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Year : 2020  |  Volume : 33  |  Issue : 4  |  Page : 1399-1404

Managing atlantoaxial instability by posterior fusion using C1 lateral mass and C2 pedicle screws

1 Department of Neurosurgical, Faculty of Medicine, Menoufia University, Menoufia, Egypt
2 Department of Neurosurgical, Faculty of Medicine, Cairo University, Cairo, Egypt

Date of Submission22-Mar-2020
Date of Decision26-Apr-2020
Date of Acceptance10-May-2020
Date of Web Publication24-Dec-2020

Correspondence Address:
Mohamed A Elnagar
3 Babel Street, Tala, Menoufia 32511
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mmj.mmj_98_20

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The aim was to evaluate the posterior atlantoaxial fixation using C1 lateral mass and C2 pedicle by a polyaxial screw in atlantoaxial instability correction.
The craniocervical junction refers to the transitional zone between the cranial base and the upper cervical spine. Owing to the complexity of this area, almost all stabilization techniques are traditionally limited. However, C1 lateral mass – C2 pedicle screw fixation is gaining popularity in handling the atlantoaxial instability.
Patients and methods
This study included patients with craniocervical instability admitted to the Departments of Neurosurgery at Menoufia University and Nasser Institute during the period from May 2016 to April 2018 (almost 2 years) with a follow-up period up to 6 months. Participants were treated during the study period by C1 lateral mass and C2 pedicle screws.
A total of nine cases were included, comprising 67% males and 33% females. Quadriparesis was the common presentation in 45% of patients, followed by those with neck pain or paresthesia. The mean operative time was ∼160 min. Of nine patients, three experienced mild complications, without mortality or morbidity, such as numbness, dural tear, and wound infection.
C1 lateral mass and C2 pedicle screw procedure is safe and provides reasonably efficient results for correcting atlantoaxial instability cases, with minimal adverse effects.

Keywords: atlantoaxial, lateral mass, pedicle, screw and instability

How to cite this article:
Elnagar MA, Hanafy AM, Ayoub BM, El-Kader HE, Sheha AF, Elnaggar AG. Managing atlantoaxial instability by posterior fusion using C1 lateral mass and C2 pedicle screws. Menoufia Med J 2020;33:1399-404

How to cite this URL:
Elnagar MA, Hanafy AM, Ayoub BM, El-Kader HE, Sheha AF, Elnaggar AG. Managing atlantoaxial instability by posterior fusion using C1 lateral mass and C2 pedicle screws. Menoufia Med J [serial online] 2020 [cited 2021 Apr 19];33:1399-404. Available from: http://www.mmj.eg.net/text.asp?2020/33/4/1399/304519

  Introduction Top

The craniocervical junction (CCJ) refers to the transitional zone between the cranial base and the upper cervical spine[1]. In terms of their anatomical and functional differences, C1 and C2 vertebrae are unique among all the other 33 vertebrae. Furthermore, C1 does not have a real corpus and spinous process, whereas the lack of a disc space between C1 and C2 and that C2 has an odontoid process subsequently lead to a complicated ligament structure[2].

In this regard, atlantoaxial instability presents a wide range of signs and symptoms, including pain; paresthesias; motor weakness and gait disturbance instigated by myelopathy; brain stem, cranial nerve, and cervical nerve root dysfunction; and vascular deficiency with segmental ischemia[3]. Here, MRI is the investigational technique of choice, by which we can confirm the diagnosis[4].

Irrespective of a given reason, atlantoaxial instability is considered a condition that may result in serious morbidity and mortality if not treated appropriately. Treatment should be determined according to many factors, such as the patient complaint at the time of consultation, neurological examination, corresponding radiological assessments, co-morbidities, and age[5].

The aim of surgery in atlantoaxial instability should be to protect neural elements. In other words, it is to provide decompression in cases of compression, stabilize the unstable structure by ensuring appropriate vertebral alignment, achieving fusion in the long term, and most importantly accomplishing that safely[6].

Upon surgical procedures, the obliteration of osseous and ligamentous structures by the underlying pathologic process, CCJ may become unbalanced. Once CCJ malalignment is reducible, they must be considered unstable, and therefore, a fusion is mandatory to initiate[7].

