The stabilizing potential of anterior, posterior and combined techniques for the reconstruction of a 2-level cervical corpectomy model: biomechanical study and first results of ATPS prototyping

Computed Tomography-Based Morphometric Analysis of Lower Cervical Anterior Transpedicular Screw Fixation and Related Factors in the Chinese Population

BACKGROUND

Anterior transpedicular screw (ATPS) internal fixation of the lower cervical spine is an alternative for patients who cannot tolerate combined anterior and posterior surgery. The cervical vertebral anatomy varies with many factors, including age, gender, height, weight, and race.

METHODS

Three-dimensional (3D) CT reconstructions were performed on 122 patients. We selected the best level and measured the relevant parameters on both sides of the cervical vertebrae.

RESULTS

We identified the entry point and orientation parameters of ATPS fixation for the C3-C7 vertebrae, and analyzed cervical pedicle parameters. Outer pedicle width (OPW), outer pedicle height (OPH), and pedicle axis length (PAL) were not correlated with body weight and age, but were positively correlated with body height (P < 0.05). After multiple linear regression analysis to exclude the effects of body height, no significant differences in OPW, OPH, and PAL were found between male and female subjects at most cervical levels. Pedicle cortical thickness was negatively correlated with age (P < 0.05). The percentage of pedicles with OPW <4.5 mm was: C3, 38.10%; C4, 34.92%; C5, 12.70%; C6, 9.52%; and C7, 0%. The percentage of pedicles with OPWs ≤4.5 mm, ≤4.0 mm, and ≤3.5 mm was higher among subjects with body height <160 cm.

CONCLUSIONS

This study presents the internal anatomy of the cervical spine and provides accurate preoperative evaluation data for ATPS fixation. OPW, OPH, and PAL are positively correlated with body height, while pedicle cortical thickness is negatively correlated with age.

Biomechanical study of anterior transpedicular root screw intervertebral fusion system of lower cervical spine: a finite element analysis

Background: The cervical anterior transpedicular screw (ATPS) fixation technology can provide adequate stability for cervical three-column injuries. However, its high risk of screw insertion and technical complexity have restricted its widespread clinical application. As an improvement over the ATPS technology, the cervical anterior transpedicular root screw (ATPRS) technology has been introduced to reduce the risk associated with screw insertion. This study aims to use finite element analysis (FEA) to investigate the biomechanical characteristics of a cervical spine model after using the novel ATPRS intervertebral fusion system, providing insights into its application and potential refinement. Methods: A finite element (FE) model of the C3-C7 lower cervical spine was established and validated. After two-level (C4-C6) anterior cervical discectomy and fusion (ACDF) surgery, FE models were constructed for the anterior cervical locked-plate (ACLP) internal fixation, the ATPS internal fixation, and the novel ATPRS intervertebral fusion system. These models were subjected to 75N axial force and 1.0 Nm to induce various movements. The range of motion (ROM) of the surgical segments (C4-C6), maximum stress on the internal fixation systems, and maximum stress on the adjacent intervertebral discs were tested and recorded. Results: All three internal fixation methods effectively reduced the ROM of the surgical segments. The ATPRS model demonstrated the smallest ROM during flexion, extension, and rotation, but a slightly larger ROM during lateral bending. Additionally, the maximum bone-screw interface stresses for the ATPRS model during flexion, extension, lateral bending, and axial rotation were 32.69, 64.24, 44.07, 35.89 MPa, which were lower than those of the ACLP and ATPS models. Similarly, the maximum stresses on the adjacent intervertebral discs in the ATPRS model during flexion, extension, lateral bending, and axial rotation consistently remained lower than those in the ACLP and ATPS models. However, the maximum stresses on the cage and the upper endplate of the ATPRS model were generally higher. Conclusion: Although the novel ATPRS intervertebral fusion system generally had greater endplate stress than ACLP and ATPS, it can better stabilize cervical three-column injuries and might reduce the occurrence of adjacent segment degeneration (ASD). Furthermore, further studies and improvements are necessary for the ATPRS intervertebral fusion system.

Biomechanical evaluation of a novel anterior transpedicular screw-plate system for anterior cervical corpectomy and fusion (ACCF): a finite element analysis

Background and objective: Cervical fusion with vertebral body screw (VBS)-plate systems frequently results in limited biomechanical stability. To address this issue, anterior transpedicular screw (ATPS) fixation has been developed and applied preliminarily to multilevel spinal fusion, osteoporosis, and three-column injury of the cervical spine. This study aimed to compare the biomechanical differences between unilateral ATPS (UATPS), bilateral ATPS (BATPS), and VBS fixation using finite element analysis. Materials and methods: A C6 corpectomy model was performed and a titanium mesh cage (TMC) and bone were implanted, followed by implantation of a novel ATPS-plate system into C5 and C7 to simulate internal fixation with UATPS, BATPS, and VBS. Internal fixation with UATPS comprises ipsilateral transpedicular screw-contralateral vertebral body screw (ITPS-CVBS) and cross transpedicular screw-vertebral body screw (CTPS-VBS) fixations. Mobility, the maximal von Mises stress on TMC, the stress distribution and maximal von Mises stress on the screws, and the maximum displacement of the screw were compared between the four groups. Results: Compared with the original model, each group had a reduced range of motion (ROM) under six loads. After ACCF, the stress was predominantly concentrated at two-thirds of the length from the tail of the screw, and it was higher on ATPS than on VBS. The stress of the ATPS from the cranial part was higher than that of the caudal part. The similar effect happened on VBS. The screw stress cloud maps did not show any red areas reflective of a concentration of the stress on VBS. Compared with VBS, ATPS can bear a greater stress from cervical spine movements, thus reducing the stress on TMC. The maximal von Mises stress was the lowest with bilateral transpedicular TMC and increased with cross ATPS and with ipsilateral ATPS. ITPS-CVBS, CTPS-VBS, and BATPS exhibited a reduction of 2.3%-22.1%, 11.9%-2.7%, and 37.9%-64.1% in the maximum displacement of screws, respectively, compared with that of VBS. Conclusion: In FEA, the comprehensive stability ranked highest for BATPS, followed by CTPS-VBS and ITPS-CVBS, with VBS demonstrating the lowest stability. Notably, utilizing ATPS for fixation has the potential to reduce the occurrence of internal fixation device loosening after ACCF when compared to VBS.

