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PubMed1995

Computed tomographic evaluation of the normal adult odontoid. Implications for internal fixation.

STUDY DESIGN: Computed tomography scans of the dens were performed on patients who had no atlantoaxial pathology. OBJECTIVES: To determine whether one or two screws is optimal for fracture fixation and whether two screws can always negotiate the intramedullary odontoid cavity. SUMMARY OF BACKGROUND DATA: Fixation of Type II dens fractures traditionally has used C1-C2 posterior wiring and fusion. Two screws placed across an odontoid fracture as a method of rigid internal fixation also has been described. However, it is not known whether two screws can always negotiate the odontoid canal. METHODS: Ninety-two consecutive computerized tomography scans of the dens were performed on adults who had no atlantoaxial pathology. Measurements were taken from the scan and compared with the cross-sectional diameter of two odontoid screws. RESULTS: The critical diameter for the placement of two 3.5-mm cortical screws with tapping was 9.0 mm. This dimension was present in 95% of the patients studied. CONCLUSIONS: Correct orientation of the computerized tomography scanner is critical for accurate measurements. Two 3.5-mm screws can be used in internal fixation of Type II dens fractures in 95% of the patients if the inner cortex is tapped.

Adolescent↗
PubMed1995

Anterior screw fixation of type II odontoid fractures. A biomechanical study.

STUDY DESIGN: This study examined the torsional and shear stiffness of Type II odontoid fractures that were stabilized with two 3.5-mm cannulated AO screws or a single 4.5-mm cannulated Herbert screw. OBJECTIVE: To determine the stability of a commonly used two-screw method versus a single-screw fixation method. Insertion of a single screw could make the procedure technically easier. SUMMARY OF BACKGROUND DATA: Biomechanical studies have shown the 4.5-mm Herbert screw to generate greater compressive forces than 3.5-mm cannulated screws, which are commonly used to anteriorly stabilize Type II odontoid fractures. No previous biomechanical studies have compared the shear or torsional stiffness of Type II odontoid fractures stabilized with these screws. METHODS: Twelve cadaver C2 vertebrae were harvested and an osteotomy was performed to simulate a Type II fracture pattern. Six were stabilized with two 3.5-mm cannulated screws, and the remaining were stabilized with a single 4.5-mm cannulated Herbert screw. Each specimen then was tested in torsion through +/- 0.75 degrees, +/- 1.25 degrees, and +/- 1.75 degrees for 10 cycles each. Shear forces then were applied from an anterior to posterior direction to a maximum load of 44.48 N. RESULTS: The mean torsional stiffness for the Herbert screw was 1196 N.m/deg, which was significantly greater than the mean stiffness of the 3.5-mm screw fixation, which measured 434 N.m/deg. The mean shear stiffness for the Herbert screw fixation was 106.9 kN/m, compared to 86.1 kN/m for the 3.5-mm cannulated screw. This was not statistically significant. CONCLUSIONS: The biomechanical properties of the 4.5-mm cannulated Herbert screw suggest it may lend itself for use in fixation of Type II odontoid fractures. With only a single screw to insert, this technically demanding procedure may be less daunting.

Aged↗
PubMed1995

Radiographic appearance of the odontoid lateral mass interspace in the occipitoatlantoaxial complex.

STUDY DESIGN: This is an anatomic study in which the odontoid lateral mass interspace is evaluated radiographically in various positions of upper cervical spine rotation. OBJECTIVES: The objectives are to determine whether odontoid lateral mass interspace asymmetry exists in the ligamentously intact cervical spine and to define odontoid lateral mass interspace behavior during atlantoaxial rotation. SUMMARY OF BACKGROUND DATA: Controversy exists regarding the behavior of the odontoid lateral mass interspace during atlantoaxial rotation. The meaning of interspace asymmetry varies depending on the author and the method of study. Atlas fractures account for 7% of cervical spine fractures and are frequently associated with other cervical fractures, so an understanding of the radiographic anatomy is crucial to the evaluation of these patients. METHODS: Ten human cadaveric cervical spines were dissected of all but ligamentous soft tissue and were mounted and prepared for radiographic study in neutral position and in varying degrees of right and left rotation. Radiographs were evaluated for odontoid lateral mass interspace asymmetry in neutral and in rotated positions, and data were analyzed. RESULTS: Measurable asymmetry could be shown when comparing neutral positions and when comparing rotated with neutral positions. A statistically significant difference could not be proven in this asymmetry, although clinical significance is suggested by the analysis of the data. CONCLUSION: Measurable asymmetry can be present in the neutrally positioned, ligamentously intact atlanto-axial complex and is not necessarily indicative of instability. This agrees with the concept of the "neutral zone" as described by White and Panjabi in Clinical Biomechanics of the Spine. There is a trend for increasing odontoid lateral mass interspace on the side to which the head is rotated, and this odontoid lateral mass interspace is measurably different from the contralateral odontoid lateral mass interspace, indicating that odontoid lateral mass interspace asymmetry is not a good indicator for cervical instability in the otherwise asymptomatic individual.

