| Objective:The atlantoaxial instability caused by fractures, rheumatoid arthritis, congenital deformity or traumatic lesions of the transverse ligament often results in acute or chronic spinal cord compression, a possible threat to a patient's life. Even though conservative management could be appropriate for many patients, surgical intervention is usually necessary. The goal of most surgical intervention is to obtain solid fixation and it is common knowledge that this is best achieved when the fixation minimizes motion.The established atlantoaxial fixation techniques include: wiring technique (Gallie and Brooks), Apofix or Halifax laminar clamp, C1-2 transarticular screw fixation, Lateral mass screw of C1 combined with pedicle screw of C2. Wiring techniques carry the potential risk of the neural injury caused by the passage of sublaminar wires; laminar clamp technique have the risk similar to the wiring techniques and a weak biomechanical stability to control the bending and rotation motion; C1-2 transarticular screw technique keep a excellent biomechanical stability in all motional directions, this technique, however, is technically demanding and generally is combined with other techniques such as Gallie or Brooks in order to accomplish the long-term stability; C1 lateral mass screw combined with C2 pedicle screw technique also requires high operative skill to avoid some complications such as an injury of vertebral artery neural or occipital nerves.Introduced by Magerl and Seeman in 1979, the bilateral C1-2 transarticular (TA) screw fixation technique, in combination with posterior wiring between C1 and C2, produced a three-point fixation resulting in a higher fusion rate relative to wiring and screws alone. Presently, this technique is considered by many spine surgeons to be the golden standard for posterior fusions of C1–C2. Some biomechanical researchers have suggested that there has been greater motion reduction with TA fixation, as compared to wiring-only techniques. The results from large clinical observations have shown lower pseudarthrosis rates in patients who are treated with the TA fixation technique. Anatomic or radiological studies of the atlantoaxial complex have shown that, in more than 20% of cases, safe placement of transarticular screws is almost impossible, mostly due to a high-riding transverse foramen. As a possible alternative, screws in the lateral mass screws of C1 and screws of the pedicle screws in C2 connected by rods have been described.Bilateral C1-2 transarticular screws and C1 laminar hooks fixation, as a modified fixation device for posterior C1-2 fusion, is introduced by NI, Bin et al. This device uses one pair of parallel placed fixation device, each device includes a laminar hook of C1, a C1-2 transarticular screw, rod and connectors; The laminar hook of C1 connects to the C1-2 transarticular screw with a rod and bone grafts between C1-2 spinous process producing a three-point fixation, among which the C1-2 transarticular screw is the most essential part that determine success or failure of the whole fixation. This bilateral C1-2 transarticular screws and C1 laminar hooks fixation has the advantage of the C1-C2 transarticular screw and Halifax laminar clamp, which allows well stability against motion in all motion direction including extension-flexion, lateral bending and rotation. In a pilot clinical practice, we managed 75 patiants who suffered form atlantoaxial instability; the result of short-term clinical follow-up shows no evidence of unstability or neurovascular injury and the complete fusion of bone graft. However, there is not a fundamental study related to the modified posterior C1-2 fusion technique, so author is going to research the biomechanics, anatomical, radiological character of this technique and evaluate its clinical application aiming at the below four points:1. To evaluate the biomechanical stability of the C1-2 transarticular screw combined with the laminar hook of C1 fixation relative to established fixation techniques;2. To investigate the safety of the modified technique at the aspect of radiology and anatomy and institute the radiological index to preoperatively judge the safety to implant this fixation;3. To prove the reliability to implanted the C1-2 transarticular screw by referring to the internal wall of C2 isthmic and investigate the risk factors related to implanting the C1-2 transarticular screw by analyzing the position of the C1-2 transarticular screw in the patient's postoperative radiological materials including the X-ray, CT scan and reconstructed imaging of cervical spine; 4. To evaluate the clinical outcome of the modified posterior fusion technique in the long-term follow-up;Materials and Methods1. Six human specimens (C0-C4) were loaded nondestructively with pure moments and the range of motion (ROM) at the level of C1-C2 was measured in the intact, destabilized and fixation condition. Six specimens were implanted with each of the following fixations, respectively: Gallie fixation(Gallie), C1-2 transarticular screw fixation combined with Gallie fixation(TA+Gallie), C1-2 transarticular screw fixation(TA), C1 laminar hook combined with C1-2 transarticular screw fixation plus bone grafts(TA+Hook), and C1 lateral mass screws combined with C2 isthmic screws fixation(C1+C2).2. The width (including superior and inferior surface) and height of C2 isthmus, the internal height of C2 lateral mass were measured on 35 human cadaveric C2 vertebrae and 105 human cervical CT scan and reconstructed images.3. From October 2004 to October 2008, 33 patients (male 30, female 3) suffering from atlantoaxial instability were managed with the bilateral C1-2 transarticular and C1 laminar hook fixation implanted by the method that chose the point that is the through isthmus of C2 pedicle sagittal line at the lower edge of the C2 lamina, approximately 2mm superior-outside the inner edge of the C2 inferior articular process as a screw entrance and determined the screw trajectory with referring to the internal wall of C2 isthmic. In postoperative 3 days, the position of C1-2 transarticular screw was analyzed in the C2 isthmic and C1 inferior articular surface on the patients'cervical X-ray and CT scan, reconstructed images. In the C2 isthmic, screw positions were checked and assigned to one of two categories:1) well positioned, if the screw passed through both C2 isthmic and lateral masses