Os odontoideum with posterior atlantoaxial instability

Novel Radiographic Parameters for Posterior Atlantoaxial Dislocation Secondary to Os Odontoideum and Its Clinical Significance

OBJECTIVE

To explore correlations of 3 novel radiographic parameters with myelopathy induced by posterior atlantoaxial dislocation (PAAD) secondary to os odontoideum (OO) and assess their reproducibility.

METHODS

Of the 51 patients with OO with PAAD enrolled in this study, 28 developed PAAD-induced myelopathy (myelopathy group), and the other 23 patients had no myelopathy (control group). Neurologic function was evaluated by the neurologic function rating system and the Japanese Orthopaedic Association score system. Three novel radiographic parameters (OP [median sagittal diameter of the spinal canal from the posteroinferior edge of the ossicle to the anterosuperior edge of the spinous process of C2]/C4 SAC [space available for spinal cord] ratio, C1 posterior inclination angle, and posterior dislocation index) were measured by lateral cervical dynamic radiography. Their correlations with neurologic function were analyzed, and their reproducibility was assessed by the intraclass correlation coefficient (ICC). In addition, receiver operating characteristic curve analysis was performed.

RESULTS

A significant correlation was observed between the OP/C4 SAC ratio and the neurologic function (P < 0.01), and between the C1 posterior inclination angle and the neurologic function (P < 0.01). Furthermore, their interobserver and intraobserver reliability was excellent (ICC ≥ 0.912). Receiver operating characteristic curve analysis showed that the optimal threshold value relating to myelopathy of the OP/C4 SAC ratio and C1 posterior inclination angle was 0.93 and 20°, respectively.

CONCLUSIONS

The OP/C4 SAC ratio and the C1 posterior inclination angle seem to be 2 effective and objective radiographic parameters for relating myelopathy in patients with OO with PAAD. When the OP/C4 SAC ratio is <0.93 and/or the C1 posterior inclination angle is >20°, the risk of developing myelopathy should be highly suspected in patients with OO with PAAD.

Os Odontoideum in Children

Os odontoideum is a rare entity of the second cervical vertebra, characterized by a circumferentially corticated ossicle separated from the body of C2. The ossicle is a distinct entity from an odontoid fracture or a persistent ossiculum terminale. The diagnosis may be made incidentally on imaging obtained for the workup of neck pain or neurologic signs and symptoms. Diagnosis usually can be made with plain radiographs. MRI and CT can assess spinal cord integrity and C1-C2 instability. The etiology of os odontoideum is a topic of debate, with investigative studies supporting both congenital and traumatic origins. A wide clinical range of symptoms exists. Symptoms may present as nondescript pain or include occipital-cervical pain, myelopathy, or vertebrobasilar ischemia. Asymptomatic cases without evidence of radiologic instability are typically managed with periodic observation and serial imaging. The presence of atlantoaxial instability or neurological dysfunction necessitates surgical intervention with instrumentation and fusion for stability.

Os Odontoideum in Children: Treatment Outcomes and Neurological Risk Factors

BACKGROUND

Treatment outcomes and risk factors for neurological deficits in pediatric patients with an os odontoideum are unclear.

METHODS

We reviewed the data for 102 children with os odontoideum who were managed at 11 centers between 2000 and 2016 and had a minimum duration of follow-up of 2 years. Thirty-one children had nonoperative treatment, and 71 underwent instrumented posterior cervical spinal arthrodesis for the treatment of C1-C2 instability. Nonoperative treatment consisted of observation (n = 29) or immobilization with a cervical collar (n = 1) or halo body jacket (n = 1). Surgical treatment consisted of atlantoaxial (n = 50) or occipitocervical (n = 21) arthrodesis. One patient also underwent transoral odontoidectomy.

RESULTS

Thirty children (29%) presented with neurological deficits, 28 of whom had radiographic atlantoaxial instability (atlantoaxial distance >5 mm) or limited space (≤13 mm) available for the spinal cord (risk ratio, 7.8 [95% confidence interval, 2.0 to 31] compared with children with no radiographic risk factors). The 27 children without neurological deficits or atlantoaxial instability at presentation underwent nonoperative treatment and remained asymptomatic. Of the initial nonoperative cohort, one child developed atlantoaxial instability, and another had a persistent neurological deficit; both children underwent spinal arthrodesis during the study period. One child with cervical instability declined surgery and remained asymptomatic. Spinal fusion occurred in 68 patients in the surgical group by the end of the study period (mean, 3.7 years; range, 2.0 to 11.8 years). Surgical complications occurred in 21 children, including nonunion in 12, new neurological deficits in 4, cerebrospinal fluid leak in 2, symptomatic instrumentation requiring removal 2, and vertebral artery injury in 1. Nine children underwent revision surgery. In the surgical group, Japanese Orthopaedic Association neurological function scores improved significantly from preoperatively to the latest follow-up for the upper extremities (p = 0.026) and lower extremities (p = 0.007).

