Cervical Spine Instrumentation Research Articles

Unanticipated Difficult Endotracheal Intubations in Patients with Cervical Spine Instrumentation

We present two cases of unanticipated difficult airway in patients requiring reoperation after cervical spine instrumentation. In both cases, the upper airway examination was normal, and fiberoptic-guided intubation proceeded with the patient sedated and breathing spontaneously. Cord visualization was difficult, but the scope was eventually advanced into the trachea and the endotracheal tube placed safely. Later review of radiographs showed the previously unrecognized protrusion of cervical hardware into the meso- and hypopharynx. We recommend that anesthesiologists review recent radiographic studies for potential airway compromise before approaching the airway of patients presenting for revision of cervical instrumentation.

Retraction: Cortical Margining Capabilities of Fins Associated with Ventral Cervical Spine Instrumentation

Fins incorporated into the design of a dynamic cervical spine implant have been employed to enhance axial load- bearing ability, yet their true biomechanical advantages, if any, have not been defined. Therefore, the goal of this study was to assess the biomechanical and axial load-bearing contributions of the fin components of the DOC ventral cervical stabilization system. Eighteen fresh cadaveric thoracic vertebrae (T1-T3) were obtained. Three test conditions were devised and studied: Condition A (DOC implants with fins were placed against the superior endplate and bone screws were not inserted); Condition B (DOC implant without fins was placed and bone screws were inserted); and Condition C (DOC implant with fins were placed against the superior endplate and bone screws were inserted). Specimens were tested by applying a pure axial compressive load to the superior platform of the DOC construct, and load-displacement data were collected. Condition C specimens had the greatest stiffness (459 +/- 80 N/mm) and yield load (526 +/- 168 N). Condition A specimens were the least stiff (266 +/- 53 N/mm), and had the smallest yield loads (180 +/- 54 N). The yield load of condition A plus condition B was approximately equal to that of condition C, with condition A contributing about one-third and condition B contributing two-thirds of the overall load-bearing capacity. Although the screws alone contributed to a substantial portion of axial load-bearing ability, the addition of the fins further increased load-bearing capabilities.

A Prospective Analysis of Intraoperative Electromyographic Monitoring of Posterior Cervical Screw Fixation

This is a prospective study of 26 patients undergoing posterior cervical spine instrumentation with lateral mass or pedicle screws to determine the correlation between intraoperative screw stimulation thresholds and the position of posterior cervical lateral mass and pedicle screws. One hundred forty-seven posterior cervical screws (122 lateral mass screws and 25 C7 pedicle screws) in 26 patients were electrically stimulated intraoperatively and stimulation thresholds recorded. Computed tomography (CT) scans were taken postoperatively and were evaluated independently to assess screw position. Electromyographic (EMG) thresholds and CT data were compared to assess the accuracy of the EMG screw stimulation technique in detecting screw malposition. Intraoperative electrical stimulation was accurate in verifying screw position. A stimulation threshold of 15 mA provided a 99% positive predictive value (89% sensitivity, 87% specificity) that the screw was within the lateral mass or pedicle. Stimulation values of 10-15 mA provided a 13% predictive value (66% sensitivity, 90% specificity) that the screw was within the lateral mass or pedicle. A stimulation value of <10 mA provided a 100% predictive value that the screw was malpositioned (70% sensitivity, 100% specificity). Intraoperative evoked EMG monitoring is a valuable tool in posterior cervical instrumentation using lateral mass and pedicle screws. Stimulation thresholds in this study correlated with screw position. Stimulation values of >15 mA reliably predict acceptable screw position. Values between 10 and 15 mA are generally associated with acceptable screw position, although exploration is recommended. Values below 10 mA are associated with screw malposition and warrant exploration, repositioning, and possible removal.

