Os odontoideum

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 11 th 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 1 st 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 l ess 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 1 st 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.