CONCLUSIONS

The risk of developing a neurological deficit was strongly associated with atlantoaxial instability and limited space available for the spinal cord in children with os odontoideum. Nonoperative treatment was safe for asymptomatic patients without atlantoaxial instability. Spinal arthrodesis resolved the neurological deficits of children with symptomatic os odontoideum.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Posterior Screw-Rod Fixation and Selective Axial Loosening for the Treatment of Atlantoaxial Instability or Dislocation Caused by Os Odontoideum: A Case Series for a Single Posterior Approach

OBJECTIVE

To evaluate the effect of screw-rod fixation and selective axial loosening in the treatment of atlantoaxial instability or dislocation (including reducible and irreducible) caused by os odontoideum (OO) via a single posterior approach.

METHODS

A consecutive series of patients with OO surgically treated in our hospital were retrospectively analyzed. For atlantoaxial instability and reducible atlantoaxial dislocation, C1-C2 screw-rod fixation and fusion were performed. OO combined with irreducible atlantoaxial dislocation was reduced after posterior axial loosening, followed by screw-rod fixation and fusion. The general information, clinical data, and radiographic data were compared between the 2 different procedures.

RESULTS

There were 41 patients with an average age of 40.6 ± 21.7 years. All the patients underwent posterior reduction and C1-2 screw rod fixation, 6 with axial loosening and 35 without axial loosening. The clinical manifestations and radiographic data significantly improved after the operation with a low rate of complications. Except for clivus-canal angle and visual analogue score of cervical pain, there were no differences in clinical and radiographic data between the 2 procedures.

CONCLUSIONS

Posterior screws-rod fixation and selective axial loosening is appropriate for treating OO complicated with atlantoaxial instability or dislocation (including reducible and irreducible) without the need for anterior decompression.

Chronic posterior atlantoaxial subluxation associated with os odontoideum: a rare condition. A case report and literature review

Introduction

Os odontoideum is a rare cervical lesion. This unusual condition is sometimes associated with atlantoaxial subluxation, which is mostly anterior subluxation. Posterior atlantoaxial subluxation due to os odontoideum is extremely rare.

Case presentation

We report an unusual case of a 60-year-old Thai female, who was diagnosed as having chronic posterior atlantoaxial subluxation associated with os odontoideum with progressive myelopathy. The patient underwent posterior arch of C1 laminectomy and an occipito-C3 fusion using an occipital plate, C2 pedicle screws, C3 lateral mass screws and autologous iliac crest strut bone graft arthrodesis. During three years of follow-up, she was clinically significantly improved and postoperative radiographs showed a solid osseous fusion without loss of correction or implant failure.

Discussion

Chronic posterior atlantoaxial subluxation associated with os odontoideum is rare. This condition can cause occipital-cervical pain, myelopathy, intracranial symptoms, or death. Surgical decompression and stabilization is the treatment of choice. Principles of treatment are to prevent sudden death from neurological compromise, improve neurological status, stabilize the cervical spine, and improve quality of life. Surgical options include atlantoaxial fusion, occipito-C2 fusion, and occipito-C3 fusion. Decision making depends on the location of spinal cord compression, area for arthrodesis, and bone quality.

Reduction of atlantoaxial dislocation prevented by pathological position of the transverse ligament in fixed, irreducible os odontoideum: operative illustrations and radiographic correlates in 41 patients

OBJECTIVE Os odontoideum (OO) is a craniovertebral junction (CVJ) abnormality in which an ossicle (small bone) is cranial to a hypoplastic dens by a variable gap. This abnormality can result in instability, which may be reducible or irreducible. What leads to irreducibility in OO is unclear. Therefore, the authors sought to better understand the causes of irreducibility in OO. METHODS A retrospective review was conducted, which identified more than 200 patients who had undergone surgical treatment for OO between 1978 and 2015 at the University of Iowa Hospitals and Clinics. Only the 41 patients who had irreducible OO were included in this study. All inpatient and outpatient records were retrospectively reviewed, and patient demographics, clinical presentation, radiographic findings, surgical treatment, and operative findings were recorded and analyzed. RESULTS The cohort of 41 patients who were found to have irreducible OO included both children and adults. A majority of patients were adults (61% were 18 years or older). Clinical presentation included neck pain and headache in the majority of patients (93%). Weakness, sensory disturbances, and myelopathy were invariably present in all 41 patients (100%). Down syndrome was much more common in the pediatric cohort than in the adult cohort; of the 16 pediatric patients, 6 had Down syndrome (38%), and none of the adults did. Of the 16 pediatric patients, 5 had segmentation failure (31%) in the subaxial spine, and none of the adults did. A form of atlantoaxial dislocation was seen in all cases. On CT imaging, atlantoaxial facets were dislocated in all 41 cases but did not have osseous changes that would have prevented reduction. On MRI, the transverse ligament was identified anterior and inferior to the ossicle and superior to the hypoplastic odontoid process in all cases in which these studies were available (i.e., post-MRI era; 36 of 36 cases). The ligament was hypointense on T2-weighted images but also had an associated hyperintense signal on T2 images. Intraoperatively, the transverse ligament was identified anterior and inferior to the ossicle and superior to the hypoplastic odontoid process in all 41 cases. CONCLUSIONS In the largest series to date of irreducible OO and the only study to examine variable factors that lead to irreducibility in OO, the authors found that the position of the transverse ligament anterior and inferior to the ossicle is the most common factor in the irreducibility of OO. The presence of granulation tissue and of the dystopic variant of OO is also associated with irreducibility. The presence of Down syndrome and segmentation failure probably leads to faster progression of ligamentous incompetence and therefore earlier presentation of instability and irreducibility. This is the first study in which intraoperative findings regarding the transverse ligament have been correlated with MRI.

