CASE REPORT

Posterior atlantoaxial dislocation without odontoid fracture

Reema Chaudhary & Kshitij Chaudhary &

Umesh Metkar & Ashok Rathod & Abhijit Raut &Darshana Sanghvi

Received: 27 September 2007 /Revised: 1 December 2007 /Accepted: 8 December 2007 / Published online: 8 February 2008# ISS 2007

Abstract We report a case of posterior atlantoaxialdislocation without a fracture of the odontoid in a 35-year-old woman. There have been nine reported cases ofsimilar injury in the English literature. The integrity of thetransverse ligament following posterior atlantoaxial dislo-cations has not been well documented in these reports. Inthe present case, MRI revealed an intact transverseligament, which probably contributed to the stability ofthe C1–C2 complex following closed reduction.

Keywords Atlantoaxial dislocation . Posterior .

Transverse ligament . MRI . CT. Trauma

Introduction

Traumatic posterior atlantoaxial dislocation is a rare injurythat is usually associated with a fracture of the odontoidprocess, rupture of the transverse ligament or a congenitalanomaly [1]. Posterior dislocation without any associatedfracture is exceedingly rare, with only nine cases reportedso far [2–10]. All patients reported in literature sustained

this injury following high velocity trauma, such as a roadtraffic accident. We present a rare instance of posterioratlantoaxial dislocation without odontoid fracture caused bytrivial trauma.

Case report

A 35-year-old woman was admitted to our hospital withsevere neck pain and neurological deficit following a fall inthe bathroom. She claimed that she slipped on the wet floorand fell on her back. Her neck hyperextended following adirect injury to the back of the neck against an elevatedportion of the door frame. She also sustained a contusedlacerated wound over the nape of the neck. In theemergency department she was fully conscious andoriented. She had a respiratory rate of 16 per minute withno signs of distress. Her vital parameters were normal.There were no evident chest, abdominal or head injuries.Neurological examination revealed grade zero power inbilateral elbow extensors with a weak hand grip. The lowerlimbs and the rest of the upper limb power were grade five.Deep tendon reflexes were normal with a positive Babin-ski’s sign. Clinically, the patient did not have any signs ofgeneralized ligamentous laxity.

Radiographs of the cervical spine demonstrated aposterior dislocation of the atlas with respect to the axis(Fig. 1) with no evident fracture. The C7 vertebra was notvisualized due to overlap of the shoulders.

A CT scan revealed the odontoid peg to lie ventral to theanterior arch of the atlas (Fig. 2a). Sagittal reconstructionsdid not show any fractures of the odontoid. However, acoincidental anterolisthesis of C6 over C7 secondary tofacetal subluxation was diagnosed (stage one flexiondistraction injury—Allen’s classification; Fig. 3). Congen-

Skeletal Radiol (2008) 37:361–366DOI 10.1007/s00256-007-0439-7

R. Chaudhary :A. Raut :D. SanghviDepartment of Radiology, King Edward VII Memorial Hospital,Parel, Mumbai, India

K. Chaudhary :U. Metkar :A. RathodDepartment of Orthopaedics,King Edward VII Memorial Hospital,Parel, Mumbai, India

D. Sanghvi (*)c/o Nilendu C. Purandare, DMRD, DNB,Second Floor, Gopal Dham, Ash Lane, Gokhale Road North,Dadar, Mumbai 28, Indiae-mail: darshanasanghvi1@hotmail.com

ital cranio-vertebral anomalies were absent. The bony speckseen in Fig. 2a was most likely an avulsion injury from anattachment of the alar or apical ligament.

Magnetic resonance imaging of the cervical spine wasperformed to evaluate the integrity of the ligaments and thestatus of the cervical spinal cord. MRI showed an intacttransverse ligament (Fig. 2b). There was no cord compres-sion or intramedullary cord signal abnormality at the levelof the atlantoaxial dislocation. A linear fluid collection wasseen tracking along the anterior cervical spine, indicating atear of the anterior ligamentous structures of the C1–C2complex (Fig. 4).

Minimal abnormal intramedullary T2 hyperintense sig-nal was seen in the cervical cord at the level of the C6 andC7 vertebrae (Fig. 4b), representing edema due to cordinjury. Hyperintense signal was seen in the interspinousarea, indicating injury to the interspinous ligament.

The patient was put on skeletal cervical traction with thehelp of Gardner Wells tongs. The initial 2-kg weight wasgradually increased to 7 kg under fluoroscopy. At this stagethe atlas had been positioned over the axis (Fig. 5). Tractionwas gradually lowered keeping the cervical spine in aslightly flexed position. Subsequent radiographs demon-strated a complete reduction of the dislocation. Neurologywas monitored clinically throughout the procedure. She did

not have neurological deterioration and the pain subsideddramatically following reduction.

