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Clinical Outcomes of Atlantoaxial Dislocation Combined with High-Riding Vertebral Artery Using C2 Translaminar Screws
Original Article
Clinical Outcomes of Atlantoaxial Dislocation Combined with High-Riding Vertebral Artery Using C2 Translaminar Screws Yongqiang Wang, Chao Wang, Ming Yan
OBJECTIVE: Atlantoaxial stabilization procedures in high-riding vertebral artery (HRVA) cases are challenging. C2 translaminar screws are rigid and pose no risk to the vertebral artery. The aim of this study was to present clinical outcomes of atlantoaxial dislocation combined with HRVA using C2 translaminar screws.
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METHODS: Cases of atlantoaxial dislocation combined with HRVA surgically treated in our institution from 2007 to 2015 were retrospectively reviewed. Atlantodental interval and clivus-axial angle were measured. The Japanese Orthopaedic Association scale was used to evaluate neurologic status.
reoperation rates in atlantoaxial dislocation cases. New treatment methods should be investigated to facilitate clinical outcomes. Extending fixed segments should be considered.
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RESULTS: There were 58 patients enrolled: 15 with instability and 43 with dislocation, 13 of which were irreducible. Incidence of bilateral HRVA was 5.2%. C1-C2 fixation was performed in 26 cases; atlantodental interval decreased from 9.9 3.7 mm to 1.0 1.7 mm (P < 0.05). C0-C2 fixation was performed in 32 cases; clivus-axial angle increased from 125 13 to 150 15 (P < 0.05). Preoperative and postoperative Japanese Orthopaedic Association scores of 56 patients with myelopathy were 11.9 2.8 and 14.6 2.4, respectively (P < 0.05). Fusion rate was 93.1% (54/58) and at 4-month follow-up was 81% (47/58). In 14 cases of redislocation, final fusion was achieved; 3 of 14 required odontoidectomy. Four cases lacking bony fusion also required revision surgery. Redislocation rate was 31% (18/58), and reoperation rate was 12.1% (7/58).
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CONCLUSIONS: Surgical results of C2 translaminar screws are unsatisfactory, with high redislocation and
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Key words Atlantoaxial dislocation - Atlantoaxial fusion - High-riding vertebral artery - Revision - Translaminar screw -
Abbreviations and Acronyms AAD: Atlantoaxial dislocation BAI: Basion-axial interval BDI: Basion-dens interval HRVA: High-riding vertebral artery JOA: Japanese Orthopaedic Association
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INTRODUCTION
M
ultiple techniques have been used to stabilize the atlantoaxial joints. Posterior atlantoaxial transarticular screw fixation with wiring developed by Magerl can provide rigid internal fixation,1 and prior publications demonstrate a fusion rate up to 100%.2,3 However, the Magerl technique is unsuitable for irreducible atlantoaxial dislocation (AAD)4 and causes vertebral artery (VA) injury in an estimated 4. 1%e8.2% of cases.5-7 Goel et al.8 introduced the C1 lateral mass screw and C2 pedicle fixation, which was later popularized by Harms and Melcher.9 Some surgeons9 believe that this method can decrease the potential risk of VA injury, but anatomic studies indicated similar risks of VA injury between C2 pedicle screws and transarticular screws.10 In high-riding vertebral artery (HRVA), a common aberrant course of the VA, the transverse foramen of C2 is too medial and/ or too high, which narrows the width of the C2 pedicle. The prevalence of HRVA is reportedly 18%e23%.6,11,12 Performing atlantoaxial stabilization procedures in HRVA cases is challenging; thus, spine surgeons developed various C2 screw fixation techniques to prevent VA injury, including short pedicle screws,13-15 pars/isthmus screws,4 translaminar screws (TLS),16,17 new trajectory/unilateral transarticular screws,12,18 and the hook-rod system.11 In this study, we used C2 TLS to treat patients with AAD
LPS: Long pedicle screw VA: Vertebral artery Department of Orthopedics, Peking University Third Hospital, Beijing, China To whom correspondence should be addressed: Chao Wang, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2018). https://doi.org/10.1016/j.wneu.2018.11.092 Journal homepage: www.journals.elsevier.com/world-neurosurgery Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2018 Elsevier Inc. All rights reserved.
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ORIGINAL ARTICLE YONGQIANG WANG ET AL.
OUTCOMES OF AAD WITH HRVA USING C2 TRANSLAMINAR SCREWS
combined with HRVA. To the best of our knowledge, this is the largest series to date.
Table 1. Basion-Axial Interval of 18 Redislocation Cases Revision Surgery (n [ 7)
Without Revision Surgery (n [ 11)
Redislocation (n [ 18)
BAI pre, mm
20.4 1.9
20.7 5.5
20.6 4.3
BAI post, mm
12.8 3.2
12.6 3.9
12.7 3.6
BAI final, mm
19.5 2.9
18.0 6.1
18.6 5.0
MATERIALS METHODS Inclusion and Exclusion Criteria This study was approved by our university hospital’s ethics committee. We retrospectively reviewed our hospital electronic database from 2007 to 2015 and identified patients meeting the following criteria: presence of atlantoaxial instability or AAD; unilateral or bilateral HRVA detected on a sagittal image that was 3 mm lateral to the cortical margin of the spinal canal wall at C2, which was defined as an isthmus height 5 mm and/or an internal height 2 mm19; history of surgical treatment with C2 TLS; and minimum 2-year regular follow-up. Each patient provided signed informed consent. Patients without intact follow-up data or who completed <2 years of regular follow-up were excluded. Radiographic Evaluation and Follow-Up All patients underwent preoperative dynamic lateral radiography, reconstructive computed tomography, magnetic resonance imaging, and postoperative lateral cervical standing radiography. At our institution, follow-up visits were routinely arranged at 4, 16, and 40 months as well as at any time when urgently indicated. Dynamic lateral radiography, reconstructive computed tomography, and magnetic resonance imaging were recommended. The atlantodental interval was measured in C1-C2 fixation cases, and clivus-axial angle and cervicomedullary angle were measured in C0-C2 fixation cases. The basion-axial interval (BAI) and basiondens interval (BDI) were also measured. The reduction criteria were atlantodental interval <3mm and C1 at the same level as the odontoid tip. During the follow-up, any increases in the abovementioned parameters indicated redislocation. Neurologic function was evaluated by the Japanese Orthopaedic Association (JOA) scale. Surgical Strategy All surgical procedures were performed by a single senior surgeon (C.W.), and the computed tomography scans were reviewed by other senior surgeons (Y.W. and M.Y.). Before each operation, general anesthesia was administered, and the patients were placed in the supine position and underwent skeletal cranial traction (one sixth to one fifth of the body weight). As reported previously, the reduction was assessed under lateral fluoroscopy; if the atlas could be elevated to the same level as the odontoid tip (or to a higher level than before), the need for transoral release might be obviated and a posterior instrumentation and fusion was performed. If not, transoral release would be performed.20,21 For patients requiring transoral release, after exposure in the surgical field, we first dissected the longus colli and longus capitis muscles bilaterally along the inferior border of the atlas, then dissected the capsule of the lateral mass articulations and removed the cartilage to release articular adhesions. Sometimes we further removed the soft tissue between the odontoid and the anterior arch of the atlas or even the scarred apical and alar ligament. Transoral release was thought to be successful if a small curette placed onto the superoposterior aspect of the odontoid could maneuver the odontoid downward and forward.