Robot-assisted anterior transpedicular screw fixation with 3D printed implant for multiple cervical fractures: A case report

RATIONALE

The anterior transpedicular screw (ATPS) fixation in the cervical spine provides the advantages of both anterior and posterior cervical surgery; however, it poses a high risk of screw insertion. In addition, a 3D printed implant can match ATPS fixation and reconstruction of the vertebral body. Robot-assisted surgery can make this process easier and potentially improve the safety and accuracy of the procedure.

PATIENT CONCERNS

A 64-year-old female was hit by a heavy object 4 days before presentation to our hospital. The patient exhibited a muscle strength of 0/5 in both the lower limbs and 3/5 in both the upper limbs. The visual analogue scale (VAS) for the neck was 5 points. Computed tomography (CT) of the cervical spine identified a burst fracture of the C5 vertebral body, and longitudinal splitting fracture of the C6 and C7 vertebral bodies accompanied with a split in the lamina. Magnetic resonance imaging (MRI) revealed a spinal cord edema from the C3 to the C7 level.

DIAGNOSIS

Multiple cervical fractures with spinal cord injury.

INTERVENTIONS

Anterior C4-5 and C5-6 disc resection, C5 corpectomy, robot-assisted ATPS fixation with the 3-D printed implant was performed.

OUTCOMES

The CT scans revealed a satisfactory location of the internal implantation without any signs of complications associated with implantations. Six months later, the muscle strength of both the upper limbs increased from level 3 to level 5, VAS of neck decreased from 5 to 0.

LESSONS

Robot-assisted ATPS internal fixation combined with custom implantation surgery using a 3D printed vertebral body provides an important solution to solve special cases.

Anterior cervical transpedicular screw fixation system in subaxial cervical spine: A finite element comparative study

Multilevel cervical corpectomy has raised the concern among surgeons that reconstruction with the anterior cervical screw plate system (ACSPS) alone may fail eventually. As an alternative, the anterior cervical transpedicular screw (ACTPS) has been adopted in clinical practice. We used the finite element analysis to investigate whether ACTPS is a more reasonable choice, in comparison with ACSPS, after a 2-level corpectomy in the subaxial cervical spine. These 2 types of implantation models with the applied 75 N axial pressure and 1 N • m pure moment of the couple were evaluated. Compared with the intact model, the range of motion (ROM) at the operative segments (C4-C7) decreased by 97.5% in flexion-extension, 91.3% in axial rotation, and 99.3% in lateral bending in the ACTPS model, whereas it decreased by 95.1%, 73.4%, 96.9% in the ACSPS model respectively. The ROM at the adjacent segment (C3/4) in the ACTPS model decreased in all motions, while that of the ACSPS model increased in axial rotation and flexion-extension compared with the intact model. Compared to the ACSPS model, whose stress concentrated on the interface between the screws and the titanium plate, the stress of the ACTPS model was well-distributed. There was also a significant difference between the maximum stress value of the 2 models. ACTPS and ACSPS are biomechanically favorable. The stability in reducing ROM of ACTPS may be better and the risk of failure for internal fixator is relatively low compared with ACSPS fixation except for under lateral bending in reconstruction the stability of the subaxial cervical spine after 2-level corpectomy.

Circumferential Operations of the Cervical Spine

Generally, a combined anterior and posterior cervical approach is associated with significant morbidity since it requires an extended operative time, greater intraoperative blood loss, and both anterior- and posterior-related surgical complications. However, there are some instances where a circumferential cervical fusion can be advantageous. Our objective is to discuss the indications for circumferential cervical spine procedures. A narrative review of the literature was performed. We include the indications for circumferential cervical approaches of the senior author (KDR). Indications for circumferential approaches include: (1) high-risk patients for pseudoarthrosis, (2) cervical deformity (e.g., degenerative, posttraumatic, cervicothoracic kyphosis), (3) cervical spine metastases (especially those with multilevel involvement), (4) cervical spine infection, (5) unstable cervical trauma, (6) movement disorders and cerebral palsy, (7) Multiply operated patient (especially postlaminectomy kyphosis and patients with massive ossification of the posterior longitudinal ligament), and when (8) early fusion is desirable. Circumferential procedures may be useful in many different cervical spine conditions requiring surgery. Despite its advantages, particularly with reducing the risk for pseudarthrosis, the benefits of a combined approach must be weighed against the risks associated with a dual approach. With appropriate preoperative planning, intraoperative decision-making, and surgical techniques, excellent clinical outcomes can be achieved.

Comparison of anterior-only versus combined anterior and posterior fusion for unstable subaxial cervical injuries: a meta-analysis of biomechanical and clinical studies

OBJECTIVE

The purpose of the present study was to perform a meta-analysis comparing biomechanical and clinical outcomes between anterior-only and combined anterior and posterior fusions to determine which method of cervical fusion yielded better results for unstable cervical injuries.

METHODS

The MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Web of Science and SCOPUS electronic databases were searched for relevant articles published through 2000-2019 that compared the biomechanical and clinical outcomes of anterior-only and combined anterior and posterior fusion for unstable cervical fracture.

RESULTS

Eight biomechanical and four clinical studies were included in the analysis. There were significant biomechanical differences between the groups with respect to flexion-extension, axial rotation and lateral bending. Combined fusion provided better biomechanical stability for unstable cervical injuries than anterior-only fusion, regardless of the number of corpectomies or the presence of a posterior column injury. However, despite significant biomechanical differences, there were no significant differences in clinical outcomes, such as the degree of neurologic improvement and complications between the two groups.