Value of intraoperative true lateral radiograph of C2 pedicle for C1-2 transarticular screw insertion

Background context Transarticular C1-2 screws are widely used in posterior cervical spine instrumentation. Injury to the vertebral artery during insertion of transarticular Cl-2 screw remains a serious complication. Use of a computer-assisted surgery system decreases this complication considerably. However, this system encounters problems in ensuring complete accuracy because of positional variations during preoperative and intraoperative imaging generation. Therefore, intraoperative fluoroscopy still is one of the commonly used methods to guide insertion of transarticular Cl-2 screw. Evaluation of a true lateral radiographic view of the C2 pedicle for screw trajectory during C1-2 transarticular screw insertion may help to minimize this potential complication. Purpose To evaluate the value of intraoperative true lateral radiograph of the C2 pedicle for screw trajectory during C1-2 transarticular screw insertion. Study design To compare the height of the C2 pedicle area allowing instrumentation on true lateral view radiograph of the C2 pedicle and computed tomographic (CT) scan with multiplanar reconstruction. Methods Twenty embalmed human cadaveric cervical spine specimens were used to insert a total of 40 C1-2 transarticular screws using Magerl and Seemann technique. One side of the C2 transverse foramen was filled with radiopaque material (lead oxide) to simulate the artery and to demarcate the danger zone for better visualization on radiography. Measurements and calculation of the mean and standard deviation of the height of the area allowing instrumentation of the C2 pedicle were done on true lateral view radiograph of the C2 pedicle, the sagittal and 30° sagittal views relative to the frontal plane passing exactly through the center of the C2 pedicle of CT scans. Student t test was applied to calculate the statistical significance of measured values. Statistical significance was defined as p≤.001. Results On true lateral radiographic views of the C2 pedicle, the height of the area allowing instrumentation of the pedicle was 7.75±0.92 mm (right) and 7.64±0.63 (left), p≥.36. Using sagittal CT scan views, the height of pedicles was 7.71±0.7 mm (right) and 7.58±1.01 mm (left), p≥.23. On 30° sagittal CT scan views, the height of pedicles was 7.84±1.00 mm (right) and 7.76±1.02 mm (left), p≥.27. The p value was ≥.78, ≥.56, and ≥.49 for true lateral radiographic view and sagittal CT scan view, true lateral radiographic view and 30° sagittal CT scan view, and sagittal CT scan view and 30° sagittal CT scan views, respectively. On lateral view of cervical spine, the decline angle of the transarticular screw was 51.3±0.50° (right) and 50.68±0.41° (left), p≥.17. Mean decline angle was 51±0.43°. On the anteroposterior (AP) view, radiograph median angle was 6.87±0.53° (right) and 6.0±0.59° (left), p≥.25. Mean median angle was 6.44±0.62°. Conclusions True lateral radiographic views of the pedicles provide useful information for defining screw trajectory intraoperatively. Using this view along with AP and lateral view of cervical spine and preoperative three-dimensional CT scan may narrow the margin of error in this delicate area.

Cortical Margining Capabilities of Fins Associated with Ventral Cervical Spine Instrumentation

Fins incorporated into the design of a dynamic cervical spine implant have been employed to enhance axial load-bearing ability, yet their true biomechanical advantages, if any, have not been defined. Therefore, the goal of this study was to assess the biomechanical and axial load-bearing contributions of the fin components of the DOC ventral cervical stabilization system. Eighteen fresh cadaveric thoracic vertebrae (T1-T3) were obtained. Three test conditions were devised and studied: Condition A (DOC implants with fins were placed against the superior endplate and bone screws were not inserted); Condition B (DOC implant without fins was placed and bone screws were inserted); and Condition C (DOC implant with fins were placed against the superior endplate and bone screws were inserted). Specimens were tested by applying a pure axial compressive load to the superior platform of the DOC construct, and load-displacement data were collected. Condition C specimens had the greatest stiffness (459 ± 80 N/mm) and yield load (526±168 N). Condition A specimens were the least stiff (266±53 N/mm), and had the smallest yield loads (180±54 N). The yield load of condition A plus condition B was approximately equal to that of condition C, with condition A contributing about one-third and condition B contributing two-thirds of the overall load-bearing capacity. Although the screws alone contributed to a substantial portion of axial load-bearing ability, the addition of the fins further increased load-bearing capabilities.

