Skeletal Radiol DOI 10.1007/s00256-013-1809-y
CASE REPORT
Posterior atlantoaxial dislocation complicating odontoid fracture without neurologic deficit: a case report and review of the literature Hao Meng & Yuan Gao & Mo Li & Zhuojing Luo & Junjie Du
Received: 8 October 2013 / Revised: 15 December 2013 / Accepted: 22 December 2013 # ISS 2014
Abstract Traumatic posterior atlantoaxial dislocation associated with odontoid fracture is extremely rare, with only eight cases reported thus far in the English literature. This report concerns a 47-year-old female who presented with considerable pain and stiffness in the neck without a neurologic deficit after injury due to a fall. Radiographs, computed tomography, and magnetic resonance imaging demonstrated a posterior dislocation of the atlas with respect to the axis with an odontoid fracture. No cord compression or intramedullary cord signal abnormalities were detected at the level of the atlantoaxial dislocation. A pedicle screw fixation/fusion was performed via a posterior approach following successful closed reduction.
Introduction Traumatic posterior atlantoaxial dislocation associated with a fracture of the odontoid process is a rare injury [1]. Only eight isolated cases have been published in the English literature [2–8]. Most of the patients were initially treated with conservative traction, and some of these patients were supplemented with posterior internal fixation. We describe the ninth case of a posterior atlantoaxial dislocation combined with an odontoid fracture without a neurological deficit, caused by a fall. Computed tomography (CT) with reconstruction and magnetic resonance imaging (MRI) each provide optimal visualization for this type of injury discussed in this report. We also discuss the management of this type of injury based our experience and data in the published literature.
Keywords Atlantoaxial dislocation . Odontoid fracture . Neurological deficit . Posterior Case report Hao Meng, Yuan Gao, and Mo Li contributed equally to this work. H. Meng Department of Orthopaedics, Military General Hospital of Beijing PLA, Beijing 100700, China H. Meng Department of Spine Surgery, General Hospital of Air Force, Beijing 100142, China Y. Gao Department of Obstetrics and Gynecology, General Hospital of PLA, Beijing 100853, China Y. Gao Department of Obstetrics and Gynecology, Changhai Hospital, Second Military Medical University, Shanghai 200433, China M. Li : Z. Luo (*) : J. Du (*) Department of Orthopaedics, Xijing Hospital, Fourth Military Medical University, 127 West Changle Road, Xi’an 710032, China e-mail: [email protected] e-mail: [email protected]
History A 47-year-old female patient walked to a local county clinic after the fall injury. According to the medical records of the county clinic, the patient walked approximately 1.2 miles to the clinic and complained of considerable pain and stiffness in the neck after a fall from a height of 5 m. Her vital signs were normal. The neurological examination showed no apparent deficit. There was no evidence of concomitant chest, abdominal or head injury except for lacerations of the cheek. The subsequent lateral radiography demonstrated a posterior dislocation of the atlas with respect to the axis combined with an odontoid process fracture (Fig. 1a). The patient was immobilized in a neck collar immediately and transferred to our hospital for further diagnosis and treatment. Physical examination On examination, the patient was fully conscious and oriented. She reported pain and tenderness in her neck and she was unable to lie down. Motion of flexion,
Skeletal Radiol
Fig. 1 a Lateral radiograph showed odontoid process fracture (arrow a) combined with posterior dislocation of the atlas (arrow b). b Sagittal CT image showed dislocation of the facet joints of C1 and C2 (arrow). c Sagittal MRI showed no cord compression or intramedullary cord signals
abnormality at C1-C2 level. d Axial CT showed posterior dislocation of the atlas associated with odontoid process fracture. e Axial MRI showed an intact transverse ligament at the level of C1-C2 (arrow)
extension and rotation of the neck was severely limited and these examinations were not performed given the diagnoses of atlas dislocation and odontoid process fracture. The vital signs and neurological examination were again normal.
the CT findings, with no imaging evidence of any cord compression or intramedullary cord signal abnormality at the level of the atlantoaxial dislocation (Fig. 1c). Posterior longitudinal ligament was intact, retaining its protective effect. An axial MRI showed an intact transverse ligament at the level of C1C2 (Fig. 1e).
