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Journal of Craniovertebral Junction and Spine
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Year : 2020  |  Volume : 11  |  Issue : 4  |  Page : 338-341  

Horizontal fracture of the atlas – A rare but unstable C1 fracture

Department of Neurosurgery, Institute of Neurological Sciences, NHS Greater Glasgow and Clyde, Glasgow, Scotland, UK

Date of Submission03-Sep-2020
Date of Acceptance11-Oct-2020
Date of Web Publication26-Nov-2020

Correspondence Address:
Ajay Hegde
Department of Neurosurgery, Institute of Neurological Sciences, NHS Greater Glasgow and Clyde, Glasgow, Scotland
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jcvjs.JCVJS_143_20

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Horizontal fractures of the atlas are uncommon fractures associated with instability of the craniocervical junction. Most commonly associated with high-speed motor vehicle accidents, these fractures need to be identified and treated appropriately. Due to its relatively benign presentation on bony imaging, magnetic resonance imaging to look for ligamentous instability is important. We present two such cases which were managed by occipitocervical fusion at our institute.

Keywords: C1 fracture, craniovertebral junction, horizontal fracture, occipitocervical fusion, unstable

How to cite this article:
Brown J, Hegde A. Horizontal fracture of the atlas – A rare but unstable C1 fracture. J Craniovert Jun Spine 2020;11:338-41

How to cite this URL:
Brown J, Hegde A. Horizontal fracture of the atlas – A rare but unstable C1 fracture. J Craniovert Jun Spine [serial online] 2020 [cited 2022 Jan 29];11:338-41. Available from: https://www.jcvjs.com/text.asp?2020/11/4/338/301622

   Introduction Top

Atlas is the first cervical vertebrae named after the Greek Titan Atlas condemned to hold up the celestial heavens for eternity. In the human body, it forms a part of craniocervical complex supporting the skull bone. Fractures of the atlas represent 3%–13% of spinal column fractures.[1] They may occur in isolation or combination with fractures of the axis (C2).[2] The most commonly described fracture is Jefferson's fracture which involves a burst fracture of the atlas ring first published by Jefferson in 1920.[3] It is a vertical type of fracture and is caused by an axial loading injury on the spine.

Horizontal fractures of the atlas are rare injuries caused by hyperextension and distraction of the neck.[4] Although they appear radiologically benign, they are associated with severe instability of the craniocervical junction. We describe two cases of this uncommon fracture of the atlas and their diagnosis and management strategies.

   Case Reports Top

Case 1

A 23-year-old man was injured in a road traffic accident and brought to the emergency department of our hospital. He was localized at the scene, with no eye-opening and verbal response. He was intubated and transferred. A computed tomography (CT) brain showed small contusions at the gray-white junction and subarachnoid hemorrhage in the prepontine cisterns and around the foramen magnum. CT of his cervical spine suggested a horizontal fracture of the anterior arch of the atlas with a fracture of the right occipital condyle. There was widening of the C1–C2 interspinous distance. He was immobilized with a Miami J Collar and stabilized. The following day he was extubated and was obeying commands with complaints of posterior neck pain. A magnetic resonance imaging (MRI) of his cervical spine demonstrated disruption of the transverse atlantoaxial, alar, and the anterior longitudinal ligaments with the atlantoaxial membrane. The patient was allowed to recover from his pulmonary contusions and then operated for an occipitocervical fusion with an occipital T plate and C2 pedicle screws. The intraoperative construct was stable, and the same was confirmed by postoperative imaging [Figure 1]. He was gradually mobilized and recovered with no focal neurological deficits.
Figure 1: (a) Pre op CT Scan demonstrating horizontal fracture of C1. (b) Pre-op MRI demonstrating ligamentous instability at CVJ. (c and d) Post op imaging with occipito cervical fusion

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Case 2

A 43-year-old man, involved in a high-speed motor vehicle accident, presented with neck pain, severe restriction of neck movements, and paresthesia of the left upper limb. On examination, he had sensory disturbances over the C5/6 dermatome on the left side with weakness of the trapezius muscle on the same side. He had no other motor deficits. X-ray of his cervical spine revealed a fracture of the anterior arch of the atlas and its displacement behind the odontoid process. A CT scan confirmed the same with retropulsion of the anterior arch of the atlas. He was immobilized with a cervical collar and operated with an occipitocervical fusion involving the occiput and C2 + C3 [Figure 2]. Postoperatively, at 1 year, his paresthesia improved and was discharged from the clinic.
Figure 2: (a and b) Pre op CT with horizontal fracture of C1 demonstrating retropulsion of the fractured C1 arch behind the dens of C2. (c) Pre- op X Ray demonstrating the fracture. (d) Post op 3D reconstruction of CT scan showing occipito cervical fusion

