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PubMed2001

Screw placement in transoral atlantoaxial plate systems: an anatomical study.

OBJECT: The placement of an anterior atlantoaxial plate after transoral odontoid resection has been described by Harms. Recently, the authors of biomechanical and clinical studies have shown that this procedure, especially in combination with posterior wiring, is a good alternative to established, isolated posterior atlantoaxial fixation techniques. Reports on the anatomy of the atlas and axis primarily focus on the posterior surgical approach. Scarce research regarding the quantitative anatomy of the anterior aspect of C-1 and C-2 has been reported. This study was undertaken to measure relevant dimensions of C-1 and C-2 and their relation to the anterior transoral approach. The aim of the study was to determine "safe zones" for screw placement in anterior atlantoaxial plate fixation. METHOD: Fifty human dry C-1 and C-2 vertebrae were obtained for direct anatomical, radiographic, and computerized tomography (CT) measurements. Thirty-two linear and four angular parameters were evaluated. All measurements were made using a digital caliper, ruler, or goniometer. Anatomical measurements were correlated with radiographic (anteroposterior, lateral, and craniocaudal) and CT (0.5-mm-slice thickness) measurements of the corresponding vertebrae. Additionally, bone mineral density (BMD) measurements of C-1 and C-2 were obtained in 20 patients. A safe zone for anterior screw placement in an atlas of bilateral trapezoid shape could be characterized. The average medial and lateral height of the trapezoid was 4.1 +/- 1.01 mm (range 1.4-6.7 mm) and 12.9 +/- 1.73 mm (range 8.7-17.4 mm), respectively. The distance between the sagittal plane and the medial and lateral walls of the trapezoid was 10.2 +/- 1.42 mm (range 8.9-12.8 mm) and 23.5 +/- 2.98 mm (range 21.7-30.7 mm), respectively. The average depth of the lateral masses was 22.3 +/- 2.04 mm (range 17.0-26.7 mm) in the sagittal plane. The average BMD in the safe zone of C-1 was 0.89 +/- 0.11 g/cm3 (range 0.75-1.01 g/cm3). Bone mineral density measurements at C-2 revealed a spheroid zone of low density at the basis of the dens (0.68 +/- 0.09 g/cm3). In contrast, high zones of BMD were found near the articular surfaces (C1-2: 0.97 +/- 0.11 g/cm3; C2-3: 0.94 +/- 0.12 g/cm3). The safe zone for anterior axis screw placement was V-shaped, limited cranially by a zone of low bone density and laterally by the vertebral artery groove. Correlations between radiographic and anatomical measurements were generally good (r2 = 0.78-0.95), but they were higher between CT and anatomical measurements (r2 = 0.86-0.99). CONCLUSIONS: A quantitative understanding of the anterior anatomy of C-1 and C-2 is necessary when considering anterior atlantoaxial plate fixation after transoral odontoid resection. In this study the authors defined safe zones for anterior atlas and axis screw placement. The anterior atlantoaxial plate, as originally described by Harms, only partially respects these safe zones.

Adult↗

PubMed1994

Craniovertebral junction: normal anatomy, craniometry, and congenital anomalies.

The craniovertebral junction (CVJ) comprises the occiput, atlas, and axis and is visible in most magnetic resonance (MR) imaging studies of the brain. Craniometric measurements used in radiologic assessment of CVJ anomalies include the Chamberlain line, Wackenheim clivus baseline, Welcher basal angle, and atlantooccipital joint axis angle. Most anomalies of the occiput are associated with decreased skull base height and basilar invagination, the latter being a primary developmental anomaly in which the vertebral column is abnormally high and prolapsed into the skull base. Occiput anomalies include condylus tertius, condylar hypoplasia, basiocciput hypoplasia, and atlanto-occipital assimilation. Most atlas anomalies produce no abnormal CVJ relationships and are not associated with basilar invagination. These anomalies include aplasias, hypoplasias, and clefts of the atlas arches and "split atlas" (ie, posterior arch rachischisis associated with anterior arch rachischisis). Except for fusion anomalies, abnormalities of the axis are primarily confined to the odontoid process and are not associated with basilar invagination. These anomalies include persistent ossiculum terminale, odontoid aplasia, and os odontoideum. With the widespread availability of MR imaging, which is well suited for evaluating the CVJ because of its direct sagittal imaging capabilities, renewed understanding of CVJ anatomy and anomalies is important for all radiologists.