Adult↗
PubMed1995

Lesions of the alar ligaments. In vivo and in vitro studies with magnetic resonance imaging.

STUDY DESIGN: This study analyzed anatomic characteristics of the alar ligaments and the possibility of imaging them with magnetic resonance imaging. Also determined was whether artificial ruptures of the alar ligament can be recognized experimentally. OBJECTIVE: To determine the ability of magnetic resonance imaging to visualize normal, torn, resected alar ligaments. SUMMARY OF BACKGROUND DATA: There are no studies about computed tomography or magnetic resonance imaging findings of alar ligaments and after anatomic sections. Direct visualization of the complete ligament is not possible for computed tomography. No precise diagnostic method for showing a ruptured alar ligaments has been described. Magnetic resonance imaging seems to be the method of choice for distinguishing between normal and pathologic soft tissue. METHODS: Fifteen specimens from accident victims underwent anatomic dissection. In addition, ligaments from three groups were examined: 1) eight volunteers, 2) seven patients, and 3) 17 fresh cadaveric specimen before anatomic exploratory dissection. In seven of these specimens, one ligament was cut to simulate an artificial disruption and magnetic resonance imaging was repeated. RESULTS: Lesions of the alar ligaments were found in four of 15 prepared specimens. Using magnetic resonance imaging, the alar ligaments could be identified in all volunteers, patients, and specimen except one. No ruptures were found in the 17 specimens. Of the seven resected specimens, all cuts could be demonstrated by magnetic resonance imaging. CONCLUSION: Magnetic resonance imaging is useful for showing lesions of the alar ligaments because of a high soft tissue contrast, plane independence imaging, possibility of functional scans, and secondary reconstruction from three-dimensional data sets.

Atlanto-Occipital Joint↗
PubMed1996

Atlantoaxial instability in os odontoideum with myelopathy.

STUDY DESIGN: This study analyzed the correlation between the atlantoaxial instability (especially sagittal plane rotatory instability) and myelopathy. Thirty-four patients with os odontoideum were reviewed in clinical symptoms and radiographs. OBJECTIVES: The results were correlated to provide a rationale for the genesis of myelopathy. SUMMARY OF BACKGROUND DATA: Instability of the atlantoaxial joint has been evaluated with atlantodental interval, space available for the spinal cord, instability index, and others. These are excellent indices for anteroposterior instability. However, they are insufficient for the evaluation of the multidirectional instability in os odontoideum. METHODS: Thirty-four patients were analyzed in three parameters on the lateral radiographs: the minimum distance from the posterior border of the C2 body to the posterior arch of atlas, the difference of the atlanto-axial angle between the flexion and extension position (sagittal plane rotation angle), and the change of space available for the spinal cord from flexion to extension (Instability Index). RESULTS: The correlation between the sagittal plane rotation angle and the instability index was low (r = 0.561). In patients with more than 20 degrees of the sagittal plane rotation angle, myelopathy was shown at a high rate (86%). Myelopathy was also shown at a high rate (90%) in the patients with more than 40% of the instability index. CONCLUSIONS: It is important to check the sagittal plane rotation angle and the instability index to evaluate the instability in os odontoideum. If the patient has either a sagittal plane rotation angle of more than 20 degrees or an instability index of more than 40%, he or she is likely to have the cord signs.

Adolescent↗
PubMed1996

Myelopathy resulting from the atlantodental hypertrophic osteoarthritis accompanying the dens hypertrophy. Two case reports.

