Atlanto-axial fusion with transarticular screw fixation

The optimal transarticular c1-2 screw length and the location of the hypoglossal nerve

BACKGROUND

Injury to the hypoglossal nerve is a complication associated with transarticular C1-2 screw placement. This complication can be caused by a misdirected or too long screw. Little is known about the optimal screw length and its relationship to the hypoglossal nerve.

METHODS

Twenty cervical spine specimens were used to study the optimal length of the transarticular C1-2 screw. Using the Magerl technique, a 3.0 mm drill bit was inserted into the C2 lateral mass, passing through the C1-2 facet joint and penetrating the upper portion of the ventral cortex of the lateral mass of the atlas. After drilling, the hole length was measured between the dorsal cortex of the C2 inferior articular process and the ventral cortex of the C1 lateral mass. In addition, six sagittal-sectioned cadavers were carefully dissected to observe the location of the hypoglossal nerve in the anterior aspect of the atlantoaxial region.

RESULTS

The results of the measurements showed that the mean optimal screw path length for all specimens was 38.1 +/- 2.2 mm with a range of 34-43 mm. There was no significant difference between sexes in the screw path length (p 0.05). The hypoglossal nerve lies vertically in front of the lateral portion of the C1 lateral mass and the C1-2 facet joint. The area where the hypoglossal nerve lies is approximately 2-3 mm lateral to the middle of the anterior aspect of the C1 lateral mass.

CONCLUSIONS

This study suggests that the mean optimal transarticular C1-2 screw length may be 38 mm; however, the determination of the accurate optimal C1-2 screw length should be made on an individual basis. Risk to the hypoglossal nerve can be eliminated if Magerl's technique is performed exactly.

Spine update: cervical spine internal fixation using screw and screw-plate constructs

Screw and screw-plate constructs have been used successfully in fixation of the cervical spine. This update focuses on the indications, complications, and nuances in the technique used for odontoid screws, transarticular C1-C2 screws, occipitocervical plating, posterior lateral mass screws, pedicle screws, and anterior plating.

Posterior occipitocervical fusion in rheumatoid arthritis and other instabilities

Occipitocervical fixation remains a surgical challenge. A Y-plate in combination with transarticular screw fixation provides a simple and economically favorable solution to this problem. By integrating the transarticular screws into the Y-plate immediate postoperative reliable stabilization is achieved. Clinical results confirm the reliability and the low rate of pseudarthrosis with this surgical technique.

C1-C2 intra-articular screw fixation for atlantoaxial posterior stabilization

STUDY DESIGN

A trial of a new posterior stabilization technique for atlantoaxial instability and a report of preliminary results.

OBJECTIVES

To describe a new posterior stabilization technique for atlantoxial instability.

SUMMARY OF BACKGROUND DATA

Magerl's transarticular screw fixation is an accepted technique for rigid atlantoaxial stabilization, which reportedly has yielded many good clinical results. However, the technique is technically demanding and poses a risk of injury to the nerves and veins.

METHODS

Eleven patients who had been treated with intra-articular screw fixation in combination with Halifax interlaminar clamp (OSTEONICS, Allendale, NJ) for atlantoaxial instability were observed. Results of their clinical examinations and biomechanical studies using resinous bones of a cervical spine model were reviewed.

RESULTS

In all patients, occipital pain, neck pain, and neural deficit improved, and bony fusion with no correction loss was shown on radiography. To date, no vascular or neural complications have been found, and no instrumentation failures have occurred. In the biomechanical study, the Halifax with transarticular screw fixation had significantly greater flexion stiffness than the Halifax only or the Halifax with intra-articular screw fixation, but the torsion stiffness of the Halifax with intra-articular screw fixation was significantly greater than that of the other Halifax combinations.

CONCLUSION

The preliminary results showed that this technique was effective in strengthening the rotational stability of the atlantoaxial fixation and was considered useful for atlantoaxial posterior stabilization.

Anatomical suitability of C1-2 transarticular screw placement in pediatric patients

OBJECT

Craniovertebral instability is a challenging problem in pediatric spinal surgery. Recently, C1-2 transarticular screw fixation has been used to assist in craniovertebral joint stabilization in pediatric patients. Currently there are no available data that define the anatomical suitability of this technique in the pediatric population. The authors report their experience in treating 31 pediatric patients with craniovertebral instability by using C 1-2 transarticular screws.

METHODS

From March 1992 to October 1998, 31 patients who were 16 years of age or younger with atlantooccipital or atlantoaxial instability, or both, were evaluated at our institution. There were 21 boys and 10 girls. Their ages ranged from 4 to 16 years (mean age 10.2 years). The most common causes of instability were os odontoideum (12 patients) and ligamentous laxity (eight patients). Six patients had undergone a total of nine previous attempts at posterior fusion while at outside institutions. All patients underwent extensive preoperative radiological evaluation including fine-slice (1-mm) computerized tomography scanning with multiplanar reconstruction to evaluate the anatomy of the C1-2 joint space. Preoperatively, of the 62 possible C1-2 joint spaces in 31 patients, 55 sides (89%) were considered suitable for transarticular screw placement. In three patients the anatomy was considered unsuitable for bilateral screw placement. In three patients the anatomy was considered inadequate on one side. Fifty-five C1-2 transarticular screws were subsequently placed, and there were no neurological or vascular complications.

