- Email: [email protected]
Stereotactic atlantoaxial transarticular screw fixation
Journal of Clinical Neuroscience (2005) 12(1), 62–65 0967-5868/$ - see front matter ª 2004 Published by Elsevier Ltd. doi:10.1016/j.jocn.2004.03.003
Technical note
Stereotactic atlantoaxial transarticular screw fixation RW Laherty
MBBS,
RJ Kahler
MBBS FRACS,
DG Walker
PHD FRACS,
FH Tomlinson PHD MD FRACS
Kenneth G. Jamieson Department of Neurosurgery, Royal Brisbane Hospital, Herston, Qld., Australia
Summary Atlantoaxial stabilisation can be performed using a variety of surgical techniques. Developments in spinal instrumentation and stereotactic technology have been incorporated into these procedures. We have recently adopted frameless stereotaxy to assist in such operations. A retrospective study of patients treated by the authors and using frameless stereotaxy from 2001 to 2002 was performed. Each patient underwent pre-operative fine-cut CT in the position of fixation. Using these images, screw trajectory was planned. Stereotaxis and fluoroscopy was utilised during fixation. A post-operative CT was performed. There were nine patients. Bilateral screw placement was achieved in eight. In the remaining case stereotactic planning predicted the single screw fixation. There were no post-operative complications. Postoperative CT showed screw placement corresponding to the planned trajectory in all 17 screws. Stabilisation was achieved in all. Stereotactic atlantoaxial screw fixation is an accessible, safe and accurate method for the management of C1-2 instability. ª 2004 Published by Elsevier Ltd. Keywords: atlantoaxial, atlas, axis, fixation, spine, stereotactic, stereotaxis, transarticular
INTRODUCTION Atlantoaxial instability follows a variety of pathologies. It occurs most commonly in patients with rheumatoid arthritis.1;2 It less frequently presents as a result of trauma. Less frequent causes include neoplastic involvement, metabolic destruction and congenital subluxation. Instability may also present as a complication of previous surgical procedures.3;4 Left untreated, this unstable segment of the axial skeleton has the potential to cause a variety of symptoms. These range from radicular neck pain and headaches to progressive myelopathy as well as acute cord syndromes and even sudden death.2;5 Treatment may be non-surgical or surgical. Some fractures may be treated non-operatively with manipulation to achieve reduction followed by external immobilisation until bony healing has effected a fusion. Non-operative methods of immobilisation include halothoracic bracing. Less rigid supports do not provide adequate immobilisation to maintain reduction. Whilst halothoracic bracing is relatively non-invasive, it does require the wearing of a cumbersome apparatus for a significant period. The most frequent problems relate to pin-site infections and pin loosening with loss of reduction.6 Wearing the apparatus may impact on social interaction, physical mobility and personal hygiene. Challenges to mobility increase the risk of deep venous thrombosis.7–9 There are case reports of major intracranial pathology following falls whilst wearing a halothoracic brace.6 Most lesions will routinely require operative management in order to achieve all required elements of fusion.10 Surgical methods for posterior atlantoaxial stabilisation have evolved over the latter half of the last century and are now favoured by many, with some authors advocating prophylactic surgery for some patients with degenerative atlantoaxial instability.11
Received 2 September 2003 Accepted 1 March 2004 Correspondence to: R. Laherty, Royal Brisbane Hospital Post Office, P.O. Box 62, Herston, Qld. 4029 Australia. Tel.: +61-7-36367470; E-mail: [email protected]
62
The larger series in the literature are performed by experienced spinal surgeons in institutions supporting large populations.1;12;13 Can the demanding technique of transarticular screw placement described and utilised by spinal experts be modified through the use of stereotaxis to enable surgeons servicing smaller populations with less frequent presentations to safely and effectively treat these patients? The purpose of this study is to review our recent experience using frameless stereotaxy as a surgical adjunct.
MATERIALS AND METHODS Patients From July 2001 to June 2002, there were nine patients whose atlantoaxial instability was treated using stereotactic atlantoaxial transarticular screw fixation. This was performed using the ‘StealthStation’ (Medtronic Sofamor Danek) with the Universal Cannulated Screw System (Medtronic Sofamor Danek).
Preoperative planning Emphasis was placed on pre-operative preparation. Functional views were obtained using plain films, computed tomography and fluoroscopy. The position of best radiologic reduction was achieved and fine-cut (2-mm slices) computed tomography was performed. This fine-cut CT was incorporated into the image guidance system and the screw entry point and trajectory was planned. Following the Magerl technique,12–14 the entry site13 was 3–4 mm above and 3–4 mm lateral to the inferomedial edge of the C2-3 facet joint. The planned trajectory was in an oblique caudocephalad direction from the posterior aspect of the lamina of the axis. In lateral projection the trajectory was towards the anterior tubercle of the atlas. The virtual screw penetrated the articular surface in the posteromedial quadrant of the joint surface and entered the lateral mass of the atlas. The course of the virtual screw was followed to appreciate its relationship to the vertebral artery, the spinal cord and the nerve roots.
