Novel 3D printable PEEK-HA-Mg2SiO4 composite material for spine implants: biocompatibility and imaging compatibility assessments.

PURPOSE: To develop a novel 3D printable polyether ether ketone (PEEK)-hydroxyapatite (HA)-magnesium orthosilicate (Mg2SiO4) composite material with enhanced properties for potential use in tumour, osteoporosis and other spinal conditions. We aim to evaluate biocompatibility and imaging compatibility of the material. METHODS: Materials were prepared in three different compositions, namely composite A: 75 weight % PEEK, 20 weight % HA, 5 weight % Mg2SiO4; composite B: 70 weight% PEEK, 25 weight % HA, 5 weight % Mg2SiO4; and composite C: 65 weight % PEEK, 30 weight % HA, 5 weight % Mg2SiO4. The materials were processed to obtain 3D printable filament. Biomechanical properties were analysed as per ASTM standards and biocompatibility of the novel material was evaluated using indirect and direct cell cytotoxicity tests. Cell viability of the novel material was compared to PEEK and PEEK-HA materials. The novel material was used to 3D print a standard spine cage. Furthermore, the CT and MR imaging compatibility of the novel material cage vs PEEK and PEEK-HA cages were evaluated using a phantom setup. RESULTS: Composite A resulted in optimal material processing to obtain a 3D printable filament, while composite B and C resulted in non-optimal processing. Composite A enhanced cell viability up to ~ 20% compared to PEEK and PEEK-HA materials. Composite A cage generated minimal/no artefacts on CT and MR imaging and the images were comparable to that of PEEK and PEEK-HA cages. CONCLUSION: Composite A demonstrated superior bioactivity vs PEEK and PEEK-HA materials and comparable imaging compatibility vs PEEK and PEEK-HA. Therefore, our material displays an excellent potential to manufacture spine implants with enhanced mechanical and bioactive property.

Design and 3D printing of novel titanium spine rods with lower flexural modulus and stiffness profile with optimised imaging compatibility.

PURPOSE: To manufacture and test 3D printed novel design titanium spine rods with lower flexural modulus and stiffness compared to standard solid titanium rods for use in metastatic spine tumour surgery (MSTS) and osteoporosis. METHODS: Novel design titanium spine rods were designed and 3D printed. Three-point bending test was performed to assess mechanical performance of rods, while a French bender was used to assess intraoperative rod contourability. Furthermore, 3D printed spine rods were tested for CT & MR imaging compatibility using phantom setup. RESULTS: Different spine rod designs generated includes shell, voronoi, gyroid, diamond, weaire-phelan, kelvin, and star. Tests showed 3D printed rods had lower flexural modulus with reduction ranging from 2 to 25% versus standard rod. Shell rods exhibited highest reduction in flexural modulus of 25% (~ 77.4 GPa) and star rod exhibited lowest reduction in flexural modulus of 2% (100.8GPa). 3D printed rod showed reduction in stiffness ranging from 40 to 59%. Shell rod displayed highest reduction in stiffness of 59% (179.9 N/mm) and gyroid had least reduction in stiffness of 40% (~ 259.2 N/mm). Rod bending test showed that except gyroid, other rod designs demonstrated lesser bending difficulty versus standard rod. All 3D printed rods demonstrated improved CT/MR imaging compatibility with reduced artefacts versus standard rod. CONCLUSION: By utilising novel design approach, we successfully generated a spine rod design portfolio with lower flexural modulus/stiffness profile and better CT/MR imaging compatibility for potential use in MSTS/other conditions such as osteoporosis. Thus, exploration of new rod designs in surgical application could enhance treatment outcome and improve quality of life for patients.

Evolution of materials for implants in metastatic spine disease till date - Have we found an ideal material?