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BAI, basion-axial interval; pre, preoperative; post, postoperative; final, at final follow-up of primary surgery.
Patients who underwent posterior C1-C2 instrumentation were placed in the prone position, maintaining cranial traction throughout the entire procedure. A posterior midline incision was made to expose the C1 posterior arch and the C2 lamina. For patients with occipitalization of the atlas, we considered occiputC2 fixation equivalent to C1-C2 constructs because of the immobile C0-C1 segment. For patients who underwent occiput-C2 fixation, the incision was extended. For patients without occipitalization of the atlas, a C1 lateral mass screw was positioned in the usual manner. A C2 long pedicle screw (LPS) was placed on the side where the HRVA was absent. Placement of the C2 TLS was performed as described by Wright17 with an entry point at the junction of the C2 spinous process and the lamina on one side, and then the contralateral lamina was carefully drilled to a depth of 24e30 mm depending on C2 lamina size. The trajectory was kept slightly less than the downslope of the lamina to prevent ventral cortical breakthrough to the spinal canal. A 4.0-mm-diameter polyaxial screw was then inserted along the same trajectory with a length of 24e30 mm. We first connected the C2 LPS with C1 lateral mass screw with plate to achieve C1-C2 joint reduction and then connected each C1 lateral mass screw to the ipsilaterally projecting screw head of the C2 TLS using connecting rods. For patients with occipitalization of the atlas, the C2 TLS were connected to the occiput. Finally, the C1 arch, C2 lamina, and spinous process were decorticated. Autogenous morselized cancellous grafts (15e20 g) harvested from the posterior iliac crest were bridged between the C1 arch and the C2 lamina. For patients who underwent occiput-C2 fixation, bone grafting was the same as described earlier except that the cancellous grafts were bridged between the occiput and the C2 lamina.
Table 2. Basion-Dens Interval of 15 Redislocation Cases
BDI pre, mm
Revision Surgery (n [ 7)
Without Revision Surgery (n [ 8)
Redislocation (n [ 15)
14.1 2.6
12.4 2.2
13.2 2.5
BDI post, mm
9.3 4.6
6.4 4.2
7.9 4.7
BDI final, mm
13.4 3.0
10.8 2.5
12.1 3.0
BDI, basion-dens interval; pre, preoperative; post, postoperative; final, at final follow-up of primary surgery.
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ORIGINAL ARTICLE YONGQIANG WANG ET AL.
OUTCOMES OF AAD WITH HRVA USING C2 TRANSLAMINAR SCREWS
Postoperative Management The drains were removed after 48 hours. A Philadelphia collar was routinely used, and 3 patients required halo-vest immobilization. Statistical Analysis Clinical data were analyzed with IBM SPSS Statistics Version 22.0 (IBM Corp., Armonk, New York, USA) and presented as mean SD. Comparison analyses were performed with c2 test or Wilcoxon test. Statistical significance was set at P < 0.05. RESULTS This study enrolled 58 patients (26 men, 32 women; mean age, 42.3 14.3 years; range, 14e73 years). Preoperative diagnoses included instability in 15 patients and dislocation in 43 patients; of the latter, 13 were irreducible and required transoral release.20,21 The incidence of bilateral HRVA was 5.2% (3 of 58 patients); thus, a total of 61 TLS were placed. C1-C2 fixation was performed in 26 patients without C1 occipitalization, 3 of whom underwent transoral release. Atlantodental interval decreased from 9.9 3.7 mm (range, 5.0e22.9 mm) to 0.2 0.8 mm (range, 0e3 mm) immediately postoperatively but increased to 1.0 1.7 mm (range, 0e5.0 mm) at the final follow-up (P < 0.05). C0-C2 fixation was performed in 32 patients combined with C1 occipitalization, 10 of whom underwent transoral release. Clivus-axial angle was 125 13 (range, 87e149 ) preoperatively, increased to 154 13 (range, 120e176 ) postoperatively, and decreased to 150 15 (range, 115e176 ) at the final follow-up (P < 0.05). BAI of the cohort was 20.2 4.9 mm (range, 10.5e33.7 mm) preoperatively and decreased to 10.9 3.0 mm (range, 2.8e20.6 mm) postoperatively (P < 0.05). Some cases had combined os odontoideum or old odontoid fracture, so BDI was measured in only 35 cases. BDI was 23.4 3.1 mm (range, 7.3e20.8 mm) preoperatively and
decreased to 7.2 3.3 mm (range, 3.1e15.8 mm) postoperatively (P < 0.05). BAI of 18 redislocation cases is presented in Table 1, and BDI of 15 redislocation cases is presented in Table 2. Both BAI and BDI decreased significantly after primary surgery but increased again before fusion or revision. BAI and BDI remained unchanged after surgery in 40 patients in whom solid fusion was achieved in 4 months. Surgical details are shown in Table 3. The mean follow-up time was 66.5 31.7 months (range, 24e124 months), mean estimated blood loss was 179 140 mL (range, 50e800 mL), and mean operative time was 155 46 minutes (range, 96e281 minutes). The average preoperative JOA score of 56 patients with myelopathy was 11.9 2.8 (range, 5.0e16.0), and JOA score at the final followup was 14.6 2.4 (range, 6.0e17.0) (P < 0.05). The fusion rate of the whole cohort was 93.1% (54 of 58 patients). At 4-month follow-up, fusion rate was 81% (47 of 58); 54 cases achieved fusion at a mean 4.9 2.7 months (range, 4e16 months). At 4-month follow-up, 40 cases appeared to have achieved bony fusion without redislocation (Figure 1). In 14 cases of redislocation, fusion was achieved at a mean 7.3 4.3 months (range, 4e16 months); 3 cases involved neurologic deterioration and required an odontoidectomy (Figure 2). Another 4 cases in which bony fusion was not achieved also required revision surgery, including extending a fixed segment in 2, replacement with bilateral transarticular screws in 1 (Figure 3), and replacement with bilateral LPS in 1 (Figure 4). The redislocation rate was 31% (18 of 58 patients), and the reoperation rate was 12.1% (7 of 58 patients). The distribution of redislocation cases was 2 in the instability group, 12 in the reducible dislocation group, and 4 in the irreducible dislocation group; the distribution of reoperation cases in these 3 groups was 1 in the instability group, 5 in the reducible dislocation group, and 1 in the irreducible dislocation group (Tables 3 and 4).
