Safe lateral-mass screw lengths in the Roy-Camille and Magerl techniques. An anatomic study

The Attallah screw: Where safety meets robustness in posterior subaxial cervical instrumentation

Posterior fixation of the subaxial cervical spine (SCS) commonly relies on the application of lateral mass screws (LMS), with pedicle screws being a less prevalent alternative. The present study provides another option: A recently introduced novel approach, the Attallah screw, intended to ensure a safety profile comparable to that of LMS, combined with a strength profile similar to that of pedicle screws. The focus of the present study is the comparative analysis of peak insertion torques for these three screw types. Employing standard surgical techniques and instruments, Attallah screws were scheduled for insertion on the right side of the SCS in 15 cadavers, pedicle screws on the left side in 8 cadavers, and LMS on the left side in the remaining 7 cadavers. The peak insertion torque was recorded using an electronic torque screwdriver. The results revealed that the peak insertion torques were similar in the pedicle and the Attallah screw at C3, C4 and C7, but differed at C5 (mean ± SD; pedicle, 79.5±19.6 cNm; Attallah, 56.7±18.5 cNm; P=0.029) and C6 (pedicle, 85.4±28.7 cNm; Attallah, 49.8±17.9 cNm; P=0.004) in favor of the superior pedicle screw measurements. The peak insertion torques of the pedicle screw were superior to the corresponding data from the LMS from C4 to C7. By contrast, the peak insertion torques of the Attallah screw were only superior to those of the LMS at C7 (Attallah, 69.5±24.5 cNm; lateral mass, 40.5±21.4 cNm; P=0.030), although similar trends were observed at the other cervical levels. On the whole, the findings presented herein indicate the level-dependent superior robustness of the Attallah screw as a posterior cervical fixation method compared to the LMS. However, from a biomechanical perspective, the pedicle screw remains the preeminent choice for fixation within the C5-C6 range.

Surgical treatment of craniocervical instability: comparison of two constructs regarding clinical and radiological outcomes of 100 patients

PURPOSE

There is an increased demand for surgical solutions to treat craniocervical instability. This retrospective study demonstrates the clinical and radiological outcomes of unstable craniocervical junction treated with occipitocervical fusion.

MATERIAL AND METHODS

The mean age of 52 females and 48 males was 56.89 years. The clinical and radiological outcomes were assessed, including NDI, VAS, ASIA score, imaging, complications and bony fusion in two used constructs: a modern occipital plate-rod-screw system (n = 59) and previous bilateral contoured titanium reconstruction plates-screws (n = 41).

RESULTS

Clinically and on imaging, patients presented with neck pain, myelopathy, radiculopathy, vascular symptoms and craniocervical instability. The mean follow-up was 6.47 years. A solid bony fusion was achieved in 93.81% of the patients. The NDI and the VAS improved significantly from 28.3 and 7.67 at the presentation to 16.2 and 3.47 at the final follow-up. The anterior and posterior atlantodental interval (AADI and PADI), the clivus canal angle (CCA), the occipitoaxial angle (OC2A) and the posterior occipitocervical angle (POCA) improved significantly. Six patients required early revision.

CONCLUSION

Occipitocervical fusion can yield excellent results regarding clinical improvement and long-term stability with a high fusion rate. Simple reconstruction plates, though more demanding surgically, achieve similar results. Preserving a neutral patient's position for fixation avoids postoperative dysphagia and may help prevent adjacent segment disease development.

Preliminary experience with a novel facet-based lateral mass drill guide for the placement of lateral mass screws compared to freehand technique: a cadaveric study

BACKGROUND CONTEXT

Lateral mass screw fixation is the standard for posterior subaxial cervical fixation. Several freehand surgical techniques for placing lateral mass screws have been described which rely on anatomical landmarks and surgeon mastery of the technique to safely place screws. The accuracy of these freehand techniques is inherently variable and can be influenced by a surgeon's level of clinical experience. A novel technique was developed that utilizes the plane of the facet joint to create lateral mass screw pilot holes parallel with the joint line to improve the safety and accuracy of lateral mass screw placement regardless of experience.

PURPOSE

To assess the safety and accuracy of lateral mass screw placement using a novel lateral mass drill guide instrument (LM Guide), compared to standard freehand technique.

STUDY DESIGN

Randomized cadaveric study utilizing multiple surgeon evaluators to compare the safety and accuracy of guided cervical lateral mass placement compared to traditional freehand techniques.

MATERIALS AND METHODS

Lateral mass screws were placed from C3 to C7 in 20 cadaver specimens by 8 spine surgeons of varying levels of clinical experience (4 attendings, 4 fellows). Screws were placed bilaterally using standard anatomic landmarks ("freehand") randomly allocated on one side and using the LM Guide on the other. Cadaveric specimens were imaged with high-resolution CT to assess screw placement. Zone grading for safety was conducted based on screw tip position and clinical severity of screw breach was based on proximity to surrounding neurovascular anatomy. Screws were graded as safe, at-risk, or critical, with at-risk and critical screws considered malpositioned. To assess the accuracy of screw trajectory placed using the LM Guide compared to freehand, sagittal screw angle was measured and compared to an "ideal" screw path parallel to the facet joint line. Freehand and LM Guide groups were compared using Pearson's chi-square correlation.

RESULTS

Screw placement using the LM guide yielded a significantly lower rate of screw malpositioning, with 7 of 91 (7.7%) compared with 18 of 99 (18.2%) screws placed in the At-Risk or Critical Zones, p<.05. Of the 91 screws inserted using the LM Guide, 84 (92.3%) were in the Safe Zone, 7 (7.7%) were At-Risk, and 0 were in Critical zones. There was no incidence of neural or transverse foramen breaches with the LM Guide. In comparison, for the 99 screws inserted freehand, 81 (81.8%) were Safe, 14 (14.1%) were At-Risk, and 4 (4.1%) were in Critical zones. The 4 Critical zone freehand screw breaches included 1 neural foramen breach, 2 transverse foramen breaches, and 1 facet breach. The LM Guide also resulted in higher accuracy of screw trajectory, as indicated by a significant reduction in sagittal screw angle compared with freehand, p<.01. Notably, in the less-experienced surgeon cohort, the LM Guide significantly reduced the sagittal screw angle and resulted in no critical screw breaches compared to 3 critical breaches with freehand technique suggesting there might be a benefit in decreasing the learning curve associated with lateral mass screw placement.

CONCLUSIONS

Lateral mass screw placement with a novel LM Guide that uses the facet joint to control screw trajectory improved the accuracy and reproducibility of screw placement with a significant reduction in screw breach rate and sagittal screw angle compared to freehand techniques regardless of surgeon experience level.

CLINICAL SIGNIFICANCE

The inherent variability of freehand lateral mass screw placement can increase the risk of clinical complications associated with screw malpositioning. The technique presented in this cadaveric study may be a viable alternative to standard freehand technique that can improve the overall safety of lateral mass screw placement.

Cervical lateral mass screw length analysis in men versus women

Posterior fixations with lateral mass screws have become popular. The Roy-Camille and the Magerl techniques have been established and screw length was identified as a particularly important element. Sex and ethnicity are significant factors in cervical spine morphology, but few studies have been performed for screw length. We performed measurements using computed tomography (CT) images of adult patients hospitalized for surgery of the cervical spine, with targeted 3D data analysis. The final number of patients was 47 (33 men, 14 women) and 235 vertebrae. With the Roy-Camille technique, the screw length was longest at C3 (men: 13.0 mm ± 1.9 mm, women: 13.0 mm ± 1.9 mm) and smallest at C7 (men: 10.8 mm ± 1.8 mm, women: 9.4 mm ± 1.2 mm). With the Magerl technique, the screw length was smallest at C3 (men: 14.8 mm ± 1.6 mm, women: 14.3 mm ± 1.6 mm) and longest at C7 for men (16.8 mm ± 2.8 mm), and at C6 for women (15.4 mm ± 3.0 mm). To differ from spinal canal or pedicle, cervical lateral mass showed no obvious morphological differences from that of subjects of other ethnicity. The placement of a standard lateral mass screw would not cause complications in Japanese patients, even with the use of devices designed in North America or Europe. However, the anatomical background is essential because it is important to optimize the selection for each patient to avoid complications considering sex and individual differences.

