- Email: [email protected]
Modified technique of transoral release in one-stage anterior release and posterior reduction for irreducible atlantoaxial dislocation
Journal of Orthopaedic Science 21 (2016) 7e12
Contents lists available at ScienceDirect
Journal of Orthopaedic Science journal homepage: http://www.elsevier.com/locate/jos
Original article
Modified technique of transoral release in one-stage anterior release and posterior reduction for irreducible atlantoaxial dislocation Haoning Ma a, b, Liang Dong a, b, Chuyin Liu b, c, Ping Yi b, Feng Yang b, Xiangsheng Tang b, Mingsheng Tan a, b, * a b c
Graduate School of Peking Union Medical College, 100005, Beijing, China Department of Spine Surgery, China-Japan Friendship Hospital, 100029, Beijing, China Graduate School of Beijing University of Chinese Medicine, 100029, Beijing, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 April 2015 Received in revised form 7 September 2015 Accepted 21 September 2015 Available online 11 December 2015
Background: One-stage anterior release and posterior reduction is one of the most effective methods for irreducible atlantoaxial dislocation. However, the criteria of appropriate tissue release for successful posterior reduction is yet to be confirmed. Hence, an assistant technique using the transoral approach to verify satisfactory release is required. To evaluate the efficacy of the modified technique of transoral release for irreducible atlantoaxial dislocation (IAAD) with patients underwent one-stage anterior release and posterior reduction. Methods: Between January 2009 and June 2014, 23 consecutive patients diagnosed with IAAD free from bony union between the C1eC2 facet joints on reconstructive computed tomography scan underwent one-stage anterior release and posterior reduction after no response to 2 weeks of skull traction. During transoral release, an elevator was used as a lever repeatedly to confirm a 3e5 mm bilateral joint space between the lateral masses of the atlas and axis. The release was accomplished since a 3e5 mm joint space was achieved. After anterior release, posterior reduction and instrumented fusion were subsequently performed. Results: All patients were observed for an average of 18 (range 6e50) months. Nineteen of 23 patients achieved complete reduction while four had an incomplete reduction. Significant differences in pre- and postoperative JOA scores and cervicomedullary angle (CMA) were found. Twenty-one patients presenting with myelopathy had a JOA score of 12.9 at final follow-up, improved from 7.8 before surgery. The mean CMA improved to 143.5 postoperatively from 101.8 preoperatively. Bony fusion was confirmed in all cases under radiologic assessment during follow-up; there were no instrument failures. Conclusion: The modified technique of transoral release provides appropriate criteria for anterior release, to achieve good posterior reduction without excessive tissue release or intraspinal manipulation, proving its value as an assistant technique in one-stage anterior release and posterior reduction for IAAD. © 2015 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
1. Introduction Irreducible atlantoaxial dislocation (IAAD) that cannot be reduced by skull traction has been a longstanding challenge for spine surgeons. In the past, anterior transoral odontoid resection combined with posterior decompression, instrumentation, and in situ craniocervical fusion were usually performed in patients with
* Corresponding author. Department of Spine Surgery, China-Japan Friendship Hospital, 100029, Beijing, China. Tel.: þ86 13911025605; fax: þ86 10 84205011. E-mail address: [email protected] (M. Tan).
IAAD. However, complex surgical manipulations near the medulla oblongata carry a high risk for cerebrospinal fluid leakage and neurological deficits [1]. Recently, several reports have shown that IAAD can be reduced by anterior transoral release if bony fusion is not detected in the facet joints between the atlas and axis by reconstructive CT [2,3]. Combined with posterior fixation and fusion, this procedure provides better correction of swan-neck malformation and avoids odontoid resection [4,5]. However, insufficient release results in unsuccessful posterior reduction, while excessive release leads to intraoperative instability, which may result in spinal cord injury, especially when changing from the supine to prone position. Hence, we defined criteria for successful
http://dx.doi.org/10.1016/j.jos.2015.10.012 0949-2658/© 2015 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
8
H. Ma et al. / Journal of Orthopaedic Science 21 (2016) 7e12
transoral release as elevation of the C1eC2 bilateral lateral mass joint space by 3e5 mm, which is sufficient for reduction via the posterior approach. Therein, we aimed to analyze the feasibility and clinical outcome of this assistant technique.
no reduction was found. Oral examinations were performed to exclude pharyngeal oralis infection; vinegar chlorhexidine (0.02%) was gargled 3e5 times daily for 3 days prior to surgery. Each surgical procedure was performed by the same senior orthopedic surgeon.
2. Material and methods
2.3. Surgical procedure
The study was approved by the ethics review boards of our institutions and was in compliance with the Helsinki Declaration. Due to the retrospective nature of the study, informed consent was waived.
2.3.1. Transoral anterior atlantoaxial joint release Patients were placed in supine position and underwent general anesthesia. Somatosensory-evoked potential (SEP) mapping was used in all cases to monitor spinal cord function. After caudal retraction of the tongue and endotracheal tube, a malleable retractor blade was placed to displace the uvula and soft palate superiorly, to expose the upper posterior oropharynx. Sterilization was performed with povidoneeiodine retractor positioning. The C1 tubercle was palpated to confirm a median incision, which was created on the posterior pharyngeal wall. The bilateral longus coli, longus capitis, and anterior longitudinal ligament were dissected just caudal to the anterior ring of C1. Tissue flaps were carefully separated subperiosteally from the anterior elements of C1eC2, in order to avoid venous plexus hemorrhage. Lateral dissociation was complete when the point where the anterior aspect of the lateral mass of C1 turned posteriolateral was reached; beyond this point, there was a risk of injury to the vertebral artery. The inferior rim of the anterior C1 arch was dissected to expose the base of the odontoid process using a high-speed burr. The anterior joint capsules, the cartilage of the bilateral C1eC2 lateral joints, and even scar tissue of revision surgery or an old fracture were excised. Then, a 10 mm wide elevator was inserted into the left and right joint spaces respectively and the handle of the elevator was rotated as a lever. Successful tissue release was achieved when the joint space between the lateral masses of the atlas and axis elevated to 3e5 mm. Repeated elevation with resection of tissues in front of the C1 lateral mass and around the C1 anterior arch were performed until the joint space reached criteria (Figs. 1, 2).
2.1. Patient selection Between January 2009 and June 2014, clinical data was collected on 23 consecutive patients (14 males and nine females, average age 39.9, range 18e65 years) with IAAD. The following selection criteria were applied: patients with IAAD that could not be reduced by 2 weeks of skull traction; no bony fusion in the C1eC2 facet joints on plain radiograph and CT scan. Exclusion criteria were as follows: deformities of the C1 posterior arch or lateral masses which impeded instrumentation; and fixed atlantoaxial dislocation with C1eC2 fusion. The etiologies of IAAD included: congenital os odontoideum (n ¼ 11), old traumatic dens fracture (n ¼ 6), iatrogenic instability (n ¼ 4), and rheumatoid arthritis (n ¼ 2). Most patients had neck pain and stiffness and limitation of cervical motion. Twenty-one patients presented with myelopathy, including extremity numbness, weakness, and gait disturbance (Table 1). 2.2. Surgery preparation All 23 patients with IAAD were assessed using preoperative cervical radiography, CT, and MRI. Atlantodental intervals (ADIs) in neutral position were measured by X-ray film, Cervicomedullary angles (CMAs) were measured by MRI and neurologic function was assessed using the Japanese Orthopedic Association (JOA) score. According to the clinical classification of atlantoaxial dislocation [6], all patients had no dynamic change of ADI from flexion to extension due to IAAD and underwent 2 weeks of skull traction (8e10 kg) and
2.3.2. Posterior reduction and instrumented fusion Two different techniques were used according to the state of dislocation and bone abnormality. Occipitocervical fusion was
Table 1 Patient demographic and clinical data. Case no.
