Review with management

1. Os Odontoideum-A review
Dr.M.Ashok kumar M.S.(Ortho),FSS (CMC-Vellore)
Consultant Spine Surgeon,
SNHRC, Vellore.

2. Synopsis
• Introduction
• Embryology
• Etiology
• Classification
• Clinical features
• Imaging
• Management

3. Introduction
• An ossicle with smooth circumferential margins and NO osseous
continuity with body of axis.
• Latin- Os- Bone, Odontoideum– Tooth like.
• First described in 1886, by Giacomini.

4. Embrology
• Craniovertebral junction has 2 components
• Central pivot- Dens, C2 body
• 2 ringed structures- foramen magnum & Atlas ring.

5. Formation of Craniovertebral Junction
*Ad- Dense zone
*Ld-Loose zone
*HBp- Hypochondral bow
Al- Loose zone of Axial
sclerotome
IBZ- Intervertebral Boundary
Zone
Scl-A- Sclerotome Axial
Scl-L- Sclerotome Lateral
*PA- Pro Atlas
*CT- Clival Tubercle
*B- Basion
*AD- Apical Dens
*CL- Clivus
*C1A-Anterior Atlas arch
*US- Upper dental
Synchondrosis
*BD- Base of Dens
*LS- Lower dental Synchondrosis
*AB- Axis Body
*OT- Opisthion
*OC- Occipital Condyle
*C1P- Posterior Arch of Atlas
Dominic et al Embryology & bony malformations of CVJ, Childs Nerv Syst2011 27
523-564

6. Embryology
S.No. Somite Final structure
1 Caudal ProAtlas Apical Dens
2 C 1 Basal portion of Dens
3 C 2 Body of Dens
Disturbances of intervertebral boundary Zone of ProAtlas and first
two Sclerotomes reults in 1. Os Odontoideum
2. Ossiculum Terminale persisistens.

7. Formation of Cranio Vertebral Junction
Dominic et al Embryology & bony malformations of CVJ, Childs Nerv Syst2011 27 523-564

8. Developmental Phases of C2
Dominic et al Embryology & bony malformations of CVJ, Childs Nerv Syst2011 27 523-564

9. Etiology - Congenital
• Failure of fusion between dens & body of axis.
• Incompletes ossification of intervertebral body disc.
• Familial cases with AD inheritance.
• Lack of gene activities BMP_4,2, PTX-1.

10. Etiology -Traumatic
• Unrecognized odontoid type II fractures, AVN, remodeling.
Early childhood
Bony/lig injury to C2- Dens
Slight separation of fracture fragments
Contracture of alar ligaments
Odontoid pulled away from axis body
Preserved blood supply from proximal
arcade
Fielding JW, OsOdontoideum: an acquired lesion: JBJS,Am: 1974: 56(1):187-190

11. Blood Supply
David C.M, Schiff- The Arterial Supply of the Odontoid Process JBJs,Am, 1973:55(7):1450-1456.

12. Connective tissue disorders
• Down syndrome
• Klippel-Feil syndrome
• Morquio’s disease
• MED
• Pseudoachondroplasia
• Achondroplasia
• Larson Syndrome
• Chondrodystrophica calcificans
congenital
• Ligament hyperlaxity
• Incomplete ossification-
traumatic os odontoideum

13. Current Hypothesis
• Trauma more favoured.
• Gap between Os Odontoideum and remnant Dens is above level of
superior facets.
• By congenital theory gap should be below superior axis facets.
Babak Arvin, M.G.Fehlings, Os Odontoideum: Etiology
and surgical management, Neurosurgery 66, 3,Mar 2010
supplement A22-31.

14. Classification
• Fielding’s Anatomic classification
S.No Orthotopic Dystopic
1 Ossicle in normal position Nearby Clivus/fused to
basion
2 Moves with anterior arch of
C1
Fused
3 Mostly reducible Irreducible
Fielding JW, Hensinger RN. Os Odontoideum. JBJS Am, 1980;62(3): 376-383.