Imaging examination Radiographs of the cervical spine demonstrated the axis was fractured at the base of odontoid process, categorized as a type II fracture based on the Anderson and D’ Alonzo classification [9]. The atlas was displaced posteriorly relative to the axis, which delineates a type IV dislocation based on the Fielding classification [10]. The sagittal and axial cervical spine CT reconstructions revealed a type II fracture of the odontoid and posterior displacement of the odontoid by its width (Fig. 1b, d). MRI of the cervical spine was performed to evaluate the status of the cervical spinal cord and the integrity of the ligaments. MRI confirmed
Initial treatment After the diagnosis was confirmed, skull traction was applied immediately with an initial weight of 3 kg and gradually increased to 6 kg under fluoroscopy. The atlas was positioned over the axis and the reduction was confirmed after 48 h of traction. The patient’s neurologic status was monitored throughout this procedure. She did not exhibit neurological abnormalities and her pain was relieved following traction. Subsequent radiographs demonstrated a successful reduction of the dislocation (Fig. 2). The traction
Skeletal Radiol
Fig. 2 Lateral radiograph made after the closed reduction (arrow: fracture line)
weight was then decreased and maintained to immobilize the neck. Operation However, because of the instability of C1-C2 was highly suspected and an intact transverse cervical ligament would keep the dens in place, C1-C2 fixation was performed using pedicle screws through a posterior approach. The traction bow was removed immediately after the operation. There were no iatrogenic neurological deficits of the spinal cord. A post-operative radiograph showed an anatomical reduction of the C1-C2 complex (Fig. 3). The patient was instructed to wear a Philadelphia collar for 3 months. At the latest followup, lateral radiograph and sagittal CT image showed bony healing of the odontoid fracture 36 months after the operation (Fig. 4).
Discussion In the axial skeleton, dislocation is described according to the displacement of the superior vertebral body. Posterior atlantoaxial dislocation combined with odontoid process fractures is exceedingly rare. The rarity of this dislocation is largely due to the configuration of the odontoid process whereby interlocking of the osseo-ligamentous ring would clearly appear to cause anterior atlantoaxial dislocation [11, 12]. This combination of dislocation and fracture accounts for
Fig. 3 Postoperative lateral radiograph
approximately 0.3 % of all cervical spine injuries and 1.7 % of upper cervical spine injuries [13]. The causes of this injury vary widely, including sports injuries, falls from great heights, and motor vehicle accidents [3]. The mechanism is extension and the dislocation occurs because the ligaments between the dens and the anterior arch of the atlas hold. Anatomically, the odontoid process articulates with the osseo-ligamentous ring formed ventrally by the anterior arch of the atlas and posteriorly by the transverse ligament to provide stability of the C1-C2 complex. Because the dorsal part of the ring is ligament rather than bone and is therefore susceptible to inflammatory conditions that may weaken it and create instability, almost all clinical cases of atlantoaxial dislocation manifest as anterior dislocation of the atlas relative to the axis. Combinations of fractures and dislocations involving the atlas and the axis can disrupt the tectoral membrane, alar and apical ligaments, cruciate ligament, and joint capsules at C1-C2. In posterior dislocation, the atlantoaxial ligaments are ruptured and a fracture of the odontoid is a more frequent occurrence [14]. Isolated posterior cervical translation has been postulated as the probable mechanism of posterior dislocation with odontoid fracture. It appears likely that trauma that is sufficient to produce such a dislocation with fracture of the odontoid would cause damage to the cord and lead to immediate death due to respiratory failure. Therefore, posterior dislocation with fracture of the odontoid may occur more frequently than is reported. In those who survived such injuries, neurological examinations were usually normal or demonstrated only mild neurological deficits. Miyamoto reported