Stereotactic atlantoaxial transarticular screw fixation 63
Operative technique Under general anaesthesia, each patient was carefully rolled prone and positioned using fluoroscopic guidance. The patient was held rigidly in position with either a halothoracic brace secured to the operating table or a Mayfield three-pin clamp. Once secured, a lateral fluoroscopic image was obtained and compared to the ‘scanogram’ of the pre-operative fine-cut CT to help confirm the position of best reduction. Shoulder and skin retraction was effected when necessary to facilitate vision. A midline incision was made from the external occipital protuberance to the mid-cervical region. Bone from the occiput to C3 was exposed, with careful dissection to expose all the bony contours in the surgical field of the spinous process, the laminae and the lateral masses of the atlas and axis. The stereotactic reference frame was fixed to the spinous process of the axis. The accuracy of the guidance system is improved by selection of operative landmarks that are recognisable on the stereotactic image. This is aided by careful dissection to expose and appreciate the subtleties of the bony contours. Contour anomalies make for better reference points than points on a smooth surface. Selection of landmarks over a greater surface area also increases the accuracy of the guidance system. This allows for accurate representation of the screw in its passage through the axis. Passage through the atlas cannot be so confident. Optimal reduction both pre- and intra-operatively helps to ensure that the image of the atlas on the guidance system correlates with its true location. The guidance system was used to determine where stab incisions were sited. A protective sheath was passed through a stab incision along the trajectory of the planned screw to the entry point. Guide-wire and screw placement was performed with two operators. One surgeon was tasked with maintaining the entry point and trajectory of the drill guide using the image guidance software. The other was able to perform the drilling with fluoroscopic guidance. Autologous bone was harvested from the iliac crest, morcellised and placed over the lateral masses after preparing the local cortical surfaces. Post-operative care Patients were admitted to the Intensive Care Facility for 24 h. Post-operative computed tomography was performed. A Philadelphia collar was prescribed for 8–12 weeks. Plain radiographs were obtained at follow-up appointments. RESULTS There were nine patients; seven were male. The mean age was 70 years (range 31–84 years). The mean follow-up period was 18 months (range 13–22 months). The youngest patient (31 years, male) had congenital subluxation. One patient’s instability was secondary to local involvement with squamous cell carcinoma. He died of this disease four months after fixation. Four male patients had traumatic causes for their instability. Three of these had a known history of rheumatoid arthritis. In one of these the rheumatoid process was thought to be significant as his injury was sustained with minimal force – he stumbled forwards and struck his head on the fridge door. During his hospitalisation he was also found to have non-Hodgkin’s B cell lymphoma and died of this 14 months after stabilisation. The forces associated with the cervical fractures of the other three patients were enough to contribute to moderate head injury in each. Three patients (two female and one male) were diagnosed ª 2004 Elsevier Ltd. All rights reserved.
with rheumatoid associated subluxation. In all, rheumatoid arthritis was present in six patients. Seventeen screws were placed. In one case, stereotactic planning predicted single screw fixation, which was achieved. This was due to kyphoscoliosis. Satisfactory screw placements corresponding to the plans were achieved for all screws. Each surgeon assessed this by comparing the screw in the postoperative CT images to the virtual screw in the image guidance system. All patients received DVT prophylaxis with subcutaneous heparin, TED stockings and sequential compression devices. Six patients were mobilised on their first post-operative day. Mobilisation was delayed in the three head-injured male patients. There were no post-operative complications. Stabilisation was assessed using flexion–extension plain radiographs at follow-up and was achieved in all patients. DISCUSSION Earlier operative techniques for achieving atlantoaxial stability utilised autologous interspinous or interlaminar bone graft held in position with sublaminar wires.5;15;16 These fusion constructs require external immobilisation. The bone was harvested typically from the iliac crest13 and less often from a rib.17 During placement of sublaminar wires, the spinal cord may be injured.18 Sublaminar wires have also been associated with such late adverse consequences as wire fracture resulting in neurologic deficit.19 More recent techniques have attempted to limit sublaminar dissection and wire placement. These include interlaminar clamps20;21 and various screw-plate22 and screw-rod systems.23 The use of the iliac crest can threaten local neurovascular elements, can be a source of ongoing pain and has been reported to contribute to pelvic fractures.24 Artificial bone substances have been utilised25 to reduce the incidence of these adverse events. The use of iliac crest remains a valid option and was utilised in our series. Magerl and Seemann14 described the placement of a screw across the facet joint between the atlas and axis. It was initially postulated as an adjunct to the more traditional methods, decreasing the need for post-operative bracing. However, it has since been shown to offer a more attractive biomechanical profile than other fusion methods, particularly because of the immediate obliteration of rotational motion26;27 and its faster fusion rate.4;28 The great concern with this technique has been the threat to the vertebral arteries.29 Whilst this is a recognised event, its incidence, significance and pre-disposing factors are difficult to extract from the literature.1 Other concerns have related to hardware failure, errant screw placement and hypoglossal nerve damage.1;29 The surgery is also technically demanding; prompting some surgeons to favour other techniques.23 Contraindications include aberrant vertebral artery anatomy, bony dimensions that will not accept a screw and poor bone quality such that screw purchase and regional immobilisation will not be maintained.1;30 Suitable pre-operative imaging is obviously paramount. A relative contraindication for atlantoaxial screw fixation is incomplete pre-operative reduction.1 Our patient with congenital subluxation was thought to have satisfactory, but not perfect, reduction during his pre-operative imaging. This was, however, improved at his post-operative CT. Better reduction may have been achieved under anaesthesia. The mechanical advantage of the bi-cortical pull of the screw was also thought to have contributed. Journal of Clinical Neuroscience (2005) 12(1), 62–65
