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Κυριακή, 28 Σεπτεμβρίου 2014 03:00


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Hon Prof in Orthopaedics

Medical School

National and Kapodistrian University of Athens


When in 1975, nearly 40 years ago, I started studying the injuries of the Cervical Spine, I was impressed by two events which attracted my attention; both, were   related to the odontoid process, this peculiar anatomical element which characterize the Axis vertebra. The first was the multiple pattern of fractures  which this element was subjected to. The second one, their evolution and their final  outcome

The incidence of  these  fractures  is  around 14% (1)  among the cervical spine  fractures and may occur at any age, with a higher risk for  patients older than 65years old but, to note that in this age group the fracture of the odontoid is more likely to be missed at the initial examination.

The cause of injury is mainly a road traffic accident or a fall, but, other causes are, also, implicated to these injuries. However, the exact prevalence is not known as a certain number of  patients who sustained such  an injury did not survive and were transported dead to the hospital.  The fracture of the odontoid is due often to high-energy trauma with the implication of a combination of forces and the major loading path that cause the lesion is not well established. According to experimental data the causes of the fractures of the odontoid process are a combination of vertical compression and horizontal shear which acting in a different angle create different patterns of fracture . In practice we can assume that the main forces responsible for a fracture of the odontoid process are  the hyperextension, the flexion and the lateral bending, but is certain that  combined   forces could also be responsible for a fractured odontoid.       

The clinical picture of  this injury varies from a mild to a  severe one (quadriplegia or even death) (1). The patient is coming in the emergencies holding his head or is transferred on stretcher complaining of pain in  the cervical region; is keeping his head unable to move it because of pain. A thorough clinical examination to exclude symptoms corresponding to a neurological damage is  needed although there are usually missing. The severity of the neurological disorder corresponds to the degree of displacement and the consequent instability of the odontoid  process. Older people have a higher  rate of  mortality (1).

It is also important to look for an involvement of the vertebral arteries which if damaged could induce symptoms not only at an early stage, but, also, days after the accident. 

The fracture of the odontoid process represents a separate entity and special attention is needed in order to recognize the fracture, but also, to apply the appropriated treatment. Now a days, it is clear that the pattern of the fracture contributes in the favorable or poor evolution, that is, in the appearance of complications, and particularly of pseudarthrosis ;  at the same time, it may indicates the way these lesions could be managed. So, there is a necessity for a complete and precise clinical and radiological approach, which will permit us to put the correct diagnosis. Problems could be arise  in children (the presence of congenital malformations, the immature skeleton etc) and in old people ( Degenerative disease, pathological condition like tumor etc).

Radiological investigation is of importance. This must include apart the conventional x-ray views (Anterolateral (open mouth view), lateral and in certain instances dynamic views), also, CT-Scan (with reconstruction imaging), M.R.I and in certain instances too, 3-D imaging. Of course this will be done in a ‘step by step’ manner. If the patient is unconscious, then, the entire spine has to be investigated. The raison for such a meticulous radiologic investigation is due to the fact that  the fracture pattern is unforeseen, as multiple forces can be applied to the upper cervical spine simultaneously or in continuity.


Two basic classification categories according to : a. The position of the fracture and b. to the direction of the line fracture are recognized.

 In the first category there are four different classifications described :

1.The Schatzker’s classification (2) in which two types are recognized, (a) the low fracture at the level or below the level of the attachment of the accessory ligaments and (b) the high fracture above the attachment of the accessory ligaments.

2.The Mourgues’ Classification (3) in which there are two types of fractures. The first is reported to fractures of the base of the odontoid process with a 100% union prognosis, and the second is reported to fractures at the neck of the odontoid  process with a union prognosis of less than 50 %.

3.The Anderson-D’Alonzo’s  classification (4) who proposed the division of the fractures into three types. In the first instance, the authors are reporting to fractures at the top of the odontoid process with a favorable prognosis for union. In the second instance they are referring to fractures of the neck with a mean rate of  pseudarthrosis of about 36 %. The last type the authors are referring is the fractures at the base of the dens. This fracture has a 90 % mean rate of union.

