ATLANTO AXIAL DISLOCATION

1. Atlantoaxial Dislocation
Evaluation and Surgical
Management
Moderator – Dr Arunkumar Sekar
Assistant Prof, Dept of Neurosurgery, AIIMS BBSR
Presenter – Dr Avinash Lakha
Senior Resident, Dept of Neurosurgery, AIIMS BBSR

2. • CVJ consists of occiput, atlas, and axis
• Majority of the spine’s rotation, flexion, and extension occur
between the occiput, the atlas, and axis. There are 6 degrees
of freedom of movements at these joints:
• (1) angular motion (flexion and extension)
• (2) rotation (right and left)
• (3) linear motion and translation (anterior and posterior, right
and left).
ANATOMY AND BIOMECHANICS

3. Ligaments – Posterior View
The most critical
ligaments to evaluate
for stability in the CVJ
are the transverse
ligament of the
cruciform complex, the
alar ligaments, and the
tectorial membrane

4. • The transverse ligament
contributes substantially to the
stability of the CVJ, preventing
the dens from folding into the
midbrain during flexion
• The primary function of the alar
ligaments is to restrict rotation
of the cranium.
• The alar ligaments are critical to
maintaining stability at the CVJ
• It helps in restricting flexion,
restricting extension,
protecting the dura from the
dens

5. • The C-1 nerve exits superior to the
atlas, by route of a groove in the
posterior ring formed by the elevation
of the superior articular surface
• The C-1 nerve exits superior to the
atlas, by route of a groove in the
posterior ring formed by the elevation
of the superior articular surface.
• The vertebral artery shares this
groove, the roof of which is formed by
the posterior occipitoatlantal ligament
• Blood supply to CVJ from vertebral
artery

6. The Occipitoatlantal Segment (Oc–C1)
• The occipital condyles articulate with
the atlas, and circumscribe the
anterior half of the foramen
magnum.
• The atlas receives the lateral-turned
occipital condyles into
superomedially facing concave
articular surfaces, permitting flexion
and extension of the cranium.

7. The Atlantoaxial Segment (C1–2)
• The atlas also communicates inferiorly with
the axis by flat, wide articular facets.
• The odontoid process and horizontal facets
permit rotation of the skull, the
predominate motion of the C1–2 vertebral
junction.
• The transverse ligament of the atlas
constrains the dens within 3 mm of the
anterior ring of the atlas by bounding the
dens posteriorly

8. Vertebral artery course

9. AAD etiology
Atlantoaxial dislocation can be broadly categorized into –
• Traumatic
• Congenital - Down syndrome, Skeletal dysplasias, Goldenhar syndrome,
Mucopolysaccharidosis type IV (Morquio syndrome)
• Inflammatory - Chronic rheumatoid arthritis patients, particularly adults
• Mixed

10. Symptoms
• Neck pain, neck movement restriction(50%),
• Weakness and/or numbness (70%),
• Pyramidal signs(90%).
• Sphincter disturbances, lower cranial nerve dysfunc- tion, and
respiratory distress.
• Myelopathy, respiratory failure, vertebral artery dissection, neurologic
compromise.
• Quadriplegia or death if left untreated.

11. Classification
• Atlantoaxial dislocation was initially classified by Greenberg into two
subcategories—reducible and irreducible

12. Types of AAD:
• (1) Anteroposterior dislocation (mobile and hyper-mobile)
• (2) Rotatory dislocation
• (3) Central dislocation
• (4) Mixed dislocation (any two or three of the above)

13. 1) Anteroposterior dislocation
• Mobile dislocation is in one plane and
one direction. This is due to laxity of
the transverse ligament.
• When there is os odontoideum, C2
body dislocates in both directions in
the sagittal plane

14. 2) Rotatory dislocation
• This type of dislocation is usually in one plane (axial) and in one
direction only i.e. to the right or to the left.
• This is due to incompetence of the alar ligament. It usually occurs in
children and is visible as the classical Cocked Robin position of the
head.