64 Laherty et al.
Madawi et al.1 report one of the larger series of posterior atlantoaxial fusions using the Magerl technique. This is one of the few papers to address malpositioned screws and their consequences, including vertebral artery damage. They advocated the transarticular screw technique but highlighted that it was demanding and required a high degree of technical precision. Stereotaxis and image guided surgery have become indispensable to many modern intracranial surgeons and are slowly being extended to spinal surgery. Welch et al.31 described the use of image guidance to assist in treatment of complex spinal cases. Four of his 11 cases involved atlantoaxial instability and were treated with transarticular screws. Welch agreed that the placement of transarticular screws requires strict technical precision and accuracy and that this is challenged by the limitations of surgical exposure in an anatomically complex region. The use of stereotaxis provided a multidimensional appreciation of the anatomic relationships. These relations could be assessed pre-operatively, increasing the efficiency and safety of surgery. Kawaguchi et al.30 described the use of stereotaxis to aid transarticular screw placement in two patients. In one, the preoperative planning identified that only one screw could be placed. This was due to a medially situated vertebral artery. In our series there was one patient whose kyphoscoliosis prevented passage of a screw on one side. The bony anatomy of the atlas and axis indicated that a screw could be accepted. However, the guidance software revealed that the required trajectory would be too low relative to the ribs. Prior to surgery the operative plan was revised to include wired interlaminar bone graft on that side. The great benefit offered by the use of stereotaxis is in the preoperative phase. As others have described, the complex relational anatomy of the region can be reviewed and appreciated individually. Suitability for screw placement can be assessed and where it is deemed unsuitable, an alternative method of fixation can be planned well in advance. The software can present the anatomy and the virtual screw such that a simulation of the actual procedure can be modelled and practiced. This allows the surgical team to appreciate the specifics of the individualised procedure ahead of them, affording greater efficiency at surgery. This operative model could also be used to help educate the patient as to the surgical plan and the inherent risks. These elements translate to improved risk management. Even though this is a relatively small series, the ability to plan, prepare and practice in advance of the operation contributes to greater surgeon comfort and confidence during the procedure. Performance of the procedure remains much as others have described.12–14 The technique uses fluoroscopy to aid screw placement. This necessitates a variable radiation dose to the surgeon. The image guidance system can be used to represent the passage of the drill or the screw as it passes through the axis. It must be remembered that the reference frame is attached to the axis and therefore the relative position of the atlas may be misrepresented. For this reason fluoroscopy must continue to be used. It may be possible to decrease radiation exposure by judicious use of the fluoroscope. We recommend its use during placement of the K wire guide. This does not have to be continuous but screening should be reasonably frequent, as the flexible wire may bend and skew its trajectory. Fluoroscopy during screw placement may be even more limited. However care must be taken to avoid advancing the K wire during subsequent drilling, tapping and screwing. The method used for assessing the adequacy of screw placement in this series may be questioned. There was no objective measurement or independent review. This reflects the limitations of a retrospective series. There is, however, only a small margin of Journal of Clinical Neuroscience (2005) 12(1), 62–65