Sex
Age (yr)
Diagnosis
Surgical protocol
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Male Female Female Male Male Female Male Male Male Male Female Male Male Male Female Female Male Female Male Male Female Female Male
39 31 26 31 65 48 26 18 31 39 54 23 31 44 43 47 65 36 37 49 50 50 35
Iatrogenic instability os odontoideum Old traumatic dens fracture os odontoideum os odontoideum Old traumatic dens fracture os odontoideum Iatrogenic instability os odontoideum os odontoideum Old traumatic dens fracture os odontoideum Old traumatic dens fracture os odontoideum Rheumatoid arthritis Iatrogenic instability iatrogenic instability Old traumatic dens fracture os odontoideum os odontoideum Rheumatoid arthritis os odontoideum Old traumatic dens fracture
ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR
ATR: anterior transoral release; PRIF: posterior reduction and instrumented fusion.
þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ
PRIF(C0eC2) PRIF(C1eC2) PRIF(C0eC2) PRIF(C1eC2) PRIF(C0eC3) PRIF(C1eC3) PRIF(C1eC2) PRIF(C0eC3) PRIF(C0eC2) PRIF(C1eC2) PRIF(C0eC4) PRIF(C1eC2) PRIF(C1eC2) PRIF(C0eC2) PRIF(C1eC2) PRIF(C0eC2) PRIF(C0eC3) PRIF(C1eC2) PRIF(C0eC2) PRIF(C1eC4) PRIF(C0eC2) PRIF(C0eC3) PRIF(C1eC2)
Reduction on radiography Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Partial Complete Complete Complete Partial Complete Partial Complete Complete Complete Partial Complete Complete
H. Ma et al. / Journal of Orthopaedic Science 21 (2016) 7e12
9
Fig. 1. Illustration of modified anterior transoral release and posterior reduction: (a) the atlas slopes anteriorly and inferiorly in IAAD. Tissues impeding reduction were dissected carefully. (b, c) A 10-mm elevator was inserted into the left and right joint spaces, respectively. Repeated elevation with resection of the soft tissue in front of the C1 lateral mass and around the C1 anterior arch were performed until a 3e5 mm joint space was achieved. (d) Reduction was performed with pull-out by a posterior screw and rod system.
recommended for patients with osteosynthesis of the C0e1 joints due to congenital deformities and trauma, and the inability to distract the joint space over 3 mm. Otherwise, atlantoaxial fusion was performed routinely. The aforementioned two procedures have been previously described in the literature [7,8]. During C1-pedicle screw placement, the vertebral artery and the vein plexus between C1 and C2 superiorly and inferiorly to the C1 posterior arch were exposed subperiosteally for screw placement. The entry point at the C1 posterior arch was approximately 18e22 mm lateral to the midline. The trajectory was approximately 10 in the medial direction and 5 in the cephalad direction. The pilot hole could be created by a high-speed burr and deepened with a drill. In case of penetration, a probe was used to explore all the walls of the trajectory. When the direction of the trajectory was confirmed by fluoroscopy, 3.5 mm screws were implanted with unicortical purchase after tapping the trajectory. All C2 screws were inserted via the C2 pedicle. When the rods were fixed to the screws with good tissue release, the pull-out strength could reduce the atlas superiorly and posteriorly. Finally, an autologous iliac crest graft was implanted. 2.3.3. Postoperative management and follow-up The endotracheal tube and nasogastric feeding tube were maintained until tongue swelling subsided. All patients were
maintained in a rigid cervical collar for 6 weeks or more based on the incorporation of the bone graft. Bone fusion was defined as no translucent line or absorption on CT scans, with no instability on dynamic radiographs; complete reduction was defined as an atlanto-dental interval (ADI) of less than or equal to 3 mm, partial reduction was defined as an ADI of less than or equal to 5 mm but more than 3 mm. The JOA scores collected at the last follow-up visit were compared with preoperative JOA scores, to evaluate neurologic functional improvement. CMA was also measured by MRI when bony fusion occurred. 2.3.4. Statistical analysis Statistical analysis was performed using SPSS statistical software (version 19.0.1; SPSS, Inc., Chicago, IL, USA). Pre- and postoperative scores and angles were compared using the paired t-test. A p-value of less than 0.05 was considered statistically significant. 3. Results Surgeries were completed without intraoperative complications and satisfactory screw position was confirmed in all 23 patients. All patients were followed up for an average of 18 (range 6e50) months. During follow up, radiographic fusion was confirmed in all
Fig. 2. (a, b) Surgical procedure and the elevated C1 lateral mass with enough joint space (picture taken by an endoscopic camera).
10
H. Ma et al. / Journal of Orthopaedic Science 21 (2016) 7e12
Table 2 Patient outcome data. Parameters
Preoperation
Postoperation
t Value
p Value
JOA score (n ¼ 21) upper limb movement lower limb movement sensory bladder function ADI (n ¼ 23) CMA (n ¼ 23)
7.8 ± 2.4 2.8 ± 0.6 1.7 ± 0.9 2.4 ± 0.3 2.2 ± 0.4 (7.41 ± 3.23) mm （101.8 ± 23.6）
12.9 ± 2.8 3.2 ± 0.2 2.4 ± 0.5 4.4 ± 0.4 2.5 ± 0.3 (2.58 ± 1.64) mm （143.5 ± 12.6）
6.337 2.898 3.116 18.33 2.75 6.394 7.143
<0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01
JOA: Japanese Orthopedic Association; ADI: atlantodental interval; CMA: cervicomedullary angle.