CONCLUSIONS

The authors conclude that C1-2 transarticular screw fixation is technically possible in a large proportion of pediatric patients with craniovertebral instability.

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.

A new occipitocervical fusion construct in pediatric patients with occipitocervical instability. Technical note

Posterior occipitocervical stabilization procedures were successfully performed in 10 patients (nine boys and one girl) 16 years of age or younger by using C1-2 transarticular screws coupled with a rigid occipitocervical construct. The average length of follow-up evaluation was 18.8 months (range 5-37 months). No implant failed and all fusions were successful without the use of an external orthotic halo device.

Modified Gallie technique versus transarticular screw fixation in C1-C2 fusion

The effectiveness of a modified Gallie technique versus Magerl and Seeman transarticular screw fixation was compared in the management of 27 patients with symptomatic atlantoaxial instability. Twelve patients were treated using a modified Gallie technique and postoperative halo vest immobilization. Atlantoaxial arthrodesis occurred in seven (58%) patients, stable fibrous union occurred in one patient, and pseudarthrosis with recurrent instability developed in four (33%) patients. Average followup was 6.9 years. All 15 patients treated using Magerl and Seeman transarticular screw fixation and postoperative soft collar immobilization had atlantoaxial arthrodesis develop. Average duration of followup was 4 years. One patient sustained vertebral artery injury during preparation for screw placement. Magerl and Seeman transarticular screw fixation provides stability and more reliably produces atlantoaxial arthrodesis than the Gallie technique provides in patients with atlantoaxial instability without the need for rigid postoperative bracing. Potential for vertebral artery exists despite apparent accurate screw placement. To ensure that safe transarticular screw placement is possible, preoperative fine cut axial computed tomography with reconstructions is required to assess vertebral artery position and C2 isthmus anatomy. A proportion of patients have anatomy unsuitable for screw placement. Traditional wiring techniques are indicated in these patients.

Occipital screw pullout strength. A biomechanical investigation of occipital morphology

STUDY DESIGN

A three-group design with consistent pullout strength measures.

OBJECTIVES

To determine pullout strength of three fixation types (unicortical screws, bicortical screws, wires) and to investigate their correlation with respect to occipital morphology.

SUMMARY OF BACKGROUND DATA

A secured, multidirectional occipitocervical fusion requires internal fixation. Devices secured at occipital protuberance were suggested to offer the greatest pullout strength because of this region's thickness.

METHODS

Twelve fresh human cadaveric occiputs were sketched with a grid delineating 21 fixation sites. Each site was drilled and hand-tapped. Four specimens were instrumented with unicortical screws on one side of the midline and bicortical screws on the other. Another four were instrumented with bicortical screws and wires, and the remaining four were instrumented with unicortical screws and wires. Two points on each specimen were secured with identical fixation to examine side-to-side symmetry. An MTS materials testing apparatus (MTS Systems Corporation, Eden Prairie, MN) was used to displace the fixators. Pullout strengths at different anatomic locations were recorded.

RESULTS

The greatest pullout strength was at the occipital protuberance for all fixation types. The bicortical pullout strength was 50% greater than unicortical. The wire pullout strength was not significantly different from that of the unicortical screw (P > 0.05). Seventy-eight percent of wires broke at 1100 N. Unicortical pullout strength at occipital protuberance was comparable with that of the bicortical screw at other locations.

CONCLUSIONS

Unicortical screw fixation at occipital protuberance offers acceptable pullout strength without the potential complications of bicortical screws or wire fixation.

Surgery in the degenerative cervical spine

Degenerative changes of the cervical spine include changes of the bony and discoligamentous structures that can create mechanical alterations of the anatomy. Compressive syndromes and deformation or instability represent basic indications for surgery. In the upper cervical spine, osteoarthritis of the C1-C2 facet manifests with suboccipital pain syndrome caused by generally unilateral degenerative changes of the atlantoaxial facet. Fixation and atlantoaxial fusion represent the treatment of choice. In rare instances the presence of os odontoideum is responsible for atlantoaxial instability. Narrowing of the lateral recess in the subaxial spine produces radicular symptoms. The clinical symptoms should be supported with imaging methods such as computed tomography or magnetic resonance imaging. Selective decompression produces satisfactory results. Spondylotic cervical myelopathy requires the addition of neurophysiologic investigations. Posterior decompression with laminoplasty or anterior decompression procedures with corpectomy of the involved segments represent therapeutic options with comparable results. In the presence of axial neck pain, the exact location of the painful segment challenges clinicians and radiologists. Only in cases in which the clinical findings correlate with the radiologic changes should surgical fusion be considered as a last therapeutic means to resolve the painful condition.

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.

The reliability of the lateral radiograph in determination of the optimal transarticular C1-C2 screw length

STUDY DESIGN

This study assessed the value of using lateral radiographs in evaluating the optimal screw length in transarticular C1-C2 screw fixation.

OBJECTIVES

To assess the reliability of the lateral radiograph in determining the optimal transarticular C1-C2 screw length.

SUMMARY OF BACKGROUND DATA

Transarticular C1-C2 screw placement is usually performed using anatomic landmarks and fluoroscopy. A lateral fluoroscopic image is valuable when directing screws in the sagittal plane, but its exact role in determining screw length has not been investigated.