STUDY DESIGN: This is a report of two patients who sustained cervical myelopathy that seemed to be associated with hypertrophic atlantodental osteoarthritis accompanying dens hypertrophy. OBJECTIVES: Pathogenesis of hypertrophic osteoarthritis in the atlantodental articulation was elucidated, and these two patients were treated by C1 decompressive laminectomy with or without posterior fusion. SUMMARY OF BACKGROUND DATA: One case of myelopathy resulting from the hypertrophic nonunion of the dens has been reported, but to the authors' knowledge, there have been no reports describing a case similar to those presented in this report. METHODS: History, physical findings, and image examination findings common to the two cases were analyzed to elucidate pathogenesis of hypertrophic osteoarthritis in the atlantodental articulation. C1 decompressive laminectomy alone was performed in one patient and additional atlantoaxial transarticular fixation in the other patient. RESULTS: Myelopathy in two patients was caused by the cervical cord compressed between the hypertrophic and sclerotic dens and the anteriorly displaced posterior arch of the atlas in the developmentally small atlas ring. Postoperative neurologic recovery was satisfactory with the atlantoaxial solid fusion. CONCLUSION: The atlantodental hypertrophic osteoarthritis accompanying the dens hypertrophy seemed to have developed because of post-traumatic atlantoaxial instability. Their developmentally small atlas ring may be a predisposing factor toward the development of myelopathy.

Aged↗
PubMed1997

Occipitocervical fusion with C1 laminectomy in children.

STUDY DESIGN: Eight children in whom atlantoaxial dislocation had developed underwent occipitocervical fusion using a rectangular rod. The postoperative results are presented, and the postoperative growth and deformation of the cervical spine were determined radiographically. OBJECTIVES: To investigate in a relatively long-term follow-up study whether occipitocervical fusion affects the growth of the cervical spine and induces spinal deformation. SUMMARY OF BACKGROUND DATA: It has been reported that children who have undergone C1-C2 posterior fusion are likely to develop abnormal curvature or deformation of the cervical spine as a result of a disturbance of growth of the fused vertebrae. There have been no studies, however, to confirm that these changes occur after occipitocervical fusion in children. METHODS: The subjects were one boy and seven girls who had undergone occipitocervical posterior fusion during childhood. The average age at the time of surgery was 8.3 years, and the average follow-up period was 5.9 years. The following were assessed radiographically: redislocation of the atlas, bone union, changes in the curvature of the cervical spine, the height and width of the vertebral bodies, and the anteroposterior diameter of the spinal canal. RESULTS: Solid bone union was achieved in all patients with maintenance of the reduced position at the time of surgery. None of the patients exhibited abnormal curvature of the cervical spine. The rate of increase in height of the C2 vertebral body was significantly less than that of vertebral bodies below C3. The rate of increase in width of the vertebral body and the anteroposterior diameter of the spinal canal of the C2 vertebral body and vertebral bodies below C3 did not differ significantly. CONCLUSIONS: Occipitocervical fusion with a rectangular rod is useful for treating atlantoaxial dislocation in children and yields excellent results because of the firm internal fixation it achieves. This surgery induced no apparent postoperative spinal deformations.

Atlanto-Axial Joint↗
PubMed1997

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.

Adolescent↗
PubMed1998

Functional outcome of surgically and conservatively managed dens fractures.

STUDY DESIGN: Fifty-seven patients with dens fractures were identified from 1986 to 1996 at the authors' institution. Forty-six were available for reevaluation by two independent observers with a mean follow-up period of 26 months. OBJECTIVE: To determine by age and fracture type which treatment regimen provided the best functional outcome in patients with dens fractures. SUMMARY OF BACKGROUND DATA: There were no Type I fractures, but there were 37 Type II and 20 Type III fractures. Twenty-nine patients were under 60 years of age, and 28 were 60 years and older. Six patients had been treated by immediate C1-C2 posterior fusion, and five received treatment with a Philadelphia collar only. Forty-six patients were placed in a halo thoracic immobilizer with a symptomatic nonunion rate of 19.5%. These patients ultimately required posterior cervical fusion. METHODS: Final functional outcome, level of pain, and cervical range of motion were all statistically evaluated using multivariate analysis (Wilcoxon's two-sample test). The influence of age, fracture type, and treatment method were determined. RESULTS: There were no cases of short- or long-term neurologic deterioration in any of the patients in the study group. There was a significantly higher rate of complications associated with halo use in the older population. Pain scores were higher in Type II fractures and in patients treated conservatively with halo immobilization, especially those patients over 60 years of age. No statistically significant difference in these parameters were found. Older patients treated surgically did not have a better functional outcome score than those treated nonoperatively (P < 0.8). Persons over 60 years of age treated in a halo had a significantly (P < 0.05) decreased range of motion when compared with younger patients treated similarly. CONCLUSION: Patients over 60 years of age with a dens fracture had a higher complication rate and lower cervical range of motion when treated conservatively with a halo. Final functional outcome and overall pain levels, however, did not differ significantly by age group or treatment modality.