Skeletal Radiol Fig. 4 Postoperative lateral radiograph (a) and sagittal CT image (b) showed healed odontoid fracture and no displacement of the atlas (36 months post-operation)
that only 16 % of upper cervical spine injuries caused neurologic deficits [15]. Until now, only eight cases of traumatic posterior atlantoaxial dislocation combined with odontoid process fracture have been reported in the literature. In these cases, a type IV posterior atlantoaxial dislocation based on the Fielding classification [10] and a type II odontoid fracture base on the Anderson and D’Alonzo classification [9] were always involved. According to the previously reported eight cases, neck pain and restricted neck motion were established by examination in all patients. Three cases had neurological deficits including spastic tetraparesis sphincter dysfunction, hemiparesis and extrapyramidal syndrome [2, 8, 16]. The other five cases had no definitive clinical symptoms or signs of neurological deficit with respect to their C1-C2 dislocations. The surprisingly low rate of spinal cord injury in these latter cases may be
explained by Steel’s rule of thirds [16]: one-third of the neural canal at the atlantoaxial level is occupied by the odontoid process, one-third by the cord, and one-third of the spinal fluid. By this concept, although the injuring force is sufficient to produce a dislocation with fracture of the odontoid process and a reduction in the area of canal, the remaining canal area is sufficient to avoid cord compromise. Typically, cervical spine radiographs including A-P or transoral views of the cervical spine do not show the atlas and axis clearly, either due to overlap of the cranial bones or to limited positioning of the head or neck. Although lateral radiograph can show the atlantoaxial dislocation and odontoid process fracture, the CT scan is the imaging modality of choice for the diagnosis of cervical fractures and dislocations. CT reconstructions can provide optimal visualization for particular injuries. Strict preoperative planning uses CT to assess the bony anatomy of the C1-C2 complex. In this case, sagittal
Table 1 Summary of the previously published eight cases Case no. Author and year
Age, sex Mechanism
1 2
Autricque et al., 1986 45, M Autricque et al., 1986 63, M
15, F
Head injury Motor vehicle accident Head and cervical injury Bicycle accident Motor vehicle accident Riding accident
3
Fuentes et al., 2001
24, M
4 5
Spoor et al., 2008 Lenehan et al., 2010
43, M 63, F
6
Hopf et al., 2009
7 8
Oh et al., 2010 Moreau et al., 2012
37, M 65, M
Cervical trauma Fall accident
Fracture/dislocation type Neurodeficit
Reduction Internal fixation
Type II/type IV Type II/not specified
Spastic tetraparesis Closed No Closed
No Occipito-C3 fusion
Type II/type IV
No
No
Posterior C1-C2 fusion
Type II/not specified Type II/not specified
Closed Closed
Type II/type IV
Hemiparesis Extrapyramidal syndrome No
Type III/not specified Type II/type IV
No No
Closed Closed
No Posterior transarticular fusion Posterior transarticular fusion No Occipito-C2 fusion
Closed
Skeletal Radiol
CT reconstructions demonstrated the odontoid fracture and helped us to evaluate the relationship of the C1-C2 facet joints and lateral masses (Fig. 1b). In contrast, MRI can provide a more sensitive method to detect the degree of soft tissue compression in the cervical spine [17], MRI for our patient showed an intact transverse ligament and no cord compression or intramedullary cord signal abnormality at the C1-C2 level. Therefore, both CT and MRI of the cervical spine are essential in selected patients with head or neck trauma who are suspicious for atlantoaxial dislocation. Traumatic atlantoaxial dislocation can sometimes pose a therapeutic challenge due to the complexity of