C1 Lateral Mass C2 Research Articles

Inferolateral Entry Point for C2 Pedicle Screw Fixation in High Cervical Lesions

The purpose of this retrospective study was to evaluate the efficacy and safety of atlantoaxial stabilization using a new entry point for C2 pedicle screw fixation. Data were collected from 44 patients undergoing posterior C1 lateral mass screw and C2 screw fixation. The 20 cases were approached by the Harms entry point, 21 by the inferolateral point, and three by pars screw. The new inferolateral entry point of the C2 pedicle was located about 3-5 mm medial to the lateral border of the C2 lateral mass and 5-7 mm superior to the inferior border of the C2-3 facet joint. The screw was inserted at an angle 30° to 45° toward the midline in the transverse plane and 40° to 50° cephalad in the sagittal plane. Patients received followed-up with clinical examinations, radiographs and/or CT scans. There were 28 males and 16 females. No neurological deterioration or vertebral artery injuries were observed. Five cases showed malpositioned screws (2.84%), with four of the screws showing cortical breaches of the transverse foramen. There were no clinical consequences for these five patients. One screw in the C1 lateral mass had a medial cortical breach. None of the screws were malpositioned in patients treated using the new entry point. There was a significant relationship between two group (p=0.036). Posterior C1-2 screw fixation can be performed safely using the new inferolateral entry point for C2 pedicle screw fixation for the treatment of high cervical lesions.

Radiographic Evaluation of the Technique for C1 Lateral Mass and C2 Pedicle Screw Fixation in Three Hundred Nineteen Cases

Retrospective radiographic study of the technique for C1 lateral mass screw (C1LMS) and C2 pedicle screw (C2PS) fixation. To evaluate (1) the accuracy of the C1LMS and C2PS placement; (2) the fusion rate between C1 and C2; (3) the risk for vertebral artery (VA) injury. C1LMS and C2PS fixation is widely used when treating atlantoaxial instability. Several authors have reported their experience focusing on the technical outcomes, with many reporting fusion rates near 100%. However, most of them are relatively small series, and many have applied only plain postoperative radiographs instead of computed tomography (CT). Thus, we feel that the accuracy of C1LMS and C2PS placement has not been fully analyzed, as well as the anatomic relationship between the VA and the screws. Between December 2000 and September 2008, the fusion status and accuracy of the screws were evaluated on the postoperative reconstructive CT of 319 patients with atlantoaxial instability. Cases with malpositioned screws underwent CT angiography or magnetic resonance angiography after surgery, to evaluate potential VA injury. C1LMS of 95.5% and C2PS of 92.8% were found to be in a "good" position. After 2007, six cases had malpositioned screws, which were all in the "out" or "down" area of the C2 pedicle. Five cases underwent CT angiography and 1 had magnetic resonance angiography to evaluate potential VA injury. No occlusion, associated aneurysm or fistula of the VA was found. All cases (100%) achieved solid fusion between C1 and C2. C1LMS of 95.5% and C2PS of 92.8% were confirmed to be in good position. None of the screws including the malpositioned caused VA injury, clinically or radiographically. The technique for C1LMS and C2PS fixation appears to be safe and effective.

Spontaneous C1 anterior arch fracture as a postoperative complication of foramen magnum decompression for Chiari malformation type 1

Background:C1 fracture accounts for 2% of all spinal column injuries and 10% of cervical spine fractures, and is most frequently caused by motor vehicle accidents and falls. We present a rare case of C1 anterior arch fracture following standard foramen magnum decompression for Chiari malformation type 1.Case Description:A 63-year-old man underwent standard foramen magnum decompression (suboccipital craniectomy and C1 laminectomy) under a diagnosis of Chiari malformation type 1 with syringomyelia in June 2009. The postoperative course was uneventful until the patient noticed progressive posterior cervical pain 5 months after the operation. Computed tomography of the upper cervical spine obtained 7 months after the operation revealed left C1 anterior arch fracture. The patient was referred to our hospital at the end of January 2010 and C1–C2 posterior fusion with C1 lateral mass screws and C2 laminar screws was carried out in March 2010. Complete pain relief was achieved immediately after the second operation, and the patient resumed his daily activities.Conclusion:Anterior atlas fracture following foramen magnum decompression for Chiari malformation type 1 is very rare, but C1 laminectomy carries the risk of anterior arch fracture. Neurosurgeons should recognize that fracture of the atlas, which commonly results from an axial loading force, can occur in the postoperative period in patients with Chiari malformation.