Activities of Daily Living↗
PubMed1999

Spontaneous regression of periodontoid pannus mass in psoriatic atlantoaxial subluxation. Case report.

STUDY DESIGN: A case report of a 41-year-old man with psoriasis who had cervical myelopathy caused by atlantoaxial subluxation and periodontoid pannus mass. OBJECTIVE: To describe the possible mechanism underlying the periodontoid pannus formation and the optimal treatment for such cases. SUMMARY OF BACKGROUND DATA: Atlantoaxial subluxation causing spinal cord compression at the craniocervical junction may develop in patients with rheumatoid or psoriatic arthritis. Periodontoid pannus formation plays an important role in compromising the anteroposterior diameter of the spinal canal and in causing neurologic deficits. Transoral transpharyngeal excision of the pannus is sometimes thought necessary for anterior decompression of the spinal cord. Spontaneous resolution of the periodontoid pannus after posterior atlantoaxial fusion and fixation has been documented in rheumatoid arthritis, but not in psoriatic arthritis. METHODS: The patient underwent posterior atlantoaxial fusion and Halifax fixation. RESULTS: The patient experienced clinical improvement. Regression of the periodontoid pannus mass was observed on magnetic resonance imaging. CONCLUSIONS: Posterior fusion and instrumentation resulted in spontaneous regression of the pannus mass and symptomatic relief. This report provides evidence that atlantoaxial instability may be the sine qua non for the formation of periodontoid pannus, and that amelioration of such instability leads to spontaneous resolution of the pannus mass.

Adult↗
PubMed1999

Differential biomechanical effects of injury and wiring at C1-C2.

STUDY DESIGN: An in vitro study compared the biomechanics of the upper cervical spine among three groups of cadaveric specimens, each with a different source of instability: transverse-alar-apical ligament disruptions, odontoid fractures, or odontoidectomies. The responses of the three groups were again compared after a uniform posterior cable and graft fixation was applied to the specimens. OBJECTIVES: To quantify and compare the effects of different injuries on atlantoaxial stability and to determine whether a single fixation technique effectively treats each injury. SUMMARY OF BACKGROUND DATA: Previous biomechanical studies of atlantoaxial instability have been focused on mechanisms of injury or on comparison among fixation types. METHODS: Cables and pulleys applied torques to human cadaveric C0-C6 specimens quasistatically while an optical system tracked three-dimensional angular and translational motion at C0-C1 and C1-C2. Specimens were tested immediately after injury, after posterior cable and graft fixation, and after 6000 cycles of fatigue. RESULTS: Odontoidectomies increased C1-C2 angular and translational range of motion significantly more than odontoid fractures or ligament disruptions, especially during flexion-extension. Odontoid fractures produced a slightly larger increase in C1-C2 angular range of motion than ligament disruptions but a smaller increase in C0-C1 range of motion. The different injuries affected the lax zone and the position of C1-C2 axis of rotation differently. Restabilization by posterior cable and graft reduced motion only moderately for each injury type. All three fixated injuries were susceptible to loosening from fatigue. CONCLUSION: The three different injuries produce different spinal biomechanical responses. To best promote fusion, posterior cable and graft fixation should be used with an adjunctive stabilizing technique to treat all three injuries.

Adult↗
PubMed1999

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.

Atlanto-Axial Joint↗
PubMed2000

Synovial cyst of the transverse ligament of the atlas in a patient with os odontoideum and atlantoaxial instability.