METHODS

Eight cervical spine specimens were used in this study. Screw placements were performed in each specimen, fixed in the exact lateral position and under direct visualization. After each placement, a lateral radiograph was taken. The odontoid process was divided into three equal portions. Another portion anterior to the odontoid process was called the anterior tubercle region. The number of screw tips appearing in each portion on the radiograph was then recorded for each placement. In addition, 30 C1 specimens were measured to evaluate the anterior part of C1.

RESULTS

The results showed that 12.5% of the screws placed 2 mm short of reaching the ventral cortex and 0 mm overpenetrating the ventral cortex of the lateral mass of C1 projected in the radiograph on the anterior tubercle region, 37.5% on the anterior region of the odontoid process, and 50% on the middle region of the odontoid process. Twenty-five percent of the screws that were placed to overpenetrate, by 2 or 4 mm, the ventral cortex of the lateral mass of C1 were projected on the anterior tubercle region in the radiograph, and 50% and 62.5% were projected on the anterior region of the odontoid process, respectively. The mean vertical distance between the anteriormost point of the anterior tubercle of the anterior ring and the middle of the ventral cortex of the lateral in all specimens was 5.6 +/- 1 mm, and the mean transverse angle of the anterior ring relative to the frontal plane was 21.1 +/- 3.5 degrees.

CONCLUSIONS

This results in this study indicate that a lateral radiograph may not be reliable in determining the optimal screw length, although it is valuable in directing accurate screw angle in the sagittal plane. Preoperative computed tomographic evaluation of the C1-C2 region may be helpful in estimating the location of the screw tip on the lateral radiograph during surgery.

Complications in spinal fusion

Complications in spinal fusion can lead to less than desirable results. The complications of spinal fusion in the cervical and lumbar spine are discussed. Methods of avoiding and correcting complications also are reviewed. Through a better understanding, it is hoped that complications can be prevented.

Clinical outcomes after cervical spine fusion

The advent of sterile technique, modern anesthesia, and organized industrial society have allowed for great advances and widespread use of cervical arthrodesis for a variety of disorders. This article defines expected outcome for cervical arthrodesis used to treat degenerative disease, trauma, deformity, and a variety of other disorders.

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.

Anatomic considerations of anterior transarticular screw fixation for atlantoaxial instability

STUDY DESIGN

Anatomic parameters of C1 and C2 were measured in 30 dried human cervical spines. Anterior transarticular C1-C2 screws were placed in 15 cadaveric spines.

OBJECTIVE

To provide anatomic data for anterior transarticular atlantoaxial screw or C1-C2 screw and plate fixation.

SUMMARY OF BACKGROUND DATA

A posterior approach to fixation in the atlantoaxial joint has been well described. Damage to the vertebral artery is documented as a rare complication of posterior atlantoaxial transarticular screw fixation. An anterior surgical approach to exposing the upper cervical spine for internal fixation and bone graft recently has been developed. No anatomic information regarding the anterior transarticular atlantoaxial screw or screw and plate fixation between C1 and C2 is available in the literature.

METHODS

Direct measurements using digital calipers and a goniometer were taken from 30 pairs of dried human C1 and C2 vertebrae. The anterior transarticular C1-C2 screw insertion point is at the junction of the lateral edge of the C2 vertebral body to 4 mm above the inferior edge of the C2 anterior arch. The parameters related to anterior transarticular atlantoaxial screw fixation or screw and plate fixation between the C1 lateral mass and the C2 vertebral body were measured. Fifteen embalmed cadavers were used for anterior C1-C2 transarticular screw placement. Longer screws (30-40 mm) were used to detect whether the screw tips violated the upper cervical canal or vertebral arteries.

RESULTS

In the anterior transarticular atlantoaxial screw placement, lateral angulation of the screw placement relative to sagittal plane ranged from 4.8 +/- 1.8 degrees to 25.3 +/- 2.6 degrees. The posterior angulation of the screw placement relative to the coronal plane ranged from 12.8 +/- 3.1 degrees to 22.6 +/- 3.2 degrees. The length of the medial screw path ranged from 14.7 +/- 1.5 mm to 25.4 +/- 2.8 mm. In the anterior screw and plate fixation, the anteroposterior diameter of the inferior facet articular surface ranged from 16.2 +/- 1.6 mm to 17.1 +/- 1.8 mm. The anteroposterior diameter of the C2 vertebral body ranged from 9.3 +/- 1 mm to 16.2 +/- 1.8 mm. The anterior prevascular retropharyngeal approach appropriately exposed the atlantoaxial joint for anterior transarticular C1-C2 screw placement. No screws violated the vertebral artery and cervical canal.

CONCLUSIONS

An anterior transarticular atlantoaxial screw 15-25 mm long can be inserted with a lateral angulation of 5-25 degrees relative to the sagittal plane and a posterior angulation of 10-25 degrees relative to the coronal plane. Additionally, in C1-C2 anterior plate fixation screws 15 mm long could be anchored in the inferior facet of the C1, and screws 9-15 mm long could be anchored in the C2 vertebral body.

Vertebral artery injury in C1-2 transarticular screw fixation: results of a survey of the AANS/CNS section on disorders of the spine and peripheral nerves. American Association of Neurological Surgeons/Congress of Neurological Surgeons

OBJECT

The 847 active members of the American Association of Neurological Surgeons/Congress of Neurological Surgeons (AANS/CNS) Section on Disorders of the Spine and Peripheral Nerves were surveyed to quantitate the risk of vertebral artery (VA) injury during C1-2 transarticular screw placement.

