Radiopaque UHMWPE sublaminar cables for spinal deformity correction: Preclinical mechanical and radiopacifier leaching assessment

Radiopacity Enhancements in Polymeric Implant Biomaterials: A Comprehensive Literature Review

Polymers as biomaterials possess favorable properties, which include corrosion resistance, light weight, biocompatibility, ease of processing, low cost, and an ability to be easily tailored to meet specific applications. However, their inherent low X-ray attenuation, resulting from the low atomic numbers of their constituent elements, i.e., hydrogen (1), carbon (6), nitrogen (7), and oxygen (8), makes them difficult to visualize radiographically. Imparting radiopacity to radiolucent polymeric implants is necessary to enable noninvasive evaluation of implantable medical devices using conventional imaging methods. Numerous studies have undertaken this by blending various polymers with contrast agents consisting of heavy elements. The selection of an appropriate contrast agent is important, primarily to ensure that it does not cause detrimental effects to the relevant mechanical and physical properties of the polymer depending upon the intended application. Furthermore, its biocompatibility with adjacent tissues and its excretion from the body require thorough evaluation. We aimed to summarize the current knowledge on contrast agents incorporated into synthetic polymers in the context of implantable medical devices. While a single review was found that discussed radiopacity in polymeric biomaterials, the publication is outdated and does not address contemporary polymers employed in implant applications. Our review provides an up-to-date overview of contrast agents incorporated into synthetic medical polymers, encompassing both temporary and permanent implants. We expect that our results will significantly inform and guide the strategic selection of contrast agents, considering the specific requirements of implantable polymeric medical devices.

Biomechanical evaluation of different semi-rigid junctional fixation techniques using finite element analysis

BACKGROUND

Proximal junctional failure is a common complication attributed to the rigidity of long pedicle screw fixation constructs used for surgical correction of adult spinal deformity. Semi-rigid junctional fixation achieves a gradual transition in range of motion at the ends of spinal instrumentation, which could lead to reduced junctional stresses, and ultimately reduce the incidence of proximal junctional failure. This study investigates the biomechanical effect of different semi-rigid junctional fixation techniques in a T8-L3 finite element spine segment model.

METHODS

First, degeneration of the intervertebral disc was successfully implemented by altering the height. Second, transverse process hooks, one- and two-level clamped tapes, and one- and two-level knotted tapes instrumented proximally to three-level pedicle screw fixation were validated against ex vivo range of motion data of a previous study. Finally, the posterior ligament complex forces and nucleus pulposus stresses were quantified.

FINDINGS

Simulated range of motions demonstrated the fidelity of the general model and modelling of semi-rigid junctional fixation techniques. All semi-rigid junctional fixation techniques reduced the posterior ligament complex forces at the junctional zone compared to pedicle screw fixation. Transverse process hooks and knotted tapes reduced nucleus pulposus stresses, whereas clamped tapes increased nucleus pulposus stresses at the junctional zone.

INTERPRETATION

The relationship between the range of motion transition and the reductions in posterior ligament complex and nucleus pulposus stresses was complex and dependent on the fixation techniques. Clinical trials are required to compare the effectiveness of semi-rigid junctional fixation techniques in terms of reducing proximal junctional failure incidence rates.

Biological Characteristics of Polyurethane-Based Bone-Replacement Materials

A study is presented on four polymers of the polyurethane family, obtained using a two-stage process. The first composition is the basic polymer; the others differ from it by the presence of a variety of fillers, introduced to provide radiopacity. The fillers used were 15% bismuth oxide (Composition 2), 15% tantalum pentoxide (Composition 3), or 15% zirconium oxide (Composition 4). Using a test culture of human fibroblasts enabled the level of cytotoxicity of the compositions to be determined by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay, along with variations in the characteristics of the cells resulting from their culture directly on the specimens. The condition of cells on the surfaces of the specimens was assessed using fluorescence microscopy. It was shown that introducing 15% bismuth, tantalum, or zinc compounds as fillers produced a range of effects on the biological characteristics of the compositions. With the different fillers, the levels of toxicity differed and the cells' proliferative activity or adhesion was affected. However, in general, all the studied compositions may be considered cytocompatible in respect of their biological characteristics and are promising for further development as bases for bone-substituting materials. The results obtained also open up prospects for further investigations of polyurethane compounds.

