Integrated intervertebral device for anterior cervical fusion: An initial experience

Peri-Implant Vertebral Body Fracture in a Cervical Integrated Cage Screw Construct: A Case Report of a Rare Complication

CASE

A 33-year-old woman underwent C5-6 anterior cervical discectomy and fusion for progressive cervical myelopathy using an intergrated cage screw construct. Five weeks postoperatively, she presented with neck pain, worsening gait, and weakness after a slight jerk, with imaging showing peri-implant transverse fracture in the C6 vertebral body across the site of Caspar distractor pins and tips of the integrated cage screws. She was treated conservatively with hard collar with close observation, and at 6 months, she was asymptomatic with complete fracture union on imaging.

CONCLUSION

Peri-implant fracture in a cervical integrated cage screw construct is a rare complication, with biomechanical implications to the pathogenesis, which shows good clinical outcome to conservative treatment.

Effectiveness of cervical zero profile integrated cage with and without supplemental posterior Interfacet stabilization

BACKGROUND

Conditions requiring cervical decompression and stabilization are commonly treated using anterior cervical discectomy and fusion using an anterior cage-plate construct. Anterior zero profile integrated cages are an alternative to a cage-plate construct, but literature suggests they may result in less motion reduction. Interfacet cages may improve integrated cage stability. This study evaluated the motion reduction of integrated cages with and without supplemental interfacet fixation. Motion reduction of integrated cages were also compared to published cage-plate results.

METHODS

Seven cadaveric (C2-T1) spines were tested in flexion-extension, lateral bending, and rotation. Specimens were tested: 1) intact, 2) C6-C7 integrated cage, 3) C6-C7 integrated cage + interfacet cages, 4) additional integrated cages at C3-C4 and C4-C5, 5) C3-C4, C4-C5 and C6-C7 integrated cages + interfacet cages. Motion, lordosis, disc and neuroforaminal height were assessed.

FINDINGS

Integrated cage at C6-C7 decreased flexion-extension by 37% (P = .06) and C3-C5 by 54% (P < .01). Integrated + interfacet cages decreased motion by 89% and 86% compared to intact (P < .05). Integrated cages increased lordosis at C4-C5 and C6-C7 (P < .01). Integrated + interfacet cages returned C3-C5 lordosis to intact values, while C6-C7 remained more lordotic (P = .02). Compared to intact, neuroforaminal height increased after integrated cages at C3-C5 (P ≤ .01) and at all levels after interfacet cages (P < .01).

INTERPRETATION

Anterior integrated cages provides less stability than traditional cage-plate constructs while supplemental interfacet cages improve stabilization. Integrated cages provide more lordosis at caudal levels and increase neuroforaminal height more at cranial levels. After interfacet cages, posterior disc height and neuroforaminal height increased more at the caudal segments.

Biomechanical evaluation comparing zero-profile devices versus fixed profile systems in a cervical hybrid decompression model: a biomechanical in vitro study

BACKGROUND CONTEXT

The use of zero-profile devices and the need for posterior fixation in conjunction with a cervical hybrid decompression model have yet to be investigated.

PURPOSE

To compare the biomechanics of zero-profile and fixed profile cervical hybrid constructs composed of anterior cervical discectomy and fusion (ACDF) and anterior cervical corpectomy and fusion (ACCF). Fixed profile devices included anterior plating, whereas zero-profile devices included integrated screws.

STUDY DESIGN

In vitro cadaveric biomechanical study.

METHODS

Twelve fresh-frozen cadaveric spines (C2-C7) were divided into two groups of equal bone mineral density, fixed profile versus zero profile (n=6). Groups were instrumented from C3-C6 with either (1) an expandable ACCF device and a static ACDF spacer with an anterior plate (Hybrid-AP) or (2) a zero-profile ACCF spacer with adjacent zero-profile ACDF spacer (Hybrid-Z). Motion was captured for the (1) intact condition, (2) a hybrid model with lateral mass screws (LMS), (3) a hybrid model without LMS, and (4) a hybrid model without LMS following simulated repetitive loading (fatigue).

RESULTS

Hybrid-AP with LMS reduced motion in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) by 77%, 88%, and 82%, respectively, compared with intact. Likewise, Hybrid-Z with LMS exhibited the greatest reduction in motion relative to intact in FE, LB, and AR by 90%, 95%, and 66%, respectively. Following simulated in vivo fatiguing, an increase in motion was observed for both groups in all planes, particularly during Hybrid-Z postfatigue condition where motion increased relative to intact by 29%. Overall, biomechanical equivalency was observed between Hybrid-AP and Hybrid-Z groups (p>.05). Three (50%) of the Hybrid-Z group specimens exhibited signs of implant migration from the inferior endplate during testing.