METHODS

This retrospective study elicited the number of patients treated with transarticular screws, the number of screws placed, the incidence of VA injury and subsequent neurological deficit, and the management of known or suspected VA injury. Two hundred thirteen (25.1%) of the 847 surgeons responded. One hundred one respondents (47.4%) had placed a total of 2492 C1-2 transarticular screws in 1318 patients. Thirty-one patients (2.4%) had known VA injuries and an additional 23 patients (1.7%) were suspected of having injuries. However, only two (3.7%) of the 54 patients with known or suspected VA injuries exhibited subsequent neurological deficits and only one (1.9%) died of bilateral VA injury. Other iatrogenic complications included dural tears, screw fractures, screw breakout, fusion failure, infection, and suboccipital numbness.

CONCLUSIONS

Including both known and suspected cases, the risk of VA injury was 4.1% per patient or 2.2% per screw inserted. The risk of neurological deficit from VA injury was 0.2% per patient or 0.1% per screw, and the mortality rate was 0.1%. The choice of management of intraoperative VA injuries was evenly divided between placing the patient under observation and initiating immediate postoperative angiography with possible balloon occlusion.

Unilateral posterior atlantoaxial transarticular screw fixation

Bilateral posterior C 1-2 transfacet screw placement with associated posterior bone graft wiring is the accepted treatment for patients with atlantoaxial instability. This technique was modified to treat 19 patients with atlantoaxial instability and unilateral anomalies that prevented placement of a screw across the C1-2 facet. In these cases, a single contralateral transarticular screw was placed in conjunction with interspinous bone graft wiring to avoid neural or vertebral artery injury and to provide C1-2 stability. Postoperatively, all 19 patients were placed in Philadelphia collars (mean immobilization 8 weeks, range 6-12 weeks). Unilateral C1-2 facet screw fixation was needed for the following reasons: a high-riding transverse foramen of the C-2 vertebra present in 13 patients (left side in eight, right side in five), poor screw purchase in two (left side in both), screw malposition in one (left side), severe degenerative arthritis in one (right side), neurofibroma in one (right side), and fracture of the C-1 lateral mass in one (left side). Six weeks postsurgery, one patient presented with a broken screw and required occipitocervical fusion with a Steinmann pin and wire cable from the occiput to C-3 to achieve solid fusion. Solid fusions were achieved in the other 18 patients (mean follow-up period 31 months, range 14-54 months); there was no delayed screw breakage, wire breakage, or spinal instability. There were no operative or postoperative neurological or vascular complications. The authors' experience demonstrates that unilateral C1-2 facet screw fixation with interspinous bone graft wiring is an excellent alternative in the treatment of atlantoaxial instability when bilateral screw fixation is contraindicated.

Rheumatoid Arthritis of the Cervical Spine

Cervical involvement in patients with rheumatoid arthritis occurs primarily in the upper cervical spine. The characteristic deformities are atlantoaxial subluxation, vertical settling, and subaxial subluxation. The typical patient complaints are neck pain and occipital pain. Subtle signs of myelopathy may also be present. Useful radiologic studies include plain radiography, tomography, and functional magnetic resonance imaging. The most helpful radiographic measurements are the anterior atlantodens interval, the posterior atlantodens interval, and assessment of vertical settling. Atlantoaxial subluxation greater than 9 mm with vertical settling and a posterior atlantodens interval less than 14 mm correlate with neurologic deficit. Nonoperative management does not change the natural history of cervical disease. Traditional surgical indications include intractable pain and neurologic deficit. The author discusses more controversial indications and proposes a rationale and protocol for treatment. The primary surgical objectives are to achieve stabilization of the affected segments and to relieve neural compression by reduction of subluxations or direct decompression. Arthrodesis provides reliable pain relief. Neurologic recovery occurs more consistently in patients with lower grades of preoperative myelopathy.

Atlantoaxial fusion and retrodental pannus in rheumatoid arthritis

STUDY DESIGN

This study analyzed the influence of atlantoaxial fusion in rheumatoid arthritis patients on inflammatory retrodental pannus.

OBJECTIVES

To determine the value of fusion on the magnitude of pannus as a compressive structure on the spinal cord.

SUMMARY OF BACKGROUND DATA

Transverse and vertical instability may lead to neurologic deficits from spinal cord compression. Increased size of the retrodental pannus can exacerbate the neurologic deterioration. Anterior removal of dens and pannus followed by posterior fusion has been proposed in such situations as a method to relieve spinal cord compression.

METHODS

Twenty-two patients with atlantoaxial instability and verified pannus on magnetic resonance imaging underwent posterior fusion of the upper cervical spine. These patients were followed 12 to 75 months after surgery by clinical, radiologic, and magnetic resonance imaging evaluations. The size of the pannus was compared before and after surgery.

RESULTS

In all patients, the retrodental pannus had significantly decreased or disappeared postoperatively.

CONCLUSIONS

Pannus reduction occurred even in patients whose disease was active or progressing, supporting the hypothesis that the pannus is more a reactive fibrous tissue resulting from instability rather than a direct consequence of the inflammatory process itself.

