Atlantoaxial Transarticular Screw Research Articles

Anatomic study of the axis for surgical planning of transarticular screw fixation.

Transarticular screw fixation has shown increased stability compared with other posterior stabilization techniques. However, there have been few reports on vertebral artery injury related to the screw insertion. The current study measured the parameters of the pedicle and vertebral artery groove of the axis and clarified the accuracy and safety of the transarticular screw fixation. Direct measurements were taken from 98 dry axis vertebrae. The width and height of the pedicle were measured. The mediolateral and anteroposterior dimensions of the vertebral artery groove also were measured. Forty-one percent had asymmetry. In 20% of the specimens, the pedicle was smaller than the diameter of the screw (3.5 mm). The pedicle of the axis has large anatomic variability and asymmetry. Some pedicles were not suitable for atlantoaxial transarticular screw fixation. The risks associated with screw fixation should be prevented by preoperative computed tomography with three-dimensional reconstruction. Screw trajectory reconstruction with coronal and sagittal reconstruction is useful to evaluate the pedicle width and height.

Measurements of C1-2 region of Cervical Spine Using MRI for C1-2 Transarticular Screw Fixation

Study design: The C1-2 region was measured using MRI for a C1-2 transarticular screw fixation. Objectives: To measure the first and second cervical spine, using MRI for a C1-2 transarticular screw fixation, and find the safe trajectory for the screw. Summary of Literature Review: Posterior atlantoaxial transarticular screw fixation is an excellent procedure that is associated with high fusion rates. However, there is a potential risk of vertebral artery injury. Materials and Methods : Sagittal MR images, of the cervical spine transecting mid portion of the C1-2 facet joints, were obtained in 24 patients. The mean age of the patients was 45.5 years. The male to female ratio of the patients was 15:9. From the sagittal images the ideal screw trajectory was made, and 48 oblique axial MR images, depending on the ideal screw trajectory in the sagittal plane, were obtained. On the oblique sagittal images, the width of the isthmic portion of the C2, the ideal length of the transarticular screw, the ideal insertion angle of the screw and the ideal entry point were measured using a PACS digital measuring instrument. The location of the vertebral artery was also evaluated. Results: The mean width of the isthmic portion of the C2 was 6.2 mm, ranging from 2.3 to 7.6 mm. The mean ideal screw length was 40.5 mm, ranging from 34.0 to 46.8 mm. The mean ideal insertion angle was 1.1°, ranging from -2.4 to 4.7°, medially. There were no significant differences in the width or the angle in relation to the sex of the patients. However, the length of the screw was significantly longer in the male (42.1 mm) than the female patients (38.0 mm). Three of 24 patients (3 of 48 C1-2 facet joints) had a narrow isthmus due to a high riding vertebral artery. Conclusions: A C1-2 transarticular screw fixation has a risk of injury to the vertebral artery. Therefore, the preoperative measurement of the C1-2 region and an evaluation of the vertebral artery are recommended in each patient. A magnetic resonance image is a useful method for easily evaluating the anatomic structure of the C1-2 region, with no additional study.

Atlantoaxial screw fixation for the treatment of isolated and combined unstable jefferson fractures - experiences with 8 patients.

The unstable atlas burst fracture ("Jefferson fracture") is a fracture of the anterior and posterior atlantal arch with rupture of the transverse atlantal ligament and an incongruence of the atlanto-occipital and the atlanto-axial joint facets. The question whether it has to be treated surgically or nonsurgically is still discussed and remains controversial. During the last decade 8 patients with unstable atlas burst fractures were examined and treated in our department. Five of the eight patients were first treated conservatively by external immobilization. Because of continuing instability due to insufficient bony fusion of the atlantal fracture all five patients underwent atlanto-axial transarticular screw fixation and fusion - as described by Magerl - with good results. In all 8 patients a good bony fusion of the atlanto-axial segment was achieved. None of the patients exhibited neurological deficits after surgical treatment. Although immobilization with a halo vest is recommended by most authors, from our view primary transarticular C1-C2 screw fixation has to be discussed as an alternative for unstable atlas burst fractures. Nonsurgical treatment with halo extension always bears the risk of insufficient healing with further instability and a fixated incongruence of the atlanto-occipital and the atlanto-axial joints, leading to arthrosis, immobility and increasing neck pain. After 10 weeks of insufficient immobilization secondary pre- and intra-operative reposition manoeuvres and surgical fixation hardly can reverse this fixated incongruence. Moreover, halo-extension needs an immobilization of the cervical spine for about 10 weeks and more, which is very uncomfortable and leads to further complications especially in elderly patients.