Comparison of the maximum possible lengths of insertable screws in the Subaxial Cervical Spine

BACKGROUND

Lateral mass screws are the most commonly used fixation technique in the Subaxial Cervical Spine (SCS), their main advantages being that they are easy to insert and safe in their application. Pedicle screws are significantly longer, are quite challenging to insert in most settings and are accompanied by the risk of serious complications such as vascular and neural injuries. We have therefore developed a new technique, which permits safe insertion of long screws in the SCS.

METHODS

A radiological evaluation was carried out to determine the maximum possible insertable screw length in the SCS when using the following techniques: pedicle, lateral mass (Magerl's) and "Attallah" screws. Scans of 66 cervical spines were analyzed to determine the maximum possible screw lengths of all three screw insertion techniques, based on the standard description through the vertebrae from C3 to C7.

RESULTS

The maximum possible length of the Attallah screw of 20.7 ± 2.5 mm (mean value ± SD) is only 2.4 mm shorter than the pedicle screw (23.1 ± 1.8 mm) along the SCS. The lateral mass screw is with 10.2 ± 1.3 mm full 12.9 mm shorter than the pedicle screw.

CONCLUSIONS

The maximum possible length of the Attallah screw is close to that of the pedicle screw and significantly greater than that of the lateral mass screw. We provide a fixation method comparable to the pedicle screw in its strength and to the lateral mass screw in its safety.

Radiological analyses of the dimensions of the pedicle and dorsal part of the transverse process of subaxial vertebrae in the context of cervical spine surgery

BACKGROUND

Knowledge of the anatomical dimensions of distinct areas of the vertebral bodies and vertebral arches of the subaxial cervical spine are indispensable in the planning of osteosynthesis. The minute dimensions and complex anatomical orientation of the posterior vertebral arch structures in the subaxial spine render the insertion of screws - where needed - a challenging procedure. The pedicle option carries the risk of serious complications while the alternative of lateral mass only permits the insertion of short screws.

OBJECTIVE

The transverse process of the subaxial vertebrae offers unique possibilities on all counts and seems quite comparable in its dimensions with the pedicle. To our knowledge it has not been used previously for the insertion of screws in the subaxial spine.

METHODS

Therefore, the scans of 66 cervical spines were analysed for distinct lines of both structures.

RESULTS

The widths and lengths of the dorsal part of the transverse processes and of the pedicles are similar between both sides. Clear differences between females and males could be observed. The widths of both structures were closer to each other in C3 than in C4 to C7, while the lengths derived the most in C7.

CONCLUSION

The dorsal part of the transverse process might be suitable for the insertion of screws to stabilize the vertebral arch of the subaxial cervical spine. Gender adaptation might be required.

Comparison of Morphometric Measurements of Traditional Posterior Cervical Screw and Paravertebral Foramen Screw in Chinese Population

STUDY DESIGN

A morphometric measurement study.

OBJECTIVE

To measure the length and angle parameters of the screw paths of pedicle screws (PS), lateral mass screws (LMS), and paravertebral foramen screws (PVFS) of subaxial cervical spine in Chinese population.

SUMMARY OF BACKGROUND DATA

Aramomi proposed a novel internal fixation technology, named PVFS, as an alternative to LMS and PS for subaxial cervical vertebrae (C3-C7).

METHODS

This study measured the length and medial angles of screw paths on the three-dimensional reconstruction model of cervical computerized tomography data of 50 patients (25 men and 25 women) in our hospital from January 2018 to June 2018.

RESULTS

In general, the optimum length and medial angle of the PVFS in Chinese population were 10.65 mm and 21.12° at C3; 10.12 mm, 22.62° at C4; 9.82 mm, 23.66° at C5; 9.19 mm, 24.13° at C6; and 9.10 mm, 27.54° at C7. The optimum axial length and medial angle of PS in Chinese population were 30.94 mm, 33.92° at C3; 30.50 mm, 34.95° at C4; 31.92 mm, 33.42° at C5; 30.50 mm, 31.94° at C6; and 29.87 mm, 31.01° at C7. The optimum lengths of LMS paths in Chinese population were C3, 14.84 mm; C4, 15.33 mm; C5, 15.44 mm; C6, 14.74 mm; and C7, 14.06 mm.

CONCLUSION

Although the length of PVFS is limited, it still can be used as an effective substitute for LMS and PS. The PVFS does not have the risk of directly injuring the vertebral artery, its safety angle of insertion is larger than that in PS, and it has higher surgical safety.Level of Evidence: 3.

Cervical decompressive laminectomy and lateral mass screw-rod arthrodesis: surgical experience and analytical review of 4120 consecutive screws

BACKGROUND

Cervical decompressive laminectomy with lateral mass arthrodesis is a common neurosurgical procedure used to address a variety of cervical spine pathologies.

PURPOSE

This study aimed to determine the safety and efficacy of this neurosurgical procedure using the Anderson-Sekhon technique for screw trajectory.

METHODS

The study retrospectively reviewed all clinical and radiological indicators for patients who underwent lateral mass arthrodesis between December 2005 and December 2017. All patients underwent polyaxial screw-rod implants using the Anderson-Sekhon technique for screw trajectory. It additionally reported all intra- and post-operative complications, along with short- and long-term outcomes for these patients. The follow-up period ranged from 2 months to 10 years.

RESULTS

The study evaluated 695 patients who received a total of 4120 lateral mass screws. This is considered the largest reported case series up to date. No patients had neuro-vascular injuries. The main complications included 51 (7.3%) cases of screw malposition, as when the screw had breached either of foramen transversarium, neural foramen, or the facet joint; 39 (5.6%) cases of lateral mass breakdown; 29 (4.2%) cases of C5 root pain which has subsided overtime; 22 (3.2%) of incidental durotomy; and 18 (2.6%) cases of postoperative wound infection. There were only 3 cases of screw pullout leading to a stability rate of 99.5%. Most cases demonstrated very good to excellent outcomes on both short- and long-term follow-up.

CONCLUSIONS

Cervical decompressive laminectomy with lateral mass arthrodesis is a safe and effective technique for the management of different cervical spine pathologies, which results in favourable short- and long-term outcomes.

Lateral Mass Screw Fixation in the Cervical Spine: Introducing a New Technique

Study Design

This was designed as a randomized double blind study to compare the classical Magerl technique of insertion of lateral mass screws with the authors’ technique. The observations regarding length, outcome, and radiology was done by a group blinded to the technique used.

Purpose

The present study was designed with the objective of identifying the optimal technique for introducing the lateral mass screws that uses the maximum possible dimension of the lateral mass.

Overview of Literature

Lateral mass screw fixation is a common surgery that is performed in the cervical spine. Various modifications for the procedure have been described, such as changes in the entry point, angulation of the screws, and modifications in the exit point. These do not allow the insertion of longer screws that can give more purchase on the bone.

Methods

From January 1, 2009 to December 31, 2018, 176 patients who were scheduled to undergo lateral mass screw fixation were enrolled. They were randomized into two groups; we inserted lateral mass screws using our new technique for one group and by using the classical Magerl technique for the other group. Intraoperative measurements were used to assess the bone-screw interface length. Postoperative radiography and postoperative computed tomography were performed to assess the trajectory of the screws.

Results

Total 88 patients were included in the study group, including 68 men. The control group included 65 men. The most common indication for surgery was cervical spondylotic myelopathy. The average bi-cortical length that was measured intraoperatively was 19.9 mm in the study group and 16.3 mm in the control group. This was significantly different from the average lengths of screws in the control group.

Conclusions

The trajectory that involves an entry point as close as possible to the posterior inferior medial angle of the lateral mass cuboid and traverses a distance of about 20 mm to obtain a bi-cortical purchase in the diagonally opposite angle may provide a much better and firmer bony purchase in the lateral mass than conventional points of entry and trajectories.

Posterior screw fixation in the subaxial cervical spine: a technique and literature review

Posterior cervical spine fixation is a key component in achieving spinal arthrodesis for treating various cervical spine pathologies including neoplastic, inflammatory, traumatic and degenerative diseases. Historically, various wiring techniques had played major roles in posterior cervical spine fixation. Today, posterior cervical screw fixation is utilized by most spine surgeons instead of wiring for its superior biomechanical strength. A review of lateral mass, pedicle, intralaminar and transfacet screw fixation techniques in the subaxial cervical spine is presented in a detailed fashion. A comparison among different posterior cervical subaxial fixation techniques is also included. Although the safety of freehand techniques was demonstrated in the majority of the existing studies, real-time navigation is becoming increasingly utilized for cervical screw insertion, especially for cervical pedicle screws, where the freehand technique is technically demanding and may carry a higher risk of neurovascular injury. Several different posterior screw fixation techniques exist for the subaxial cervical spine with generally low complication rate. Spine surgeons should be familiar with these techniques and choose the optimal technique based on each patient's individual anatomy and surgical needs.

