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 »  Case report
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Year : 2000  |  Volume : 48  |  Issue : 2  |  Page : 164-9

C1-C2 rotary subluxation following posterior stabilization for congenital atlantoaxial dislocation.


Departments of Neurosurgery and Radiology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, 226014, India.

Correspondence Address:
Departments of Neurosurgery and Radiology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, 226014, India.

  »  Abstract

The authors report a rare complication of C1-C2 rotary subluxation in two children following posterior stabilization for congenital atlantoaxial dislocation (AAD). A patient, with mobile AAD, underwent Brook's C1-C2 fusion while the other, with fixed AAD, underwent transoral decompression followed by Jain's occipitocervical fusion. A pre-existing ligamentous laxity associated with an asymmetrical wire tightening or slippage of the wires due to rotation of the neck in the former, and the drilling of the C1-C2 lateral joints during the transoral procedure in the latter, could have contributed to the rotary subluxation. Both patients presented with persistent torticollis due to fusion in an asymmetrical position with dislocated facet joints. Rotary C1-C2 subluxation, when coexisting with anterior dislocation, has the potential to cause severe and occasionally fatal cord compression. Well defined criteria to diagnose this entity by conventional radiology exist, however, due to the overlap of anatomy, the condition is often overlooked. In the present study, three dimensional reconstruction images using helical computerized tomography were very useful in delineating the subluxation and in planning its surgical reduction and arthrodesis.

How to cite this article:
Behari S, Jain V K, Phadke R V, Banerji D, Kathuria M, Chhabra D K. C1-C2 rotary subluxation following posterior stabilization for congenital atlantoaxial dislocation. Neurol India 2000;48:164


How to cite this URL:
Behari S, Jain V K, Phadke R V, Banerji D, Kathuria M, Chhabra D K. C1-C2 rotary subluxation following posterior stabilization for congenital atlantoaxial dislocation. Neurol India [serial online] 2000 [cited 2014 Oct 24];48:164. Available from: http://www.neurologyindia.com/text.asp?2000/48/2/164/1553




   »   Introduction Top

Posterior fusion for congenital atlantoaxial dislocation (AAD) by Brooks'[1] (for C1-C2 fusion) or Jain's[2] (for occipitocervical fusion) techniques is simple and biomechanically sound.[3] However, the occurrence of atlantoaxial rotary subluxation due to facet dislocation following posterior stabilization leading to persistent torticollis has not been previously reported. The C1-C2 rotary subluxation, especially when occurring in conjunction with anterior dislocation, has the potential to compromise the spinal canal and cause neural damage.[4],[5] The role of three dimensional CT scanning in delineating the rotary dislocation and in planning the surgical reduction is discussed.


