Trivial trauma with atlantoaxial instability in Os odontoideum: Need for cervical fusion

Muniappan Arunbalaji; Shunmugam Syamala; Ranganathan Jothi

doi:10.4103/EJSS.EJSS_7_17

ORIGINAL ARTICLE

Year : 2017 | Volume : 1 | Issue : 2 | Page : 35-39

Trivial trauma with atlantoaxial instability in Os odontoideum: Need for cervical fusion

Muniappan Arunbalaji, Shunmugam Syamala, Ranganathan Jothi
Department of Neurosurgery, Institute of Neurosurgery, RGGGH, MMC, Chennai, Tamil Nadu, India

Date of Web Publication

15-Sep-2017

Correspondence Address:
Muniappan Arunbalaji
Institute of Neurosurgery, RGGGH, MMC, Chennai, Tamil Nadu
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/EJSS.EJSS_7_17

Abstract

Background: Os odontoideum is a congenital anomaly or a posttraumatic event of the C2 vertebra (dens), in which the odontoid process is separated from the body of the axis by a transverse gap. Trivial trauma aggravates the condition resulting in atlantoaxial dislocation (AAD) which needs stabilization. Materials and Methods: In our study, we have five patients with os odontoideum, who had developed quadriparesis after minor cervical trauma. All of them underwent C1–C2 posterior stabilization by Harms technique (C1 lateral mass screw and C2 pedicle screw with rod reconstruction), and postoperatively, all the five patients showed a significant improvement from the quadriparesis. Results: All the patients in this case series showed significant improvement in motor power following posterior C1 C2 stabilization. Conclusion: AAD following a trivial trauma in cases of os odontoideum needs to be stabilized to form solid fusion. To achieve that, the Harms technique of C1–C2 fusion is a very effective method.

Keywords: C1 lateral mass, C2 pedicle screw, Harms technique, os odontoideum, quadriparesis, spine trauma, stabilization

How to cite this article:
Arunbalaji M, Syamala S, Jothi R. Trivial trauma with atlantoaxial instability in Os odontoideum: Need for cervical fusion. J Spinal Stud Surg 2017;1:35-9

How to cite this URL:
Arunbalaji M, Syamala S, Jothi R. Trivial trauma with atlantoaxial instability in Os odontoideum: Need for cervical fusion. J Spinal Stud Surg [serial online] 2017 [cited 2023 May 28];1:35-9. Available from: https://www.jsss-journal.com/text.asp?2017/1/2/35/214886

Introduction

The os odontoideum is a congenital anomaly/posttraumatic event of C2 vertebra, in which the odontoid process is separated from the body of the axis by a transverse gap, and it is a smooth, well-corticated ossicle.^[1],[2] An “orthotopic” type is closely approximated to C1 anterior arch and moves in unison with it, and a “dystopic” one is intimately related to the clivus; C1–C2 anterolisthesis and retrolisthesis may cause cervicomedullary injury both from anterior and posterior aspects and commonly leads to reducible atlantoaxial dislocation (AAD). Many of them remain asymptomatic (>70%). However, some present with neck pain or weakness of both upper and lower limbs and even quadriparesis. Here, we have studied five patients who presented with quadriparesis following a trivial trauma for whom we have performed posterior C1–C2 stabilization by Harms technique.

Materials and Methods

We analyzed the following five patients who were treated at our institution.

Patient 1

A 32-year-old male patient with a history of fall from relatively low height (<5 feet) with quadriparesis presented to our hospital. The motor strength in both upper limbs was 4/5 and in lower limbs 4/5. The patient has an X-ray of the C-spine (anteroposterior view, lateral view with flexion and extension) which showed the atlantoaxial instability with os odontoideum. Further evaluation with computed tomography (CT) [Figure 1]a and magnetic resonance imaging MRI [Figure 1]b revealed AAD and spinal cord compression with hyperintensity at C2 spinal cord level. The patient underwent a C1 lateral mass with C2 pedicle screw fixation and stabilization using the Harms technique [Figure 1]c. The postoperative course was uneventful. The patient demonstrated full neurologic recovery at 6-month follow-up, and the subsequent imaging showed a good C1 and C2 alignment.

Figure 1: (a) Computed tomography C-spine shows os odontoideum, (b) magnetic resonance imaging C-spine shows atlantoaxial dislocation with spinal cord compression, (c) C1–C2 fixation by Harms technique, (d) computed tomography C-spine shows os odontoideum with atlantoaxial dislocation, (e) magnetic resonance imaging C-spine shows significant spinal cord compression, (f) postoperative computed tomography C-spine shows good C1–C2 reduction and stabilization, (g) X-ray C-spine shows C1–C2 fusion by Harms technique, (h) intraoperative image of C1 lateral mass and C2 pedicle screw in situ, (i) X-ray C-spine lateral view showing Harms stabilization of atlantoaxial dislocation with os odontoideum, (j) X-ray C-spine anteroposterior view with C1–C2 fusion and stabilization (Harms technique).