Atlantoaxial arthrodesis is technically required for its anatomic relations and abundant joint motion but may result in delaying good-quality bone fusion[8]. Surgical C1–C2 fusion was first described by Gallie in 1939 and involved posterior wiring[9]. Later, interlaminar hooks with improved biomechanical properties than wiring were introduced[10]. Transarticular atlantoaxial screw fixation was suggested by Magerl in 1986[11]. It provided optimal biomechanical stability with better-quality fusion rates, especially when compared with the earlier posterior wiring techniques[12]. There were, though, numerous drawbacks. Issues include the difficulty of performance in case of atlantoaxial dislocation or subluxation with loss of C1–C2 alignment. In a way of tackling such issues, Harms, based on Goel's work on atlantoaxial screw fixation, presented a stabilization technique whereby C1 lateral masses and C2 pedicle fixation is done by polyaxial screws[13]. The research work aimed to evaluate the efficacy of posterior atlantoaxial fusion using C1 lateral mass and C2 pedicle by a polyaxial screw to correct atlantoaxial instability.

  Patients and Methods Top

This retrospective study included patients presented with craniocervical instability in the Departments of Neurosurgery at Menoufia University and Nasser Institute during the period from May 2016 to April 2018 with a follow-up period up to 6 months.

After the research protocol was approved by the Ethical Committee of the Faculty of Medicine, Menoufia University, in its monthly session dated May 8, 2016, informed written consent was obtained from each patient. Only nine patients were managed during the study period, following the inclusion criteria, by C1 lateral mass and C2 pedicle screws. Initially, all patients underwent detailed clinical investigation that encompassed the following: First, history taking; second, general examination; third, and neurological examination including assessment of motor power, sensory level, deep tendon reflexes, and pathological reflexes, and visceral manifestations. We paid special attention to the preoperative neurological status in the Frankel classification for all patients[14].

All patients were assessed radiologically via plain radiography standard views, computed tomography scan (CT), and MRI to detect different pathologies. Moreover, this procedural step provided fundamental information regarding the stability of the occipitoatlantoaxial joint complex. Then, under general anesthesia, the patient positioned in prone and after sterilization, a skin incision was performed. Along the avascular plane, the cephalad dissection was started at the external occipital protuberance and extended inferiorly 10 cm.

The posterior aspect of the lateral C1 mass is exposed to well-defined borders, which enabled a safer identification of the appropriate entry point. The posterior aspect of the lateral mass is more or less dome shaped. The definitive hole was drilled under lateral fluoroscopic control with a convergent angulation of 10–20° based on the lateral mass's orientation. Thus, the optimal length of the screw could be exploited, and further the tip of the screw would be placed in a safe zone that fits the oropharyngeal wall. In the sagittal plane, the direction of the drill was controlled fluoroscopically. The drill tip was directed toward the anterior tubercle, to be positioned almost in parallel to the upper boundary of the posterior arch of C1. Biocritical drilling was followed to enhance screw stability. After palpation of the hole confirming the integrity of bony walls, the hole was carefully tapped, and the screw was inserted as to avoid secondary misplacement of the screw. The screw length measures 3.5 or 4 mm.

The screw had to be verified fluoroscopically. C2 pedicle screw placement starts at the cranial medial portion of the C2 lateral mass. We consider the cranial margin of the C2 lamina, the landmark of the screw insertion point for C2. We, then, inserted a hook into the spinal canal along the cranial margin of the C2 lamina to the medial surface of the pedicle of C2. Afterward, we inserted a pedicle probe, tap, and screws into the pedicle under the guidance of lateral fluoroscopy to make sure of the right direction and insertion depth. The direction was ∼15–20° medially in the horizontal plane and perpendicular to the anterior surface of the axis.

Before applying rods to the screws, we performed posterior neural decompression with laminectomy in patients with narrow spinal canals to evade neurological deterioration which could occur in the aftermath of cervical malalignment correction and longitudinal connection between them. For bone grafting, the cortex of the lateral masses and laminae were decorticated. Obtained bone chips from the spinous processes and laminae were placed. In the final stage of instrumentation, the rods were connected. Additional distraction/compression maneuver on the screw heads was done to achieve reduction or realignment. Blood loss, operative time, and possible intraoperative complication were recorded.