patients without loss of reduction. Nineteen of 23 patients had complete reduction and four had incomplete reduction based on CT scan and MRI findings at the final follow up visit. The mean CMA improved from 101.8 to 143.5 (increase of 41.7 ); 21 patients' CMA improved to normal but two patients had a lower than normal CMA due to incomplete reduction. Twenty-one patients had an improvement in their JOA (17) score from 7.8 before surgery to 12.9 at final follow-up, with no postoperative neurologic deterioration (Table 2, Fig. 3). While no patients developed pharyngeal wall infection, one patient had a superficial infection related to the posterior approach, which was noted 2 months later. This healed after intermittent debridement and 3 weeks of antibiotics. Two patients had neck pain which remained unchanged at the final follow-up visit. 4. Discussion IAAD, for which there is a lack of consensus regarding the concept and surgical management, usually presents for dislocations that cannot be reduced by cervical traction and which do not achieve bony union in the facet joints between the atlas and axis [2,3]. IAAD can result from trauma, inflammation, and congenital
abnormalities. With the atlas sloped anteriorly and inferiorly from the axis, basilar invagination may occur with ventral compression of the spinal cord in IAAD. In the past, posterior suboccipital craniectomy or transoral odontoidectomy combined with in situ fixation were performed for IAAD patients. However, this protocol has several disadvantages. For example, the posterior approach requires head flexion during surgery to achieve exposure, which increases the risk for spinal cord injury, especially when the posterior arch severely compresses the cord. Additionally, without the dislocation reduced, restoration of cervical spine alignment and improvement of vertebral artery blood supply may not be achieved [5]. Hence, one stage anterior release and posterior fixation and fusion was established to treat IAAD [4,9,10]. The advantages of the combined anterior and posterior approach can be summarized as follows [8]: 1) with muscle contracture and scar tissue development, the impinging pathology that accompanies chronic instability can only be accessed via the ventral route; 2) the patient is in the supine position with the neck in extension, as opposed to flexion, thus decreasing the angulation of the brainstem during surgery; 3) the anterior approach was performed through the avascular median pharyngeal raphe and through the clivus. When the formerly irreducible C1eC2 becomes reducible, a sufficient
Fig. 3. Case 8, 18-year-old male diagnosed with iatrogenic upper cervical instability with revision surgery. (a) Sagittal CT scan showed absence of the foramen magnum and C1eC2 posterior lamina due to previous surgery. C1eC2 dislocation was noted with penetration of the C2 vertebral body and odontoid process into the cranium by 25 mm. (b) Sagittal MRI showed ventral compression of the spinal cord and a reduced CMA of 76 . (c) One month after revision surgery, lateral radiographs showed reduction of C1 and the odontoid process out of the cranium and the swan-neck deformity was corrected. (d) CT sagittal films one month after revision surgery. (e) MRI sagittal T2-weighted films one month after revision surgery showed ventral medullary decompression with CMA recovery to normal, approximately 148 . (f) Twelve months after revision surgery, lateral radiographs showed no instrument loosening, no loss of reduction, and evidence of bony fusion at the craniocervical region. (g, h) At 50 months' follow-up, lateral radiographs and CT sagittal scan showed bony union and no loss of reduction.
H. Ma et al. / Journal of Orthopaedic Science 21 (2016) 7e12
sagittal canal diameter can be achieved and the alignment of the cervical spine can be corrected. Combined with rigid internal fixation and bony grafts, IAAD can be treated with a satisfactory outcome. Of note, when bony fusion of C1/2 showed in preoperative reconstructive CT of IAAD, reduction seems to be difficult to achieve through anterior soft tissue release. In this situation, decompression of foramen magnum and/or resection of posterior arch of atlas combined with occipitocervical instrumented fusion are priority. Anterior release is of key importance for combined anterior and posterior approach surgery. Insufficient release results in incomplete reduction; however, excessive removal of muscle or bony structures will cause instability and an increased risk for the morbidity of cerebrospinal fluid leakage or spinal cord injury [11,12]. In recent years, researchers focused on the combined anterior and posterior approach. The point at which complete or partial reduction can be achieved with adequate flexibility between C1 and C2 is shown during surgery and seems obvious [13e15]. However, few studies have provided the criteria for good anterior release or the details of manipulation. Only Wang et al. [16] pointed out that successful release was achieved when the dens could be levered up to contact the C1 anterior arch by a curette, which also indicated anatomic reduction of an atlantoaxial dislocation (AAD). This reduction technique should be used after excising the apical and alar ligaments, and when the curette was levering near the compressed spinal cord. This technique calls for cautious manipulation and has potential risks for intraoperative spinal cord injury. Based on our clinical experience, we defined criteria for successful transoral release as elevation of the C1eC2 bilateral lateral mass joint space by 3e5 mm, which is sufficient for reduction via the posterior approach. During anterior release, when the bilateral facet joints were exposed by excising the joint capsules and cartilages, a 10 mm wide elevator was inserted into the left and right facet joint spaces respectively and the handle of the elevator was rotated and used as a lever to confirm a 3e5 mm joint space. If little motion was found, further release was added by excising the fibrous tissues and contractured muscles until adequate flexibility of C1 was achieved. According to previous research [17,18], the sagittal diameter of the atlas was approximately 30 mm, the neutral zone for flexion and extension of C1eC2 was 3.2 , and the extension range of motion of C1eC2 was 10.9 . When the C1 lateral mass was levered up 3e5 mm, the atlas extended by 5.73 e9.56 (with the tuberculum posterius atlantis as the center in a circle and the sagittal diameter of the atlas as the radius). The extension of the atlas by a lever covers the neutral zone of flexion/extension and almost reaches the maximum extension range of motion of C1eC2. Without an accurate morphometric study, a 5 mm width means adequate flexibility of C1eC2 as deduced by the speculation above. Partial reduction were obtained in 4 of 23 patients (17.4%), because of the same including standard and small sample size, no significant differences are found between complete and partial reduction cases. Without intra-spinal canal manipulations, there may be still soft tissues and scar tissues within the spinal canal which impeded reducing C1 to anatomical position through posterior approach. This assistant technique provides advantages for combined anterior and posterior surgery as follows: (1) when C1/2 has adequate flexibility matching the aforementioned criterion, complete reduction can be achieved in most cases and there is no need to dissect the odontoid process, which reduces the morbidity of dura mater tearing or spinal cord injury. (2) There is no need for excessive removal of tissue, in case of iatrogenic instability or loss of necessary structure for rigid fixation. (3) The reduction is reached sequentially by instruments' pull strength via the posterior approach. (4) Realignment of the atlantoaxial joint can prevent subaxial spine degeneration due to longstanding C1eC2 dislocation.