Targeting a Safe Entry Point for C2 Pedicle Screw Fixation in Patients with Atlantoaxial Instability

This investigation was conducted to evaluate a new, safe entry point for the C2 pedicle screw, determined using the anatomical landmarks of the C2 lateral mass, the lamina, and the isthmus of the pars interarticularis. Fifteen patients underwent bilateral C1 lateral mass-C2 pedicle screw fixation, combined with posterior wiring. The C2 pedicle screw was inserted at the entry point determined using the following method : 4 mm lateral to and 4 mm inferior to the transitional point (from the superior end line of the lamina to the isthmus of the pars interarticularis). After a small hole was made with a high-speed drill, the taper was inserted with a 30 degree convergence in the cephalad direction. Other surgical procedures were performed according to Harm's description. Preoperatively, careful evaluation was performed with a cervical X-ray for C1-C2 alignment, magnetic resonance imaging for spinal cord and ligamentous structures, and a contrast-enhanced 3-dimensional computed tomogram (3-D CT) for bony anatomy and the course of the vertebral artery. A 3-D CT was checked postoperatively to evaluate screw placement. Bone fusion was achieved in all 15 patients (100%) without screw violation into the spinal canal, vertebral artery injury, or hardware failure. Occipital neuralgia developed in one patient, but this subsided after a C2 ganglion block. C2 transpedicular screw fixation can be easily and safely performed using the entry point of the present study. However, careful preoperative radiographic evaluation, regardless of methods, is mandatory.

Clinical and radiological Comparison of treatment of atlantoaxial instability by posterior C1–C2 transarticular screw fixation or C1 lateral mass-C2 pedicle screw fixation

We compared the clinical and radiological results of posterior atlantoaxial fixation surgery using transarticular screws to those using a polyaxial screw–rod system in 55 patients with symptomatic atlantoaxial instability. Patients underwent posterior C1–C2 fixation: 28 patients (group 1) underwent C1–C2 transarticular screw fixation and 27 patients (group 2) underwent C1 lateral mass–C2 pedicle screw fixation. Patients were followed-up for at least 24 months. The clinical and radiological results were evaluated in the early postoperative period and at 3, 6, 12 and 24 months after surgery. Long-term postoperative stability and bone fusion were examined. After surgery, 93% of patients in group 1 and 96% of patients in group 2 were free of neck pain. The solid fusion rates were 82% for group 1 patients and 96% for group 2 patients at 12 months ( p < 0.092). In group 1, three patients showed fibrous union. Four patients had hardware failure due to a screw malposition (one in group 1) and pseudoarthrodesis (two in group 1 and one in group 2). One patient in group 1 had cerebrospinal fluid leakage. One patient in group 2 had occipital neuralgia. One vertebral artery injury occurred during the screw placement in group 1 and another in group 2 during the muscle dissection. C1–C2 transarticular screw fixation and C1 lateral mass–C2 pedicle screw fixation both produced excellent results for stabilization of the atlantoaxial complex, but the radiological outcome tended to be superior in C1 lateral mass–C2 pedicle screw fixation.

