. Posterior stabilization of the cervical spine (C2C7) with hook plates. Spine 1991; 16 (3s): 5663 Orozco Delclos R, Llovet Topes J. Osteosintesis en las fracturas de raquis cervical. Nota de technica. Revista Orthop Traumatoll970; 14: 285-288 Senegas J, Gauzere J M. Plaidoyer pour la chirurgie anterieure dans le traitement des traumatismes graves des 5 demieres vertibres cervicales. Revue de Chirurgie Orthoptdique 1976; 62 (Suppl II): 1233128
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15. Aebi M, Mohler J, Zlch G, Morscher E. Indication, surgical technique and results of 100 surgically treated fractures and fracture dislocations of the cervical spine. Clin Orthop 1986; 203 : 244257 16. Caspar W. Advances in cervical spine surgery. First experiences with the trapezia1 osteosynthetic plate and a new surgical instrumentation for anterior interbody stabilization. Orthopaedic News, USA 1982; 4 (6) 17. Morscher E, Sutter F, Jenny H, Olerud S. Die vordere Verplattung der Halswirbelsaule mit dem HohlschraubenPlattensystem aus Titanium. Chirurg 1986; 57: 702-707 18. Aebi M, Zuber K, Marchesi D. The treatment of cervical spine injuries by anterior plating. Spine 1991; 16 (3s): 3845 19. Ulrich Chr, Worsdorfer 0, Kalff R, Claes L, Wilke H J. Biomechanics of fixation systems to the cervical spine. Spine 1991; 16(3S):49 20. Sutterlin C E, McAfee P C, Warden K C, Rey R M, Farey I D. A biomechanical evaluation of cervical spinal stabilization methods in a bovine model. Spine 1988; 13 : 795-802 21. Coe J D, Warden K E, Sutterlin C E, McAfee P C. Biomechanical evaluation of cervical spinal stabilization methods in a human cadaveric model. Spine 1989; 14. 11221131 22. Stauffer E S, Kelly E G. Fracture-dislocations of the cervical spine. J Bone Joint Surg 1977; 59-A: 4548