   »   Case report Top

Case 1: This nine year old boy presented with progressive weakness and tightness of all four limbs for one and a half years. Examination revealed a short neck with low hairline, grade IV spastic quadriparesis with impaired posterior column sensations. There was no restriction of cervical spinal movements and no evidence of neurofibromatosis. His dynamic craniovertebral junction radiographs in lateral view revealed a hypoplastic odontoid with mobile AAD [Figure. 1a]. On anteroposterior tomograms, the C1-C2 facet joints were symmetrically aligned [Figure. 1b]. Magnetic resonance imaging (MRI) revealed marked cervical cord compression due to the posteriorly dislocated odontoid causing hyperintense cord signal changes on T2 weighted images. At surgery, the patient was placed prone with his head resting on a horse shoe head rest and a Crutchfield's cervical traction was applied. Atlantoaxial posterior fusion was achieved by using sublaminar wiring (using no. 22 stainless steel wires) and autologous rib graft using the wedge compression technique of Brooks' et al.[1] Immediately following surgery, the patient developed a neck tilt with restricted neck movements which were considered to be due to pain and muscle spasm. At the time of discharge from the hospital after a week, his spasticity and weakness had progressively improved to near normal level. At follow up after six weeks, he had no neurological deficit and no pain at the operative site. However, he had persistent torticollis with tiliting of head towards the left shoulder and rotation of chin towards the right [Figure. 2a]. Radiographs of the craniovertebral junction in lateral view showed reduction of the AAD with the wire and bone graft in place. However, anteroposterior tomograms revealed bilateral C1-C2 facet dislocation with rotation and tilting of atlas over axis. The lateral masses of atlas and facet joint spaces on either side appeared asymmetrical [Figure. 3].
During the reoperation undertaken to correct the atlantoaxial rotary subluxation, it was found that C1-C2 facet joints were bilaterally dislocated with the lateral tilting of the atlas. The atlas was also rotated so that its right lateral mass was anterior and the left lateral mass, posterior in relation to the body of axis.
The lateral wires were in position on the lamina of axis. However, on the posterior arch of atlas, the left lateral wire was displaced laterally towards the left C1-C2 facet joint and the right lateral wire medially towards the posterior tubercle of atlas. The sublaminar wires and bone grafts between the atlas and axis were removed. The articular capsule of the C1-C2 facet joints was excised to render the joint mobile. While maintaining distraction between the atlas and axis by cervical traction, the occiput and atlas were rotated over the axis reducing the facet dislocation and aligning the posterior tubercle of atlas to the spine of axis. The bony surfaces of C1-C2 articular joints were decorticated using drill and bone pieces instilled into the joint space. One midline and two lateral notches were made on the superior border of the posterior arch of atlas and corresponding lateral notches were also made along the inferior border of the lamina of axis. One stainless steel braided wire was passed in the midline under the posterior arch of atlas and the lamina of axis and anchored in the midline notch of the atlas and under the bifid spine of the axis. Two wires were placed on either side of the braided wire and anchored in the lateral notches. These sublaminar wires were tightened and bone grafts wedged between the atlas and axis. Following surgery, the patient retained his motor improvement and his torticollis was corrected [Figure. 2b]. A Minerva jacket was placed for three months to prevent excessive neck mobility. At follow up after one year, he had no neurological deficit. Dynamic lateral radiographs of the craniovertebral junction revealed adequate C1-C2 fusion with the atlantoaxial joints being maintained in reduced position.
Case 2: This thirteen year old boy presented with progressive weakness, tightness and tingling sensation of all four limbs for six months. Examination revealed a short neck with low hairline, grade IV spastic quadriparesis and impaired posterior column sensations. There was no torticollis or restriction of neck movements. His preoperative dynamic plain radiographs (in flexion and extension) and intrathecal contrast CT sagittal reconstruction images revealed a fixed AAD with basilar invagination and occipitalized atlas and fusion of the second and third cervical vertebrae [Figure. 4a]. Coronal MRI and three dimensional CT reconstruction images revealed asymmetrical facet joints [Figure. 4B] and [Figure. 4C].
On applying Crutchfield's cervical traction, there was a significant reduction in spasticity. However, during transoral decompresion (TOD) , following excision of part of the anterior arch of atlas, odontoid, body of axis and medial portion of the left C1-C2 facet joint [Figure.5], there was brisk bleeding from the vertebral venous plexus due to which further surgery was deferred. Postoperatively, there was no neurological deterioration. After one and a half months, the TOD was completed by excising the inferior clivus, anterior arch of atlas, odontoid and body of axis and posterior stabilization was achieved by occipitocervical fusion using Jain's technique [Figure. 6].[2] Postoperatively, his spasticity and limb weakness improved. However, a persistent torticollis with neck tilt to the right was noticed. Three dimensional reconstructed helical CT images revealed rotation of the occiput and the assimilated atlas on the axis with complete left sided and partial right sided C1-C2 facet subluxation [Figure. 7] and [Figure. 4B].
During resurgery, the occipitocervical junction including bilateral facet joints were re-exposed by the posterior route. The occipitocervical wires were loosened and the bone grafts removed. The facet joint capsule was excised and the occiput and the assimilated atlas were rotated on the axis realigning the facet joints and bringing the posterior tubercle of atlas in close proximity to the spine of axis. A strut bone graft was placed between the 'artificial arch' created on the occipital bone and the spine and lamina of axis and bone chips were instilled within the C1-C2 facet joint space. The sublaminar wires were retightened taking care that the midline wire was held in place in the midline notch on the 'artificial arch' and under the bifid spine of axis and the lateral wires were held in place in the lateral notches created on the 'artificial arch' and lamina of axis on either side of the midline wire.
Postoperatively, the head tilt and torticollis were corrected and the child progressively improved in neurological status. A Minerva jacket was applied for three months to prevent excessive neck mobility. At follow up after two months, his spasticity had markedly reduced and power had improved to near normal levels.


