Download Atlantoaxial Instability of the Atlas Posterior Arch Associated with

Atlantoaxial Instability of the Atlas Posterior
Arch Associated with Ossiculum Odontoideum
in a High School Gymnast
LaKiesha N. Bohannon, LMT, BS*
Master of Science in Athletic Training Graduate Student, Department of Health and Kinesiology, Texas
A&M University, USA
Michael Lozano, MAT, ATC, LAT
Athletic Trainer, Spearman ISD, USA
Lori Greenwood, Ph.D., ATC, LAT
Director, Master of Science in Athletic Training, Department of Health and Kinesiology, Texas A&M
University, USA
Edited By:
Michael J. Pringle, Orthopaedic Specialists of North Carolina/Lincoln Memorial University, USA
www.jampub.com, email: [email protected]
*Correspondence:
LaKiesha Bohannon, C/O Dr. Lori Greenwood, Texas A&M University, Department of Health
and Kinesiology, 332 Blocker, 155 Ireland Street, MS 4243, College Station, TX 77843-4243,
USA
Email: [email protected]
ABSTRACT
The objective of the study was to examine a case report of a 17 year old female gymnast who
presented with quadriplegia after landing on her neck in the flexed position while performing a
backhand spring. She was suspected to have: cervical/odontoid fracture, cervical dislocation,
multidirectional instability of C1 on C2, spinal cord impingement, persistent ossiculum terminale,
odontoid hypoplasia or a combination of the previously listed conditions. Imaging via X-Rays and
CT scans identified an ossiculum odontoideum. It was later determined that a closed dislocation
of C1 and lesions of C1-C4 of the spinal cord accompanied the ossiculum odontoideum. The
gymnast underwent trans articular screw fixation surgery and was able to make a full recovery,
but unable to return to gymnastics or any contact sports. Cases such as this one are often seen early
in infants or in individuals with Down’s syndrome, mucopolysaccharidosis, Morquio’s syndrome
or connective tissue/skeletal development disorders. It is also uncommon to have a condition this
severe that does not present symptoms prior to an injury. Approximately 90% of patients with this
condition have improvement or resolution of presenting symptoms once undergoing surgical
intervention. The physician’s recommendation to treat the condition surgically was based on the
patient’s age and activity level.
KeyWords: ossiculum odontoideum, atlantoaxial instability, trans articular screw fixation
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INTRODUCTION
Ossiculum (Os) Odontoideum is defined as an ossicle with smooth cortical margins representing
the odontiod process that has no osseous continuity with the body of the C2 vertebrae (Bach,
Arbab, & Thaler, 2013; Matsui, Imada, & Tsuji, 1997; Meng & Xu, 2011). Atlantoaxial instability
secondary to os odontoideum is a serious condition that may require surgical stabilization. The
variability of signs and symptoms may make diagnosis difficult. Currarino, Rollins and Diehl
(1994) classified the anomalous of atlas (C1) posterior arch into five types on the basis of CT scans
and radiographs as follows: Type A: a failure of the posterior midline fusion of the two hemiarches;
Type B: unilateral cleft; Type C: bilateral clefts; Type D: total absence of the posterior arch with
a persistent posterior tubercle; and Type E: total absence of the posterior arch with missing
posterior tubercle. A study by Yang, Ni, Yan, Zhou and Chen (2011) concluded that Type A
defects occur in about 3-4% of the general population, but represent 97% of all posterior defects.
Type B through E defects has been reported to occur in only 0.69% of the general population
making up the remaining 3% of all posterior defects.
ANATOMY
The base of the dens forms from the occiput (C0) and atlas (C1) sclerotomes as 2 paired structures
that ossify just before birth. The axis (C2) and C3 sclerotomes give rise to the body of the axis,
which fuses with the dens at age 4 (Menezes, 2008; Menezes & Ryken, 1992). At birth, the
odontoid process is separated from the body of the C2 vertebra by a cartilaginous band that
represents a vestigial disc and is later referred to as the neural central synchondrosis (Menezes &
Ryken, 1992). This is important in the understanding of the formation of os odontoideum. The
neural central synchondrosis lies below the level of the superior articular facets of the axis and
does not represent the anatomical base of the dens. This synchondrosis is present in most children
younger than 3–4 years of age and disappears by 8 years of age (Menezes & Ryken, 1992).