11
Several instrumentations for fusion have been described in the literature and the fixation method is still a matter of debate. Yin et al. [19] used a novel transoral atlantoaxial reduction plate (TARP) system designed to facilitate a one-stage anterior operation capable of simultaneously decompressing the ventral spinal cord, as well as reducing and fixing the atlantoaxial segment. The successful use of TARP was reported for several situations, including basilar invagination, odontoid fracture, and revision surgery [20,21]. However, anterior instruments placed on the pharyngeal wall predisposes to local infection; as a result, anterior screw loosening has been reported [22]. Posterior fixation with a C1eC2 pedicle screw is becoming popular because there is more pullout strength, less irritation of the C2 nerve root and venous plexus, and a more visible entry point [23e25]. In addition, several studies found that C1eC2 pedicle screw fixation with more cortical purchase and a longer screw trajectory had higher biomechanical stiffness than C1 lateral mass-C2 pedicle screw fixation [26,27]. Moreover, with the pedicle exposure technique, the screw can be inserted safely in the C1 posterior arch measuring less than 4 mm. Although several patients finally underwent posterior occipitocervical fusion, reduction was achieved by pedicle screws' pull strength. Of note, the endoscopically assisted anterior approach to the craniovertebral junction has been frequently reported [11,13,28]. Under fluoroscopic guidance, anterior release will be more invasive and safer. The criteria for a good release with this modified technique of anterior release can be used under endoscopy as well. 5. Conclusion Under the condition of no osteosynthesis around the C1eC2 facet joints in IAAD, complete C1eC2 reduction can be achieved by our method. If a 3e5 mm joint space is achieved during anterior transoral release by levering the atlas upwards, most factors from the vertebral anterior aspect which impede C1eC2 reduction are removed. C1eC2 can be reduced sequentially by the posterior approach. Our method requires further investigation and possible clinical application. Conflict of interest The authors declare that they have no conflict of interest. Acknowledgment This research was supported by the National Natural Science Foundation of China (81173423). References [1] Jain VK, Behari S, Banerji D, Bhargava V, Chhabra DK. Transoral decompression for craniovertebral osseous anomalies: perioperative management dilemmas. Neurol India 1999;47:188e95. [2] Xu J, Yin Q, Xia H, Wu Z, Ma X, Zhang K, Wang Z, Yang J, Ai F, Wang J, Liu J, Mai X. New clinical classification system for atlantoaxial dislocation. Orthopedics 2013;36:e95e100. [3] Wang S, Wang C, Yan M, Zhou H, Dang G. Novel surgical classification and treatment strategy for atlantoaxial dislocations. Spine 2013;38:E1348e56. Phila Pa 1976. [4] Hao D, He B, Zheng Y, Zhang Z. Single stage anterior release and sequential posterior fusion for irreducible atlantoaxial dislocation. J Spinal Disord Tech 2013. http://dx.doi.org/10.1097/BSD.0b013e31826be885. [5] Tan M, Jiang X, Yi P, Yang F, Tang X, Hao Q, Zhang G. Revision surgery of irreducible atlantoaxial dislocation: a retrospective study of 16 cases. Eur Spine J 2011;20:2187e94. [6] Tan M, Zhang G, Wang W, Tan Y, Zou H, Yi P, Jiang X, Wei H, Yang F. The pilot study of clinical classification for atlantoaxial dislocation. Chin J Spine Spinal Cord 2007;17:111e5 [In Chinese]. [7] Resnick DK. Benzel EC.C1-C2 pedicle screw fixation with rigid cantilever beam construct: case report and technical note. Neurosurgery 2002;50:426e8.
12
H. Ma et al. / Journal of Orthopaedic Science 21 (2016) 7e12
[8] Zileli M, Cagli S. Combined anterior and posterior approach for managing basilar invagination associated with type I Chiari malformation. J Spinal Disord Tech 2002;15:284e9. [9] Goel A, Kulkarni AG, Sharma P. Reduction of fixed atlantoaxial dislocation in 24 cases: technical note. J Neurosurg Spine 2005;2:505e9. [10] Subin B, Liu JF, Marshall GJ, Huang HY, Ou JH, Xu GZ. Transoral anterior decompression and fusion of chronic irreducible atlantoaxial dislocation with spinal cord compression. Spine 1995;20:1233e40. Phila Pa 1976. [11] Lu G, Passias PG, Li G, Kozanek M, Rehak L, Wood KB, Li G, Deng Y. Endoscopically assisted anterior release and reduction through anterolateral retropharyngeal approach for fixed atlantoaxial dislocation. Spine 2010;35: 544e51. Phila Pa 1976. [12] Scalici E, Indorato F, Portelli F, Savi T, Maresi E, Busardo FP. A fatal iatrogenic right vertebral injury after transoral odontoidectomy and posterior cervical stabilization for a type II odontoid fracture. J Forensic Leg Med 2014;22:41e4. [13] Ma H, Lv G, Wang B, Kuang L, Wang X. Endoscopic transcervical anterior release and posterior fixation in the treatment of irreducible vertical atlantoaxial dislocation. Eur Spine J 2014;23:1749e54. [14] Liu T, Li F, Xiong W, Du X, Fang Z, Shang H, Chen A. Video-assisted anterior transcervical approach for the reduction of irreducible atlantoaxial dislocation. Spine 2010;35:1495e501. Phila Pa 1976. [15] Lee SH, Park K, Kong DS, Kim ES, Eoh W. Long-term follow up of transoral anterior decompression and posterior fusion for irreducible bony compression of the craniovertebral junction. J Clin Neurosci 2010;17:455e9. [16] Wang C, Yan M, Zhou HT, Wang SL, Dang GT. Open reduction of irreducible atlantoaxial dislocation by transoral anterior atlantoaxial release and posterior internal fixation. Spine 2006;31:E306e13. Phila Pa 1976. [17] Tan M, Wang H, Wang Y, Zhang G, Yi P, Li Z, Wei H, Yang F. Morphometric evaluation of screw fixation in atlas via posterior arch and lateral mass. Spine 2003;28:888e95. Phila Pa 1976. [18] Panjabi M, Dvorak J, Duranceau J, Yamamoto I, Gerber M, Rauschning W, Bueff HU. Three-dimensional movements of the upper cervical spine. Spine 1988;13:726e30. Phila Pa 1976.
[19] Yin Q, Ai F, Zhang K, Chang Y, Xia H, Wu Z, Quan R, Mai X, Liu J. Irreducible anterior atlantoaxial dislocation: one-stage treatment with a transoral atlantoaxial reduction plate fixation and fusion. Report of 5 cases and review of the literature. Spine 2005;30:E375e81. Phila Pa 1976. [20] Yang J, Ma X, Xia H, Wu Z, Ai F, Yin Q. Transoral anterior revision surgeries for basilar invagination with irreducible atlantoaxial dislocation after posterior decompression: a retrospective study of 30 cases. Eur Spine J 2014;23:1099e108. [21] Xia H, Yin Q, Ai F, Ma X, Wang J, Wu Z, Zhang K, Liu J, Xu J. Treatment of basilar invagination with atlantoaxial dislocation: atlantoaxial joint distraction and fixation with transoral atlantoaxial reduction plate (TARP) without odontoidectomy. Eur Spine J 2014;23:1648e55. [22] Kerschbaumer F, Kandziora F, Klein C, Mittlmeier T, Starker M. Transoral decompression, anterior plate fixation, and posterior wire fusion for irreducible atlantoaxial kyphosis in rheumatoid arthritis. Spine 2000;25: 2708e15. Phila Pa 1976. [23] Lee SH, Kim ES, Eoh W. Modified C1 lateral mass screw insertion using a high entry point to avoid postoperative occipital neuralgia. J Clin Neurosci 2013;20:162e7. [24] Yeom JS, Kafle D, Nguyen NQ, Noh W, Park KW, Chang BS, Lee CK, Riew KD. Routine insertion of the lateral mass screw via the posterior arch for C1 fixation: feasibility and related complications. Spine J 2012;12:476e83. [25] Thomas JA, Tredway T, Fessler RG, Sandhu FA. An alternate method for placement of C-1 screws. J Neurosurg Spine 2010;12:337e41. [26] Zarro CM, Ludwig SC, Hsieh AH, Seal CN, Gelb DE. Biomechanical comparison of the pullout strengths of C1 lateral mass screws and C1 posterior arch screws. Spine J 2013;13:1892e6. [27] Ma XY, Yin QS, Wu ZH, Xia H, Liu JF, Xiang M, Zhao WD, Zhong SZ. C1 pedicle screws versus C1 lateral mass screws: comparisons of pullout strengths and biomechanical stabilities. Spine 2009;34:371e7. Phila Pa 1976. [28] Gkekas N, Primikiris P, Sfikas S, Vyziotis A, Georgakoulias N. Endoscopic transoral decompression of cervicomedullary junction: a rational alternative to the traditional microscopic transoral approach. World Neurosurg 2014;82: e573e575.