Anterior microsurgery in multisegmental cervical spondylosis

Objective: To study the anterior surgical approach, single or multisegmental extensive spondylectomy, vertebral body replacement combined with microsurgical decompression and anterior osteosynthesis with titanium steel plate in the multisegmental cervical spondylosis. Methods: According to the clinical symptoms of advanced cervical myelopathy and the neuroradiologic detection of multisegmental cervical spondylosis (MSCS) of the patients, 24 cases were selected and operated with the Caspar cervical spine instrumentation system, the recently developed bony fusion and osteosynthetic techniques and the microsurgical skills. Results: The pre- and postoperative neurological statuses of the patients were evaluated by the Nurick grading system of cervical spondylotic myelopathy (CSM). Upgrade was found in 22 of the 24 patients (91%) in varying degrees postoperatively. Two patients (8%) were unchanged and none of the patients became worse. Conclusion: The techniques we used for multisegmental cervical spondylosis, where the relevant compressive abnormality is located anterior to the spinal cord, can, even in advanced cases, be performed in a safe and effective manner, with satisfactory effects of decompression and fixation and resulting in a significant relief of preoperative clinical symptoms and signs in the majority of the patients.

4:10 Instrumented posterior occipitocervical fusion in inflammatory arthritis

Purpose of study: This study evaluates the outcome of posterior instrumented occipitocervical fusion (PIOF) in an inflammatory arthritis population.Methods used: Eighteen consecutive patients undergoing PIOF were evaluated. Patient demographics and joint counts, Ranawat grades (RGs) and neck pain visual analogue scores (VAS) were collected prospectively during clinic visits before and after surgery. All patients had PIOF with autograft, and six patients had a preceding transoral odontoidectomy during the same anesthetic. All patients were braced postoperatively for a 3-month duration. All patients were seen and assessed at 6 weeks, 3 months, 6 months and 1 year annually.of findings: Seventeen of the 18 patients had rheumatoid arthritis, including 1 with juvenile onset rheumatoid arthritis and 1 with psoriatic arthritis. There were 4 males and 14 females; 8 were Caucasian, 8 were Aboriginal. Mean age was 58 years (range, 32 to 85), mean disease duration was 20 years (range, 10 to 35) and mean number of joints affected was 41 (range, 16 to 71). Sixty-seven percent were taking corticosteroids. RG before surgery was 2 in 28%, 3a in 55% and 3b in 17%. Mean VAS score before surgery was 8.8 of 10. All patients had an atlantodens interval of greater than 5 mm and vertical migration of the odontoid (VMO), and six patients had posterior atlantodens interval of less than 13 mm. Six patients had a transoral odontoidectomy for an irreducible C1–C2 subluxation and VMO. All patients had a PIOF. Eight patients (44%) had fusion to C3, six (33%) to C4 and two each (11% each) to C6 and C7, respectively. Mean odds ratio (OR) time was 239 minutes (range, 100 to 600), mean blood loss was 392 ml (range, 100 to 1,000). Mean follow-up was 24 months (range, 3 to 56; there was one death at 3 months). Fourteen patients (78%) had a postoperative RG of zero (no paresthesia or weakness), and 83% had an improvement of at least two grades on the RG. The postoperative VAS declined by a mean of 7.8 (range, 3 to 10). There were three deaths at 3, 18 and 21 months, respectively. Causes of death were pneumonia with respiratory failure and two cases of cardiopulmonary failure. Two patients (11%) had a major complication (hardware failure in one, and a soft palate dehiscence and hydrocephalus in the other), and four patients (22%) had minor complications. Those patients who died had significantly worse underlying arthritis (disease duration 28 vs. 18 years: p=.017; mean affected joint count 58 vs. 38; p=.026), had worse preoperative RG (100% at least grade 3A vs. 67% at least grade 3A; p=.035) required more extensive surgery (mean OR time 447 vs. 197 minutes; p=.002; transoral approach in all three deaths vs. 3 of 15 survivors; p=.025; level of cervical fusion to C6–C7 in 67% vs. 13%; p=.043); more blood loss (617 cc vs. 347 cc; p=.047) and had less improvement in their postoperative RG (67% less than 1 grade improved vs. 7% less than 1 grade improved; p=.038). Age and corticosteroid use were not significantly associated with death.Relationship between findings and existing knowledge: This study supports previous findings that PIOF is a safe and effective procedure for inflammatory arthritis patients with craniocervical involvement, but that the long-term outcome is less favorable in patients with high preoperative RG.Overall significance of findings: Overall inflammatory arthritis patients undergoing PIOF had markedly improved RG and VAS. Although there were no perioperative deaths, patients requiring transoral odontoidectomy had worse underlying inflammatory arthritis, worse radiographic and neurologic parameters and a higher long-term risk of death.Disclosures: Device or drug: posterior cervical spine instrumentation: Synthes Starlock. Status: approved. Device or drug: posterior cervical spine instrumentation: Sofamor Danek Lateral Mass Plates. Status: approved.Conflict of interest: No conflicts.