Os odontoideum is located in the position of the odontoid process near the basiocciput
where it may fuse with the clivus. The gap between the C2 and the free ossicle usually extends
above the level of the superior facets of the axis. The entire complex leads to incompetence of the
cruciate ligament and subsequently to atlantoaxial instability. In intact spines the stability of C1C2 complex during translational motion is provided by strong transverse ligaments, trapping the
intact odontiod process within the anterior arch of C1. Discontinuity of the odontoid process to the
body of C2, traumatic or non-traumatic os odontoideum, leads to atlantoaxial weakness and
biomechanical insufficiency of the apical odontiod and alar ligaments (Bach, Arbab & Thaler,
2013). The mass of bone may be fused to the base of the skull, dystopic os odontoideum, or it may
articulate and move with the C2 vertebrae, orthotopic os odontoideum (Rozzelle, Aarabi, Dhall,
Gelb, Hurbert, Ryken, Theodore, Walters, & Hadley 2013).
Etiology
Fielding, Hensinger and Hawkins (1980) attributed os odontoideum to a disunited fracture
by presenting cases where there was a history of trauma and normal radiographic exams prior to
the development of os odontoideum. They contended that after the odontoid process fractures, the
proximal fragment is pulled by contracture of the alar ligament, causing disruption of the blood
supply to the odontoid process which contributes to nonunion. The radiographs of Fielding,
Hensinger and Hawkins (1980) study showed os odontoideum is marked by a small corticated
ossicle separated from the base of the odontoid. Although it is uncommon, os odontoideum
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frequently leads to atlantoaxial instability and spinal cord compression (Fielding, Hensinger and
Hawkins 1980; Henderson & Henderson 2006; Rozzelle et al. 2013).
The etiology of os odontoideum remains controversial and debatable regarding whether it is a posttraumatic or congenital condition (Clements & Mezue, 1995; Dai, Yuan, Nia, & Jia 2000;
Henderson & Henderson, 2006). Anomalies of the os odontoideum are more common in patients
with Down’s syndrome, Klippel-Feil malformation, or other skeletal disorders than the general
population (Bach, Arbab & Thaler, 2013; Menezes, 2008; Meng & Xu, 2011). Os odontoideum
is often discovered incidentally with routine cervical radiographs in these specific populations (
Henderson &Henderson, 2006). Os odontoideum has been noted to have a round or oval shape
and a smooth margin. Initially, os odontoideum was thought to represent a congenital failure of
fusion of the dens to the remainder of the axis. The failure of the secondary ossification center of
the dens to fuse with the base of the odontoid represents a separate entity known as persistent
ossiculum terminale. Os odontoideum is the failure of the odontoid process (C1) to fuse with the
body of the axis (C2), or failure of the apex of the odontoid process (proatlas) to fuse with the main
portion of the odontoid process (Yang et al., 2011). Differentiation between os odontoideum and
persistent ossiculum terminale is clinically critical. The ossicle of the ossiculum terminale is much
smaller than that of the os odontoideum. Ossiculum terminale, unlike os odontoideum, is not
associated with significant instability.
CASE REPORT
The patient was a 17 year old female Caucasian, high school gymnast who weighed 61.18kg
(134.9lbs.) and was175cm (5’9”). She had participated in sports during middle school, but had
only been participating in gymnastics since eighth grade. At the time of injury, the patient was in
the eleventh grade.
CHIEF COMPLAINT
During gymnastics practice, the patient fell on her neck with her head in a flexed position when
attempting to perform a backhand spring. She reported feeling a pop and sharp shooting pain in
her neck. Athletic trainers immediately came to her aid. When she reported that she was
experiencing quadriplegia, the emergency activation plan for cervical spine injuries was then
activated. Athletic trainers stabilized the athlete and kept her calm until the arrival of emergency
medical services at which time she was placed in a cervical collar, spine boarded, and transported
to the hospital. The athlete reported that she was unable to move her extremities for 10-15 minutes.
When she began to gain motor function of the extremities again, she experienced numbness and
tingling.
PREVIOUS HISTORY
There was no previous history of neck injuries. Family history also revealed no spinal injuries,
Down’s syndrome, Morquio’s syndrome or any other skeletal disorders in the family, immediate
or extended.
EXAMINATION FINDINGS
Neurological symptoms of numbness and tingling had subsided prior to arrival at the emergency
room. The patient’s motor testing was normal and symmetrical in the upper and lower extremities.
