C1 Lateral Mass Screw Placement in Occipitalization With ...

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CERVICAL SPINE

SPINE Volume 39 , Number 24 , pp 2013 - 2018 ©2014, Lippincott Williams & Wilkins

C1 Lateral Mass Screw Placement in Occipitalization With Atlantoaxial Dislocation and Basilar Invagination

A Report of 146 Cases

Yi-heng Yin , MD, * † Xin-guang Yu , MD , * Guang-yu Qiao , MD , * Sheng-li Guo , MD , * and Jian-ning Zhang , MD †

DOI: 10.1097/BRS.0000000000000611

Study Design. Retrospective study of 146 patients with the diag-nosis of occipitalization, atlantoaxial dislocation (AAD) and basilar invagination, using a novel surgical treatment strategy. Objective. To introduce a novel fi xation and reduction technique. Summary of Background Data. Atlas occipitalization associ-ated with basilar invagination often result in fi xed AAD that need reduction and occipitocervical fi xation. The widely used occipito-cervical fi xation with suboccipital screws has several limitations such as the poor screw purchase in maldevelopment of the occipital bone, limited area available for implants in previous suboccipital craniectomy. The placement of occipitalized C1 lateral mass screw is an alternative option. Methods. From June 2007 to June 2013, 146 patients of occipitalized atlas with fi xed AAD and basilar invagination, underwent fi xation and reduction via C1 lateral mass and C2 pars/pedicle screw. Results. A total of 143 patients achieved the follow-up in the range from 6 months to 4 years (average, 30 mo). Neurological improvement was seen in all the 143 patients, with the averaged Japanese Orthopedic Association scores increasing from 11.6 to 15.5. Radiographical evaluation showed that solid bony fusion was achieved in all patients, and complete reduction was attained in 95 patients, and partial reduction (>60%) in 40 patients, and no effective reduction in 8 patients who had additional transoral

From the * Department of Neurosurgery, PLA General Hospital, Beijing, China; and † Department of Neurosurgery, PLA Navy General Hospital, Beijing, China.

Acknowledgment date: May 21, 2014. Revision date: August 10, 2014. Acceptance date: August 14, 2014.

The manuscript submitted does not contain information about medical device(s)/drug(s).

The National Natural Science Foundation of China (81301274) and China Postdoctoral Science Foundation (2014M552653) funds were received in support of this work.

No relevant fi nancial activities outside the submitted work.

Address correspondence and reprint requests to Guang-yu Qiao, MD, Department of Neurosurgery, PLA General Hospital, 28 Fuxing Rd, Haidian District, Beijing 100853, China; E-mail: [email protected]

Occipitalization of the atlas represents the most com-mon congenital anomaly involving the cranioverte-bral junction (CVJ) with a prevalence rate of 0.08%

to 2.79% among the general population. 1 It is always associ-ated with basilar invagination and fi xed atlantoaxial disloca-tion (AAD) that contribute to the ventral cervicomedullary compression. To successfully stabilize the mechanically com-promised CVJ, one must surgically correct deformity or dis-placement and decompress neural structures. Occipitocervical fi xation spanning from occiput to C2 is widely used in disor-ders related with instability of the CVJ. 2 However, several lim-itations of the occipitocervical fi xation reside in the occiput part of the construct that does not easily accommodate instru-mentation especially in conditions of maldevelopment of the occipital bone and suboccipital craniectomy. 3 The acute angle between the occipital bone and the cervical spine also impose geometrical constraints on the contour of occipitocervical construct. These limitations may lead to poor occipital screw purchase, or even screw pull out. 4

Recently, a new technique of occipital condyle screw in normal anatomy or C1 lateral mass screw in occipitalization has been described, 5–8 although the reported cases were lim-ited. In this study, we modifi ed this technique, 8 , 9 and achieved

decompression. Magnetic resonance imaging demonstrated that the ventral cervicomedullary compression was relieved in all patients. Conclusion. Although technically demanding, the C1 lateral mass placement in occipitalization is very useful in the rescue situation where more conventional stabilization alternatives are not technically possible, or as routine occipitocervical stabilization. It provides fi rm stabilization offering an optimum situation for bony fusion, and meanwhile the effective reduction of fi xed AAD and basilar invagination. An extremely high fusion rate can be expected with minimal complications and minimal postoperative immobilization with this technique. Key words: atlantoaxial dislocation , basilar invagination , C1 lateral mass , occipitocervical fi xation , occipitalization , reduction . Level of Evidence: 4 Spine 2014;39:2013–2018

Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.