tolerance whereby a screw could be misplaced and not cause a complication. CONCLUSIONS Stereotactic atlantoaxial transarticular fixation is a modification of an already proven technique that offers the potential for improved outcomes by enabling greater pre-operative assessment and planning. It also facilitates an individualised surgical model for pre-operative preparation and practice leading to improved surgical efficiency and safety. In our experience the technique is accessible, safe and accurate. ACKNOWLEDGEMENTS Medtronic Sofamor Danek – Financial support for travel to present at Broome Neurosurgical Society of Australasia meeting, 2002. REFERENCES 1. Madawi AA, Casey AT, Solanki GA, Tuite G, Veres R, Crockard HA. Radiological and anatomical evaluation of the atlantoaxial transarticular screw fixation technique. J Neurosurg 1997; 86(6): 961–968. 2. Papadopoulos SM, Dickman CA, Sonntag VK. Atlantoaxial stabilization in rheumatoid arthritis. J Neurosurg 1991; 74(1): 1–7. 3. Dickman CA, Sonntag VK. Surgical management of atlantoaxial nonunions. J Neurosurg 1995; 83(2): 248–253. 4. Grob D. Surgery in the degenerative cervical spine. Spine 1998; 23(24): 2674–2683. 5. Dickman CA, Sonntag VK, Papadopoulos SM, Hadley MN. The interspinous method of posterior atlantoaxial arthrodesis. J Neurosurg 1991; 74(2): 190–198. 6. Dorfmuller G, Hollerhage HG. Severe intracranial injury from a fall in the halo external fixator. J Orthop Trauma 1992; 6(3): 366–369. 7. Cogo A, Bernardi E, Prandoni P, et al. Acquired risk factors for deep-vein thrombosis in symptomatic outpatients. Arch Intern Med 1994; 154(2): 164–168. 8. Gebremedhin A, Shamebo M. Deep venous thrombosis in a university teaching hospital, Addis Ababa, Ethiopia. East Afr Med J 1998; 75(7): 432–435. 9. Samama MM. An epidemiologic study of risk factors for deep vein thrombosis in medical outpatients: the Sirius study. Arch Intern Med 2000; 160(22): 3415–3420. 10. Ranawat CS, O'Leary P, Pellicci P, Tsairis P, Marchisello P, Dorr L. Cervical spine fusion in rheumatoid arthritis. J Bone Joint Surg Am 1979; 61(7): 1003–1010. 11. Grob D. Atlantoaxial immobilization in rheumatoid arthritis: a prophylactic procedure. Eur Spine J 2000; 9(5): 404–409. 12. Grob D, Jeanneret B, Aebi M et al. Atlantoaxial fusion with transarticular screw fixation. J Bone Joint Surg (Br) 1991; 73: 972–976. 13. Haid Jr RW. C1-C2 transarticular screw fixation: technical aspects. Neurosurgery 2001; 49(1): 71–74. 14. 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, New York 1987; 322–327. 15. Brooks A, Jenkins E. Atlantoaxial arthrodesis by the wedge compression method. J Bone Joint Surg (Am) 1978; 60: 279–284. 16. Gallie W. Fractures and dislocations of the cervical spine. Am J Surg 1939; 46: 495–499. 17. Brockmeyer DL. A bone and cable girth-hitch technique for atlantoaxial fusion in pediatric patients. Technical note. J Neurosurg 2002; 97(3 Suppl): 400–402. 18. Fraser AB, Sen C, Casden AM, Catalano PJ, Post KD. Cervical transdural intramedullary migration of a sublaminar wire. A complication of cervical fixation. Spine 1994; 19(4): 456–459. 19. Blacklock JB. Fracture of a sublaminar stainless steel cable in the upper cervical spine with neurological injury. Case report. J Neurosurg 1994; 81(6): 932–933. 20. Holness RO, Huestis WS, Howes WJ, Langille RA. Posterior stabilization with an interlaminar clamp in cervical injuries: technical note and review of the long term experience with the method. Neurosurgery 1984; 14(3): 318–322. 21. Moskovich R, Crockard HA. Atlantoaxial arthrodesis using interlaminar clamps. An improved technique. Spine 1992; 17(3): 261–267. 22. Goel A, Desai KI, Muzumdar DP. Atlantoaxial fixation using plate and screw method: a report of 160 treated patients. Neurosurgery 2002; 51(6): 1351–1356. 23. Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine 2001; 26(22): 2467–2471.
ª 2004 Elsevier Ltd. All rights reserved.
Stereotactic atlantoaxial transarticular screw fixation 65
24. Hu RW, Bohlman HH. Fracture at the iliac bone graft harvest site after fusion of the spine. Clin Orthop 1994; 309: 208–213. 25. Bryan WJ, Inglis AE, Sculco TP, Ranawat CS. Methylmethacrylate stabilization for enhancement of posterior cervical arthrodesis in rheumatoid arthritis. J Bone Joint Surg Am 1982; 64(7): 1045–1050. 26. Grob D, Crisco 3rd JJ, Panjabi MM, Wang P, Dvorak J. Biomechanical evaluation of four different posterior atlantoaxial fixation techniques. Spine 1992; 17(5): 480–490. 27. Richter M, Schmidt R, Claes L, Puhl W, Wilke HJ. Posterior atlantoaxial fixation: biomechanical in vitro comparison of six different techniques. Spine 2002; 27(16): 1724–1732.
ª 2004 Elsevier Ltd. All rights reserved.