   »   Discussion Top

Forty seven degrees of axial rotation, ten degrees of flexion/extension (including some anteroposterior translation) and some lateral bending occurs at the atlantoaxial joint.[3],[6],[7] This wide range of motion increases the susceptibility of this joint to instability and dislocation.[3],[6],[7],[8] However, certain inherent anatomical features at the atlantoaxial joint resist the injuring vectors and consequent dislocation. The transverse ligament retains the dens behind the anterior arch so that the median atlantoaxial joint is a pivot between the dens and the ring formed by the anterior arch and the transverse ligament. The lateral atlantoaxial joints are classified as plane. At these joints, the inferior surface of each lateral mass presents an almost circular facet, flat or slightly concave, which articulates with a similar superior articular facet of axis. The alar ligaments check excessive lateral rotation to either side.[9]
Brook's wedge compression technique of atlantoaxial fusion[1] and Jain's technique of occipitocervical fusion[2] are simple and retain similar biomechanical advantages. By wiring and compressing the bone grafts between the posterior arch of atlas and the spine of axis on both sides of the midline, all potential movements at the atlantoaxial joint are blocked. The rotary motion is resisted by the rigid column of posterior elements of atlas and axis held in contact with the bone graft by the encircling wire. Flexion is prevented by wires bending the posterior elements and extension by the bone graft.[6]
The occurrence of atlantoaxial rotary subluxation due to facet dislocation following posterior fusion using wire and bone graft has not been previously reported. Both the children reported here had transverse ligament incompetence with consequent AAD.[10] The dens facet angle of axis is steeper in children than in adults.[11],[12] Therefore, the AAD and excessive C1-C2 rotation due to the steeper angle, compounded by ligamentous laxity, rendered the atlas freely mobile over the axis and predisposed to rotary subluxation.[12] Congenital torticollis often coexists with anomalies like basilar invagination, asymmetrical facet joints, AAD, occipitalized atlas and deformities of the odontoid.[5] De Barros has noted that 68% of patients with skeletal wry neck had basilar invagination and 20% with Klippel Feil syndrome had associated torticollis.[13] The second patient of this report had asymmetrical facet joints. Therefore, the possibility of a pre-existing rotary displacement, well compensated for by the rotation at the lower neck, existed.[5] This may have been aggravated by the excision of transverse and alar ligaments and drilling of facet joints during the TOD.[8]
The other possibilities contributing to the rotary subluxation in our patients included a tilt of the head while it was resting prone on the horse-shoe head rest during surgery, that went unnoticed due to the surgical draping. The resultant asymmetrical tightening of wires may have precipitated the facet dislocation and rotary subluxation. Once the articular facets were dislocated, their spontaneous repositioning was prevented by the locking of the overlapping lateral joint edges of the articular facets[12] as well as the tightened wires. Following posterior fusion, movements at the neck had been restricted by the use of the hard cervical collar that varies in its effectiveness in controlling different degrees of freedom at the cervical spine. Flexion, extension and lateral bending are effectively stabilized. However, it has no control over axial rotation.[6],[14] After reversal from anaesthesia, lateral rotation at the neck may have caused displacement of the wires that aggravated the rotary displacement. Following atlantoaxial fusion, both patients developed the characterstic 'cocked robin' torticollis with the head tilted to one side and rotated to the opposite side.[4] There was a diminished range of movement so that they were able to increase the deformity but could not correct it beyond the neutral position.