Radiological and anatomical evaluation of the atlantoaxial transarticular screw fixation technique

Sixty-one patients treated with C1-2 transarticular screw fixation for spinal instability participated in a detailed clinical and radiological study to determine outcome and clarify potential hazards. The most common condition was rheumatoid arthritis (37 patients) followed by traumatic instability (15 patients). Twenty-one of these patients (one-third) underwent either surgical revision for a previously failed posterior fusion technique or a combined anteroposterior procedure. Eleven patients underwent transoral odontoidectomy and excision of the arch of C-1 prior to posterior surgery. No patient died, but there were five vertebral artery (VA) injuries and one temporary cranial nerve palsy. Screw malposition (14% of placements) was comparable to another large series reported by Grob, et al. There were five broken screws, and all were associated with incorrect placement. Anatomical measurements were made on 25 axis bones. In 20% the VA groove on one side was large enough to reduce the width of the C-2 pedicle, thus preventing the safe passage of a 3.5-mm diameter screw. In addition to the obvious dangers in patients with damaged or deficient atlantoaxial lateral mass, the following risk factors were identified in this series: 1) incomplete reduction prior to screw placement, accounting for two-thirds of screw complications and all five VA injuries; 2) previous transoral surgery with removal of the anterior tubercle or the arch of the atlas, thus obliterating an important fluoroscopic landmark; and 3) failure to appreciate the size of the VA in the axis pedicle and lateral mass. A low trajectory with screw placement below the atlas tubercle was found in patients with VA laceration. The technique that was associated with an 87% fusion rate requires detailed computerized tomography scanning prior to surgery, very careful attention to local anatomy, and nearly complete atlantoaxial reduction during surgery.

Posterior rod system of the cervical spine: a new implant allowing optimal screw insertion

A new implant system for posterior stabilisation of the occipitocervical junction and the cervical and upper thoracic spine is described. The system consists of rods and clamps. For fixation to the occiput, the 3.5-mm titanium rod goes over into a 3.5-mm AO-reconstruction plate. Several clamps may be fixed to the rod at variable intervals, depending on the anatomical situation and the specific needs. Five types of clamps with different angulations of the screw hole with respect to the rod allow optimal screw insertion and fixation of the rod at all levels instrumented. Locking screws may be used to allow fixed stabilisation of the screw to the rod. Hooks for sublaminar anchoring, connectors to other rods and a cross-linking device are also available. Unlike plate fixators, the system allows screw insertion at any angle and at any interval. Therefore, optimal screw insertion is possible in any anatomical situation. Furthermore, ample space is available for bone grafting of the posterior aspect of the lateral masses. This is especially important following a laminectomy. Preliminary clinical results in 20 patients are presented; no complications have been seen to date. Our system has recently been approved as an AO-implant.

An anatomic study of the thickness of the occipital bone. Implications for occipitocervical instrumentation

STUDY DESIGN

The authors measured the thickness and quality of occipital bone regions to determine screw placement during occipitocervical fusion and described the projection of the posterior dural venous sinuses.

OBJECTIVE

This study provides anatomic data relevant to areas of screw placement into the occiput during occipitocervical fixation.

SUMMARY OF BACKGROUND DATA

Few reports exist regarding the morphometrics of the occipital bone and intracranial structures relevant to occipitocervical fusion.

METHOD

The thickness of the posterior inferior occipital bone was measured relative to a 10 x 5 cm grid. Sections were evaluated grossly and histologically. The projections of the posterior dural venous sinuses were determined by direct measurements.

RESULTS

The maximum thickness of the occipital bone, which ranged from 11.5 to 15.1 mm in males and from 9.7 to 12.0 mm in females, was at the level of the external occipital protuberance. The occipital bone was thicker than 8 mm in an area extending laterally from the external occipital protuberance for 23 mm and consisted of dense cortical bone with little or no diploic bone. The projection of most of the torcula on the external surface of the occipital bone was located superior to the center of the external occipital protuberance (mean, 12.6 mm superior and 4.7 mm inferior to external occipital protuberance), whereas that of the transverse sinus was distributed more evenly above and below the external occipital protuberance (mean, 7.3 mm superior and 6.5 mm inferior).

CONCLUSIONS

Screws that are 8-mm long may be inserted in the region of the superior nuchal line (Level 0) extending 2 cm laterally from the center of the external occipital protuberance, 1 cm from the midline at a level 1 cm inferior to the external occipital protuberance (Level 1), and 0.5 cm from the midline at a level 2 cm inferior to the external occipital protuberance (Level 2). The major dural venous sinuses are situated immediately beneath the thickest regions of the occiput and are at risk of penetrative injury during screw placement.

The anatomical suitability of the C1-2 complex for transarticular screw fixation

Posterior transarticular screw fixation of the C1-2 complex has become an accepted method of rigid internal fixation for patients requiring posterior C1-2 fusion. The principal limitation of this procedure is the location of the vertebral artery, because an anomalous position may prohibit screw placement. In this study, a consecutive series of computerized tomography (CT) scans was reviewed, and the suitability of each patient for transarticular screw fixation was evaluated. All of the fine-slice axial C1-2 CT scans and reconstructions performed on a spiral scanner over 2 years were reviewed. A novel screw trajectory reconstruction was designed to visualize the potential path of a transarticular screw in the plane of the reconstruction. Scans were reviewed for bone anatomy and the position of the transverse foramen. Seventeen (18%) of 94 patients had a high-riding transverse foramen on at least one side of the C-2 vertebra that would prohibit the placement of transarticular screws. The left side was involved in nine patients and the right in five. Three patients had bilateral anomalies. The mean age of the group with anomalies (35.9 years, range 10-76) was not significantly different from the overall mean age (35.7 years, range 6-94). An additional five patients (5%) were considered to have anatomy in which screw placement was feasible but risky. On the basis of these data, it is postulated that 18% to 23% of patients may not be suitable candidates for posterior C1-2 transarticular screw fixation on at least one side.