Chronic posterior atlantoaxial subluxation associated with os odontoideum: a rare condition. A case report and literature review

Introduction

Os odontoideum is a rare cervical lesion. This unusual condition is sometimes associated with atlantoaxial subluxation, which is mostly anterior subluxation. Posterior atlantoaxial subluxation due to os odontoideum is extremely rare.

Case presentation

We report an unusual case of a 60-year-old Thai female, who was diagnosed as having chronic posterior atlantoaxial subluxation associated with os odontoideum with progressive myelopathy. The patient underwent posterior arch of C1 laminectomy and an occipito-C3 fusion using an occipital plate, C2 pedicle screws, C3 lateral mass screws and autologous iliac crest strut bone graft arthrodesis. During three years of follow-up, she was clinically significantly improved and postoperative radiographs showed a solid osseous fusion without loss of correction or implant failure.

Discussion

Chronic posterior atlantoaxial subluxation associated with os odontoideum is rare. This condition can cause occipital-cervical pain, myelopathy, intracranial symptoms, or death. Surgical decompression and stabilization is the treatment of choice. Principles of treatment are to prevent sudden death from neurological compromise, improve neurological status, stabilize the cervical spine, and improve quality of life. Surgical options include atlantoaxial fusion, occipito-C2 fusion, and occipito-C3 fusion. Decision making depends on the location of spinal cord compression, area for arthrodesis, and bone quality.

Use of the "dual construct" for the management of complex spinal reconstructions

BACKGROUND CONTEXT

Surgical management of complex spinal reconstructions remains a clinical challenge, as pseudoarthrosis with subsequent rod breakage can occur. Increased rod density in the form of "satellite" or "outrigger" rods have been described; however, rod-fracture above or below satellite rods persist and can result in dissociation of the construct, loss of correction, and recurrence of deformity. The use of four distinct and mechanically independent rods (dual construct) reduces this concern. Since the original case description in 2006, there have been no other studies that use the dual construct for the surgical management of complex spinal reconstructions.

PURPOSE

The purpose of this study is to review the long-term experience and surgical technique using the dual construct, and to present our complications, rod fracture rates, and outcomes for the surgical management of complex spinal reconstructions.

STUDY DESIGN

This study used a surgical technique with case series outcomes.

PATIENT SAMPLE

Patients were from a single-institute who underwent dual construct between 2010 and 2014 and who were available for 2-year follow-up.

OUTCOME MEASURES

Radiographic and functional outcomes, complications, rod fracture rates, and revision surgery rates were the outcome measures.

METHODS

A retrospective review was conducted from a single institution between 2010 and 2014, with a subsequent 2-year follow-up period. Extensive review of patients' medical record, radiographs, and advanced imaging where available was performed. Medical record was evaluated for patient demographics, surgical procedure, and complications. Radiographic measurements included presence or absence of implant failure and proximal junctional kyphosis or distal junctional kyphosis.

RESULTS

A total of 36 patients underwent surgical reconstruction. The average estimated blood loss was 1,856 cc (range, 400-4,000 cc). The average length of stay was 7.3 days (range, 4-22 days). Clinical follow-up reported 21 patients (58.3%) with no or minimal pain. There were six deaths during the follow-up unrelated to the index procedure. Radiographic follow-up revealed three patients (8.3%) with rod fracture; one patient with one rod fracture, and two patients with two rod fractures. No patient had three or all four rod fractures. There were no screw fractures. None of the patients with rod fractures required revision surgery.

CONCLUSIONS

The biggest advantage of the dual construct is that rod breakage, although uncommon, is typically minimal, or asymptomatic, and more importantly does not result in loss of alignment, and therefore has not required revision surgery. The dual construct approach is a safe alternative to traditional two-rod constructs, with encouraging outcomes at follow-up.

Posterior Rigid Instrumentation of C7: Surgical Considerations and Biomechanics at the Cervicothoracic Junction. A Review of the Literature

BACKGROUND

The cervicothoracic junction is a challenging anatomic transition in spine surgery. It is commonly affected by different types of diseases that may significantly impair stability in this region. The seventh cervical vertebra (C7) is an atypical cervical vertebra with unique anatomic features compared to subaxial cervical spine (C3 to C6). C7 has relatively broader laminae, larger pedicles, smaller lateral masses, and a long nonbifid spinous process. These features allow a variety of surgical methods for performing posterior rigid instrumentation in the form of different types of screws, such as lateral mass screws, pedicle screws, transfacet screws, and intralaminar screws. Many biomechanical studies on cadavers have evaluated and compared different types of implants at C7.

METHODS

We reviewed PubMed/Medline by using specific combinations of keywords to summarize previously published articles that examined C7 posterior rigid instrumentation thoroughly in an experimental fashion on patients or cadavers with additional descriptive radiologic parameters for evaluation of the optimum surgical technique for each type.

RESULTS

A total of 44 articles were reported, including 22 articles that discussed anatomic considerations (entry points, sagittal and axial trajectories, and features of screws) and another 22 articles that discussed the relevant biomechanical testing at this transitional region if C7 was directly involved in terms of receiving posterior rigid implants.

CONCLUSIONS

C7 can accommodate different types of screws, which can provide additional benefits and risks based on availability of bony purchase, awareness of surgical technique, biomechanics, and anatomic considerations.

Is It "In" or "Out"? The Optimal Fluoroscopic Views for Intraoperative Determination of Proper Lateral Mass Screw Placement

STUDY DESIGN

Cadaveric.

OBJECTIVE

Determine optimal fluoroscopic views for detecting cervical lateral mass screw (LMS) violations.

SUMMARY OF BACKGROUND DATA

Single plane intraoperative x-rays are commonly used but frequently inadequate due to its complex trajectory. Fluoroscopy can be taken in multiple planes, but the ideal fluoroscopic view to assess malposition is not known: depending on the view, any given screw may look "in" or "out."

METHODS

C3-6 LMS were inserted in three cadavers. To evaluate neuroforaminal violation, LMS were inserted into the foramen with the tip penetrating the anterior cortex by 0, 2, and 4 mm. To assess facet joint violation, LMS were inserted toward the subjacent facet joint with the tip penetrating the anterior cortex by 0 and 2 mm. Fluoroscopic views were taken 0°, 10°, 20°, 30°, and 40° to the lateral plane. Views were independently evaluated by three blinded spine surgeons.

RESULTS

Twenty-degree oblique view correctly identified a 2 mm penetration into the neuroforamen in 79%, and a 4 mm penetration in 86%, for a sensitivity of 83% and specificity of 90%. Thirty-degree view had lower sensitivity (76%) but slightly higher specificity (93%). Twenty-degree and 30° views were significantly more sensitive than the other views. Zero-degree view correctly identified a 2 mm penetration into the facet joint in 93%, for a sensitivity of 93% and specificity of 92%. Ten-degree view had lower sensitivity (72%) but higher specificity (100%). The 0° view was significantly more sensitive than the other views.

CONCLUSION

Twenty-degree and 30° oblique views significantly provided the most sensitive assessment of LMS potentially violating the neuroforamen, whereas the 0° neutral lateral view significantly provided the most sensitive assessment of facet violations. The specificities were also high (in the 90% range) for these views. We recommend the use of these views intraoperatively when assessing proper placement of LMS fluoroscopically.

LEVEL OF EVIDENCE

N/A.

Free hand technique of cervical lateral mass screw fixation

Study Design:

We introduce a simple free hand technique with great ease of application, without angles, measures or degrees, and without any fluoroscopic guidance. It is a safe and reproducible technique. We present our preliminary experience with the use this technique, with inimitable simplicity.

Purpose:

The primary aim of the procedure was to achieve adequate screw trajectory in an apparent challenging ease which is reproducible with a good outcome.

Overview of Literature:

Lateral mass screw fixation is used for posterior subaxial cervical fixation. It was described by Louis and Magerl, then by Anderson, An, and Ebraheim et al. Each one described the procedure with a unique screw entrance point and trajectory.

Technical Note:

This study is a prospective case study of 45 patients who underwent subaxial cervical lateral mass screw fixation. The screws were inserted using a free hand method. The described free hand technique was found to minimize the morbidity associated with other techniques without compromising the quality of fixation.

Conclusions:

Surgical experiences with this technique found it equally safe, rapid, easy, and reproducible.