CONCLUSION

Anterior-only and combined anterior and posterior fusions for unstable subaxial cervical injuries can both restore cervical stability. Although combined fusion might have some advantages in terms of stability biomechanically, there were no significant differences in clinical outcomes, such as the degree of neurologic improvement and perioperative complications. Therefore, rather than the routine use of combined fusion for unstable cervical injuries, the selective use of anterior-only or combined fusion according to the type of injury is recommended.

Effectiveness of 2 Types of Drill Templates for Cervical Anterior Transpedicular Screw Placements: A Comparative Study

OBJECTIVE

To evaluate effectiveness of regular and modified drill templates used to guide cervical anterior transpedicular screw (ATPS) placement.

METHODS

This study included 15 adult cadaveric specimens. Computed tomography images were imported into Mimics software. Three-dimensional modeling of all cervical vertebrae was done, and the ideal trajectories were designed for ATPSs. Models of regular and modified templates were designed for every level on the left or right side randomly. After three-dimensional printing, 2 types of templates were used to guide the insertion. Postoperative computed tomography scans were used to measure deviations between real and ideal trajectories in the direction and positioning of entry points. The deviations in the 2 groups were compared using paired t test.

RESULTS

There were 120 templates and ATPSs fabricated and placed. Postoperative images showed that 7 screws perforated pedicles in the regular group, with an accuracy rate of 88.3%. Deviations between real and ideal trajectories in cranially inclined angles and extroversive angles were 1.13° ± 0.61° and 0.97° ± 0.60°, respectively, and deviations of entry point position in the x-axis and y-axis were 0.72 ± 0.38 mm and 0.95 ± 0.47 mm, respectively. In the modified group, there were 2 malposition screws with accuracy rate of 96.7%. Deviations in cranially inclined angles were 0.66° ± 0.53° and 0.66° ± 0.55° in extroversive angles, respectively, and deviations in entry point positions in the x-axis and y-axis were 0.45 ± 0.37 mm and 0.51 ± 0.34 mm, respectively. The differences in deviations between groups were statistically significant.

CONCLUSIONS

Compared with regular drill templates, modified drill templates can provide higher accuracy and stronger trajectory control in ATPS insertions.

The Effect of Rod Pattern, Outrigger, and Multiple Screw-Rod Constructs for Surgical Stabilization of the 3-Column Destabilized Cervical Spine - A Biomechanical Analysis and Introduction of a Novel Technique

Objective

Anterior-only reconstructions for cervical multilevel corpectomies are prone to fail under continuous mechanical loading. This study sought to define the mechanical characteristics of different constructs in reducing a range of motion (ROM) of the 3-column destabilized cervical spine, including posterior cobalt-chromium (CoCr)-rods, outrigger-rods (OGR), and a novel triple rod construct using lamina screws (6S3R). The clinical implications of biomechanical findings are discussed in depth from the perspective of the challenges surgeons face cervical deformity correction.

Methods

Three-column deficient cervical spinal models were produced based on reconstructed computed tomography scans. The corpectomy defect between C3 and C7 end-level vertebrae was restored with anterior titanium (Ti) mesh-cage. The ROM was evaluated in a customized 6-degree of freedom spine tester. Tests were performed with different rod materials (Ti vs. CoCr), varying diameter rods (3.5 mm vs. 4.0 mm), with and without anterior plating, and using different construct patterns: bilateral rod fixation (standard-group), OGR-group, and 6S3R-Group. Construct stability was expressed in changes and differences of ROM (°).

Results

The largest reduction of ROM was noticed in the 6S3R-group compared to the standard- and the OGR-group. All differences observed were emphasized with an increasing number of corpectomy levels and if anterior plating was not added. For all simulated 1-, 2-, and 3-level corpectomy constructs, the OGR-group revealed decreased ROM for all motion directions compared to the standard-group. An increase of construct stiffness was also recorded for increased rod diameter (4.0 mm) and stiffer rod material (CoCr), though these effects lacked behind the more advanced construct pattern.

Conclusion

A novel reconstructive technique, the 6S3R-construct, was shown to outperform all other constructs and might resemble a new standard of reference for advanced posterior fixation.

Progress of the Anterior Transpedicular Screw in Lower Cervical Spine: A Review

The anterior transpedicular screws (ATPS) fixation is a valuable discovery in the field of lower cervical spine (LCS) reconstruction, as it has the advantages of both anterior and posterior approaches. In recent years, with in-depth research on ATPS fixation related to anatomy, biomechanical tests, and clinical applications, its firm stability and excellent biomechanical properties have been recognized by more and more surgeons. Although ATPS fixation has been gradually applied in clinic settings under the promotion of emerging distinctive instruments, its long-term efficacy still needs to be further clarified due to the lack of large sample size studies and long-term follow-up. Nevertheless, it is believed that with the maturity of digital devices and the development of precision medicine, ATPS fixation has a promising prospect.

Preparation and Assessment of an Individualized Navigation Template for Lower Cervical Anterior Transpedicular Screw Insertion Using a Three-Dimensional Printing Technique

STUDY DESIGN

Prospective trial.

OBJECTIVE

To establish an individualized navigation template for safe and accurate insertion of lower cervical anterior transpedicular screw (ATPS) based on a three-dimensional (3D) printing technique.

SUMMARY OF BACKGROUND DATA

Conventional screw insertion manually under fluoroscopy easily leading to deviation of ATPS screw channel, cervical instrumentation procedures demand the need for a precise technique for screw placement.