Contents lists available at ScienceDirect
Journal of Orthopaedic Science journal homepage: http://www.elsevier.com/locate/jos
Original article
Modified technique of transoral release in one-stage anterior release and posterior reduction for irreducible atlantoaxial dislocation Haoning Ma a, b, Liang Dong a, b, Chuyin Liu b, c, Ping Yi b, Feng Yang b, Xiangsheng Tang b, Mingsheng Tan a, b, * a b c
Graduate School of Peking Union Medical College, 100005, Beijing, China Department of Spine Surgery, China-Japan Friendship Hospital, 100029, Beijing, China Graduate School of Beijing University of Chinese Medicine, 100029, Beijing, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 April 2015 Received in revised form 7 September 2015 Accepted 21 September 2015 Available online 11 December 2015
Background: One-stage anterior release and posterior reduction is one of the most effective methods for irreducible atlantoaxial dislocation. However, the criteria of appropriate tissue release for successful posterior reduction is yet to be confirmed. Hence, an assistant technique using the transoral approach to verify satisfactory release is required. To evaluate the efficacy of the modified technique of transoral release for irreducible atlantoaxial dislocation (IAAD) with patients underwent one-stage anterior release and posterior reduction. Methods: Between January 2009 and June 2014, 23 consecutive patients diagnosed with IAAD free from bony union between the C1eC2 facet joints on reconstructive computed tomography scan underwent one-stage anterior release and posterior reduction after no response to 2 weeks of skull traction. During transoral release, an elevator was used as a lever repeatedly to confirm a 3e5 mm bilateral joint space between the lateral masses of the atlas and axis. The release was accomplished since a 3e5 mm joint space was achieved. After anterior release, posterior reduction and instrumented fusion were subsequently performed. Results: All patients were observed for an average of 18 (range 6e50) months. Nineteen of 23 patients achieved complete reduction while four had an incomplete reduction. Significant differences in pre- and postoperative JOA scores and cervicomedullary angle (CMA) were found. Twenty-one patients presenting with myelopathy had a JOA score of 12.9 at final follow-up, improved from 7.8 before surgery. The mean CMA improved to 143.5 postoperatively from 101.8 preoperatively. Bony fusion was confirmed in all cases under radiologic assessment during follow-up; there were no instrument failures. Conclusion: The modified technique of transoral release provides appropriate criteria for anterior release, to achieve good posterior reduction without excessive tissue release or intraspinal manipulation, proving its value as an assistant technique in one-stage anterior release and posterior reduction for IAAD. © 2015 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
1. Introduction Irreducible atlantoaxial dislocation (IAAD) that cannot be reduced by skull traction has been a longstanding challenge for spine surgeons. In the past, anterior transoral odontoid resection combined with posterior decompression, instrumentation, and in situ craniocervical fusion were usually performed in patients with
* Corresponding author. Department of Spine Surgery, China-Japan Friendship Hospital, 100029, Beijing, China. Tel.: þ86 13911025605; fax: þ86 10 84205011. E-mail address: [email protected] (M. Tan).
IAAD. However, complex surgical manipulations near the medulla oblongata carry a high risk for cerebrospinal fluid leakage and neurological deficits [1]. Recently, several reports have shown that IAAD can be reduced by anterior transoral release if bony fusion is not detected in the facet joints between the atlas and axis by reconstructive CT [2,3]. Combined with posterior fixation and fusion, this procedure provides better correction of swan-neck malformation and avoids odontoid resection [4,5]. However, insufficient release results in unsuccessful posterior reduction, while excessive release leads to intraoperative instability, which may result in spinal cord injury, especially when changing from the supine to prone position. Hence, we defined criteria for successful
http://dx.doi.org/10.1016/j.jos.2015.10.012 0949-2658/© 2015 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
8
H. Ma et al. / Journal of Orthopaedic Science 21 (2016) 7e12
transoral release as elevation of the C1eC2 bilateral lateral mass joint space by 3e5 mm, which is sufficient for reduction via the posterior approach. Therein, we aimed to analyze the feasibility and clinical outcome of this assistant technique.
no reduction was found. Oral examinations were performed to exclude pharyngeal oralis infection; vinegar chlorhexidine (0.02%) was gargled 3e5 times daily for 3 days prior to surgery. Each surgical procedure was performed by the same senior orthopedic surgeon.
2. Material and methods
2.3. Surgical procedure
The study was approved by the ethics review boards of our institutions and was in compliance with the Helsinki Declaration. Due to the retrospective nature of the study, informed consent was waived.
2.3.1. Transoral anterior atlantoaxial joint release Patients were placed in supine position and underwent general anesthesia. Somatosensory-evoked potential (SEP) mapping was used in all cases to monitor spinal cord function. After caudal retraction of the tongue and endotracheal tube, a malleable retractor blade was placed to displace the uvula and soft palate superiorly, to expose the upper posterior oropharynx. Sterilization was performed with povidoneeiodine retractor positioning. The C1 tubercle was palpated to confirm a median incision, which was created on the posterior pharyngeal wall. The bilateral longus coli, longus capitis, and anterior longitudinal ligament were dissected just caudal to the anterior ring of C1. Tissue flaps were carefully separated subperiosteally from the anterior elements of C1eC2, in order to avoid venous plexus hemorrhage. Lateral dissociation was complete when the point where the anterior aspect of the lateral mass of C1 turned posteriolateral was reached; beyond this point, there was a risk of injury to the vertebral artery. The inferior rim of the anterior C1 arch was dissected to expose the base of the odontoid process using a high-speed burr. The anterior joint capsules, the cartilage of the bilateral C1eC2 lateral joints, and even scar tissue of revision surgery or an old fracture were excised. Then, a 10 mm wide elevator was inserted into the left and right joint spaces respectively and the handle of the elevator was rotated as a lever. Successful tissue release was achieved when the joint space between the lateral masses of the atlas and axis elevated to 3e5 mm. Repeated elevation with resection of tissues in front of the C1 lateral mass and around the C1 anterior arch were performed until the joint space reached criteria (Figs. 1, 2).
2.1. Patient selection Between January 2009 and June 2014, clinical data was collected on 23 consecutive patients (14 males and nine females, average age 39.9, range 18e65 years) with IAAD. The following selection criteria were applied: patients with IAAD that could not be reduced by 2 weeks of skull traction; no bony fusion in the C1eC2 facet joints on plain radiograph and CT scan. Exclusion criteria were as follows: deformities of the C1 posterior arch or lateral masses which impeded instrumentation; and fixed atlantoaxial dislocation with C1eC2 fusion. The etiologies of IAAD included: congenital os odontoideum (n ¼ 11), old traumatic dens fracture (n ¼ 6), iatrogenic instability (n ¼ 4), and rheumatoid arthritis (n ¼ 2). Most patients had neck pain and stiffness and limitation of cervical motion. Twenty-one patients presented with myelopathy, including extremity numbness, weakness, and gait disturbance (Table 1). 2.2. Surgery preparation All 23 patients with IAAD were assessed using preoperative cervical radiography, CT, and MRI. Atlantodental intervals (ADIs) in neutral position were measured by X-ray film, Cervicomedullary angles (CMAs) were measured by MRI and neurologic function was assessed using the Japanese Orthopedic Association (JOA) score. According to the clinical classification of atlantoaxial dislocation [6], all patients had no dynamic change of ADI from flexion to extension due to IAAD and underwent 2 weeks of skull traction (8e10 kg) and
2.3.2. Posterior reduction and instrumented fusion Two different techniques were used according to the state of dislocation and bone abnormality. Occipitocervical fusion was
Table 1 Patient demographic and clinical data. Case no.