Craniocervical Fixation With Occipital Condyle Screws

A human cadaveric biomechanical study comparing craniocervical fixation techniques. To quantitatively compare the biomechanical stability of a new technique for occipitocervical fixation using the occipital condyles with an established method for craniocervical spine fusion. Stabilization of the occipitocervical junction remains a challenge. The occiput does not easily accommodate instrumentation because of access and spatial constraints. In fact, the area available for the implant fixation is limited and can be restricted further when a suboccipital craniectomy has been performed, posing a challenge to current fixation techniques. Occipital screws are also associated with the potential for intracranial complications. Six fresh frozen cadaveric specimens occiput-C4 were tested intact, after destabilization and after fixation as follows: (1) occipital plate with C1 lateral mass screws and C2 pars screws and (2) occipital condyle screws with C1 lateral mass screws and C2 pars screws. Specimens were loaded in a custom spine testing apparatus and subjected to the following tests, all performed under 50-N unconstrained axial preload: flexion, extension, lateral bending, and axial rotation at 1.5 Nm. The constructs were statistically compared with a one-way analysis of variance and compared with the intact condition. Motions were reduced by approximately 80% compared with the intact condition for both configurations under all motions. There were no statistically significant differences in the range of motion (ROM) between the 2 instrumentation conditions. The mean values indicated decreased ROM with the novel occipital condyle screw construct in comparison with the standard occipital plate and rod system. Craniocervical stabilization using occipital condyle screws as the sole cephalad fixation point is biomechanically equivalent with regard to the modes tested (ROM and stiffness) to the standard occipital plate construct.

C2 translaminar screw as the optimal choice for atlantoaxial dislocation with C2–C3 congenital fusion

The entry point and trajectory are very important for transarticular screw (TAS) and C2 pedicle screw (PDS) plantation. When the physical size is not large enough for the screw passing through, an accurate entry point is the most important point for successful screw insertion without vertebral artery (VA) injury and spinal cord injury. Once the laminas of C2 and C3 are fused, the normal anatomic mark might disappear and the insertion point would be hard to find. As a result, the complication of TAS or PDS implantation increases rapidly. We used C2 translaminar screws (TLSs) with C1 lateral mass screws as the optimal fixation for atlantoaxial dislocation in order to reduce the risk of VA injury and spinal cord injury. A 37-year-old woman with atlantoaxial dislocation due to obsolete odontoid fracture complained of neck pain and myelopathy. Preoperative CT reconstruction showed C2-C3 fusion and small size of C2 isthmus. The patient underwent posterior atlantoaxial fusion using C1 lateral mass screws and C2 TLSs. The posterior arch of atlas was removed for decompression and fusion was done at C1-C2 joints by grafting bone fragments from the posterior iliac crest. TLSs combined with C1 lateral mass screws might be a useful technique for patients with atlantoaxial dislocation and C2-C3 fusion, especially with small size of C2 isthmus. Also, the fusion of posterior elements between C2 and C3 might be a relative contraindication for TAS fixation.

Biomechanical Analysis Comparing Three C1–C2 Transarticular Screw Salvaging Fixation Techniques

This is an in vitro biomechanical study. To compare the biomechanical stability of the 3 C1-C2 transarticular screw salvaging fixation techniques. Stabilization of the atlantoaxial complex is a challenging procedure because of its complicated anatomy. Many posterior stabilization techniques of the atlantoaxial complex have been developed with C1-C2 transarticular screw fixation been the current gold standard. The drawback of using the transarticular screws is that it has a potential risk of vertebral artery injury due to a high riding transverse foramen of C2 vertebra, and screw malposition. In such cases, it is not recommended to proceed with inserting the contralateral transarticular screw and the surgeon should find an alternative to fix the contralateral side. Many studies are available comparing different atlantoaxial stabilization techniques, but none of them compared the techniques to fix the contralateral side while using the transarticular screw on one side. The current options are C1 lateral mass screw and short C2 pedicle screw or C1 lateral mass screw and C2 intralaminar screw, or C1-C2 sublaminar wire. Nine fresh human cervical spines with intact ligaments (C0-C4) were subjected to pure moments in the 6 loading directions. The resulting spatial orientations of the vertebrae were recorded using an Optotrak 3-dimensional Motion Measurement System. Measurements were made sequentially for the intact spine after creating type II odontoid fracture and after stabilization with unilateral transarticular screw placement across C1-C2 (TS) supplemented with 1 of the 3 transarticular salvaging techniques on the contralateral side; C1 lateral mass screw and C2 pedicle screw (TS+C1LMS+C2PS), C1 lateral mass and C2 intralaminar screw (TS+C1LMS+C2ILS), or sublaminar wire (TS + wire). The data indicated that all the 3 stabilization techniques significantly decreased motion when compared to intact in all the loading cases (left/right lateral bending, left/right axial rotation, flexion) except extension. All the 3 instrumented specimens were equally stable in extension/flexion and lateral bending modes. TS+C1LMS+C2PS was equivalent to TS+C1LMS+C2ILS (P > 0.05) and superior to TS + wire in axial rotation (P < 0.05). Also, TS+C1LMS+C2ILS was superior to TS + wire in axial rotation (P < 0.05). Fixation of atlantoaxial complex using unilateral transarticular screw supplemented with contralateral C1 lateral mass and C2 intralaminar screws is biomechanically equivalent to C1 lateral mass and C2 pedicle screws and both are biomechanically superior to C1-C2 sublaminar wire in axial rotation.