Robot-Assisted Posterior C1-2 Transarticular Screw Fixation for Atlantoaxial Instability: A Case Report

STUDY DESIGN

Case report.

OBJECTIVES

The aim of this study was to assess the feasibility, safety, and accuracy of a new robotic system for performing posterior C1-2 transarticular screw fixation for atlantoaxial instability.

SUMMARY OF BACKGROUND DATA

C1-2 transarticular fixation is a reliable procedure. However, the procedure is high-risk because of the important structures and frequent anatomical variation around the atlantoaxial region. Navigation improves the accuracy, but it might require repeated adjustments of the trajectories, which is inconvenient. Robot-assisted surgery can make this process easier and has the potential to improve the safety and accuracy.

METHODS

A 43-year-old man with atlantoaxial deformity and instability underwent posterior C1-2 transarticular screw fixation under the guidance of the new robotic system (TiRobot, co-designed by Beijing Jishuitan hospital and TINAVI Medical Technologies Co., Ltd.). We performed a surgery of posterior decompression and C0-2 fusion. Based on the intraoperative 3D images, we planned the trajectory on the robot system. Then, the robotic arm spontaneously moved to guide the screw insertion.

RESULTS

A unilateral C1-2 transarticular screw was safely placed with good accuracy. The calculated deviation of the planned position and actual position was 0.8798 mm. There were no intraoperative complications. Postoperative computed tomography showed there were no perforations and loosening of the screw.

CONCLUSION

We report the first case of atlantoaxial transarticular screw fixation using the TiRobot system. Robotic guidance for complex upper cervical deformity based on intraoperative 3D images could be feasible, safe, and accurate, and has a significant clinical potential in spine surgery.

LEVEL OF EVIDENCE

4.

The effect of hubbing on the pull-out strength of lateral mass screws in the cervical spine: a biomechanical experiment

STUDY DESIGN

This was a cadaveric biomechanical experiment.

OBJECTIVE

To compare the pull-out strength of polyaxial screws that are either hubbed or not hubbed when inserted into the lateral mass.

SUMMARY OF BACKGROUND DATA

It has been shown in a study on pedicle screws in the thoracic spine that "hubbing" the head of the screw against the dorsal laminar cortex results in significantly lower pull-out strength of the screws.

MATERIALS AND METHODS

Fifteen segments of the human cervical spine (from C3 to C7) were prepared. Polyaxial screws 3.5 mm in diameter were used. On one side screws 12 mm in length were inserted until the screw head touched the lateral mass; they were then turned 2.5 more times until they were fully hubbed (hubbed screws). On the other side screws 14 mm in length were inserted until the screw head just touched the lateral mass (nonhubbed screws). The 2 mm difference in length was to ensure that the screws were buried to the same length. All screws inserted into the lateral masses underwent tensile pull-out by applying a tensile force down the long axis of the screw. The difference in pull-out strength between the 2 groups was evaluated using a nonparametric paired test (the Wilcoxon signed rank test), which compared side to side on each vertebra.

RESULTS

One specimen was excluded because of cement breakage during the biomechanical test. A total of 14 vertebrae were tested. Four vertebrae in the hubbed group showed small fractures or cracks around the screw hole after screw insertion. In a side to side comparison, the hubbed screws had significantly lower pull-out strengths as compared with the nonhubbed screws (P=0.033).

CONCLUSIONS

Hubbing of lateral mass screws lowers the potential pull-out strength of the screws as compared with the pull-out strength of nonhubbed screws. Thus, hubbing of lateral mass screws, on the basis of the parameters applied in this study, is not recommended.

Clinical outcome of modified cervical lateral mass screw fixation technique

Objective

The purpose of this study was 1) to analyze clinically-executed cervical lateral mass screw fixation by the Kim's technique as suggested in the previous morphometric and cadaveric study and 2) to examine various complications and bicortical purchase that are important for b-one fusion.

Methods

A retrospective study was done on the charts, operative records, radiographs, and clinical follow up of thirty-nine patients. One hundred and seventy-eight lateral mass screws were analyzed. The spinal nerve injury, violation of the facet joint, vertebral artery injury, and the bicortical purchases were examined at each lateral mass.

Results

All thirty-nine patients received instrumentations with poly axial screws and rod systems, in which one hundred and seventy-eight screws in total. No vertebral artery injury or nerve root injury were observed. Sixteen facet joint violations were observed (9.0%). Bicortical purchases were achieved on one hundred and fifty-six (87.6%). Bone fusion was achieved in all patients.

Conclusion

The advantages of the Kim's technique are that it is performed by using given anatomical structures and that the complication rate is as low as those of other known techniques. The Kim's technique can be performed easily and safely without fluoroscopic assistance for the treatment of many cervical diseases.

Cervical lateral mass screw fixation without fluoroscopic control: analysis of risk factors for complications associated with screw insertion

OBJECTIVE

To examine the outcome of cervical lateral mass screw fixation focusing on analysis of the risk factors for screw-related complications.

METHODS

Ninety-four patients who underwent posterior cervical fixation with a total of 457 lateral mass screws were included in the study. The lateral mass screws were placed using a modified Magerl method. Computed tomographic (CT) images were taken in the early postoperative period in all patients, and the screw trajectory angle was measured on both axial and sagittal plane images.

RESULTS

In the postoperative CT analysis for the screw trajectory, 56.5 % of the screws were directed within the acceptable range (within 21-40° on both axial and sagittal planes). As intraoperative screw-associated complications, 9.6 % of the screws were found to contact with or breach the vertebral artery foramen. In this group, the screw trajectory angle on axial plane was significantly lower than in the group without contact. Facet violation was observed in 13 screws (2.8 %). This complication was associated with a significantly lower trajectory angles in the sagittal plane, predominantly at C6 level (69.2 %). In the patient chart review, no serious neurovascular injuries were documented.

CONCLUSIONS

In the analysis of potential risk factors for violation of the VA foramen as well as FV during screw insertion, the former incidence was significantly related to the screw trajectory angle (lack of lateral angulation) in the axial plane, while the latter incidence was related to a poor screw trajectory angle in the sagittal plane.

Reconstruction of the subaxial cervical spine using lateral mass and facet screw instrumentation

STUDY DESIGN

Review article.

OBJECTIVE

To review the indications, technical details, and complications of lateral mass and transfacet mass fixation methods.

SUMMARY OF BACKGROUND DATA

Potential advantages of rigid fixation in subaxial cervical spine have been defined as early mobilization, faster healing and fusion, and increased fusion rates. Lateral mass screw fixation has been the most popular fixation technique for posterior instrumentation. Transfacet screw fixation, on the other hand, is an alternative method less commonly used.

METHODS

Narrative and review of the literature.

RESULTS

Several different techniques aiming for the most safe and secure lateral mass screw fixation have been described by several different authors. Lateral mass screws provide rigid fixation and high fusion rates in patients with healthy bone. Complications are rare when patients' anatomy is well documented and proper technique is used. Transfacet screw fixation is another method less commonly used and with better biomechanical stability.

CONCLUSION

Lateral mass screw provides excellent 3-dimensional fixations from C3 to C7, and currently it is also the most commonly performed posterior fixation method.

Anatomy of subaxial cervical foramens: the safety zone for lateral mass screwing

INTRODUCTION

The purpose of this study was to measure the structures of the ventral of lateral masses using cadaver specimens and to quantitatively compare the safety zone for the two major techniques used on each vertebral level from C3 to C6.

METHODS

This study is based on 52 cervical vertebrae of 13 cadavers. The anatomical measurements focused on the anterior surface of the lateral mass. We investigated the safety width, heights, and the height of nerve roots.

RESULTS

The mean values of the safety width of the Magerl technique from C3 to C6 were 6.1, 7.3, 6.4 and 4.3 mm, respectively. The mean values of the safety width of the Roy-Camille technique were 6.7, 6.6, 5.8 and 5.4 mm, respectively. The mean values of the safety height of the Magerl technique were 5.0, 5.4, 5.8 and 5.2 mm, respectively. The mean values of the safety height of the Roy-Camille technique were 4.9, 4.0, 1.0 and -1.2 mm, respectively. The mean values of the nerve root height were 3.9, 4.9, 5.9 and 6.9 mm, respectively.

CONCLUSION

The safety width of the Magerl technique was shorter at C6 because the vertebral artery runs more laterally at C6. The height for the Magerl technique was not significantly different from C3 to C6, however, the safety height for the Roy-Camille technique was significantly shorter at C5 and C6. Our findings suggest that it is important to ensure that the screw(s) penetrate through the cranial side of the ventral aspect of a lateral mass when performing the Magerl technique at all vertebral levels, and to carefully select the screw length when using the Roy-Camille technique, especially at C5 and C6, in order to avoid nerve root injury.