atlantoaxial misalignment. Our patient had a type IV posterior atlantoaxial dislocation with misalignment of the atlas and axis following a type II fracture of the odontoid process. To date, there are no definitive guidelines for traumatic atlantoaxial dislocation, and therapeutic management is still open to debate. Most studies have favored closed reduction. In the previously reported eight cases (Table 1), closed reduction with traction was successful in three cases. Subsequent external immobilization with a halo-vest was used for 3 to 6 months. In the other five cases, after failed closed reduction, a surgical procedure was performed. In our case, we initially attempted to reduce the dislocation through gradual manual traction. While the dislocation of the atlas and axis in our patient was directly manipulated by closed reduction, this type of fracture has a relatively high rate of nonunion. In addition, because higher complication rates have been associated with use of a halo-vest, especially in older patients, surgery has been performed, either by an anterior or a posterior approach. In our case, the type II fracture of the odontoid process was viewed as less stable, especially in combination with a type IV posterior atlantoaxial dislocation. Although the rotational motion of C1-C2 can be preserved with anterior screw fixation [18], a posterior approach was selected due to the ease of dissection, its familiarity among surgeons, and the stabilization of C1-C2. Since Gallie first described the posterior C1-C2 wiring technique in 1939 [19], a number of other posterior surgical techniques have been detailed. Brooks and Jenkins reported the alternative wiring technique in 1978 [20]. As described by Lapsiwala et al. [21], an alternative method using pedicle screws can increase rotational and lateral bending stiffness compared to the posterior wiring technique and intralaminar screw fixation, yet may also decreased the potential for complications such as postoperative dysphagia due to over retraction in an anterior approach [22]. Most importantly, the fusion achieved by the latter technique precludes without the need for halo-vest immobilization after surgery, and allows for the use of a collar for 8–12 weeks instead. In conclusion, this report describes a posterior atlantoaxial dislocation associated with an odontoid fracture and achievement of a solid fusion by a successful closed reduction and
subsequent pedicle screw fixation/fusion through a posterior approach.
Conflict of interest No funds were received in support of this work. The authors declare that they have no conflict of interest.
References 1. Garber JN. Abnormalities of the atlas and axis vertebrae-congenital and traumatic. J Bone Joint Surg Am. 1964;46:1782–91. 2. Autricque A, Lesoin F, Villette L, Franz K, Pruvo JP, Jomin M. Fracture of the odontoid process and C1-C2 lateral luxation. Two cases. Ann Chir. 1986;40:397–400. 3. Fuentes S, Bouillot P, Palombi O, Ducolombier A, Desgeorges M. Traumatic atlantoaxial rotatory dislocation with odontoid fracture: case report and review. Spine. 2001;26:830–4. Phila Pa 1976. 4. Spoor AB, Diekerhof CH, Bonnet M, Oner FC. Traumatic complex dislocation of the atlantoaxial joint with odontoid and C2 superior articular facet fracture. Spine. 2008;33:E708–11. Phila Pa 1976. 5. Hopf S, Buchalla R, Elhöft H, Rubarth O, Borm W. Atypical dislocated dens fracture type II with rotational atlantoaxial luxation after a riding accident. Unfallchirurg. 2009;112:517–20. 6. Lenehan B, Guerin S, Street J, Poynton A. Lateral C1-C2 dislocation complicating a type II odontoid fracture. J Clin Neurosci. 2010;17: 947–9. 7. Oh JY, Chough CK, Cho CB, Park HK. Traumatic atlantoaxial rotatory fixation with accompanying odontoid and C2 articular facet fracture. J Korean Neurosurg Soc. 2010;48:452–4. 8. Moreau PE, Nguyen V, Atallah A, Kassab G, Thiong’o MW, Laporte C. Traumatic atlantoaxial dislocation with odontoid fracture: a case report. Orthop Traumatol Surg Res. 2012;98:613–7. 