Surgical Treatment of Craniovertebral Junction Instability : Clinical Outcomes and Effectiveness in Personal Experience

Craniovertebral junction (CVJ) consists of the occipital bone that surrounds the foramen magnum, the atlas and the axis vertebrae. The mortality and morbidity is high for irreducible CVJ lesion with cervico-medullary compression. In a clinical retrospective study, the authors reviewed clinical and radiographic results of occipitocervical fusion using a various methods in 32 patients with CVJ instability. Thirty-two CVJ lesions (18 male and 14 female) were treated in our department for 12 years. Instability resulted from trauma (14 cases), rheumatoid arthritis (8 cases), assimilation of atlas (4 cases), tumor (2 cases), basilar invagination (2 cases) and miscellaneous (2 cases). Thirty-two patients were internally fixed with 7 anterior and posterior decompression with occipitocervical fusion, 15 posterior decompression and occipitocervical fusion with wire-rod, 5 C1-2 transarticular screw fixation, and 5 C1 lateral mass-C2 transpedicular screw. Outcome (mean follow-up period, 38 months) was based on clinical and radiographic review. The clinical outcome was assessed by Japanese Orthopedic Association (JOA) score. Nine neurologically intact patients remained same after surgery. Among 23 patients with cervical myelopathy, clinical improvement was noted in 18 cases (78.3%). One patient died 2 months after the surgery because of pneumonia and sepsis. Fusion was achieved in 27 patients (93%) at last follow-up. No patient developed evidence of new, recurrent, or progressive instability. The authors conclude that early occipitocervical fusion to be recommended in case of reducible CVJ lesion and the appropriate decompression and occipitocervical fusion are recommended in case of irreducible craniovertebral junction lesion.

C1 Lateral Mass-C2 Pedicle Screws and Crosslink Compression Fixation for Unstable Atlas Fracture

Primary clinical trial of limited fixation for unstable Atlas fracture. To clinically validate feasibility, safety and value of the C1 later-mass screw C2 pedicle screw and crosslink compression fixation technique. [corrected] In previous clinical studies, several techniques have been introduced to fix Atlas fracture. But all these treatments have intrinsic disadvantages. Now seeking a means of limited internal fixation has become a worthwhile subject of clinical study. From January 2001 to December 2004, 17 cases of atlas fracture were diagnosed consecutively, 11 cases were operated on with C1 lateral mass and C2 pedicle screws and crosslink fixation, of whom 6 patents had axial instability and rupture of transverse ligament, 1 patient had C2 laminal fracture, and the remaining 4 patients had axial instability. With the assistant of regional anatomy study and fluoroscopy C1 lateral mass screws and C2 pedicle screws were implanted in place, between which connecting rods were applied bilaterally. A crosslink compression was applied between the 2 rods to achieve realignment of C1 lateral mass fracture and C0-C1-C2 into the anatomic position. C1-C2 fusion with posterior bone grafting was performed in patients with axial instability or transverse ligament discontinuity. Operative time ranged from 90 to 176 minutes with a mean of 124 minutes. Intraoperative blood loss ranged from 270 to 1200 mL with a mean of 432 mL. There were no neurologic deficits, vertebral artery related complications or other complications in all patients. No deterioration of the neurologic deficits was noticed 5 days after operation when the patients were brace fixed and began to ambulate. No cerebral hemodynamic deficit was observed in this patient. Radiograph examination showed bone fusion and stability in all patients 3 months after operation. Healing of C2 fracture was confirmed by computed tomography scan. Osteosynthesis of the atlas by C1 lateral mass screws C2 pedicle screws and crosslink compression fixation is an ideal option for C1 burst fracture with or without rupture of the transverse ligament. The procedure allows for partially physiologic reconstruction of the C0-C1-C2 joint and shortens external fixation.