Use of an aiming device in posterior atlantoaxial transarticular screw fixation. Technical note.

Posterior atlantoaxial transarticular screw fixation is an excellent procedure associated with high fusion rates. There is, however, the potential risk of vertebral artery (VA) injury. The authors designed a special aiming device that allows a cannulated screw to be inserted accurately in the most posterior part of the C1-2 joint via the most posterior and medial part of the isthmus of C-2; this screw pathway most safely avoids VA injury. The instruments include an aiming device and a flexible screw-inserting system. The tip of the aiming device is placed on the ridge of the C-2 isthmus just posterior to the atlantoaxial joint. The guide wire should then pass 1 mm below the device tip. The system consists of flexible guide wires, a drill, a tap, and a screwdriver, and the screw is inserted easily via a posterior approach in which the patient's back is not obstructive. Ten patients with atlantoaxial subluxation or osteoarthritis underwent surgery in which the device was used. In all cases, the screws were inserted safely without causing VA injury, although preoperative computerized tomography (CT) reconstructions revealed a high-risk high-riding unilateral VA in three patients. Postoperative CT reconstructions demonstrated that all screws but one were inserted as planned, and successfully cleared the vertebral groove. In conclusion, this newly designed device is practical and useful for the accurate insertion of screws, thus avoiding VA injury during atlantoaxial transarticular screw fixation.

Atlantal lateral mass screws for posterior spinal reconstruction

A variety of techniques may be used to achieve fixation of the upper cervical spine. Transarticular atlantoaxial screws, posterior interspinous cable and graft constructs, and interlaminar clamps have been used effectively to achieve atlantoaxial fixation. Various anatomical factors, however, may preclude the successful application of these techniques. These factors include aberrant vertebral artery anatomy, irreducible atlantoaxial subluxation, exaggerated cervicothoracic kyphosis, and the absence of the osseous substrate for fixation. In these cases, an alternative method of fixation must be performed. The authors present an alternative method to achieve fixation of the atlas in which lateral mass screws can be applied to atlantoaxial and occipitocervical fixation. Between February 1998 and November 2001, eight patients who ranged in age from 16 to 74 years underwent posterior fixation for upper cervical instability. Diagnoses included C-2 metastastic disease in two patients, irreducible odontoid fractures in two patients, atlantoaxial subluxation in two patients, and transverse ligament synovial cyst in two patients. Various anatomical factors precluded transarticular atlantoaxial screw fixation in seven patients. One patient with a highly unstable spine due to a C-2 metastasis and pathological fracture underwent occipitocervical fusion. Atlantocervical fixation was achieved in seven patients by using varying constructs incorporating C-1 lateral mass screws. Occipitocervical fixation was achieved in one patient by incorporating C-1 lateral mass screws as an additional fixation point. A total of 14 C-1 lateral mass screws were placed in eight patients. There were no intraoperative complications. In all patients rigid fixation was achieved as demonstrated on postoperative radiographs. One patient died on postoperative Day 9 of aspiration pneumonia. At a mean follow-up time of 7.4 months, rigid fixation was maintained in all patients. Atlantal lateral mass screws can be used to provide a safe and efficacious means of achieving atlantoaxial fixation when anatomical constraints preclude the use of a more traditional procedure. Atlantal lateral mass screws may also be incorporated in occipitocervical constructs to provide additional fixation points which may prevent construct failure.