4.The Althoof’s classification (5) who proposed 4 types of fractures. The first type with the lesion situated above the neck and having a rate of pseudarthrosis around 64 %. The second type concerns fractures through the neck with a rate of pseudarthrosis of about 55 %. The third type is the one where one of the  lateral masses is involved; this lesion has a mean rate of union around 50% and the fourth type in which the fracture is situated at the body of the axis vertebra with a high rate of union as 93 %.

The second category, in which the direction of the line is considered, includes the classification of Roy-Camille (6) with  three types of fractures :

(a) Anterior oblique fractures with posterior-superior  towards anterior-inferior direction  of the fracture line originating at the level of the neck and directed through the body to the anterior surface of the axis vertebra. This fracture is the result of an impact of the strong transverse ligament on the odontoid process at the time of the applied flexion momentum, and represent the commonest type.

(b) Posterior oblique fractures with anterior-superior towards posterior-inferior direction of the fracture’s line. These fractures are caused by an applied extension momentum, when the anterior rim of the foramen magnum strikes the apex of the odontoid process, and have the tendency to displace posterior.

(c) horizontal fractures with the line of fracture through the neck only; these fractures are the result of the application of a lateral force and are the most unstable. In some cases the fracture’s line extends to the axis body and becomes  trans-articular representing the “English Polishmen’s helmet”.

The evolution in the diagnostic methods revealed  the  existence of other types of fractures like the vertical one, and  the complex fractures . The vertical fracture is characterized by the division of the odontoid process into two parts with the line fracture extending from the apex to the base, while the complex fractures are characterized by a diversity of fractures lines creating the compound or double level fractures. (Fig 2E)

The fractures  of  the odontoid  process  represent  the mechanical failure of  this particular anatomic element following the application of  forces (1). The direction  of these forces, the  internal  architecture, the mechanical  strength of  the  bone trabeculae, the  proportion of the cortical and cancellous bone, the  magnitude of the odontoid process displacement, the vascular supply of the odontoid process and the age of the patients are  the  most important  factors in  the creation of specific fracture types and the prognosis of these injuries.  In line, but not, well documented, in the literature, radiographic, and histomorphometric  studies  outlined  the structural difference between the odontoid process and  the body of the axis. Data from  these studies could distinguish the fractures at  the base of the odontoid process and  the underlying body of the axis. This was also  shown in a recent study using peripheral  quantitative computed tomography (pQCT) in cadaveric specimens of  the axis (7). Moreover, this study showed the difference of the internal architecture of the axis  between young and older patients; in subjects more than 40-year-old a large void of thin trabecular bone has been identified extending from anterior-inferior  to superior- posterior to the base  of  the  odontoid  process  indicating  a  mechanically  weak region  that  may predispose to specific fracture patterns (7).

The Anderson - D’Alonzo classification offers a simple and topographic approach  to odontoid process fractures. However, it does not contribute  to the thorough understanding  of   the  mechanism  of   the  fracture, nor  it  incorporates  any  bio-   mechanical characteristics  or specific  characteristics of the internal architecture of the odontoid process and has  limitations .

In addition, the many attempts made for its improvement or replacement , the   existence of alternative classifications based on the direction of the   fracture’s  line, the  heterogenity  of  the  reported  pseudarthrosis  rates  at type II fractures  and  the presence  of various unclassified fracture  types  such  as some vertical or oblique fractures may suggest the inadequacy of   the aforementioned classification  schemes.

The classification  proposed  by Anderson and D’Alonzo  is  misleading   and contributes  to  confusion  regarding fracture  location . The Anderson and D’Alonzo type III  fracture  is  not  a  fracture of  the odontoid process, but  rather a  horizontal  rostral fracture  through  the upper aspect of  the body  of   the  axis (8). Further  adding   of   subtypes,  such as type  IIA(9), type IIB (10), type IIC, type II 1-5 (11)  and  type  IIIA (12) perpetuate   the confusion. At the same time, Koller stressed the point of a lack of comprehensive classification for fractures of the body and the odontoid process (13)     

In the literature there are fractures not corresponding  to  the   already  existing classifications and there is a confusion to be present, so, it is clear that  a  more  appropriate  one  would  be obligatory (14).