Treatment of pediatric atlantoaxial instability with traditional and modified Goel–Harms fusion constructs

There are several treatment options for rigid fixation at C1-C2 including Brooks and Gallie type wired fusions and C1-2 transarticular screws. The use of a Goel-Harms type fusion, a construct with C1 lateral mass screws and C2 pedicle screws, has not been extensively described in pediatric patients. Here, we describe its relatively safe and effective use for treating pediatric patients by retrospective chart review of patients treated by the senior author for atlantoaxial instability with a Goel-Harms-type constructs during a 3-year period (2005-2007). Six patients were treated using Goel-Harms-type constructs. Five patients were treated utilizing a construct containing C1 lateral mass screws and C2 pedicle screws; one patient was treated using construct containing C1 lateral mass screws and C2 trans-laminar screws. The patients ranged in age from 7 to 17 years old (mean 12.7). All patients had findings of an os odontoideum on CT scans and three of the six patients had T2 hyperintensity on MRI. Three of the six patients presented with transient neurologic deficits: quadraplegia in two patients and paresthesias in two patients. In each patient C1 lateral mass and C2 screws were placed and the subluxation was reduced to attain an anatomical alignment. No bone grafts were harvested from the iliac crest or rib. Local morsalized bone and sub-occipital skull graft was used. All patients tolerated the procedure well and were discharged home on post-operative day 3-4. The patients wore a hard cervical collar and no halo-vests were needed. All patients had solid fusion constructs and normal alignment on post-operative imaging studies performed on average 14 months post-operatively (range: 7-29). The results demonstrated that Goel-Harms fusions are a relatively safe and effective method of treating pediatric patients with atlantoaxial instability and are not dependent on vertebral anatomy or an intact ring of C1. Follow-up visits and studies in this limited series of patients demonstrated solid fusion constructs and anatomical alignment in all patients treated.

Posterior atlanto-axial fixation with polyaxial C1 lateral mass screws and C2 pars screws

C1-C2 instability or painful osteoarthritis are recognised indications for posterior atlanto-axial fixation. In the traditional trans-articular C1-C2 screw fixation, up to 20% of patients cannot have safe placement of bilateral screws in the event of a medially located vertebral artery and a straight screw trajectory in the sagittal plane. The more recently developed C1-C2 fixation technique with individual C1 lateral mass screws and converging C2 pars screws can be employed in case of a medially located vertebral artery and has comparable biomechanical strength. This is a prospective observational study to investigate the advantages, the safety, and the drawbacks of posterior atlanto-axial fixation with polyaxial C1 lateral mass screws and C2 pars screws. Twelve consecutive patients with C1-2 instability (n = 11) and painful osteoarthritis (n = 1) underwent a posterior atlanto-axial fixation with polyaxial C1 lateral mass screws and C2 pars screws. The average follow-up was 16 months and all patients reached the 12-month follow-up. No hardware failure occurred in any of the patients. Correct screw placement and construct stability was found in all 12 patients (100%) at 6 and 12 months after surgery. Mean neck pain on a visual analogue scale (VAS) was 2.1 at 6 months and 2.0 at 12 months. Only transient complications were observed: one patient presented with progressive intestinal herniation through the iliac crest scar; one suffered from severe pain at the posterior iliac crest for 3 months and three patients complained of annoying pain/dysaesthesia in the C2 dermatome for 3-6 months after surgery. This study confirms that posterior atlanto-axial fixation with polyaxial C1 lateral mass screws and C2 pars screws is a safe and effective surgical option in the treatment of atlanto-axial instability or painful osteoarthritis.