Sex
Age (yr)
Diagnosis
Surgical protocol
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Male Female Female Male Male Female Male Male Male Male Female Male Male Male Female Female Male Female Male Male Female Female Male
39 31 26 31 65 48 26 18 31 39 54 23 31 44 43 47 65 36 37 49 50 50 35
Iatrogenic instability os odontoideum Old traumatic dens fracture os odontoideum os odontoideum Old traumatic dens fracture os odontoideum Iatrogenic instability os odontoideum os odontoideum Old traumatic dens fracture os odontoideum Old traumatic dens fracture os odontoideum Rheumatoid arthritis Iatrogenic instability iatrogenic instability Old traumatic dens fracture os odontoideum os odontoideum Rheumatoid arthritis os odontoideum Old traumatic dens fracture
ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR ATR
ATR: anterior transoral release; PRIF: posterior reduction and instrumented fusion.
þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ
PRIF(C0eC2) PRIF(C1eC2) PRIF(C0eC2) PRIF(C1eC2) PRIF(C0eC3) PRIF(C1eC3) PRIF(C1eC2) PRIF(C0eC3) PRIF(C0eC2) PRIF(C1eC2) PRIF(C0eC4) PRIF(C1eC2) PRIF(C1eC2) PRIF(C0eC2) PRIF(C1eC2) PRIF(C0eC2) PRIF(C0eC3) PRIF(C1eC2) PRIF(C0eC2) PRIF(C1eC4) PRIF(C0eC2) PRIF(C0eC3) PRIF(C1eC2)
Reduction on radiography Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Partial Complete Complete Complete Partial Complete Partial Complete Complete Complete Partial Complete Complete
H. Ma et al. / Journal of Orthopaedic Science 21 (2016) 7e12
9
Fig. 1. Illustration of modified anterior transoral release and posterior reduction: (a) the atlas slopes anteriorly and inferiorly in IAAD. Tissues impeding reduction were dissected carefully. (b, c) A 10-mm elevator was inserted into the left and right joint spaces, respectively. Repeated elevation with resection of the soft tissue in front of the C1 lateral mass and around the C1 anterior arch were performed until a 3e5 mm joint space was achieved. (d) Reduction was performed with pull-out by a posterior screw and rod system.
recommended for patients with osteosynthesis of the C0e1 joints due to congenital deformities and trauma, and the inability to distract the joint space over 3 mm. Otherwise, atlantoaxial fusion was performed routinely. The aforementioned two procedures have been previously described in the literature [7,8]. During C1-pedicle screw placement, the vertebral artery and the vein plexus between C1 and C2 superiorly and inferiorly to the C1 posterior arch were exposed subperiosteally for screw placement. The entry point at the C1 posterior arch was approximately 18e22 mm lateral to the midline. The trajectory was approximately 10 in the medial direction and 5 in the cephalad direction. The pilot hole could be created by a high-speed burr and deepened with a drill. In case of penetration, a probe was used to explore all the walls of the trajectory. When the direction of the trajectory was confirmed by fluoroscopy, 3.5 mm screws were implanted with unicortical purchase after tapping the trajectory. All C2 screws were inserted via the C2 pedicle. When the rods were fixed to the screws with good tissue release, the pull-out strength could reduce the atlas superiorly and posteriorly. Finally, an autologous iliac crest graft was implanted. 2.3.3. Postoperative management and follow-up The endotracheal tube and nasogastric feeding tube were maintained until tongue swelling subsided. All patients were
maintained in a rigid cervical collar for 6 weeks or more based on the incorporation of the bone graft. Bone fusion was defined as no translucent line or absorption on CT scans, with no instability on dynamic radiographs; complete reduction was defined as an atlanto-dental interval (ADI) of less than or equal to 3 mm, partial reduction was defined as an ADI of less than or equal to 5 mm but more than 3 mm. The JOA scores collected at the last follow-up visit were compared with preoperative JOA scores, to evaluate neurologic functional improvement. CMA was also measured by MRI when bony fusion occurred. 2.3.4. Statistical analysis Statistical analysis was performed using SPSS statistical software (version 19.0.1; SPSS, Inc., Chicago, IL, USA). Pre- and postoperative scores and angles were compared using the paired t-test. A p-value of less than 0.05 was considered statistically significant. 3. Results Surgeries were completed without intraoperative complications and satisfactory screw position was confirmed in all 23 patients. All patients were followed up for an average of 18 (range 6e50) months. During follow up, radiographic fusion was confirmed in all
Fig. 2. (a, b) Surgical procedure and the elevated C1 lateral mass with enough joint space (picture taken by an endoscopic camera).
10
H. Ma et al. / Journal of Orthopaedic Science 21 (2016) 7e12
Table 2 Patient outcome data. Parameters
Preoperation
Postoperation
t Value
p Value
JOA score (n ¼ 21) upper limb movement lower limb movement sensory bladder function ADI (n ¼ 23) CMA (n ¼ 23)
7.8 ± 2.4 2.8 ± 0.6 1.7 ± 0.9 2.4 ± 0.3 2.2 ± 0.4 (7.41 ± 3.23) mm （101.8 ± 23.6）
12.9 ± 2.8 3.2 ± 0.2 2.4 ± 0.5 4.4 ± 0.4 2.5 ± 0.3 (2.58 ± 1.64) mm （143.5 ± 12.6）
6.337 2.898 3.116 18.33 2.75 6.394 7.143
<0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01
JOA: Japanese Orthopedic Association; ADI: atlantodental interval; CMA: cervicomedullary angle.