9. Anderson LD, D’Alonzo RT. Fractures of the odontoid process of the axis. J Bone Joint Surg Am. 1974;56:1663–74. 10. Fielding JW, Hawkins RJ. Atlantoaxial rotatory fixation (Fixed rotatory subluxation of the atlantoaxial joint). J Bone Joint Surg Am. 1977;59:37–44. 11. Bohlman HH. Acute fractures and dislocations of the cervical spine. An analysis of three hundred hospitalized patients and review of the literature. J Bone Joint Surg Am. 1979;61:1119–42. 12. Carroll EA, Gordon B, Sweeney CA, Joy S, Connolly PJ. Traumatic atlantoaxial distraction injury: a case report. Spine. 2001;26:454–7. Phila Pa 1976. 13. Gleizes V, Jacquot FP, Signoret F, Feron JM. Combined injuries in the upper cervical spine: clinical and epidemiological data over a 14-year period. Eur Spine J. 2000;9:386–92. 14. Silbergeld DL, Laohaprasit V, Grady MS, Anderson PA, Winn HR. Two cases of fatal atlantoaxial distraction injury without fracture or rotation. Surg Neurol. 1991;35:54–6. 15. Myamoto H, Doita M, Nishida K, et al. Traumatic anterior atlantoaxial subluxation occurring in a professional rugby athlete. Case report and review of literature related tot atlantoaxial injuries in sports activities. Spine. 2004;29:E61–4. Phila Pa 1976. 16. Steel HH. Anatomical and mechanical consideration of the atlantoaxial articulation. J Bone Joint Surg Am. 1968;50:1481–2. 17. Ellis GL. Imaging of the atlas (C1) and axis (C2). Emerg Med Clin North Am. 1991;9:719–32. 18. Apfelbaum RI. Anterior screw fixation of odontoid fractures. In: Camins MB, O’Leary PF, editors. Diseases of the cervical spine. Baltimore: Williams and Wilkins; 1992. p. 603–8. 19. Gallie WE. Fractures and dislocations of the cervical spine. Am J Surg. 1939;3:495–9.
Skeletal Radiol 20. Brooks AL, Jenkins EB. Atlanto-axial arthrodesis by the wedge compression method. J Bone Joint Surg Am. 1978;60-A: 279–84. 21. Lapsiwala SB, Anderson PA, Oza A, Resnick DK. Biomechanical comparison of four C1 to C2 rigid fixative technique: anterior
transarticular, posterior transarticular, C1 to C2 pedicle, and C1 to C2 intralaminar screws. Neurosurgery. 2006;58:516–21. 22. Dailey AT, Hart D, Finn MA, Schmidt MH, Apfelbaum RI. Anterior fixation of odentoid fractures in an elderly population. J Neurosurg Spine. 2010;12:1–8.
CASE REPORT
Posterior atlantoaxial dislocation complicating odontoid fracture without neurologic deficit: a case report and review of the literature Hao Meng & Yuan Gao & Mo Li & Zhuojing Luo & Junjie Du
Received: 8 October 2013 / Revised: 15 December 2013 / Accepted: 22 December 2013 # ISS 2014
Abstract Traumatic posterior atlantoaxial dislocation associated with odontoid fracture is extremely rare, with only eight cases reported thus far in the English literature. This report concerns a 47-year-old female who presented with considerable pain and stiffness in the neck without a neurologic deficit after injury due to a fall. Radiographs, computed tomography, and magnetic resonance imaging demonstrated a posterior dislocation of the atlas with respect to the axis with an odontoid fracture. No cord compression or intramedullary cord signal abnormalities were detected at the level of the atlantoaxial dislocation. A pedicle screw fixation/fusion was performed via a posterior approach following successful closed reduction.
Introduction Traumatic posterior atlantoaxial dislocation associated with a fracture of the odontoid process is a rare injury [1]. Only eight isolated cases have been published in the English literature [2–8]. Most of the patients were initially treated with conservative traction, and some of these patients were supplemented with posterior internal fixation. We describe the ninth case of a posterior atlantoaxial dislocation combined with an odontoid fracture without a neurological deficit, caused by a fall. Computed tomography (CT) with reconstruction and magnetic resonance imaging (MRI) each provide optimal visualization for this type of injury discussed in this report. We also discuss the management of this type of injury based our experience and data in the published literature.