STUDY DESIGN: A case report and review of the literature. OBJECTIVE: To describe the diagnosis and successful treatment of a synovial cyst arising from the transverse ligament in a patient with os odontoideum and atlantoaxial instability. SUMMARY OF BACKGROUND DATA: Synovial cysts arising from the transverse ligament of the atlas are extremely rare. Development of a synovial cyst is thought to be attributable to degenerative changes of the C1-C2 facet joints or to microtrauma. Direct excision of the cyst is the only treatment cited in previous reports. METHODS: A synovial cyst arising from the transverse ligament of the atlas in a 45-year-old man with os odontoideum and atlantoaxial instability was treated surgically with posterior atlantoaxial fusion alone. The magnetic resonance images, surgical treatment, and related literature are reviewed. RESULTS: Preoperative magnetic resonance images of the cervical spine showed a large cystic mass located ventral to the cord arising at the level of the transverse ligament of the atlas: the mass was of low signal intensity on T1-weighted images, was of high signal intensity on T2-weighted images, and was enhanced marginally with gadolinium-DTPA on T1-weighted images. Spontaneous regression of the cyst was identified on the follow-up magnetic resonance images taken 3 months after C1-C2 posterior wiring and fusion. CONCLUSIONS: A patient with a synovial cyst arising at the C1-C2 junction ventrally at the level of the transverse ligament showed spontaneous regression of the lesion after C1-C2 posterior wiring and fusion.

Atlanto-Axial Joint↗
PubMed2000

Os odontoideum with cerebellar infarction: a case report.

STUDY DESIGN: A case report. OBJECTIVES: To report the case of a child with os odontoideum associated with cerebellar infarction and to discuss the correlation between atlantoaxial instability with os odontoideum and vertebrobasilar artery insufficiency. SUMMARY OF BACKGROUND DATA: Knowledge of the influence of atlantoaxial instability on vertebrobasilar artery insufficiency remains limited despite the publication of several reports. METHODS: A 5-year-old boy with ataxic gait disturbance was hospitalized in the pediatric ward. Magnetic resonance imaging revealed multiple cerebellar infarctions, and cerebral angiogram showed occlusions of several branches of the basilar artery and a winding of the left vertebral artery. Stress lateral radiographs of the cervical spine showed atlantoaxial instability with os odontoideum. Posterior C1-C2 transarticular screw fixation with iliac bone graft was applied to obtain firm stability and fusion. RESULTS: There was no damage to the vertebral arteries or spinal nerves in the perioperative period. Solid union of the grafted bone and rigid stability of the atlantoaxial joint were seen on lateral flexion-extension radiographs 1 year after the operation. There has been no sign of recurrent arterial insufficiency, and the patient has been free from cerebellar dysfunction to date. CONCLUSIONS: Atlantoaxial instability may cause insufficiency of the vertebral artery as well as spinal cord injury. More attention should be paid to the possible relation between atlantoaxial instability and vertebrobasilar artery insufficiency.

Atlanto-Axial Joint↗
PubMed2000

Management of type II dens fractures: a case-control study.

STUDY DESIGN: A case-control study of patients with isolated type II dens fractures treated with halo vest immobilization. OBJECTIVES: To evaluate age as a risk factor for failure of halo immobilization in patients with type II dens fractures. SUMMARY OF BACKGROUND DATA: The literature reports an average fusion rate of approximately 70% in patients with type II dens fractures treated by halo vest immobilization. Although many investigators have examined patient age as a risk factor for nonfusion using halo immobilization, all studies have been supported only by Class III data. These studies, consequently, carry little or no statistical significance. Therefore, a case-control study based on Class II data was designed to evaluate age as a risk factor for failure of halo vest immobilization in patients with type II dens fractures. METHODS: Thirty-three patients with isolated type II dens fractures treated with halo vest immobilization at the University of Iowa Hospitals and clinics between 1983 and 1997 were included. Type II fractures were defined with plain radiography as per the Anderson-D'Alonzo classification. Cases were defined as nonfusions after halo immobilization, whereas control subjects represented successful bony unions attained with halo immobilization. RESULTS: When the case and control groups were compared, there was no significant difference between the groups in the presence of concomitant medical conditions, sex, the amount of fracture displacement, the direction of fracture displacement, the length of hospital stay, or length of follow-up. Age more than 50 years was found to be a highly significant risk factor for failure of halo immobilization (P = 0.002; Fisher's exact test, two-tailed). The odds ratio of these data indicate that the risk of failure of halo immobilization is 21 times higher in patients aged 50 years or more. CONCLUSIONS: Surgical intervention should be considered in those patients aged 50 years or more who have a type II dens fracture, if it can be accomplished with acceptable risk of morbidity and death.