Cervical palpation was difficult to perform due to the patient reporting extreme pain over occipital
region, along with anterior and posterior neck. Radiating
pain continued to be reported when
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passively moved through neck range of motion. Computed tomography (CT scan) of the cervical
spine and brain was ordered without contrast, as well as radiographs of the cervical spine. Prior to
imaging results, the following differential diagnoses were considered: cervical/odontoid fracture,
cervical dislocation, multidirectional instability of C1 on C2, spinal cord impingement, persistent
ossiculum terminale or odontoid hypoplasia
RADIOLOGICAL EXAMINATION
Radiographic images identified an anomaly in C1 and C2 complex (Figure 1). The physician
requested multiple contiguous axial images to be obtained in a CT of the brain and of the cervical
spine without contrast for further diagnosing. The results concluded that the brain was normal in
morphology and attenuation without focal lesions or confluent areas of infraction. There was no
evidence of hydrocephalus, intracranial hemorrhage, extra-axial fluid collection or acute
intracranial abnormalities. The CT of the cervical spine without contrast identified there was no
evidence of acute fracture, however the anomaly noted in the radiograph was identified as an os
odontoideum, which was well corticated (Figure 2). The vertebral bodies and intervertebral disk
demonstrated normal height and alignment without a fracture or subluxation in the remaining area.
It was emphasized that the os odontoideum present did not appear to be an acute fracture of the
odontoid process.
Figure 1. Radiograph of cervical spine.
This figure illustrates the anomoly
noted in the cervical spine of the athlete.
Figures 2. CT scan of cervical spine without
contrast. This figure illustrates the anomaly
of an os odontoideum.
TREATMENT
The patient was admitted to the hospital for 48 hours post injury. Upon discharge she was placed
in a cervical collar for stability of the neck and was advised to follow up with a brain and spine
specialist at a nearby institute. After discussion with the specialist, the patient was advised that she
had os odontoideum with a 5-6 mm gap where bone failed to form. She was scheduled for C1-C2
fusion surgery 3 months after the initial injury to give her time to finish her school year. In the
meantime, the patient was placed in a cervical orthosis until surgery. The patient was identified
as having little to no development of what would be the transverse atlanto ligament. In order to
stabilize the bone structure, a trans articular screw fixation with cervical screws and a plate were
placed to support C1/C2. The screw fixation included 4 screws and a metal plate. Three months
after the surgery, the patient returned for follow up imaging that revealed that her screws were
beginning to loosen. She was then provided with a bone stimulator to help increase the healing and
growth of bone to hold the screws in place. Imaging completed a month later showed the success
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of the bone stimulator and there was no need to further discuss non-invasive or invasive
interventions.
RETURN TO PLAY
The physician advised the athlete that she would not be allowed to return to gymnastics even after
completion of the surgery and recovery time. She was on bed rest for 2 weeks before being able
to move around comfortably in daily living activities. The patient was cleared to begin light
walking for aerobic exercises when she felt comfortable 5 weeks post-surgery and was able to
return to school at the beginning of her senior year without the need for any devices or extra
support. Over the past year, the patient was allowed to gently increase aerobic activity from
walking to running and light weight lifting to moderate weight lifting, as long as no weights were
above her head. One year post injury, the patient was informed she was cleared to resume normal
activities except for gymnastics and all contact sports. She was advised of proper technique when
returning to lifting weights above her head and how to release the bar as to not injure her skull or
neck. The patient was not referred for any specific rehabilitation program but was advised that
when able she should begin physical activity within her restrictions and comfort level. She
continued to be monitored by the athletic training staff as she progressed her activity and engaged
in weight lifting.
DISCUSSION
The etiology of os odontoideum is still debated; however, current studies have concluded that the
etiology of os odontoideum is not relevant to its diagnosis or subsequent management (. Henderson
& Henderson 2006; Meng & Xu 2011; Rozzelle et al. 2013). Os odontoideum occurs in
approximately 4-5% of the general population. These cases are often seen early in infants or in
individuals with Down’s syndrome, mucopolysaccharidosis, Morquio’s syndrome or connective
tissue/skeletal development disorders. In the current case the os odontoideum was not caused by
the gymnast’s fall, but investigation of the surrounding tissue and bones could not identify if the
condition was due to a previous injury in early childhood or if it was congenital.
