os odon, axis fractures, c spine / t/L spine trauma Flashcards
what does os odontoideum look like on bony imaging?
- round ossicle with smooth border located in position of normal odontoid or closer to base of the occipital bone
- wide radiolucent zone separates the os odontoideum from the base of the remaining odontoid process
what is the likely etiology of os odon?
likely represents old nonunion fracture or injury to vascular supply of developing odontoid
what is the blood supply to the dens?
“apical arcade”, formed by anastomoses between branches of:
o VA - gives off paired anterior and posterior ascending arteries which reach base of odontoid via accessory ligaments and run cephalad at the periphery to reach the tip of the process
o ICA - gives off transverse superior and inferior arteries
o ECA - gives off ascending pharyngeal which joins the arcade after passing through the occipital condyle.
what are the two types of os odontoideum?
o orthotopic
moves with C1-2 complex
o dystopoic
lies near base of clivus and moves with clivus
ant arch C1 hypertrophied
post arch C1 hypoplastic
how do os odon patients present?
can present with sudden neuro deficit from minor injury - 3 types of presentations: o occipitocervical pain only o myelopathy o vertebro-basilar ischemia
What imaging finding is strongly associated with myelopathy?
sagittal canal compromise on fl/ex
How is os odon treated?
-if stable on flex/ext, may be followed
o warn about potential for injury, esp. with URTI
-if neuro Sx, or unstable on flex/ext (even if no neuro Sx), should have C1-C2 fusion (screws if possible)
o must check to see if neural compression is present and reducible, if not add C1 lami, if irreducible ventral compression must consider transoral resection of odontoid
how are odontoid fractures classified?
Anderson and D’Alonzo
Type I:
- rare – 1% of odontoid fractures
- oblique fracture line through superior 1/3 of the odontoid process
- avulsion fracture where the apical ligament attaches: stable, high rate of fusion.
Type II:
- Most common – 60% of odontoid fractures, and 36% of C2 fractures
- at junction between odontoid process and body of axis = unstable, high rate nonunion.
Type IIA:
- comminuted fracture
Type III:
- 40% of odontoid fractures
- extends down into cancellous bone of body of axis and in reality is a fracture of the body of C2
- strictly defined, fracture should extend into one or both superior articular facets
- usually stable, with high rate of fusion.
what are common causes of odontoid #s and what is the usual mechanism?
> 60 years = falls are commonest cause
How are type I odontoid fractures treated?
- do flex/ext and rule out any assoc. TAL injury and/or atlantooccipital dislocation, then treat with collar only
how are type III fractures treated?
- halo vest and check for stability - if stable will fuse well [consider collar in elderly]
- if unstable in halo or TAL disrupted then fuse - anterior odontoid screw (if TAL intact) or posterior fusion construct
How are type II fractures treated?
If displaced - reduce in traction with 2.5-3 lbs
can manage in halo - overall non-union rate is high - about 30%
What are indications for early surgery in type II / i.e. factors that affect fusion in halo?
> 6 mm displacement
- age >50 years
- movement in halo
- Type IIA – comminuted fracture
- TAL injury
- fracture presenting late (>2 wks from injury won’t heal as well)
what are the spine trauma study group recomendations for the treatment of odontoid fractures in the elderly?
Type II odontoid # often best Rx by surgical internal fixation
- A posterior approach may be preferable than anterior odontoid screw in the elderly, due to lower risk of postoperative dysphagia and airway compromise
- Recognize that for a subset of elderly with Type II #, a course of non-operative Rx may be chosen for a variety of reasons, and suggest that in this population, treatment in hard collar is as efficacious for achieving union as Halo, with less morbidity compared to halo immobilization in this population
- For type III # in elderly, based on low quality evidence, and clinical experience, the recommendation is rx in hard Collar
What is a hangman’s fracture?
bilateral C2 pars fractures (or pedicles)
a.k.a. “traumatic spondylolisthesis of the pars interarticularis of C2, with variable C2 on C3 displacement”
what is the weakest link in the cervicocranial axis?
pars interarticularis of C2
What are mechanisms of hangman #?
o usually MVA during rapid deceleration victim thrown forward in car with head striking windshield
o combination of axial loading and hyperextension forces disruption of cervicocranium from lower cspine occurs
o cervicocranium moves as one unit as axial loading and extension are applied, while C2 posterior arch and lower cervical vertebrae move and act together as a counterforce
How are hangman’s fractures classified?
Effendi
Type I:
3mm displacement or >11deg angulation of C2 on C3
- UNSTABLE
- d/t axial + extension + rebound flexion
- implies disruption of PLL and disc
Type IIA:
How do hangman’s fractures typically present?
95% neuro intact
- pain radiating along the greater occipital nerve (C2)
- facial injuries suggesting axial loading and extension.
- high incidence of head injuries
what are surgical indications for hangmans #
Surgical indications (very few will need this)
o inability to reduce # (97-100% should reduce in traction)
o failure to maintain reduction in halo.
o C2-3 disk herniation with s.c. compromise
o established non-union (late)
How are type I hangman’s # treated
- Sternal-occipital-mandibular immobilizer (SOMI) or halo vest for 12 weeks – virtually all will heal – 100%