The V2 segment of the vertebral artery: anatomical considerations and surgical implications

Object

Iatrogenic injury of the V2 segment of the vertebral artery (VA) is a rare but serious complication and can be catastrophic. The purpose of this study was to characterize the relationship of the V2 segment of the VA to the surrounding anatomical structures and to highlight the potential site and mechanisms of injury that can occur during common neurosurgical procedures involving the subaxial cervical spine.

Methods

Ten adult cadaveric specimens (20 sides) were included in this study. Quantitative anatomical measurements between selected landmarks and the VA were obtained. In addition, lateral mass screws were placed bilaterally, from C-3 to C-7, reproducing either the Magerl technique or a modified technique. The safety angle, defined as the axial deviation from the screw trajectory needed to injure the VA, and the distance from the entry point to the VA were measured at each level for both techniques.

Results

The VA coursed closer to the midline at C3–4 and C4–5 (mean distance [SD] 14.9 ± 1.1 mm) than at C2–3 or C5–6. Within the intertransverse space it coursed closer to the uncinate processes of the vertebral bodies (1.8 ± 1.1 mm) than to the anterior tubercle of the transverse processes (3.4 ± 1.6 mm). The distance between the VA and the uncinate process was less at C3–6 (1.3 ± 0.7 mm) than at C2–3 (3.3 ± 0.8 mm). The VA coursed on average at a distance of 11.9 ± 1.7 mm from the anterior and 4.2 ± 2.6 mm from the posterior aspect of the intervertebral disc space. Lateral mass screw angles were 25° lateral and 39.1° cranial for the Magerl technique, and 36.6° lateral and 46.1° cranial for the modified technique. The safety angle was greater and screw length longer when using this modified technique.

Conclusions

The relation of the V2 segment of the VA to anterior procedures and lateral mass instrumentation at the subaxial cervical spine was reviewed in this study. A detailed anatomical knowledge of the V2 segment of the VA combined with careful preoperative imaging is mandatory for safe cervical spine surgery.

Freehand determination of the trajectory angle for cervical lateral mass screws: how accurate is it?

Different methods of lateral mass screw placement in the cervical spine have been described with separate trajectories for each technique in the sagittal and parasagittal planes. In the latter, plane 30° has been recommended in the modified Magerl's technique as the optimum angle to avoid injury to the vertebral artery and nerve root. The estimation of this angle remains arbitrary and very much operator dependant. The aim of this study was to assess how accurately the lateral trajectory angle of 30° is achieved by visual estimation amongst experienced surgeons in a tertiary spinal unit and to determine the likelihood of neurovascular injury during the procedure. We chose an anatomical 'sawbone' model of the cervical spine with simulated lordosis. The senior author marked the entry points. Five spinal consultants and five senior spinal fellows were asked to insert 1.6-mm K wires into the lateral masses of C3 to C6 bilaterally at 30° to the midsagittal plane using the marked entry points. The lateral angulation in the transverse plane was measured using a custom protractor and documented for each surgeon at each level and side. The mean and standard deviation (SD) of the data were obtained to determine the inter observer variability. Utilising this data, measurements were then made on a normal axial computerised tomography (CT) scan of the cervical spine of an anonymous patient to determine if there would have been any neurovascular compromise. Among the 10 surgeons, a total of 80 insertion angles were measured from C3 to C6 on either side. The overall mean angle of insertion was 25.15 (range 20.4-34.8). The overall SD was 4.78. Amongst the 80 measurements between the ten surgeons, two episodes of theoretical vertebral artery violation were observed when the angles were simulated on the CT scan. A moderate but notable variability in trajectory placement exists between surgeons during insertion of cervical lateral mass screws. Freehand estimation of 30° is not consistently achieved between surgeons and levels. In patients with gross degenerative or deformed cervical spine anatomy, this may increase the risk of neurovascular injury. The use of the ipsilateral lamina as an anatomical reference plane is supported.

Radiological assessment of cervical lateral mass screw angulations in Asian patients

BACKGROUND

Various lateral mass screw fixation methods have been described in the literature with various levels of safety in relation to the anterior neurovascular structures. This study was designed to radiologically determine the minimum lateral angulations of the screw to avoid penetration of the vertebral artery canalusing three of the most common techniques: Roy-Camille, An, and Magerl.

MATERIALS AND METHODS

Sixty normal cervical CT scans were reviewed. A minimum lateral angulation of a 3.5 mm lateral mass screw which was required to avoid penetration of the vertebral artery canal at each level of vertebra were measured.

RESULTS

The mean lateral angulations of the lateral mass screws (with 95% confidence interval) to avoid vertebral artery canal penetration, in relation to the starting point at the midpoint (Roy-Camille), 1 mm medial (An), and 2 mm medial (Magerl) to the midpoint of lateral mass were 6.8° (range, 6.3-7.4°), 10.3° (range, 9.8-10.8°), and 14.1° (range, 13.6-14.6°) at C3 vertebrae; 6.8° (range, 6.2-7.5°), 10.7° (range, 10.0-11.5°), and 14.1° (range, 13.4-14.8°) at C4 vertebrae; 6.6° (range, 6.0-7.2°), 10.1° (range, 9.3-10.8°), and 13.5° (range, 12.8-14.3°) at C5 vertebrae and 7.6° (range, 6.9-8.3°), 10.9° (range, 10.3-11.6°), and 14.3° (range, 13.7-15.0°) at C6 vertebrae. The recommended lateral angulations for Roy-Camille, Magerl, and An are 10°, 25°,and 30°, respectively. Statistically, there is a higher risk of vertebral foramen violation with the Roy-Camille technique at C3, C4 and C6 levels, P < 0.05.

CONCLUSIONS

Magerl and An techniques have a wide margin of safety. Caution should be practised with Roy-Camille's technique at C3, C4, and C6 levels to avoid vertebral vessels injury in Asian population.

Biomechanical comparison between C-7 lateral mass and pedicle screws in subaxial cervical constructs

Object

The aim of this study was to conduct the first in vitro biomechanical comparison of immediate and postcyclical rigidities of C-7 lateral mass versus C-7 pedicle screws in posterior C4–7 constructs.

Methods

Ten human cadaveric spines were treated with C4–6 lateral mass screw and C-7 lateral mass (5 specimens) versus pedicle (5 specimens) screw fixation. Spines were potted in polymethylmethacrylate bone cement and placed on a materials testing machine. Rotation about the axis of bending was measured using passive retroreflective markers and infrared motion capture cameras. The motion of C-4 relative to C-7 in flexion-extension and lateral bending was assessed uninstrumented, immediately after instrumentation, and following 40,000 cycles of 4 Nm of flexion-extension and lateral bending moments at 1 Hz. The effect of instrumentation and cyclical loading on rotational motion across C4–7 was analyzed for significance.

Results

Preinstrumented spines for the 2 cohorts were comparable in bone mineral density and range of motion in both flexion-extension (p = 0.33) and lateral bending (p = 0.16). Lateral mass and pedicle screw constructs significantly reduced motion during flexion-extension (11.3°–0.26° for lateral mass screws, p = 0.002; 10.51°–0.30° for pedicle screws, p = 0.008) and lateral bending (7.38°–0.27° for lateral mass screws, p = 0.003; 11.65°–0.49° for pedicle screws, p = 0.03). After cyclical loading in both cohorts, rotational motion over C4–7 was increased during flexion-extension (0.26°–0.68° for lateral mass screws; 0.30°–1.31° for pedicle screws) and lateral bending (0.27°–0.39° and 0.49°–0.80°, respectively), although the increase was not statistically significant (p > 0.05). There was no statistical difference in postcyclical flexion-extension (p = 0.20) and lateral bending (0.10) between lateral mass and pedicle screws.

Conclusions

Both C-7 lateral mass and C-7 pedicle screws allow equally rigid fixation of subaxial lateral mass constructs ending at C-7. Immediately and within a simulated 6-week postfixation period, C-7 lateral mass screws may be as effective as C-7 pedicle screws in biomechanically stabilizing long subaxial lateral mass constructs.

Comparative analysis of three different cervical lateral mass screw fixation techniques by complications and bicortical purchase : cadaveric study

OBJECTIVE

The purpose of this study is to compare the incidence of possible complications of cervical lateral screw fixation and the achievements of bicortical purchase using the Roy-Camille, Magerl and the modified methods.