METHODS

Twenty adult cervical spine specimens (10 men and 10 women, with a mean age of 50.29 ± 6.98) were selected for computed tomography pre- and postoperatively. A 3D lower cervical spine model was reconstructed using Mimics software to measure the screw-related parameters and generate a reverse template with optimal screw channel as well as a prototype using 3D printing. Assisted by the navigation template, bilateral ATPS were inserted into the cadavers.

RESULTS

The mean outer width and height of pedicle were 5.31 ± 1.23 and 6.78 ± 1.10 mm, respectively. The average length, sagittal, and axial angles of the optimal screw channel obtained through the optimal entry point were 36.34 ± 4.39 mm, 40.67° ± 5.10°, and 93.7° ± 7.96°, respectively. The adjustable safe ranges of sagittal and axial angles were 3.89° ± 1.13° and 5.64° ± 0.97°, respectively. The axial and sagittal accuracies of the 200 screws were 99.5% and 97%, respectively. The average deviations of the actual entry point and the preset opening in the X, Y, and Z axes were 0.39 ± 0.43, 0.21 ± 0.41, and 0.29 ± 0.14 mm, respectively (P > 0.05).

CONCLUSION

An individualized ATPS navigation template was developed using Mimics software and 3D printing prototyping, based on computed tomography, for highly accurate screw insertion.

LEVEL OF EVIDENCE

4.

Stability of two anterior fixations for three-column injury in the lower cervical spine: biomechanical evaluation of anterior pedicle screw-plate fixation

Objectives This study aimed to evaluate the stability of anterior pedicle screw-plate (APSP) fixation and anterior vertebral body screw-plate (AVBSP) fixation for three-column injury in the lower cervical spine. Methods Six fresh-frozen human cadaveric specimens of the lower cervical spine were prepared. After measurement of the range of motion (ROM) in the intact state, the specimens were prepared as three-column injury models. The models were stabilized by AVBSP or APSP fixation. The ROM of the models in the two states was measured. The ROM in the two states was compared. Results The ROM of the intact state in all directions was significantly smaller than that of the AVBSP state and significantly larger than that of the APSP state. The ROM of the AVBSP state in all directions was significantly larger than that of the APSP state. Conclusions This study shows that APSP fixation can provide sufficient stability for three-column injury in the lower cervical spine. The primary stability of our models using APSP fixation is superior to that of AVBSP fixation. These results suggest that APSP can be used for three-column injury in the lower cervical spine.

Anterior pedicle spreader reduction for unilateral cervical facet dislocation

OBJECTIVE

The anterior only surgical procedure including discectomy, open reduction and fusion is used as a recommended approach in the treatment of unilateral cervical facet dislocations, but is difficult to achieve satisfactory anterior open reduction by vertebra distractor to spread the facet joints, especially for delayed management of unilateral cervical facet dislocation (7-21days). The goal of this study was to report an anterior pedicle spreader technique to distract directly the facet joint for anterior reduction and the results of 4 patients with successful application and describe safety.

METHODS

Four patients with unilateral cervical facet dislocation who failed to open anterior reduction by vertebra spreader procedure were surgically treated by the anterior pedicle spreader reduction. In these 4 patients (3 males and 1 female), the distribution of spine level was from C4/5 to C6/7; the neurological status was comprised 2 patients with ASIA E, 1 with D and 1 with A; the surgical management was ranged from 7 to 18days. After discectomy, if failed to open anterior reduction procedure, the anterior pedicle spreader was inserted along the pedicle axis with the fluoroscope-assisted view imaging. The spreader was distracted directly to the facet joint and pushed in a caudad direction to achieve posterior translation of the upper segment.

RESULTS

Postoperatively, all patients had obtained successful reduction and satisfactory anatomic sagittal alignment. There was no complication owing to the use of this technique. The ASIA A showed no neurological improvement; the patient with ASIA D was improved neurologically to ASIA E; no ASIA E patients showed neurological deterioration.

CONCLUSIONS

Anterior pedicle spreader reduction represents an efficacious but technically challenging option for the delayed treatment of unilateral cervical facet dislocation.

Cervical corpectomies: results of a survey and review of the literature on diagnosis, indications, and surgical technique

OBJECTIVES

Cervical corpectomy is an uncommon procedure and there are only limited data on the procedure's indications, surgical approaches, and complications. The diagnosis, indications, surgical planning, and complications of cervical corpectomy were therefore surveyed to clarify the treatment strategies used by spinal surgeons in central Europe, with special attention to preoperative planning and decision-making for additional dorsal approaches in multilevel cases.

MATERIALS AND METHODS

An online survey with 18 questions on the preoperative, intraoperative, and postoperative management of cervical corpectomies was conducted. The relevant specialist societies in Germany and Austria provided 1137 contacts for surgeons, and the responses were compared with recent literature reports.

RESULTS

In all, 302 surgeons (27 %) completed the survey, with wide variability in the treatment options offered. Most (51 %) perform fewer than five anterior cervical corpectomy and fusion (ACCF) procedures per year; 35 % do 5-20 per year. Anterior cervical discectomy and fusion (ACDF) was preferred by 41 % of the participants to laminoplasty/laminectomy (19 %/16 %) and ACCF (12 %). Most indications for ACCF involved degenerative (27 %), traumatic (17 %), and neoplastic (20 %) conditions. Intraoperative and postoperative complications were mainly associated with hardware failure. One-third of the surgeons tend to use an additional dorsal approach to increase the corpectomy construct's stability for either two-level or three-level corpectomies.

CONCLUSIONS

There is no current consensus in central Europe on the treatment of complex cervical disease and cervical corpectomy. The procedure is still rare, and the need for additional dorsal fixation is unclear. Further studies are needed in order to establish evidence-based standards for patient care.

Anterior Facetectomy for Reduction of Cervical Facet Dislocation

STUDY DESIGN

Technique report and case series.

OBJECTIVE

The aim of this study was to develop a new surgical technique for anterior reduction in management of unilateral/bilateral facet dislocations and to report the results of 8 patients with successful outcomes associated with this approach.