15. Classification
• Orthotopic • Dystopic
Fielding JW, Hensinger RN. Os Odontoideum. JBJS Am, 1980;62(3): 376-383

16. Classification
• Matsui e al –AP open mouth
Xrays.
• Round
• Open
• Blunt tooth
Matsui H, Imada. K , Radiographic classifiaction of Os Odontoideum and its clinical
significance, Spine- 1997(15);1706-1709.

17. Pathogenesis

18. Clinical features
• Asymptomatic
• Symptomatic
S.No. Symptoms
1 Occipitocervical pain
2 Myelopathic features
3 Quadriparesis
4 Intracranial manifestations- vertebrobasilar ischemia,
cerebellar infarction, brainstem damage

19. Imaging- Xrays
• AP, Lateral, Open mouth views
• Dynamic Xrays
• Severity of Myelopathy doesn’t correlates with C1-2 instability.
• It was the smallest diameter of spinal canal at C1-2, closely
correlated with permanent cord injury and not degree of instability’
• SAC <13mm, more chances of myelopathy.
• ’Round’ type
-Spierings et al- The management of Os Odontoideum analysis of 37 cases. JBJS Br.1982:64(4): 422-28
- Matsui H, Imada. K , Radiographic classifiaction of Os Odontoideum and its clinical significance, Spine-
1997(15);1706-1709

20. Imaging - Xrays
• Wattanabe saggital plane
rotation angle.
• Instability index(II) = Max dist-Min.dist.*100%
• Max distance
• Sagittal plane angle(SPA) = 13-15 deg.
• II >40%
• SPA >20%, increased myelopathy onset.
-Wantanabe et al- Atalantoaxial instability in Os Odontoideum with myelopathy Spine 21,12,1990 1435-1439.
-Abe H et al- Atlantoaxial instability index, indications for surgery. Neurological surgery (Tokyo), 1976;4;57-72.

21. Imaging
S.No. Os Odontoideum Acute Dens #
1 Smooth well corticated Non corticated
2 Round/oval shape with regular margins Irregular margins
CT scan- to R/O osseous anomalies
CT angiography- To R/o Vertebral artery anomalies

22. Imaging- MRI
• IOC for assessing spinal cord compression.
• Intramedullary Hyperintensity signal in T2W sequences, hypointensity
signal in T1w.
• Contrast enhancement.
• Pannus, retro odontoid synovial cyst.

23. Treatment - conservative
• Clinically – no motor/sensory deficits.
• Imaging- no obvious compression.
• Spierring et al– 20/37- conservatively managed, 15 had no
neurological deficits.
• Fielding -37cases, treated conservatively.
Spierring & Braakman et al- The management of Os Odontoideum, analysis of 37cases, JBJS Br, 1982: 64(4):
422-428.
Fielding JW, Os odontoideum, JBJS, Am:1980:62(3), :376-383.

24. Treatment – conservative
• Yearly Flexion- extension plain Xrays & MRI of CVJ.
• Pts should be counselled.
• No participation in contact sports.

25. Surgical management -AAI
• Greenberg et al divided AAI into
• RAAD – Reducible Atlanto Axial Dislocation
• IAAD - Irreducible Atlanto Axial Dislocation
• Instability of AAI biomechanically identical to T II odontoid fracture.
Paul Klimo et al JNS Spine—9:332-342:2008.

26. Atlantoaxial instability- Fielding classification
Campbell s text book Of Orthopaedics 11th edition.

27. Atlantoaxial instability- Wang classification

28. Wang classification

29. RAAD Types I, II
S.no. Method Limitation
1 Transarticular C1-2 fixation(Mod. Magrel) -No C1 occipitalisation
-No Swan Neck deformity of neck
2 C1 lateral mass & C2 pedicle screw fixation(Goel& Harms) -No C1 occipitalisation
-Can be done in swan neck deformity of
neck
3 Occiput to C2 fusion(Abumi Technique) -Occipitalisation of C1
-Dysplasia of C1 posterior arch
4 C1-C2/C0-C2 using C2 laminar wires, C2 translaminar
screws(Wrigt technique)
-high riding VA
- C2 pedicle anatomy abnormalities
Wang et al Novel surgical classification & treatment strategy for AAD,Spine Vol.38, No.21, PPE-1348-1356