METHODS

Six fresh-frozen cervical spine segments were harvested. The Roy-Camille technique was applied to C3 and C4, and the Magerl technique was applied to C5, C6, and C7 of one side of each cadaver. The modified technique was applied to the other side of each cadaver. The nerve root injury, violation of the facet joint, vertebral artery injury, and the bicortication were examined at each screwing level.

RESULTS

No vertebral artery injury was observed in any of the three methods. One nerve root injury was observed in each cervical spine segment using the Roy-Camille method (8.3%), the Magerl method (5.6%), and the modified method (3.3%). Facet joint injuries were observed in two cervical spinal segments using the Roy-Camille method (16.7%) and three with the Magerl method (16.7%), while five facet joint violations occurred when using the modified method (16.7%). Bicortical purchases were achieved on ten cervical spinal segments with the Roy-Camille method (83.3%) and Magerl method (55.6%), while twenty bicortical purchases were achieved in the modified method (66.7%).

CONCLUSION

The advantages of the modified method are that it is performed by using given anatomical structures and that the complication rate is as low as those of other known methods. This modified method can be performed easily and safely without fluoroscopic assistance for the treatment of many cervical diseases.

Lamina-guided lateral mass screw placement in the sub-axial cervical spine

Lateral mass (LM) screws are commonly used in posterior instrumentation of the cervical spine because of their perceived safety over pedicle screws. A possible complication of cervical LM screw placement is vertebral artery injury or impingement. Several screw trajectories have been described to overcome the risks of neurovascular injury; however, each of these techniques relies on the surgeon's visual estimation of the trajectory angle. As the reliability hereof is poorly investigated, alignment with a constant anatomical reference plane, such as the cervical lamina, may be advantageous. The aim of this investigation was to determine whether alignment of the LM screw trajectory parallel to the ipsilateral cervical lamina reliably avoids vertebral artery violation in the sub-axial cervical spine. 80 digital cervical spine CT were analysed (40 female, 40 male). Exclusion criteria were severe degeneration, malformations, tumour, vertebral body fractures and an age of less than 18 or greater than 80 years. Mean age of all subjects was 39.5 years (range 18-78); 399 subaxial cervical vertebrae (C3-C7) were included in the study. Measurements were performed on the axial CT view of C3-C7. A virtual screw trajectory with parallel alignment to the ipsilateral lamina was placed through the LM. Potential violation of the transverse foramen was assessed and the LM width available for screw purchase measured. There was no virtual violation of the vertebral artery of C3-C7 with lamina-guided LM screw placement. LM width available for screw purchase using this technique ranged from 5.2 to 7.4 mm. The sub-axial cervical lamina is a safe reference plane for LM screw placement. LM screws placed parallel to the ipsilateral lamina find sufficient LM width and are highly unlikely to injure the vertebral artery, even in bi-cortical placement. Placing LM screws parallel to the lamina appears favourable over conventional techniques.

A biomechanical evaluation of three revision screw strategies for failed lateral mass fixation

STUDY DESIGN

This is a biomechanical study evaluating 3 revision strategies for failed cervical lateral mass screw fixation.

OBJECTIVE

Our primary objective was to compare, following a Magerl trajectory screw failure in the subaxial cervical spine, the pullout strength of (1) a revision screw in the same trajectory, (2) a Roy-Camille trajectory, and (3) pedicle screw fixation. We additionally analyzed the contributions of bone mineral density (BMD) and peak insertional torque to pullout strength.

SUMMARY OF BACKGROUND DATA

Biomechanical studies that have examined revision screw strategies for lateral mass fixation have found either unsatisfactory or highly variable performance.

METHODS

Fresh frozen cervical spinal segments were harvested and BMD testing performed. Bicortical (3.5-mm Vertex) lateral mass screws were placed in a Magerl trajectory in 57 fresh frozen human subaxial cervical vertebrae. All screws were then stripped and revision screws (4.0-mm Vertex) placed using either the same screw path or conversion to a Roy-Camille trajectory. In line pullout testing was performed on each of the revision screws (57 in Magerl revision group, 55 in Roy-Camille). Specimens that had not fractured during testing then had cervical pedicle screws (3.5-mm Vertex) placed and in-line pullout testing repeated (64 pedicles were instrumented) The pullout failure results of the Magerl revision, Roy-Camille revision, and pedicle screw revision groups were compared.

RESULTS

No significant difference was noted in insertional torque (0.28-Nm Magerl, 0.35 Nm Roy-Camille, P > 0.05) or pullout (382-N Magerl, 351 N Roy-Camille, P > 0.05) between the Magerl and Roy-Camille revision groups. Pedicle screw revision had greater pullout strength (566 N) when compared with either the Magerl (382 N) or Roy-Camille (351 N) revision groups (P < 0.01) but also had a 20% pedicle wall breech rate by visual inspection. Insertional torque and pullout strength increased with increased BMD and were significantly correlated in all 3 revision groups (P < 0.05). Similarly, increased BMD was associated with increased pullout strength as demonstrated by the significant positive correlation (P < 0.05).

CONCLUSION

Conversion of a stripped lateral mass screw to an alternate trajectory appears to offer no biomechanical advantage over placement of an increased diameter salvage screw using the same trajectory. Pedicle screw fixation provides superior biomechanical fixation but was associated with a significant breech rate.

Comparative Analysis of Cervical Lateral Mass Screw Insertion among Three Techniques in the Korean Population by Quantitative Measurements with Reformatted 2D CT Scan Images: Clinical Research

OBJECTIVE

Our purpose of this study is to compare insertion angles and screw lengths from Roy-Camille, Magerl, and our designed method for cervical lateral mass screw fixation in the Korean population by quantitative measurement of reformatted two dimensional (2D) computed tomography (CT) images.

METHODS

We selected thirty Korean patients who were evaluated with thin section CT scans and reconstruction program to obtain reformatted 2D-CT images of the transversal plane passing the cranio-caudal angle using three different techniques. We measured the minimum angle to avoid vertebral artery (VA) injury, the ideal angle and depth for bicortical screwing of cervical lateral mass. Morphometric measurements of the lateral masses from C3-C7 were also taken.

RESULTS

In all three techniques, the mean safety angles from the VA were less than 8 degrees and the necessary depth of the screw was about 14 mm for safety to the VA and for the bicortical purchase. In our designed technique, the mean beta angles of each level from C3 to C7 were 29.0, 29.8, 29.5, 26.3, and 23.9 degrees, respectively.

CONCLUSION

Results of this study and data from the literature indicate that differences may exist between the Korean and Western people in the length and angle for ideal lateral mass screw fixation. In addition, our technique needs further cadaveric and clinical study for safety and efficacy for being performed as alternative method for cervical lateral mass fixation.

Quantitative anatomy of subaxial cervical lateral mass: an analysis of safe screw lengths for Roy-Camille and magerl techniques

STUDY DESIGN

Determination of lateral mass screw lengths with Roy-Camille and Magerl techniques of screw insertion using computerized tomography in 98 young, asymptomatic North American volunteers.

OBJECTIVE

To provide reliable and normative data on safe screw lengths using the Roy-Camille and Magerl techniques of lateral mass fixation in the subaxial cervical spine.

SUMMARY OF BACKGROUND DATA

Lateral mass screw lengths have been studied in the past using differing subject and measurement characteristics and small sample sizes. Results demonstrated considerable variation in screw length and influencing factors. Inappropriate screw lengths can result in neurovascular injury during screw insertion, facet joint damage, or inadequate fixation.

METHODS

Bicortical screw lengths were bilaterally measured at each spinal level from C3-C7 in 98 young volunteers using computed tomography reconstructions through the lateral masses obtained in the plane of the screw in Roy-Camille and Magerl techniques.

RESULTS

With both techniques, trajectories were longest at C4-C6, shorter at C3, and shortest at C7. Screw lengths were greater in males when compared with females at all levels. Average Magerl screw lengths were approximately 2.6 mm longer at C3-C6 levels, and approximately 1.3 mm longer at the C7 level when compared with Roy-Camille technique. There was minimal correlation between screw lengths and anthropometric measurements including stature, body weight, and neck length.

CONCLUSION

Significant variations exist at each subaxial level with either technique. We recommend the surgeon determine screw lengths for fixation at each level using preoperative sagittal oblique computed tomography scans, which provide the most accurate technique of preoperative templating for screw length.