環軸関節固定術の３Ｄ‐ＣＴによる術後評価 Ｔｒａｎｓａｒｔｉｃｕｌａｒ ｓｃｒｅｗの安全性に関する検討

In recent years, atlanto-axial transarticular screw fixation performed as described by Magerl for atlanto-axial subluxation has been popular because of its excellent biomechanical stability. However, there is a risk of vertebral artery injury with placement of transarticular screws.Twelve patients (age range: 18 to 72 years, mean: 60 years) underwent surgery as described by Magerl & Brooks for reducible atlanto-axial subluxation. Four were men and eight were women. Computed tomography (CT) was performed after surgery. We evaluated the position of the transarticular screw by means of sagittal reconstruction CT images. There was no screw that deviated from the C2 isthmus and had been placed incorrectly in the spinal canal. One screw (4.2%) passed through the C2 isthmus and bordered on the foramen of the transverse process. The screw angle measured between a line through the axis of the screw and the mid-sagittal line was -3-13 degrees. The screw length projected out of the C1 lateral mass was -3.6-10.8mm. There was no complication such as vertebral artery injury during screw insertion.Because of translational or rotational atlanto-axial subluxation, presurgical computed tomographic scans with sagittal reconstruction may provide information necessary to perform transarticular screw fixation safely.

Preoperative 3D-CT imaging for the placement of atlantoaxial transarticular screws

Preoperative 3D-CT imaging for the placement of atlantoaxial transarticular screws

Effect of frameless stereotaxy on the accuracy of C1-2 transarticular screw placement.

In recent studies some authors have indicated that 20% of patients have at least one ectatic vertebral artery (VA) that, based on previous criteria in which preoperative computerized tomography (CT) and standard intraoperative fluoroscopic techniques were used. may prevent the safe placement of C1-2 transarticular screws. The authors conducted this study to determine whether frameless stereotaxy would improve the accuracy of C1-2 transarticular screw placement in healthy patients, particularly those whom previous criteria would have excluded. The authors assessed the accuracy of frameless stereotaxy for C1-2 transarticular screw placement in 17 cadaveric cervical spines. Preoperatively obtained CT scans of the C-2 vertebra were registered on a stereotactic workstation. The dimensions of the C-2 pars articularis were measured on the workstation, and a 3.5-mm screw was stereotactically placed if the height and width of the pars interarticularis was greater than 4 mm. The specimens were evaluated with postoperative CT scanning and visual inspection. Screw placement was considered acceptable if the screw was contained within the C-2 pars interarticularis, traversed the C 1-2 joint, and the screw tip was shown to be within the anterior cortex of the C-1 lateral mass. Transarticular screws were accurately placed in 16 cadaveric specimens, and only one specimen (5.9%) was excluded because of anomalous VA anatomy. In contrast, a total of four specimens (23.5%) showed significant narrowing of the C-2 pars interarticularis due to vascular anatomy that would have precluded atlantoaxial transarticular screw placement had previous nonimage-guided criteria been used. Frameless stereotaxy provides precise image guidance that improves the safety of C1-2 transarticular screw placement and potentially allows this procedure to be performed in patients previously excluded because of the inaccuracy of nonimage-guided techniques.

Biomechanical assessment of transoral plate fixation for atlantoaxial instability.

