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PubMed1997

Traumatic vertical atlantoaxial instability in a case of atlanto-occipital coalition.

STUDY DESIGN: This is a report of a woman with an atlanto-occipital coalition who experienced a traumatic vertical atlantoaxial facet dislocation and severe associated neurologic injury. OBJECTIVE: To describe the radiographic and pathoanatomic characteristics of the injury process. SUMMARY OF BACKGROUND DATA: Severe injuries of the occipito-atlantoaxial complex are uncommon and only rarely are associated with patient survival. This is the first report of this particular injury. METHODS: Plain radiography and tomography demonstrated the facet dislocation and instability of the injury. Surgical exploration for repair of the torn dura mater and bony arthrodesis demonstrated the gross pathoanatomy. RESULTS: The patient's vertical atlantoaxial instability was stabilized, her dura mater reconstructed, and her necrologic status has improved to allow mobilization with a cane. CONCLUSION: Vertical atlantoaxial instability has not been described previously. From the somewhat subtle radiographic findings, one might underestimate the severity of the neurologic damage. Aggressive work-up and management of this injury is suggested to avoid potential further necrologic sequelae.

Accidents, Traffic↗

PubMed1997

Acute axis fractures. Analysis of management and outcome in 340 consecutive cases.

STUDY DESIGN: Retrospective review of acute axis fractures treated at a tertiary referral center. OBJECTIVE: To determine the optimal treatment of axis fractures based on 340 cases from a single institution. SUMMARY OF BACKGROUND DATA: Axis fractures account for almost 20% of acute cervical spine fractures. However, their management and the clinical criteria predictive of nonoperative failure remain unclear. METHODS: Admission imaging studies and clinical variables were obtained for 340 consecutive axis fracture patients. Fractures were classified as as odontoid Type I, II, or III with dena displacement on admission roentgenograms; hangman's fractures of Francis grade and Effendi type; and miscellaneous fractures. Treatment methods were documented, and outcomes were based on dynamic lateral roentgenograms, clinical examination, or telephone interviews at last follow-up. RESULTS: Follow-up data were available in 92% of cases. Type II odontoid fractures comprised 35% of all axis fractures, were the most difficult to treat, and had the highest nonunion rate (28.4%). Odontoid displacement of 6 mm or more was associated with Type II nonunion (chi-square = 33.74, P < 0.0001). Patients underwent surgical fusion if fracture alignment could not be maintained by an external orthosis, or if they had odontoid fractures with transverse ligament disruption, Type II odontoid fractures with dens displacement of at least 6 mm, or hangman's fractures of severe Francis grade or Effendi type. CONCLUSIONS: Type II odontoid fractures have the highest nonunion rate and were associated with dens displacement of 6 mm or greater. Early surgical fusion is recommended for acute fracture instability despite external immobilization, transverse ligament disruption, Type II odontoid fractures with dens displacement of at least 6 mm on admission, or severe Francis grade or Effendi-type hangman's fractures. Otherwise, nonoperative management is sufficient.

Adolescent↗

PubMed1998

Anatomic study for ideal and safe posterior C1-C2 transarticular screw fixation.

STUDY DESIGN: Directions of the C1-C2 posterior transarticular screw trajectories making the longest path or violating the transverse foramen were measured by using an objective measuring method. OBJECTIVES: To clarify the directions of the screw trajectory marking the longest paths without violating the transverse foramen. To achieve this, diverse directions of the screw trajectories were objectified by measuring the locations of the points of screw intersection on the superior articular surface of C2. SUMMARY OF BACKGROUND DATA: The principal limitation of posterior C1-C2 transarticular screw fixation is the location of the vertebral artery. Because of the lack of an objective measuring method, surgical unsuitability has been decided on the basis of individual experiences as reported in 18% to 23% of cases. METHODS: Sagittal reconstructed computed tomographic images were made at 3.5 mm and 6 mm from the spinal canal. C1-C2 transarticular screw trajectories making the longest path or violating the transverse foramen (dangerous trajectory) were drawn, and their points of screw intersection on the superior articular surface of C2 were measured from the posterior rim of the superior articular surface of C2. When the space available for the screw behind the points of screw intersection by the dangerous trajectory was equal to or less than 3.5 mm, the case was defined as "unacceptable"; when the space available for the screw was more than 3.5 mm but equal to or less than 4.5 mm, it was defined as "risky" for the placement of the screw. RESULTS: Trajectories make the longest paths when they pass an average of 3.6 mm and 2.8 mm anterior to the posterior rim of the posterior articular surface of C2 at 3.5-mm lateral images and 6-mm lateral images, respectively. Four of 64 cases were unacceptable or risky unilaterally on 3.5-mm lateral images, and 21 cases were unacceptable or risky on 6-mm lateral images. A sigmoid-shaped increment curve of the risk was noted as the increasing forward inclination of the screw trajectories increased. CONCLUSIONS: The areas on the superior articular surface of C2 intersected by the trajectories making the longest paths without violating the transverse foramen are clarified as a guide to the ideal and safe trajectories. The theoretical minimal risk and usual risk of the posterior C1-C2 transarticular screw fixation are presented as well.