SPINE140671_LR 2013SPINE140671_LR 2013 29/10/14 2:44 AM29/10/14 2:44 AM

CERVICAL SPINE C1 Screw Placement in Occipitalization • Yin et al

2014 www.spinejournal.com November 2014

simultaneously the fi xation and reduction via C1 lateral mass and C2 pars/pedicle screw fi xation in 146 patients of occipi-talization and fi xed AAD and basilar invagination, the largest case series reported thus far.

MATERIALS AND METHODS

Patient Population From June 2007 to June 2013, 146 patients of occipital-ized atlas combined with fi xed AAD and basilar invagina-tion underwent direct fi xation and reduction via C1 lateral mass and C2 pars/pedicle screw fi xation at the Department of Neurosurgery of PLA General Hospital. The series patients included 93 females and 53 males, in the age range from 12 years to 59 years (mean, 36 yr). The common presenting symptoms and associated radiological anomalies are summa-rized in Tables 1 and 2 .

A thorough preoperative assessment including the radio-graphical image, thin-slice computed tomography (CT)/CT angiography and magnetic resonance imaging (MRI) was performed in all patients. Dynamic radiographical evaluation (hyperextension and fl exion position) was also performed to check the cervical spine stability and reducibility of AAD unless severe oblongata or spine cord compression existed. The atlantodental interval at the narrowest CVJ region was measured in sagittal reconstructed CT scans.

Operative Technique No cervical traction was needed before or during the oper-ation. The patient was placed in the prone position with a Mayfi eld head holder. A posterior midline incision was made to expose the posterior edge of the foramen magnum and the C2 lamina. The vessels and C2 nerve roots were retracted cephalad to expose the superior and internal aspect of the isthmus of the C2 vertebra. The infraoccipital margin or the

C1 posterior arch (if not totally fused) were drilled to expose the C1–C2 facet joints. During the process, the vertebral arteries should be detected and protected in case of injury. Then, C1–C2 facet joint capsule and scars and osteophytes were removed to attain the mobility between C1 and C2. The cartilage endplate was curetted and drilled to further increase the mobility so as to reduction. C1 screw entry points were exposed at the middle of posterior surface of C1–C2 facet (within 1 mm above the facet) with a burr and were prepared with a 3.0-mm hand drill before a 3.5-mm screw (length, 18–24 mm; VERTEX; Medtronic Sofamor Danek, Minneap-olis, MN) was inserted ( Figures 1, 2 ). C2 pars/pedicle screws were implanted as described in the previous text. 10 , 11 Bilat-eral titanium rods (diameter, 3.5 mm; VERTEX; Medtronic Sofamor Danek) contoured in a slight curved shape were fi xed with screws. During the process, the lever system drew occiput backward and pushed C2 downward and forward and achieved the reduction of AAD and BI as described in the previous text. 12 Cancellous or decorticated massive bone from the posterior iliac bone was placed into the C1–C2 facet joint and during the decorticated occiput and C2 spinous process. Hard cervical collars were placed for 3 months.

Radiographical Evaluation and Follow-up All patients underwent postoperative reconstructive CT and MRI at discharge and 6 months after surgery. Radiographies/CT and MRI were repeated at 12 months follow-up and then depending on the pathogenetic condition. The neuro-logical status of Japanese Orthopedic Association score was evaluated. A postoperative atlantodental interval less than 3 mm was considered to be complete reduction, and more than 3 mm without cord compression was considered partial reduction, and more than 3 mm with cord compression was considered no effective reduction. Fusion was defi ned when there was defi nite osseous union between the occiput and C2 lamina as shown by postoperative reconstructive CT.