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   Discussion Top

C1 fractures are a relatively rare fracture of the spinal column. Mechanisms of injury include motor vehicle collisions, falls, and athletic injuries.[5] Anatomically, fractures of the atlas can be classified as vertical or horizontal based on the mechanism of injury. From a surgeon's perspective, it would be convenient to group them as stable and unstable fractures which direct their management. Vertical fractures involve the anterior or posterior arch with/without the involvement of the lateral mass. Jefferson's fracture, the most commonly described fracture, involves a burst fracture of the arch caused by an axial loading force.[2],[3] Stability is contributed by the numerous ligamentous structures that anchor the C1–C2 and the base of the occiput. A disruption of the transverse atlantoaxial ligament remains an essential factor in labeling a C1 fracture unstable necessitating surgical fixation.[1] Horizontal fractures of the atlas are relatively uncommon and are not mentioned in conventional classification systems. They are caused by hyperextension injuries of the neck and may occur in isolation or with fractures of the axis or the base of the skull. Stewart et al. reported that 70% of the cases are associated with fractures of the dens.[4]

The atlas is ring shaped and differs from other cervical vertebrae in that it lacks a body and spinous process. Two laterally placed lateral masses unite the anterior and posterior arches. The ventral surface of the anterior arch bears the anterior tubercle to which the anterior longitudinal ligament attaches. On either side of the anterior tubercle are two large hallows which serve as an attachment to the superior oblique portion of the longus colli muscle.[4] The anterior atlantooccipital membrane courses from the superior surface of the anterior arch to the foramen magnum.[2] In a hyperextension injury, the inferior portion of the anterior arch of C1 may be pulled caudally due to contraction of the longus colli leading to a bony avulsion and a horizontal fracture pattern.[4],[6] With the neck in extension, the atlas usually rides on the dens. Thus, it is possible for the dens to shear off the inferior margin of the anterior arch of the atlas. In one of our cases, excessive hyperextension resulted in the displacement of C1 behind the C2 (Case 2). Few cases have also been reported following direct oropharyngeal trauma.[7] The instability of horizontal fractures is attributed to the degree of disruption of ligamentous structures around them.

Horizontal fractures are the most commonly the result of high-speed injury, and the mechanism is seldom restricted to hyperextension. This may result in severe disruption of the alar, apical, tectorial membrane, atlantoaxial membranes the transverse and vertical atlantoaxial ligaments. It is the disruption of these ligamentous structures that make it a severely unstable injury.

Neurological deficits are uncommon, and both our patients had no deficits attributable to this fracture. Severe neck pain and restriction of movements seem to be a common mode of presentation.[6] The diagnosis is generally made by a CT scan which shows a linear horizontal fracture of the anterior arch associated with widening of the occipitoatlantal and/or atlantoaxial joints on coronal images. Blood around the foramen magnum in a plain CT should raise the suspicion of a severe injury of the craniovertebral junction (CVJ). As most patients with high-speed motor vehicle accidents today undergo imaging with CT scans, recognition of this variety of fracture as unstable remains the biggest challenge in its management.[8] Plain X-ray films, seldom used to diagnose these fractures in recent times, may demonstrate a retropharyngeal/prevertebral swelling with a horizontal fracture line running through the anterior arch of the atlas. MRI scans in these patients are the most valuable as they demonstrate the extent of damage to the ligamentous structures surrounding the occipitocervical complex. They may have a normal atlantodental interval (ADI) with no dynamic instability noted. An increased basion–dens interval and a more than 2-mm widening of the occipitoatlantal joint space may indicate occipitocervical instability.[8],[9]

A National Library of Medicine (PubMed) search for “horizontal fractures of the atlas” yielded 24 reported cases (23 antemortem and 1 postmortem) to date (isolated C1 with no associated C2 fractures). The cases are summarized in [Table 1].
Table 1: Reported cases of isolated Horizontal fracture of Atlas with mode of presentation and treatment

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This type of fracture seemed to be common in the younger age group, necessitating a strong neck musculature to avulse the anterior tubercle in hyperextension. Most were involved in motor vehicle accidents, and hyperextension was the mechanism of injury. Cases, until the 1990s, were managed by immobilization with a cervical collar, while post-2000s in situ fixation is the standard of care. It is interesting to note that all patients who had MRI in [Table 1] were treated with fixation in comparison to patients who had only body imaging. The identification of ligamentous instability with availability of MRI and development of fixation techniques seems to have contributed to this change. No long-term follow-up was available to comment on the superiority of either technique. However, due to the ligamentous nature of injury and distraction of the fractured segment by the longus coli, fixation seems to be an appropriate treatment choice. Surgical treatment is aimed at stabilizing the occipitocervical junction. Both our cases were stabilized with an occipital plate and a C2/C3 fusion. Atlantoaxial fusion has also been described when occipitocervical junction remains stable.[8][20]