Table 3. Surgery-Related Information of Cohort Variable Number of patients
Instability
Reducible Dislocation
Irreducible Dislocation
Total
15
30
13
58
8
13
5
26 32
Sex Male Female
7
17
8
44.7 15.9
40.3 13.9
43.8 13.8
C1-C2
11 (1B)
11 (1B)
4 (1B)
26
C0-C2
4
19
9
32
Transoral
Age, years, mean SD Operation
—
—
13
13
Fusion cases
14
28
12
54
Redislocation
2
12
4
18
Revision surgery
1
5
1
7
C1-C2, posterior C1-C2 fixation; C0-C2, posterior C0-C2 fixation; Transoral, transoral release þ posterior fixation; 1B, bilateral translaminar screws in 1 case, unilateral pedicle screw combined with unilateral translaminar screw in others.
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ORIGINAL ARTICLE YONGQIANG WANG ET AL.
OUTCOMES OF AAD WITH HRVA USING C2 TRANSLAMINAR SCREWS
Figure 1. A 36-year-old man with a C1-C2 reducible dislocation. Japanese Orthopaedic Association score was 10, and atlantodental interval was 7.5 mm. (A) Lateral extension x-ray indicating dislocation. (B) High-riding vertebral artery on the right side. (C) Normal pedicle on the left side. (D)
Considering the redislocation rate, there was a significant difference between the instability group (13.3%; 2 of 15) and the reducible dislocation group (40%; 12 of 30), but no significant differences were detected between the instability and irreducible dislocation groups or the reducible dislocation and irreducible dislocation groups (30.8%; 4 of 13). Considering the reoperation rate, no significant difference was detected among the 3 groups (Table 3). All revision cases achieved bony fusion at the final follow-up. The mean reoperation time of the 7 revision cases was 6.0 5.0 months (range, 0.2e12 months) after the primary operation, and the mean age of the patients was 37 8 years (range, 29e52 years). Perioperative complications included cerebrospinal fluid leakage in 2 cases, fever in 5 cases, poor wound healing in 2 cases, and donor site complications in 4 cases; all were cured by conservative treatment.
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Postoperative anatomic reduction. (E) Long pedicle screw on the left side. (F) Translaminar screw on the right side. (G) Solid fusion at 4-month follow-up; atlantodental interval was 0. (H) Sufficient decompression of the spinal cord. Japanese Orthopaedic Association score was 15.
DISCUSSION The reported risk of VA injury in a clinical series was 4.1%e 8.2%,5-7 which is predominant in cases combined with HRVA. Harms et al.9 recommended their technique as an efficient alternative to the Magerl technique with no vascular damage. Goel et al.8 also considered C2 pedicle screws to be able to decrease the risk of VA injury compared with the Magerl technique. However, Yoshida et al.10 judged approximately 10% of screw trajectories risky in both techniques, indicating the C2 pedicle screw placement has nearly the same risk as atlantoaxial transarticular screw placement. Yeom et al.19 reported that the rate of VA groove violation was significantly lower with pedicle (49%) than transarticular (63%) screws. However, the VA groove violation did not equal a VA injury.
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ORIGINAL ARTICLE YONGQIANG WANG ET AL.
Figure 2. A 51-year-old woman with a C1-C2 reducible dislocation and cranial settling. Japanese Orthopaedic Association score was 14. (A) Preoperative computed tomography demonstrating an increased atlantodental interval; clivus-axial angle was 117 . (B) Preoperative magnetic resonance imaging. Cervicomedullary angle was 113 . (C) Anatomic reduction was achieved during the operation and C0-C2 was instrumented with a unilateral C2 pedicle screw and a contralateral C2 translaminar screw. Clivus-axial angle was 145 . (D and E) Lateral x-ray and sagittal computed tomography at 4-month follow-up showing redislocation
Neo et al.12 introduced a novel trajectory for transarticular screw placement; they preferred to purchase the most posterior and medial part of the isthmus and successfully treated 7 cases of unilateral HRVA. Lee et al.22 reported similar results with transarticular screws by choosing a more medial and superior entry point. Song et al.18 also reported good surgical results using unilateral transarticular screw fixation and interspinous bone graft wiring to treat 13 cases of atlantoaxial instability combined with HRVA. However, transarticular screws could not avoid the risk of VA injury, and a new trajectory would decrease the purchase of the C1 lateral mass, which would lessen the stiffness of the constructs. Daentzer11 used a hook-rod system
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with solid fusion of C0-C2. (F) Sagittal magnetic resonance imaging at 4-month follow-up showing compression of the cord. Cervicomedullary angle was 136 , and Japanese Orthopaedic Association score was 12 (neurologic deterioration). (G) Computed tomography 4 months after transoral odontoidectomy as a revision surgery. Clivus-axial angle was 135 . (H) Magnetic resonance imaging 4 months after revision surgery. Cervicomedullary angle was 154 , and Japanese Orthopaedic Association score was 17.
combined with wiring to treat a case of atlantoaxial instability with bilateral HRVA, but no biomechanical testing reports have been available for this system with C1-C2 fixation until now. Wright17 first introduced crossing C2 laminar screws for incorporation of the axis into atlantoaxial or craniocervical constructs. The major advantage is the removal of the risk to the VA, and the only potential drawback would be unrecognized laminar screw breakout ventrally into the spinal canal. Meyer et al.23 verified this result by treating a cohort of 27 patients with a mean age of 68.9 years with 52 TLS; the fusion rate was 92.9%. As the safety and efficacy of TLS have been reported by clinical series and biomechanical studies, we used this
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OUTCOMES OF AAD WITH HRVA USING C2 TRANSLAMINAR SCREWS
Figure 3. A 52-year-old man with a C1-C2 instability. Japanese Orthopedic Association score was 15. (A) Instability of C1-C2; atlantodental interval was 13.5 mm. (B and C) Preoperative computed tomography showing high-riding vertebral artery. (D) Preoperative magnetic resonance imaging. (E) Posterior reduction and fixation of C1-C2 with C1 lateral mass screws and C2 bilateral translaminar screws. Atlantodental interval decreased to 3
technique to manage AAD cases. However, our surgical results are unsatisfactory with high redislocation and reoperation rates. We speculate the increased morbidity is due to differences in diagnoses: 26 of 27 cases in the report by Meyer et al.23 were trauma cases in which the purchase of TLS is sufficient for fracture healing. In the present study, the LPS was the optimal choice for C2 fixation if the pedicle was wide enough; only when the LPS pathway was violated by HRVA did we use TLS. Almost all 58 cases achieved anatomic reduction during the operation. However, during the follow-up, many patients presented with redislocation; the redislocation rate in the reducible dislocation group was significant higher than in the instability group. We speculate that the purchase required to maintain reduction in the reducible dislocation group was higher than that of the instability group. Dislocation was more severe in the irreducible dislocation group than in the reducible dislocation group; however, after transoral release, the required purchase decreased and should be lower than that in the reducible dislocation group. For patients with combined occipitalization of the atlas, we considered that occiput-C2 fixation was equivalent to the C1-C2 constructs because of the immobile C0-C1 segment. Although it makes the surgical strategy heterogeneous and the differences in purchase between occipital screws and C1 lateral mass screws are
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mm. (F and G) Postoperative sagittal computed tomography and magnetic resonance imaging immediately after primary surgery. (H and I) Redislocation was detected 4 months after primary surgery. (J) Solid fusion was achieved 4 months after C1-C2 transarticular screw fixation as a revision surgery. Atlantodental interval was 5 mm, and Japanese Orthopaedic Association score was 17.