RESULTS One patient (0.7%) had sudden respiratory and cardiac arrest 12 hours after the extubation without explainable reasons. After the cardiopulmonary resuscitation, the patient sustained deep coma and eventually died 35 days later because of multi-ple organ failure. There were 22 patients (15%) complaining


TABLE 1. Principal Presenting Clinical Features of 146 Cases With Occipitalization

Symptoms and Signs n (%)

Appearance changes 118 (81)

Restricted neck movement 104 (71)

Occiput/neck pain 80 (55)

Monoparesis 6 (4)

Hemiparesis 25 (17)

Quadriparesis 113 (77)

Sensory loss 102 (70)

Ataxia 86 (59)

Lower cranial nerve dysfunction 74 (51)

Dyspnea or sleep apnea 22 (15)

Intracranial hypertension 6 (4)

Sphincter disturbance 19 (13)

TABLE 2. Associated Radiological Anomalies of 146 Cases With Occipitalization

Associated Anomalies n (%)

Atlantoaxial dislocation 146 (100)

Basilar invagination 146 (100)

Chiari malformation 96 (66)

Syringomyelia 64 (44)

C2–C3 fusion 54 (37)

Rotational deformity 19 (13)




Figure 1. Three-dimensional construction of the CVJ with the VA passing through this region in atlas occipitalization. The black dots indicate the ideal entry points for C1 screw placement locating at the midpoint of the posterior surface of C1 facet and C2 pedicle screw. A , posterior view. B , Lateral view. VA indicates vertebral artery; CVJ, craniover-tebral junction.

of dyspnea or sleep apnea symptoms prior to surgery, and after reduction surgery the symptoms released immediately in 12 patients and released partially in 10 patients who were treated with respirator support. Among the 10 patients, 8 patients recovered at approximately 1 to 3 days later and another 2 had tracheotomy and sustained respirator for 1 week and then gradually recovered. One patient had the C1 screws inserted too rostrally that could have penetrated the hypoglossal canal and vertebral artery (VA) canal in the non-dominant side and no events occurred. Five patients had slight break of the C2 pars and no neurovascular injuries occurred. The detailed clinical outcomes and complications were shown in Table 3 .

A total of 143 patients achieved the follow-up in the range from 6 months to 4 years (average, 30 mo). Neuro-logical improvement was seen in all the 143 patients, with the averaged Japanese Orthopedic Association scores increasing from 11.6 to 15.5. Radiographical evaluation showed that solid bony fusion was achieved in all patients, and complete reduction was attained in 95 patients, and partial reduction (>60%) in 40 patients, and no effective reduction ( < 50%) in 8 patients. Among the 8 patients, although the postoper-ative symptoms had partial relief, there still existed ventral compression at 6-month follow-up and additional transoral decompression was performed. At the latest follow-up, MR image demonstrated the ventral cervicomedullary compres-sion was relieved well in all 143 patients ( Figures 3, 4 ).

DISCUSSION In 1910, occipitocervical fi xation was initially described by Pilcher 13 for the treatment of AAD. Since then, numerous techniques have emerged and undergone refi nement includ-ing the wire/cable technique, rod-wire technique, screw-plate

constructs, screw-rod constructs, and transarticular screw fi xation, etc . No single procedure currently used addresses of all the clinical conditions adequately. As mentioned before, the suboccipital screw has several disadvantages such as the poor screw purchase in maldevelopment of the occipital bone, limited area available for implants in previous suboccipital craniectomy, and the uncomfortable complain in the suboc-cipital area due to the thin subcutaneous tissue. 4 A continuous evolution of fi xation options is needed.