Biomechanical Evaluation of Semi-rigid Junctional Fixation Using a Novel Cable Anchor System to Prevent Proximal Junctional Failure in Adult Spinal Deformity Surgery

STUDY DESIGN

A porcine cadaveric biomechanical study.

OBJECTIVE

To biomechanically evaluate a novel Cable Anchor System as semi-rigid junctional fixation technique for the prevention of proximal junctional failure after adult spinal deformity surgery and to make a comparison to alternative promising prophylactic techniques.

SUMMARY OF BACKGROUND DATA

The abrupt change of stiffness at the proximal end of a pedicle screw construct is a major risk factor for the development of proximal junctional failure after adult spinal deformity surgery. A number of techniques that aim to provide a gradual transition zone in range of motion (ROM) at the proximal junction have previously been studied. In this study, the design of a novel Cable Anchor System, which comprises a polyethylene cable for rod fixation, is assessed.

METHODS

Ten T6-T13 porcine spine segments were subjected to cyclic 4 Nm pure-moment loading. The following conditions were tested: uninstrumented, 3 level pedicle screw fixation (PSF), and PSF with supplementary Cable Anchors applied proximally at 1-level (Anchor1) or 2-levels (Anchor2), transverse process hooks (TPH), and 2-level sublaminar tapes (Tape2). The normalized segmental range of motion in the junctional zone was compared using one-way analysis of variance and linear regression.

RESULTS

Statistical comparison at the level proximal to PSF showed significantly lower ROMs for all techniques compared to PSF fixation alone in all movement directions. Linear regression demonstrated a higher linearity for Anchor1 (0.820) and Anchor2 (0.923) in the junctional zone in comparison to PSF (1-level: 0.529 and 2-level: 0.421). This linearity was similar to the compared techniques (TPH and Tape2).

CONCLUSION

The Cable Anchor System presented in this study demonstrated a gradual ROM transition zone at the proximal end of a rigid pedicle screw construct similar to TPH and 2-level sublaminar tape semi-rigid junctional fixation constructs, while providing the benefit of preserving the posterior ligament complex.Level of Evidence: 5.

Banding with lesser trochanter fragment using nonabsorbable tape in trochanteric femoral fractures

Introduction: Trochanteric femoral fracture is one of the most common fractures in the elderly. Trochanteric femoral fracture with involvement of the lesser trochanter is considered unstable and recognized as having a poor prognosis. However, fixation of lesser trochanter fragment is scarce because of technical difficulties. In this study, we reported the simple surgical procedure and the effect of using nonabsorbable tape in lesser trochanter fixation. Methods: From January 2014 to December 2017, 114 patients treated with proximal intramedullary nailing for trochanteric fractures with the lesser trochanter fragment were reviewed. Among patients enrolled in this study, 73 were followed up until radiographic bone union, of which 26 were treated with lesser trochanter fragment banding (group B) and 47 without banding (group N). Radiographs and/or computed tomography images were used to evaluate bone union of the lesser trochanter fragment at three months postoperatively. Results: The bone union of the lesser trochanter fragment was achieved in 24 cases (92%) in group B and 30 cases (64%) in group N. Compared with group N, group B showed a significantly increased number of mild and moderate deformities but decreased number of severe deformity and nonunion (P < 0.001). Postoperative complications were not observed in both groups. Conclusions: From the viewpoint of increasing lesser trochanteric bone union ratio, fixation of the lesser trochanter fragment using nonabsorbable tape in the treatment of trochanteric fractures could be an effective procedure.