unknown, the placement of C0 screws is much easier than that of C1 lateral mass screws. Many biomechanical studies have compared different posterior atlantoaxial fixations. Sim et al.13 noted that intralaminar screws were inferior to pedicle screws in the lateral bending models. Lehman et al.16 concluded that pedicle screws provided the strongest fixation for initial and salvage applications. In cases of failure, lamina screws appeared to provide stronger and more reproducible fixation than pars screws. Lapsiwala et al.24 reported that C1 lateral masseC2 intralaminar screw fixation restored resistance to lateral bending but not to the same degree as transarticular or C1 to C2 pedicle fixation techniques. Gorek et al.25 indicated the potential of the intralaminar screw technique to provide equivalent stability to that of the C2 pedicle screw technique. TLS appears good in biomechanical tests, but in the present study, the redislocation and reoperation rates were high, and the surgical outcomes were unsatisfactory. In some cases, although anatomic reduction was achieved during the primary operation with the help of cranial traction and LPS, maintaining reduction was difficult (Figure 2), which demonstrates the poor biomechanical performance of TLS. To the best of our knowledge, this is the largest clinical series to focus on AAD
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ORIGINAL ARTICLE YONGQIANG WANG ET AL.
Figure 4. A 40-year-old man with a C1-C2 instability. Japanese Orthopaedic Association score was 14. (A and B) Flexion-extension x-ray indicates instability of C1-C2. Atlantodental interval was 10.7 mm. (C) Preoperative computed tomography showing bilateral high-riding vertebral artery. (D) Preoperative magnetic resonance imaging. (E) Anatomic reduction was achieved, and atlantodental interval decreased to 0 during the operation, but postoperative x-ray 6 days after surgery shows redislocation. (FeI)
combined with HRVA. We advocate that new treatment methods should be investigated to facilitate the clinical outcomes. In this study, in 14 cases of redislocation, fusion was ultimately achieved: 3 patients had neurologic deterioration and required odontoidectomy owing to the bony fusion of atlantoaxial joint, whereas the other 11 cases appeared not to have neurologic deterioration, making salvage surgery unnecessary. Two of the other 4 revision cases underwent fixed segment extension; 2 were revised using transarticular screws or C2 LPS at high risk of VA injury (Figures 3 and 4); thus, long segment fixation should be considered in cases of severe dislocation. Some authors try to manage AAD with an anterior approach technique, but anterior atlantoaxial transarticular screw technique has the same limitation as Magerl technique, which is unsuitable for irreducible AAD.26 The limitations of transoral atlantoaxial reduction plate technique are the increased opportunity of surgical site infection and C2 vertebrae screws loosening.27 Despite the high reoperation and redislocation rates, the neurologic recovery rate was good in the present study, and the JOA score increased significantly at the final follow-up. Perhaps the combined C2 pedicle screws and salvage surgeries contributed to the results.
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X-ray and computed tomography after revision surgery using bilateral C2 long pedicle screws. Violation of C2 vertebral artery groove could be detected, but no evidence of vertebral artery injury was noted. (J) Computed tomography 8 months after revision surgery showing bony fusion of the articular lateral mass (arrow). Japanese Orthopaedic Association score was 16.
CONCLUSIONS As an alternative option for C1-C2 or C0-C2 fixation, C2 TLS does not carry the risk of VA injury; however, the surgical results of TLS are unsatisfactory, and salvage surgery may be required. Thus, C2 TLS is unsuitable for AAD cases, and new treatment methods should be investigated to facilitate the clinical outcomes of AAD combined with HRVA. Perhaps extending fixed segments should be considered.
Table 4. Surgical Outcomes Reduction and Fusion
Redislocation and Fusion
Redislocation without Fusion
Number
40
14
4
Fusion time, months
4
7.3 4.3
*
Revision cases
0
3
4
*Nonfusion before revision surgery, achieving fusion at 5.5 1.9 months after revision surgery.
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OUTCOMES OF AAD WITH HRVA USING C2 TRANSLAMINAR SCREWS
and atlantoaxial transarticular screw. Spine (Phila Pa 1976). 2006;31:E513-E517. 11. Daentzer D. Operative management for atlantoaxial instability in case of bilateral high-riding vertebral artery. Arch Orthop Trauma Surg. 2009; 129:177-182. 12. Neo M, Matsushita M, Iwashita Y, Yasuda T, Sakamoto T, Nakamura T. Atlantoaxial transarticular screw fixation for a high-riding vertebral artery. Spine (Phila Pa 1976). 2003;28:666-670. 13. Sim HB, Lee JW, Park JT, Mindea SA, Lim J, Park J. Biomechanical evaluations of various C1-C2 posterior fixation techniques. Spine (Phila Pa 1976). 2011;36:E401-E407. 14. Park YS, Kang DH, Park KB, Hwang SH. Posterior atlantoaxial screw-rod fixation in a case of aberrant vertebral artery course combined with bilateral high-riding vertebral artery. J Korean Neurosurg Soc. 2010;48:367-370. 15. Tan LA, Kasliwal MK, Gerard CS, Traynelis VC, Fontes RBV. Surgical considerations in posterior C1-2 instrumentation in the presence of vertebral artery anomalies: case illustration and review of literature [e-pub ahead of print]. Br J Neurosurg. https://doi.org/10.1080/02688697.2017.1346170. accessed June 29, 2017. 16. Lehman RA Jr, Dmitriev AE, Helgeson MD, Sasso RC, Kuklo TR, Riew KD. Salvage of C2 pedicle and pars screws using the intralaminar technique: a biomechanical analysis. Spine (Phila Pa 1976). 2008;33:960-965. 17. Wright NM. Posterior C2 fixation using bilateral, crossing C2 laminar screws: case series and technical note. J Spinal Disord Tech. 2004;17:158-162. 18. Song GS, Theodore N, Dickman CA, Sonntag VK. Unilateral posterior atlantoaxial transarticular screw fixation. J Neurosurg. 1997;87:851-855.