SUMMARY OF BACKGROUND DATA

The anterior-only surgical procedure, including discectomy, open reduction, fusion, and fixation, is a recommended approach in the treatment of cervical facet dislocations. This approach is with a failure rate of up to 40%. When it fails, a posterior approach is usually required. We have developed a new surgical approach with facetectomy for anterior reduction of cervical facet dislocations. This technique is especially useful for delayed management of unilateral/bilateral facet dislocation patients who failed the conventional anterior open reduction to avoid a posterior procedure.

METHODS

Eight patients with cervical facet dislocations who failed in the conventional anterior reduction were surgically treated by the anterior facetectomy reduction technique. After discectomy, anteromedial foraminotomy was performed by resection of posterior foraminal part or total of uncovertebral joint. After the nerve root was retracted cephalad in the neuroforamina, the edge of the dislocated superior facet was broken to achieve reduction.

RESULTS

Postoperatively, all patients have obtained successful reduction and satisfactory anatomic sagittal alignment. There were no complications attributable to the use of this technique.

CONCLUSION

Anterior facetectomy reduction represents a safe and efficacious but technically challenging option for the treatment of cervical facet dislocation.

LEVEL OF EVIDENCE

5.

Anterior pedicle screw and plate fixation for cervical facet dislocation: case series and technical note

BACKGROUND CONTEXT

The anterior-only surgical procedure is used as a recommended approach in the treatment of cervical facet dislocations, but an anterior cervical spine implant that offers higher three-column instabilities for stronger fixation is lacking.

PURPOSE

This study aimed to report a new surgical technique of anterior pedicle screw (APS) fixation for cervical facet dislocations and the results of 12 patients with successful application and described safety.

STUDY DESIGN

The study design includes case series and technical report.

PATIENT SAMPLE

The sample comprises 12 patients with cervical facet dislocations.

OUTCOME MEASURES

Analyses of plain lateral neutral and oblique radiographs and computed tomography scans were conducted to assess reduction, fusion, and the accuracy of pedicle screw placement. Spinal cord compression and decompression was defined by a 1.5-Tesla magnetic resonance imaging. Neurologic status was evaluated according to classification of American Spinal Injury Association (ASIA).

METHODS

Twelve patients with cervical facet dislocations were surgically treated by the anterior cervical pedicle screw and plate fixation. In these 12 patients (9 male and 3 females), the distribution of spine level was from C3-C4 to C6-C7; the etiologic diagnosis included four unilateral and eight bilateral facet dislocations; the neurologic status comprised four patients with ASIA A, two with ASIA B, two with ASIA D, and four with ASIA E. After discectomy, reduction, and insertion of a peek cage containing autologous bone graft, the APS was inserted along the pedicle axis with the fluoroscope-assisted view imaging.

RESULTS

Postoperatively, all patients had obtained successful reduction and satisfactory anatomic sagittal alignment. There was no complication or instrument failure owing to the use of this technique. Four ASIA A and one ASIA B patients showed no neurologic improvement; one ASIA B patient was improved neurologically to ASIA C; two patients with ASIA D were improved neurologically to ASIA E; no ASIA E patients showed neurologic deterioration.

CONCLUSIONS

Anterior pedicle screw and plate fixation represents a safe and efficacious but technically challenging option for the treatment of cervical facet dislocations.

Biomechanical testing of circumferential instrumentation after cervical multilevel corpectomy

STUDY DESIGN

Biomechanical investigation.

PURPOSE

This study describes ex vivo evaluation of the range of motion (ROM) to characterize the stability and need for additional dorsal fixation after cervical single-level, two-level or multilevel corpectomy (CE) to elucidate biomechanical differences between anterior-only and supplemental dorsal instrumentation.

METHODS

Twelve human cervical cadaveric spines were loaded in a spine tester with pure moments of 1.5 Nm in lateral bending (LB), flexion/extension (FE), and axial rotation (AR), followed by two cyclic loading periods for three-level corpectomies. After each cyclic loading session, flexibility tests were performed for anterior-only instrumentation (group_1, six specimens) and circumferential instrumentation (group_2, six specimens).

RESULTS

The flexibility tests for all circumferential instrumentations showed a significant decrease in ROM in comparison with the intact state and anterior-only instrumentations. In comparison with the intact state, supplemental dorsal instrumentation after three-level CE reduced the ROM to 12% (±10%), 9% (±12%), and 22% (±18%) in LB, FE, and AR, respectively. The anterior-only construct outperformed the intact state only in FE, with a significant ROM reduction to 57% (±35 %), 60% (±27%), and 62% (±35%) for one-, two- and three-level CE, respectively.

CONCLUSIONS

The supplemental dorsal instrumentation provided significantly more stability than the anterior-only instrumentation regardless of the number of levels resected and the direction of motion. After cyclic loading, the absolute differences in stability between the two instrumentations remained significant while both instrumentations showed a comparable increase of ROM after cyclic loading. The large difference in the absolute ROM of anterior-only compared to circumferential instrumentations supports a dorsal support in case of three-level approaches.

Anterior transpedicular screw fixation of cervical spine: Is it safe? Morphological feasibility, technical properties, and accuracy of manual insertion

OBJECT

Due to lack of construct stability of the current anterior cervical approaches, supplemental posterior cervical approaches are frequently employed. The use of an anterior-only approach with anterior transpedicular screws (ATPSs) has been proposed as a means of providing 3-column fixation. This study was designed to investigate the feasibility of anterior transpedicular screw (ATPS) fixation of cervical spine, to obtain the morphological measurements for technical prerequisites, and to evaluate the accuracy of the ATPS using fluoroscopy.