The fi xation technique of occipital condyle screw or C1 lateral mass screw in occipitalization was not new. La Marca et al 5 and Uribe et al 6 performed occipital condyle screw placement in cadaveric heads, although they had different angles of screw trajectory. Dvorak et al 14 reported an ante-rior transarticular occipitocervical fi xation case ending in the occipital condyle. Frankel et al 15 reviewed the CT scans of 80 occipital condyles and thought that condyle screw could be safely placed at an angle of 20 ° to 33 ° cranially and they also performed a clinical case with this technique. In earlier reports published by Goel and Kulkarni, 8 patients with occipitalized atlas and AAD underwent atlantoaxial lateral mass fi xation. Jian et al 7 measured the volume of C1 lateral mass via recon-structed CT in 16 patients of atlas assimilation with the width of 13.9 ± 1.9 mm and length of 16.9 ± 3.0 mm, suggesting the feasibility and limitation of this screw placement.

In this study, we reported the largest case series with C1 lateral mass fi xation technique in patients of occipitalization. Meanwhile, we attained effective reduction of fi xed AAD and basilar invagination in most cases. The main mecha-nism of reduction is that the implanted screws and rods drew C1 backward and pushed C2 downward and forward as described in the earlier text. 12 In our personal experience, this technique has several advantages: fi rst, the lateral mass screw

Figure 2. The trajectory of the C1 lateral mass and C2 pedicle screws in atlas occipitalization. A , Pos-terior view. B , Lateral view.





purchase has more stability than that of suboccipital screw. The mean C1 screw length obtaining bone purchase in our study was 18.5 mm (range: 15–21 mm), whereas the thick-ness of occipital bone was usually not more than 10 mm and was even thinner in conditions of occipitalization. Second, for the treatment of fi xed AAD and basilar invagination, we have achieved simultaneously reliable stability and reduction of the malalignment at the CVJ, avoiding of transoral odontoidec-tomy or periodontoid-tissue release. 16 Third, the reduction of AAD and basilar imagination achieved by the lever system has

more reduction effi cacy than the method proposed by Goel, 9 which was mainly attained by intraoperative cervical traction and inserted titanium plate spacers.

As the C1 facet is usually ventral declined in patients of occipitalization combined with AAD, 1 the posterior surface of C1 lateral mass is much shorter than the anterior surface. The ideal entry point for C1 screw is located at the midpoint of the posterior surface of C1 facet ( Figures 1, 2 ), although the location is very deep and diffi cult to expose. If the entry point were too cephalad or on the fused C1 posterior arch (if present), the risk of injuring VA or hypoglossal nerve would be much higher. The screw trajectory should be tailored and adjusted with the length of the anterior and posterior surface of C1 lateral mass and the facet incline angles. Our results showed that the screw is directed approximately between 0 ° and 40 ° cephalad and medially approximately between 0 ° and 20 ° . The vast differences of the trajectory angles lie in the irregularity of the morphology of C1 lateral mass, and the pro and con of safety and operability. The more cephalad angles would make the screw placement more comfortable, but may increase the risks of injuring VA and hypoglossal.

The opening of joint capsule of facet is the key to mobilize the fi xed dislocation of C1–C2. The subperiosteum dissection of the C1–C2 facet should be performed with great caution under operating microscope, especially when the aberrant VA travels on the posterior surface of the occipitalized C1 lat-eral mass medially and superiorly. As the aberrant VA is not uncommon in occipitalization, 17–19 preoperative evaluation and intraoperative protection is equally important. If possible, the 3-dimensional reconstruction of the bone together with VA will help learn the full view of VA and bony deformity


TABLE 3. Clinical Outcomes and Complications Outcomes and Complications Treatment n

Effective reduction 135

No effective reduction Additional transoral decompression 8

Bony fusion 143

Death 1

Lung infection Tracheotomy, antibiotics 5

Deep vein thrombosis Anticoagulation, thrombolytic therapy 2

Postoperative dyspnea Ventilator support 10

Break of the C2 pars No events 5

Break of HP/VA canal No events 1

HP canal indicates hypoglossal canal; VA canal, vertebral artery canal.