30. IAAD
• Deformity neither corrected in dynamic Xrays nor with clinical
traction.
Repititive flexion movements of head- forward displacement of C1 on C2 facet joints
Slippage of C1, it gradually losses support of PLC
Synovial enfolding, scar tissues, contracture of C1-2 facet capsule
IAAD

31. ROLE OF TRACTION
• Reducing a deformity by traction confirms that instability is not really
irreducible.
• Adults- traction in a conscious patient- 2kgs to 20kgs.
• Children(till 18 yrs)- 7% of body weight.
• Neural impairment if occurs, release weights immediately.
• Closed reduction under GA.

32. Surgery in IAAD
• Samuel Mixter et. al performed first for an irreducible variant.
• Remove all the compromising tissues at the cervicomedullary jn. and
enlarge foramen magnum- failure with catastrophic consequences.
• 1968- Greenberg et al 1st described transoral odontoidectomy.
• 1980- Menzes et. al popularized the approach.
• Currently- Resection & Release strategies.
-Greenberg et.al, Transoral decompression of Atlanto Axial dislocation due to Odontoid
hypoplasia,Jneurosurgery, 1968:28(3):266-269.
-Menzes et al Craniocervical abnormalities: A comprehensive surgical approach , J
Neurosurgery,1980:53(4):444-455.

33. Releasing Strategy- Anterior releasing -Type 3
• Opening up of C1-2 facet Joint, wide removal of articular cartlilage,
manipulation of facets.
• Anterior release of C1-2 facet joints under skull traction by
transoral/retropharyngeal/endoscopic/endonasal/transcervical
corridors.
• 1995- Subin et. al 1st performed C1-2 facet release trans orally.
Postop Minerva Casting.
• 2006- Wang et al transoral C1-C2 facet release and reduction by
traction, posterior C1-2 screw fixation.
-Subin B et al. Transoral anterior decompression and fusion of chronic irreducible atlantoaxial dislocation with spinal cord
compression, Spine 1995;20(11):1233-1240.
-Wang C et al, Open Reduction of Irreducible AAD by Transoral anterior Atlanto Axial Release & Posterior internal Fixation,
Spine 2006;31(11): E306-313.

34. Releasing strategy
Advantages in anterior release
• less invasive, no Odontoid
resection.
• Realignment of AA jt. Reduces
degenerative changes in subaxial
spine.
• Reduction of C1 posterior arch
closer to C2allows simple
posterior fusion.
Disadvantages of Transoral RESECTION
• Increased operative
time/complexity
• High chances of dural and cord
injury
• Removal of clivus and lower C2
body worsens AAI.

35. Releasing Strategy Anterior releasing methods
• Retropharyngeal approach with posterior internal fixation is
preffered.
• MIS- Endoscopic assisted anterior release and reduction by
retropharngeal approach- novel method.
Lu et al- endoscopically assisted anterior release and reduction through anterolateral retropharyngeal approach for
fixed atalantoaxial dislocation. Spine 2010; 35(5): 544-551.
S.No. Advantages
1 Better illumination and visualisation
2 Hard palate/soft palate resection not required.
3 Preservation of velopharyngeal function

36. Releasing methods- Posterior releasing methods
• Goel et al- sectioning C2 ganglion, atalantoaxial joints widely exposed,
reduction by plates and screws. C2 screw 1st tighented followed by C1
screw.
• 2001- Harms et al, modified into C1 lateral mass & C2 Pedicle
polyaxial screws.
• 2010- Chang et al, rotating rod reduction strategy.
-Goel A, Laheri.V, Plate and screw fixation for atalantoaxial subluxation. Acta Neurochir, 1994 129(1-2):47-53.
-Harms J. C1-2 fusion with polyaxial screw and rod fixation. Spine 2001: 26(22):2467-2471.
Chang-Wei et al, Posterior rotating rod reduction strategy for irreducible atalantoaxial subluxation with congenital odontoid
aplasia, Spine 2010: 35(23):20164-2070.