METHODS

The study included both radiological and anatomical investigations. The radiological investigations were based on data from cervical spine CT scans performed in 65 patients. Technical prerequisites of ATPS were calculated using OsiriX for Mac OS. In the anatomical part of the study, 30 pedicles (C3–7) from 6 formalin-preserved cadavers were manually instrumented. Measurements obtained included pedicle width (PW), pedicle height (PH), pedicle transverse angle (PTA), distance of the entry point from the midline (DEPM), and distance of the entry point from the superior endplate (DEPSEP). The authors also analyzed screw position in the manually instrumented vertebrae.

RESULTS

The mean PW and PH values showed a tendency to increase from C-3 to C-7 in both males and females. The means were significantly larger for both PW and PH in males than in females at all levels (p = 0.001). The overall mean PTA value was significantly lower at C-7 (p < 0.0001). The mean value for the distance of entry point from the midline (DEPM) represented a point at the contralateral side of the pedicle for every level except C-7. The mean DEPSEP values showed significant differences between all levels (p < 0.0001). Seven of the 30 screws were identified as breaching the pedicle (23.3%); these screw malplacements were seen at C-3 (3 screws), C-4 (2 screws), and C-5 (2 screws).

CONCLUSIONS

The morphological measurements of this study demonstrated that ATPS fixation is feasible in selected cases. They indicate that ATPS insertion using a fluoroscopy-assisted pedicle axis view is safe at the C-6 and C-7 levels, but the results at the other levels did not prove the safety of this technique.

Zero-profile hybrid fusion construct versus 2-level plate fixation to treat adjacent-level disease in the cervical spine

OBJECT

Single-level anterior cervical discectomy and fusion (ACDF) is an established surgical treatment for cervical myelopathy. Within 10 years of undergoing ACDF, 19.2% of patients develop symptomatic adjacent-level degeneration. Performing ACDF adjacent to prior fusion requires exposure and removal of previously placed hardware, which may increase the risk of adverse outcomes. Zero-profile cervical implants combine an interbody spacer with an anterior plate into a single device that does not extend beyond the intervertebral disc space, potentially obviating the need to remove prior hardware. This study compared the biomechanical stability and adjacent-level range of motion (ROM) following placement of a zero-profile device (ZPD) adjacent to a single-level ACDF against a standard 2-level ACDF.

METHODS

In this in vitro biomechanical cadaveric study, multidirectional flexibility testing was performed by a robotic spine system that simulates flexion-extension, lateral bending, and axial rotation by applying a continuous pure moment load. Testing conditions were as follows: 1) intact, 2) C5-6 ACDF, 3) C4-5 ZPD supraadjacent to simulated fusion at C5-6, and 4) 2-level ACDF (C4-6). The sequence of the latter 2 test conditions was randomized. An unconstrained pure moment of 1.5 Nm with a 40-N simulated head weight load was applied to the intact condition first in all 3 planes of motion and then using the hybrid test protocol, overall intact kinematics were replicated subsequently for each surgical test condition. Intersegmental rotations were measured optoelectronically. Mean segmental ROM for operated levels and adjacent levels was recorded and normalized to the intact condition and expressed as a percent change from intact. A repeated-measures ANOVA was used to analyze the ROM between test conditions with a 95% level of significance.

RESULTS

No statistically significant differences in immediate construct stability were found between construct Patterns 3 and 4, in all planes of motion (p > 0.05). At the operated level, C4-5, the zero-profile construct showed greater decreases in axial rotation (-45% vs -36%) and lateral bending (-55% vs -38%), whereas the 2-level ACDF showed greater decreases in flexion-extension (-40% vs -34%). These differences were marginal and not statistically significant. Adjacent-level motion was nearly equivalent, with minor differences in flexion-extension.

CONCLUSIONS

When treating degeneration adjacent to a single-level ACDF, a zero-profile implant showed stabilizing potential at the operated level statistically similar to that of the standard revision with a 2-level plate. Revision for adjacent-level disease is common, and using a ZPD in this setting should be investigated clinically because it may be a faster, safer alternative.

Cervical spine instability following axial compression injury: a biomechanical study

BACKGROUND

Axial compression injuries of the cervical spine occur during contact sports, automobile collisions, and falls. The objective of this study was to use flexibility tests to determine biomechanical instability of the cervical spine due to simulated axial compression injuries.

HYPOTHESIS

We hypothesized that the axial compression injuries cause severe biomechanical instability throughout the cervical spine.

MATERIALS AND METHODS

The injuries were simulated using 2.4m/s head-first impacts of a cadaveric cervical spine model (n=10) mounted horizontally to a torso-equivalent mass on a sled and carrying a surrogate head in protruded posture. Intact and post-impact flexibility tests were performed up to 1.5, 3, and 1.5 Nm in flexion-extension, axial torque, and lateral bending, respectively. Instability parameters of range of motion (RoM) and neutral zone (NZ) were determined for injured spinal levels and statistically compared (P<0.05) between intact and post-impact.

RESULTS

The sagittal instability parameters indicated extension-compression injuries at the upper and middle cervical spine and flexion-compression injuries at the lower cervical spine. Increases in extension RoM were 14.9° at the upper cervical spine and 24.9° (P<0.05) at the middle cervical spine and in flexion RoM at C7/T1 were 25.6°. RoM and NZ increases in axial rotation and lateral bending were nearly symmetric among left and right.

DISCUSSION

Multidirectional instability of the upper cervical spine caused by atlas and dens fractures was evidenced by increases between 36% and 53% in RoM and NZ due to the impacts. The sagittal RoM of injured spinal levels of the middle and lower cervical spine exceeded a proposed threshold for clinical instability by between 67% and 114%. The instability documented throughout the cervical spine was consistent with clinical observations of cord injuries and paralysis in patients.

LEVEL OF EVIDENCE

Level IV, controlled laboratory investigation.

Anterior cervical intercorporal fusion in patients with osteoporotic or tumorous fractures using a cement augmented cervical plate system: first results of a prospective single-center study

STUDY DESIGN

Prospective observational clinical study.

