SabaN_Fusion of axis


 

 

 

 

 
284 | Saba et al - Fusion of axis with third cervical vertebra 

 

 

 

 

 

 

 

Fusion of axis with third cervical vertebra: a case report 

N. Saba1, A. Rani1, G. Sehgal1, Rk Verma1, Ak Srivastava1, M. Faheem2 

1Department of Anatomy, King George’s Medical University, Lucknow-226003, Uttar Pradesh, 

India 
2Department of Neurosurgery, King George’s Medical University, Lucknow-226003, Uttar 

Pradesh, India 

 
Abstract: Introduction: Fusion of one or more contiguous vertebral segments is usually 

the result of embryological failure of normal spinal segmentation. It may be associated 

with syndromes such as Klippel-Feil.  Fused cervical vertebrae (FCV) may also be 

acquired or pathologic. FCV is generally associated with disease like tuberculosis, other 

infections, juvenile rheumatoid arthritis and trauma. The commonest site of 

involvement is C2-C3. In condition of fusion the two vertebrae appear not only 

structurally as one but also function as one. This anomaly may be asymptomatic; 

however, it may also manifest in the form of serious clinical features such as myelopathy, 

limitation of the neck movement, muscular weakness, atrophy or neurological sensory 

loss. Case report: We observed the fusion of axis with 3rd cervical vertebra. Body, laminae 

and spines of C2 and C3 were completely fused on both anterior and posterior aspects, 

whereas the pedicles and transverse processes were not fused. Foramen transversarium 

was present on both the vertebrae bilaterally. Conclusion: This variation is noteworthy to 

neurosurgeons and radiologists in studying computed tomography (CT) and magnetic 

resonance imaging (MRI) scans.    

Key words: Axis, 3rd cervical vertebra, fusion, block vertebra, foramen transversarium,  

variation 

 
Introduction 

Cervical vertebrae are seven in number of 

which C3-6 are typical, sharing similar 

features whereas C1 (atlas), C2 (axis), and C7 

(vertebrae prominence) are atypical having 

different characteristic features. (1) Vertebrae 

and intervertebral discs are one of the main 

manifestations of body segmentation or 

metamerism. (2) Developmental and 

ossification process of C2 vertebra is the most 

complex among all the vertebrae. (3)Fusion of 

one or more contiguous vertebral segments 

results from the embryological failure of 

normal spinal segmentation. The incidence is 

0.4% to 0.7% with no sex predilection. (4) 

Recent studies have documented associations 

between fusion of the cervical vertebral 

column and craniofacial morphology, 



 

 

 

 

 
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including head posture in patients with severe 

skeletal malocclusions. This finding is 

expected to have importance for diagnostics 

and elucidation of etiology and thereby for 

optimal treatment. (5) Skeletal abnormalities 

of cervical region or in cranio-cervical region 

are of interest to the anatomists, 

neurosurgeons radiologists and even 

orthodontists. (6) 

Block vertebrae, formed after fusion of 

adjacent vertebrae is a condition which has 

embryological importance and clinical 

implications. Since the fusion of cervical 

vertebrae 2nd with 3rd has a clinical 

importance, we need to emphasize the 

importance of multidisciplinary approach to 

help establish the precise occurrence of this 

congenital anomaly for preventing any serious 

damage such as osteoarthritis by early 

diagnosis and treatment.  

Case report 

During routine survey of bones in the 

Department of Anatomy, King George’s 

Medical University, Lucknow, Uttar Pradesh, 

India, it was observed that the axis was fused 

with 3rd cervical vertebra. Features of this 

block vertebra were analyzed and the 

specimen was photographed from different 

aspects. Body, laminae and spines of C2 and 

C3 were completely fused on both anterior and 

posterior aspects. A ridge was noted on the 

dorsal surface of fused arches. Joints between 

the inferior articular facet of C2 and superior 

articular facet of C3 displayed synostosis 

bilaterally (Figures 1 and 2). Diameters of 

foramen transversaria were measured from 

supero-lateral aspect of C2 and inferior aspect 

of C3. The diameters of foramen 

transversarium of C2 on right and left side 

were 5.5 mm and 5.0 mm respectively while of 

C3 vertebra was 6.0 mm on right side and 6.5 

mm on left side. The pedicles and transverse 

processes were not fused (Figure 3). 
 

 
Figure 1 - Photograph showing complete fusion of 

body of C2 and C3 from anterior aspect 

 

 
Figure 2 - Photograph showing complete fusion of 

laminae and spines of C2 and C3 from posterior 

aspect, presence of ridge on dorsal surface of fused 

arches (arrow 1), bilateralsynostosis between inferior 

articular facet of C2 and superior articular facet of C3 

(arrow 2), foramen transversarium is seen in C2 

vertebra superolaterally (arrow 3). 



 

 

 

 

 
286 | Saba et al - Fusion of axis with third cervical vertebra 

 

 

 

 

 

 

 

 
Figure 3 - Photograph showing non-fusion of 

pedicles and transverse processes of C2 and   

C3 in left lateral aspect 

Discussion 

In condition of the fusion of cervical 

vertebrae, two vertebrae appear not only 

structurally as one but also function as one. (7) 

It is important to identify the cause of FCV i.e. 

congenital, acquired or pathologic. 