21. 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 (Phila Pa 1976). 2006;31:E306-E313. 22. Lee JH, Jahng TA, Chung CK. C1-2 transarticular screw fixation in high-riding vertebral artery: suggestion of new trajectory. J Spinal Disord Tech. 2007;20:499-504. 23. Meyer D, Meyer F, Kretschmer T, Börm W. Translaminar screws for the axis—an alternative technique for rigid screw fixation in upper cervical spine instability. Neurosurg Rev. 2012;35:255-261. 24. Lapsiwala SB, Anderson PA, Oza A, Resnick DK. Biomechanical comparison of four C1 to C2 rigid fixative techniques: anterior transarticular, posterior transarticular, C1 to C2 pedicle, and C1 to C2 intralaminar screw. Neurosurgery. 2006;58:516-521. 25. Gorek J, Acaroglu E, Berven S, Yousef A, Puttlitz CM. Constructs incorporating intralaminar C2 screw provide rigid stability for atlantoaxial fixation. Spine (Phila Pa 1976). 2005;30: 1513-1518. 26. Padua MR, Yeom JS, Lee SY, et al. Fluoroscopically guided anterior atlantoaxial transarticular screws: a feasibility and trajectory study using CTbased simulation software. Spine J. 2013;13: 1455-1463. 27. Yin Q, Ai F, Zhang K, et al. 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 (Phila Pa 1976). 2005;30:E375-E381. Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Received 25 August 2018; accepted 12 November 2018
19. Yeom JS, Buchowski JM, Kim HJ, Chang BS, Lee CK, Riew KD. Risk of vertebral artery injury: comparison between C1-C2 transarticular and C2 pedicle screws. Spine J. 2013;13:775-785. 20. Wang S, Wang C, Yan M, Zhou H, Dang G. Novel surgical classification and treatment strategy for atlantoaxial dislocations. Spine (Phila Pa 1976). 2013;38:E1348-E1356.
Citation: World Neurosurg. (2018). https://doi.org/10.1016/j.wneu.2018.11.092 Journal homepage: www.journals.elsevier.com/worldneurosurgery Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2018 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.11.092
Clinical Outcomes of Atlantoaxial Dislocation Combined with High-Riding Vertebral Artery Using C2 Translaminar Screws Yongqiang Wang, Chao Wang, Ming Yan
OBJECTIVE: Atlantoaxial stabilization procedures in high-riding vertebral artery (HRVA) cases are challenging. C2 translaminar screws are rigid and pose no risk to the vertebral artery. The aim of this study was to present clinical outcomes of atlantoaxial dislocation combined with HRVA using C2 translaminar screws.
-
METHODS: Cases of atlantoaxial dislocation combined with HRVA surgically treated in our institution from 2007 to 2015 were retrospectively reviewed. Atlantodental interval and clivus-axial angle were measured. The Japanese Orthopaedic Association scale was used to evaluate neurologic status.
reoperation rates in atlantoaxial dislocation cases. New treatment methods should be investigated to facilitate clinical outcomes. Extending fixed segments should be considered.
-
RESULTS: There were 58 patients enrolled: 15 with instability and 43 with dislocation, 13 of which were irreducible. Incidence of bilateral HRVA was 5.2%. C1-C2 fixation was performed in 26 cases; atlantodental interval decreased from 9.9 3.7 mm to 1.0 1.7 mm (P < 0.05). C0-C2 fixation was performed in 32 cases; clivus-axial angle increased from 125 13 to 150 15 (P < 0.05). Preoperative and postoperative Japanese Orthopaedic Association scores of 56 patients with myelopathy were 11.9 2.8 and 14.6 2.4, respectively (P < 0.05). Fusion rate was 93.1% (54/58) and at 4-month follow-up was 81% (47/58). In 14 cases of redislocation, final fusion was achieved; 3 of 14 required odontoidectomy. Four cases lacking bony fusion also required revision surgery. Redislocation rate was 31% (18/58), and reoperation rate was 12.1% (7/58).
-
CONCLUSIONS: Surgical results of C2 translaminar screws are unsatisfactory, with high redislocation and
-
Key words Atlantoaxial dislocation - Atlantoaxial fusion - High-riding vertebral artery - Revision - Translaminar screw -
Abbreviations and Acronyms AAD: Atlantoaxial dislocation BAI: Basion-axial interval BDI: Basion-dens interval HRVA: High-riding vertebral artery JOA: Japanese Orthopaedic Association
WORLD NEUROSURGERY -: e1-e8, - 2018
INTRODUCTION
M
ultiple techniques have been used to stabilize the atlantoaxial joints. Posterior atlantoaxial transarticular screw fixation with wiring developed by Magerl can provide rigid internal fixation,1 and prior publications demonstrate a fusion rate up to 100%.2,3 However, the Magerl technique is unsuitable for irreducible atlantoaxial dislocation (AAD)4 and causes vertebral artery (VA) injury in an estimated 4. 1%e8.2% of cases.5-7 Goel et al.8 introduced the C1 lateral mass screw and C2 pedicle fixation, which was later popularized by Harms and Melcher.9 Some surgeons9 believe that this method can decrease the potential risk of VA injury, but anatomic studies indicated similar risks of VA injury between C2 pedicle screws and transarticular screws.10 In high-riding vertebral artery (HRVA), a common aberrant course of the VA, the transverse foramen of C2 is too medial and/ or too high, which narrows the width of the C2 pedicle. The prevalence of HRVA is reportedly 18%e23%.6,11,12 Performing atlantoaxial stabilization procedures in HRVA cases is challenging; thus, spine surgeons developed various C2 screw fixation techniques to prevent VA injury, including short pedicle screws,13-15 pars/isthmus screws,4 translaminar screws (TLS),16,17 new trajectory/unilateral transarticular screws,12,18 and the hook-rod system.11 In this study, we used C2 TLS to treat patients with AAD
LPS: Long pedicle screw VA: Vertebral artery Department of Orthopedics, Peking University Third Hospital, Beijing, China To whom correspondence should be addressed: Chao Wang, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2018). https://doi.org/10.1016/j.wneu.2018.11.092 Journal homepage: www.journals.elsevier.com/world-neurosurgery Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2018 Elsevier Inc. All rights reserved.
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ORIGINAL ARTICLE YONGQIANG WANG ET AL.
OUTCOMES OF AAD WITH HRVA USING C2 TRANSLAMINAR SCREWS
combined with HRVA. To the best of our knowledge, this is the largest series to date.