CONCLUSIONS

Fixed profile systems using an anterior plate for supplemental fixation is biomechanically more favorable to maintain stability and prevent dislodgement. Dislodgement of 50% of the Hybrid-Z group without LMS emphasizes the necessity for posterior fixation in a zero-profile cervical hybrid decompression model.

Optimizing surface characteristics for cell adhesion and proliferation on titanium plasma spray coatings on polyetheretherketone

BACKGROUND

Titanium plasma spray coating on polyetheretherketone (PEEK) is a recent innovation to interbody spacer technology. The inherent hydrophobic properties of standard, uncoated PEEK implants can hamper cell attachment and bone healing during fusion. The addition of titanium coating not only offers initial stability due to increased surface roughness but also long-term stability due to bony ongrowth created from osteoconductive microenvironment on the device surface. The previously established hydrophilic and osteophilic properties of commercially pure titanium (CPTi) can potentially provide an ideal environment promoting cell attachment and bony ongrowth when applied at the end plate level of the fusion site. Because the surface material composition and topography is what seems to directly affect cell adhesion, it is important to determine the ideal titanium coating for the highest effectiveness.

PURPOSE

The purpose of the study is to determine whether there is an optimal surface roughness for the titanium coatings and whether different polishing methods have a greater effect than roughness or topography in mediating cell adhesion to the surface.

STUDY DESIGN/SETTING

The study was divided into two phases. In Phase 1, the effects of varying surface roughnesses on identical polishing method were compared. In Phase 2, the effect of varying polishing methods was compared on identical surface roughnesses.

METHODS

Coating thickness, porosity, and surface roughness were characterized using an optical microscope as per ASTM F 1854 standards. For both phases, PEEK coupons with plasma-sprayed CPTi were used, and human mesenchymal stem cells (hMSCs) at an initial density of 25,000 cells/cm² were seeded and cultured for 24 hours before fixation in 10% formalin. The cultured hMSCs were visualized by 4',6-diamidino-2-phenylindole (DAPI) staining, a fluorescent stain that binds to the DNA of living cells. Samples were imaged using an environmental scanning electron microscope (eSEM) (Carl Zeiss Microscopy, Thornwood, NY, USA) using a backscattered detector.

RESULTS

Image analysis of the CPTi coatings showed uniform and rough surfaces. For Phase 1, roughness was evaluated as fine, medium, and coarse. The eSEM image analysis and cell counting by DAPI demonstrated that hMSCs have a tendency to form stronger adhesion and greater pseudopodia extensions on fine roughness surfaces. Individual hMSCs were seen forming cytoplasmic processes extending across the width of a pore. There was a 4- and 20-fold reduction in adhered hMSCs with an increase to medium and coarse roughnesses, respectively. For Phase 2, studied groups are (1) medium CPTi coating with zirconia polishing, (2) medium CPTi coating with CPTi polishing, and (3) fine CPTi coating with CPTi polishing. The eSEM image analysis and cell counting by DAPI demonstrated that hMSCs have a tendency to form stronger adhesion and greater pseudopodia extensions on Group 3 over the other two groups. There was a twofold reduction in adhered hMSCs on medium roughness relative to fine. No difference in cell adhesion was found between Groups 1 and 2. Individual hMSCs were seen forming cytoplasmic processes extending across the width of a pore.

CONCLUSIONS

Previously, it was accepted without much scrutiny that surface coatings were beneficial. This study begins to discover that surface topography directly affects the potential for cells to adhere and proliferate and lead to greater surgical efficacy.

A Meta-Analysis of the Incidence of Patient-Reported Dysphagia After Anterior Cervical Decompression and Fusion with the Zero-Profile Implant System

Dysphagia is a well-known complication following anterior cervical surgery. It has been reported that the Zero-profile Implant System can decrease the incidence of dysphagia following surgery, however, dysphagia after anterior cervical decompression and fusion (ACDF) with the Zero-profile Implant System remains controversial. Previous studies only focus on small sample sizes. The objective of this study was to determine the incidence of dysphagia after ACDF with the Zero-profile Implant System. Studies were collected from PubMed, EMBASE, the Cochrane library and the China Knowledge Resource Integrated Database using the keywords "Zero-profile OR Zero-p) AND (dysphagia OR [swallowing dysfunction]". The software STATA (Version 13.0) was used for statistical analysis. Statistical heterogeneity across the various trials, a test of publication bias and sensitivity analysis was performed. 30 studies with a total of 1062 patients were included in this meta-analysis. The occurrence of post-operative transient dysphagia ranged from 0 to 76 % whilst the pooled incidence was 15.6 % (95 % CI, 12.6, 18.5 %). 23 studies reported no persistent dysphagia whilst seven studies reported persistent dysphagia ranging from 1 to 7 %). In summary, the present study observed a low incidence of both transient and persistent dysphagia after ACDF using the Zero-profile Implant System. Most of the dysphagia was mild and gradually decreased during the following months. Moderate or severe dysphagia was uncommon. Future randomized controlled multi-center studies and those focusing on the mechanisms of dysphagia and methods to reduce its incidence are required.