Next, a clinical follow-up was done on the first day after surgery to assess the general condition and report any complications. Day 3 was devoted to wound and drain assessment, such as a removal and discharge assessment for the clinical state. Instructions for dressing and outpatient medications were duly given. Radiological follow-up included early postoperative radiograph and CT scan to investigate the screw position and any encroachment on vascular or nervous structures. Plain radiography, CT scan, and MRI were performed 6 months later when needed.

The outcomes of this type of fixation were thoroughly assessed in light of the neurological state of the patient using Frankel classification. Bony fusion was observed, bony trabeculation and bridges between C1 and C2, and the occurrence of any complexity, such as wound infection or mechanical issues, because of the screw rod system.

  Results Top

In this study, the ages of the included nine cases fell within the range of 31–66 years old, with a median age of 40 years. Of our nine patients, six (two-thirds) were males, with a percentage of ∼67%, whereas female Participants constituted a third (only three cases, 33%). Clinical investigations varied among patients, especially after a history of trauma. Motor power weakness represented the main complaint, in the form of quadriparesis and myelopathy in four cases, cervical neck pain in three cases, and sensory affection in the form of paresthesia in one or more limbs (in two cases) at time of assessment. Preoperative assessment, also, revealed five cases with no motor deficit, and therein, graded as Frankel 'E,' and two cases were Frankel 'D' and two other cases were marked as Frankel 'C' [Table 1].
Table 1: Frankel grading classification

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Regarding the operation time, the longest operation took ∼5 h, whereas the shortest one took ∼2.5 h, with a median time of ∼3 h and a mean of nearly 160 min. Estimated operative blood loss ranged from a minimum of 150 ml to a maximum of 400 ml in most cases, with a median of ∼200 ml blood loss per case. Average blood loss reached ∼240 ml. Nevertheless, no blood transfusion was conducted intraoperatively for any case.

Moreover, there was no postoperative neurological aggravation. All the four neurologically impaired patients showed clinical neurological improvement, with a final result of seven cases of Frankel E and two cases of Frankel D [Table 2]. In particular, in eight of our nine cases, four screws were inserted conveniently in each case, and the length of either in lateral mass of C1, in C2 pedicle without neurological, or vascular insult except one screw in left lateral mass of C1 was slight medially located without any neurological deterioration or cerebrospinal fluid (CSF) leak.
Table 2: Frankel grading preoperatively and postoperatively

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Concerning the one hypoplastic case in which we failed to insert screws in the right C2 pedicle, we decided to do unilateral fixation in the left side with sublaminar wiring. As a result, the case improved clinically without complications, and no revision operation was required. Moreover, there were no clinical or radiological consequences.

Complications, however, could only be spotted in three cases who experienced mild problems without mortality or morbidity. One complication was observed in the form of bilateral occipital region numbness owing to C2 root irritation. We treated them medically. Subsequently, they were resolved within a few weeks. Another complicated case occurred owing to small dural tears during the decompression and direct repair with the aid of fibrin glue. The third case had a superficial wound infection owing to low immunity for being aged diabetic. It was managed by antibiotic therapy and daily dressing without debridement.

Findings of follow-up CT cervical spine after 6 months revealed no displacement of the screws. All nine cases showed satisfactory stability achieved by the screws rod system, and bony fusion appeared as C1–C2 bone bridges in the facets; fusions occurred in almost all cases (100% fusion rate), and there is still no hardware failure [Figure 1] and [Figure 2].
Figure 1: (a and b) CT cervical spine preoperative axial and coronal cuts showed dense fracture. (c) Sagittal immediate postoperative CT scan with C1–C2 fixation. (d) Axial CT scan showed bilateral C1 lateral mass screws. (e) Axial CT scan showed bilateral C2 pedicle screws. CT, computed tomography.

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Figure 2: Examples for fusion showed in coronal CT scan in two different cases (a and c). Sagittal CT preoperative showed dens fractures. (b and d) Sagittal CT 6 months postoperatively showed dense fusion and bony trabeculation in the facets. CT, computed tomography.

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  Discussion Top

In the present work, the number of studied patients (nine with a mean age of 45 years) was smaller than that of the study by Bourdillon et al .[15], which included 26 cases and a mean age of 57 years. Male participants represented 67%, whereas ∼33% were females. This male dominance could be explained by their relatively higher activity, which results in more liability for trauma. Such percentages correlate with the study of Stulik et al .[16], in which 18 were males and 10 were females. Furthermore, most cases were middle-aged males, which is usually explained by their liability for traumatic incidence owing to higher activity.