The proposed herein classification  is  based  on  the structural,  anatomical and  bio- mechanical properties of the odontoid process (7).

The  anatomical  classification  we  propose,  accepts  four  types of  fractures and recognizes a zone where practically no fractures  are noted (the neutral  zone), which  is found  at  the  level of  transverse ligament,  an area of  phylogenically strong bone.

Type A fractures  are rare. It is an avulsion  fracture  at  the  points  of  insertion  of  the  alars  or  apical ligaments with an incidence of 2,3 % in our series ; It’s stability is questionable, but they responded favorable to a conservative treatment.

 Type B fractures  represent the most common fractures  of  the dens  fracture in the literature, and particularly in the elderly population  although  in our series were second in incidence with 44,1 % . They  are  the  result of lateral force which initiates a rotational movement. In the presence of osteoarthritic changes this leads easier to a type B or C fracture seeing most frequently in older persons. These fractures represent an unstable lesions with a tendency to pseudarthrosis, so, they  need  a careful  evaluation  and  appropriate  treatment, conservative  or  surgical, particularly in the old patients .

Type C fractures  were found to represent 46,6 % ; they  have a more favorable outcome than type B , responding to a less aggressive management, finally,

Type D  fractures are not  so  uncommon (7 % in our series). The  axial loading, while the neck is in extension, as well as, a combination  of  applied  forces, which act either  simultaneously or not, are probably responsible  for  this  injury. Although  it is an unstable lesion, it  seems to respond better to a non-surgical treatment.

To note that is easy to recognize a type B from a type C fracture  in the lateral view. In type B fracture the Harris ring is intact as the fracture’s line  is  above this ring. In type C the fracture line is projected at  the upper part of the Harris ring.

This classification is considered more realistic since  it  is simple, it includes the whole   spectrum  of   fractures, it  refers  only  to  one   anatomical  structure  ( the odontoid process), it  correlates  to the bio-mechanical characteristics of  the axis, it indicates  the prognosis  of  the  different fracture types, it suggests the adequate evaluation and management of the fractures. Fractures not involving the odontoid process, like the type III in the Anderson - D’ Alonzo classification, could not be called odontoid fractures as they are, anatomically speaking, fractures of  the axis’ body.

Fractures of the odontoid process should be divided into (a) stable and (b) unstable(6)  This is necessary in order to proceed with the correct therapeutic plan. Stable injuries are


managed conservatively, while  unstable  injuries  are  treated surgically. Fracture’s instability depends mostly on the presence of associated lesions, the type  of  fracture and the initial displacement, particularly if there is vertical displacement

Type A fractures are treated conservatively by using external mobilization, like a  rigid cervical collar or a halo vest ; rarely an operation should be required.

In  type B  fractures, although  there  are  unstable, a controversy is still  on-going among different authors  regarding  the  surgical approach and  management of this lesion. To us an initially conservative treatment should be attempted unless a score of more than 10 points is found.

In type C, either conservative or operative management  is applied in relation to the instability these injuries shown.

In type D, the appropriated conservative management is offering excellent results.

Several treatment modalities are proposed in the presence of this injury, but, before take any decision, it is wise, particularly in the elderly patients, to look for any clinical co- morbidities  that may affect the management, and to rule out any concomitant or double level fracture of the cervical spine.       

Conservative treatment is suggested by  the use of traction with  the application of a  Crutchfield skull tongs, in order to reduce and stabilize the fracture or with the use  of external immobilization as custom-made orthosis, halo vest or cervical collar.

In case of application of traction, the weight applied should not exceed  2-3 Kg, in order to avoid distract the fractured fragments. Special  care  must  be  given,  not  only  to the  application  of  traction, but, also, in it’s   direction. Attention  must  be  paid  when  traction in  flexion is applied, because of  the potential danger of a vertebral artery lesion or of a neurological injury  which  may  induce respiratory compromise or other neurological symptoms .