Adolescent↗

PubMed2004

Chiari I malformation associated with ventral compression and instability: one-stage posterior decompression and fusion with a new instrumentation technique.

OBJECTIVE AND IMPORTANCE: We describe an alternative surgical technique for treatment of Chiari I malformation associated with ventral compression and instability of the region. An expansive suboccipital cranioplasty and a rigid occipitocervical fixation are performed in one stage. METHODS: The occipitocervical fixation is performed by use of metal rods fixed on the cranial side by screws inserted into the diploic layer of occipital bone and on the caudal side by screws inserted into the pedicle of the axis or in a transarticular fashion into the lateral masses of axis and atlas vertebra. A large piece of autologous bone is placed in the region between the rostral edge of cranial decompression and the axis, with the aim of achieving both expansive suboccipital cranioplasty and occipitocervical fusion. RESULTS: We performed this procedure in two patients with Chiari I malformation associated with basilar invagination and occipitalization of the atlas. Postoperatively, decompression of the brainstem and restoration of normal cerebrospinal fluid flow at the craniovertebral junction were confirmed radiologically, and the patients were relieved of their symptoms. At 1 and 3 years of follow-up, respectively, solid bone fusion was observed between the occipital bone and axis in both patients. CONCLUSION: Simultaneous posterior decompression and occipitocervical fixation with an alternative instrumentation technique is discussed. The procedure can be performed regardless of the size of suboccipital craniectomy. Screw insertion into the diploic layer of the occipital bone has not been described previously.

Adult↗

PubMed1999

Trivial injuries, associated congenital anomaly and medicolegal interpretation of death.

Congenital hypoplasia of the odontoid process is a relatively rare phenomenon. A case is presented of a 12-year-old girl who was admitted to hospital with a history of having sustained trivial external injuries when falling after an alleged push. Later, she developed signs of compression of the spinal cord in the cervical region, resulting in quadriplegia and muscle wasting. A laminectomy was performed to relieve the symptoms but the child died 2 1/2 months later. Autopsy revealed a congenital anomaly of the atlas and axis vertebrae in the form of hypoplasia of the dens. The case being associated with a criminal assault, the post-mortem analysis and autopsy were significant in resolving medicolegal issues pertaining to the assailant, the operating surgeon and the law-enforcement agencies.

Adolescent↗

PubMed2002

Posterior atlantoaxial fixation: biomechanical in vitro comparison of six different techniques.

STUDY DESIGN: Six different techniques for atlantoaxial fixation were biomechanically compared in vitro by nondestructive testing. OBJECTIVE: To evaluate the immediate three-dimensional stability of a new atlas claw combined with transarticular screws and alternative techniques for transarticular screw fixation in comparison with established techniques. SUMMARY OF BACKGROUND DATA: Posterior transarticular screw fixation in combination with wire-bone graft constructs is frequently used for C1-C2 fixation. Sublaminar wire passage carries the potential risk of neurologic complication. Transarticular screw fixation is technically demanding and, for anatomic reasons, not always feasible. METHODS: Six human cervical specimens were loaded nondestructively with pure moments, and unconstrained motion at C1-C2 was measured. The six specimens were instrumented with each of the following fixation techniques: Gallie fixation, transarticular screws and Gallie fixation, transarticular screws, transarticular screws and a new atlas claw, isthmic screws in the axis and the atlas claw, and lateral mass screws in the atlas and isthmic screws in the axis connected with rods. RESULTS: The transarticular screws restricted lateral bending and axial rotation best. The three-point fixations (transarticular + Gallie and transarticular + claw) additionally restricted flexion-extension, with lowest values for transarticular screws and the atlas claw. The alternative techniques were not as stable as the three-point fixations, but more stable than the Gallie fixation. CONCLUSIONS: Biomechanically, the three-point fixation with transarticular screws and the atlas claw provides a rigid internal fixation that is not dependent on bone graft and sublaminar wiring. In cases wherein transarticular screws are not feasible, the isthmic screws and claw or the lateral mass screws and isthmic screws are biomechanical alternatives with less immediate stability.

Aged↗

PubMed2004

Vertebral malformation, syringomyelia, and ventricular septal defect in a dromedary camel (Camelius dromedarius).