The percentage of patients with quadriparesis in our study was significantly higher than in the study by Stulik et al .[16] because a large number of neurologically intact patient with atlantoaxial instability in the study period refused surgical intervention. However, our percentage was lower than the study by Singh et al .[17] in which all patients had muscle weakness.

Of nine cases, two cases reported sensory affection in our findings. The study by Singh et al .[17] indicated a much lower rate of only one out of 14 patients with sensory affection. Moreover, in our study, three of nine cases presented with neck pain and were neurologically intact without motor or sensory affection. This was 33% lower than the outcomes of Isik et al .[6]. They illustrated ∼60% with cervical pain, which was attributed to the refusal of surgery by a large number of neurologically intact patients .

In terms of preoperative assessment, the study outcomes revealed five cases with no motor deficit and ranged as Frankel 'E' and two cases were Frankel 'D' and two cases Frankel 'C.' Postoperative follow-up showed no clinical aggravation and all the four neurologically impaired patient had signs of improvement. This was a better result than what Bourdillon reported, where five out of seven neurologically impaired patients showed clinical neurological improvement[15]. Similarly, our study surpassed the study by Singh et al .[17], in which only 10 of 14 neurologically impaired patients showed improvement.

To add, the estimated operative blood loss ranged from 150 to 400 ml, with a median of ∼200 ml blood loss. Average blood loss in our evaluation (∼240 ml) is similar to the study by Bourdillon et al .[15], in which they reported an average blood loss of 260 ml. Nevertheless, some other studies expounded even higher rates of blood loss. For instance, the study by Stulik et al .[16] reported significantly higher levels, where intraoperative blood loss ranged from 50 to 1500 ml, with an average of 540 ml.

Regarding screw accuracy, just a single screw out of the total 34 screws was misdirected to the C1 lateral mass without clinical complication. We claim here a 97% screw accuracy, in eight cases of our nine cases. This finding does correlate with the study by Stulik et al ., who reported three misdirected screws of total 112 screws, comprising only two of them encroaching vertebral artery foramen and one medially passed into the spinal canal, with total accuracy of ∼97.5%[16]. We reported more accurate screwing results in comparison with the 92% accuracy of the study by Gautschi and colleagues and 84% in the study by Yehya[18],[19].

The current study presents no mortality and morbidity in general. Only three cases experienced mild complications. C2 nerve root irritation occurred in the form of bilateral occipital region numbness and was successfully managed and resolved through medication within a few weeks. These incidents agree with the study of Gautschi et al .[18], in which C2 neuralgia was evident in 4 of 41 patients (9.3%).

Outcomes in the present work describe relatively higher rates of C2 root irritation than the study of Lee and colleagues. In the latter study, only a single patient of 55 patients had occipital neuralgia, with a percentage of ∼2%[20].

One sort of complications, our study reports, was in the small dural tear during decompression and direct repair, but no CSF leak occurred postoperatively. Such observation was 11% higher than the study of Lee et al .[20] in which the CSF leakage was healed by a lumbar drain.

Furthermore, another complicated case was reported as a superficial wound infection owing to the low-immunity state for being diabetic and aged. Our complication represents 11% compared with 16% in the study by Yehya[19] (two of 12 patients).

In our study, the rate of infection was almost close to the study of Gautschi et al .[18], in which surgical site infection occurred in 3 of 41 patients (7.3%) during the follow-up phase. Similarly, it agrees with the study by Saro[21], in which surgical site infections occurred in one (8%) of 12 cases, which improved with antibiotics.

The literature reports mostly matching results with our research investigation in terms of the follow-up CT scan, which was primarily done in a way to assess the hardware and fusion. No hardware failure could be observed, with a satisfactory bony fusion in all the facets on C1 lateral mass and C2 pedicle screws fixation. However, our outcomes appeared even better than the result revealed by Lee et al .[20], as fusion rates in our study was 100%, whereas the fusion rates in the study by Lee et al .[20] reached only 82.1%.

  Conclusion Top

C1 lateral mass and C2 pedicle screws provide an alternative safe method for atlantoaxial stabilization, with the advantage that laminectomy or fracture of posterior arch of C1 and C2 does not prevent this fixation procedure.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Table 1], [Table 2]


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