Stabilization must be kept for at least 4 to 6 weeks during which   radiographic  control of  the position of  the fracture is necessary, as well as  careful examination for avoidance of  complications  related to the traction and prolonged bed rest. After this  period the  patient may be  mobilized using  a four-point support brace for  a  period  of  four  to  six more weeks. At  the  end  of  10  to 12 weeks, dynamic x-ray views  in flexion and extension are taken in order to detect  any sign of instability. If instability is proven, then, surgical treatment must be considered. If  no instability is detected  and  the fusion is  complete, the patient  must use  a  soft collar for a short period of time.


The use of a Halo vest (fig 3) is not always recommended as the rate of complication  reported is  as high as 26 % with older persons suffering more from discomfort. Even  more, the traction obtained at the beginning, is slowly turned  into compression, in the mobilized patient, resulting in  mal-union, if  the  reduction of  the  fracture should be lost due  to sliding.

The fusion rate in the conservatively treated patients is reported to be from 35 % as high as 85 %, but this  is related to the age and other  parameters, like the time the treatment was applied, the type of  the  fracture  and  the  initial  displacement; the later is being correlated to the direction (anterior or posterior) the fracture  is displaced off.

 Also, often, the traction applied leads to distraction at the  fracture site; this leads to development of  late instability and pseudarthrosis.

Vieweg and Schultheib  in contrast  to  Wolter and Reimann(1), advocate  the  use of  Halo vest  in  type II  fractures, as the  percentage  of  healing  is  as  high as  85%, particularly  in  the  no-displaced  ones ;  they conclude, also, that  in type III the  Halo vest  is the treatment of choice   as the rate  of  healing is about  97%.

The fractures of the odontoid process are prone to complications  either at the trauma   scene or later in the hospital.

Two of the complications appearing in a late period  are  of importance and have to  be  well clarified : pseudarthrosis and  mal-union.

Of  importance  is  the pseudarthrosis  these fractures  may develop and the potential danger for late myelopathy or for direct  injury of  the spinal cord.

According to the  literature  the  percentage of  pseudarthrosis  related to the applied treatment, is  between   4%   to  100 %  for  all  types  of   fractures  and   consequently complicating  their  treatment. The predisposing  factors which have been accused for pseudarthrosis   include age, mechanism of injury, displacement, the blood supply of   the odontoid  process, the direction of  fracture’s  line and type of  fracture. Also, the application  of  excessive   traction, the  stability  of   immobilization,  the  timing  of   immobilization, as well as  the  co-existence of  an other  fracture, either  in  the  atlas   or even  in  the  axis  itself. The internal architecture  of  the  axis seems to  play  an   important role in the  development of  pseudarthrosis. Finally, the possibility  of  interference  of  the transverse ligament  between  the  fragments  may, also, cause  difficulties   in   the   reduction  of  the   fracture,  resulting   in  the     development  of  pseudarthrosis. Some authors may disagree  as  to  the importance of  some  of   the  above  factors.  To our experience all  the above mentioned factors play a certain role and contribute   to  the development of pseudarthrosis resulting in instability at the fracture site.

Age has an important role in pseudarthrosis since it has been proved that nonunion  or pseudarthrosis is found at a higher incidence in patients over the age of 50 years.  Fracture displacement according to Blokey and Purser (1) should not be  correlated to pseudarthrosis. However, other authors did not  accept this opinion.  Appuzo et al (1) described  that  a  shown  displacement  of more  than  4 mm  is   of   significance. However, it   is  extremely difficult  to be  aware  of  the original   displacement  that  was present at the time of the accident.

The traction applied, as well as  its direction, play  a  significant  role according  to  Ryan and Taylor(1). This  is  due  to the possibility of creating  a greater wedging at the fracture level than the one desired, and to lead to a deformed odontoid process.

The type of fracture is also implicated in the development of pseudarthrosis since in fractures  involving  the neck of the dens as well as  the direction  of  the  fracture’s line  this was in a rate of 32 % and as high as 90 % . In our experience the  types A, C and D are prone to unite, while type B fracture have    a high rate of  pseudarthrosis, particularly the one that shown a posterior displacement  of more  than 5mm or an angulation of more than  10 degrees. 