In cases of os odontoideum with no previously stated conditions, the patients tend to be
mature adults and the condition is not discovered after direct trauma, such as the one in the current
case study, but often after complaints of constant neck pain with no direct cause or explainable
symptoms (Currarino, Rollins and Diehl 1994; Klimo, Kan, Rao, Apfelbaum, & Brockmeyer 2008;
Spierings & Braakman, 1982;). In a study reported by Henderson S. and Henderson D. (2006), a
45 year old female complained of neck pain and experienced “fainting spells” as well as “clicking”
in her neck. Her physical examination was normal except for a palpable clicking during passive
flexion. However, even though the patient was identified to have an os odontoideum and
instability, there was no recommendation for her to pursue surgical intervention. Instead, the
patient was told to limit her activity and monitor her own symptoms. She became symptom free
and able to live a low-activity level lifestyle two years after diagnosis. This brings up the discussion
of whether surgical intervention is being prescribed too often in individuals who may not actually
need it.
Bach, Arbab, and Thaler (2013) explains how there is disagreement in the literature
regarding the treatment of os odontoideum in asymptomatic patients, explaining why an evidence
based standard of care is yet to exist. Shirasaki, Okada, Oka, Hosono, Yonenobu and Ono (1991)
and Spiering and Braakman (1982) conclude that asymptomatic os odontoideum with or without
instability in flexion/extension radiographs can result in late neurological deterioration with or
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without trauma or can result in a long-term asymptomatic course. While some physicians propose
a more conservative approach of no treatment with recommendations of lifestyle changes, others
propose operative treatment regardless to avoid the occurrence or worsening of neurological
injuries. Generally direct trauma over a present os odontoideum can be life threatening and even
fatal making intervention choices a serious debate. A successful treatment of os odontoideum aims
to stabilize the C1-C2 joint. Modern surgical techniques involve trans articular screw fixation or
rigid atlantoaxial fixation (Bach, Arbab & Thaler, 2013). These procedures have been associated
with high fusion rates and provide immediate spinal stability in all planes (Jeanneret & Magerl,
1994; Kim, Hongg, Jang, Yand, Sung, Son, & Lee, 2011).
While manipulation of any suspected cervical spine injury where neurological symptoms
are seen is contraindicated, imaging provides valuable information. In a case study by Yang at el.
(2011), they reported how physical examinations only revealed tenderness at the dorsal area of the
cervical spine and no neurological defect was found. However imaging via radiograph, CT, and
MRI showed non-unions of the odontoid process and atlantoaxial subluxation, along with spinal
cord compression due to the subluxation. Meng and Xu (2011) studied the reliability of CT
measurements for the dimensions of C2 pedicle and lamina in os odontoideum patients. The
researchers recruited 29 adult patients that presented with symptoms of neck movement
restrictions, neck pain, extremity weakness, numbness, pyramid sign and or sphincter disturbances.
The CT was completed on all patients prior to surgery and compared to invasive measurement
during os odontoideum correction. CT scans measurements showed a high (0.95 & 0.96)
reliability. While radiograph was not the first option in the Meng and Xu (2011) study, CT imaging
was completed and later a combination of both radiographs and CT scans were used to track the
patient’s progress.
CONCLUSION
In cases where surgical intervention was not chosen patients were required to maintain a low level
of activity and closely monitor their symptoms. Approximately 90% of patients with this condition
have improvement or resolution of presenting symptoms once undergoing surgical intervention.
In many of these cases patients were allowed to return to a more active lifestyle and were less
likely to report symptoms a year post surgery (Klimo et al. 2008).With two opposing possible
intervention plans, surgical and conservative non-surgical, the physician’s recommendation to
treat the condition surgically was based on the patient’s age, activity level and previous experience.
In this case, the acute injury led to the identification of a problem that if not recognized and treated
could have resulted in a more severe problem in the future.
As athletic trainers, injuries such as these are not commonly seen in the majority of our
patient population. An understanding of the anatomy and pathomechanics of the condition is a
vital component in injuries such as these when helping to manage the healing phases and helping
to transition the athlete into a functional level for daily living. Proper initial care of this injury is
critical, especially when attempting to reduce the chances of continued and further damage.
Understanding and activation of proper EAP’s and spinal stabilization are vital protocols after such
injuries and should be reviewed and practiced often. Without the immediate identification of the
severity of the injury sustained and the coordinated efforts of the health care team, the outcome of
the situation could have posed a greater risk to the athlete.
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