Adult↗

PubMed1998

Safety and accuracy of transarticular screw fixation C1-C2 using an aiming device. An anatomic study.

STUDY DESIGN: In this anatomic study, the safety and accuracy of C1-C2 transarticular screw placement was tested in a normal anatomic situation in cadaver specimens using a specially designed aiming device. OBJECTIVES: To assess the safety and accuracy of transarticular screw placement using the technique described by Magerl and a specially designed aiming device. SUMMARY OF BACKGROUND DATA: Transarticular C1-C2 screw fixation has been shown to be biomechanically superior to posterior C1-C2 wiring techniques. Several clinical series have been reported in the literature. However, no previous study assessing the accuracy or safety of this technique has been published. Structures at risk are the vertebral arteries, spinal canal, and the occiput-C1 joint. METHODS: Five frozen human cadaveric specimens were thawed and instrumented with 10 C1-C2 transarticular screws, according to the technique described by Magerl but using a specially designed aiming device described by the senior author (Jeanneret). After screw placement, the accuracy of screw positioning and the distance of the screws from the spinal canal, vertebral arteries, and atlanto-occipital joint were determined by anatomic dissection and radiographic analysis. RESULTS: The structure at greatest risk was the atlanto-occipital joint, with one screw found to be damaging the joint. Vertebral artery or spinal canal penetration was not observed in any of the specimens. Screw length averaged 45 mm and, with proper length, the screw tip was found to be located approximately 7.5 mm behind the anterior tubercle of C1 on lateral radiographs. CONCLUSIONS: This anatomic study demonstrates that C1-C2 transarticular screw fixation can be performed safely in a normal anatomic situation by surgeons who are familiar with the pertinent anatomy. The aiming device allowed safe instrumentation in all patients. In case of an irregular anatomic situation (e.g., congenital abnormalities or trauma), computed tomographic scan with sagittal reconstruction is recommended-in particular, to obtain information about the course of the vertebral artery.

Axis, Cervical Vertebra↗

PubMed1999

Atlas-axis facet asymmetry. Implications in manual palpation.

STUDY DESIGN: A basic study of six human cervical spines, documenting displacement with applied forces mimicking palpation. OBJECTIVES: To assess the issues of motion palpation of joint restrictions and the inferred link to disease. SUMMARY OF BACKGROUND DATA: Although several investigators have suggested that the issue of asymmetry and normal-abnormal function should be assessed, data are unavailable. METHODS: Atlas-axis specimens were harvested from six cadavers, cleaned of ligamentous and muscle tissue, and potted and secured with dental plaster. Forces (5-25 N) were applied along the mediolateral axis, and the corresponding displacement along three orthogonal axes were documented with infrared diodes and the Optotrak camera system (Northern Digital, Waterloo, Ontario, Canada). Specimen geometry and asymmetry were documented with plain radiographic film and a gimbal apparatus. RESULTS: Each of the six specimens displayed different behavior and differing degrees of asymmetry (e.g., facet inclination 17-35 degrees) so that each was analyzed as a case study. Asymmetrical and discontinuous force-displacement correlations were linked to anatomic asymmetry that appeared to be of natural occurrence. CONCLUSIONS: Asymmetrical joint geometry is common and causes asymmetrical joint dynamics. Thus, a clinician attempting to palpate vertebral motion would be misled by assuming that perceived restricted joint motion universally represented a finding potentially amenable to manipulation. For spine palpation to be a valid indicator for manipulation, the clinician applying it must first be able to differentiate between asymmetrical motion caused by vertebral fixation and that caused by asymmetrical joint anatomy.