15. 3)Central Dislocation
• The opposing facetal surfaces
of the normal C1-C2 joints are
horizontal and parallel in the
sagittal plane
• However, if these are
oriented obliquely in the
sagittal plane then the C2
body has a tendency to slip
upwards due to the weight of
the patient’s head during
flexion movements
4) Mixed

17. White and Panjabi classification

18. INVESTIGATIONS
1)XRays
• Antero-posteriorview
• Lateral view
• Open mouth view for dens
Dynamic X-Rays
(neutral,flexion,extention)
2)CT Scan and3D recon
3) MRIconventional anddynamic
4) CT Angiography

19. CRANIOMETRY:
• Craniometry of the CVJ uses a seriesof lines, planes & angles
to define the normal anatomic relationships of theCVJ.
• Thesemeasurements can be taken on plain Xrays, 3D CT or on
MRI.
• No single measurement ishelpful.
• Disadvantage --anatomic structuresand planes vary within a
normal range.

22. Anterior Atlanto-Dental
Interval(AADI)
AAS is + when >3mm in adults & >5mm in children
Measured from posteroinferior margin of ant arch of C1
to the ant surface of odontoid

23. Posterior Atlanto-Dental
Interval (PADI):
Distance b/w posterior
surface of odontoid &
anterior margin of postring
of C1
Considered bettermethod
as it directly measures the
spinal canal
Normal :17-29 mm at C1
PADI <14mm :predictscord
compression

27. McGregor’s line (basal line)
Line drawn from posterior tip of
Hard palate to lowest part of
Occiput

28. FISHGOLD’SDIGASTRICLINE
• Connects the digastric grooves ( fossae
for digastric muscles on undersurface of
skull just medial to mastoid process)
• Line is normally 10mm above the
atlanto-occipital junction.
• Upper limit of dens.
• Central axis of dens should
perpendicular to this line.
• Corresponds to McRae’s line on lateral
view
• If not suggest unilateral condylar
hypoplasia.

29. FISHGOLD’S BIMASTOIDLINE
• Line connecting tip of mastoid process.
• At level of atlanto-occipital junction
• Odontoid process should be less than 10 mm above
this line

30. TREATMENT –
The aims of the surgical treatment of AAD are: -
(1) All dislocations should be reduced
(2) If the AAD cannot be reduced by the closed method (traction), then
the open method (i.e. by opening the joints) should be used for
reducing the AAD
(3) If the dislocation is irreducible by the above means then sufficient
decompression of underlying neural structures should be done.
In all cases, after achieving the above aims, arthrodesis has to be done
for achieving permanent bone fusion to prevent movement between
C1 and C2

31. Non operative management
• Cervical halter traction in the supine position and active range-of-
motion exercises for 24 to 48 hours first, followed by ambulatory
orthotic immobilization with active range of motion exercises until
free motion returns.
• Children presenting acutely with evidence of transverse ligament
disruption, diagnosed within 3 weeks, can be treated nonoperatively
in the absence of neurologic injury.
• Nonoperative treatment in symptomatic adults is generally not
advised in the absence of surgical contraindications.

32. Attempt at Conversion of Irreducible to Reducible
Atlantoaxial Dislocation via Traction
• The first step in correcting atlantoaxial dislocation is attempt- ing
reduction of the dislocation

33. • Traction weight should start at 7 to 8% of body weight and gradually
increase to a maximum of 7 kg, and reduction should be monitored
by sequential lateral radiographs.
• The entire reduction procedure with curarization takes 10 minutes.
• If the reduction procedure is successful, defined by achieving an ADI
measuring less than 3 mm in adults and 5 mm in children, the
operation may proceed with a posterior fusion to stabilize the
reduced reducible atlantoaxial dislocation