An uncommon case mimicking cervical trauma: Os odontoideum

Os odontoideum is a separate odontoid process from the body of the axis. It is the most common anomaly of the odontoid process. Patients with this condition can be asymptomatic or present with a wide range of neurological dysfunctions. It may cause cervical instability, atlantoaxial dislocation and myelopathy. This anomaly can mimic Type I and II odontoid fractures. There is a role for conservative treatment of an asymptomatic incidentally found, radiologically stable and non-compressive os odontoideum. However, surgical treatment has a definitive role in symptomatic cases. In this study, the case is presented of a 31 year-old male patient with neck pain who was diagnosed with incidental os odontoideum. The diagnosis of acute odontoid fracture was discarded in this case as the radiological findings were of a characteristic cortex with smooth contours, and there was no history of recent trauma, sclerosis or hypertrophy of the anterior tubercle of the atlas.

Cervical myelopathy involving os odontoideum and retro-odontoid cyst treated with Harms C1-C2 arthrodesis

An episode of acute decompensation of cervical myelopathy occurred after an injury without fracture of an os odontoideum associated with a compressive retro-odontoid cyst. The 51-year-old female patient presented Fränkel C, Nurick grade 4 neurological status and pyramid syndrome. The initial MRI demonstrated an intramedullary T2 hyperintense signal in the context of spinal cord narrowing. The retro-odontoid cyst demonstrates atlantoaxial instability related to the os odontoideum. Harms C1-C2 arthrodesis without laminectomy was performed and the cyst disappeared completely. Spinal cord decompression was thus obtained on the MRI taken 3 months later. Neurological recovery was complete and continued at 1 year.

The Role of Conservative Management in Incidental Os Odontoideum

BACKGROUND

Os odontoideum is a relatively rare but significant condition of the cervical spine that has potentially life-threatening complications, including vertebral artery dissection, leading to permanent neurologic disability and even death. Unfortunately, the literature is not clear as to the best management approach for os odontoideum. As such, clinicians and their patients are still left with difficult and uncertain treatment decisions in the absence of a clinical consensus.

CASE DESCRIPTION

A 20-year-old male was brought in after an assault and found to have os odontoideum on routine investigation. He was informed of management options and elected to undergo a conservative management approach with radiologic surveillance. The patient subsequently became symptomatic and required surgical fixation.

CONCLUSIONS

This case illustrates that in the event an asymptomatic case of os odontoideum with radiological instability is managed conservatively, careful clinical and radiologic follow-up is essential as such cases can become symptomatic.

Acute Traumatic Cervical Cord Injury in Pediatric Patients with os Odontoideum: A Series of 6 Patients

OBJECTIVE

Os odontoideum can lead to instability of the atlantoaxial joint and places the spinal cord at significant risk for acute traumatic catastrophic events or chronic neurologic change. The purpose of this study was to retrospectively review acute cervical cord injury after minor trauma in 6 pediatric patients with os odontoideum.

METHODS

Between 2012 and 2013, 6 pediatric patients with os odontoideum who suffered acute traumatic cervical cord injury were reviewed retrospectively. Their clinical history, neurologic symptoms, radiological investigations, follow-up period, American Spinal Injury Association (ASIA) impairment classification, and motor score were reviewed.

RESULTS

There were 2 male and 4 female subjects ranging in age from 4 to 18 years (mean 11.8 years). Before the traumatic injury, 2 cases were asymptomatic and 4 complained of myelopathic feature with unsteadiness on feet. Falls were the most common injury (n = 5), followed by a minor motor vehicle accident (n = 1). Atlantoaxial instability and cord compression were presented in all cases with dynamic cervical lateral radiographs and magnetic resonance imaging. Most patients presented with spinal cord thinning and hyperintensity on T2-weighted sequences in magnetic resonance imaging. Spinal cord compression was anterior in 2 cases and both anterior and posterior in 4. Two patients was classified as ASIA B, 1 as ASIA C, and 3 as ASIA D category on admission. Two patients presented with respiratory failure with mechanical ventilation for over 2 weeks in perioperative period. Postoperatively, all patients improved neurologically and clinically after underwent posterior atlantoaxial fixation and fusion.

CONCLUSIONS

Pediatric patients with asymptomatic or myelopathic atlantoaxial instability secondary to os odontoideum are at risk for acute spinal cord injury even after minor traumatic injury. Sufficient fixation and fusion should be undertaken as prophylactic treatment of developing myelopathy and to improve neurologic symptoms with acute traumatic cervical cord injury in pediatric patients with os odontoideum.

