| ObjectiveBasilar Invagination is caused by occipital-cervical region dysplasia leading to compression of the spinal cord and appearance of slow hand fine movements,walking on cottons,increased muscle tension in the limbs,pathological signs and other clinical manifestations and signs in patients.The main treatment is still surgery,and the preferred surgical treatment is foramen magnum decompression and occipital-cervical fusion surgery.Occipital bone and cervical fixation needed to be done in occipital cervical fusion surgery.However,Basilar Invagination patients are often accompanied by Axis dysplasia,which will initiate many difficulties in Axis fixation and affect the surgeon’s choice of surgical strategy.The purpose of this study is to study characteristics of the Axis deformity and its subsidiary structure and make classification of Axis dysplasia,so that make each patient’s treatment individualized,choose the most optimal method of fixation,avoid intraoperative injury of vertebral artery and nerve and other important structures around Axis.MethodsIn this study,we collected 26 patients with Basilar Invagination from December 2013 to December 2016.Among them,there were 10 males and 16 females with an average age of 41.8 years(25-63 years).Among them,the number of persons under the age of 50 was 18,accounting for about 69.23%of the total number of persons.There were 8 patients over the age of 50 which accounts for 30.76%.All 26 patients were diagnosed as Basilar Invagination.The onset of the disease was slow.The average time of onset of the disease was about two years and the longest was about thirteen years.The main clinical manifestations were numbness and weakness of the limbs,slow fine movements of the hands,increased muscle tension of the limbs,pathological signs and tendon reflex.All 26 patients were required to take cervical lateral radiographs,cervical computed tomography scans and cervical spinal magnetic resonance image examinations.Diagnostic criteria of basilar invagination:Chamberlain line:Odontoid process was 3-4mm higher than this line;McRae line:The line between the lowest point of the slope and the foramen magnum trailing edge,odontoid process should not exceed this line over 7mm,more than 7mm indicates the Basilar Invagination;Bilateral mastoid connection line:Odontoid process was over 2mm higher than this line indicating that it might be basilar invagination;The Boogard angle:The angle between the slope and the connecting line of the anterior and posterior margin of the foramen magnum.The normal reference is between:120°-130°.It is recognized as Basilar Invagination when it is more than 130°.Operation method:Among all the 26 patients,2 patients did not undertake surgical treatment,1 patient was given posterior single open-door laminoplasty,1 patient was given Suboccipital muscle decompression of the foramen magnum without any fixation,the remaining 22 patients underwent foramen magnum decompression and occipital-cervical fusion surgery.Among the 22 cases who were given occipital-cervical fusion surgery,there are 12 cases underwent C2 bilateral pedicle screw,2 cases underwent C2 lateral mass screw,1 case underwent C2 unilateral pedicle screw and none in contralateral,1 case underwent C2 pedicle screw on the right side and lateral mass screw on the left side,6 cases underwent C3-4 lateral mass screw with none on C2.All patients recovered well after operation and were discharged smoothly.Axis dysplasia classification:according to preoperative and postoperative imaging data of cervical CT scans and cervical lateral radiographs of 26 cases,deformity is divided into the following several types:type I(development is close to normal),type Ⅱ(lateral mass dysplasia),type III(pedicle dysplasia),type IV(lamina fusion),type Ⅴ(vertebral body fusion).We measured the width of bilateral pedicle and valid major axis of bilateral lateral mass in order to compare different type malformation.ResultsAmong the 26 cases in this study,11 cases developed closely to normal Axis,3 cases grew with lateral mass dysplasia,12 cases grew with pedicle dysplasia,lamina fusion and vertebral body fusion showed up in 2 cases simultaneously.The pedicle width measurement results:the average width of type Ⅰ patients’ left pedicle was 6.4818 + 1.3mm,the average width of right was 7.1909 + 1.4mm,average width type Ⅱ patients’ left pedicle was 6.43 + 1.1mm,the average width of right was 5.93 + 1.2mm,the average width of type Ⅲ patients’ left pedicle was 2.7 +1.3mm,the average width of right was 3.283 + 1.2mm.Analyzed by SPSS software,the pedicle width between patients with I type and Ⅲ type,type Ⅱ and type Ⅲ on both sides were statistically significant(P<0.01),however,there is no significant differences between type Ⅰ and Ⅱ on the right side(P>0.01).Lateral sagittal diameter measurement results:the average diameter of the type I patients’ left lateral mass was 12.127 + 1.3mm,the average diameter of right side was 13.091 + 1.2mm,the average diameter of type Ⅱ patients’ left side was 6.58 + 1.2mm,the average diameter of the right side was 6.75 + 1.4mm,the average diameter of type Ⅲ patients5 left lateral mass was 8.5 + 1.4mm,the right side was 9.25 + 1.3mm.Analyzed by SPSS software,there is statistically difference between type Ⅰ and type Ⅱ,type Ⅰ and type Ⅲ,type Ⅱ and type Ⅲ patients on the left and right lateral mass width(P<0.01).Among 11 normal cases,9 of them underwent bilateral pedicle screws,1 patient underwent posterior single open door laminoplasty,1 patient was given Suboccipital muscle decompression of the foramen magnum without any fixation.The pedicle dysplasia showed up in 12 cases.Among the 12 type Ⅲ patients,1 of them was discharged without surgery,2 patients were given bilateral lateral mass screw,1 patient had peidicle dysplasia on the left side,therefore,pedicle screw was carried out on its right side and lateral mass screw was carried out on its left side.The other 8 patients grew up with lateral mass dysplasia combined with pedicle dysplasia.One of them was discharged without any surgery.1 patient underwent unilateral pedicle screw because of bilateral lateral mass dysplasia and unilateral pedicle dysplasia;1 case was operated with unilateral lateral mass screw because of bilateral pedicle dysplasia and unilateral mass dysplasia.In the remaining 6 cases failed to undergo fixation on C2,so that fixation was committed on C3-4 instead of C2.The lateral mass dysplasia developed in 3 cases and all 3 patients underwent bilateral pedicle screw fixation.ConclusionsFor patients with basilar invagination,thorough decompression of occipital cervical region and stable fixation are the keys to its treatment.It is crucial for us to fully understand the characteristics of the development of the Axis and its deformity will greatly affect the choice of surgical strategy for surgeons.The most common abnormal development of Axis is pedicle dysplasia in patients with Basilar Invagination,and the second common deformity is lateral mass dysplasia.Lamina fusion and vertebral body fusion are relatively uncommon and have little influence on occipital cervical fusion.Pedicle screw fixation is still the first choice for the operation of occipital-cervical fusion because of its good stability and three-dimensional fixation.Under the condition of well developed pedicle,pedicle screw fixation should be the first attempt for Axis.For those Axis with unilateral pedicle dysplasia,pedicle screw on one side with assistance of lateral mass screw on the other side is well accepted.If both two side pedicles developed not well,the lateral mass screw fixation is a good substantial.Basilar Invagination patients often associated with vertebral artery abnormalities.Because of the vertebral artery being adjacent to pedicle,abnormal vertebral artery will deviate closer to spinal cord and be located outside to the pedicle.Pedicle,even lateral mass,was pushed into deformation.Vertebral artery ran into the center of lateral mass and turn outside and kept running upward into cranial.Under such circumstances,the lateral mass screw has a great risk,which can damage the vertebral artery and affect the intracranial blood supply.The best operation way is to do fixation on C3-4 instead of C2.So there are a few factors about fixation on Axis surgeons need to consider carefully for the patients with basilar invagination:the width of pedicle;shape and size of lateral mass;vertebral artery running line.In order to protect the patients’ safety,it is crucial for doctors to eliminate all potential risk factors.Preoperative cervical CT,CT three-dimensional reconstruction and vertebral artery angiography should be done. |
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