"Metastatic Spine Disease" (MSD) often requires surgical intervention and instrumentation with spinal implants. Ti6Al4V is widely used in metastatic spine tumor surgery (MSTS) and is the current implant material of choice due to improved biocompatibility, mechanical properties, and compatibility with imaging modalities compared to stainless steel. However, it is still not the ideal implant material due to the following issues. Ti6Al4V implants cause stress-shielding as their Young's modulus (110 gigapascal [GPa]) is higher than cortical bone (17-21 GPa). Ti6Al4V also generates artifacts on CT and MRI, which interfere with the process of postoperative radiotherapy (RT), including treatment planning and delivery. Similarly, charged particle therapy is hindered in the presence of Ti6Al4V. In addition, artifacts on CT and MRI may result in delayed recognition of tumor recurrence and postoperative complications. In comparison, polyether-ether-ketone (PEEK) is a promising alternative. PEEK has a low Young's modulus (3.6 GPa), which results in optimal load-sharing and produces minimal artifacts on imaging with less hinderance on postoperative RT. However, PEEK is bioinert and unable to provide sufficient stability in the immediate postoperative period. This issue may possibly be mitigated by combining PEEK with other materials to form composites or through surface modification, although further research is required in these areas. With the increasing incidence of MSD, it is an opportune time for the development of spinal implants that possess all the ideal material properties for use in MSTS. Our review will explore whether there is a current ideal implant material, available alternatives and whether these require further investigation.

Is there a place for surgical repair in adults with spondylolysis or grade-I spondylolisthesis-a systematic review and treatment algorithm.

OBJECTIVES: Pars repair is less explored in adults due to associated disc degeneration with advancing age. The aim of our systematic review was to define optimal characteristics of adults with spondylolysis/grade-I spondylolisthesis suitable for pars repair and evaluate the feasibility, effectiveness, and safety of standard repair techniques in these adults. METHODS: This systematic review is reported in line with PRISMA-P and protocol is registered with PROSPERO (CRD42020189208). Electronic searches were conducted in PubMed, Embase, Scopus, and Web of Science in June 2020 using systematic search strategy. Studies involving adults aged ≥18-years with spondylolysis/grade-1 isthmic spondylolisthesis treated with standard pars repair techniques were considered eligible. A two-staged (titles/abstracts and full-text) screening was conducted independently by three authors followed by quality assessment using the Joanna Briggs Institute critical appraisal checklist for selection of final articles for narrative synthesis. RESULTS: A total of 5,813-articles were retrieved using systematic search strategy. First screening followed by removal of duplicates resulted in 111-articles. Second (full-text) screening resulted in exclusion of 64-articles. A final 47-articles were considered for data extraction after quality assessment. A total of 590-adults were enrolled across 47-studies; 93% were 'young adults' (18-35 years); 82% were males. Persistent low back pain was the common presenting complaint. Lysis defect was primarily bilateral (96.4%) and L5 was the most involved level (68.5%). Majority had no disc degeneration (83.5%) and had spondylolysis as the primary diagnosis (86%); only 14% had grade-I spondylolisthesis. Pars infiltration test was conducted in 22-studies and discography in 8-studies. Duration of prior conservative therapy was 3 to 72-months. Buck's repair was the commonest technique (27-studies, 372-adults). Successful repair was reported in 86% of patients treated with Buck's and ≥90% treated with Scott's, Morscher's and pedicle-screw-based techniques. Improvement in pain/functional outcomes, union rate and rate-of-return to sports/activity was high and comparable across all techniques. Intraoperative blood loss was low with minimally invasive versus traditional repair. The overall complication rate was 11.9%, with implant failure being the major complication. CONCLUSIONS: Our systematic review establishes a definite place for lysis repair in carefully selected adults with spondylolysis/grade-I spondylolisthesis. We propose a treatment algorithm for optimizing patient selection and outcomes. We conclude that adults with age 18 to 45 years, no/mild disc or facet degenerative changes, positive diagnostic infiltration test, and normal preoperative discography will have successful outcomes with pars repair, regardless of the technique.