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.     

Posterior C1-C2 transarticular screw fixation for atlantoaxial arthrodesis

OBJECTIVE: To assess the outcomes associated with C1-C2 transarticular screw fixation. METHODS: The clinical outcomes of 121 patients treated with posterior C1-C2 transarticular screws and wired posterior C1-C2 autologous bone struts were evaluated prospectively. Atlantoaxial instability was caused by rheumatoid arthritis in 48 patients, C1 or C2 fractures in 45, transverse ligament disruption in 11, os odontoideum in 9, tumors in 6, and infection in 2. RESULTS: Altogether, 226 screws were placed under lateral fluoroscopic guidance. Bilateral C1-C2 screws were placed in 105 patients; each of 16 patients had only one screw placed because of an anomalous vertebral artery (n = 13) or other pathological abnormality. Postoperatively, each patient underwent radiography and computed tomography to assess the position of the screw and healing. Most screws (221 screws, 98%) were positioned satisfactorily. Five screws were malpositioned (2%), but none were associated with clinical sequelae. Four malpositioned screws were reoperated on (one was repositioned, and three were removed). No patients had neurological complications, strokes, or transient ischemic attacks. Long-term follow-up (mean, 22 mo) of 114 patients demonstrated a 98% fusion rate. Two nonunions (2%) required occipitocervical fixation. In comparison, our C1-C2 fixations with wires and autograft (n = 74) had an 86% union rate. CONCLUSION: Rigidly fixating C1-C2 instability with transarticular screws was associated with a significantly higher fusion rate than that achieved using wired grafts alone. The risk of screw malpositioning and catastrophic vascular or neural injury is small and can be minimized by assessing the position of the foramen transversaria on preoperative computed tomographic scans and by using intraoperative fluoroscopy and frameless stereotaxy to guide the screw trajectory.     

Synovial cyst at the C1-C2 junction and spondyloarthropathy

A spinal synovial cyst is a rare extradural benign tumor generally located at the lumbar spine, arising at the facet joint capsule, and usually associated with degenerative changes. We describe a 64-year-old woman with a synovial cyst involving the quadrate ligament of the odontoid process, which caused neurologic signs. Her family history was positive for spondyloarthropathy. The radiologic investigations, preoperative differential diagnosis, and association of spondyloarthropathy with this rare benign foramen magnum tumor are of particular interest.     

The effect of translation of the C1-C2 on the spinal canal

The stability of the atlantoaxial articulation depends fundamentally on the integrity of the odontoid process and the ligaments. Ligament stability mostly is maintained by two ligaments: the transverse ligament and the alar, apical ligaments. Failure of the transverse ligament can result in anterior translation of the atlas on the axis. The anteroposterior diameter of the ring of the atlas is approximately 3 cm. The spinal cord and the odontoid process are each approximately 1 cm in diameter, approximately 1/3 the diameter of the ring. According to Steel's rule of thirds, the remaining centimeter of free space allows for some degree of pathologic displacement. The current anatomic study showed that the space available for the spinal cord was limited. The sagittal diameter C1-C2 canal is 18.71 +/- 2.88 mm (excluding 10 mm thickness of the dens and 2.91 +/- 0.69 mm thickness of transverse ligament), with the spinal cord occupying 7.73 +/- 0.87 mm of the available space. Space available for spinal cord at the level of the atlas is 3.44 +/- 1.19 mm plus 1.01 +/- 0.20 mm space anterior to the cord (anterior epidural space) and 5.64 +/- 2.22 mm space posterior to the cord (posterior epidural space), which is approximately in agreement with the normal diameter by Steel's rule of thirds.     

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.     

Biomechanical comparison of C1-C2 posterior fixations. Cable, graft, and screw combinations