OBJECTIVE

The aim of this study is to evaluate the technical feasibility and the safety of additional cement augmentation of anterior cervical implants in patients with poor bone quality because of osteoporosis or tumor infiltration.

SUMMARY OF BACKGROUND DATA

With an increasing number of elderly patients in spinal surgery the problem of implant dislocation after cervical instrumentation will become a more and more important problem. Whereas in the thoracolumbar area cement augmented screws have become widely accepted to ensure a rigid fixation in patients with reduced bone quality there are no data concerning an additional intravertebral cement augmentation after cervical plating.

METHODS

Nine patients (4 males, 5 females, mean age 62.8 y) with newly diagnosed fractures of 1 or 2 cervical vertebrae because of tumor infiltration (6 cases) or osteoporosis (3 cases) were included in our study. A standard 1-level or 2-level cervical corpectomy with vertebral body replacement by an in situ expandable titanium cage and additional anterior plating was carried out. After this, additional cement augmentation was performed as a vertebroplasty of the anterior two thirds of the cranial and caudal adjacent vertebra by a new anterior hole. The cement should enclose the screws and stabilize the endplates of the adjacent vertebrae. Follow-up comprised clinical examinations, SF-36 questionnaire and visual analog scale 3, 6, and 12 months after surgery. Cervical spine radiographs were obtained 3 and 6 months after surgery and computed tomography scans 6 and 12 months after surgery.

RESULTS

The median follow-up was 10 months with a range of 4-18 months. There was no intraoperative cement leakage into the spinal canal. The visual analog scale decreased from 8.2 to 4.2 at 6 months, physical and mental component summaries of SF-36 increased significantly from 27.7 to 36.1 and 31.5 to 48.6 at 6 months, respectively. Loosening of screws or plates was not detected throughout the whole observation period. There was 1 subsidence of a titanium cage into an adjacent vertebra without any clinical consequences. There was no adjacent fracture during the follow-up period and other surgical interventions or revisions were not necessary in any patient.

CONCLUSIONS

In patients with severe osteoporosis or in patients with advanced tumor disease, excellent surgical, clinical, and radiologic results are possible following our method. In our opinion, a second-step posterior approach can be avoided by this technique.

Long-term impacts of different posterior operations on curvature, neurological recovery and axial symptoms for multilevel cervical degenerative myelopathy

Purpose

To investigate the long-term impacts of different posterior operations on curvature, neurological improvement and axial symptoms for multilevel cervical degenerative myelopathy (CDM), and to study the relationship among loss of cervical lordosis, recovery rate and axial symptom severity.

Methods

We retrospectively reviewed 98 patients with multilevel CDM who had undergone laminoplasty (Group LP, 36 patients), laminectomy (Group LC, 30 patients), or laminectomy with lateral mass screw fixation (Group LCS, 32 patients) between January 2000 and January 2005. Loss of curvature index (CI) was measured according to the preoperative and final follow-up radiographic parameters. The recovery rate was calculated based on the Japanese Orthopedic Association (JOA) score. Axial symptom severity was quantified by Neck Disability Index (NDI).

Results

Analysis of final follow-up data showed significant differences among the three groups regarding loss of CI (F = 41.46, P < 0.001) between preoperative and final follow-up JOA scores (P < 0.001), final follow-up JOA score (F = 7.81, P < 0.001), recovery rate (F = 12.98, P < 0.001) and axial symptom severity (χ² = 18.04, P < 0.001). Loss of CI showed negative association with neurological recovery (r = −0.555, P < 0.001) and positive correlation with axial symptom severity (r = 0.696, P < 0.001).

Conclusions

Excellent neurological improvement was obtained by LP and LCS for patients with multilevel CDM, while loss of CI in groups LP and LC caused a high incidence of axial symptoms. Loss of CI was correlated with poor neurological recovery and axial symptom severity. Lateral mass screw fixation can effectively prevent loss of postoperative cervical curvature and reduce incidence of axial symptoms.

Perioperative characteristics, complications, and outcomes of single-level versus multilevel thoracic corpectomies via modified costotransversectomy approach

STUDY DESIGN

Retrospective case series.

OBJECTIVE

To compare perioperative end points and outcomes of single-level versus multilevel corpectomy performed using a modified costotransversectomy approach.

SUMMARY OF BACKGROUND DATA

Single-level corpectomy via posterolateral approach has been shown to be an effective alternative to the traditional anterior thoracotomy approach. However, there is a paucity of studies that have examined multilevel thoracic corpectomy via posterolateral approach.

METHODS

Using electronic medical records, we identified a consecutive population of adult patients who underwent modified costotransversectomy corpectomy in the thoracic region between 2006 and 2009. Patients were stratified by number of corpectomies performed into either a single-level or multilevel group. With the use of baseline descriptive statistics and multivariate analysis, perioperative parameters and follow-up outcomes were assessed between the 2 groups.

RESULTS

A total of 40 patients were included in the final analysis, with 25 patients in the single-level group and 15 patients in the multilevel group. Mean follow-up was 16.1 months. Overall complication rate was 37.5%. Between the 2 groups, there were no significant differences in operative time, blood loss, transfusion rate, quantity of blood transfused, length of hospital stay, or complication rates. Also, there were no significant differences in repeat surgery rate, Medical Research Council strength, Nurick score, or pain at most recent follow-up, and all groups gained a comparable magnitude of benefit from surgery.

CONCLUSION

Multilevel corpectomy via modified costotransversectomy approach in the thoracic region is a feasible and effective option that does not seem to be associated with significantly increased morbidity. The degree of clinical improvement also seems comparable with single-level corpectomy.