28. Coyne T, Fehlings M, Wallace M, Bernstein M, Tator C. C1-2 posterior cervical fusion: Long term evaluation of results and efficacy. Neurosurgery 1995; 37: 688–692. 29. Haid Jr RW, Subach BR, McLaughlin MR, Rodts Jr GE, Wahlig Jr JB. C1-C2 transarticular screw fixation for atlantoaxial instability: a 6-year experience. Neurosurgery 2001; 49(1): 65–68. 30. Kawaguchi Y, Ishihara H, Ohmori K, Kanamori M, Kimura T. Computerassisted Magerl's transarticular screw fixation for atlantoaxial subluxation. J Orthop Sci 2002; 7(1): 131–136. 31. Welch WC, Subach BR, Pollack IF, Jacobs GB. Frameless stereotactic guidance for surgery of the upper cervical spine. Neurosurgery 1997; 40(5): 958–963.
Journal of Clinical Neuroscience (2005) 12(1), 62–65
Technical note
Stereotactic atlantoaxial transarticular screw fixation RW Laherty
MBBS,
RJ Kahler
MBBS FRACS,
DG Walker
PHD FRACS,
FH Tomlinson PHD MD FRACS
Kenneth G. Jamieson Department of Neurosurgery, Royal Brisbane Hospital, Herston, Qld., Australia
Summary Atlantoaxial stabilisation can be performed using a variety of surgical techniques. Developments in spinal instrumentation and stereotactic technology have been incorporated into these procedures. We have recently adopted frameless stereotaxy to assist in such operations. A retrospective study of patients treated by the authors and using frameless stereotaxy from 2001 to 2002 was performed. Each patient underwent pre-operative fine-cut CT in the position of fixation. Using these images, screw trajectory was planned. Stereotaxis and fluoroscopy was utilised during fixation. A post-operative CT was performed. There were nine patients. Bilateral screw placement was achieved in eight. In the remaining case stereotactic planning predicted the single screw fixation. There were no post-operative complications. Postoperative CT showed screw placement corresponding to the planned trajectory in all 17 screws. Stabilisation was achieved in all. Stereotactic atlantoaxial screw fixation is an accessible, safe and accurate method for the management of C1-2 instability. ª 2004 Published by Elsevier Ltd. Keywords: atlantoaxial, atlas, axis, fixation, spine, stereotactic, stereotaxis, transarticular
INTRODUCTION Atlantoaxial instability follows a variety of pathologies. It occurs most commonly in patients with rheumatoid arthritis.1;2 It less frequently presents as a result of trauma. Less frequent causes include neoplastic involvement, metabolic destruction and congenital subluxation. Instability may also present as a complication of previous surgical procedures.3;4 Left untreated, this unstable segment of the axial skeleton has the potential to cause a variety of symptoms. These range from radicular neck pain and headaches to progressive myelopathy as well as acute cord syndromes and even sudden death.2;5 Treatment may be non-surgical or surgical. Some fractures may be treated non-operatively with manipulation to achieve reduction followed by external immobilisation until bony healing has effected a fusion. Non-operative methods of immobilisation include halothoracic bracing. Less rigid supports do not provide adequate immobilisation to maintain reduction. Whilst halothoracic bracing is relatively non-invasive, it does require the wearing of a cumbersome apparatus for a significant period. The most frequent problems relate to pin-site infections and pin loosening with loss of reduction.6 Wearing the apparatus may impact on social interaction, physical mobility and personal hygiene. Challenges to mobility increase the risk of deep venous thrombosis.7–9 There are case reports of major intracranial pathology following falls whilst wearing a halothoracic brace.6 Most lesions will routinely require operative management in order to achieve all required elements of fusion.10 Surgical methods for posterior atlantoaxial stabilisation have evolved over the latter half of the last century and are now favoured by many, with some authors advocating prophylactic surgery for some patients with degenerative atlantoaxial instability.11
Received 2 September 2003 Accepted 1 March 2004 Correspondence to: R. Laherty, Royal Brisbane Hospital Post Office, P.O. Box 62, Herston, Qld. 4029 Australia. Tel.: +61-7-36367470; E-mail: [email protected]
62
The larger series in the literature are performed by experienced spinal surgeons in institutions supporting large populations.1;12;13 Can the demanding technique of transarticular screw placement described and utilised by spinal experts be modified through the use of stereotaxis to enable surgeons servicing smaller populations with less frequent presentations to safely and effectively treat these patients? The purpose of this study is to review our recent experience using frameless stereotaxy as a surgical adjunct.
MATERIALS AND METHODS Patients From July 2001 to June 2002, there were nine patients whose atlantoaxial instability was treated using stereotactic atlantoaxial transarticular screw fixation. This was performed using the ‘StealthStation’ (Medtronic Sofamor Danek) with the Universal Cannulated Screw System (Medtronic Sofamor Danek).