STUDY DESIGN: Four combinations of cable-graft-screw fixation at C1-C2 were compared biomechanically in vitro using nondestructive flexibility testing. Each specimen was instrumented successively using each fixation combination. OBJECTIVES: To determine the relative amounts of movement at C1-C2 after instrumentation with various combinations of one or two transarticular screws and a posterior cable-secured graft. Also to determine the role of each component of the construct in resisting different types of loading. SUMMARY OF BACKGROUND DATA: Spinal stiffness increases after instrumentation with two transarticular screws plus a posterior wire-graft compared with a wire-graft alone. Other C1-C2 cable-graft-screw combinations have not been tested. METHODS: Eight human cadaveric occiput-C3 specimens were loaded nondestructively with pure moments, and nonconstrained motion at C1-C2 was measured. The instrumented states tested were a C1-C2 interposition graft attached with multistranded cable; a cable-graft plus one transarticular screw; two transarticular screws alone; and a cable-graft plus two transarticular screws. RESULTS: The transarticular screws prevented lateral bending and axial rotation better than the posterior cable-graft. The cable-graft prevented flexion and extension better than the screws. Increasing the number of fixation points often significantly decreased the rotation and translation (paired t test; P < 0.05). Axes of rotation shifted from their normal location toward the hardware. CONCLUSIONS: It is mechanically advantageous to include as many fixation points as possible when atlantoaxial instability is treated surgically.     

Odontoid process and C1-C2 corrective osteotomy through a posterior approach: technical case report

OBJECTIVE AND IMPORTANCE: To demonstrate a new posterior approach to the anterior elements of the atlas and the axis including the odontoid process. CLINICAL PRESENTATION: A 36-year-old woman presented with ankylosing spondylitis and severe flexion deformity of the cervical spine. She had sustained a trauma 5 years previously, causing the inability to look forward or to open the jaw adequately. An examination demonstrated fixed flexion and rotation of the cervical spine, with no neurological deficit. Radiologically, there was fusion of C1, C2, and the clivus. TECHNIQUE: The upper cervical vertebrae were exposed via a midline posterior incision, the posterior arch of C1 was excised, and the vertebral arteries were mobilized. A wedge osteotomy was performed through the lateral masses of C1 and subsequently through the odontoid. The head was repositioned, and C1-C2 lateral mass screws and a Ransford loop were inserted. CONCLUSION: It is possible to gain sufficient surgical access to the odontoid process via a posterior approach. The technique described is of benefit when the alternative anterior approaches to the upper cervical spine are technically difficult or impossible.     

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.     

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.     

Human rectal absorption of short- and medium-chain C2-C10 fatty acids

PURPOSE: To study the effects of running suture adjustment for reduction of astigmatism after penetrating keratoplasty. Suture adjustments performed during surgery and during the early postoperative and late postoperative periods were retrospectively compared. METHODS: We studied 53 patients who received running suture adjustment after penetrating keratoplasty, either intraoperatively (ISA group, n = 18), early (< 2 weeks) postoperatively (EPSA group, n = 19), or late (> 1 month) postoperatively (LPSA group, n = 16). Refractive and topographic astigmatism and corneal topography were examined at 1, 3, and 6 months after surgery. RESULTS: Overall mean refractive astigmatism and topographic astigmatism at 6 months were 2.55 +/- 1.61 D and 3.12 +/- 1.89 D, respectively (mean +/- SD). The mean refractive astigmatism and topographic astigmatism were 1.88 +/- 1.04 D and 2.35 +/- 1.35 D in the ISA group, 2.32 +/- 1.17 D and 2.70 +/- 1.21 D in the EPSA group, and 3.01 +/- 1.62 D and 4.62 +/- 2.51 D in the LPSA group, respectively (mean +/- SD). The LPSA group demonstrated significantly increased topographic astigmatism compared to the ISA group (p = 0.0048) and the EPSA group (p = 0.015). Although 31.6 and 25.0% of the EPSA and LPSA groups, respectively, did not require postoperative suture adjustments, more eyes (10/18 eyes, 55.6%) in the ISA group did not require the procedure. CONCLUSIONS: Early postoperative suture adjustment was more effective than late postoperative adjustment. Intraoperative suture adjustment may further reduce final astigmatism and the necessity for postoperative suture manipulation.     