patients without loss of reduction. Nineteen of 23 patients had complete reduction and four had incomplete reduction based on CT scan and MRI findings at the final follow up visit. The mean CMA improved from 101.8 to 143.5 (increase of 41.7 ); 21 patients' CMA improved to normal but two patients had a lower than normal CMA due to incomplete reduction. Twenty-one patients had an improvement in their JOA (17) score from 7.8 before surgery to 12.9 at final follow-up, with no postoperative neurologic deterioration (Table 2, Fig. 3). While no patients developed pharyngeal wall infection, one patient had a superficial infection related to the posterior approach, which was noted 2 months later. This healed after intermittent debridement and 3 weeks of antibiotics. Two patients had neck pain which remained unchanged at the final follow-up visit. 4. Discussion IAAD, for which there is a lack of consensus regarding the concept and surgical management, usually presents for dislocations that cannot be reduced by cervical traction and which do not achieve bony union in the facet joints between the atlas and axis [2,3]. IAAD can result from trauma, inflammation, and congenital
abnormalities. With the atlas sloped anteriorly and inferiorly from the axis, basilar invagination may occur with ventral compression of the spinal cord in IAAD. In the past, posterior suboccipital craniectomy or transoral odontoidectomy combined with in situ fixation were performed for IAAD patients. However, this protocol has several disadvantages. For example, the posterior approach requires head flexion during surgery to achieve exposure, which increases the risk for spinal cord injury, especially when the posterior arch severely compresses the cord. Additionally, without the dislocation reduced, restoration of cervical spine alignment and improvement of vertebral artery blood supply may not be achieved [5]. Hence, one stage anterior release and posterior fixation and fusion was established to treat IAAD [4,9,10]. The advantages of the combined anterior and posterior approach can be summarized as follows [8]: 1) with muscle contracture and scar tissue development, the impinging pathology that accompanies chronic instability can only be accessed via the ventral route; 2) the patient is in the supine position with the neck in extension, as opposed to flexion, thus decreasing the angulation of the brainstem during surgery; 3) the anterior approach was performed through the avascular median pharyngeal raphe and through the clivus. When the formerly irreducible C1eC2 becomes reducible, a sufficient
Fig. 3. Case 8, 18-year-old male diagnosed with iatrogenic upper cervical instability with revision surgery. (a) Sagittal CT scan showed absence of the foramen magnum and C1eC2 posterior lamina due to previous surgery. C1eC2 dislocation was noted with penetration of the C2 vertebral body and odontoid process into the cranium by 25 mm. (b) Sagittal MRI showed ventral compression of the spinal cord and a reduced CMA of 76 . (c) One month after revision surgery, lateral radiographs showed reduction of C1 and the odontoid process out of the cranium and the swan-neck deformity was corrected. (d) CT sagittal films one month after revision surgery. (e) MRI sagittal T2-weighted films one month after revision surgery showed ventral medullary decompression with CMA recovery to normal, approximately 148 . (f) Twelve months after revision surgery, lateral radiographs showed no instrument loosening, no loss of reduction, and evidence of bony fusion at the craniocervical region. (g, h) At 50 months' follow-up, lateral radiographs and CT sagittal scan showed bony union and no loss of reduction.
H. Ma et al. / Journal of Orthopaedic Science 21 (2016) 7e12
sagittal canal diameter can be achieved and the alignment of the cervical spine can be corrected. Combined with rigid internal fixation and bony grafts, IAAD can be treated with a satisfactory outcome. Of note, when bony fusion of C1/2 showed in preoperative reconstructive CT of IAAD, reduction seems to be difficult to achieve through anterior soft tissue release. In this situation, decompression of foramen magnum and/or resection of posterior arch of atlas combined with occipitocervical instrumented fusion are priority. Anterior release is of key importance for combined anterior and posterior approach surgery. Insufficient release results in incomplete reduction; however, excessive removal of muscle or bony structures will cause instability and an increased risk for the morbidity of cerebrospinal fluid leakage or spinal cord injury [11,12]. In recent years, researchers focused on the combined anterior and posterior approach. The point at which complete or partial reduction can be achieved with adequate flexibility between C1 and C2 is shown during surgery and seems obvious [13e15]. However, few studies have provided the criteria for good anterior release or the details of manipulation. Only Wang et al. [16] pointed out that successful release was achieved when the dens could be levered up to contact the C1 anterior arch by a curette, which also indicated anatomic reduction of an atlantoaxial dislocation (AAD). This reduction technique should be used after excising the apical and alar ligaments, and when the curette was levering near the compressed spinal cord. This technique calls for cautious manipulation and has potential risks for intraoperative spinal cord injury. Based on our clinical experience, we defined criteria for successful transoral release as elevation of the C1eC2 bilateral lateral mass joint space by 3e5 mm, which is sufficient for reduction via the posterior approach. During anterior release, when the bilateral facet joints were exposed by excising the joint capsules and cartilages, a 10 mm wide elevator was inserted into the left and right facet joint spaces respectively and the handle of the elevator was rotated and used as a lever to confirm a 3e5 mm joint space. If little motion was found, further release was added by excising the fibrous tissues and contractured muscles until adequate flexibility of C1 was achieved. According to previous research [17,18], the sagittal diameter of the atlas was approximately 30 mm, the neutral zone for flexion and extension of C1eC2 was 3.2 , and the extension range of motion of C1eC2 was 10.9 . When the C1 lateral mass was levered up 3e5 mm, the atlas extended by 5.73 e9.56 (with the tuberculum posterius atlantis as the center in a circle and the sagittal diameter of the atlas as the radius). The extension of the atlas by a lever covers the neutral zone of flexion/extension and almost reaches the maximum extension range of motion of C1eC2. Without an accurate morphometric study, a 5 mm width means adequate flexibility of C1eC2 as deduced by the speculation above. Partial reduction were obtained in 4 of 23 patients (17.4%), because of the same including standard and small sample size, no significant differences are found between complete and partial reduction cases. Without intra-spinal canal manipulations, there may be still soft tissues and scar tissues within the spinal canal which impeded reducing C1 to anatomical position through posterior approach. This assistant technique provides advantages for combined anterior and posterior surgery as follows: (1) when C1/2 has adequate flexibility matching the aforementioned criterion, complete reduction can be achieved in most cases and there is no need to dissect the odontoid process, which reduces the morbidity of dura mater tearing or spinal cord injury. (2) There is no need for excessive removal of tissue, in case of iatrogenic instability or loss of necessary structure for rigid fixation. (3) The reduction is reached sequentially by instruments' pull strength via the posterior approach. (4) Realignment of the atlantoaxial joint can prevent subaxial spine degeneration due to longstanding C1eC2 dislocation.