The radiographic findings of rotary displacement have been elucidated by Wortzman et al and Fielding et al.[4],[5],[15] In anteroposterior projections, the lateral mass of atlas that has rotated forward appears wider and close to the midline while the opposite lateral mass is narrower and away from the midline.[15] The facet joint spaces on either side appear asymmetrical. The spinous process of axis is usually tilted in one and rotated in the opposite direction. Anteroposterior tomograms may show the two lateral masses in different coronal planes. In our patients, bilateral facet dislocation was also demonstrable. Fielding has also classified atlantoaxial rotary dislocation into four types[4]:Type I - rotary dislocation without anterior shift; Type II - rotary dislocation with an anterior shift of 5mm or less; Type III - rotary dislocation with an anterior shift of greater than 5mm; and; Type IV - rotary dislocation with a posterior shift. Following atlantoaxial arthrodesis, both our patients showed neurological improvement despite the occurrence of rotary dislocation. This is because of an increase in the spinal canal diameter facilitated by the reduction of anterior atlantoaxial displacement. Therefore, their condition corresponded to Fielding's type I rotary dislocation.
The correction of the cosmetic deformity of torticollis may be as important as functional recovery to a discerning patient. The use of intraoperative biplaner X-ray image intensifier during posterior fusion would have been useful in the present case as it would have helped in the detection of the rotational subluxation
and remedial steps could have been undertaken. Recent studies have demonstrated the value of CT and MR images to diagnose atlantoaxial rotary subluxation.[16],[17],[18],[19],[20] Apart from detection of anterolisthesis, widening of facet joint space, change in orientation of facets and 'naked facet sign' resulting from distraction of elements constituting the facet joints,[20] contiguous facet surfaces can be seen on one parasagittal image and facet subluxation can therefore be diagnosed with relative ease.[20] We used three dimensional spiral CT images in our second patient and found them to be complementary to the standard CT two dimensional images in the evaluation of facet anatomy, yielding high quality surface images. The images were helpful in understanding the mechanics of rotary dislocation as they replaced the volume usually reconstructed mentally from CT axial sections and standard radiography.[21]
In the present cases, during reoperation, the sublaminar wires were removed and the facet joints on both the sides were mobilized. With the cervical traction maintaining C1-C2 distraction, the facet dislocation was removed manually and facet arthrodesis performed by instillation of bone chips. The central braided wire passed beneath the posterior tubercle of atlas in the first case or the 'artificial arch' in the second and beneath the spine of axis ensured bony alignment and corrected anteroposterior as well as rotational dislocation. Thus, it provided a three dimensional reduction of the AAD. The lateral wires provided further stability and held the graft in place. The notches made on the superior border of the posterior arch of atlas and along the inferior border of the lamina of axis anchored the wires and prevented their lateral and medial shifting.[2] Postoperative Minerva jacket restricted both flexion/extension and axial rotation at the neck and facilitated bony union.