Arteriovenous fistula as a complication of C1-2 transarticular screw fixation. Case report and review of the literature

A case is reported of a vertebral artery-to-epidural venous plexus fistula as a complication of posterior atlantoaxial facet screw fixation. The use of transarticular screws to stabilize the C1-2 joint has become an increasingly popular fixation technique, most notably for atlantoaxial instability due to trauma or rheumatoid disease. Despite the fact that this approach is technically challenging, there have been few reports of complications associated with C1-2 transarticular fixation. Although damage to the vertebral artery is a documented hazard of transarticular fixation at this level, a symptomatic arteriovenous fistula resulting from the procedure has not been described previously. The etiology, presentation, and treatment of this unusual complication are discussed.

C1-C2 transarticular screw fixation for treatment of C1-C2 instability

C1-C2 instability has traditionally been treated by C1-C2 posterior wiring and bone grafting. However, this technique has an incidence of non-union which may exceed 10%. Transarticular screw fixation has developed as a technique of providing increased strength of fixation of C1-C2 arthrodesis, while at the same time avoiding the need for postoperative halo bracing and avoiding the risk of neurological injury associated with the passage of sublaminar wires. We present a retrospective review of 12 patients with C1-C2 instability treated by C1-C2 transarticular screw fixation. Eight patients underwent this procedure as primary treatment, and 4 after a failed Gallie fusion. Five patients had a cruciate ligament rupture, 5 had an odontoid process fracture, 1 had os odontoideum, and 1 had rheumatoid instability. There was no surgical morbidity or mortality and, at a mean follow up of 12.1 +/- 3 months (range 8-14 months), all patients had achieved solid fusion, and all neurological symptoms referable to the instability had resolved. C1-C2 transarticular screw fixation has been shown to be safe and effective and has a number of advantages when compared to traditional posterior wiring techniques. We recommend that this technique be considered as a primary treatment of C1-C2 instability.

Fatal transdental posterior rotary subluxation of the cervical spine. A case report

STUDY DESIGN

The cervical spine of an 86-year-old man known to have a fracture of the odontoid process was removed at autopsy and dissected.

OBJECTIVES

To establish the cause of death, which was not apparent.

SUMMARY OF BACKGROUND DATA

Ruptures of the vertebral arteries in patients with fractures of the odontoid process are rare. Only a few reports are published in the literature. Those that address postmortem findings in patients with fractures of the odontoid process do not make any reference to associated capsular and ligamentous injuries and the resultant instabilities.

METHODS

Because of legal constraints, the cervical spine was removed en bloc 1 week after the patient's death and carefully dissected.

RESULTS

In addition to the known bony injury, rupture of the left vertebral artery, epidural hematoma, disruption of the posterior atlantoaxial ligaments, hemorrhage into the anterior ligamentous structures, rupture of the capsule of the right atlantoaxial joint, and stretching of the capsule of the left joint were found to be present. Displacement of the spinal cord by an epidural hematoma secondary to rupture of the left vertebral artery was recorded as the apparent cause of death. The rupture had obviously been caused by the abnormal rotation of the atlas on the axis in a clockwise direction.

CONCLUSIONS

Both the fatal outcome and the pathologic examination showed that established management concepts, particularly screw fixation of a fractured odontoid process, should be reconsidered in light of the potential occurrence of transdental posterior rotary subluxation. Because the incidence of capsular, ligamentous, and vascular injuries associated with fractures of the odontoid process is still poorly understood, more autopsies would be needed. The case also raises the question of whether, in an elderly patient like ours, a fracture of the odontoid process should prompt immediate surgical stabilization.

C1-C2 posterior cervical fusion: long-term evaluation of results and efficacy

Posterior wiring techniques are the most commonly used methods of achieving C1-C2 arthrodesis. Recently, transarticular screw fixation and interlaminar clamping have been advocated to achieve more secure fixation. A retrospective review of patients undergoing C1-C2 fusion for nonneoplastic disease was undertaken at the University of Toronto Hospital, with the aim of determining the long-term outcome of the selected procedures. Thirty-two patients underwent 36 procedures from 1986 to 1992, with a mean follow-up of 4.7 +/- 2.2 years (range, 2.0-8.0 yr). The most common disease processes were odontoid fracture (18 patients), transverse atlantal ligament injury (5 patients), os odontoideum (5 patients), and rheumatoid C1-C2 instability (3 patients). Thirty-one Gallie fusions, one Brooks-Jenkins fusion, two transarticular screw fusions, and two Halifax clamp applications were performed. Six (19%) of Gallie/Brooks-Jenkins fusions failed. These occurred with os odontoideum (three patients), Type II odontoid fracture (two patients), and transverse atlantal ligament injury (one patient). All transarticular screw and Halifax clamp procedures resulted in successful fusions. Two procedures (6%) resulted in new neurological deficit; both of these patients underwent posterior wiring for os odontoideum. This study suggests that Type II odontoid fractures may be successfully managed by a posterior wiring technique alone. Rheumatoid C1-C2 instability may be managed by posterior wiring supplemented with halo immobilization. Transarticular screw fixation has several potential advantages as a technique for C1-C2 arthrodesis and, in particular, may be appropriate for os odontoideum that had a high failure rate (75%) with conventional posterior wiring, even when this was supplemented with halo bracing.