Pediatric craniovertebral junction trauma

The craniovertebral junction consists of the occiput, atlas, and axis, along with their strong ligamentous attachments. Because of its unique anatomical considerations, trauma to the craniovertebral junction requires specialized care. Children with potential injuries to the craniovertebral junction and cervical spinal cord demand specific considerations compared to adult patients. Prehospital immobilization techniques, diagnostic studies, and spinal injury patterns among young children can be different from those in adults. This review highlights the unique aspects in diagnosis and management of children with real or potential craniovertebral junction injuries.

Os odontoideum: case report

OBJECTIVE: To report the difficulties in managing a case of os odontoideum. METHODS: Female patient, 12 years old who developed a quadiparesis after minor cervical trauma in October 2005. In the emergency department a congenital cervical anomaly was identified. The patient was placed in a Stryker® frame and, few days later, in a halo bracing. After 3 months, an infection around the pins emerged and the halo vest had to be removed. A severe C1-2 instability persisted and a C1-C2 Gallie procedure was attempted. In the following weeks the bone disappeared and another procedure was attempted in June 2006 - C1 laminectomy and occiput-C3 fusion. In the following months the neurological status of the patient improved and a complete mass of occiput-C3 fusion was observed. RESULTS: We choose a posterior cervical arthrodesis of C1-C2 using the Gallie technique. Since the condition was not resolved we performed a second surgery, C1 laminectomy (determined by SAC of 8, 3 mm in MRI) followed by posterior occiput-C3 fusion. In our case, until now, there is no evidence of axial decompensation, but a more prolonged follow-up is needed. CONCLUSIONS: The treatment of os odontoideum has many considerations but the essential that in the presence of instability and neurological deficit a solid fusion is achieved. In case of failure of posterior atlantoaxial wiring, the occiput-C2 or C3 fusion with rods seems to be an excellent option with a high rate of success, avoiding the need for additional support.

Treatment strategies for severe C1C2 luxation due to congenital os odontoideum causing tetraplegia

PURPOSE

High-grade C1C2 luxation is a rare pathology. There is no clear evidence as to how to treat this deformity. There is only limited evidence about the different surgical techniques and possible approaches including advantages, disadvantages, and complications.

METHODS

This is an uncommon case of a 13-year-old child with progressive, tetraplegia due to congenital os odontoideum with translational instability between C1 and C2, and progressive luxation of C2. An irreducible dislocation of the C0/C1 complex caused significant compression at the cervicomedullary junction and neurologic deficit. In this paper we highlight the different types of os odontoideum, a review of existing evidence of surgical correction. We will discuss the different treatment strategies which could be applied and the current solution will be described.

RESULTS

Continuous skeletal traction and translational reduction was achieved by a specially designed halo traction system including continuous skeletal traction in a wheelchair for 6 weeks. The surgical treatment consisted of a posterior only release, translational reduction and posterior instrumentation from C0 to C4 with a Y plate and homologous bone graft. Neurological deficits started to improve during halo traction. After surgery the patient was ambulatory without any assistance and reached a Frankel stage E. Postoperative X-rays and CT scan revealed complete reduction at the C1/C2 level and a decompressed cervicomedullary junction.

CONCLUSION

Treatment of severe C1C2 luxation is difficult with limited evidence in the literature. The current case shows a successful treatment strategy to reduce the deformity and lists alternative approaches.

Pediatric cervical spine injuries: a comprehensive review

INTRODUCTION

Cervical spine injuries can be life-altering issues in the pediatric population. The aim of the present paper was to review this literature.

CONCLUSIONS

A comprehensive knowledge of the special anatomy and biomechanics of the spine of children is essential in diagnosis and treating issues related to spine injuries.

Os odontoideum with "free-floating" atlantal arch causing C1-2 anterolisthesis and retrolisthesis with cervicomedullary compression

BACKGROUND

Os odontoideum (OO) with C1-2 anterolisthesis and retrolisthesis may cause cervicomedullary injury both from anterior and posterior aspects. We analyzed fourteen such patients for biomechanical issues, radiological features and management of OO with free-floating atlantal arch and review pertinent literature.

MATERIALS AND METHODS

Fourteen patients having nonsyndromic, reducible atlantoaxial dislocation (AAD) with orthotopic OO were analyzed. During neck flexion, their C1 anterior arch-os complex displaced anteriorly relative to remnant odontoid-C2 body. The posteriorly directed hypoplastic remnant odontoid sliding below the atlas and forward translation of the C1 posterior arch caused concomitant cervicomedullary compression. During neck extension, there was retrolisthesis of the "free-floating" C1 arch-os complex into spinal canal. Spinal stenosis and lateral C1-2 facet dislocation; Klippel-Feil anomaly; and posterior circulation infarcts were also present in one patient each, respectively. Posterior C1-2 (n=10) or occipitocervical fusion (n=3) was performed in neutral position to stabilize atlantoaxial movements.

RESULTS

Follow-up (mean, 3.9 years) assessment revealed improvement in spasticity and weakness in 13 patients. One patient had neurological deterioration following C1-2 posterior sublaminar fusion, requiring its conversion to occipitocervical contoured rod fusion. One patient with posterior circulation stroke died prior to any operative intervention. Follow-up lateral view radiographs showed a bony union or a stable construct in these 13 patients.