In an experimental study using human cadaver specimens the biomechanical data of anterior atlantoaxial plating according to Harms were evaluated. The purpose of this study was to evaluate this method biomechanically. The optimum fixation method to achieve fusion at the atlantoaxial joint after odontoid resection is still a matter of discussion. Isolated posterior surgical procedures for treatment of irreducible atlantoaxial kyphosis with spinal cord compression are associated with high rates of morbidity and mortality. Transoral atlantoaxial plate fixation has been designed by Harms as a fixation technique after odontoid resection. In a modification, this procedure has been combined with the posterior wire fusion according to Brooks. Eight human cadaver craniocervical specimens were tested in flexion, extension, rotation, and bending with a nondestructive flexibility method using a nonconstrained testing apparatus. Five different groups were examined: 1) control group (intact); 2) unstable group (after dissection of the atlantoaxial ligaments and odontoidectomy), 3) Harms group (transoral atlantoaxial plate fixation) 4) Harms-Brooks group (transoral atlantoaxial plate fixation and dorsal atlantoaxial wire fixation); and 5) Magerl group (transarticular atlantoaxial screw fixation). In a second experimental series, failure loads of the Harms-Brooks and the Magerl fixation methods were determined. The angular displacement of the Harms-Brooks group and the Magerl group was less than in any other group. Stiffness values at 0-3.0 Nm loads in any direction were larger for the Harms-Brooks-and Magerl-fixated specimens than for the Harms, control, or unstable specimens. No statistically significant difference was observed between Harms-Brooks and Magerl reconstruction stiffness. Ultimate failure load in the Harms-Brooks group was higher than in the Magerl group. Experimentally, isolated anterior atlantoaxial plating was less stable than the combined reconstruction procedures. Transoral plate fixation according to Harms in combination with posterior wire fixation according to Brooks provided a failure load and stiffness equal to transarticular screw fixation according to Magerl.

Anatomical evaluation of the groove for the vertebral artery in the axis vertebrae for atlanto-axial transarticular screw fixation technique.

Anatomical measurements were studied on 40 dry axis vertebrae to determine the suitability of the groove for the vertebral artery for atlanto-axial transarticular screw fixation technique. We measured 13 parameters including three angular and 10 linear dimensions related to the groove of the vertebral artery, pedicle, and pars interarticularis and evaluated 80 measurements for each parameter. All measurements were done after placing a Kischner guide wire through the pedicle. We found that differences between measurements on the left and right sides of each vertebra were nonsignificant. In spite of the variability in measurements such as height, width, and median angle of the pedicle, the decline angle for instrumentation, the depth of the groove for the vertebral artery, and the internal height of the pars interarticularis, all of these had good symmetry. However, there were statistically significant differences between the sides in measurements for both the width (P=0.05) and the angle (P<0.02) of the pedicle allowing instrumentation and they did not show good symmetry. The risk of vertebral artery injury was found to be 22.5% per specimen, or 16.25% per screw inserted because the internal height of the pars interarticularis at point of fixation was </= 2.1 mm. In addition, we found that the pedicle width allowing instrumentation was not suitable in 12.5% of screws inserted because their values were </= 6 mm. When the width of the pedicle for instrumentation and the internal height of the pars interarticularis were both evaluated together, we also found that this technique would be extremely dangerous in 7.5% of specimens. In conclusion, the internal height of the pars interarticularis and the width of the pedicle for instrumentation should be evaluated together in thin CT sections preoperatively, because of the risk of vertebral artery injury in patients upon which atlanto-axial transarticular screw fixation is to be performed.

Transarticular screw fixation C1/C2 in traumatic atlantoaxial instabilities. Comparison between percutaneous and open procedures.