Morphological character of cervical spine for anterior transpedicular screw fixation

BACKGROUND

Anterior cervical interbody grafts/cages combined with a plate were frequently used in multilevel discectomies/corpectomies. In order to avoid additional posterior stabilization in patients who undergo anterior reconstructive surgery, an anterior cervical transpedicular screw fixation, which offers higher stability is desirable. We investigated in this study the anatomical (morphologic) characters for cervical anterior transpedicular screw fixation.

MATERIALS AND METHODS

Left pedicle parameters were measured on computed tomography (CT) images based on 36 cervical spine CT scans from healthy subjects. The parameters included outer pedicle width (Distance from lateral to medial pedicle surface in the coronal plane), outer pedicle height (OPH) (Distance from upper to lower pedicle surface in the sagittal plane), maximal pedicle axis length (MPAL), distance transverse insertion point (DIP), distance of the insertion point to the upper end plate (DIUP), pedicle sagittal transverse angle (PSTA) and pedicle transverse angle (PTA) at C3 to C7.

RESULTS

The values of outer pedicle width and MPAL in males were larger than in females from C3 to C7. The OPH in males was larger than in females at C3 to C6, but there was no difference at C7. The DIP and PTA were significantly greater in males than in females at C3, but there was no difference in the angle at C4-7. The PSTA was not statistically different between genders at C3, 4, 7, but this value in males was larger than females at C5, 6. The DIUP was significantly greater in males at C3, 4, 6, 7 but was non significant at C5.

CONCLUSIONS

The placement of cervical anterior transpedicular screws should be individualized for each patient and based on a detailed preoperative planning.

A new technique for anterior cervical pedicle screw implantation

OBJECTIVE

To introduce and evaluate a new technique, anterior pedicle screw implantation, for anterior cervical reconstruction.

METHODS

Seven patients (five men and two women) with an average age of 65 years were included in this group. After carefully preparation, anterior pedicle screws were implanted under fluoroscopy in all patients. The position of the anterior pedicle screws was evaluated three days postoperatively by X-ray and CT imaging. The mean recovery rate as assessed by the Japanese Orthopaedic Association (JOA) score was recorded at final follow-up.

RESULTS

A total of fourteen anterior pedicle screws were implanted in our group. The average follow up period was 8 months. The mean JOA score was 12.5 preoperatively and 14.8 postoperatively. The mean improvement in the JOA score was 50.5% at final follow-up. The average local alignment improved from 4.0 of kyphosis preoperatively to 6.5 of lordosis at final follow-up. Early bony union was observed in four cases that were followed up for more than 3 months. There were no serious complications. No "pedicle perforation" was observed in any of the fourteen anterior pedicle screws, whereas one screw exposure occurred.

CONCLUSION

Anterior cervical pedicle screw implantation is a feasible method for selected cases. It provides another choice for strong anterior cervical reconstruction.

Biomechanical comparison of anterior cervical spine instrumentation techniques with and without supplemental posterior fusion after different corpectomy and discectomy combinations: Laboratory investigation

OBJECT

The objective of this study was to compare the stiffness and range of motion (ROM) of 4 cervical spine constructs and the intact condition. The 4 constructs consisted of 3-level anterior cervical discectomy with anterior plating, 1-level discectomy and 1-level corpectomy with anterior plating, 2-level corpectomy with anterior plating, and 2-level corpectomy with anterior plating and posterior fixation.

METHODS

Eight human cadaveric fresh-frozen cervical spines from C2-T2 were used. Three-dimensional motion analysis with an optical tracking device was used to determine motion following various reconstruction methods. The specimens were tested in the following conditions: 1) intact; 2) segmental construct with discectomies at C4-5, C5-6, and C6-7, with polyetheretherketone (PEEK) interbody cage and anterior plate; 3) segmental construct with discectomy at C6-7 and corpectomy of C-5, with PEEK interbody graft at the discectomy level and a titanium cage at the corpectomy level; 4) corpectomy at C-5 and C-6, with titanium cage and an anterior cervical plate; and 5) corpectomy at C-5 and C-6, with titanium cage and an anterior cervical plate, and posterior lateral mass screw-rod system from C-4 to C-7. All specimens underwent a pure moment application of 2 Nm with regards to flexion-extension, lateral bending, and axial rotation.

RESULTS

In all tested motions the statistical comparison was significant between the intact condition and the 2-level corpectomy with anterior plating and posterior fixation construct. All other statistical comparisons between the instrumented constructs were not statistically significant except between the 3-level discectomy with anterior plating and the 2-level corpectomy with anterior plating in axial rotation. There were no statistically significant differences between the 1-level discectomy and 1-level corpectomy with anterior plating and the 2-level corpectomy with anterior plating in any tested motion. There was also no statistical significance between the 3-level discectomy with anterior plating and the 2-level corpectomy with anterior plating and posterior fixation.

CONCLUSIONS

This study demonstrates that segmental plate fixation (3-level discectomy) affords the same stiffness and ROM as circumferential fusion in 2-level cervical spine corpectomy in the immediate postoperative setting. This obviates the need for staged circumferential procedures for multilevel cervical spondylotic myelopathy. Given that the posterior segmental instrumentation confers significant stability to a multilevel cervical corpectomy, the surgeon should strongly consider the placement of segmental posterior instrumentation to significantly improve the overall stability of the fusion construct after a 2-level cervical corpectomy.

Anterior approach for complex cervical spondylotic myelopathy

Cervical spondylotic myelopathy (CSM) is a slowly progressive disease resulting from age-related degenerative changes in the spine that can lead to spinal cord dysfunction and significant functional disability. The degenerative changes and abnormal motion lead to vertebral body subluxation, osteophyte formation, ligamentum flavum hypertrophy, and spinal canal narrowing. Repetitive movement during normal cervical motion may result in microtrauma to the spinal cord. Disease extent and location dictate the choice of surgical approach. Anterior spinal decompression and instrumented fusion is successful in preventing CSM progression and has been shown to result in functional improvement in most patients.