   Conclusion Top

Horizontal fractures are rare fractures of the atlas. A result of high-speed hyperextension and distraction injuries they are to be identified as unstable fractures. MRI is valuable in establishing instability. Treatment involves stabilizing the CVJ most commonly with an occipitocervical fusion.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Ryken TC, Aarabi B, Dhall SS, Gelb DE, Hurlbert RJ, Rozzelle CJ, et al. Management of isolated fractures of the atlas in adults. Neurosurgery 2013;72 Suppl 2:127-31.  Back to cited text no. 1
Kakarla UK, Chang SW, Theodore N, Sonntag VK. Atlas fractures. Neurosurgery 2010;66:60-7.  Back to cited text no. 2
Jefferson G. Fracture of the atlas vertebra. Report of four cases, a review of those previously recorded. Br J Surg 1920;7:407-22.  Back to cited text no. 3
Stewart GC, Gehweiler JA, Laib RH, Martinez S. Horizontal fracture of the anterior arch of the atlas. Radiology 1977;122:349-52.  Back to cited text no. 4
Landells CD, Van Peteghem PK. Fractures of the atlas: Classification, treatment and morbidity. Spine 1988;13:450-2.  Back to cited text no. 5
Proubasta IR, Sancho RN, Alonso JR, Palacio AH. Horizontal fracture of the anterior arch of the atlas. Report of two cases and review of the literature. Spine 1987;12:615-8.  Back to cited text no. 6
Mendelsohn DB, Meyerson M, Friedman R. Fracture of the anterior arch of the atlas: The result of direct oropharyngeal trauma. Clin Radiol 1983;34:157-60.  Back to cited text no. 7
Vilela MD, Bransford RJ, Bellabarba C, Ellenbogen RG. Horizontal C-1 fractures in association with unstable distraction injuries of the craniocervical junction. J Neurosurg Spine 2011;15:182-6.  Back to cited text no. 8
Chang W, Alexander MT, Mirvis SE. Diagnostic determinants of craniocervical distraction injury in adults. AJR Am J Roentgenol 2009;192:52-8.  Back to cited text no. 9
Boni R. A rare case of fracture of the anterior tubercle of the atlas. Radiat Med 1957;43:455-62.  Back to cited text no. 10
Belis V, Manolescu A. Isolated direct fracture of the atlas. Ann Med Leg Criminol Police Sci Toxicol 1965;45:536-9.  Back to cited text no. 11
Torklus von D, Gehle W. The Upper Cervical Spine: Regional Anatomy. Pathology and Traumatology. New York: Grune and Stratton; 1972.  Back to cited text no. 12
Kattan KR. Trauma and “No-Trauma” of the Cervical Spine. Thomas: Springfield; 1975.  Back to cited text no. 13
Schild H, Schweden F, Weigand H. Horizontal fracture of the ventral atlas curve. Rofo 1982;136:485-6.  Back to cited text no. 14
Lutman M, Girelli G, Galassi G. Isolated horizontal fraction of the anterior arch of the atlas. Presentation of a case. Radiol Med 1985;71:538-40.  Back to cited text no. 15
Jevtich V. Horizontal fracture of the anterior arch of the atlas. Case report. J Bone Joint Surg Am 1986;68:1094-5.  Back to cited text no. 16
Jakim I, Sweet MB, Wisniewski T, Gantz ED. Isolated avulsion fracture of the anterior tubercle of the atlas. Arch Orthop Trauma Surg 1989;108:377-9.  Back to cited text no. 17
Bettini N, Di Silvestre M, Maggi G, Savini R. Horizontal fracture of the anterior arch of the atlas: A case report. Chir Organi Mov 1990;75:185-7.  Back to cited text no. 18
Wiens J, Freyschmidt J, Kasperczyk A. Isolated horizontal fracture of the anterior arch of the atlas. Rofo 1993;159:566-8.  Back to cited text no. 19
Tsuboi H, Takazakura R, Idota N, Takaso M, Ikegaya H. Rare atlas fracture detected using postmortem computed tomography: A case report. J Forensic Leg Med 2018;60:38-41.  Back to cited text no. 20


  [Figure 1], [Figure 2]

  [Table 1]


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