Advances in cervical spine instrumentation

This review covers original studies from the past 2 years pertaining to the use of instrumentation in the treatment of degenerative disease of the cervical spine. Although the use of anterior instrumentation in single-level anterior diskectomy and fusion remains controversial, good evidence now exists that the use of anterior cervical plates leads to improved clinical results in patients undergoing two-level diskectomy and fusion. Several anterior cervical plating systems are currently available, but those systems that employ unicortical screw fixation and incorporate a locking mechanism for fixing screws to the plate appear to provide optimal stability along with minimal risk to neurovascular structures. Numerous methods have been introduced for posterior fusion and instrumentation of the cervical spine. Staying abreast of evolving indications and recognized pitfalls of these techniques can provide the surgeon with a powerful armamentarium for treating degenerative disease of the cervical spine. Finally, several new techniques for accomplishing occipitocervical fusion are presented. Abbreviations:ACDF anterior cervical diskectomy and interbody fusion, CT computed tomography The purpose of this paper is to review some of the most recent developments in terms of indications and options for instrumentation of the cervical spine, with special emphasis on the treatment of degenerative conditions. To avoid repetition of previous reviews, this report covers only original studies published within the past 2 years. The cervical spine afflicted by rheumatoid arthritis or degenerative spondylosis is a frequent target for surgical intervention, either to relieve pain or to treat or prevent development of neurologic injury. An additional goal is the re-establishment or preservation of structural stability, usually in the form of stable interosseous fusion. Modern instrumentation techniques have evolved from a perceived need to maintain alignment, enhance fusion rates, and avoid pseudarthroses. This review examines recent studies involving the use of instrumentation in three different categories of cervical spine surgery: anterior fusions, posterior fusions, and occipitocervical fusions.

Introduction to odontoid fractures: controversies in the management of odontoid fractures

Although odontoid fractures were first classified more than 25 years ago,5 the management of these fractures remains controversial. Whereas the nonoperative management with external immobilization devices often leads to successful healing, certain fracture features and patient characteristics have been associated with an increased risk of bone nonunion.6,17 Recent technological advances in cervical spine instrumentation techniques have provided additional options for the management of these common fractures.1,12,13,24,27,28 However, an absence of rigorous studies in which the investigators compare management methods may contribute to the varying methods used by spine surgeons when approaching similar injuries. In this issue of Neurosurgical Focus, various aspects of the management of odontoid fractures are examined. In an evidence-based analysis of methods for treating odontoid fractures the authors examine the best available published data to determine the level of scientific data supporting the use of various treatment options.3 In epidemiological studies the investigators examine factors contributing to the unusual incidence of spinal cord injury with odontoid fractures as well as the unique considerations that may be attendant on the management of posteriorly displaced fractures. In two other studies the authors discuss the application of specific surgical techniques in treating odontoid fractures, whereas in an additional two reports the authors evaluate the difficulties in managing elderly patients with these injuries. Finally, the use of newer osteoinductive agents is examined as a potential adjunct in the surgical management of bony defects in the dens.

