Does titanium cage subsidence affect clinical outcomes in ACDF surgery? A tertiary centre experience

BACKGROUND

Cage subsidence after anterior cervical discectomy and fusion (ACDF) surgery has been well documented with rates of up to 40%. Cages fill the void after cervical discectomy and promote fusion. These materials have different biomechanical profiles with differing rates of subsidence. This retrospective cohort study aimed to determine subsidence rates specifically associated with the novel Emerging Implant Technologies (EIT) titanium cage, identify risk factors associated with subsidence, and evaluate whether subsidence affects clinical outcomes.

METHODS

ACDF with insertion of stand-alone EIT cage was performed in 39 patients (64 levels) between December 2016 and February 2019 with a median follow-up of 11 months. Patients were classified into two groups; subsidence and non-subsidence, and were compared in terms of the resultant clinical outcomes as well as presence of risk factors. Health-related quality of life (HRQOL) outcomes were assessed using Visual Analogue Scale (VAS) for neck and arm pain, EuroQol 5-Dimension 5-Level (EQ-5D-5L), EuroQol Visual Analogue Scale (EQ VAS) and Neck Disability Index (NDI) scores.

RESULTS

Cage subsidence (>3mm) was present in nine patients (23%), which corresponded to ten levels treated (16%). Development of subsidence was not associated with gender (p = 0.12), age (p = 0.27), smoking (p = 0.13), number of treatment levels (p = 0.10) or cage size used (p = 0.34). It had no effect on any of the HRQOL outcomes, namely VAS Neck (p = 0.07), VAS Arms (p = 0.08), EQ-5D-5L (p = 0.36), EQ VAS (p = 0.85) and NDI (p = 0.80).

CONCLUSIONS

The EIT cage seems to be associated with lower rates of subsidence compared with other cage types. Cage subsidence was not associated with HRQOL outcomes or risk factors.

Quasi-static loading of glass fiber-reinforced composite cervical fusion cage

OBJECTIVES

Anterior decompression and fusion in cervical spine has become one of the most common procedures in neurosurgery. In the surgery, cervical cage implants made of different biomaterials are used. Our purpose was to create a cervical cage made of glass fiber-reinforced composite (FRC) filled with bioactive glass particles and to characterize its behavior in quasi-static compression/shear stress loading conditions.

MATERIALS AND METHODS

FRC cages (n = 6) were manufactured with 2, 4, 6, 8 and 10 layers of glass fiber laminates and thermoset dimethacrylate resin matrix resulting in wall thickness from 0.70 to 2.1 mm. Control cage was a commercial PEEK cage (CeSpaceXP) implant with asymmetrical wall thickness of up 4.0 mm. Interior of the cage was filled with glass particles of the size 500-1250 μm simulating the bioactive glass which are used in FRC cranial implants. The FRC cages were quasi-statically loaded (compressive/shear stress) at a constant speed of 1 mm/min in the air.

RESULTS

The average yield strength force (YF) of the control PEEK cage was 3483.6 N (±134.3 N). The average YFs for tested FRC cage with 2, 4, 6, 8 and 10 layers of FRC fabric varied from 1336.5 N (±403.8 N) to 7675.0 N (±670.0 N), respectively. The average ultimate forces (UF) for tested FRC cages varied from 1535.8 N (±406.2 N) to 9975.0 N (±1492.4 N). With six layers of FRC fabric, YF of the FRC cage was comparable to the PEEK implants.

CONCLUSIONS

In this study, it was demonstrated that it is possible to manufacture a cervical interbody fusion device made of FRC and filled with bioactive glass with proper load bearing capacities. Because of physical properties of FRC-bioactive glass, the FRC cage might have some advances compared to the state-of-the-art cages, like faster bony union and smaller rate of subsidence, which will be studied in the future.

A comparison of experimental compressive axial loading testing with a numerical simulation of topologically optimized cervical implants made by selective laser melting

In recent years, the number of cervical interventions has increased. The stress shielding effect is a serious complication in cervical spine interventions. Topological optimization is based on finite element method structural analysis and numerical simulations. The generated design of cervical implants is made from Ti6Al4V powder by selective laser melting while the optimized cage is numerically tested for compressive axial loading and the results are compared with experimental measurement. Additive manufacturing technologies and new software possibilities in the field of structural analysis, which use the finite element method tools, help to execute implant topological optimization that is useful for clinical practice. The inner structures of the implant would be impossible to make by conventional manufacturing technologies. The resulting implant design, after modification, must fulfill strict application criteria for the area of cervical spine with respect to its material and biomechanical properties. The aim of this work was to alter the mechanical properties of the cervical intervertebral cage to address the clinical concern of the stress shielding effect by topological optimization. A methodology of cervical implant compressive axial loading numerical simulation was created, and subsequent experimental testing was done to obtain real material properties after a selective laser melting process. The weight of the optimized implant was reduced by 28.92 %. Results of the experimental testing and numerical simulation of topologically optimized design showed 10-times lower stiffness compared to the solid cage design, and the real yield strength of the optimized structure is 843.8 MPa based on experimental results.

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.

Application of biodegradable 3D-printed cage for cervical diseases via anterior cervical discectomy and fusion (ACDF): an in vitro biomechanical study

OBJECTIVES

To design and fabricate a 3D-printed cervical cage composite of polylactic acid (PLA)/nano-sized and β-tricalcium phosphate (β-TCP).

RESULTS

CAD analysis provided a useful platform to design the preliminary cage. In vitro cell culture and in vivo animal results showed promising results in the biocompatibility of the constructs. Endplate matching evaluation showed better matching degree of 3D-printed cages than those of conventional cages. Biomechanical evaluation showed better mechanical properties of 3D-printed cages than those of conventional cages.

CONCLUSION

The novel 3D printed PLA/pβ-TCP cage showed good application potential, indicating a novel, feasible, and inexpensive method to manufacture cervical fusion cages.

Perioperative complications in patients treated with posterior cervical fusion and bilateral cages

Context:

Posterior cervical cages have recently become available as an alternative to lateral mass fixation in patients undergoing cervical spine surgery.

Aims:

The purpose of this study was to quantify the perioperative complications associated with cervical decompression and fusion in patients treated with a posterior cervical fusion (PCF) and bilateral cages.

Settings and Design:

A retrospective, multicenter review of prospectively collected data was performed at 11 US centers.

Subjects and Methods:

The charts of 89 consecutive patients with cervical radiculopathy treated surgically at one level with PCF and cages were reviewed. Three cohorts of patients were included standalone primary PCF with cages, circumferential surgery, and patients with postanterior cervical discectomy and fusion pseudarthrosis. Follow-up evaluation included clinical status and pain scale (visual analog scale).

Statistical Analysis Used:

The Wilcoxon test was used to test the differences for the data. The P level of 0.05 was considered significant.

Results:

The mean follow-up interval was 7 months (range: 62 weeks - 2 years). The overall postsurgery complication rate was 4.3%. There were two patients with neurological complications (C5 palsy, spinal cord irritation). Two patients had postoperative complications after discharge including one with atrial fibrillation and one with a parietal stroke. After accounting for relatedness to the PCF, the overall complication rate was 3.4%. The average (median) hospital stay for all three groups was 29 h.

Conclusions:

The results of our study show that PCF with cages can be considered a safe alternative for patients undergoing cervical spine surgery. The procedure has a favorable overall complication profile, short length of stay, and negligible blood loss.