Figure 3. A 21-year-old male presented with weakness of the extremities and bucking and ataxia. Preoperative MR im-age ( A ) and CT ( B ) indicated AAD, basilar invagination, C1 assimilation and Chiari malformation and syringomyelia. After C1 lateral mass ( C ) and C2 pedicle screw fi xation was performed, the VA canal (red arrow) and the hypoglossal canal (yellow arrow) were still intact. At 2-year follow-up, postoperative MR image ( D ) and CT ( E , F ) showing complete reduction and the regressed syrinx. MR image indicates magnetic resonance image; CT, computed tomography; VA, vertebral artery; AAD, at-lantoaxial dislocation.




➢ Key Points

Although technically demanding, the C1 lateral mass placement in occipitalization is very useful in the rescue or salvage situation where more conventional stabilization alternatives are not technically possible, or as routine occipitocervical stabilization. The screw trajectory should be tailored and

adjusted with the length of the anterior and posterior surface of C1 lateral mass and the facet incline angles. It provides fi rm stabilization off ering an optimum

situation for bony fusion, and meanwhile the eff ective reduction of fi xed AAD and basilar invagination.

Figure 4. A 44-year-old male presented with a 3-year history of weakness of the extremities, bucking, and dyspnea. Pre-operative MR image ( A ) and CT ( B ) indi-cated occipitalization of the atlas, AAD and basilar invagination. Postoperative CT ( C , E ) and MR image ( D ) demonstrated the bony fusion at the CVJ and reduction of AAD and basilar invagination. CT in sagit-tal plane ( C ) and coronal plane ( F ) showed the VA canal (red arrow) and hypoglossal canal (yellow arrow) were intact. MR im-age indicates magnetic resonance image; CT, computed tomography; VA, vertebral artery; AAD, atlantoaxial dislocation; CVJ, craniovertebral junction.

( Figure 1 ). Study of the VA canal and hypoglossal canal in the fused occipital condyle/C1 lateral mass and C2 transverse foramen and isthmus on sagittal and coronal CT scans pro-vides detailed information on the operational scheme ( Figures 3, 4 ). Wang et al 17 described 4 distinct types of VA in occipi-talization with type II and type III of higher risks of injuries. The type II VA is passing on the posterior surface of C1 lateral mass or making a curve on it. In our experience, the nut of C1 screw may pinch the type II VA when the screw is fastened with rod. Accordingly, the screw and nut should be designed at proper location when the mobilization of VA is diffi cult. The type III VA is entering the cranium through an osseous foramen between the fused atlas and occiput. As the osseous foramen is concealed in the occiput, the C1 screw may pen-etrate into the canal and injury the VA. In addition, fenestra-tion of the VA and fi rst intersegmental artery and high-riding VA are also the common variations that should be noticed during the C2 pars/pedicle screw insertion. 19

In fact, the VA canal offers protection to the VA as it is surrounded by cortical bone. We had only 1 side of the VA canal and hypoglossal canal penetrated, and no related com-plications occurred. The reason was that the area available of entry points was limited and meanwhile the screw was placed too cephalad.

CONCLUSION This study represents the largest series of clinical report of combined anomalies of atlas occipitalization, AAD, and basi-lar invagination. Because numerous pathologies involve the CVJ, the choice of operational procedure should be tailored

depending on patient pathology, anatomy, and surgeon pref-erence. Although technically demanding, the C1 lateral mass placement in occipitalization is very useful in the rescue or salvage situation where more conventional stabilization alter-natives are not technically possible, or as routine occipitocer-vical stabilization. The result that all the patients achieved good outcomes at follow-up indicates that this is a promis-ing technique for patients with occipitalization. An extremely high fusion rate can be expected with minimal complica-tions and minimal postoperative immobilization with this technique.





Acknowledgments Authors Yi-heng Yin, MD, and Xin-guang Yu, MD, contributed equally to this work and should be considered as co-fi rst authors.

References 1. Yin YH , Yu XG , Zhou DB , et al. Three-dimensional confi gura-

tion and morphometric analysis of the lateral atlantoaxial articula-tion in congenital anomaly with occipitalization of the atlas . Spine (Phila Pa 1976) 2012 ; 37 : E170 – 3 .

2. Sasso RC , Jeanneret B , Fischer K , et al. Occipitocervical fusion with posterior plate and screw instrumentation. A long-term follow-up study . Spine (Phila Pa 1976) 1994 ; 19 : 2364 – 8 .