For posttraumatic atlantoaxial instabilities posterior transarticular screw fixation according to Magerl represents the treatment of choice. In order to be able to insert the screws steep enough the soft tissues of the neck have to be dissected down to C7. Several authors therefore described a percutaneous technique. We analysed 30 patients with a sagittal atlantoaxial instability treated with one of both methods between the years 1995 and 1998 to detect amny differences of either technique. In 19 cases we used a modified percutaneous technique with special instruments as has been published by McGuire and Harkey. On lateral plain films the angle between the screws and the lower endplate of C2 was measured. 6 to 24 months after the accident 26 patients could be seen clinically and controlled radiologically, 4 patients had died in the meanwhile. The angle of the screws were significantly different with 10 degrees (percutaneous group 73,9 degrees, open group 63,9 degrees, p = 0,001). Time needed for the operativ procedure averaged 35 minutes shorter with the canulated technique (93 to 128 minutes, p = 0.05). All posterior fusions had healed radiologically. Active motion of the c-spine was restricted in both groups equally. We checked subjective criteria concerning pain and function with a visual analog scale and a special score. With these instruments advantages for the percutaneous procedure could be found (freedom of pain 43 points (percutaneous) versus 39 points (open), p = 0.05). We conclude that the soft tissue preserving percutaneous technique of screw application for C1/C2 posterior fusion allows for a better and easier placement of screws. It also leads to a shorter operating time and better subjective results. The method offers particularly advantages in cases where only a temporary satbilization of the C1/C2 complex without a regular fusion is needed.

Posterior atlantoaxial facet screw fixation in rheumatoid arthritis.

This retrospective review was conducted to determine the efficacy of transarticular screw fixation in a group of patients who were treated for rheumatoid atlantoaxial instability. Thirty-six patients (mean age 63 years) with rheumatoid atlantoaxial instability were treated with posterior atlantoaxial transarticular screw fixation supplemented with an interspinous C1-2 strut graft-cable construct to provide immediate three-point fixation to facilitate bone fusion. Previous attempts at fusions by using bone grafting with wire fixation at other institutions had failed in six of these patients. Six patients underwent transoral odontoid resections for removal of large irreducible pannus as a first-stage procedure, which was followed within 2 to 3 days by the posterior procedure. Postoperatively, 33 patients were placed in hard cervical collars and three required halo vests because of severe osteoporosis. Of eight patients categorized as Ranawat Class II preoperatively, all eight returned to normal after surgery; of eight patients in Ranawat Class III-A preoperatively, four improved to Class II and four remained unchanged. All 20 patients classified as Ranawat Class I preoperatively recovered completely. Pain decreased or resolved in all patients, and there were no complications related to instrumentation. At follow-up review (mean 2 years), 33 patients (92%) had solid bone fusions, and three (8%) had stable fibrous unions. Posterior atlantoaxial transarticular screw fixation provides a good surgical alternative for the management of patients with rheumatoid atlantoaxial instability. This technique provides immediate three-point rigid fixation of the C1-2 region, thus obviating the need for halo vest immobilization in most cases.

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.

Anatomic and Biomechanical Assessment of Transarticular Screw Fixation for Atlantoaxial Instability

The purpose of this study is to elucidate anatomically the atlantoaxial transarticular screw fixation described by Magerl in 1979 and compare it biomechanically with Gallie wiring. Five human C1-C2 specimens were tested in flexion/extension and rotation intact, then after wiring and screw fixation. Mean screw length was 39 mm, 25 mm in the C2 lamina and 14 mm in the lateral mass. Angular displacement of screwed specimens was significantly less than control or wired groups. Stiffness at 0-0.5 Nm loads was significantly greater for screwed specimens than for wired or controls (101 +/- 49 Nm, 10.3 +/- 9.2 Nm, and 1.96 +/- 0.18 Nm, respectively). All specimens withstood 5 Nm in flexion and extension without failure. Screw fixation provides stability comparable to Gallie wiring and is stiffer at low-range forces and rotational angles.

Posterior Occipitocervical Fusion

A new technique for occipitocervical fusion is described. The fixation of the upper cervical spine with plates and screws avoids the possible disadvantages of the commonly used wiring technique. By the establishment of a rigid fixation between the occiput and upper cervical spine with a combination of plates and screws, especially with transarticular atlantoaxial screw fixation, reliable, multidirectional, and immediate stability is achieved. The clinical picture and analysis of 14 patients with a variety of pathologies of the upper cervical spine is presented. The satisfactory outcome and solid bony fusion in all 14 patients and the absence of severe complications encourages the continued use of this technique of occipitocervical fusion.