Age Factors↗
PubMed2000

Symptomatic cervical synovial cyst associated with an os odontoideum diagnosed by magnetic resonance imaging: case report and review of the literature.

STUDY DESIGN: The first case of a synovial cyst of the upper cervical spine associated with os odontoideum diagnosed by magnetic resonance imaging is presented. OBJECTIVES: To evaluate distinct magnetic resonance imaging findings of a cervical synovial cyst located anterior to the cord and discuss its association with os odontoideum. These findings may guide further investigations. BACKGROUND: Synovial cysts of the spine are uncommon findings. They occur mostly dorsolaterally and with greatest frequency in the lumbar spine and are rarely symptomatic. No association with os odontoideum has been reported before. METHODS: A single subject with symptoms of deterioration in his hand functions was examined by a 2. 0-T magnetic resonance imager. RESULTS: Magnetic resonance imaging of the cervical spine showed an os odontoideum connected to the body of C2 by a synovial joint that had a cystic extension posteriorly compressing the cord. CONCLUSION: Synovial cysts should be considered in the differential diagnosis of an extradural mass of the upper cervical spine. Magnetic resonance imaging should be the choice in the investigation of such cases.

Humans↗
PubMed2000

Hypertrophic dens resulting in cervical myelopathy: histologic features of the hypertrophic dens.

STUDY DESIGN: A case report of a 43-year-old woman who had hypertrophic dens in the developmentally narrow atlas ring that resulted in cervical myelopathy. OBJECTIVES: To present histologic findings of the hypertrophic dens, which was excised en block the transoral approach, and to discuss the pathogenesis of the hypertrophic change of the dens. SUMMARY OF BACKGROUND DATA: Few cases have been reported of cervical myelopathy associated with hypertrophic dens, and there have been no previous reports describing the histologic features of hypertrophic dens. METHODS: Clinical data were reviewed from the patient's chart, and histologic features of the hypertrophic dens were examined in the sagittally cut section. RESULTS: After posterior decompression surgery, cervical myelopathy in the patient subsided. Myelopathy reappeared 4 years after surgery. Imaging studies showed osteoarthritis of the atlantodental joint, hypertrophic dens, and degeneration of the cruciate ligament. In the second surgery, transoral removal of the dens with posterior occipitocervical fusion was performed. Histologic studies showed thickening of the cortical bone of the anterior and cranial parts of the dens. The apical portion, which was the insertion portion of the ala ligaments, showed degenerative changes of tide marks. CONCLUSION: Atlantoaxial instability and enthesopathy were probably the causes of the hypertrophic changes of the dens in this case.

Adult↗
PubMed2000

Accuracy of atlantoaxial transarticular screw insertion.

STUDY DESIGN: The accuracy and safety of atlantoaxial transarticular screw insertion were evaluated in clinical cases. OBJECTIVES: To evaluate the accuracy and safety of atlantoaxial transarticular screw insertion under lateral fluoroscopic monitoring without opening the joint. SUMMARY OF BACKGROUND DATA: Atlantoaxial transarticular screw fixation has been reported to be biomechanically superior to posterior atlantoaxial wiring techniques. Several clinical series have been reported in the literature. In some reports, the risk of screw insertion in this technique has been pointed out. MATERIALS AND METHODS: Fifty-six consecutive patients with atlantoaxial instability were treated by transarticular screw fixation. One hundred twelve screw insertions in these 56 patients were assessed by surgical record and computed tomographic examination. One screw could not be inserted because of the difficulty of adequate placement during operation; 111 screws were therefore inserted. Adequate position was defined as when the screw perforated the lateral atlantoaxial joint. RESULTS: In this series, neither vertebral artery injury nor spinal cord injury was experienced clinically. One guide wire was broken during drilling with a cannulated drill. Computed tomographic examination demonstrated that 106 screws perforated the atlantoaxial joint. Therefore, 95.5% of screws were adequately positioned. There were two screws positioned lateral to the joint, two medially, and one anteroinferiorly to the joint. CONCLUSIONS: Atlantoaxial transarticular screw insertion using image intensifier without opening the lateral joint was performed safely, but not accurately, in all cases.

Adolescent↗