34. Treatment algorithm

35. Gallies Fusion -
• Gallie first described posterior C1-C2
sublaminar wire fixation in 1939 with the use
of steel wire.
• Single autograft harvested form the iliac crest is
notched inferiorly and placed over the C2
spinous process and leaned against the posterior
arch of C1.
• The graft is held in place by a sublaminar wire
that passes beneath the arch of C1 and then C2.
• Passage of the sublaminar wire under the lamina
of C2 is avoided in order to decrease the risk of
neural or dural injury.
• The Gallie fusion offers good stability in flexion
and extension. But offers poor stabilization and
rotational maneuvers
Posterior approaches - Midline Methods of Fixation

36. Sonntag’s Modification of Gallie Fusion.
• A single bicortical bone graft is fit into
the interlaminar space between the
atlas and the axis and notched to
accommodate the spinous processes of
the axis.
• Two strands of #24 wire are passed
around the posterior arch of the atlas,
over the bone graft, and around the
notched spinous process of the axis.

37. Brooks-JenkinsFusion
Doubled 20-gauge wires are
passed under the laminae of
the atlas and axis bilaterally.
Two posterolateral
autologous iliac crest bone
grafts are beveled to fit both
interlaminar spaces and held
in place by the overlying wire

38. Interlaminar Clamp Technique (Halifax technique)
• A double hook and screw
construct stabilizes the
laminae of C1 and C2
bilaterally and secures bilateral
interlaminar bone grafts
• Biomechanical experiments
have shown it providing
excellent anteroposterior
stability. However, the
rotational movement has been
less successful

39. Occipitocervical Fixation
• The use of occipital screws requires careful assessment of the thickness of
the occipital bone and the location of the dural venous sinuses
• crews up to 8 mm long can be inserted in the region of the superior nuchal
line up to 2 cm laterally from the center of the external occipital
protuberance, 1 cm from the midline at a level 1 cm inferior to the external
occipital protuberance, and 0.5 cm from the midline at a level 2 cm below
the external occipital protuberance.
• The cervical end of the implant is fixed to one or more of the cervical
vertebrae, more frequently to the posterior elements of the axi
• occipitocervical fixation can be an alternative form of fixation in case of
technical difficulties.

40. Posterior approaches –
Lateral mass fixation procedures include
• Magerl’s C1-C2 transarticular technique
• Goel and Laheri’s C1 lateral mass
• C2 pedicle–pars mono–polyaxial screw and plate–rod fixation(Harms
Technique)
• C2 Translaminar Screws with C1 lateral mass

41. Goel and Laheri’s C1 lateral mass Technique
• Advantage - anatomic alignment of the C1-C2
complex is not necessary prior to
instrumentation.
• Can be utilized in cases where there is an
aberrant vertebral artery.
• The plates act as tension-band, providing stability
in flexion/extension, hence a midline procedure is
not necessary.
• Large venous plexuses in the lateral gutter need
to be handled appropriately.

42. Technique
• The neck is kept neutral and the head is
placed in the military tuck position
• The C2-C3 facet joints are exposed and the
dorsal arch of C1 is exposed laterally
exposing the vertebral artery in the
vertebral groove on the superior aspect of
the C1 arch
• The lateral mass of C1 inferior to the C1
arch is exposed
• The medial aspect of the transverse
foramen at C1 and C2 can also be identified
and serve as a lateral limit for screw
placement
• The entry point for the C1 lateral mass
screw is identified at the centre of the C1
lateral mass

43. • Another entry is at the junction
of midpoint of C1 lateral mass
and the inferior aspect of the
C1 arch
• Vertebral artery often runs in a
sulcus on the superolateral
aspect of the C1 arch and care
should be taken to avoid drilling
in this area

44. • screw is placed into the atlas,
directed at an angle of
approximately 15 degrees medial
to the sagittal plane and 15
degrees superior to the axial
plane.
• The preferred site of screw
insertion is at the center of the
posterior surface of the lateral
mass, 1 to 2 mm above the
articular surface.