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Patient 2

A 25-year-old male with a history of fall from bicycle came to our hospital resulting in weakness of all four limbs, with the motor strength of 4+/5^[3] in all limbs. On investigation, an X-ray, CT, and MRI of the C-spine showed os odontoideum with AAD [Figure 1]d and [Figure 1]e. The patient underwent Harms fusion – fixation of C1 lateral mass/C2 pedicle screws and rods [Figure 1]f. The postoperative period was uneventful; the patient recovered fully. At 6-month follow-up, radiographic evaluation showed good C1–C2 fusion and alignment.

Patient 3

A 12-year-old girl was brought in after a trivial fall while playing in her residence. On admission, she had the motor strength of 3/5 in all 4 limbs. Extensive imaging studies (X-ray, CT, and MRI) showed an atlantoaxial instability with os odontoideum and cord compression. The patient underwent Harms fusion of C1 lateral mass with C2 pedicle screw fixation and stabilization. Postoperative period was uneventful, and eventually, she showed significant improvement in her quadriparesis (motor strength of 4+/5 in upper limbs and 5/5 in lower limbs), and at 6-month follow-up, X-ray and CT showed solid fusion [Figure 1]g.

Patient 4

A 35-year-old male came to our hospital with a history of tree fall, immediately followed by weakness of all 4 limbs with the motor strength of 3/5 in upper and 4/5 in lower limbs. An X-ray, CT, and MRI of the C-spine showed os odontoideum with AAD and cord compression associated with cord edema. He underwent C1 lateral mass with C2 pedicle screw fixation and stabilization by Harms technique [Figure 1]h. On follow-up, upper limb muscle strength improved to 4/5 and in lower limbs remained at 4/5. Follow-up X-ray showed good alignment [Figure 1]i.

Patient 5

A 32-year-old male with a history of fall from two-wheeler presented with weakness of all four limbs with motor power 4/5; X-ray, CT, and MRI of C-spine showed os odontoideum with AAD. He underwent C1 lateral mass with C2 pedicle screw fixation and stabilization by Harms technique [Figure 1]j. The postoperative images showed the good alignment of C1 and C2.

In all our five patients, there was well-corticated, smooth-edged odontoid process separated from the body of the axis and diagnosed as odontoideum.

In all cases, the same Harms technique was used: C1 lateral mass with C2 pedicle screw fixation and stabilization with rods. The patient was positioned prone using a Mayfield, head holder. The neck is kept neutral, and the head is placed in the military tuck position, and the arms are tucked at the sides. The shoulders are retracted caudally using tape. A midline incision is made extending from the external occipital protuberance to the spinous process of C3. The dorsal arch of C1 is exposed laterally exposing the vertebral artery in the vertebral groove. The medial wall of the C1 lateral mass is identified using the forward angle curette, to palpate the medial limit of screw placement. The medial aspect of the transverse foramen at C1 and C2 can also be identified and served as a lateral limit for screw placement. The entry point for the C1 lateral mass screw is identified at the junction point of the midpoint of the C1 lateral mass and the inferior aspect of the C1 arch. Using a C-arm, a 3 mm drill bit and guide are used to drill a hole with 10–15° medial angulation to penetrate the anterior cortex of C1. The hole is tapped, and subsequently, a C1 lateral mass screw (12–14 mm) is placed. The entry point of the C2 pedicle screw was located at the superior, and medial quadrant of the lateral mass 16–18 mm screws was used. Titanium rods of appropriate size were used for fusion.

Results

All the patients showed significant clinical improvement in the motor weakness following surgery, in the form of an increase in motor power as shown in [Table 1].

Table 1: Medical research council grading of motor power

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Discussion

The axis vertebra is derived from the pro Atlas ^{More Details} and the first and second cervical sclerotomes. Failure of the entire odontoid process (derived from the C1 sclerotome) or the apex of the odontoid process (derived from the proatlas) to fuse with the remnant odontoid process or to the body of axis results in os odontoideum. The superior portion of the C1 posterior arch is derived from a dorsal caudal portion of the proatlas and its inferior portion from the first cervical spinal sclerotome.

The lateral atlantal masses are derived from the dorsal, caudal segment of the neural arch of proatlas. Similarly, the lamina of the axis, as well as its lateral masses, are derived from the neural arch of the second spinal sclerotome.^[4],[5] One hypothesis considers os odontoideum to be a disunited fracture following trauma during early childhood.^[6]

The first account of congenital AAD (CAAD) according to Wollin was recorded by Giacomini in 1886.^[7] He found at autopsy of a cretinous female a separate odontoid process (dens) – a specific type of bony anomaly later named os odontoideum – which had led to the dislocation.