Keywords Atlantoaxial dislocation . Odontoid fracture . Neurological deficit . Posterior Case report Hao Meng, Yuan Gao, and Mo Li contributed equally to this work. H. Meng Department of Orthopaedics, Military General Hospital of Beijing PLA, Beijing 100700, China H. Meng Department of Spine Surgery, General Hospital of Air Force, Beijing 100142, China Y. Gao Department of Obstetrics and Gynecology, General Hospital of PLA, Beijing 100853, China Y. Gao Department of Obstetrics and Gynecology, Changhai Hospital, Second Military Medical University, Shanghai 200433, China M. Li : Z. Luo (*) : J. Du (*) Department of Orthopaedics, Xijing Hospital, Fourth Military Medical University, 127 West Changle Road, Xi’an 710032, China e-mail: [email protected] e-mail: [email protected]
History A 47-year-old female patient walked to a local county clinic after the fall injury. According to the medical records of the county clinic, the patient walked approximately 1.2 miles to the clinic and complained of considerable pain and stiffness in the neck after a fall from a height of 5 m. Her vital signs were normal. The neurological examination showed no apparent deficit. There was no evidence of concomitant chest, abdominal or head injury except for lacerations of the cheek. The subsequent lateral radiography demonstrated a posterior dislocation of the atlas with respect to the axis combined with an odontoid process fracture (Fig. 1a). The patient was immobilized in a neck collar immediately and transferred to our hospital for further diagnosis and treatment. Physical examination On examination, the patient was fully conscious and oriented. She reported pain and tenderness in her neck and she was unable to lie down. Motion of flexion,
Skeletal Radiol
Fig. 1 a Lateral radiograph showed odontoid process fracture (arrow a) combined with posterior dislocation of the atlas (arrow b). b Sagittal CT image showed dislocation of the facet joints of C1 and C2 (arrow). c Sagittal MRI showed no cord compression or intramedullary cord signals
abnormality at C1-C2 level. d Axial CT showed posterior dislocation of the atlas associated with odontoid process fracture. e Axial MRI showed an intact transverse ligament at the level of C1-C2 (arrow)
extension and rotation of the neck was severely limited and these examinations were not performed given the diagnoses of atlas dislocation and odontoid process fracture. The vital signs and neurological examination were again normal.
the CT findings, with no imaging evidence of any cord compression or intramedullary cord signal abnormality at the level of the atlantoaxial dislocation (Fig. 1c). Posterior longitudinal ligament was intact, retaining its protective effect. An axial MRI showed an intact transverse ligament at the level of C1C2 (Fig. 1e).
Imaging examination Radiographs of the cervical spine demonstrated the axis was fractured at the base of odontoid process, categorized as a type II fracture based on the Anderson and D’ Alonzo classification [9]. The atlas was displaced posteriorly relative to the axis, which delineates a type IV dislocation based on the Fielding classification [10]. The sagittal and axial cervical spine CT reconstructions revealed a type II fracture of the odontoid and posterior displacement of the odontoid by its width (Fig. 1b, d). MRI of the cervical spine was performed to evaluate the status of the cervical spinal cord and the integrity of the ligaments. MRI confirmed
Initial treatment After the diagnosis was confirmed, skull traction was applied immediately with an initial weight of 3 kg and gradually increased to 6 kg under fluoroscopy. The atlas was positioned over the axis and the reduction was confirmed after 48 h of traction. The patient’s neurologic status was monitored throughout this procedure. She did not exhibit neurological abnormalities and her pain was relieved following traction. Subsequent radiographs demonstrated a successful reduction of the dislocation (Fig. 2). The traction
Skeletal Radiol
Fig. 2 Lateral radiograph made after the closed reduction (arrow: fracture line)
weight was then decreased and maintained to immobilize the neck. Operation However, because of the instability of C1-C2 was highly suspected and an intact transverse cervical ligament would keep the dens in place, C1-C2 fixation was performed using pedicle screws through a posterior approach. The traction bow was removed immediately after the operation. There were no iatrogenic neurological deficits of the spinal cord. A post-operative radiograph showed an anatomical reduction of the C1-C2 complex (Fig. 3). The patient was instructed to wear a Philadelphia collar for 3 months. At the latest followup, lateral radiograph and sagittal CT image showed bony healing of the odontoid fracture 36 months after the operation (Fig. 4).