A post-reduction CT scan and MRI showed an anatom-ical reduction of the C1–C2 complex. The C6–C7 facetalsubluxation had partially reduced with residual anterolis-thesis and posterior element distraction (Figs. 6, 7). Axialimages at the level of C6–C7 and the cranio-vertebraljunction showed no cord compression. The patient wasmaintained in cervical traction to immobilize the neck for 6weeks. She had functional neurological recovery at the endof 6 weeks. The cervical spine was kept immobilized in arigid cervical collar for an additional 3 months. Flexion-extension radiographs did not show instability at the C1–C2complex at the final follow-up after 6 months (Fig. 8). Anopen mouth view with manual cervical traction did notshow any distraction at the C1–C2 joint. However, C6–C7anterolisthesis remained unreduced at 6 months. Patient hada complete neurological recovery with no residual neckpain or radiculopathy.

Discussion

Posterior atlantoaxial dislocation without fracture of theodontoid is a rare injury. It has been proposed by severalauthors [8–11] that trauma sufficient to cause such adislocation would tend to cause severe distraction of thespinal cord and immediate death. A lesion at this level maybe missed on routine post-mortem examination [2, 11].Thus, posterior dislocation without fracture may occurmore frequently in fatal accidents. Older patients withextensive degenerative disease within the cervical spine areprobably far less tolerant of such an injury due to thepresence of osteophytes and other degenerative phenomena.Thus, it is possible that most patients surviving such injurymight be relatively young (Table 1).

Stability of the atlantoaxial complex is provided by theodontoid process interlocking in the osseo-ligamentous ringformed ventrally by the anterior arch of the atlas anddorsally by the transverse ligament. Thus, the ring isweaker dorsally and allows anterior dislocations of the

Fig. 1 Lateral cervical spineradiograph following injuryshows posterior atlantoaxial dis-location without fracture of theodontoid process

Fig. 2 a Axial CT at the levelof the C1–C2 dislocation. Thebony speck seen posterior to theanterior arch of the atlas isprobably a ligament avulsioninjury. b Axial MRI at the samelevel shows that the transverseligament is intact (arrow) andthat there is no cordcompression

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atlas more frequently than posterior dislocations. Forposterior dislocation to occur, either the odontoid processmust fracture (which is a more frequent occurrence [12]) orall the atlantoaxial ligaments must rupture to allow theanterior arch of the atlas to slip over the tip of the odontoid.Hyperextension with variable amounts of distraction hasbeen proposed as the probable mechanism of posteriordislocation without a fracture of the odontoid [2]. This issupported by the fact that most of the reported cases haveassociated facial injuries following road accidents (Table 1).

In our patient, the severity of trauma was relatively trivial.Moreover, an associated flexion injury to the sub-axialcervical spine (C6–C7) suggested that the patient probablyhad components of hyper-extension as well as hyper-flexion injury.

All previously reported cases had either mild or noneurological deficit (Table 1). In our case the neurologicaldeficit corresponded to the C6–C7 facetal subluxationrather than the C1–C2 dislocation. If the initial distractionof the C1–C2 complex does not cause a neurologicaldeficit, then a significant amount of displacement can betolerated in this region owing to the large size of the spinalcanal [2]. A skeletal study has demonstrated that posteriordislocation without fracture of the odontoid reduced thecanal area to 36%, which is sufficient to avoid cordcompromise [13]. Thus, patients actually seen in clinicalpractice are probably those who have escaped a severedistraction injury to the spinal cord. Therefore, a high indexof suspicion is required, especially in patients who haveconcomitant head injuries and altered mental state.

The integrity of the transverse ligament followingposterior atlantoaxial dislocations has not been welldocumented in published reports. Patients who weremanaged with closed reduction achieved stability withoutinternal fixation, except for one case [7]. This has promptedauthors to speculate that the transverse ligament is usuallyspared in these types of injuries [2, 10]. An intact transverseligament probably provides the atlantoaxial complex withsufficient stability following reduction of the odontoid peginto the osseo-ligamentous ring.