Aged↗

PubMed1999

Unilateral osseous bridging between the arches of atlas and axis after trauma.

STUDY DESIGN: This is a case report. OBJECTIVE: To present a case of osseous bridging between C1 and C2 of posttraumatic origin and with an associated closed head injury and to discuss its pathogenesis and clinical outcome after surgical resection. SUMMARY OF BACKGROUND DATA: Heterotopic ossifications of posttraumatic origin in the spine are rare. To the authors' knowledge, no cases have been reported of spontaneous bony bridging between C1 and C2 with a posttraumatic origin. METHODS: Heterotopic ossifications were detected when pain and limited axial rotation (left/right 10 degrees/0 degree/20 degrees) were persistent, despite intensive physical therapy. Because heterotopic ossifications were ankylosing C1 and C2, the decision was to resect the osseous bridge in combination with a careful mobilization of the cervical spine. Functional computed tomography was performed for analysis of the postoperative results. RESULTS: Four months after surgery, clinical examination showed asymptomatic increased axial rotation. Functional computed tomography indicated that left C1-C2 axial rotation was reduced, possibly related to impingement caused by residual bony spurs. Pathologic changes in the surrounding soft tissue may be another important factor in the persistent limitation of rotation. CONCLUSIONS: Osseous bridging between C1 and C2 may be considered when persistent pain and limited axial rotation are observed after trauma. Operative resection, together with careful intraoperative and postoperative mobilization, may be the treatment of choice.

Abdominal Injuries↗

PubMed2000

Intraosseous calcifying pseudotumor of the axis: a case report.

STUDY DESIGN: A case report and review of the literature. OBJECTIVE: To present the first case of intraosseous calcifying pseudotumor arising from the axis. SUMMARY OF BACKGROUND DATA: Calcifying pseudotumor is a very rare disease. Only 24 cases have been previously reported. METHODS: A case of calcifying pseudotumor involving the body, dens, and laminae of the axis in a 60-year-old male patient was managed with total laminectomy of the axis and instrumented occipitocervical fusion, followed by the curettage of the body and dens of the axis and autogenous iliac bone graft. Medical records, imaging studies, microscopic findings, and related literature are reviewed. RESULTS: Microscopic examination showed amorphous, basophilic, and chondroid calcifying masses surrounded with palisading histiocytes and foreign body-type giant cells. The findings were consistent with those of calcifying pseudotumors previously reported in other sites of the body. At 24 months after operation, a significant reduction of neck pain was achieved. But there was evidence of local recurrence of the lesion in the body and dens of the axis with a local progression of the preexisting lesion in the facet joints. CONCLUSION: This is the first report of intraosseous calcifying pseudotumor arising from the axis.

Axis, Cervical Vertebra↗

PubMed2000

Atlantoaxial subluxation associated with ossification of posterior longitudinal ligament of the cervical spine.

STUDY DESIGN: Two case reports. OBJECTIVE: To demonstrate two rare cases of atlantoaxial subluxation associated with ossification of the posterior longitudinal ligament of the cervical spine, in which spastic quadriplegia developed. SUMMARY OF BACKGROUND DATA: There are only two reports of an association of diffuse idiopathic skeletal hyperostosis with atlantoaxial subluxation. This condition often accompanies ossification of the posterior longitudinal ligament of the cervical spine, but there is nothing in the literature about the association of ossification of the posterior longitudinal ligament with atlantoaxial subluxation. METHODS: Clinical and radiographic findings of these two cases were demonstrated. In both cases laminoplasty of the cervical spine was performed with occipitoaxial arthrodesis. RESULTS: The spastic quadriplegia of these two patients caused by myelocompression improved after surgical intervention. CONCLUSION: Ossification of the posterior longitudinal ligament of the cervical spine may cause atlantoaxial subluxation.

Aged↗

PubMed2000

Spontaneous atlantoaxial rotatory fixation in old age after cerebral infarction: case report.