C1 dome-like laminotomy and posterior C1–C2 polyaxial screw-rod fixation for a patient with cervical myelopathy due to a retro-odontoid pseudotumor

A 49-year-old man presented with progressive cervical myelopathy caused by a retro-odontoid mass, with associated developmental canal stenosis at C1, and C1–C2 instability. Surgery was scheduled for a dome-like laminotomy at C1, posterior C1–C2 fixation using C1 lateral mass screws and C2 pedicle screws, and structural bone grafting between C1 and C2. Prior to surgery, we produced a 3-dimensional full-scale model of the patient’s cervical spine and performed a simulation of the scheduled surgery. Through the simulation, we accurately evaluated the laminotomy sites and the screw insertion points. During the actual surgery, all procedures were successful. After surgery, the patient’s neurological deficits markedly improved. Successful C1–C2 fusion, adequate decompression of the spinal cord, and spontaneous regression of the retro-odontoid mass were achieved by this procedure without any apparent restriction in neck movement.

OPEN REDUCTION OF C1–C2 SUBLUXATION WITH THE USE OF C1 LATERAL MASS AND C2 TRANSLAMINAR SCREWS

Abstract Objective: Spinal cord compression secondary to a subluxation of one vertebral body over another can be achieved with reduction of the translational deformity. Intraoperative reduction of C1–C2 subluxations can be technically challenging when one uses traditional techniques (e.g., wiring and transarticular screw fixation). The popularization of C1 lateral mass and C2 pedicle screws has allowed surgeons to achieve a more complex realignment at this region of the spine. Control of both C1 and C2 with independent fixation can be used to obtain reduction. In certain instances, placement of C2 pedicle screws is not possible. The use of C2 translaminar screws (if the C2 lamina is present and suitable) is an alternative method of fixation in C2 and can be used for intraoperative reduction. Clinical Presentation: A 15-year-old boy with juvenile rheumatoid arthritis presented with spinal cord compression secondary to a C1–C2 subluxation. The C2 pedicle anatomy precluded safe placement of C2 pedicle screws. An alternative method of fixation with the use of C2 translaminar screws and reduction was performed to obtain proper alignment and decompress the spinal cord. Technique: C1 lateral mass screws and C2 translaminar screws are inserted in the usual fashion. Two contoured rods, two rod holders, and two distractors, combined with C1 lateral mass screws and C2 translaminar screws, were used to achieve reduction. Concomitant distraction between the C2 translaminar screw head and the rod holder resulted in ventral translation of C2 on C1, decompressing the spinal cord. The reduction was maintained by tightening the C2 locking nut onto the rod. Conclusion: The use of C2 translaminar screws (if the C2 lamina is present and suitable) is an alternative method of fixation in C2. C1 lateral mass and C2 translaminar screw fixation provide a powerful means of reducing C1–C2 subluxations and maintaining alignment, achieving indirect decompression of the spinal cord.

Old Atlantoaxial Rotary Subluxation Associated with High-riding Vertebral Arteries: Arthrodesis Using C1 Lateral Mass Screws and C2 Laminar Screws: A Case Report

Old Atlantoaxial Rotary Subluxation Associated with High-riding Vertebral Arteries: Arthrodesis Using C1 Lateral Mass Screws and C2 Laminar Screws: A Case Report

Minimally Invasive Atlantoaxial Fixation with a Polyaxial Screw-rod Construct: Technical Case Report

Posterior C1-C2 fusion with polyaxial screw and rod fixation has become an accepted means of atlanto-axial stabilization. We describe a novel technique for minimally invasive placement of C1 lateral mass screws and C2 pedicle screws for polyaxial screw-rod stabilization. The patient presented with a history of chronic neck pain, as well as a 6-month history of weakness and paresthesias involving her left hand. An Os Odontoideum was present on computed tomographic imaging of the cervical spine. Significant instability was noted on flexion-extension imaging, and magnetic resonance imaging demonstrated mild T2 signal change within the spinal cord. Under fluoroscopic guidance, serial dilators were passed through a 2.5 cm paramedian skin incision to allow placement of an expandable tubular retractor. The exposure was centered on the C2 lateral mass. After expansion of the retractor and further subperiosteal dissection, the C1 and C2 lateral masses were visible permitting placement of a polyaxial screw rod construct. This procedure was carried out bilaterally. Placement of C1 lateral mass and C2 pedicle screws using minimally invasive techniques is technically feasible.