Table 1. Basion-Axial Interval of 18 Redislocation Cases Revision Surgery (n [ 7)
Without Revision Surgery (n [ 11)
Redislocation (n [ 18)
BAI pre, mm
20.4 1.9
20.7 5.5
20.6 4.3
BAI post, mm
12.8 3.2
12.6 3.9
12.7 3.6
BAI final, mm
19.5 2.9
18.0 6.1
18.6 5.0
MATERIALS METHODS Inclusion and Exclusion Criteria This study was approved by our university hospital’s ethics committee. We retrospectively reviewed our hospital electronic database from 2007 to 2015 and identified patients meeting the following criteria: presence of atlantoaxial instability or AAD; unilateral or bilateral HRVA detected on a sagittal image that was 3 mm lateral to the cortical margin of the spinal canal wall at C2, which was defined as an isthmus height 5 mm and/or an internal height 2 mm19; history of surgical treatment with C2 TLS; and minimum 2-year regular follow-up. Each patient provided signed informed consent. Patients without intact follow-up data or who completed <2 years of regular follow-up were excluded. Radiographic Evaluation and Follow-Up All patients underwent preoperative dynamic lateral radiography, reconstructive computed tomography, magnetic resonance imaging, and postoperative lateral cervical standing radiography. At our institution, follow-up visits were routinely arranged at 4, 16, and 40 months as well as at any time when urgently indicated. Dynamic lateral radiography, reconstructive computed tomography, and magnetic resonance imaging were recommended. The atlantodental interval was measured in C1-C2 fixation cases, and clivus-axial angle and cervicomedullary angle were measured in C0-C2 fixation cases. The basion-axial interval (BAI) and basiondens interval (BDI) were also measured. The reduction criteria were atlantodental interval <3mm and C1 at the same level as the odontoid tip. During the follow-up, any increases in the abovementioned parameters indicated redislocation. Neurologic function was evaluated by the Japanese Orthopaedic Association (JOA) scale. Surgical Strategy All surgical procedures were performed by a single senior surgeon (C.W.), and the computed tomography scans were reviewed by other senior surgeons (Y.W. and M.Y.). Before each operation, general anesthesia was administered, and the patients were placed in the supine position and underwent skeletal cranial traction (one sixth to one fifth of the body weight). As reported previously, the reduction was assessed under lateral fluoroscopy; if the atlas could be elevated to the same level as the odontoid tip (or to a higher level than before), the need for transoral release might be obviated and a posterior instrumentation and fusion was performed. If not, transoral release would be performed.20,21 For patients requiring transoral release, after exposure in the surgical field, we first dissected the longus colli and longus capitis muscles bilaterally along the inferior border of the atlas, then dissected the capsule of the lateral mass articulations and removed the cartilage to release articular adhesions. Sometimes we further removed the soft tissue between the odontoid and the anterior arch of the atlas or even the scarred apical and alar ligament. Transoral release was thought to be successful if a small curette placed onto the superoposterior aspect of the odontoid could maneuver the odontoid downward and forward.
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BAI, basion-axial interval; pre, preoperative; post, postoperative; final, at final follow-up of primary surgery.
Patients who underwent posterior C1-C2 instrumentation were placed in the prone position, maintaining cranial traction throughout the entire procedure. A posterior midline incision was made to expose the C1 posterior arch and the C2 lamina. For patients with occipitalization of the atlas, we considered occiputC2 fixation equivalent to C1-C2 constructs because of the immobile C0-C1 segment. For patients who underwent occiput-C2 fixation, the incision was extended. For patients without occipitalization of the atlas, a C1 lateral mass screw was positioned in the usual manner. A C2 long pedicle screw (LPS) was placed on the side where the HRVA was absent. Placement of the C2 TLS was performed as described by Wright17 with an entry point at the junction of the C2 spinous process and the lamina on one side, and then the contralateral lamina was carefully drilled to a depth of 24e30 mm depending on C2 lamina size. The trajectory was kept slightly less than the downslope of the lamina to prevent ventral cortical breakthrough to the spinal canal. A 4.0-mm-diameter polyaxial screw was then inserted along the same trajectory with a length of 24e30 mm. We first connected the C2 LPS with C1 lateral mass screw with plate to achieve C1-C2 joint reduction and then connected each C1 lateral mass screw to the ipsilaterally projecting screw head of the C2 TLS using connecting rods. For patients with occipitalization of the atlas, the C2 TLS were connected to the occiput. Finally, the C1 arch, C2 lamina, and spinous process were decorticated. Autogenous morselized cancellous grafts (15e20 g) harvested from the posterior iliac crest were bridged between the C1 arch and the C2 lamina. For patients who underwent occiput-C2 fixation, bone grafting was the same as described earlier except that the cancellous grafts were bridged between the occiput and the C2 lamina.
Table 2. Basion-Dens Interval of 15 Redislocation Cases
BDI pre, mm
Revision Surgery (n [ 7)
Without Revision Surgery (n [ 8)
Redislocation (n [ 15)
14.1 2.6
12.4 2.2
13.2 2.5
BDI post, mm
9.3 4.6
6.4 4.2
7.9 4.7
BDI final, mm
13.4 3.0
10.8 2.5
12.1 3.0
BDI, basion-dens interval; pre, preoperative; post, postoperative; final, at final follow-up of primary surgery.
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ORIGINAL ARTICLE YONGQIANG WANG ET AL.