45. • A C2 pars screw is placed in a trajectory
similar to that of a C1-C2 transarticular
screw except that it is much shorter. The
entry point for the C2 pars screws 3 mm
rostral and 3mm lateral to the inferior
medial aspect of the inferior articular
surface of C2. The screw follows a steep
trajectory paralleling the C2 pars (Often 40
degrees or more)
• The screws are passed with 10 degrees of
medial angulation.
• The screws used are 2.9 to 3.4 mm in
diameter in adult patients and 2.7 to 3 mm
in diameter in pediatric patients
• Screw length is typically 16 mm, which
often stops short of the transverse foramen

46. Pars vs Pedicle screw

47. • The entry point for a C2 pedicle screw is in
the pars of C2, lateral to the superior margin
of the C2 lamina.
• This point is usually 2 mm superior and 2
mm medial to the entry point for the C2 pars
screw
• The screw is placed with 15-25 degrees of
medial angulation.
• The thick medial wall of the C2 pedicle will
help redirect the screw if necessary and
prevent medial wall break out and entry into
the spinal canal.
• The trajectory of the C2 pedicle screw is 20
degrees up angle and 15-25 degrees medial
from the entry point.

48. C2 pedicle–pars mono–polyaxial screw and plate–
rod fixation(Harms Technique)
The dorsal root ganglion of C2 is retracted in a caudal di- rection to expose the entry point for the C1
screw.
middle of the junction of the C1 posterior arch and the midpoint of the posterior inferior part of the C1 lateral
mass
A number 4 Penfield is used to delineate the medial border of the C2 pars interarticularis, and the entry point
for place- ment of a C2 pedicle screw is marked with a high-speed burr

49. After screw placement in C1 and C2, a reduction ma-
neuver can be carried out, either by repositioning of the
patient’s head or by direct manipulation of C1 and C2,
using the instrumentation as the reduction device. The
reduction maneuver is monitored under fluoroscopy and
then stabilized by attachment of a small rod to the screws

50. Mageral’s C1 C2 Transarticular Technique
• Advantage - complete obliteration of
rotational motion of the atlantoaxial joint.
• Disadvantage- steep learning curve and the
potential for serious complications including
errant screw placement leading to spinal
cord injury, hypoglossal nerve injury, or
vertebral artery laceration
• One very important consideration when
placing C-1 lateral mass screws is the location
of the internal carotid arteries

51. • Recommend - pre-operative MRI scanning in
order to assess the degree of neural
compression and the integrity of the
transverse atlantal ligament prior to
performing this procedure.
• The screws used in the CVJ are generally a
larger diameter than the cervical screws with
a smaller pitch and blunt tips to prevent
piercing the dura.
• Neck in a neutral position and flex the head
on the neck in a “military tuck” position.

52. • Identify and palpate the bony limits of the C2
lateral mass. The superior and medial aspect
of the C2 pars are exposed and palpated.
• There is typically a robust epidural venous
plexus on the medial aspect of the pars of C2
which can be controlled by bipolar cautery.
• Do not dissect on the lateral portion of the
pars of C2, it increases the risk of bleeding
from the paravertebral venous plexus.
• This trajectory should cross the C1-C2 facet
joint and at the anterior arch of the atlas.

53. C2 Translaminar screws
• This involves the insertion of polyaxial
screws into the laminae of C2 in a
bilateral, crossing fashion
• Connected to C1 lateral mass screws in
a manner sim- ilar to the C1–C2 rod-
cantilever technique.
• Because the C2 screws are not placed
near the vertebral artery, this technique
allows safer rigid fixation of C2 without
fluoroscopy or surgical navigation.
• Requires intact posterior elements of
C2.

54. • High-speed drill is used to open a small cortical
window at the junction of the C2 spinous process
and lamina, close to the rostral margin of the C2
lamina.
• Lamina is carefully drilled to a depth of 30 mm,
with the drill visually aligned along the angle of the
exposed contralateral laminar surface.
• The trajectory is kept slightly less than the
downslope of the lamina to ensure that any
possible cortical breakthrough would occur dorsally
through the laminar surface rather than ventrally
into the spinal canal.
• A 4.0 x 30-mm polyaxial screw is carefully inserted
along the same trajectory.