11
Several instrumentations for fusion have been described in the literature and the fixation method is still a matter of debate. Yin et al. [19] used a novel transoral atlantoaxial reduction plate (TARP) system designed to facilitate a one-stage anterior operation capable of simultaneously decompressing the ventral spinal cord, as well as reducing and fixing the atlantoaxial segment. The successful use of TARP was reported for several situations, including basilar invagination, odontoid fracture, and revision surgery [20,21]. However, anterior instruments placed on the pharyngeal wall predisposes to local infection; as a result, anterior screw loosening has been reported [22]. Posterior fixation with a C1eC2 pedicle screw is becoming popular because there is more pullout strength, less irritation of the C2 nerve root and venous plexus, and a more visible entry point [23e25]. In addition, several studies found that C1eC2 pedicle screw fixation with more cortical purchase and a longer screw trajectory had higher biomechanical stiffness than C1 lateral mass-C2 pedicle screw fixation [26,27]. Moreover, with the pedicle exposure technique, the screw can be inserted safely in the C1 posterior arch measuring less than 4 mm. Although several patients finally underwent posterior occipitocervical fusion, reduction was achieved by pedicle screws' pull strength. Of note, the endoscopically assisted anterior approach to the craniovertebral junction has been frequently reported [11,13,28]. Under fluoroscopic guidance, anterior release will be more invasive and safer. The criteria for a good release with this modified technique of anterior release can be used under endoscopy as well. 5. Conclusion Under the condition of no osteosynthesis around the C1eC2 facet joints in IAAD, complete C1eC2 reduction can be achieved by our method. If a 3e5 mm joint space is achieved during anterior transoral release by levering the atlas upwards, most factors from the vertebral anterior aspect which impede C1eC2 reduction are removed. C1eC2 can be reduced sequentially by the posterior approach. Our method requires further investigation and possible clinical application. Conflict of interest The authors declare that they have no conflict of interest. Acknowledgment This research was supported by the National Natural Science Foundation of China (81173423). References [1] Jain VK, Behari S, Banerji D, Bhargava V, Chhabra DK. Transoral decompression for craniovertebral osseous anomalies: perioperative management dilemmas. Neurol India 1999;47:188e95. [2] Xu J, Yin Q, Xia H, Wu Z, Ma X, Zhang K, Wang Z, Yang J, Ai F, Wang J, Liu J, Mai X. New clinical classification system for atlantoaxial dislocation. Orthopedics 2013;36:e95e100. [3] Wang S, Wang C, Yan M, Zhou H, Dang G. Novel surgical classification and treatment strategy for atlantoaxial dislocations. Spine 2013;38:E1348e56. Phila Pa 1976. [4] Hao D, He B, Zheng Y, Zhang Z. Single stage anterior release and sequential posterior fusion for irreducible atlantoaxial dislocation. J Spinal Disord Tech 2013. http://dx.doi.org/10.1097/BSD.0b013e31826be885. [5] Tan M, Jiang X, Yi P, Yang F, Tang X, Hao Q, Zhang G. Revision surgery of irreducible atlantoaxial dislocation: a retrospective study of 16 cases. Eur Spine J 2011;20:2187e94. [6] Tan M, Zhang G, Wang W, Tan Y, Zou H, Yi P, Jiang X, Wei H, Yang F. The pilot study of clinical classification for atlantoaxial dislocation. Chin J Spine Spinal Cord 2007;17:111e5 [In Chinese]. [7] Resnick DK. Benzel EC.C1-C2 pedicle screw fixation with rigid cantilever beam construct: case report and technical note. Neurosurgery 2002;50:426e8.
12
H. Ma et al. / Journal of Orthopaedic Science 21 (2016) 7e12
[8] Zileli M, Cagli S. Combined anterior and posterior approach for managing basilar invagination associated with type I Chiari malformation. J Spinal Disord Tech 2002;15:284e9. [9] Goel A, Kulkarni AG, Sharma P. Reduction of fixed atlantoaxial dislocation in 24 cases: technical note. J Neurosurg Spine 2005;2:505e9. [10] Subin B, Liu JF, Marshall GJ, Huang HY, Ou JH, Xu GZ. Transoral anterior decompression and fusion of chronic irreducible atlantoaxial dislocation with spinal cord compression. Spine 1995;20:1233e40. Phila Pa 1976. [11] Lu G, Passias PG, Li G, Kozanek M, Rehak L, Wood KB, Li G, Deng Y. Endoscopically assisted anterior release and reduction through anterolateral retropharyngeal approach for fixed atlantoaxial dislocation. Spine 2010;35: 544e51. Phila Pa 1976. [12] Scalici E, Indorato F, Portelli F, Savi T, Maresi E, Busardo FP. A fatal iatrogenic right vertebral injury after transoral odontoidectomy and posterior cervical stabilization for a type II odontoid fracture. J Forensic Leg Med 2014;22:41e4. [13] Ma H, Lv G, Wang B, Kuang L, Wang X. Endoscopic transcervical anterior release and posterior fixation in the treatment of irreducible vertical atlantoaxial dislocation. Eur Spine J 2014;23:1749e54. [14] Liu T, Li F, Xiong W, Du X, Fang Z, Shang H, Chen A. Video-assisted anterior transcervical approach for the reduction of irreducible atlantoaxial dislocation. Spine 2010;35:1495e501. Phila Pa 1976. [15] Lee SH, Park K, Kong DS, Kim ES, Eoh W. Long-term follow up of transoral anterior decompression and posterior fusion for irreducible bony compression of the craniovertebral junction. J Clin Neurosci 2010;17:455e9. [16] Wang C, Yan M, Zhou HT, Wang SL, Dang GT. Open reduction of irreducible atlantoaxial dislocation by transoral anterior atlantoaxial release and posterior internal fixation. Spine 2006;31:E306e13. Phila Pa 1976. [17] Tan M, Wang H, Wang Y, Zhang G, Yi P, Li Z, Wei H, Yang F. Morphometric evaluation of screw fixation in atlas via posterior arch and lateral mass. Spine 2003;28:888e95. Phila Pa 1976. [18] Panjabi M, Dvorak J, Duranceau J, Yamamoto I, Gerber M, Rauschning W, Bueff HU. Three-dimensional movements of the upper cervical spine. Spine 1988;13:726e30. Phila Pa 1976.
[19] Yin Q, Ai F, Zhang K, Chang Y, Xia H, Wu Z, Quan R, Mai X, Liu J. Irreducible anterior atlantoaxial dislocation: one-stage treatment with a transoral atlantoaxial reduction plate fixation and fusion. Report of 5 cases and review of the literature. Spine 2005;30:E375e81. Phila Pa 1976. [20] Yang J, Ma X, Xia H, Wu Z, Ai F, Yin Q. Transoral anterior revision surgeries for basilar invagination with irreducible atlantoaxial dislocation after posterior decompression: a retrospective study of 30 cases. Eur Spine J 2014;23:1099e108. [21] Xia H, Yin Q, Ai F, Ma X, Wang J, Wu Z, Zhang K, Liu J, Xu J. Treatment of basilar invagination with atlantoaxial dislocation: atlantoaxial joint distraction and fixation with transoral atlantoaxial reduction plate (TARP) without odontoidectomy. Eur Spine J 2014;23:1648e55. [22] Kerschbaumer F, Kandziora F, Klein C, Mittlmeier T, Starker M. Transoral decompression, anterior plate fixation, and posterior wire fusion for irreducible atlantoaxial kyphosis in rheumatoid arthritis. Spine 2000;25: 2708e15. Phila Pa 1976. [23] Lee SH, Kim ES, Eoh W. Modified C1 lateral mass screw insertion using a high entry point to avoid postoperative occipital neuralgia. J Clin Neurosci 2013;20:162e7. [24] Yeom JS, Kafle D, Nguyen NQ, Noh W, Park KW, Chang BS, Lee CK, Riew KD. Routine insertion of the lateral mass screw via the posterior arch for C1 fixation: feasibility and related complications. Spine J 2012;12:476e83. [25] Thomas JA, Tredway T, Fessler RG, Sandhu FA. An alternate method for placement of C-1 screws. J Neurosurg Spine 2010;12:337e41. [26] Zarro CM, Ludwig SC, Hsieh AH, Seal CN, Gelb DE. Biomechanical comparison of the pullout strengths of C1 lateral mass screws and C1 posterior arch screws. Spine J 2013;13:1892e6. [27] Ma XY, Yin QS, Wu ZH, Xia H, Liu JF, Xiang M, Zhao WD, Zhong SZ. C1 pedicle screws versus C1 lateral mass screws: comparisons of pullout strengths and biomechanical stabilities. Spine 2009;34:371e7. Phila Pa 1976. [28] Gkekas N, Primikiris P, Sfikas S, Vyziotis A, Georgakoulias N. Endoscopic transoral decompression of cervicomedullary junction: a rational alternative to the traditional microscopic transoral approach. World Neurosurg 2014;82: e573e575.