OUTCOMES OF AAD WITH HRVA USING C2 TRANSLAMINAR SCREWS
Postoperative Management The drains were removed after 48 hours. A Philadelphia collar was routinely used, and 3 patients required halo-vest immobilization. Statistical Analysis Clinical data were analyzed with IBM SPSS Statistics Version 22.0 (IBM Corp., Armonk, New York, USA) and presented as mean SD. Comparison analyses were performed with c2 test or Wilcoxon test. Statistical significance was set at P < 0.05. RESULTS This study enrolled 58 patients (26 men, 32 women; mean age, 42.3 14.3 years; range, 14e73 years). Preoperative diagnoses included instability in 15 patients and dislocation in 43 patients; of the latter, 13 were irreducible and required transoral release.20,21 The incidence of bilateral HRVA was 5.2% (3 of 58 patients); thus, a total of 61 TLS were placed. C1-C2 fixation was performed in 26 patients without C1 occipitalization, 3 of whom underwent transoral release. Atlantodental interval decreased from 9.9 3.7 mm (range, 5.0e22.9 mm) to 0.2 0.8 mm (range, 0e3 mm) immediately postoperatively but increased to 1.0 1.7 mm (range, 0e5.0 mm) at the final follow-up (P < 0.05). C0-C2 fixation was performed in 32 patients combined with C1 occipitalization, 10 of whom underwent transoral release. Clivus-axial angle was 125 13 (range, 87e149 ) preoperatively, increased to 154 13 (range, 120e176 ) postoperatively, and decreased to 150 15 (range, 115e176 ) at the final follow-up (P < 0.05). BAI of the cohort was 20.2 4.9 mm (range, 10.5e33.7 mm) preoperatively and decreased to 10.9 3.0 mm (range, 2.8e20.6 mm) postoperatively (P < 0.05). Some cases had combined os odontoideum or old odontoid fracture, so BDI was measured in only 35 cases. BDI was 23.4 3.1 mm (range, 7.3e20.8 mm) preoperatively and
decreased to 7.2 3.3 mm (range, 3.1e15.8 mm) postoperatively (P < 0.05). BAI of 18 redislocation cases is presented in Table 1, and BDI of 15 redislocation cases is presented in Table 2. Both BAI and BDI decreased significantly after primary surgery but increased again before fusion or revision. BAI and BDI remained unchanged after surgery in 40 patients in whom solid fusion was achieved in 4 months. Surgical details are shown in Table 3. The mean follow-up time was 66.5 31.7 months (range, 24e124 months), mean estimated blood loss was 179 140 mL (range, 50e800 mL), and mean operative time was 155 46 minutes (range, 96e281 minutes). The average preoperative JOA score of 56 patients with myelopathy was 11.9 2.8 (range, 5.0e16.0), and JOA score at the final followup was 14.6 2.4 (range, 6.0e17.0) (P < 0.05). The fusion rate of the whole cohort was 93.1% (54 of 58 patients). At 4-month follow-up, fusion rate was 81% (47 of 58); 54 cases achieved fusion at a mean 4.9 2.7 months (range, 4e16 months). At 4-month follow-up, 40 cases appeared to have achieved bony fusion without redislocation (Figure 1). In 14 cases of redislocation, fusion was achieved at a mean 7.3 4.3 months (range, 4e16 months); 3 cases involved neurologic deterioration and required an odontoidectomy (Figure 2). Another 4 cases in which bony fusion was not achieved also required revision surgery, including extending a fixed segment in 2, replacement with bilateral transarticular screws in 1 (Figure 3), and replacement with bilateral LPS in 1 (Figure 4). The redislocation rate was 31% (18 of 58 patients), and the reoperation rate was 12.1% (7 of 58 patients). The distribution of redislocation cases was 2 in the instability group, 12 in the reducible dislocation group, and 4 in the irreducible dislocation group; the distribution of reoperation cases in these 3 groups was 1 in the instability group, 5 in the reducible dislocation group, and 1 in the irreducible dislocation group (Tables 3 and 4).
Table 3. Surgery-Related Information of Cohort Variable Number of patients
Instability
Reducible Dislocation
Irreducible Dislocation
Total
15
30
13
58
8
13
5
26 32
Sex Male Female
7
17
8
44.7 15.9
40.3 13.9
43.8 13.8
C1-C2
11 (1B)
11 (1B)
4 (1B)
26
C0-C2
4
19
9
32
Transoral
Age, years, mean SD Operation
—
—
13
13
Fusion cases
14
28
12
54
Redislocation
2
12
4
18
Revision surgery
1
5
1
7
C1-C2, posterior C1-C2 fixation; C0-C2, posterior C0-C2 fixation; Transoral, transoral release þ posterior fixation; 1B, bilateral translaminar screws in 1 case, unilateral pedicle screw combined with unilateral translaminar screw in others.
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ORIGINAL ARTICLE YONGQIANG WANG ET AL.
OUTCOMES OF AAD WITH HRVA USING C2 TRANSLAMINAR SCREWS
Figure 1. A 36-year-old man with a C1-C2 reducible dislocation. Japanese Orthopaedic Association score was 10, and atlantodental interval was 7.5 mm. (A) Lateral extension x-ray indicating dislocation. (B) High-riding vertebral artery on the right side. (C) Normal pedicle on the left side. (D)
Considering the redislocation rate, there was a significant difference between the instability group (13.3%; 2 of 15) and the reducible dislocation group (40%; 12 of 30), but no significant differences were detected between the instability and irreducible dislocation groups or the reducible dislocation and irreducible dislocation groups (30.8%; 4 of 13). Considering the reoperation rate, no significant difference was detected among the 3 groups (Table 3). All revision cases achieved bony fusion at the final follow-up. The mean reoperation time of the 7 revision cases was 6.0 5.0 months (range, 0.2e12 months) after the primary operation, and the mean age of the patients was 37 8 years (range, 29e52 years). Perioperative complications included cerebrospinal fluid leakage in 2 cases, fever in 5 cases, poor wound healing in 2 cases, and donor site complications in 4 cases; all were cured by conservative treatment.
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Postoperative anatomic reduction. (E) Long pedicle screw on the left side. (F) Translaminar screw on the right side. (G) Solid fusion at 4-month follow-up; atlantodental interval was 0. (H) Sufficient decompression of the spinal cord. Japanese Orthopaedic Association score was 15.
DISCUSSION The reported risk of VA injury in a clinical series was 4.1%e 8.2%,5-7 which is predominant in cases combined with HRVA. Harms et al.9 recommended their technique as an efficient alternative to the Magerl technique with no vascular damage. Goel et al.8 also considered C2 pedicle screws to be able to decrease the risk of VA injury compared with the Magerl technique. However, Yoshida et al.10 judged approximately 10% of screw trajectories risky in both techniques, indicating the C2 pedicle screw placement has nearly the same risk as atlantoaxial transarticular screw placement. Yeom et al.19 reported that the rate of VA groove violation was significantly lower with pedicle (49%) than transarticular (63%) screws. However, the VA groove violation did not equal a VA injury.
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ORIGINAL ARTICLE YONGQIANG WANG ET AL.
Figure 2. A 51-year-old woman with a C1-C2 reducible dislocation and cranial settling. Japanese Orthopaedic Association score was 14. (A) Preoperative computed tomography demonstrating an increased atlantodental interval; clivus-axial angle was 117 . (B) Preoperative magnetic resonance imaging. Cervicomedullary angle was 113 . (C) Anatomic reduction was achieved during the operation and C0-C2 was instrumented with a unilateral C2 pedicle screw and a contralateral C2 translaminar screw. Clivus-axial angle was 145 . (D and E) Lateral x-ray and sagittal computed tomography at 4-month follow-up showing redislocation
Neo et al.12 introduced a novel trajectory for transarticular screw placement; they preferred to purchase the most posterior and medial part of the isthmus and successfully treated 7 cases of unilateral HRVA. Lee et al.22 reported similar results with transarticular screws by choosing a more medial and superior entry point. Song et al.18 also reported good surgical results using unilateral transarticular screw fixation and interspinous bone graft wiring to treat 13 cases of atlantoaxial instability combined with HRVA. However, transarticular screws could not avoid the risk of VA injury, and a new trajectory would decrease the purchase of the C1 lateral mass, which would lessen the stiffness of the constructs. Daentzer11 used a hook-rod system
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OUTCOMES OF AAD WITH HRVA USING C2 TRANSLAMINAR SCREWS
with solid fusion of C0-C2. (F) Sagittal magnetic resonance imaging at 4-month follow-up showing compression of the cord. Cervicomedullary angle was 136 , and Japanese Orthopaedic Association score was 12 (neurologic deterioration). (G) Computed tomography 4 months after transoral odontoidectomy as a revision surgery. Clivus-axial angle was 135 . (H) Magnetic resonance imaging 4 months after revision surgery. Cervicomedullary angle was 154 , and Japanese Orthopaedic Association score was 17.