One piece cervical device for cervical spine surgery

STUDY DESIGN

This study analyzed the use of the one piece cervical device (OPCD) surgically inserted to treat atlanto-axial or subaxial subluxation. Operative results, techniques, and the enhanced correction mechanism were studied.

OBJECTIVES

The results were correlated to provide a rationale for posterior cervical spinal fusion.

SUMMARY OF BACKGROUND DATA

Wiring techniques were generally performed for posterior fusion. Recently, the Luque rod has been used on the cervical spine.

METHODS

One hundred eighty-seven patients were analyzed clinically and radiologically. The operative techniques were detailed and the corrective mechanism explained through biomechanical considerations.

RESULTS

The patients were followed from 2 to 13 years. The results were 94% satisfactory. No poor or worsening cases were encountered.

CONCLUSIONS

Satisfactory operative results showed that the OPCD is safe, convenient, and reliable. It can be used in all areas of the cervical spine. The primary reason for these benefits is the enhanced correction mechanism of the OPCD.

Cannulated screws for odontoid screw fixation and atlantoaxial transarticular screw fixation. Technical note

Cannulated screw systems use thin Kirschner wires (K-wires) that have been drilled into the bone to direct screw trajectories accurately into small bone fragments. Use of the K-wires avoids overdrilling the pilot holes and allows fixation of adjacent bone fragments during screw insertion. Hollow tools and hollow screws are inserted into the bone over the K-wires. Cannulated screw fixation is useful in the cervical spine to stabilize odontoid fractures and to treat atlantoaxial instability. This report describes techniques for successful cannulated screw insertion and methods to minimize complications. Cannulated screws have several distinct advantages compared to noncannulated screws: 1) the K-wires guide the screw position into the bone; 2) the K-wire trajectory can be repositioned easily if the original trajectory was not ideal; 3) the K-wires allow continuous fixation of adjacent unstable bone fragments; and 4) the K-wires prevent migration of unstable bone fragments during screw insertion. Complications associated with the K-wire (breakage, repositioning, and advancement) can be minimized using precise operative techniques, a specialized tool system, and intraoperative fluoroscopic monitoring. A unique cannulated screw tool system was developed specifically for upper cervical fixation to allow percutaneous drilling using long tunneling devices, tissue sheaths, drill guides, and long K-wires. These tools allow delivery of cannulated fracture-fixation screws at a low angle to the spine through long soft-tissue trajectories. Cannulated screws have significant advantages compared to noncannulated screws for fixation of the unstable cervical spine.

C1-C2 posterior cervical fusion: long-term evaluation of results and efficacy

Posterior wiring techniques are the most commonly used methods of achieving C1-C2 arthrodesis. Recently, transarticular screw fixation and interlaminar clamping have been advocated to achieve more secure fixation. A retrospective review of patients undergoing C1-C2 fusion for nonneoplastic disease was undertaken at the University of Toronto Hospital, with the aim of determining the long-term outcome of the selected procedures. Thirty-two patients underwent 36 procedures from 1986 to 1992, with a mean follow-up of 4.7 +/- 2.2 years (range, 2.0-8.0 yr). The most common disease processes were odontoid fracture (18 patients), transverse atlantal ligament injury (5 patients), os odontoideum (5 patients), and rheumatoid C1-C2 instability (3 patients). Thirty-one Gallie fusions, one Brooks-Jenkins fusion, two transarticular screw fusions, and two Halifax clamp applications were performed. Six (19%) of Gallie/Brooks-Jenkins fusions failed. These occurred with os odontoideum (three patients), Type II odontoid fracture (two patients), and transverse atlantal ligament injury (one patient). All transarticular screw and Halifax clamp procedures resulted in successful fusions. Two procedures (6%) resulted in new neurological deficit; both of these patients underwent posterior wiring for os odontoideum. This study suggests that Type II odontoid fractures may be successfully managed by a posterior wiring technique alone. Rheumatoid C1-C2 instability may be managed by posterior wiring supplemented with halo immobilization. Transarticular screw fixation has several potential advantages as a technique for C1-C2 arthrodesis and, in particular, may be appropriate for os odontoideum that had a high failure rate (75%) with conventional posterior wiring, even when this was supplemented with halo bracing.

Surgical management of atlantoaxial nonunions

Sixteen patients referred for atlantoaxial fixation failures were treated surgically with revision procedures during the past decade. Of these 16 patients, atlantoaxial instability occurred because of rheumatoid arthritis in five, as odontoideum in seven, transverse ligament disruption in two, and odontoid fracture nonunion in two. The 16 individuals (10 men, six women; mean age 43.7 years; age range 20-77 years) had undergone a total of 20 C1-2 internal fixation procedures that failed. Surgical strategies for definitive revision of the nonunions in these 16 subjects included 10 rigid internal fixations with transarticular screws, three revised C1-2 fixations with autogenous bone struts and wire or cables, and three extended fixations with occipitocervical instrumentation. Autogenous grafts were used in all revisions. A postoperative halo brace was used in five individuals with osteoporotic bone; all patients wore a restrictive postoperative cervical orthosis. Postoperatively, 15 patients (94%) had a stable construct (mean follow up 35 months; range 12-79 months), which included 13 osseous unions and two stable fibrous unions. One patient had nonunion; he fractured his anterior C1-2 transarticular screws 2 years postoperatively. He had occipital radicular pain without myelopathy but refused further surgery. Atlantoaxial pseudarthroses were effectively treated by addressing the pathological, biomechanical, and technical reasons for failed fusion. Successful fusion after reoperation was improved by using autologous bone grafts, adequately controlling atlantoaxial motion (with rigid transarticular screws internally or externally with a halo vest), compressing the bone grafts between the arches of C-1 and C-2 with wire cables, meticulously preparing the fusion bed, and by optimizing the pharmacological and clinical parameters to promote bone healing.