There is no doubt that the presence of co-existing injuries, as well as a delay in the diagnosis or if the immobilization is not the proper one, then this  will increase  the  instability of the fracture.

The knowledge  of  these parameters as factors  influencing  the  development  of  a pseudarthrosis, obliged us to proceed in their grading, according to the role each one  plays. In this manner,  the  evaluation of a fracture is more easier, as we will predict  the  risk  for  pseudarthrosis. It  has been estimated  that if  the  sum  of the graded factors is greater than 10 points, then the fracture  must  be characterized as being at risk of pseudarthrosis and surgical treatment must be considered (1,15).

The blood supply of the odontoid process is not considered to participate in the development of pseudarthrosis. Although a recent experimental study of ours revealed decreased blood supply at the area where type B fractures happen, which is the area where pseudarthrosis often develop (16).

Pseudarthrosis  in the elderly  is not always  a major problem  as it was proven ; this  is  not  accompanied always  by  a  clinically significant instability due  to  the development of  fibrous tissue  at the fracture site. However   operation has to be considered if instability persists or if signs of myelopathy are present.

Operative treatment of dens non-unions is not without risk, taking into consideration the age of the patients the high  co-morbidity those patients have and, also, knowing  that the success rate is low.

The second most frequent and severe complication of the fractures of the odontoid  process concerns their mal-union(1). Special care so must be  given to this complication as may result in spinal  canal stenosis which may  induce, in long  term,  cervical   myelopathy. 

The greater the displacement and wedging of  the fracture, the less  the width  of  the spinal canal. This results in chronic compression or friction of the dura matter  and the spinal cord on  the upper posterior corner of the body of the axis and hence cervical  myelopathy. The treatment of  this  complication is  difficult. It requires anterior or posterior decompression combined with posterior fusion extending from the occipital bone to C1,C2 or C3 and even lower.

A number of minor complications may accompany a  fractured odontoid. Stiffness, decreased  range of  movements, discomfort  or  even mild pain are  easy managed with physiotherapy or other conservative methods. Younger patients response better and an uneventful outcome is usually achieved.

Failure to treat conservatively a  fractured  odontoid  is  an indication  for surgical intervention.

Instability must be treated operatively as soon as possible. The operative approach is suggested  by many authors. There are several methods that allow the safe management of the unstable  fractures. This is done  by closed  or open  reduction, the use of osseous  graft, and stabilization  by means  of  a  wire  or  nylon  or  use  of  implant(s). Auto-graft  is  the  most  suitable     material to be used for achievement of  a stable fusion. The approach used  is  either    anterior, lateral,  posterior  or combined.

Posterior stabilization includes :

Posterior  C1-C2  wiring  technique  with  Gallie’s  or  Brooks’ techniques  or other        methods (fig4).

Anterior stabilization includes:

a. Application of  a plate between the anterior arch of the atlas and the body of  the axis or the vertebral body of C3 

b. Internal  fixation  with   screw(s). This  technique is  gaining popularity, but  indications  have  to   be  set  very  carefully   as   osteoporosis,  fracture  of   the  anterior   wall  of the   body  of   C2,  posterior  displacement,  comminuted or type D fractures or even a

   narrow diameter of the spinal canal  are  among  the contraindications. The osteosynthesis  of  the odontoid process permits a nearly normal function of the C1-C2 level (5).


Lateral stabilization includes :

Fusion using the Dutoit technique. The lateral approach is used for a C1- C2arthrodesis in case of traumatic instability, tumors or infections and for cases in whic in which  an other, previously used approach, or a counter-indication is present.


The surgical results seems to be better than these achieved  with a  non-operative management as the reported fusion rate is high between 80-100% . However, there  is  not  unanimous  acceptance  of  an  appropriate  treatment  of patients with  these  fractures, particularly  in  the  elderly population. (Table I  summarizes  the indications for the appropriated management of an odontoid fracture). Physiotherapy in both instances, has an important role to play in the final  outcome  those  patients  should  have.