55. Joint Jamming Technique
• Jamming of spiked spacers within the atlantoaxial joints can provide a
satisfactory method of atlantoaxial stabilization
• Wide opening of the articular cavity, denuding of the articular
cartilage, stuffing of bone graft within the cavity, and firm and strong
impaction of the customized titanium metal Goel spacers are
prerequisites for successful stabilization.

56. Anterior Methods
• Irreducible atlantoaxial dislocation must be either released or
decompressed prior to fixation.
• Currently, the most accepted treatment for irreducible atlantoaxial
dislocation is transoral odontoidectomy.
• Other methods are transoral anterior release and transoral
atlantoaxial reduction plate (TARP).
• More recent advances have made it possible to do a less invasive
odontoidectomy endoscopically via a transnasal, transoral, or
retropharyngeal approach

57. Indications of transoral procedures
• 1) An anterior release followed by posterior fixation: an anterior
release of ligaments would allow a better posterior reduction and
realignment
• 2) An incomplete or nonreduction following a posterior approach: this
is currently the most common indication for a transoral approach.
• 3) Reduction and fixation from the anterior approach

58. Prior to transoral odontoidectomy include the following:
• 1) Consider the degree of mouth opening. This should be about three
fingers breadth to allow ingress to the surgical approach.
• 2) Consider examining the oral cavity; exclude any infective conditions
and assess oral hygiene prior to surgery.

59. Transoral odontoidectomy
• Fiberoptic oral intubation is
performed with an armored
endotracheal tube while the
patient is awake
• Once the Spetzler-Sonntag
retractor is in place, a red
rubber catheter is placed
through one of the nares and
is sutured to the uvula using
4-0 Vicryl suture

60. • The incision is typically
1.5 to 2 cm in length
and is carried through
the posterosuperior
pharyngeal constrictor
muscle in the midline
raphe

61. • Bovie to skeletonize the anterior surface of the arch of C1
• Once the arch of C1 has been exposed,we identify the midline and drill and
remove the anterior arch of C1 to expose the anterior portion of the
odontoid process
• This typically requires the removal of two-thirds of the anterior arch of C1.
• Once the ligaments have been detached, we perform a “top- down”
removal of the odontoid process by drilling the dens using an eggshell
drilling technique
• The posterior pharyngeal mucosa and muscle are closed by
reapproximating the muscle and mucosa with interrupted 3-0 chromic
suture in a single- or double-layer fashion.

62. Complications
• Cerebrospinal fluid leakage
• Incomplete decompression
• Infection, abscess formation
• Vertebral artery injury
• Spinal cord injury

63. DCER
• The principle of the surgical procedure remained the same and
consisted of 3 steps:
• (1) removal of posterior margin of the foramen magnum
• (2) distraction and placement of a spacer leading to vertical
reduction of BI
• (3) compression and extension of C1 or C1/occipital complex over C2
over the fulcrum created by the placement of the spacer leading to
the reduction of AAD

64. • A distractor with tips of the blades was now kept between C1 and C2
posterior arches and very gently distracted
• The cartilage over the joint was drilled by using a fine diamond drill to
expose the cortical bone
• the size of the spacer was determined
• The C1 and C2 joint spaces were opened on both sides per the
standard Goel technique
• This was followed by placement of C1 lateral mass screws. Following
this, C2 translaminar screws (3.5-mm diameter) were placed

65. • compression was provided with the tips of the blades placed
superiorly between the offset and the laminar clamp and inferiorly
below the C2 screw

66. • To facilitate the opening of joining spaces, the arms of the distractor
were placed between the occiput superiorly and the upper border of
the C2 inferiorly
• spacer placement resulted in the correction of BI but not AAD
• Following this, the C2 translaminar screws were inserted and a
temporary screw was placed on the occiput
• A compressor was next placed with 1 arm over the gap between the
offset and the screw superiorly and the other below the C2
translaminar screw inferiorly

68. THANK YOU