An occipitoatlantoaxial malformation and ventricular septal defect (VSD) were diagnosed in a 36-hour-old female camel. Physical examination revealed a firm protrusion of the dorsal aspect of the atlas and axis, tilting of the head to the left, and a grade V/VI systolic murmur. Neurological examination revealed proprioceptive deficits and ataxia of all 4 limbs. Radiographic examination and necropsy demonstrated malformation, fusion of the atlas to the occiput and hypoplasia of the dens of the axis, and subluxation of the atlantoaxial joint. Dorsoventral laxity of the atlantoaxial joint was also present, with compression of the cervical spinal cord. A 1.5-cm-diameter VSD was observed also. Histopathologic examination of the cervical spinal cord revealed a cavity extending from the level of the first to fourth cervical segment, dorsal to the central canal, 5 cm long and 1-2 mm in diameter. The cells around the cavity were positive for glial fibrillary acidic protein and sporadically positive for vimentin. This cavitary structure was consistent with syringomyelia, which was lined by glial cells, surrounded by edematous white matter with Wallerian-like degeneration and with neuronal necrosis in the adjacent dorsal horns.

Animals↗

PubMed1986

[Forms of fracture of the dens axis in the application of ventral flexion force].

In fracture experiments in 220 cast models of the axis and atlas, an attempt was made to separate two different factors influencing the position of the dens fracture (superior and inferior type): the direction of the force application and the inclination of the dens axis. For this purpose, two extreme forms of dens inclination in the sagittal plane were used, namely a form with a ventrally inclined axis (kyphotic form) and a dorsally oriented axis (lordotic form). The force was applied in ventral flexion in 11 single steps between 10 and 75 degrees. The fracture types occurring under natural conditions could be reproduced with this experimental paradigm. Depending on the direction of the force application, both types of dens fracture occurred in ventral flexing traction alone. Independent of the inclination of the dens axis, this ventral flexion led to an inferior fracture type with a shallow angle, and a superior fraction type with a steep angle. With 75 degrees flexion, no longer the dens fracture, but the Hangman's fracture was the usual fracture type in both dens forms. With fundamental agreement of both dens forms with regard to the direction-dependent genesis of the fracture pattern, the lordotic dens and kyphotic dens displayed differences in the details which are discussed exhaustively. In this connection, the differences in the size of the horizontal thrust component due to the primary form of the dens with the same direction of force application is pointed out. According to the present investigations, a classification of dens fractures should be made more precise by specification of the dens form.

Axis, Cervical Vertebra↗

PubMed1994

Transverse atlantal ligament disruption associated with odontoid fractures.

OBJECTIVES: The authors evaluated transverse atlantal ligament integrity in patients with fractures of the odontoid process of the axis. SUMMARY OF BACKGROUND DATA: Injuries of the transverse atlantal ligament can result in atlantoaxial instability after fractures of the atlas or axis, even if osseous healing occurs. METHODS: The clinical histories and follow-up examinations and radiographic data of 30 patients with odontoid fractures were reviewed, using a combination of magnetic resonance (MR) imaging, thin-cut computed tomography (CT), and plain radiographs to evaluate osseous and ligamentous injuries. RESULTS AND CONCLUSIONS: Osteoperiosteal ligamentous avulsion injuries were identified on MR imaging in three patients and were associated with acute and delayed instability and nonunion. The combination of MR imaging, CT, and plain radiographs is useful in evaluating unstable odontoid fractures to facilitate rational treatment planning. Odontoid fractures with transverse ligament injuries should be considered for early surgical stabilization because this combination of injuries is unlikely to heal nonoperatively. Anterior odontoid screw fixation should be avoided when the ligament is injured.

Adolescent↗

PubMed1979

Unilateral lateral mass compression fractures of the axis.

Lateral mass compression fractures of the axis involve compression of the pedicle and displacement of the overlying facet, with or without an accompanying fracture of the odontoid. These unilateral fractures are not rare. Correlation is made between clinical cases and cadaver material with analysis of microradiographs. Criteria for recognition of the resultant healed fracture deformity include: (1) Tilting of the odontoid; (2) Loss of the odontoid shoulder on the affected side; (3) Increased downward slope of the affected facet; (4) Lateral compression, possibly with buckling; (5) Asymmetrical apophyseal joints between axis and atlas; and (6) Tilting downward of occiput on affected side, often with evidence of rotation between the occiput and the axis. Not all criteria need be present. Clinical sequelae often include persistent neck pain, limited rotation of the head, and occipital headaches radiating anteriorly.

Adult↗

PubMed1997

Natural history of upper cervical lesions in rheumatoid arthritis.