Discussion In the axial skeleton, dislocation is described according to the displacement of the superior vertebral body. Posterior atlantoaxial dislocation combined with odontoid process fractures is exceedingly rare. The rarity of this dislocation is largely due to the configuration of the odontoid process whereby interlocking of the osseo-ligamentous ring would clearly appear to cause anterior atlantoaxial dislocation [11, 12]. This combination of dislocation and fracture accounts for
Fig. 3 Postoperative lateral radiograph
approximately 0.3 % of all cervical spine injuries and 1.7 % of upper cervical spine injuries [13]. The causes of this injury vary widely, including sports injuries, falls from great heights, and motor vehicle accidents [3]. The mechanism is extension and the dislocation occurs because the ligaments between the dens and the anterior arch of the atlas hold. Anatomically, the odontoid process articulates with the osseo-ligamentous ring formed ventrally by the anterior arch of the atlas and posteriorly by the transverse ligament to provide stability of the C1-C2 complex. Because the dorsal part of the ring is ligament rather than bone and is therefore susceptible to inflammatory conditions that may weaken it and create instability, almost all clinical cases of atlantoaxial dislocation manifest as anterior dislocation of the atlas relative to the axis. Combinations of fractures and dislocations involving the atlas and the axis can disrupt the tectoral membrane, alar and apical ligaments, cruciate ligament, and joint capsules at C1-C2. In posterior dislocation, the atlantoaxial ligaments are ruptured and a fracture of the odontoid is a more frequent occurrence [14]. Isolated posterior cervical translation has been postulated as the probable mechanism of posterior dislocation with odontoid fracture. It appears likely that trauma that is sufficient to produce such a dislocation with fracture of the odontoid would cause damage to the cord and lead to immediate death due to respiratory failure. Therefore, posterior dislocation with fracture of the odontoid may occur more frequently than is reported. In those who survived such injuries, neurological examinations were usually normal or demonstrated only mild neurological deficits. Miyamoto reported
Skeletal Radiol Fig. 4 Postoperative lateral radiograph (a) and sagittal CT image (b) showed healed odontoid fracture and no displacement of the atlas (36 months post-operation)
that only 16 % of upper cervical spine injuries caused neurologic deficits [15]. Until now, only eight cases of traumatic posterior atlantoaxial dislocation combined with odontoid process fracture have been reported in the literature. In these cases, a type IV posterior atlantoaxial dislocation based on the Fielding classification [10] and a type II odontoid fracture base on the Anderson and D’Alonzo classification [9] were always involved. According to the previously reported eight cases, neck pain and restricted neck motion were established by examination in all patients. Three cases had neurological deficits including spastic tetraparesis sphincter dysfunction, hemiparesis and extrapyramidal syndrome [2, 8, 16]. The other five cases had no definitive clinical symptoms or signs of neurological deficit with respect to their C1-C2 dislocations. The surprisingly low rate of spinal cord injury in these latter cases may be
explained by Steel’s rule of thirds [16]: one-third of the neural canal at the atlantoaxial level is occupied by the odontoid process, one-third by the cord, and one-third of the spinal fluid. By this concept, although the injuring force is sufficient to produce a dislocation with fracture of the odontoid process and a reduction in the area of canal, the remaining canal area is sufficient to avoid cord compromise. Typically, cervical spine radiographs including A-P or transoral views of the cervical spine do not show the atlas and axis clearly, either due to overlap of the cranial bones or to limited positioning of the head or neck. Although lateral radiograph can show the atlantoaxial dislocation and odontoid process fracture, the CT scan is the imaging modality of choice for the diagnosis of cervical fractures and dislocations. CT reconstructions can provide optimal visualization for particular injuries. Strict preoperative planning uses CT to assess the bony anatomy of the C1-C2 complex. In this case, sagittal