A Novel Technique for Spondylolysis Repair With Pedicle Screws, Rod and Polyester Band: Case Report With Technical Note and Systematic Literature Review

STUDY DESIGN

Systematic review and case report.

OBJECTIVE

Our study aims to present a new technique using three components to repair the pars defect: pedicle screws, rod and polyester band. Furthermore, we perform a systematic literature review of the previously described techniques.

SUMMARY OF BACKGROUND

Spondylolysis is a common condition in children and adolescents. Depending on the severity it may be treated either nonoperatively or surgically. Surgery is required if nonoperative treatment failed to give sustained pain relief. Several surgical techniques have been described.

METHODS

The literature review investigates the database (MEDLINE-EMBASE-Cochrane-ScienceDirect) up to May 2019 for studies presenting a surgical technique for spondylolysis.The Screw-Rod-Band (SRB) technique combines the use of pedicle screws, a rod and a polyester band to repair the spondylolysis. The horizontal rod connects the pedicle screws. The polyester band linked to the rod passes below the spinous process to apply compressive forces on the pars.

RESULTS

Twenty-one out of 982 studies described a surgical procedure. Eight main different techniques were identified: Isthmic Screw, Wiring, Butterfly-Plate, Hook-Screw Construct, Shaped-Rod, Laminar-Screw, and two combination technique (Lag Screw and Tension Band Fixation and Cortical Screws and Spinous-Process ModularLink). Our technique showed immediate postoperative clinical improvement. No surgical or perisurgical complication occurred.

CONCLUSION

The systematic literature review revealed a great number of surgical techniques for the spondylolysis, demonstrating the lack of consensus.SRB technique is an effective and simple treatment for pars fixation. The surgical procedure puts the pars under strong compression. The results are comparable with procedures present in the literature and seems capable to reduce the invasiveness and the risk of neurological injury.

LEVEL OF EVIDENCE

2.

Ultra-high-molecular-weight polyethylene sublaminar tape as semirigid fixation or pedicle screw augmentation to prevent failure in long-segment spine surgery: an ex vivo biomechanical study

OBJECTIVE

Complications after adult spinal deformity surgery are common, with implant-related complications occurring in up to 27.8% of cases. Sublaminar wire fixation strength is less affected by decreasing trabecular bone density in comparison to pedicle screw (PS) fixation due to the predominant cortical bone composition of the lamina. Sublaminar fixation may thus aid in decreasing implant-related complications. The goal of this study was to compare fixation characteristics of titanium sublaminar cables (SCs), ultra-high-molecular-weight polyethylene (UHMWPE) tape, PSs, and PSs augmented with UHMWPE tape in an ex vivo flexion-bending setup.

METHODS

Thirty-six human cadaver vertebrae were stratified into 4 different fixation groups: UHMWPE sublaminar tape (ST), PS, metal SC, and PS augmented with ST (PS + ST). Individual vertebrae were embedded in resin, and a flexion-bending moment was applied that closely resembles the in vivo loading pattern at transitional levels of spinal instrumentation.

RESULTS

The failure strength of PS + ST (4522 ± 2314 N) was significantly higher compared to the SC (2931 ± 751 N) and PS (2678 ± 827 N) groups, which had p values of 0.028 and 0.015, respectively (all values expressed as the mean ± SD). Construct stiffness was significantly higher for the PS groups compared to the stand-alone sublaminar wiring groups (p = 0.020). In contrast to SC, ST did not show any case of cortical breach.

CONCLUSIONS

The higher failure strength of PS + ST compared to PS indicates that PS augmentation with ST may be an effective measure to reduce the incidence of screw pullout, even in osteoporotic vertebrae. Moreover, the lower stiffness of sublaminar fixation techniques and the absence of damage to the cortices in the ST group suggest that ST as a stand-alone fixation technique in adult spinal deformity surgery may also be clinically feasible and offer clinical benefits.