The natural history of the upper cervical lesions in rheumatoid arthritis (RA) was investigated, based on a follow-up study of 79 patients. At the beginning of this study, anterior atlantoaxial subluxation (AAS) was found in 35 patients, AAS combined with vertical subluxation (VS) in 34, and VS alone in 10. During the follow-up period (mean, 6.4 years), these lesions deteriorated in 30 of the 79 patients. To evaluate the occipitoatlantoaxial relation, the angles between occiput and atlas (C0/C1 angle) and between atlas and axis (C1/C2 angle) were measured, and the correlation between these angles and deterioration of the lesions was investigated. The severity of RA was classified according to the "disease subset" advocated by one of us (T.O.): the least erosive subset (LES), the more erosive subset (MES), and the mutilating subset (MUD). There was a significant positive correlation between the C1/C2 angle and atlantodental interval (ADI) and a significant negative correlation between the C0/C1 angle and the ADI. This indicates that the atlas not only shifts forward but also slips down and forward at an incline from the axis. With an increase of the atlantal inclination, the anterior arch of atlas displaces in an anteroinferior direction, and VS combines with AAS. The development of associated VS lessens the amount of the ADI. At the advanced stage of the natural course, AAS is concealed, and VS alone is demonstrated. We concluded that the upper cervical lesion deteriorated in the order of AAS, AAS + VS, and VS alone. In patients classified as the LES subset, only AAS was found, and VS was never combined with AAS at the terminal stage. In patients in the MES, VS frequently combined with AAS. All patients who deteriorated to VS alone were ranked as MUD.

Adult↗

PubMedDate not supplied

Craniovertebral junction tuberculosis: a review of 29 cases.

PURPOSE: The purpose of this work was to describe the various imaging findings in craniovertebral tuberculosis and the importance of imaging in treatment in these patients. METHOD: A retrospective review of MR and CT scans in 29 patients with craniovertebral tuberculosis was performed. The images were reviewed, paying special attention to both bony (skull base, atlas, and axis) and soft tissue involvement in addition to atlantoaxial dislocation, lateral subluxation of the dens, and compression of the spinal cord. RESULTS: Suboccipital pain with neck stiffness was the most common presenting symptom in our patients. The skull was involved in 19 of the 29 cases, clivus involvement was seen in 11 patients, and occipital condyle involvement was present in 14 patients. Detailed analysis of atlas involvement due to tuberculosis showed the lateral masses to be predominantly affected. The dens was involved in 18 cases (62%). Soft tissue masses in the prevertebral area were seen in 22 patients, paravertebral in 27 patients, and epidural involvement in 25 patients was identified. Atlantoaxial displacement was present in seven cases, lateral mass-dens subluxation in five, and superior subluxation of the dens through the foramen magnum compressing the medulla was seen in two cases. Spinal cord compression with intrinsic cord changes was noted in 12 cases. All patients received multidrug antituberculous therapy for 1 year. The presence of neurologic deficit and instability of the atlantoaxial complex was pivotal in further management in these patients. CONCLUSION: A high degree of clinical suspicion is necessary when confronted with patients with neck stiffness and tenderness over the upper cervical vertebrae. MRI in these patients provides a sensitive method for the diagnosis of craniovertebral tuberculosis.

Abscess↗

PubMed1992

[Congenital malformation of the skeleton in Weiser-Maples guinea pigs].

Some abnormalities were observed in the occipital bone, cervical vertebrae and thoracic vertebrae of Weiser-Maples guinea pigs. In the occipital bone, the medial basilar impression was suggested to occur in 40 (32.8%) out of 122 animals. The basilar impression was classified into right, left and both side types and observed in 24, 11 and 5 animals, respectively. The basilar impression was known to be accompanied in human with some anomalies such as platybasia, Klippel-Feil syndrome, deformation of foramen magnum and so-on. These anomalies were also observed in guinea pigs. The fusion of the axis with the 3rd cervical vertebra was observed in 12 (10.5%) out of 114 animals. The deformation was sometimes observed in the temporal, interparietal, atlas and axis as well as the occipital bone. The fusion of the 7th cervical vertebra with the 1st thoracic vertebra was found in 46 (51.7%) out of 89 animals. This fusion was thought to have no relation with the basilar impression. Weiser-Maples guinea pigs are now in 19 generations of sibmating. Because these abnormalities as mentioned above are all thought to be inherited, the selective breeding will make Weiser-Maples guinea pigs suitable for the study of the basilar impression.