combined with wiring to treat a case of atlantoaxial instability with bilateral HRVA, but no biomechanical testing reports have been available for this system with C1-C2 fixation until now. Wright17 first introduced crossing C2 laminar screws for incorporation of the axis into atlantoaxial or craniocervical constructs. The major advantage is the removal of the risk to the VA, and the only potential drawback would be unrecognized laminar screw breakout ventrally into the spinal canal. Meyer et al.23 verified this result by treating a cohort of 27 patients with a mean age of 68.9 years with 52 TLS; the fusion rate was 92.9%. As the safety and efficacy of TLS have been reported by clinical series and biomechanical studies, we used this
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OUTCOMES OF AAD WITH HRVA USING C2 TRANSLAMINAR SCREWS
Figure 3. A 52-year-old man with a C1-C2 instability. Japanese Orthopedic Association score was 15. (A) Instability of C1-C2; atlantodental interval was 13.5 mm. (B and C) Preoperative computed tomography showing high-riding vertebral artery. (D) Preoperative magnetic resonance imaging. (E) Posterior reduction and fixation of C1-C2 with C1 lateral mass screws and C2 bilateral translaminar screws. Atlantodental interval decreased to 3
technique to manage AAD cases. However, our surgical results are unsatisfactory with high redislocation and reoperation rates. We speculate the increased morbidity is due to differences in diagnoses: 26 of 27 cases in the report by Meyer et al.23 were trauma cases in which the purchase of TLS is sufficient for fracture healing. In the present study, the LPS was the optimal choice for C2 fixation if the pedicle was wide enough; only when the LPS pathway was violated by HRVA did we use TLS. Almost all 58 cases achieved anatomic reduction during the operation. However, during the follow-up, many patients presented with redislocation; the redislocation rate in the reducible dislocation group was significant higher than in the instability group. We speculate that the purchase required to maintain reduction in the reducible dislocation group was higher than that of the instability group. Dislocation was more severe in the irreducible dislocation group than in the reducible dislocation group; however, after transoral release, the required purchase decreased and should be lower than that in the reducible dislocation group. For patients with combined occipitalization of the atlas, we considered that occiput-C2 fixation was equivalent to the C1-C2 constructs because of the immobile C0-C1 segment. Although it makes the surgical strategy heterogeneous and the differences in purchase between occipital screws and C1 lateral mass screws are
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mm. (F and G) Postoperative sagittal computed tomography and magnetic resonance imaging immediately after primary surgery. (H and I) Redislocation was detected 4 months after primary surgery. (J) Solid fusion was achieved 4 months after C1-C2 transarticular screw fixation as a revision surgery. Atlantodental interval was 5 mm, and Japanese Orthopaedic Association score was 17.
unknown, the placement of C0 screws is much easier than that of C1 lateral mass screws. Many biomechanical studies have compared different posterior atlantoaxial fixations. Sim et al.13 noted that intralaminar screws were inferior to pedicle screws in the lateral bending models. Lehman et al.16 concluded that pedicle screws provided the strongest fixation for initial and salvage applications. In cases of failure, lamina screws appeared to provide stronger and more reproducible fixation than pars screws. Lapsiwala et al.24 reported that C1 lateral masseC2 intralaminar screw fixation restored resistance to lateral bending but not to the same degree as transarticular or C1 to C2 pedicle fixation techniques. Gorek et al.25 indicated the potential of the intralaminar screw technique to provide equivalent stability to that of the C2 pedicle screw technique. TLS appears good in biomechanical tests, but in the present study, the redislocation and reoperation rates were high, and the surgical outcomes were unsatisfactory. In some cases, although anatomic reduction was achieved during the primary operation with the help of cranial traction and LPS, maintaining reduction was difficult (Figure 2), which demonstrates the poor biomechanical performance of TLS. To the best of our knowledge, this is the largest clinical series to focus on AAD
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ORIGINAL ARTICLE YONGQIANG WANG ET AL.
Figure 4. A 40-year-old man with a C1-C2 instability. Japanese Orthopaedic Association score was 14. (A and B) Flexion-extension x-ray indicates instability of C1-C2. Atlantodental interval was 10.7 mm. (C) Preoperative computed tomography showing bilateral high-riding vertebral artery. (D) Preoperative magnetic resonance imaging. (E) Anatomic reduction was achieved, and atlantodental interval decreased to 0 during the operation, but postoperative x-ray 6 days after surgery shows redislocation. (FeI)
combined with HRVA. We advocate that new treatment methods should be investigated to facilitate the clinical outcomes. In this study, in 14 cases of redislocation, fusion was ultimately achieved: 3 patients had neurologic deterioration and required odontoidectomy owing to the bony fusion of atlantoaxial joint, whereas the other 11 cases appeared not to have neurologic deterioration, making salvage surgery unnecessary. Two of the other 4 revision cases underwent fixed segment extension; 2 were revised using transarticular screws or C2 LPS at high risk of VA injury (Figures 3 and 4); thus, long segment fixation should be considered in cases of severe dislocation. Some authors try to manage AAD with an anterior approach technique, but anterior atlantoaxial transarticular screw technique has the same limitation as Magerl technique, which is unsuitable for irreducible AAD.26 The limitations of transoral atlantoaxial reduction plate technique are the increased opportunity of surgical site infection and C2 vertebrae screws loosening.27 Despite the high reoperation and redislocation rates, the neurologic recovery rate was good in the present study, and the JOA score increased significantly at the final follow-up. Perhaps the combined C2 pedicle screws and salvage surgeries contributed to the results.
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X-ray and computed tomography after revision surgery using bilateral C2 long pedicle screws. Violation of C2 vertebral artery groove could be detected, but no evidence of vertebral artery injury was noted. (J) Computed tomography 8 months after revision surgery showing bony fusion of the articular lateral mass (arrow). Japanese Orthopaedic Association score was 16.
CONCLUSIONS As an alternative option for C1-C2 or C0-C2 fixation, C2 TLS does not carry the risk of VA injury; however, the surgical results of TLS are unsatisfactory, and salvage surgery may be required. Thus, C2 TLS is unsuitable for AAD cases, and new treatment methods should be investigated to facilitate the clinical outcomes of AAD combined with HRVA. Perhaps extending fixed segments should be considered.
Table 4. Surgical Outcomes Reduction and Fusion
Redislocation and Fusion
Redislocation without Fusion
Number
40
14
4
Fusion time, months
4
7.3 4.3
*
Revision cases
0
3
4
*Nonfusion before revision surgery, achieving fusion at 5.5 1.9 months after revision surgery.
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