STUDY DESIGN: Case report of spontaneous Fielding and Hawkins Type I atlantoaxial rotatory fixation in a 78-year-old man after hemiplegia and homonymous hemianopsia caused by cerebral infarction. OBJECTIVES: To describe a case of spontaneous atlantoaxial rotatory fixation in old age and review previous adult cases of atlantoaxial rotatory fixation without fracture. SUMMARY OF BACKGROUND DATA: Atlantoaxial rotatory fixation in adults is a relatively rare finding and is mainly caused by trauma. To the author's knowledge, there has been no previous report of spontaneous atlantoaxial rotatory fixation in old age. METHODS: The patient's head was fixed in a 40 degrees left-rotated position. Left hemiplegia and homonymous left-side hemianopsia developed due to cerebral infarction. Computed tomography of the cervical spine clearly showed rotatory fixation of the atlas on the axis. RESULTS: Successful reduction was obtained after 1 day of skull traction. CONCLUSIONS: It was hypothesized that repeated left-rotational stress due to homonymous hemianopsia loaded to the atlantoaxial joint caused abnormal laxity of the joint.

Aged↗

PubMed2000

Modification of C1-C2 transarticular screw fixation by image-guided surgery.

STUDY DESIGN: This is a feasibility study of image-guided surgery for C1-C2 transarticular screw fixation comparing postoperative screw position in a nonrandomized prospective cohort with a historic control group in which fluoroscopic guidance was used alone. OBJECTIVES: To evaluate the potential benefits and disadvantages of image-guided surgery for C1-C2 screw placement. SUMMARY OF BACKGROUND DATA: C1-C2 transarticular screw fixation is biomechanically superior to other current surgical stabilization procedures. The original technique for C1-C2 screw placement relies on anatomic landmarks and intraoperative fluoroscopy. Screw misplacement or anatomic variations can result in vertebral artery injury. Image-guided surgery involves using computed tomography (CT) data to plan the optimal screw trajectory before surgery and then use this data to guide screw placement during the actual surgery. Promising results of this technique are reported in the literature, but no direct comparison between image-guided surgery and conventional surgical techniques has been previously reported. METHODS: The image-guided surgery group consisted of 37 prospective patients. The historic control group included 78 patients who had similar surgeries performed using only fluoroscopic guidance. For the image-guided surgery group, subluxation was reduced by positioning at the time of CT examination. The CT data were transferred to a StealthStation (Sofamor-Danek, Memphis, TN) surgical planning and guidance computer system, and an optimal screw trajectory was determined for the right and left transarticular screws. After matching the surgical field to the virtual computer field, C2 was drilled according to the planned screw trajectory, and screws were placed. Plain radiographs and CT were used for postoperative evaluation of the image-guided surgery group. RESULTS: Image-guided surgery reduced but did not eliminate the risk of screw misplacement. Surgical time was not increased overall. CONCLUSIONS: Image-guided surgery is an effective tool for the achievement of correct screw placement in C1-C2 transarticular screw fixation procedures. The procedure remains technically demanding.

Axis, Cervical Vertebra↗

PubMed2000

Transoral decompression, anterior plate fixation, and posterior wire fusion for irreducible atlantoaxial kyphosis in rheumatoid arthritis.

STUDY DESIGN: Fifteen consecutive patients with irreducible atlantoaxial kyphosis caused by rheumatoid arthritis were treated by combined transoral odontoid resection, anterior plate fixation, and posterior wire fusion. OBJECTIVES: To investigate the clinical results of this new surgical procedure. SUMMARY AND BACKGROUND DATA: Irreducible atlantoaxial kyphosis in rheumatoid arthritis results from a destruction of the craniocervical joint ligaments and the anterior aspects of the lateral atlantoaxial joints. The development of a paradental synovial pannus and atlantoaxial joint impaction prevents reduction by conservative treatment, such as skull traction. Posterior surgical procedures for the treatment of the irreducible atlantoaxial kyphosis with spinal cord compression have been associated with high morbidity and mortality. METHODS: Fifteen consecutive patients were treated by transoral odontoid resection. The fixation was performed with anterior plating, according to the method of Harms in combination with posterior wire fusion according to Brooks. Before and after surgery, evaluation was performed using the parameters of pain (visual analog scale), range of motion, and subjective assessment of improvement and the Health Assessment Questionnaire. The neurologic deficit was defined according to the classifications proposed by Ranawat, Frankel, and Nurwick. Plain radiographs, including lateral flexion and extension views, and magnetic resonance scans were obtained. RESULTS: No perioperative fatality occurred. The average clinical and radiographic follow-up was 50.7 +/- 15.6 months (range, 26-77). Postoperative pain was relieved (mean pain score before surgery, 7.9 +/- 1.87; after surgery, 3.8 +/- 1.27), and the range of motion of all patients increased (mean 21.5 +/- 14.0 degrees for rotation; mean 17.2 +/- 5. 54 degrees for bending). The score on the Health Assessment Questionnaire increased in three patients, remained unchanged in three and decreased in six patients (three had died). All patients improved at least one Ranawat level after surgery, except a patient in Ranawat Class II, whose condition remained unchanged. All patients were satisfied with the procedure and reported subjective improvement. CONCLUSION: Transoral plate fixation combined with posterior wire fixation after transoral odontoid resectionis an effective, reliable, and safe procedure for the treatment of irreducible atlantoaxial kyphosis in rheumatoid arthritis.