Animals↗

PubMed1999

OP-1 for cervical spine fusion: bridging bone in only 1 of 4 rheumatoid patients but prednisolone did not inhibit bone induction in rats.

We used OP-1 (also called BMP-7) on a collagen type-1 carrier in atlanto-axial posterior fusions to promote bony healing after wire fixation. 4 patients who had instability between the atlas and axis due to rheumatoid disease received the implants. The patients were examined with conventional radiography postoperatively at 2, 6 and 10 months. In 3 patients, no new bone formation was detectable. In 1 patient, new bone bridged the fusion site at 6 months. 3 patients were on chronic steroid treatment, including the patient in whom bone formation was detected. To determine whether steroid treatment could be responsible for the low rate of bone induction, 24 rats each received OP-1 implants in an abdominal muscle pouch. They were divided into 3 groups receiving saline, 0.1 or 1.0 mg/kg BW of prednisolone daily until they were killed 3 weeks postoperatively. Specimens were decalcified for histology and the amount of calcium in the decalcifying solution was measured. All groups showed ossicles induced by OP-1, and no effect of prednisolone was detected. Thus the failures in the patients may have causes other than prednisolone treatment.

Animals↗

PubMedDate not supplied

Laminotomy of the axis for surgical access to the cervical spinal cord. A case report.

A cranially hinged laminotomy of vertebra C2 was used to expose the cervical spinal cord of a dog with a meningioma in the region of the atlantoaxial articulation. By preserving the dorsal atlantoaxial ligament, the technique seemed to result in greater and more physiologic stability between the atlas and axis than dorsal laminectomy and prosthetic replacement of the dorsal atlantoaxial ligament. The procedure allowed a dorsal approach, avoiding injury to the vertebral arteries and limited exposure, which are potential problems with hemilaminectomy of C1-C2. Further investigation is needed to evaluate long-term consequences of this procedure.

Animals↗

PubMed1978

Atlanto-axial fusion for instability.

The problem of how best to treat a patient with instability of the atlanto-axial complex is still somewhat controversial. In this follow-up study of fifty-nine patients, nineteen were treated by a plaster jacket and brace; eleven, by single midline wiring and onlay bone grafts; and thirty, by four circumferential wires around the posterior elements of the axis and atlas with two bone grafts wedged between these elements on each side according to the method described by Brooks and Jenkins. (One patient had both types of fusion.) Although direct comparison of the results of treatment in three groups was not possible because of the many variables that may have influenced the results, the incidence of solid fusion was distinctly higher after the Brooks fusions despite less postoperative immobilization.

Adolescent↗

PubMed1996

[A case of atlanto-axial rotatory fixation associated with Jefferson's fracture].

The authors present a case of atlanto-axial rotatory fixation associated with Jefferson's fracture. A 52-year-old man was admitted to our hospital complaining of severe neck pain and torticollis after a traffic accident. Cervical x-ray films showed fracture of the atlas. CT scans demonstrated traumatic subarachnoid hemorrhage and atlanto-axial rotatory fixation. The patient was managed with skull traction and reposition was achieved. Although he was maintained in a halo device for 4 months, rotary fixation recurred. He underwent posterior fusion between the atlas and axis. We review the literature and discuss the diagnostic problems and methods of treatment for atlanto-axial rotatory fixation.

Atlanto-Axial Joint↗

PubMed1981

Atlantoaxial instability in Marfan's syndrome. Diagnosis and treatment. A case report.

A case of Marfan's syndrome is described in which progressive neurological signs and symptoms were produced by flexion of the head. Radiological examinations revealed hypermotility between the atlas and axis, as well as compression of the medulla oblongata by the odontoid process on flexion, since low positioned cerebellar tonsils prevented dorsal shift of the oblongata. The signs and symptoms disappeared after occipitocervical internal transfixation.

Adult↗

PubMed2002

Atlantoaxial instability in a white-tailed deer fawn (Odocoileus virginianus).

On 14 March 2001, an 8 mo old, male white-tailed deer (Odocoileus virginianus) was found in lateral recumbency exhibiting neurologic signs including inability to rise, opisthotonus, paddling, and respiratory distress. There was evidence of minor cranial trauma. Postmortem examination revealed atlantoaxial instability with ventral deviation of the axis due to malformation of the caudal atlas and cranial axis. Given the age of the fawn, the instability was assumed to be congenital with minor trauma inducing severe, acute neurologic signs.

Animals↗