Vertebral body fracture after anterior cervical discectomy and fusion with zero-profile anchored cages in adjacent levels: a cautionary tale

BACKGROUND CONTEXT

Zero-profile (also called self-locking, anchored or stand-alone cages) have been recently proposed as an interesting alternative for anterior cervical discectomy and fusion (ACDF), as they are supposed to reduce the rates of post-operative cage extrusion without necessarily incurring in the additional surgical time and increased rates of dysphagia associated with plating. Nevertheless, the exact indications of zero-profile anchored cages have not yet been established in the literature.

PURPOSE

To report the first case of a vertebral body fracture between the blades of zero-profile anchored cages after ACDFs in adjacent levels and to review the available literature on hardware-related complications after multi-level ACDFs with zero-profile anchored cages.

STUDY DESIGN

Case report and systematic literature review.

METHODS

The authors report the first case of a vertebral body fracture between the blades of zero-profile anchored cages after ACDFs in adjacent levels. The patient presented with refractory mechanical neck pain at the 1-month post-operative follow-up, ultimately requiring a posterior instrumented fusion. A comprehensive systematic literature review on the available data regarding the safety, complications as well as radiological and clinical outcomes of zero-profile anchored cages is also performed.

RESULTS

In the reported case, the use of zero-profile anchored cages in adjacent levels on the cervical spine led to a fracture of the vertebral body between the cages at the 1-month follow-up, with anterior avulsion of the part of the vertebral body where the blades from the two cages converged. According to the systematic literature review which included 409 patients from 10 different clinical series (with a total cumulative follow-up of approximately 535 patients-year), there were only two reported hardware-related complications after ACDF with zero-profile anchored cages, none of them involving fracture at the level of convergence of blades or screws.

CONCLUSIONS

Although hardware-related complications after the use of zero-profile anchored cages seem to be rare events, future biomechanical and clinical studies are warranted in order to evaluate the safety of employing such devices for the treatment of multilevel degenerative disc disease in the cervical spine.

Biomechanical comparison of a novel transoral atlantoaxial anchored cage with established fixation technique - a finite element analysis

BACKGROUND

The transoral atlantoaxial reduction plate (TARP) fixation has been introduced to achieve reduction, decompression, fixation and fusion of C1-C2 through a transoral-only approach. However, it may also be associated with potential disadvantages, including dysphagia and load shielding of the bone graft. To prevent potential disadvantages related to TARP fixation, a novel transoral atlantoaxial fusion cage with integrated plate (Cage + Plate) device for stabilization of the C1-C2 segment is designed. The aims of the present study were to compare the biomechanical differences between Cage + Plate device and Cage + TARP device for the treatment of basilar invagination (BI) with irreducible atlantoaxial dislocation (IAAD).

METHODS

A detailed, nonlinear finite element model (FEM) of the intact upper cervical spine had been developed and validated. Then a FEM of an unstable BI model treated with Cage + Plate fixation, was compared to that with Cage + TARP fixation. All models were subjected to vertical load with pure moments in flexion, extension, lateral bending and axial rotation. Range of motion (ROM) of C1-C2 segment and maximum von Mises Stress of the C2 endplate and bone graft were quantified for the two devices.

RESULTS

Both devices significantly reduced ROM compared with the intact state. In comparison with the Cage + Plate model, the Cage + TARP model reduced the ROM by 82.5 %, 46.2 %, 10.0 % and 74.3 % in flexion, extension, lateral bending, and axial rotation. The Cage + Plate model showed a higher increase stresses on C2 endplate and bone graft than the Cage + TARP model in all motions.

CONCLUSIONS

Our results indicate that the novel Cage + Plate device may provide lower biomechanical stability than the Cage + TARP device in flexion, extension, and axial rotation, however, it may reduce stress shielding of the bone graft for successful fusion and minimize the risk of postoperative dysphagia. Clinical trials are now required to validate the reproducibility and advantages of our findings using this anchored cage for the treatment of BI with IAAD.