Preoperative oblique axial computed tomographic imaging for C1-C2 transarticular screw fixation: technical note

C1-C2 transarticular screw fixation is an increasingly popular surgical method of treating atlantoaxial instability. When properly performed, it can safely provide fusion rates near 100%. However, the technique of screw insertion into this region allows only a small margin for error. Preoperative radiological assessment is essential to analyze the morphology of the region, assess for vertebral bony and vascular anomalies, and define the tolerances for the transarticular screws along their planned trajectory. As an adjunct to the preoperative planning of C1-C2 transarticular screw fixation, a unique, easily obtainable method of computed tomographic imaging, using thin-section oblique axial computed tomographic images of the C1-C2 region, is described.

Occipito-cervical fixation in rheumatoid arthritis--an analysis of surgical risk factors in 163 patients

163 patients with rheumatoid arthritis (RA) and atlanto-axial subluxation treated by posterior occipito-cervical fixation (OCF) over a period of twenty-one years (November 1970-January 1991) were followed. Common complaints prior to surgery were occipital headache, neck pain, radicular pain and myelopathy. The mean age at time of surgery was 61 years. The mean follow-up time was 54 months. Clinical improvement was obtained in 88% of the patients, whereas 7% were unchanged and 5% had progressive symptoms in spite of surgery. There was no pre-operative or immediate postoperative mortality. In 79 patients, one or more potential surgical risk factors were identified. Twenty-four reoperations were performed in the neck. The most common cause for reoperation was mechanical failure due to wire-break or spinous process fracture. Wound infection in the neck was recorded in 16 patients. Five were deep and required removal of the fixation material. Following OCF, new or progressive subaxial subluxation (SAS) led to further surgery in 4%. The study offers support for the beneficial effect of OCF in rheumatoid AAS. We conclude that, in spite of a number of identified risk factors, OCF with the Brattström-Granholm technique remains a safe and effective method for stabilization of upper cervical subluxations in RA.

Atlanto-axial stabilization with posterior transarticular screw fixation: technical description and report of 22 cases

Magerl's technique of combining C1-C2 posterior screw fixation with a supplemental bone-wire fusion has been advocated for the management of atlanto-axial instability. Between October 1990 and August 1992, a modification of this technique was used in the treatment of 22 patients with this disorder. In the absence of spinal deformity or neoplastic disease, screw fixation and bony fusion were used alone without associated wiring, thus avoiding the risk of neural injury resulting from the sublaminar passage of wire and the retrodisplacement of ventral structures. Patient ages ranged from 30 months to 80 years; follow-up ranged from 5 to 27 months, with a mean of 14.9 months. The causes of the instabilities were as follows: eight cases of nonunion of Type II odontoid fracture, four cases of rheumatoid arthritis, three cases of tumor, two cases of ligamentous instability, two cases of pseudoarthrosis after bone-wire fusion, two cases of halo noncompliance, and one case of Os odontoideum. All 20 patients who underwent fusion were placed in a Philadelphia collar for 12 weeks. Nineteen of 20 (95%) patients achieved solid fusion. Twenty-one of 22 (95%) had significant reduction in preoperative pain. No patient developed myelopathy or bulbar findings. The one intraoperative complication was an inability to achieve secure screw purchase on one side that required unilateral screw placement with a Gallie fusion-using cable. Postoperative complications included one patient with a superficial wound infection that resolved after local debridement and antibiotics and suboccipital numbness in two patients. Progression of spinal deformity, screw pullout or breakage, and neurological or vascular complications did not occur.(ABSTRACT TRUNCATED AT 250 WORDS)

Progressive myelopathy secondary to odontoid fractures: clinical, radiological, and surgical features

Late-onset progressive myelopathy, years after odontoid fracture, is considered a rarity. Sixteen patients with diagnosis of their odontoid fractures delayed from four months to 45 years have been studied and treated. Three had forgotten about the injury and, in the rest, the significance had been minimized by their clinicians. Fifteen patients had characteristic C-2 nerve root pain and 10 had noted weak hands and walking difficulties. Fifteen patients had Type II fractures, which were mobile in 11; hypertrophic pseudoarthrosis was marked in two. In seven patients it was confirmed at surgery that all or part of the transverse ligament was interposed in the fracture. Transoral surgery, combined with a variety of posterior fusion techniques, has allowed cord decompression, an understanding of the pathomechanics, and sound posterior bone fusion with arrest of the myelopathic condition. Measurements of craniovertebral angles and cord cross-sectional area in this series revealed a rough correlation, but the most striking relationship was between length of delay in diagnosis and diminished cord area in both non-union and malunion, suggesting a progressive injury mechanism. It is proposed that late myelopathy following odontoid fracture may be more common than hitherto believed and should be considered in the evaluation of patients with cervical spondylosis. The condition may be progressive. Finally, non-union may be due to interposition of the transverse ligament.