of C-2, crossed the joint in between C1 and C2, and protruded through the anterior cortex of C-1 by less than 5 mm; or 2) malpositioned, if the screw being too high or too low, too lateral, or too media in the C2 isthmic, it can protrude the cortex of C2 isthmic that cause the neurovascular injury. In the C1 inferior articular surface, screw positions were checked and assigned to one of five zones: zone A is that screw inside the facet joint, zone B1 is that screw is anterior to the B2 inferior articular surface, zone C1 is that screw is in the spinal canal, zone C2 is that screw is in the foramen of vertebral artery.4. There were total 31 cases with an atlantoaxial instability 29 males and 2 females, age ranging 6–72. All patients were operated on posterior atlantoaxial fusion using bilateral C1-2 transarticular screw and C1 laminar hook and followed up for 12–24 months. Each patient underwent a complete cervical radiograph series including lateral and flexion-extension X-ray, CT scan and reconstructed images to evaluate the atlantoaxial articular stability. The ASIA 2000 grades and scores were applied to assess the preoperative and postoperative neurologic status.Results1.TA+hook fixation compared to other fixation techniques has a minimal ROM, the difference is significant between TA+hook and Gallie ,C1+C2 in all motion directions, TA+hook and TA,TA+Gallie in extension-flexion direction. The C1+C2 compared to Gallie has much smaller ROM, the difference is significant, however it compared to TA have a significant difference in lateral bending and extension-flexion directions.2. In the anatomical measure. the width of C2 isthmic superior surface of 12.8% specimen were smaller than and equal to 4.5mm, 8.6% in the left, 14.1% in the right ( 1 specimen was smaller than and equal to 3.5mm); the internal height of C2 lateral mass of 9% specimens were smaller than 2.1mm, 2.9% in the left, 8.6% in the right; the height of C2 isthmic of 17.1% specimens were smaller than and equal to 4.5mm, 2.9% in the left, 17.2% in the right ( 4 specimen is smaller than and equal to 3.5mm); the width of C2 isthmic inferior surface of 17.2% specimen were smaller than and equal to 4.5mm, 2.9% in the left, 17.2% in the right ( 4 specimen were smaller than and equal to 3.5mm) In radiological measure, the widths of C2 left isthmic superior surface is significantly larger than that of the right and there have a significant difference between the right and the left; this widths of 16% female were smaller than and equal to 4.5mm (2 specimens were smaller than and equal to 3.5mm), 2% in the left and 14% in the right, there were no male specimen whose width is smaller than 4.5mm. the heights of C2 left isthmic is significantly larger than that of the left, and there have a significant difference between the right and the left, this heights of 40% female were smaller than and equal to 4.5mm (3 specimens were smaller than and equal to 3.5mm), 12% in the left and 40% in the right, there were no male specimen whose height is smaller than 4.5mm. The internal heights of C2 lateral mass of 9.5% specimens all of whom were male were smaller than 2.1mm, 12% in the left, 6% in the right. The widths of C2 isthmic inferior surface of 5.5% male specimens were smaller than and equal to 4.5mm (6 specimens is smaller than and equal to 3.5mm), this widths of 24% female specimens were smaller than and equal to 4.5mm, there were3.6% of male specimens whose widths were smaller than and equal to 4.5mm in the left, 3.6% in the right, there were 16% of female specimens whose widths were smaller than and equal to 4.5mm in the left, 20% in the right.3. Of the 66 screws, 6 screws were malpositioned, 2 screws of which were too high, 4 screws were too low, and no screw was too lateral or medial, 4 screws of which were in the zone A, 2 screws were in the zone B2; other 60 screws were well positioned, 58 of which were in the zone A, 2 screws in the B2, no screw in the zone B1 and C1. There was no cervical artery injury during surgery and follow-up interval, there was no atlantoaxial aritular instability during the follow-up interval, and high fusion rate of bone graft and good clinical improvements were achieved.4. The clinical outcomes including neurologic status, graft bone fusion rate and stability of Atlantoaxial joint were evaluated in follow-up term. Of these 31 patients, 2 sustained an incomplete injury whose ASIA grades were respectively C and D after postoperative 3 months; 29 patients were neurologically intact whose ASIA grades improve 1 or 2 degree (average 1.1 degree) after postoperative 3 months. All 26 patients had no instability on their follow-up plain radiographs and computerized tomography in follow-up interval. All patients'bone grafts were well fused after postoperatively 6 months.Conclusions1. The modified C1 laminar hook combined with C1-2 transarticular screws and bone graft fixation provided the best biomechanical stability. The C1 lateral mass screws in the atlas combined with isthmic screws in axis fixation is a sound alternative, when the C1-2 transarticular screw fixation is not feasible.2. 19.4% Chinese are unsuitable for posterior C1-2 transarticular screw,and the rate of female was significantly greater than that of male, the rate of the right was significantly greater than that of the left. It is important that a preoperative radiological evaluation be made to determine the safety to implant the C1-2 transarticular screw by cervical x-ray and CT reconstructed images.3. The method that chose the point that is the through isthmus of C2 pedicle sagittal line at the lower edge of the C2 lamina, approximately 2mm superior-outside the inner edge of the C2 inferior articular process as a screw entrance and determined the screw trajectory with referring to the internal wall of C2 isthmic is reliable. The risk factors related to implant C1-2 transaricular screw included (1) incomplete of atlas lateral mass (2) unreduced atlantoaxial articulation (3) absence of odontoid process (4) rheumatoid arthritis (5) female or children (6) poor surgery skill. 4. On the condition to seriously determine its operative indication and carefully evaluate the safety of using transarticular screw in patients'cervical imaging, the bilateral C1-2 tansarticular screw combined with C1 laminar hook fixationwas reliable to reconstruct the stability of atlantoaxial articulation.
|
PDF Full Text Request