We can easily appreciate the importance of dens fractures ; they need correct diagnosis and appropriated treatment trying to minimize the side effects to the patient and to the society. In the later, the financial cost is very important as in the last decade, the cost for the treatment of these fractures is very high with the increased hospitalization and the increased number of patients treated surgically (17)


Table I

Type                 Treatment 


A                     Conservative  

B                      Surgical or conservative  

C1                    Conservative or surgical

C2                    Conservative 

D                     Conservative                          



Fractures of the odontoid process represent a particular entity.; they need a careful handling us their behavior is not easy  predictable. Diagnosis of the correct type of fracture is very important. Complications due to multiple factors, are not rare and have to be carefully managed and treated. Pseudarthrosis is the most common complication related to many factors the most important being the instability at the fracture site.

The proposed new classification has been proven successful lasting in time and is now considered more realistic as it is simple, is including the whole spectrum of fractures, it refers to one anatomical structure (the odontoid process), it correlates to the bio-mechanical characteristics of the axis, it indicates the prognosis and it suggests the management of the fracture.

The study of our cases revealed some directions for the development and treatment of these fractures. The evaluation of our cases showed that type A and D fractures can and should be treated conservatively ; they usually have a good prognosis. Type B fractures are prone to further complications and hence should be treated - in their majority - surgically. Type C, need to be followed closely and in case of instability and/or late displacement have to be operated             



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        2. Schatzker J et al. (1971) Fractures of thedens (odontoid process): an analysis of thirty-seven cases. J Bone Jt Surg – Br. 53 : 392-405

        3. De Mourgues  Fischer LP et al. (1981)  Fractures of the odontoid process (in French). Rev Chir Orthop   Reparatrice   App Mot 67 : 783-790

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        7.  Korres DS, Karachalios Th et al. (2004)  The structural properties of the Axis studied in cadaveric speciments Clin Orthop Rel Research. 418 ; 134-140

        8.  Benzel EC, Hart BL et al (1994) Fractures of the C2 vertebral body. J Neurosurgery 81 : 206-212

        9.  Hadley MN, Brown CM et al. (1988) New subtype of acute odontoid fractures (type IIA) Neurosurgery 22 : 67-71

      10. Gauer JN, Shaft B et al (2005) Proposal of a modified, treatment-oriented classification of  odontoid fractures Spine L 5 : 123-129

      11.  Reihold M, Bellabarba C et al (2011) Radiographic analysis of type II odontoid fractures in a  geriatric patient population :description and pathomechanism of the “Geier”–deformity. Eur Spine J 20:1928-1939

      12. Jea A, Tatsui CI et al (2006) Vertically unstable type III odontoid fractures:case report. Neurosurgery 58 : E 797

      13.  Koller H, Kammermeier V et al.(2006) Spinal stenosis C1-C2 following redo surgery for failed odontoid screw fixation-scrutinizing the odontoid fracture classification. Internet J Spine Surgery 3;1-11

      14.  Korres DS, Mavrogenis FA, et al. (2008) It is time to reconsider the classification of dens fractures. Eur J Orthop  Surg Traumatol 18 : 189-195

      15.  Korres DS, Stamos KG,Andreakos AG et al (1989) Fractures of the dens and risk of pseudarthrosis. Arch Orthop Trauma Surg 108 :373-376

      16. Γκανταΐφης Νικολαος (2014) Η μελέτη του περιοστέου και της περιοστικής αιμάτωσης της οδοντοειδούς απόφυσης του δευτέρου αυχενικού σπονδύλου ως πιθανού παράγοντα ψευδάρθρωσης διαφόρων τύπων καταγματων του οδόντος.

            Διδακτορική Διατριβή. Αθήνα 2014

      17. Daniels, Alan H.; Arthur, Melanie; Esmende, Sean al.  (2014) Incidence and Cost of Treating Axis Fractures in the United States From 2000 to 2010 Spine: 15 August 2014 - Volume 39 - Issue 18 - p 1498–1505












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