CONCLUSIONS

OO with free-floating atlantal arch may precipitate cord injury both during neck flexion and extension. This condition may be overlooked unless lateral radiographs of craniovertebral junction are undertaken in neck extension, along with the usual ones in neutral and flexed positions. Etiological factors include C1 ring-OO unrestrained movements above the hypoplastic odontoid; upward pull on OO by alar and apical ligaments; lax C1-2 facet joint ligaments; and congenital presence of horizontal facet joint surfaces that facilitates C1-2 translation.

Cervical spine injuries in children: attention to radiographic differences and stability compared to those in the adult patient

The relative rarity of pediatric cervical spine injuries can impede rapid response and efficient care of this patient population. An understanding of the unique anatomical, radiographic, and biomechanical characteristics of the pediatric cervical spine is essential to the appropriate care of these challenging patients. Patterns of injury, diagnosis, and issues related to operative and nonoperative management are discussed with a focus on the developing spine. Our aim is to improve the understanding of traumatic cervical spine injuries in children for all practitioners involved with their care.

Endonasal endoscopic resection of an os odontoideum to decompress the cervicomedullary junction: a minimal access surgical technique

STUDY DESIGN

We report the case of a 50 year-old woman with os odontoideum and posterior atlantoaxial subluxation, who underwent an occipitocervical fusion followed by endonasal endoscopic anterior decompression of the cervicomedullary junction (CMJ).

OBJECTIVE

To describe the feasibility of performing endonasal endoscopic anterior decompression of CMJ pathology in conjunction with occipitocervical fusion in 1 operative setting.

SUMMARY OF BACKGROUND DATA

The recommended management of symptomatic atlantoaxial instability secondary to os odontoideum with irreducible ventral compression is occipitocervical fusion with anterior decompression. The traditional method for anterior decompression of CMJ abnormalities is the transoral approach. The endonasal endoscopic approach is an emerging minimal access technique that reduces the potential morbidity of the transoral approach.

METHODS

The patient underwent an occipitocervical fusion and anterior decompression in 1 operative setting. Occiput to C5 fusion was first undertaken in the prone position. After a wake-up test, the patient was flipped into a supine position for the endonasal endoscopic procedure. Anterior decompression was achieved by resecting the anterior arch of C1 and the os odontoideum with the aid of frameless stereotactic navigation.

RESULTS

The patient tolerated the procedure well and was extubated on the first postoperative day. Liquids were started that afternoon and advanced to a regular diet on the second postoperative day. The patient was discharged to rehabilitation after a short postoperative stay. Postoperative imaging demonstrated excellent decompression of the anterior CMJ pathology. At 3-month follow-up, the patient showed clear improvements in hand strength and ability to ambulate.

CONCLUSION

The endonasal endoscopic approach to the CMJ provides an effective and minimally invasive alternative for anterior decompression of irreducible CMJ pathology.

Os odontoideum: presentation, diagnosis, and treatment in a series of 78 patients

OBJECT

The most contentious issue in the management of os odontoideum surrounds the decision to attempt atlantoaxial fusion in patients with asymptomatic lesions. The authors examined the clinical presentation and outcome in patients with os odontoideum who underwent surgical stabilization, with an emphasis on 3 patients who initially received conservative treatment and suffered delayed neurological injury.

METHODS

Seventy-eight patients (mean age 20.5 years; median 15 years) were identified in a 17-year retrospective review. The median follow-up period was 14 months (range 1-115 months). Neck pain was the most common symptom (64%), and 56% of patients presented after traumatic injury. Eighteen patients had neurological signs or symptoms at presentation, and an additional 15 had a history of intermittent or prior neurological symptoms. Fifteen patients had undergone > or = 1 attempt at atlantoaxial fusion elsewhere.

RESULTS

Seventy-seven patients underwent posterior fusion and rigid screw fixation combined with a graft/wire construct: 75 had C1-2 fusion and 2 had occipitocervical fusion. One patient had an odontoid screw placed. Fusion was achieved in all patients at a median of 4.8 months (range 2-17 months). Approximately 90% of patients had resolution or improvement of their neck pain or neurological symptoms.

CONCLUSIONS

The authors believe that patients with os odontoideum are at risk for future spinal cord compromise. Forty-four percent of our patients had myelopathic symptoms at referral, and 3 had significant neurological deterioration when a known os odontoideum was left untreated. This risk of late neurological deterioration should be considered when counseling patients. Stabilization using internal screw fixation techniques resulted in 100% fusion, whereas 15% of patients had previously undergone unsuccessful wire and external bracing attempts.

Upper cervical ligament testing in a patient with os odontoideum presenting with headaches

STUDY DESIGN

Resident's case problem.

BACKGROUND

The role of premanipulative testing of the cervical spine is an area of controversy, and there are very few data to inform and guide practitioners on the use of ligamentous stability tests when assessing the upper cervical spine.