Preoperative planning Emphasis was placed on pre-operative preparation. Functional views were obtained using plain films, computed tomography and fluoroscopy. The position of best radiologic reduction was achieved and fine-cut (2-mm slices) computed tomography was performed. This fine-cut CT was incorporated into the image guidance system and the screw entry point and trajectory was planned. Following the Magerl technique,12–14 the entry site13 was 3–4 mm above and 3–4 mm lateral to the inferomedial edge of the C2-3 facet joint. The planned trajectory was in an oblique caudocephalad direction from the posterior aspect of the lamina of the axis. In lateral projection the trajectory was towards the anterior tubercle of the atlas. The virtual screw penetrated the articular surface in the posteromedial quadrant of the joint surface and entered the lateral mass of the atlas. The course of the virtual screw was followed to appreciate its relationship to the vertebral artery, the spinal cord and the nerve roots.
Stereotactic atlantoaxial transarticular screw fixation 63
Operative technique Under general anaesthesia, each patient was carefully rolled prone and positioned using fluoroscopic guidance. The patient was held rigidly in position with either a halothoracic brace secured to the operating table or a Mayfield three-pin clamp. Once secured, a lateral fluoroscopic image was obtained and compared to the ‘scanogram’ of the pre-operative fine-cut CT to help confirm the position of best reduction. Shoulder and skin retraction was effected when necessary to facilitate vision. A midline incision was made from the external occipital protuberance to the mid-cervical region. Bone from the occiput to C3 was exposed, with careful dissection to expose all the bony contours in the surgical field of the spinous process, the laminae and the lateral masses of the atlas and axis. The stereotactic reference frame was fixed to the spinous process of the axis. The accuracy of the guidance system is improved by selection of operative landmarks that are recognisable on the stereotactic image. This is aided by careful dissection to expose and appreciate the subtleties of the bony contours. Contour anomalies make for better reference points than points on a smooth surface. Selection of landmarks over a greater surface area also increases the accuracy of the guidance system. This allows for accurate representation of the screw in its passage through the axis. Passage through the atlas cannot be so confident. Optimal reduction both pre- and intra-operatively helps to ensure that the image of the atlas on the guidance system correlates with its true location. The guidance system was used to determine where stab incisions were sited. A protective sheath was passed through a stab incision along the trajectory of the planned screw to the entry point. Guide-wire and screw placement was performed with two operators. One surgeon was tasked with maintaining the entry point and trajectory of the drill guide using the image guidance software. The other was able to perform the drilling with fluoroscopic guidance. Autologous bone was harvested from the iliac crest, morcellised and placed over the lateral masses after preparing the local cortical surfaces. Post-operative care Patients were admitted to the Intensive Care Facility for 24 h. Post-operative computed tomography was performed. A Philadelphia collar was prescribed for 8–12 weeks. Plain radiographs were obtained at follow-up appointments. RESULTS There were nine patients; seven were male. The mean age was 70 years (range 31–84 years). The mean follow-up period was 18 months (range 13–22 months). The youngest patient (31 years, male) had congenital subluxation. One patient’s instability was secondary to local involvement with squamous cell carcinoma. He died of this disease four months after fixation. Four male patients had traumatic causes for their instability. Three of these had a known history of rheumatoid arthritis. In one of these the rheumatoid process was thought to be significant as his injury was sustained with minimal force – he stumbled forwards and struck his head on the fridge door. During his hospitalisation he was also found to have non-Hodgkin’s B cell lymphoma and died of this 14 months after stabilisation. The forces associated with the cervical fractures of the other three patients were enough to contribute to moderate head injury in each. Three patients (two female and one male) were diagnosed ª 2004 Elsevier Ltd. All rights reserved.
with rheumatoid associated subluxation. In all, rheumatoid arthritis was present in six patients. Seventeen screws were placed. In one case, stereotactic planning predicted single screw fixation, which was achieved. This was due to kyphoscoliosis. Satisfactory screw placements corresponding to the plans were achieved for all screws. Each surgeon assessed this by comparing the screw in the postoperative CT images to the virtual screw in the image guidance system. All patients received DVT prophylaxis with subcutaneous heparin, TED stockings and sequential compression devices. Six patients were mobilised on their first post-operative day. Mobilisation was delayed in the three head-injured male patients. There were no post-operative complications. Stabilisation was assessed using flexion–extension plain radiographs at follow-up and was achieved in all patients. DISCUSSION Earlier operative techniques for achieving atlantoaxial stability utilised autologous interspinous or interlaminar bone graft held in position with sublaminar wires.5;15;16 These fusion constructs require external immobilisation. The bone was harvested typically from the iliac crest13 and less often from a rib.17 During placement of sublaminar wires, the spinal cord may be injured.18 Sublaminar wires have also been associated with such late adverse consequences as wire fracture resulting in neurologic deficit.19 More recent techniques have attempted to limit sublaminar dissection and wire placement. These include interlaminar clamps20;21 and various screw-plate22 and screw-rod systems.23 The use of the iliac crest can threaten local neurovascular elements, can be a source of ongoing pain and has been reported to contribute to pelvic fractures.24 Artificial bone substances have been utilised25 to reduce the incidence of these adverse events. The use of iliac crest remains a valid option and was utilised in our series. Magerl and Seemann14 described the placement of a screw across the facet joint between the atlas and axis. It was initially postulated as an adjunct to the more traditional methods, decreasing the need for post-operative bracing. However, it has since been shown to offer a more attractive biomechanical profile than other fusion methods, particularly because of the immediate obliteration of rotational motion26;27 and its faster fusion rate.4;28 The great concern with this technique has been the threat to the vertebral arteries.29 Whilst this is a recognised event, its incidence, significance and pre-disposing factors are difficult to extract from the literature.1 Other concerns have related to hardware failure, errant screw placement and hypoglossal nerve damage.1;29 The surgery is also technically demanding; prompting some surgeons to favour other techniques.23 Contraindications include aberrant vertebral artery anatomy, bony dimensions that will not accept a screw and poor bone quality such that screw purchase and regional immobilisation will not be maintained.1;30 Suitable pre-operative imaging is obviously paramount. A relative contraindication for atlantoaxial screw fixation is incomplete pre-operative reduction.1 Our patient with congenital subluxation was thought to have satisfactory, but not perfect, reduction during his pre-operative imaging. This was, however, improved at his post-operative CT. Better reduction may have been achieved under anaesthesia. The mechanical advantage of the bi-cortical pull of the screw was also thought to have contributed. Journal of Clinical Neuroscience (2005) 12(1), 62–65