Adult↗

PubMed2001

Traumatic atlantoaxial distraction injury: a case report.

STUDY DESIGN: Case report. OBJECTIVES: Description of a rarely reported variant of traumatic C1-C2 dislocation and discussion of a favorable outcome in a nonsurgical treatment approach. SUMMARY OF BACKGROUND DATA: Atlantoaxial dislocation most commonly involves an anterior movement of C1 in relation to C2. Often, the integrity of the transverse ligament or odontoid process is compromised, and the atlantodental interval changed. The described patient sustained a purely craniocaudal atlantoaxial distractive lesion secondary to injury sustained in a high-speed motor vehicle accident. RESULTS: The initial treatment plan involved surgical stabilization subsequent to healing of a C1 ring fracture. After 12 weeks of external stabilization, ligamentous damage appeared well resolved. That there was no gross instability delayed using a surgical option. At periodic checkup, the patient was without symptoms. CONCLUSION: In this case, conservative management of a ligamentous C1-C2 injury was effective. At 5 years after trauma the patient was without sequelae. This outcome is in contrast to previous management of injuries of this type, all of which involved surgical intervention.

Accidents, Traffic↗

PubMed2001

Fractures of the posterior part of the body and unilateral spinous process of the axis: a case report.

STUDY DESIGN: A case report and review of the literature. OBJECTIVES: To present a case of the fractures of the posterior part of the body and unilateral spinous process of the axis. SUMMARY OF BACKGROUND DATA: A few authors have described fractures involving the body of the axis. Fractures of the posterior part of the body and unilateral spinous process of the axis are extremely rare. METHODS: A fracture of the posterior part of the body and unilateral spinous process was treated nonsurgically by a halo and a Philadelphia brace. The relevant literature was reviewed. RESULTS: Solid bony union was shown by plain radiographs and computed tomography. The patient was free of pain and obtained a full range of motion. CONCLUSION: The presumed mechanism of injury in the fracture described here was flexion and axial rotation.

Aged↗

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↗

PubMed2002

Early halo immobilization of displaced traumatic spondylolisthesis of the axis.

STUDY DESIGN: A retrospective study evaluating early halo immobilization of Types II and IIA hangman's fractures. OBJECTIVE: To determine the treatment efficacy of early halo immobilization of Type II and IIA hangman's fractures. SUMMARY OF BACKGROUND DATA: The treatment of hangman's fractures with traction reduction is well established, but the time required in traction before the institution of halo-vest immobilization is controversial. METHODS: A retrospective review of all patients admitted to a level one spinal cord injury center between 1986 and 1999 with either a Type II or IIA hangman's fracture was performed. Initial and final radiographs were measured for translation and angulation. The need for reapplication of traction was also recorded. RESULTS: There were a total of 27 Type II and four Type IIA fractures. Of the Type II fractures, 21 went onto union after early halo immobilization. Six patients required reapplication of traction reduction because of fracture displacement. The Type IIA fractures all progressed to union. The discerning factor between the failure group and the success group was the initial degree of angulation on lateral cervical radiography. The patients requiring reapplication of traction had an initial fracture angulation of 12 degrees or greater. CONCLUSIONS: Early halo immobilization after traction reduction of Type II and IIA hangman's fractures is an effective method of management. Type II fractures with an angulation of greater than or equal to 12 degrees may require an extended period of traction to ensure adequate long-term fracture alignment.