Embryologically, C2-C3 fusion was explained 

as improper separation of adjacent somites or 

their associated mesenchyme. (8) Also it was 

found to be due to non-segmentation of 

primitive sclerotome.(9) In a condition known 

as chorda dorsalis, congenital fused cervical 

vertebra is one of the primary malformations 

believed to be due to defects during the 

development of the occipital and cervical 

somites. Between 3rd to 8th weeks of 

embryonic life, cartilaginous framework of a 

vertebra is formed from paraxial mesoderm. 

(10) Congenital fusion of two or more cervical 

vertebrae as seen in Klippel-Feil syndrome was 

believed to result from faulty segmentation 

along the embryos developing axis during 

weeks 3-8 of gestation. (11) Cause of this 

anomaly is often a combination of 

environment and genetics which occurs 

during the third week post-conception. It has 

been described as an autosomal dominant 

condition. Mutation in Pax gene and notch 

signaling pathway and a chromosomal 

inversion inv (8) (q22.2q23.3) causes familial 

Klippel-Feil syndrome. (9) This syndrome was 

also hypothesized to result from embryological 

subclavian artery supply disruption sequence. 

(12) It was suggested that decreased local 

blood supply during third to eighth week of 

development may be a causative factor4. 

Absence of the joints between articular facets 

in the fused vertebrae suggests failure of 

normal development and differentiation of 

vertebrae (i.e. fusion at the pre-cartilaginous 

stage of vertebral development).  Independent 

pedicle, transverse process and ridge on dorsal 

surface of fused arches suggest normal initial 

development followed by fusion. Acquired 

FCV is generally associated with diseases like 

tuberculosis, other infections, juvenile 

rheumatoid arthritis and trauma. Cause of 

these abnormalities may be multifactorial 

which also includes the role of certain drugs 

like thalidomide, lovastatin and 

progestin/estrogen on the developing fetus.  

The present case is very much similar to 

some previous studies in which the body, 

laminae and pedicles of C2 and C3 were 

completely fused on both anterior and 

posterior aspects. (1, 6) But in our case the 

pedicles were not fused while spines of the two 

vertebrae were fused on both anterior and 

posterior aspects. This anomaly may be 



 

 

 

 

 
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asymptomatic, may appear with 

manifestations of serious clinical features such 

as myelopathy, muscular weakness, atrophy 

and neurological sensory loss or may be 

associated with syndromes such as Klippel-

Feil in the form of limitation of neck 

movement. (7) The orthodontist may be the 

first person to detect cervical spine 

abnormalities as they are asymptomatic until 

adolescence or young adulthood and early 

diagnosis is based on incidental radiographic 

findings. Symptoms vary according to the 

extent of pathology and may result in severe 

neck pain, decreased neck mobility, muscular 

weakness or sensory deficits of both upper 

limbs and sudden unexpected death. (6) 

Normally aligned congenital synostosis of C2-

3 is rarely associated with a junctional 

problem, whereas a kyphoticsynostosis is 

associated with a caudal junctional 

problem.(13) Persons with Klippel-Feil 

syndrome and cervical stenosis may be at 

increased risk for spinal cord injury after 

minor trauma as a result of hypermobility of 

the various cervical segments. Cervical 

spondylosis, disc herniation and secondary 

degenerative changes are more at levels 

adjacent to fused vertebra. There is increased 

incidence of osteophyte formation in the 

adjacent levels in cervical fusion. Neurological 

signs and symptoms are variable, depending 

on the degree of pathology. Another syndrome 

associated with this anomaly is Wildervanck 

syndrome, characterized by Klippel–Feil (KF) 

deformity of the cervical spine in association 

with abducens palsy with retracted bulbi and 

hearing loss. The main clinical consideration 

of this deformity is a difficult airway due to the 

short, thick and immobile neck secondary to 

fused cervical segments, which compromises 

bag and mask ventilation if airway 

management is required. (14) Persons with 

Klippel-Feil syndrome may be at high risk for 

developing a transient neurolgoic deficit due 

to cervical spinal cord injury following minor 

trauma, as these subjects are particularly prone 

to hyperextension trauma.  

Conclusion 

Fusion of axis and third cervical vertebrae 

is a rare and unusual finding which is clinically 

significant. This variation is noteworthy to 

neurosurgeons and radiologists in studying 

computed tomography (CT) and magnetic 

resonance imaging (MRI) scans. It is of equal 

significance to the anaesthetists doing 

endotracheal intubation as in persons with 

block vertebra in cervical region 

hyperextension may precipitate disc prolapse. 

If cisternal puncture or lumbar puncture is to 

be done, we should look for possibility of block 

vertebrae in cervical and lumbar regions 

respectively. 

 

Acknowledgement 

I would like to thank the faculty of the 

Department of Anatomy, King George’s Medical 

University, Uttar Pradesh, Lucknow, India and my 

husband for providing necessary help and valuable 

suggestions. 

 

Correspondence 

Dr. Noor us Saba 

Department of Anatomy, King George’s Medical  

University, Lucknow-226003, Uttar Pradesh, India 

E-mail: noorussaba83@gmail.com 

Phone (Mobile): 91-9368480101 



 

 

 

 

 
288 | Saba et al - Fusion of axis with third cervical vertebra 

 

 

 

 

 

 

 

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