Clinical experiences and usefulness of cervical posterior stabilization with polyaxial screw-rod system

OBJECTIVE

The objective of this study is to investigate the safety, surgical efficacy, and advantages of a polyaxial screw-rod system for posterior occipitocervicothoracic arthrodesis.

METHODS

Charts and radiographs of 32 patients who underwent posterior cervical fixation between October 2004 and February 2006 were retrospectively reviewed. Posterior cervical polyaxial screw-rod fixation was applied on the cervical spine and/or upper thoracic spine. The surgical indication was fracture or dislocation in 18, C1-2 ligamentous injury with trauma in 5, atlantoaxial instability by rheumatoid arthritis (RA) or diffuse idiopathic skeletal hyperostosis (DISH) in 4, cervical spondylosis with myelopathy in 4, and spinal metastatic tumor in 1. The patients were followed up and evaluated based on their clinical status and radiographs at 1, 3, 6 months and 1 year after surgery.

RESULTS

A total of 189 screws were implanted in 32 patients. Fixation was carried out over an average of 3.3 spinal segment (range, 2 to 7). The mean follow-up interval was 20.2 months. This system allowed for screw placement in the occiput, C1 lateral mass, C2 pars, C3-7 lateral masses, as well as the lower cervical and upper thoracic pedicles. Satisfactory bony fusion and reduction were achieved and confirmed in postoperative flexion-extension lateral radiographs and computed tomography (CT) scans in all cases. Revision surgery was required in two cases due to deep wound infection. One case needed a skin graft due to necrotic change. There was one case of kyphotic change due to adjacent segmental degeneration. There were no other complications, such as cord or vertebral artery injury, cerebrospinal fluid leak, screw malposition or back-out, or implant failure, and there were no cases of postoperative radiculopathy due to foraminal stenosis.

CONCLUSION

Posterior cervical stabilization with a polyaxial screw-rod system is a safe and reliable technique that appears to offer several advantages over existing methods. Further biomechanical testings and clinical experiences are needed in order to determine the true benefits of this procedure.

Early results from posterior cervical fusion with a screw-rod system

PURPOSE

We performed 65 cases of posterior fusion surgery for cervical and/or high thoracic lesions using a polyaxial screw-rod system.

PATIENTS AND METHODS

A total of 486 screws were implanted in 65 patients.

RESULTS

Fixation of the screws was carried out over an average of 2.9 spinal segments. Upon evaluation by postoperative CT scans, twelve (2.5%) screws had suboptimal trajectories but two of these revealed radiculopathy in one patient and required screw repositioning. No vascular sequelae resulted. There has been no segmental motion in any of the cases to date. As for other complications, there was one case of dural tearing and two cases of lateral mass fractures. There were no infections or other wound healing problems or hardware failures. No patients had neurological deterioration after surgery. There were statistically significant improvements in the mean Neck Disability Index (NDI) scores and Visual Analogue Scale (VAS) scores in the preoperative and late postoperative follow-up evaluations. Although further studies are required to establish the long-term results of fusion rates and clinical outcomes.

CONCLUSION

We cautiously suggest that the posterior polyaxial screw-rod system can be safely used as a primary or additional fusion method in this risky region. The successful and safe use of this method is dependent on a precise preoperative surgical plan and tactics for ensuring safe screw fixation.

A Comparative Biomechanical Analysis of Spinal Instability and Instrumentation of the Cervicothoracic Junction

OBJECTIVE

Stabilization of the cervicothoracic junction is challenging but commonly required in patients with traumatic, neoplastic, congenital, and postlaminectomy conditions. Although extensive research has been performed on stabilization of the cervical spine, there remains a paucity of published data on instrumentation at the cervicothoracic junction. Using 2-column, 3-column, and corpectomy instability models, a biomechanical analysis was performed on the effects of increasing the number of posterior segmental fixation points and/or anterior column reconstruction at the cervicothoracic junction.

METHODS

Multidirectional flexibility testing was performed utilizing a 6-degree-of-freedom spine simulator and 7 fresh-frozen human cadaveric spines (occiput-T6). After intact spine analysis, each specimen was destabilized and reconstructed as follows: (1) C7/T1 2-column injury with posterior instrumentation; (2) C7/T1 3-column injury with posterior instrumentation; (3) C7/T1 3-column injury with anterior interbody cage/plate and posterior instrumentation; and (4) C7/T1 3-column injury plus C7 corpectomy with anterior cage/plate and posterior instrumentation. All reconstruction groups were tested with posterior instrumentation (screws connected by dual-diameter rods) from C5-T1, C5-T2, and C5-T3.

RESULTS

For 2-column injuries, there were no statistically significant differences in flexibility (P>0.05), although there was a trend toward reduced flexibility with increasing levels of thoracic fixation. For 3-column injuries, posterior fixation alone resulted in excessive flexibility in flexion/extension even with instrumentation to T3 (P<0.05). With the addition of anterior column instrumentation, there were no observed differences in flexion/extension and lateral bending. For axial rotation, instrumentation to T1 alone demonstrated increased motion relative to the intact spine (P<0.05). The 3-column injury with corpectomy model demonstrated similar flexibility properties to the 3-column injury model.

CONCLUSIONS

With 3-column instability posterior segmental fixation alone from C5-T3 was inadequate, and the addition of anterior instrumentation restored flexibility to the intact condition. There was a strong trend toward reduced flexibility with increasing levels of thoracic fixation in all instability models.

Stabilizing potential of anterior, posterior, and circumferential fixation for multilevel cervical arthrodesis: an in vitro human cadaveric study of the operative and adjacent segment kinematics

STUDY DESIGN

This is an in vitro biomechanical study.

OBJECTIVE

The current investigation was performed to evaluate the stabilizing potential of anterior, posterior, and circumferential cervical fixation on operative and adjacent segment motion following 2 and 3-level reconstructions.

SUMMARY OF BACKGROUND DATA

Previous studies reported increases in adjacent level range of motion (ROM) and intradiscal pressure following single-level cervical arthrodesis; however, no studies have compared adjacent level effects following multilevel anterior versus posterior reconstructions.

MATERIALS AND METHODS

Ten human cadaveric cervical spines were biomechanically tested using an unconstrained spine simulator under axial rotation, flexion-extension, and lateral bending loading. After intact analysis, all specimens were sequentially instrumented from C3 to C5 with: (1) lateral mass fixation, (2) anterior cervical plate with interbody cages, and (3) combined anterior and posterior fixation. Following biomechanical analysis of 2-level constructs, fixation was extended to C6 and testing repeated. Full ROM was monitored at the operative and adjacent levels, and data normalized to the intact (100%).

RESULTS

All reconstructive methods reduced operative level ROM relative to intact specimens under all loading methods (P < 0.05). However, circumferential fixation provided the greatest segmental stability among 2 and 3-level constructs (P < 0.05). Moreover, anterior cervical plate fixation was least efficient at stabilizing operative segments following C3-C6 arthrodesis (P < 0.05). Supradjacent ROM was increased for all treatment groups compared to normal data during flexion-extension testing (P < 0.05). Similar trends were observed under axial rotation and lateral bending loading. At the distal level, flexion-extension and axial rotation testing revealed comparable intergroup differences (P < 0.05), while lateral bending loading indicated greater ROM following 2-level circumferential fixation (P < 0.05).

CONCLUSIONS

Results from our study revealed greater adjacent level motion following all 3 fixation types. No consistent significant intergroup differences in neighboring segment kinematics were detected among reconstructions. Circumferential fixation provided the greatest level of segmental stability without additional significant increase in adjacent level ROM.

THE USE OF RIGID INTERNAL FIXATION IN THE SURGICAL MANAGEMENT OF CERVICAL SPONDYLOSIS

IN THE SURGICAL management of cervical spondylosis, the application of rigid internal fixation can enhance the immediate stability of the cervical spine. The sophistication of such internal fixation systems and the indications for their use are continuously evolving. A sound understanding of regional anatomy, biomechanics, and kinematics within the cervical spine is essential for the safe and effective application of internal fixation. Numerous options currently exist for anterior cervical plating systems; some lock the screws to the plate rigidly (constrained), whereas others allow for some rotational or translational motion between the screw and plate (semiconstrained). The role of anterior fixation in single and multilevel fusions is still the subject of some controversy. Long anterior cervical reconstructions may require additional posterior fixation to reliably promote fusion. Rigid fixation in the posterior cervical spine can be achieved with lateral mass screws or pedicle screws. Although lateral mass screws provide excellent fixation within the subaxial cervical spine, the regional anatomy of C2 and C7 often make it difficult to place such screws, and pedicle screws at these levels are advocated. Pedicle screws achieve fixation into both the anterior and posterior column and are arguably the most stable form of rigid internal fixation within the cervical spine. Familiarity with these internal fixation techniques can be an extremely valuable tool for the spine surgeon managing these degenerative disorders of the cervical spine.

