Study rationale and context
Os odontoideum is a rare condition defined radiographically as an ossicle with smooth
circumferential cortical margins representing the odontoid process that has no osseous
continuity with the body of C2. It may be classified as stable or unstable based on
the extent of excursion of the atlas from the axis on dynamic imaging [1].
The pathogenesis of this lesion remains controversial with arguments for both acquired
and congenital causes postulated in the literature. At present, however, most authors
believe that it results from a previous trauma leading to a chronic nonunion fracture
of the odontoid process [2]
[3]
[4]
[5].
Although os odontoideum has a clear radiographic definition, its clinical manifestations
are variable with patients existing on a spectrum of symptom severity from completely
asymptomatic or with neck pain to severe spinal cord injury. Due to the paucity of
cases and the poorly understood natural history of this condition it is difficult
for clinicians to predict which patients require surgical fusion to prevent symptomatic
progression and potentially devastating neurologic injury.
In order to review the collective experience and to help augment our current understanding
of this condition we have undertaken a systematic review of the literature to evaluate
the clinical outcomes in the treatment of asymptomatic and symptomatic cases of os
odontoideum.
Materials and methods
Study design:
Systematic review.
Sampling:
-
Search: Pubmed, EMBASE, Cochrane, and National Guideline Clearinghouse Databases;
bibliographies of key articles
-
Dates searched: 1970 to August 2009.
-
Inclusion criteria
-
Asymptomatic: case reports, case series of any size, adults and children
-
Symptomatic: case series that included 15 or more patients, adults and children
-
Outcomes: fusion (%), relief of symptoms
-
Analysis: descriptive statistics
Details about methods can be found in the web appendix at www.aospine.org / ebsj.
Results
We identified eleven articles meeting our inclusion criteria (Figure [1]). Seven studies included patients with asymptomatic os odontoideum discovered incidentally
from which it was possible to examine data on 18 individuals [3]
[4]
[6]
[7]
[8]
[9]
[10]. Six studies were identified containing more than 15 patients with symptomatic os
odontoideum [2]
[3]
[5]
[10]
[11]
[12].
Asymptomatic incidental os odontoideum
-
Eighteen individual asymptomatic patients were identified, for which the demographics,
treatment, and outcomes are shown in Table [1] [3]
[4]
[6]
[7]
[8]
[9]
[10].
-
Among the eleven patients for which demographic data were supplied, 64% were pediatric,
and 64% were male. Three had Klippel-Feil syndrome, two had Down’s syndrome, and one
had ectodermal dysplasia.
-
Follow-up time was reported in only seven of the patients and ranged from 1.4 – 11
years.
-
Nine patients were treated with spinal fusion procedures to stabilize C1 and C2, and
in these cases, solid fusion was achieved. These patients continued to be asymptomatic,
although one paper pointed out that the neck range of motion was reduced secondary
to fusion.
-
Nine patients were treated conservatively, and these were reported to remain stable
with no symptomatolgy attributable to their os odontoideum having developed over the
course of follow-up. One patient died from pulmonary cancer at 11-years follow-up,
but his spinal condition remained stable until that time.
Symptomatic os odontoideum
-
Three-hundred-and-forty-four patients in six studies with symptomatic os odontoideum
are summarized with respect to demographics, treatment, and outcomes, Table [2] [2]
[3]
[5]
[10]
[11]
[12]. Ages ranged from 3 – 73 years and 62% were males. Forty-seven patients had a preexisting
diagnosis including Klippel-Feil syndrome, Down's syndrome, dysplasia, occipitalization,
hypertrophy of the anterior atlantal arch, basilar impression, spondyloepiphyseal
dysplasia, metatrophic dwarfism, or Morquio's syndrome. All but 19 patients underwent
cervical fusion.
-
Fusion rate
The rate of fusion reported in four studies was 99% (214 / 216) [5]
[10]
[11]
[12].
-
Symptoms
Three case series report on the change in symptoms following spinal fusion. After
fusion, symptoms were completely resolved or significantly reduced in all patients
(n = 39) in one study [10], and completely resolved in 88% in another [2]. Klimo et al reported that symptoms resolved in 68% of patients with pain and 39%
with neuropathy (20% with myelopathy and 100% with intermittent neuropathy) [5]. It is unclear how many different patients this represents of the total study population
as patients may have more than one symptom. No case series reported worse symptoms
or neurological status following treatment.In the one retrospective cohort study,
patients were grouped by cord sign status and treatment mode [3]. In patients with no cord signs, symptoms resolved in 50% of those patients who
were treated conservatively and only 11% of those treated with surgery. In patients
with cord signs, 25% of patients were symptom free whether they received conservative
or operative treatment (Figure [2]).
Clinical guidelines
In 2001, the American Association of Neurological Surgeons and the Congress of Neurological
Surgeons (AANS/CNS) provided evidence-based clinical recommendations for the treatment
of os odontoideum [1].
-
No clinical evidence was found supporting the recommendation of operative treatment
standards or guidelines for os odontoideum.
-
For asymptomatic patients, clinical and radiographic surveillance may be the appropriate
management.
-
Patients with neurological symptoms / signs and C1 – 2 instability are generally managed
with posterior fixation and fusion.
-
Other operative measures may be warranted in cases of irreducible cervicomedullary
compression and / or occipitocervical instability.
-
The paucity of high quality studies was noted.