Computer-assisted surgery in posterior instrumentation of the cervical spine: an in-vitro feasibility study.

Transarticular C1/2 screws are widely used in posterior cervical spine instrumentation. The use of pedicle screws in the cervical spine remains uncommon. Due to superior biomechanical stability compared to lateral mass screws, pedicle screws can be used, especially for patients with poor bone quality or defects in the anterior column. Nevertheless there are potential risks of iatrogenic damage to the spinal cord, nerve roots or the vertebral artery associated with both posterior cervical spine instrumentation techniques. Therefore, the aim of this study was to evaluate whether C1/2 transarticular screws as well as transpedicular screws in C3 and C4 can be applied safely and with high accuracy using a computer-assisted surgery (CAS) system. We used 13 human cadaver C0-C5 spine segments. We installed 1.4-mm Kirschner wires transarticular in C 1/2, using a specially designed guide, and drilled 2.5-mm pedicle holes in C3 and C4 with the assistance of the CAS system. Hole positions were evaluated by palpation, CT and dissection. Forty-eight (92%) of the 52 drilled pedicles were correctly positioned after palpation, imaging and dissection. The vertebral artery was not injured in any specimen. All of the 26 C1/2 Kirschner wires were placed properly after imaging and dissection evaluations. No injury to vascular or bony structures was observed. C /2 transarticular screws as well as transpedicular screws in the cervical spine can be applied safely and with high accuracy using a CAS system in vitro. Therefore, this technique may be used in a clinical setting, as it offers improved accuracy and reduced radiation dose for the patient and the medical staff. Nevertheless, users should take note of known sources of possible faults causing inaccuracies in order to prevent iatrogenic damage. Small pedicles, with a diameter of less than 4.0 mm, may not be suitable for pedicle screws.

Comparison of Biomechanical Human Neck Models: Muscle Forces and Spinal Loads at C4/5 Level

This study developed a three-dimensional biomechanical model to investigate the internal loads on the human neck that result from isometrically generated loads resisted by a force on the head. The first goal was to apply the double-optimization (DOPT) method, the EMG-based method, and the EMG assisted optimization (EMGAO) method to the neck model, calculating muscle forces and C4/5 cervical joint loads for each method. The second goal was to compare the results of the different methods, and the third was to determine maximum exertion forces in the cervical spine for isometric contractions. To formulate the EMG-based model, electromyographic signals were collected from 10 male subjects. EMG signals were obtained from 8 sites around the C4/5 level of the neck by surface electrodes, while the subject performed near maximum, isometric exertions. The mean maximum values (±SD) calculated for C4/5 joint compressive forces during peak exertions were 1654 (±308) N in flexion by the EMG method, 1674 (±319) N in flexion by the EMGAO method, and 1208 (±123) N in extension by the DOPT method. In contrast to the DOPT method, the EMG and EMGAO methods showed activation of all the muscles, including the antagonists, and accommodated various load distribution patterns among the agonist muscles during generation of the same magnitude of moments, especially in lateral bending. The EMG and EMGAO methods predicted higher cervical spinal loads than previously published results by the DOPT method. These results may be helpful to engineers and surgeons who are designing and using cervical spine implants and instrumentation.

Complications of Cervical Spine Instrumentation

Summary: Because of the multitude of hardware types and methods of use, the spine surgeon should be aware of the potential of complications and how best to avoid them. This article reviews several instrumentation techniques and their associated anatomic, mechanical, and clinical complications.