 

  »   References Top

1.Brooks AL, Jenkins EB: Atlanto-axial arthrodesis by the wedge compression method. J Bone Joint Surg 1978; 60A(3): 279-284.   Back to cited text no. 1    
2.Jain VK, Mittal P, Banerji D et al: Posterior occipitoaxial fusion for atlantoaxial dislocation associated with occipitalized atlas. J Neurosurg 1996; 84: 559-564.   Back to cited text no. 2    
3.White AA III, Panjabi MM: Clinical biomechanics of the spine. Philedelphia, JB Lippincott 1978; 191-276.   Back to cited text no. 3    
4.Fielding JW, Hawkins RJ: Atlantoaxial rotary fixation (fixed rotary subluxation of the atlantoaxial joint). J Bone Joint Surg Am 1977; 59: 37-44.   Back to cited text no. 4    
5.Fielding JW, Hawkins RJ, Hensinger RN et al: Atlantoaxial rotary deformities. Orthop Clin North Am 1978; 9(4): 955-967.   Back to cited text no. 5    
6.White AA III, Panjabi MM: The clinical biomechanics of the occipitoatlantoaxial complex. Orthop Clin North Am 1978; 9: 867-878.   Back to cited text no. 6    
7.Panjabi MM, Thibodeau LL, Crisco JJ III: What constitutes spinal instability? Clin Neurosurg 1988; 34: 313-339.   Back to cited text no. 7    
8.Dickman CA, Locantro J, Fessler RG: The influence of transoral odontoid resection on stability of the craniovertebral junction. J Neurosurg 1992; 77: 525-530.   Back to cited text no. 8    
9.William PL, Warwick R: The craniovertebral joints. In: Gray's anatomy, 36th Edition. Ed. William PL, Warwick R, Edinburgh, Churchill Livingstone 1980:447.   Back to cited text no. 9    
10.Fielding JW, Cochran GVB, Lawsing JF III et al: Tears of the transverse ligament of the atlas: A clinical and biomechanical study. J Bone Joint Surg Am 1974; 56: 1683-1691.   Back to cited text no. 10    
11.Kawabe N, Hirotani H, Tanaka O: Pathomechanism of atlantoaxial rotary fixation in children. J Pediatr Orthop 1989; 9: 569-574.   Back to cited text no. 11    
12.Loder RT, Hensinger RN: Developmental abnormalities of the cervical spine. In: The Pediatric Spine, Principles and Practice. Ed. Weinstein SL, New York, Raven Press 1994; 408-411.   Back to cited text no. 12    
13.De Barros MC, Farias W, Ataide L et al: Basilar impression and Arnold Chiari malformation; a study of 66 cases. J Neurol Neurosurg Psychiatry 1968; 31:596-605.   Back to cited text no. 13    
14.Johnson RM, Owen JR, Hart DL et al: Cervical orthoses: A guide to their selection and use. Clin Orthop 1981; 154: 34-45.   Back to cited text no. 14    
15.Wortzman G, Dewar FP: Rotary fixation of the atlantoaxial joint: Rotational atlantoaxial subluxation. Radiology 1968; 90: 479-487.   Back to cited text no. 15    
16.Kowalski HM, Cohen WA, Cooper P et al: Pitfalls in the CT diagnosis of atlanto axial rotary subluxation. AJNR 1987; 8: 697-702.   Back to cited text no. 16    
17.Moss JG, Sellar RJ, Bradnock B: Atlantoaxial rotary fixation diagnosed by functional computed tomography. Br J Radiol 1989; 62: 755-758.   Back to cited text no. 17    
18.Leventhal MR, Magaire JK, Jr, Christian CA: Atlantoaxial rotary subluxation in ankylosing spondylitis. A case report. Spine 1990; 15: 1374-1376.   Back to cited text no. 18    
19.Godard J, Jaequet G, Bonneville JF et al: Torticollis et subluxation rotatoire C1-2. J de Neuroradiologie 1994; 21: 223-227.   Back to cited text no. 19    
20.Leite CC, Escobar BE, Bazan III C et al: MRI of cervical facet dislocation. Neuroradiology 1997; 39: 583-588.   Back to cited text no. 20    
21.Bonnier L, Ayadi L, Vasdev A et al: Three dimensional reconstruction in routine computerized tomography of the skull and spine. J de Neuroradiologie 1991; 18: 250-266.   Back to cited text no. 21    

 

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