In 1960, Wadia ^[8] came to recognize the distinctive myelopathy seen in those with CAAD. It was the first Indian report on AAD due to a congenital anomaly of the odontoid process that includes os odontoideum.

In all our patients, the quadriparesis was precipitated by trauma. In none of the cases, the trauma was severe enough to cause bony injury of this magnitude; there was no history of associated neck pain or neck stiffness which would have been inevitable accompaniments with significant trauma, and the radiology showed well-corticated intervening margins of os odontoideum and the remnant odontoid process in all cases.

The differential diagnosis for os odontoideum typically includes ossiculum terminale and TYPE II odontoid fracture.

The former appears as a secondary ossification center of the dens between 3 and 6 years of age and normally fuses by the age of 12 years. Failure of fusion results in a persistent ossiculum terminale (also called Bergmann's ossicle or ossiculum terminale of Bergmann) and is considered a normal anatomical variant of the axis. It lies above the transverse alar ligament and is therefore deemed to be stable, and it very rarely causes symptoms.

The Type II odontoid fracture passes through the base of the odontoid process as opposed to other two types: the Type I fracture involves only the proximal tip of the odontoid process while the Type III fracture passes through the body of C2.

On reviewing the literature, various techniques for C1–C2 fixations are available. These include C1–C2 wire fixation, first described by Hadra in 1891, and modified by Cone in 1937. Basic cable wire fixation of C1 and C2 was done ^{[9],[10],[11],[12]} as described by Gallie and Brooks. The Gallie technique, although simple to perform, does not provide sufficient stability of the fixation site. Brooks and Jenkins further offered an alternative method of posterior C1–C2 laminar wiring in 1978. They described double-graft compression between the lamina of the atlas and axis with a sublaminar wire. Brooks' posterior fixation of the atlantoaxial vertebrae seems to be more complicated, but it yielded a more stable repair compared to the Gallie technique. The posterior wiring technique popularized by Gallie and Brooks and Jenkins had been the most common means of stabilization in the past. Although the posterior wiring procedure is easy to accomplish, this technique carries a possible risk of dural or neuronal injury during the procedure and the halo vest immobilization is required to accomplish successful bone fusion. Fusion rates increase when external orthosis is used, and neurological complication including quadriparesis can occur in up to 5%–7% of cases due to breakage of wire.

Another technique, first described by Magerl,^[13] utilizes transarticular screws. This is a relatively straightforward and inexpensive way to fix the C1–C2 joint. The disadvantage is that screw insertion requires fluoroscopy. Furthermore, the C2 pars must be large enough to accommodate a 3.5 mm diameter screw. This technique is preferred when C1 and C2 posterior arches are incompetent and is superior to wiring methods in comparison to fusion rates.

C1 lateral mass screws with C2 pars screws is an alternative method of posterior C1–C2 fixation. The C1 lateral mass screw with C2 pedicle screw construct was initially created with plates and screws by Goel et al.^[14],[15] where they used plates for stabilization [Figure 2]. In the 1980s and then subsequently popularized by Harms and Melcher ^[16] in 2001, rods were used for stabilization [Figure 3]. Harms reported a 100% fusion rate using C1 lateral mass and C2 pedicle screws. The complications reported in his study were deep wound infection, which occurred in 2.7% of cases. No vertebral artery injury or neurological complications were reported. Other studies also reported significant rates of perforation during C1 lateral mass and C2 pedicle screw insertion. Kwan et al. reported that the union rate of Harms technique was 100% with an average union time of 5.3 months (range from 3 to 8 months) in their patients.

Figure 2: Posterior C1 lateral mass-C2 pedicle screw stabilization with Goel's plate (Goel's technique).

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Figure 3: Harms technique.

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Conclusion

Patients with os odontoideum with C1–C2 instability have an increased likelihood of future spinal cord injury. Although not supported by Class I or Class II medical evidence from the literature, multiple case series (Class III medical evidence) suggest that stabilization and fusion of C1–C2 is meritorious in this circumstance.

Patients with an initially stable os odontoideum have been reported to develop delayed C1–C2 instability, and there are examples of patients with untreated stable os odontoideum who have developed neurological deficits following minor trauma. Hence, clinical and radiographic surveillance of patients with os odontoideum without instability is to be done periodically to analyze neurological deterioration.

In case of atlantoaxial instability with os odontoideum, posterior C1–C2 internal fixation is the treatment of choice which provides effective stabilization of the atlantoaxial joint in the majority of patients. In our study, we have attempted Harms technique fusion of C1 lateral mass screw and C2 pedicle screw with rod fixation and achieved good stabilization as well as clinical improvement of quadriparesis. Hence, we recommend Harms technique of C1–C2 fusion for os odontoideum with AAD presenting with quadriparesis.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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