DIAGNOSIS

A 23-year-old female was referred to physical therapy by a neurologist for the management of intractable headaches of possible musculoskeletal origin. Her Neck Disability Index score was 54% and she rated her headache pain from 3/10 to 9/10 on a Numerical Pain Rating Scale. She reported a 2-year history of intermittent lower extremity paresthesias without a known mechanism or current symptoms. She was treated in physical therapy for 11 visits with improvements in cervical range of motion, strength, and intensity of her headaches, but noted no change in the frequency of headaches. She was subsequently referred to the primary author for a second opinion and potential manual therapy interventions. Initial neurological screening examination for upper and lower motor neuron lesions was unremarkable. Assessment of the transverse ligament, using the anterior shear test in supine, brought on paresthesias in both feet and her toes. The paresthesias continued after the cessation of the test. The Sharp-Purser test performed in sitting, immediately after the transverse ligament test, abolished the paresthesias. She was then referred back to her primary care physician for further evaluation. Subsequent radiographs and magnetic resonance imaging revealed that the patient had a C2-C3 Klippel-Feil congenital fusion and os odontoideum. The patient was examined by a neurosurgeon who concluded that she was not a surgical candidate. Her neurological symptoms completely resolved, but she continued to have headaches.

DISCUSSION

Os odontoideum is a clinically important condition, given that the mobile dens may render the transverse ligament incompetent, leading to atlantoaxial instability. Both the role and sequencing of upper cervical ligamentous testing is controversial. The results of this case report suggest that physical therapists should be cognizant of this condition and consider screening the upper cervical ligaments prior to manual or mechanical interventions to this region.

LEVEL OF EVIDENCE

Differential diagnosis, level 4.

Os odontoideum: report of three cases

Os odontoideum is a condition in which a smoothly corticated ossicle exists dorsal to the anterior arch of C1, taking the place of the rostral dens, but with no bony connection to the body of the axis. Three patients presented with this condition: the first with Lhermitte's phenomenon 10 years after significant trauma, the second as an incidental finding during routine cervical spine imaging following a road traffic accident, and the third with recurrent transient quadriparesis precipitated by falls from a surfboard. Patients had at least 10 mm of sagittal instability on dynamic imaging and the second patient had a minimum sagittal canal diameter of only 11.5 mm. Posterior atlanto-axial fixation was successfully achieved in all cases using polyaxial screws and rods with the assistance of computed tomography-based image guidance. Image guidance provided an invaluable aid to preoperative planning and intraoperative placement of the posterior spinal instrumentation.

Posterior atlantoaxial subluxation due to os odontoideum combined with cervical spondylotic myelopathy: a case report

In patients with os odontoideum and posterior atlantoaxial subluxation are extremely rare. No reports have described posterior atlantoaxial subluxation associated with os odontoideum combined with cervical spondylotic canal stenosis, both of which require surgical treatment. We report one case of a 75-year-old female who underwent arthrodesis between the occiput and C3 using a hook-and-rod system and also a double-door laminoplasty from levels C3 to C7. The claw mechanism was applied between the C2 lamina and the C3 inferior articular process. The posterior atlantoaxial subluxation was completely reduced by the method that the rod gradually pushed the posterior arch of C1 anteriorly during connection to the occiput. Twelve months after surgery, the patient showed improvement in preoperative clumsiness and gait disturbance, and the latest plain radiographs showed solid osseous fusion, with no loss of correction or instrumentation failure.

C1-C2 posterior fusion in growing patients: long-term follow-up

STUDY DESIGN

A retrospective review of patients undergoing C1-C2 posterior fusion during childhood was undertaken.

OBJECTIVES

The aim of this study was to investigate the change in the sagittal curvature of the cervical spine in children after C1-C2 posterior fusion.

SUMMARY OF BACKGROUND DATA

There have been only a few reports on postoperative changes in the sagittal curvature of the cervical spine after C1-C2 posterior fusion in children. However, they have all described the onset of sagittal postoperative cervical deformities.

METHODS

Between January 1977 and December 1992, a total of 12 children underwent C1-C2 posterior fusion for atlantoaxial instability resulting from congenital malformation in eight, juvenile rheumatoid arthritis in one, and rotatory subluxation in three. The average age at the time of surgery was 10.9 years (range 7-12 years). All children underwent a similar treatment program with gradual preoperative reduction in halo cast, followed by C1-C2 posterior fusion with Mersilene loops in two cases, wiring in eight (Gallie's or Brooks' techniques), and interlaminar clamps in the remaining two. The halo cast made it possible to avoid a hyperextended or hyperflexed C1-C2 position while performing the atlantoaxial fusion, thus ensuring a more anatomic position during C1-C2 fusion. In the postoperative period, the halo cast was maintained for 7 to 9 weeks. RESULTS Follow-up ranged from 7 years to 13 years. Preoperative alignment of the cervical spine was classified into two groups: lordosis (eight patients) and straight (four patients). Postoperative subaxial malalignment (kyphosis) occurred in four cases (33%): these patients showed evidence of spontaneous and gradual sagittal improvement and presented either a straight (two cases) or a lordotic (two cases) cervical spine at follow-up. Immediately after surgery, the cervical spine was normally aligned in the remaining eight patients (lordosis and straight alignment in six and two cases, respectively) and was unchanged at follow-up. At follow-up, none of the 12 patients had a cervical deformity on sagittal plane.