64 Laherty et al.
Madawi et al.1 report one of the larger series of posterior atlantoaxial fusions using the Magerl technique. This is one of the few papers to address malpositioned screws and their consequences, including vertebral artery damage. They advocated the transarticular screw technique but highlighted that it was demanding and required a high degree of technical precision. Stereotaxis and image guided surgery have become indispensable to many modern intracranial surgeons and are slowly being extended to spinal surgery. Welch et al.31 described the use of image guidance to assist in treatment of complex spinal cases. Four of his 11 cases involved atlantoaxial instability and were treated with transarticular screws. Welch agreed that the placement of transarticular screws requires strict technical precision and accuracy and that this is challenged by the limitations of surgical exposure in an anatomically complex region. The use of stereotaxis provided a multidimensional appreciation of the anatomic relationships. These relations could be assessed pre-operatively, increasing the efficiency and safety of surgery. Kawaguchi et al.30 described the use of stereotaxis to aid transarticular screw placement in two patients. In one, the preoperative planning identified that only one screw could be placed. This was due to a medially situated vertebral artery. In our series there was one patient whose kyphoscoliosis prevented passage of a screw on one side. The bony anatomy of the atlas and axis indicated that a screw could be accepted. However, the guidance software revealed that the required trajectory would be too low relative to the ribs. Prior to surgery the operative plan was revised to include wired interlaminar bone graft on that side. The great benefit offered by the use of stereotaxis is in the preoperative phase. As others have described, the complex relational anatomy of the region can be reviewed and appreciated individually. Suitability for screw placement can be assessed and where it is deemed unsuitable, an alternative method of fixation can be planned well in advance. The software can present the anatomy and the virtual screw such that a simulation of the actual procedure can be modelled and practiced. This allows the surgical team to appreciate the specifics of the individualised procedure ahead of them, affording greater efficiency at surgery. This operative model could also be used to help educate the patient as to the surgical plan and the inherent risks. These elements translate to improved risk management. Even though this is a relatively small series, the ability to plan, prepare and practice in advance of the operation contributes to greater surgeon comfort and confidence during the procedure. Performance of the procedure remains much as others have described.12–14 The technique uses fluoroscopy to aid screw placement. This necessitates a variable radiation dose to the surgeon. The image guidance system can be used to represent the passage of the drill or the screw as it passes through the axis. It must be remembered that the reference frame is attached to the axis and therefore the relative position of the atlas may be misrepresented. For this reason fluoroscopy must continue to be used. It may be possible to decrease radiation exposure by judicious use of the fluoroscope. We recommend its use during placement of the K wire guide. This does not have to be continuous but screening should be reasonably frequent, as the flexible wire may bend and skew its trajectory. Fluoroscopy during screw placement may be even more limited. However care must be taken to avoid advancing the K wire during subsequent drilling, tapping and screwing. The method used for assessing the adequacy of screw placement in this series may be questioned. There was no objective measurement or independent review. This reflects the limitations of a retrospective series. There is, however, only a small margin of Journal of Clinical Neuroscience (2005) 12(1), 62–65