Operative techniques for fusion across the cervical-thoracic junction

BACKGROUND AND SIGNIFICANCE

The cervical-thoracic junction represents a significant challenge for stabilization because of anatomical constraints.

PURPOSE

To review the indications, techniques, and results of various stabilization techniques applied to the cervical-thoracic junction.

CONCLUSIONS

Innovative instrumentation design, improved operative techniques, and detailed knowledge of the regional anatomy and biomechanics have significantly improved the surgeon's ability to address instability at the cervical-thoracic junction.

Posterior cervical screw placement without image guidance: a safe and reliable practice

The use of lateral mass screws for posterior cervical fixation has become widespread. It allows for stable fixation in the absence of the posterior elements and confers immediate stability. Lateral mass fixation has been shown to impart equal or greater biomechanical stability when compared to posterior interosseous wiring or anterior plating. The utilization of intraoperative fluoroscopy to guide screw placement has been recommended previously and is considered routine practice in many centers. This prospective study shows that lateral mass screws can be safely positioned without intraoperative fluoroscopy. The procedure is both safe and effective, provided that the operator has a thorough understanding of lateral mass anatomy coupled with careful adherence to the established guidelines for screw positioning. Exposure to radiation is reduced and time taken for operation can be shortened.

Die rheumatisch bedingte Instabilität der oberen Halswirbelsäule

Rheumatic manifestation at the cervical spine occurs in more than 50% of all cases in the natural course of this disease. The first cervical manifestation takes place in the upper cervical spine. The initial involvement of the C1/C2 segment leads to atlantodental subluxation. Progressive destruction can result in vertical instability, which is characterized by cranial subluxation of the odontoid process with the danger of resulting stenosis and cervical myelopathy. The goal of diagnosis has to be the early recognition of these changes to establish an effective treatment protocol. Persistent pain, neurological deficits, and progressive radiological signs for instability are indications for operative stabilizing procedures. These procedures avoid progressive destruction and improve the prognosis regarding pain decrease, regression of neurological deficits, and life expectancy.

Posterior stabilization of subaxial cervical spine trauma: indications and techniques

The use of instrumentation for stabilization following cervical trauma has evolved rapidly in the past few decades. Nonoperative maneuvers, including traction, extended bed rest, and cast immobilization, have given way to wiring or screw rod constructs that allow immediate fixation and early mobilization of the patient. These procedures can be performed soon after trauma and with a minimum of surgical risk. They offer immediate stability of the injured spine, and can prevent the sequelae of acute cervical spinal cord injury that may accompany prolonged bed rest, thus allowing early rehabilitation and the potential for improved recovery. Current techniques for posterior cervical spine stabilization following trauma include spinous process or facet wiring [1-9], lateral mass plating [10-18], and cervical pedicle screws [19-27]. Several radiological tools, including MRI [28] and reformatted CT, yield precise details of the injured spine and allow the treating physician to determine which, if any, fixation technique offers the best chance of recovery with the least amount of risk. The goals of surgery following acute cervical spine injury include decompressing the injured spinal cord or nerve root, maintaining alignment, providing stability to the spine, promoting healing and fusion, and allowing early mobilization. This article will review indications for posterior cervical spine surgery, as well as the techniques that are currently available to help achieve the above-noted goals. We also report a recent retrospective review of 5-year data in treating posterior cervical trauma with lateral mass and pedicle screw fixation.

Anatomic consideration for standard and modified techniques of cervical lateral mass screw placement

BACKGROUND CONTEXT

Posterior screw placement techniques have been previously described. Each technique differs with respect to starting point, lateral angulation and sagittal orientation.

PURPOSE

To examine the potential for injury to critical anatomic structures, such as nerve roots and vertebral arteries, during posterior cervical screw placement and to determine safe screw placement.

STUDY DESIGN/SETTING

An anatomic study was conducted to determine the optimal screw angulation for posterior cervical lateral mass screws. SPECIMEN SAMPLE: Ten fresh-frozen human cadaveric cervical spine specimens were used, consisting of four females and six males, ranging in age from 32 to 68 years.

OUTCOME MEASURES

Angular measurements and distance from nerve root and vertebral arteries were measured with a single caliper and recorded. One millimeter of proximity to a vital structure was considered a violation of that structure.

METHODS

Ten fresh-frozen human cadaveric cervical spine specimens were instrumented from C2 to C7 by a single surgeon. Kirschner wires (2.0 mm) were used to reproduce the Roy-Camille, Anderson and Magerl screw trajectories. The wire was drilled through each lateral mass, simulating overdrill error. Each technique was instrumented according to the original description and with additional modifications. The modification consisted of varying the angle of screw placement in the axial plane of the original description from 0 to 30 degrees. Distances to the closest neurovascular structures were averaged for all assays.

RESULTS

The Magerl technique is safe at the standard position and modified positions of 20 degrees and 30 degrees from C3-C6. The Roy-Camille technique frequently violates neurovascular structures below C3, especially the nerve root with more lateral screw angulation. The standard technique is noted to have good bone purchase only at C2 and C3. The Anderson technique is safe at 20 degrees and 30 degrees modified positions from C3-C7. Posterior screw placement at the C7 vertebral level was safe only with a modified Anderson technique of 20 degrees and 30 degrees of lateral screw angulation.

CONCLUSIONS

The present study indicates that there are significant differences of potential neurovascular injury, which is dependent on the technique used for screw entry, the level instrumented and the angle of screw trajectory in the parasagittal plane.

Posterior fusion of the subaxial cervical spine: indications and techniques

The biomechanical stability of the subaxial cervical spine (C3–7) can be compromised by numerous pathological processes, and the restoration of stability may ultimately require fusion and placement of rigid internal fixation devices. A posterior fusion and stabilization procedure is often used to treat cervical instability secondary to traumatic injury, rheumatoid arthritis, ankylosing spondylitis, neoplastic disease, infections, and previous laminectomy. Numerous techniques and advances in spinal instrumentation have evolved over the last 30 years. The authors review the indications and the various methods for stabilizing and fusing the subaxial cervical spine via posterior approaches.

Design of an occipito-cervical fixation device

Metal plates may be used to stabilize the cervical spine. The plates are attached to the posterior of the vertebra by placing screws into the lateral masses. The plating may be extended, in the form of rod or plate, to connect with and support the occiput. Several problems, such as screw loosening and the plate obscuring the surgeon's view as a screw is being inserted, have been identified with present plate systems. This paper describes the initial design for a cervical fixation device to overcome these problems, and the design and development that was undertaken to enable a prototype device to be manufactured.

Management of cervical spinal fractures in ankylosing spondylitis with posterior fixation

STUDY DESIGN

Introduction of a posterior approach for internal fixation of fractures of the ankylosed cervical spine.

OBJECTIVES

To evaluate the clinical outcome of patients with ankylosing spondylitis and cervical spinal fractures treated with posterior instrumentation and a collar orthosis.

SUMMARY OF BACKGROUND DATA

Cervical spinal fractures in patients with ankylosing spondylitis almost always extend completely across the vertebral segment to include both anterior and posterior elements. Treatment with immobilization alone is often inadequate. Generalized spinal rigidity and exaggerated thoracic kyphosis may hinder anterior exposure. Posterior approaches have been described but generally require postoperative halo immobilization. In the authors' technique for patients whose spinal alignment is relatively well preserved, a posterior exposure is used that achieves three-point internal fixation along multiple segments. The complications associated with halo immobilization are avoided.

METHODS

Seven patients with ankylosing spondylitis and fractures of the cervical spine were stabilized with posterior instrumentation. Patients were immobilized after surgery with either a cervical collar or a sternal occipital mandibular immobilizing brace and observed for neurologic outcome, radiographic evidence of bony fusion, and complications.

RESULTS

No patient experienced neurologic deterioration with surgery. Two patients died at acute rehabilitative facilities after discharge. Radiographic evidence of fusion was observed in the five patients available for follow-up.

CONCLUSIONS

Patients with ankylosing spondylitis and cervical spinal fractures can be adequately treated with lateral mass plating and interspinous wiring of autologous rib graft. Adequate postoperative immobilization can be attained with a cervical collar and does not require a halo vest.