37. Resection strategy Type 4 AAD
• Remove the Os Odontoideum to remove persistent compressive
effect on Cervicomedullary region, then Occipitocervical fusion.
• Transoral approach preferred initially now Retropharyngeal route.
• Anterior bony mass, redundant ligaments, granulation tissue,
hrpertrophic scar removed.
• Drawbacks
S.No. complications
1 Local infection
2 Retropharyngeal abscess
3 Velopalatine incompetence
4 Persistent hoarseness
5 Persistent CSF fistulas

38. IAAD- Type 4

39. Babak, M G. Fehlings et al, Os Odontoideum: Etiology and surgical mamnagement, Neurosurgery Vol-
66.No-3, Mar2010Sa22-31

40. Case-1

41. Case-1

42. Case-1

43. Case 2

44. Case-2

45. Case-2

46. References
• Fielding JW, Hensinger RN. Os Odontoideum. JBJS Am, 1980;62(3): 376-383
• Matsui H, Imada. K , Radiographic classifiaction of Os Odontoideum and its clinical significance,
Spine- 1997(15);1706-1709
• Subin et al. Transoral anterior decompression and fusion of chronic irreducible atlantoaxial
dislocation with spinal cord compression, Spine 1995;20(11):1233-1240.
• -Wang C et al, Open Reduction of Irreducible AAD by Transoral anterior Atlanto Axial Release &
Posterior internal Fixation, Spine 2006;31(11): E306-313.
• M G. Fehlings et al, Os Odontoideum: Etiology and surgical mamnagement, Neurosurgery Vol-
66.No-3, Mar2010Sa22-31
• Lu et al- endoscopically assisted anterior release and reduction through anterolateral
retropharyngeal approach for fixed atalantoaxial dislocation. Spine 2010; 35(5): 544-551.
• Goel. A, Laheri V Plate and screw fixation for atalantoaxial subluxation. Acta Neurochir, 1994
129(1-2):47-53.
• -Harms J. C1-2 fusion with polyaxial screw and rod fixation. Spine 2001: 26(22):2467-2471.
• Chang-Wei et al, Posterior rotating rod reduction strategy for irreducible atalantoaxial subluxation
with congenital odontoid aplasia, Spine 2010: 35(23):20164-2070

47. References
• Single stage anterior release & posterior instrumented fusion for irreducible Atlantoaxial
dislocation with basilar invagination- Sudhir kumar et al. The SpineJournal16, 2016, 1-9.
• Chao Wang ,Reduction of irreducible Atlantoaxial dislocation by Transoral anterior atlantoaxial
release and posterior internal fixation, Spine- Vol.31, 11, PP E306-E313.
• Os odontoideum:presentation, diagnosis, treatment in a series of 78 pts. Paul Klimo et al- J
Neurosrg Spine 9:332-342, 2008.
• Menzes et al, craniocervical abnormalities: A comprehensive surgical approach J Neurosurgery,
1980;53(4): 444-455.
• Harms J, C1-2 fusion with polyaxial screw& rod fixation. Spine 2001:26(22); 2467-2471.
• Fieldings et al. Atlantoaxial rotatory fixation, JBJS Am, 1977;59(1):37-44.
• Wang et al Novel surgical classification & treatment strategy for AAD,Spine Vol.38, No.21, PPE-
1348-1356
• Wantanabe

48. References
• Wantanabe et al- Atalantoaxial instability in Os Odontoideum with myelopathy Spine 21,12,1990
1435-1439.
• -Abe H et al- Atlantoaxial instability index, indications for surgery. Neurological surgery (Tokyo),
1976;4;57-72.
• Dominic et al Embryology & bony malformations of CVJ, Childs Nerv Syst2011 27 523-564.