Table 1 Summary of the previously published eight cases Case no. Author and year
Age, sex Mechanism
1 2
Autricque et al., 1986 45, M Autricque et al., 1986 63, M
15, F
Head injury Motor vehicle accident Head and cervical injury Bicycle accident Motor vehicle accident Riding accident
3
Fuentes et al., 2001
24, M
4 5
Spoor et al., 2008 Lenehan et al., 2010
43, M 63, F
6
Hopf et al., 2009
7 8
Oh et al., 2010 Moreau et al., 2012
37, M 65, M
Cervical trauma Fall accident
Fracture/dislocation type Neurodeficit
Reduction Internal fixation
Type II/type IV Type II/not specified
Spastic tetraparesis Closed No Closed
No Occipito-C3 fusion
Type II/type IV
No
No
Posterior C1-C2 fusion
Type II/not specified Type II/not specified
Closed Closed
Type II/type IV
Hemiparesis Extrapyramidal syndrome No
Type III/not specified Type II/type IV
No No
Closed Closed
No Posterior transarticular fusion Posterior transarticular fusion No Occipito-C2 fusion
Closed
Skeletal Radiol
CT reconstructions demonstrated the odontoid fracture and helped us to evaluate the relationship of the C1-C2 facet joints and lateral masses (Fig. 1b). In contrast, MRI can provide a more sensitive method to detect the degree of soft tissue compression in the cervical spine [17], MRI for our patient showed an intact transverse ligament and no cord compression or intramedullary cord signal abnormality at the C1-C2 level. Therefore, both CT and MRI of the cervical spine are essential in selected patients with head or neck trauma who are suspicious for atlantoaxial dislocation. Traumatic atlantoaxial dislocation can sometimes pose a therapeutic challenge due to the complexity of atlantoaxial misalignment. Our patient had a type IV posterior atlantoaxial dislocation with misalignment of the atlas and axis following a type II fracture of the odontoid process. To date, there are no definitive guidelines for traumatic atlantoaxial dislocation, and therapeutic management is still open to debate. Most studies have favored closed reduction. In the previously reported eight cases (Table 1), closed reduction with traction was successful in three cases. Subsequent external immobilization with a halo-vest was used for 3 to 6 months. In the other five cases, after failed closed reduction, a surgical procedure was performed. In our case, we initially attempted to reduce the dislocation through gradual manual traction. While the dislocation of the atlas and axis in our patient was directly manipulated by closed reduction, this type of fracture has a relatively high rate of nonunion. In addition, because higher complication rates have been associated with use of a halo-vest, especially in older patients, surgery has been performed, either by an anterior or a posterior approach. In our case, the type II fracture of the odontoid process was viewed as less stable, especially in combination with a type IV posterior atlantoaxial dislocation. Although the rotational motion of C1-C2 can be preserved with anterior screw fixation [18], a posterior approach was selected due to the ease of dissection, its familiarity among surgeons, and the stabilization of C1-C2. Since Gallie first described the posterior C1-C2 wiring technique in 1939 [19], a number of other posterior surgical techniques have been detailed. Brooks and Jenkins reported the alternative wiring technique in 1978 [20]. As described by Lapsiwala et al. [21], an alternative method using pedicle screws can increase rotational and lateral bending stiffness compared to the posterior wiring technique and intralaminar screw fixation, yet may also decreased the potential for complications such as postoperative dysphagia due to over retraction in an anterior approach [22]. Most importantly, the fusion achieved by the latter technique precludes without the need for halo-vest immobilization after surgery, and allows for the use of a collar for 8–12 weeks instead. In conclusion, this report describes a posterior atlantoaxial dislocation associated with an odontoid fracture and achievement of a solid fusion by a successful closed reduction and
subsequent pedicle screw fixation/fusion through a posterior approach.
Conflict of interest No funds were received in support of this work. The authors declare that they have no conflict of interest.
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