Distal femoral osteotomy for lateral compartment osteoarthritis of the knee

Arachidonic acid (AA) in the diet can be efficiently absorbed and incorporated into tissue membranes, resulting in an increased production of thromboxane A2 by platelets and increased ex vivo platelet aggregability. Results from previous studies have shown that AA is concentrated in the membrane phospholipids of lean meats. However, the concentration of AA in the visible fat portion of meats also may be significant despite being ignored in most studies. The aim of this study was to accurately quantitate the AA content of visible fat and the lean portion of beef, lamb, pork, chicken, duck, and turkey. The visible fat of meat contained a significant quantity of AA, ranging from 20 to 180 mg/100 g fat, whereas the AA content of the lean portion of meat was lower, ranging from 30 to 99 mg/100 g lean meat. Beef and lamb meats contained lower levels of AA in both the visible fat and lean portion than that from the other species. The highest level of AA in lean meat was in duck (99 mg/100 g), whereas pork fat had the highest concentration for the visible fats (180 mg/100 g). The lean portions of beef and lamb contained the higher levels of n-3 polyunsaturated fatty acids (PUFA) compared with white meats which were high in AA and low in n-3 PUFA. The present data indicate that the visible meat fat can make a contribution to dietary intake of AA, particularly for consumers with high intakes of fat from pork or poultry meat.     

Transoropharyngeal approach to C 1 and C 2

In rare cases of diseases or traumatic lesions of C1 and C2 it is possible to prefer the short way with the transoropharyngeal approach. The operative procedure is described. Specialities are explained in three cases. A metallic osteosynthesis in case of odontoid fracture is seldom indicated.     

2-[N-Acylamino(C1-C3)alkyl]indoles as MT1 melatonin receptor partial agonists, antagonists, and putative inverse agonists

The synthesis of several novel indole melatonin analogues substituted at the 2-position with acylaminomethyl (8-11), acylaminoethyl (5a-k), or acylaminopropyl (13) side chains is reported. On the basis of a novel in vitro functional assay (specific binding of [35S]GTPgammaS), which can discriminate agonist from partial agonist, antagonist, and inverse agonist ligands, 5a,g, h,j and 13 were shown to be partial agonists, 5d,e and 8-11 competitive antagonists, and 5b,c,k putative inverse agonists. Binding and functional assays were performed on cloned human MT1 receptor. Structure-activity relationship considerations indicate that N-[1-aryl-2-(4-methoxy-1H-indol-2-yl)(C1-C2)alkyl]alkanamides represent a lead structure for this type of ligands.     

C1 inhibitor removes the entire C1qr2s2 complex from anti-C1Q monoclonal antibodies with low binding affinities

Evidence is presented for a new C1 Inhibitor (C1 INH) function. C1 INH was capable of dislodging the entire C1qr2s2 complex from C1-activating substances that bound weakly to the globular heads of C1q. Two different mouse IgG1 monoclonal antibodies with different affinities for C1q globular heads were compared for their complement-activating properties in the presence of normal human serum. As expected the higher affinity monoclonal antibody (Qu) was more effective in binding C1q and causing C1-mediated C4b deposition. Unexpectedly, time responses of C1 (C1q) binding to immobilized 3C7 reached a peak then gradually decreased. However, C1q remained constantly bound to immobilized Qu. These results indicated that after C1 activation in human serum, the entire C1 complex (including C1q) was dislodged from 3C7, but not from immobilized Qu. The addition of purified C1 INH to purified C1, which had bound to immobilized 3C7, resulted in removal of C1 (C1q). Removal of the entire C1qr2s2 did not occur when C1 INH preparations were first neutralized by the addition of purified activated C1s. In summary, it is suggested that C1 INH plays a prominent role in dislodging the entire C1qr2s2 from immunoglobulin preparations which have a low binding affinity for the globular heads of C1q.     

Visualization of C7-T1 on portable lateral cervical spine radiographs using a lead-lined acrylic filter

OBJECTIVE: To determine whether lead-lined acrylic cervical filters can improve the quality of portable lateral cervical spine (c-spine) radiographs for trauma patients. METHODS: Twenty trauma patients who required portable c-spine x-rays had these taken with a lead filter attached to the collimator of the portable x-ray machine to improve penetration and visualization of lower cervical structures without overpenetrating upper cervical structures. The radiographs of these patients were compared with the first portable c-spine radiographs without filters for 20 controls matched for gender and injury severity. The comparison of radiographs was done by an experienced emergency physician and a neuroradiologist blinded to whether the filter was used. RESULTS: The two groups were similar for demographic and clinical characteristics. There was a significant improvement in the ability to visualize the C7-T1 level for the filter group compared with the control group (65% vs 30%, p < 0.05). Agreement between the physicians was excellent (kappa = 0.79, 95% CI = 0.60-0.99). CONCLUSIONS: Lead-lined acrylic filters improve the ability to visualize the lower c-spine in trauma patients.