tolerance whereby a screw could be misplaced and not cause a complication. CONCLUSIONS Stereotactic atlantoaxial transarticular fixation is a modification of an already proven technique that offers the potential for improved outcomes by enabling greater pre-operative assessment and planning. It also facilitates an individualised surgical model for pre-operative preparation and practice leading to improved surgical efficiency and safety. In our experience the technique is accessible, safe and accurate. ACKNOWLEDGEMENTS Medtronic Sofamor Danek – Financial support for travel to present at Broome Neurosurgical Society of Australasia meeting, 2002. REFERENCES 1. Madawi AA, Casey AT, Solanki GA, Tuite G, Veres R, Crockard HA. Radiological and anatomical evaluation of the atlantoaxial transarticular screw fixation technique. J Neurosurg 1997; 86(6): 961–968. 2. Papadopoulos SM, Dickman CA, Sonntag VK. Atlantoaxial stabilization in rheumatoid arthritis. J Neurosurg 1991; 74(1): 1–7. 3. Dickman CA, Sonntag VK. Surgical management of atlantoaxial nonunions. J Neurosurg 1995; 83(2): 248–253. 4. Grob D. Surgery in the degenerative cervical spine. Spine 1998; 23(24): 2674–2683. 5. Dickman CA, Sonntag VK, Papadopoulos SM, Hadley MN. The interspinous method of posterior atlantoaxial arthrodesis. J Neurosurg 1991; 74(2): 190–198. 6. Dorfmuller G, Hollerhage HG. Severe intracranial injury from a fall in the halo external fixator. J Orthop Trauma 1992; 6(3): 366–369. 7. Cogo A, Bernardi E, Prandoni P, et al. Acquired risk factors for deep-vein thrombosis in symptomatic outpatients. Arch Intern Med 1994; 154(2): 164–168. 8. Gebremedhin A, Shamebo M. Deep venous thrombosis in a university teaching hospital, Addis Ababa, Ethiopia. East Afr Med J 1998; 75(7): 432–435. 9. Samama MM. An epidemiologic study of risk factors for deep vein thrombosis in medical outpatients: the Sirius study. Arch Intern Med 2000; 160(22): 3415–3420. 10. Ranawat CS, O'Leary P, Pellicci P, Tsairis P, Marchisello P, Dorr L. Cervical spine fusion in rheumatoid arthritis. J Bone Joint Surg Am 1979; 61(7): 1003–1010. 11. Grob D. Atlantoaxial immobilization in rheumatoid arthritis: a prophylactic procedure. Eur Spine J 2000; 9(5): 404–409. 12. Grob D, Jeanneret B, Aebi M et al. Atlantoaxial fusion with transarticular screw fixation. J Bone Joint Surg (Br) 1991; 73: 972–976. 13. Haid Jr RW. C1-C2 transarticular screw fixation: technical aspects. Neurosurgery 2001; 49(1): 71–74. 14. 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, New York 1987; 322–327. 15. Brooks A, Jenkins E. Atlantoaxial arthrodesis by the wedge compression method. J Bone Joint Surg (Am) 1978; 60: 279–284. 16. Gallie W. Fractures and dislocations of the cervical spine. Am J Surg 1939; 46: 495–499. 17. Brockmeyer DL. A bone and cable girth-hitch technique for atlantoaxial fusion in pediatric patients. Technical note. J Neurosurg 2002; 97(3 Suppl): 400–402. 18. Fraser AB, Sen C, Casden AM, Catalano PJ, Post KD. Cervical transdural intramedullary migration of a sublaminar wire. A complication of cervical fixation. Spine 1994; 19(4): 456–459. 19. Blacklock JB. Fracture of a sublaminar stainless steel cable in the upper cervical spine with neurological injury. Case report. J Neurosurg 1994; 81(6): 932–933. 20. Holness RO, Huestis WS, Howes WJ, Langille RA. Posterior stabilization with an interlaminar clamp in cervical injuries: technical note and review of the long term experience with the method. Neurosurgery 1984; 14(3): 318–322. 21. Moskovich R, Crockard HA. Atlantoaxial arthrodesis using interlaminar clamps. An improved technique. Spine 1992; 17(3): 261–267. 22. Goel A, Desai KI, Muzumdar DP. Atlantoaxial fixation using plate and screw method: a report of 160 treated patients. Neurosurgery 2002; 51(6): 1351–1356. 23. Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine 2001; 26(22): 2467–2471.
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28. Coyne T, Fehlings M, Wallace M, Bernstein M, Tator C. C1-2 posterior cervical fusion: Long term evaluation of results and efficacy. Neurosurgery 1995; 37: 688–692. 29. Haid Jr RW, Subach BR, McLaughlin MR, Rodts Jr GE, Wahlig Jr JB. C1-C2 transarticular screw fixation for atlantoaxial instability: a 6-year experience. Neurosurgery 2001; 49(1): 65–68. 30. Kawaguchi Y, Ishihara H, Ohmori K, Kanamori M, Kimura T. Computerassisted Magerl's transarticular screw fixation for atlantoaxial subluxation. J Orthop Sci 2002; 7(1): 131–136. 31. Welch WC, Subach BR, Pollack IF, Jacobs GB. Frameless stereotactic guidance for surgery of the upper cervical spine. Neurosurgery 1997; 40(5): 958–963.
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