3. Vale FL , Oliver M , Cahill DW . Rigid occipitocervical fusion . J Neurosurg 1999 ; 91 : 144 – 50 .

4. Fehlings MG , Cooper PR , Errico TJ . Posterior plates in the man-agement of cervical instability: long-term results in 44 patients . J Neurosurg 1994 ; 81 : 341 – 9 .

5. La Marca F , Zubay G , Morrison T , et al. Cadaveric study for place-ment of occipital condyle screws: technique and effects on sur-rounding anatomic structures . J Neurosurg Spine 2008 ; 9 : 347 – 53 .

6. Uribe JS , Ramos E , Vale F . Feasibility of occipital condyle screw place-ment for occipitocervical fi xation: a cadaveric study and description of a novel technique . J Spinal Disord Tech 2008 ; 21 : 540 – 6 .

7. Jian FZ , Su CH , Chen Z , et al. Feasibility and limitations of C1 lateral mass screw placement in patients of atlas assimilation . Clin Neurol Neurosurg 2010 ; 114 : 590 – 6 .

8. Goel A , Kulkarni AG . Mobile and reducible atlantoaxial disloca-tion in presence of occipitalized atlas: report on treatment of eight cases by direct lateral mass plate and screw fi xation . Spine (Phila Pa 1976) 2004 ; 29 : E520 – 3 .

9. Goel A . Treatment of basilar invagination by atlantoaxial joint distraction and direct lateral mass fi xation . J Neurosurg Spine 2004 ; 1 : 281 – 6 .

10. Goel A , Laheri V . Plate and screw fi xation for atlantoaxial sublux-ation . Acta Neurochir (Wien) 1994 ; 129 : 47 – 53 .

11. Harms J , Melcher RP . Posterior C1–C2 fusion with poly-axial screw and rod fi xation . Spine (Phila Pa 1976) 2001 ; 26 : 2467 – 71 .

12. Yin YH , Qiao GY , Yu XG , et al. Posterior realignment of irreduc-ible atlantoaxial dislocation with C1–C2 screw and rod system: a technique of direct reduction and fi xation . Spine J 2013 ; 13 : 1864 – 71 .

13. Pilcher LS . Subluxation of the atlas . Ann Surg 1910 ; 51 : 208 – 11 . 14. Dvorak MF , Fisher C , Boyd M , et al. Anterior occiput-to-axis screw

fi xation: part I: a case report, description of a new technique, and anatomical feasibility analysis . Spine (Phila Pa 1976) 2003 ; 28 : E54 – 60 .

15. Frankel BM , Hanley M , Vandergrift A , et al. Posterior occipitocer-vical (C0–C3) fusion using polyaxial occipital condyle to cervical spine screw and rod fi xation: a radiographic and cadaveric analysis . J Neurosurg Spine 2010 ; 12 : 509 – 16 .

16. Wang C , Yan M , Zhou HT , et al. Open reduction of irreduc-ible atlantoaxial dislocation by transoral anterior atlantoaxial release and posterior internal fi xation . Spine (Phila Pa 1976) 2006 ; 31 : E306 – 13 .

17. Wang S , Wang C , Liu Y , et al. Anomalous vertebral artery in cranio-vertebral junction with occipitalization of the atlas . Spine (Phila Pa 1976) 2009 ; 34 : 2838 – 42 .

18. Yamazaki M , Okawa A , Furuya T , et al. Anomalous vertebral arteries in the extra- and intraosseous regions of the craniovertebral junction visualized by 3-dimensional computed tomographic angi-ography: analysis of 100 consecutive surgical cases and review of the literature . Spine (Phila Pa 1976) 2012 ; 37 : E1389 – 97 .

19. Salunke P , Futane S , Sahoo SK , et al. Operative nuances to safe-guard anomalous vertebral artery without compromising the surgery for congenital atlantoaxial dislocation: untying a tough knot between vessel and bone . J Neurosurg Spine 2014 ; 20 : 5 – 10 .



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