Biomechanical Comparison of Four C1 to C2 Rigid Fixative Techniques: Anterior Transarticular, Posterior Transarticular, C1 to C2 Pedicle, and C1 to C2 Intralaminar Screws

We performed a biomechanical comparison of several C1 to C2 fixation techniques including crossed laminar (intralaminar) screw fixation, anterior C1 to C2 transarticular screw fixation, C1 to 2 pedicle screw fixation, and posterior C1 to C2 transarticular screw fixation. Eight cadaveric cervical spines were tested intact and after dens fracture. Four different C1 to C2 screw fixation techniques were tested. Posterior transarticular and pedicle screw constructs were tested twice, once with supplemental sublaminar cables and once without cables. The specimens were tested in three modes of loading: flexion-extension, lateral bending, and axial rotation. All tests were performed in load and torque control. Pure bending moments of 2 nm were applied in flexion-extension and lateral bending, whereas a 1 nm moment was applied in axial rotation. Linear displacements were recorded from extensometers rigidly affixed to the C1 and C2 vertebrae. Linear displacements were reduced to angular displacements using trigonometry. Adding cable fixation results in a stiffer construct for posterior transarticular screws. The addition of cables did not affect the stiffness of C1 to C2 pedicle screw constructs. There were no significant differences in stiffness between anterior and posterior transarticular screw techniques, unless cable fixation was added to the posterior construct. All three posterior screw constructs with supplemental cable fixation provide equal stiffness with regard to flexion-extension and axial rotation. C1 lateral mass-C2 intralaminar screw fixation restored resistance to lateral bending but not to the same degree as the other screw fixation techniques. All four screw fixation techniques limit motion at the C1 to 2 articulation. The addition of cable fixation improves resistance to flexion and extension for posterior transarticular screw fixation.

Atlantoaxial Fixation using C2 Subarticular Screws and C1 Lateral Mass Screws: A Technical Report

Segmental screw fixation is a useful procedure for the surgical treatment of atlantoaxial subluxation. Currently, C1 lateral mass screws and C2 pedicle screws are the standard screws used in this procedure. However, the C2 pedicle screw can cause serious complications such as vertebral artery injury. Recently we suggested a new trajectory for the C2 screw, the subarticular screw, which has a lower probability of vertebral artery injury compared with the pedicle screw, based on a study using 1 mm-sliced CT scan images and simulation software. We report the first case of segmental screw fixation using C2 subarticular screws along with C1 lateral mass screws. The patient had atlantoaxial subluxation and myelopathy and showed satisfactory results after surgery.

C1-2 Fixation Using Polyaxial Screws and Rods Assisted by Computer Simulation for Revision of Failed Posterior Fusion: A Technical Report

Segmental C1-2 screw fixation using C1 lateral mass screws and C2 pedicle screws is a technically demanding procedure which can cause injuries to the vertebral artery or neural structures as well as massive bleeding from the epidural venous plexus. In particular, this procedure is more difficult in revision cases because of the lack of normal anatomical landmarks, adhesion, and bleeding. The authors report a case of a patient in whom preoperative surgical simulation and planning using computer software was very helpful in the direct screwing of the atlas and axis for a revision of atlantoaxial fusion.

Evaluation of Spinal Laminar Fixation by a New, Flexible Stainless Steel Cable (Sof'wire)

Segmental spinal stabilizations have been carried out in 72 patients (age, 5-79 yr) during the first 2 years of the availability of a new, flexible, multistranded stainless steel cable (Sof'wire, Hillway Surgical Ltd., London). A total of 519 sublaminar and occipital cables have been passed at 280 levels to fix an occipitocervical loop (36 patients) or contoured rectangle (14 patients). In 15 other patients, a Gallie fusion was combined with a C1-C2 lateral mass screw fixation; a cable-bone construct was used in five patients. Clinical and radiological follow-up at 1, 3, 6 (61 patients), 12 (48 patients), and 18 months (29 patients) and at 2 years (8 patients) has demonstrated no cable breakage or loosening. One postoperative death was due to inadequate transoral decompression before posterior fixation, and, in the 32 patients who underwent spinal monitoring, there were no major changes noted during surgery and no new postoperative neurological symptoms or signs. These preliminary observations are encouraging and merit further multicenter investigations.