Adolescent↗

PubMed2004

Case-control study comparing the efficacy of surgical techniques for C1-C2 arthrodesis.

Atlantoaxial fusion rates between 85% and 98% using C1-C2 transarticular screw (TAS) fixation have been reported; however, all of these studies are class III data. As such, these studies carry little or no statistical significance. The authors thus designed a case-control study (class II data) to evaluate the efficacy of C1-C2 TAS fixation as compared with posterior wiring techniques (PWTs). Records of adult subjects were reviewed for fusions isolated to C1-C2. Immobilization requirements were a collar for patients treated with TAS fixation and a halo for those treated by PWT. The minimum acceptable interval of radiographic follow-up was 12 months, and the outcome (fusion or nonunion) was determined through independent interpretation by a radiologist. Twenty-seven of 72 patients undergoing a posterior atlantoaxial arthrodesis met enrollment criteria. Sixteen males and 11 females combined for an average age of 54.1 years and mean follow-up of 31 months. Successful fusions (n = 18) were defined as controls, and cases represented nonunions (n = 9). Successful fusion was achieved in 13 of 14 patients treated with the TAS technique as compared with 5 of 13 subjects who underwent a PWT. Patients with a radiographically solid fusion were 21 more times likely to have undergone TAS than PWT (P = 0.004). This study demonstrated a statistically increased rate of arthrodesis as determined by specific radiographic criteria with the use of TAS fixation as compared with PWT.

Arthrodesis↗

PubMedDate not supplied

Digital radiographic measurement of the atlantodental interval in children.

The atlantodental interval (ADI) is assessed after trauma to the head and neck region to determine whether the transverse ligament of the atlas is intact. Atlantodental interval measurement from conventional screen-film radiographs is characterized by the need for magnification correction and by low reliability. Assessment of normal ADI values using digital radiography with computer-assisted measurement has not been reported. We compared with published values the digital radiographic measurements of ADI in children, examined the reliability of measurements, and examined the interaction between age, sex and ADI. Computer-assisted digital measurements of ADI in 101 children, aged 1 to 12 years, were obtained from lateral supine head-neutral radiographs. We found intraobserver reliability of 0.72 and 0.85, interobserver reliability of 0.50, a maximum ADI value of 3.5 mm, no effect of sex and age, and weak evidence for an interaction between sex and age. Computer-assisted digital ADI measurement provides higher intraobserver reliability than what has previously been reported, and interobserver reliability and a maximum ADI value similar to that found in the literature.

Axis, Cervical Vertebra↗

PubMed2003

Anterior occiput to axis screw fixation: part II: a biomechanical comparison with posterior fixation techniques.

STUDY DESIGN: This biomechanical study used flexibility testing on fresh-frozen human cadaveric specimens (occiput to C3) and compared the range of motion and neutral zone for three occipitocervical fixation techniques. OBJECTIVES: To contrast the stabilization provided by a new technique of anterior occipitocervical screw fixation with two other commonly used posterior occipitocervical fixation techniques. SUMMARY OF BACKGROUND DATA: There are no published reports describing this novel technique of anterior occipitocervical screw fixation. METHODS: Six human occipitocervical spine specimens were mounted in a custom-designed, spine-testing machine that applied a pure moment in flexion-extension, lateral bending, and axial rotation. The specimens were tested intact, after an odontoid osteotomy with capsular injury, and after each of three fixation methods: posterior wiring, posterior plate fixation with C1-C2 transarticular screws, and finally with anterior occipitocervical screws. Intervertebral motion was measured with an optoelectronic measurement system, and the range of motion and neutral zone were the kinematic variables measured and used for analysis. RESULTS: In flexion and extension testing, the posterior plate with transarticular screws provided greater stabilization than posterior wiring or anterior occipitocervical screws. In lateral bending and rotation, the anterior screws were similarly effective to the posterior plate, both of which were more effective than posterior wiring. CONCLUSION: The anterior screw fixation technique was as effective as a posterior plate with transarticular screws in stabilizing between the occiput and C2 in axial rotation and lateral bending. In extension and flexion, the anterior screw technique was not as effective as a posterior plate with transarticular screws in providing stability.

Axis, Cervical Vertebra↗