Magnetic resonance imaging provides a sensitive methodof detecting the integrity of the transverse ligament, whichmay have a bearing in future treatment of such injury. If the

Fig. 3 a Sagittal cervical spine CT reconstruction shows a C6–C7 anterolisthesis in addition to a posterior atlantoaxial dislocation. b Right and cleft parasagittal CT reconstructions show facetal subluxations (arrow) at C6–C7, representing an Allen stage one flexion distraction injury

Fig. 4 a Sagittal T2-weighted image shows the tortuous course takenby the cord at the level of the posterior atlantoaxial dislocation. bSagittal T2-weighted image shows focal cord edema at the level of theC6–C7 vertebrae (black arrow). A linear fluid collection (whitearrows) is seen anterior to the cervical spine

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transverse ligament is found to be compromised on MRI,internal fixation should strongly be considered. MRI can alsodetermine the degree of cord compression, hemorrhage, cordcontusions, and associated disc herniation. An MR angio-gram of the vertebral arteries may be helpful in cases inwhich vertebro-basilar insufficiency is suspected [9].

Various stages of flexion distraction injury to thesubaxial cervical spine are described by Allen and Ferguson(cited in [14]). Stage one injury includes failure of theposterior ligamentous complex, as demonstrated by facetsubluxation in flexion, with abnormal divergence of the

spinous process. Stages two and three are unilateral andbilateral facet dislocations respectively. Stage four, which isthe most severe form of injury, is a complete spondylop-tosis of the cervical vertebra. Our patient had a stage oneflexion distraction injury with bilateral subluxations of thefacet joints. In such purely ligamentous injuries, healing isunlikely with external immobilization, and chronic painmay be a frequent occurrence [14]. However, this patientwas asymptomatic at the final follow-up and thereforefurther treatment was deferred.

In conclusion, posterior atlantoaxial dislocation withoutodontoid fracture usually presents without a significantneurological deficit. Closed reduction under fluoroscopicguidance is usually successful. As the transverse ligament is

Fig. 7 a Sagittal, b axial, and c coronal CT scan images confirminganatomical reduction of the C1–C2 complex

Fig. 5 Serial lateral cervicalspine radiographs showingvarious stages of reduction

Fig. 6 a Sagittal and b axial MRI shows reduction of the C1–C2complex. There is no cord compression at the C1–C2 and C6–C7vertebral levels

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frequently spared; late instability is a rare occurrence.Surgical fusion may be necessary in cases with documentedtransverse ligament ruptures or in those with demonstrableinstability on flexion extension radiographs.

References

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2. Haralson RH III, Boyd HB. Posterior dislocation of the atlas onthe axis without fracture. Report of a case. J Bone Joint Surg Am1969; 51: 561–566.

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Table 1 Summary of previously published case reports

Reference Age, sex Mode ofinjury

Faciallacerations

Neurodeficit Reduction Internal fixation Lateinstability

Follow-up

[2] 30, male PolytraumaRTA

+ No Closedreduction

Posterior wiring at 6 weeks – 1 year

[3] 20, female PolytraumaRTA

+ Mild Closedreduction

No No 10 years

[4] 37, male PolytraumaRTA

+ No Closedreduction

No No 3 years

[5] 65, male RTA NA Transient quadriplegia Open reductionb Transoral odontoidectomyand posterior fixation

– NA

[6] 22, male RTA + No Closedreduction

Posterior cervical wiring – NA

[7] 23, male RTA NA No Closedreduction

Posterior cervical wiringd – 7 years

[8] 38, male PolytraumaRTA

NA Upper limb weaknessa Open reductionc Partial odontoidectomy andposterior fixation

– 3 months

[10] 22, male PolytraumaRTA

+ No Closedreduction

No No 2 years

[9] 64, male PolytraumaRTA

+ Mild Open reductionb Transarticular screwfixation

– 6 months

Polytrauma indicates patients with associated appendicular skeleton injuriesRTA: road traffic accident; NA: data not availablea Secondary to brachial plexus injurybWithout trial of closed reductionc Closed reduction unsuccessfuld Non-anatomical reduction and residual instability following closed reduction

Fig. 8 a Lateral cervical spine flexion and b extension radiographsshowing no instability at the C1–C2 complex. C6–C7 anterolisthesisremains unreduced

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11. Carroll EA, Gordon B, Sweeney CA, Joy S, Connolly PJ.Traumatic atlantoaxial distraction injury: a case report. Spine2001; 26: 454–457.

12. Daffner RH, Brown RR, Goldberg AL. A new classification forcervical vertebral injuries: influence of CT. Skeletal Radiol 2000;29: 125–132.

13. Tucker SK, Taylor BA. Spinal canal capacity in simulateddisplacements of the atlantoaxial segment: a skeletal study. JBone Joint Surg Br 1998; 80: 1073–1078.

14. Leventhal M. Dislocations and fracture—dislocations of spine. In:Campbell’s operative orthopaedics. 10th ed. Philadelphia: Mosby;2003.

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