CONCLUSION

In children, a spontaneous realignment of the subaxial kyphosis observed after C1-C2 posterior fusion can be noted at follow-up, when a postoperative deformity occurs (33% in the present series). According to the present findings, it is not always mandatory to perform occipitocervical fusion in children with atlantoaxial instability just to prevent subaxial deformity in the cervical spine.

Os odontoideum

DIAGNOSIS

STANDARDS

There is insufficient evidence to support diagnostic standards.

GUIDELINES

There is insufficient evidence to support diagnostic guidelines.

OPTIONS

Plain x-rays of the cervical spine (anteroposterior, open-mouth odontoid, and lateral) and plain dynamic lateral x-rays performed in flexion and extension are recommended. Tomography (computed or plain) and/or magnetic resonance imaging of the craniocervical junction may be considered.

MANAGEMENT

STANDARDS

There is insufficient evidence to support treatment standards.

GUIDELINES

There is insufficient evidence to support treatment guidelines.

OPTIONS

Patients with os odontoideum, either with or without C1--C2 instability, who have neither symptoms nor neurological signs may be managed with clinical and radiographic surveillance. Patients with os odontoideum, particularly with neurological symptoms and/or signs, and C1--C2 instability may be managed with posterior C1--C2 internal fixation and fusion. Postoperative halo immobilization as an adjunct to posterior internal fixation and fusion is recommended unless successful C1--C2 transarticular screw fixation and fusion can be accomplished. Occipitocervical fusion with or without C1 laminectomy may be considered in patients with os odontoideum who have irreducible cervicomedullary compression and/or evidence of associated occipitoatlantal instability. Transoral decompression may be considered in patients with os odontoideum who have irreducible ventral cervicomedullary compression.

Retro-dental reactive lesions related to development of myelopathy in patients with atlantoaxial instability secondary to Os odontoideum

STUDY DESIGN

A retrospective analysis of 13 patients with atlantoaxial instability secondary to Os odontoideum who underwent posterior atlantoaxial fusion.

OBJECTIVE

To assess the relationships between the development of myelopathy and plain radiographic parameters in patients with atlantoaxial instability secondary to Os odontoideum and to determine whether the pathologic structures, which compress the spinal cord, are visualized using magnetic resonance imaging.

SUMMARY OF BACKGROUND DATA

The development of myelopathy, which is the most serious complication associated with Os odontoideum, was thought to be related to either the degree of instability or direction of instability, or a decrease in the space available for the cord. However, such indirect radiographic parameters measured using plain radiographs cannot provide direct information concerning the causes of myelopathy in patients with atlantoaxial instability secondary to Os odontoideum.

METHODS

Thirteen patients who underwent posterior atlantoaxial fusion for clinical symptoms due to Os odontoideum were classified into two groups depending on whether they had (n = 9) or did not have (n = 4) myelopathy. Four radiographic parameters were measured using flexion and extension lateral radiographs; the degree of instability, the direction of instability, and the space available for the cord in flexion and extension. MRI was performed on all patients in the myelopathy group. The radiologic and clinical data were compared for the two groups.

RESULTS

There were no significant statistical differences in the degree of instability (6.83 vs. 7.38, P = 0.816), space available for the cord in flexion (6.94 vs. 7.13, P = 0.938), and space available for cord in extension (7.56 vs. 5.75, P = 0.434) between the two groups. There was a poor agreement between the direction of instability and the development of myelopathy (kappa = 0.268, P = 0.308). Magnetic resonance imaging did demonstrate, however, cord compression caused by retro-dental reactive lesions in the myelopathy; cystic masses were present in two patients; and fibrocartilaginous masses were present in seven.

CONCLUSION

The current study suggests that the value of plain radiographic parameters should be reevaluated as a means of evaluating myelopathy in patients with atlantoaxial instability secondary to Os odontoideum, and that retro-dental reactive lesions should be considered as the potential cause of myelopathy.

Os odontoideum: etiology, diagnosis, and management

BACKGROUND

There have been few reports of os odontoideum since the initial description.

METHODS

Forty-four patients with os odontoideum treated during the period 1980 through 1996 were reviewed. There were 33 males and 11 females. Their ages ranged from 7 to 56 years, with an average of 24.6 years. Five patients with no symptoms were treated conservatively. Thirty-nine patients underwent operative treatment including nine posterior atlantoaxial fusions and 33 occipitocervical fusions.

RESULTS

The patients were followed up for one to 16 years, with an average of 6.5 years. Five patients treated conservatively have remained stable. All 39 treated patients achieved solid arthrodesis. The results were satisfactory.

CONCLUSIONS

We conclude that fusion is indicated if atlantoaxial instability or clinical symptoms are significant, and that occipitocervical fusion should be considered in the operative management of os odontoideum if atlantoaxial arthrodesis is impossible.

Complete reduction of retro-odontoid soft tissue mass in os odontoideum following the posterior C1-C2 tranarticular screw fixation

STUDY DESIGN

A case report of os odontoideum with retro-odontoid soft tissue hypertrophy treated by the transarticular screw fixation.

OBJECTIVES

To present a case of os odontoideum that showed complete reduction of retro-odontoid soft tissue mass caused by atlantoaxial subluxation after the C1-C2 transarticular screw fixation.

SUMMARY OF BACKGROUND DATA

Hypertrophy of the periodontoid soft tissue has been reported to be associated with chronic atlantoaxial subluxation and progressive myelopathy. While the rheumatoid pannus has been reported to become reduced of disappear after fixation of the unstable segment, the reduction of the hypertrophied soft tissue mass has never been reported in atlantoaxial subluxation of nonrheumatoid origin, especially in the case of os odontoideum.

METHODS

Posterior C1-C2 transarticular screw fixation was performed in a patient with os odontoideum, who showed signs of progressive myelopathy by the compression of retro-odontoid soft tissue mass and atlantoaxial subluxation.

RESULTS

The fixation of atlantoaxial subluxation achieved not only the complete reduction of the retro-odontoid soft tissue mass, but also clinical improvement of the myelopathy.

CONCLUSIONS

Posterior atlantoaxial fixation is worth trying in slow progressing myelopathy by the compression of hypertrophy of the soft tissue even in nonrheumatoid atlantoaxial subluxation, thereby obviating the need for direct removal of the mass via the transoral route.

Radiographic classification of Os odontoideum and its clinical significance

STUDY DESIGN

This study analyzed the relationship between the configuration of the atlantoaxial joint and the clinical characteristics of patients with os odontoideum.

OBJECTIVES

To compare three types of atlantoaxial configurations of os odontoideum from the viewpoint of clinical characteristics.

METHODS

Twelve patients were classified into the following three types according to their atlantoaxial configuration on an anteroposterior radiogram: round (n = 6), cone (n = 4), and blunt-tooth (n = 2). Clinical features in each group were compared in terms of mean age, gender distribution, severity and type of myelopathy, and degenerative findings of the atlantoaxial joint.

RESULTS

The patients in the round type group were predominantly women and had more severe myelopathy than that of patients in the other groups. According to Crandall's classification of myelopathy, all patients showed the transverse lesion syndrome in the cone and blunt-tooth types. Four of six patients with the round type of atlantoaxial configuration had the Brown-Séquard syndrome. With the round type, it appeared that the lateral mass of the axis tended to dislocate laterally, and this lateral instability associated with anteroposterior instability was believed to induced the Brown-Séquard syndrome.

CONCLUSIONS

Myelopathy in patients in the round type group was the most severe compared with that of patients in the other three groups. This classification is considered useful for estimating clinical findings in os odontoideum.

Os odontoideum. A case report of one identical twin

STUDY DESIGN

This case report identifies one identical twin with an os odontoideum after trauma and the other twin with a normal cervical spine and no history of trauma.

OBJECTIVES

To highlight the etiology of os odontoideum as posttraumatic as opposed to congenital in nature.

SUMMARY OF BACKGROUND

The etiology of os odontoideum has been debated since its original description by Giacomini in 1886. Although proponents of the congenital origin are supported by association with various congenital anomalies, including Down's syndrome, Klippel-Feil syndrome, and multiple epiphyseal dysplasia, the majority of reports suggest a posttraumatic etiology.

METHODS

We reviewed the cervical radiographs of an identical twin with transient paresis and significant trauma to her neck as a child after a motor vehicle accident. The radiographs were compared with those of her twin sister, who had no history of trauma.

RESULTS

Os odontoideum was identified in one identical twin with a history of trauma. She was treated with a posterior C1-C2 arthrodesis using the Magerel transarticular screw technique supplemented by a modified Gallie's wiring. At a 12-month follow-up, she was asymptomatic and had a solid fusion based on flexion and extension views.

CONCLUSIONS

This case report of an os odontoideum occurring in one identical twin after a traumatic injury supports the possibility of a posttraumatic, as opposed to congenital, theory of origin.

The cervical spine in the Klippel-Feil syndrome. A report of 57 cases

We report 57 cases of the Klippel-Feil syndrome. Five had type I congenital cervical fusion, 48 type II and 4 type III. The symptoms and signs varied considerably. Patients with C2-C3 fusion often had symptoms associated with odontoid dysplasia and occipito-cervical instability. Twenty-one had progressive neurological symptoms and 19 were operated on: 3 had occiput-C3 posterior arthrodeses, 2 a single level fusion, 1 a laminectomy and anterior arthrodesis, and 13 had laminoplasties. Degenerative changes at the unfused segment and a narrow bony canal are high risk factors in the development of neurological compromise.

Unusual mechanism of lethal cervical spinal cord injury in a case of atlanto-axial diastasis

A case of traumatic cervical spinal cord injury due to congenital craniocervical abnormalities is described. The autopsy revealed evidence of hyperextension of the neck due to frontal impact, congenital occipitalization of the atlas accompanied by basilar invagination of the odontoid process and atlanto-axial diastasis. The subsequent narrowing of the spinal canal led to a predisposition for this unusual mechanism of spinal cord injury.