Safety of terminally gamma-ray-sterilized screws coated with fibroblast growth factor 2-calcium phosphate composite layers in non-human primates.

Screws coated with fibroblast growth factor 2 (FGF-2)-calcium phosphate (CP) composite layers exhibit enhanced soft tissue and bone formation and angiogenesis because of the biological activity of FGF-2. Furthermore, the mitogenic activity of the FGF-2 within the composite layers remains unchanged after gamma-ray sterilization, which may improve the storage stability prior to clinical use. However, the in vivo safeties of these screws as spinal implants remain unknown. Here, a randomized controlled trial, involving non-human primates, investigated the safety of using FGF-2-CP composite layer-coated screws after either gamma-ray sterilization or aseptic processing. Titanium alloy screws coated with FGF-2-CP composite layers and subjected to either gamma-ray sterilization at 25 kGy (GS group) or aseptic storage (AS group) were implanted into the vertebral bodies of two cynomolgus monkeys exceeding 12 weeks (day 99). Physiological, histological, and radiographic investigations were performed to evaluate the safeties of the screws. There were no serious adverse events, such as surgical site infection, significant loss of body weight, or abnormal blood test results. No radiolucent areas were observed around the screws from the GS or AS group throughout the study. In the intraosseous region, no significant differences were observed in bone and fibrous tissue apposition rates and rate of bone formation between the two groups (p = 0.49, 0.77, and 0.11, respectively). Neither tumor lesions nor accumulation of lymphocytes and neutrophils were observed in either group. Our data suggest that FGF-2-CP composite layer-coated screws subjected to terminal gamma-ray sterilization are as safe as those fabricated in aseptic processing.

Unidirectional porous ß-tricalcium phosphate induces bony fusion in lateral lumbar interbody fusion.

Lateral lumbar interbody fusion (LLIF) often requires the use of allograft or artificial bone. We used ß-tricalcium phosphate artificial bone with a porosity of 57% consisting of a novel unidirectional porous structure (Affinos®) in patients (5 male and 9 female) who underwent LLIF from August 2015 as a substitute for autologous bone. We evaluated 60 graft windows in the cages at 30 intervertebral levels. To evaluate interbody bony fusion, CT multi-planar reconstruction coronal and sagittal images obtained 1 year after surgery were assessed. Intra-cage bony fusion was observed in 39 of 60 graft windows and so total bony fusion rate was 65%. Intra-cage bony fusion was confirmed in 17 of 29 (58.6%) graft windows with autologous bone and 22 of 31 (70.9%) graft windows with Affinos®. There was no significant difference in the rate of bony fusion between autologous bone and Affinos® (p = 0.418). In conclusion, the rate of bony fusion using Affinos® in LLIF cages was not inferior to that using autologous bone graft. Affinos® is a candidate for graft material in LLIF surgery and further exploration is warranted.

Bone bonding, displacement, and absorption in cases of double-door laminoplasty with unidirectional porous hydroxyapatite spacers.

We used a newly developed, high-porosity unidirectional porous hydroxyapatite spacer (Regenos spacer, not approved by the FDA). To assess the short-term bone bonding capacity of Regenos spacer used in a double-door laminoplasty, including displacement, deformation, and absorption after implantation. Fifty patients underwent a double-door laminoplasty using Regenos spacers, with computed tomography (CT) images obtained at 2-4 weeks and 6-12 months, post-surgery, in 30 patients. Bone bonding rate, amount of displacement, and the incidence of deformation and absorption were evaluated from the early and late postoperative CT images. Bone bonding rate for Regenos spacers, using our modified classification, was 48.9% at 6 months, post- surgery, and 67.0% at 12 months. The change in anterior-posterior diameter of the spinal canal (ΔH) was significantly greater for Regenos spacers than for autologous bone spacers (p < 0.05). There was no difference in the change in angle between the vertebral arch and the posterior wall of the vertebral body (ΔR) between the Regenos and autologous bone spacers. Deformation was identified in 21.3% (10/47). Though, no evidence of breakage along their long axis was identified among these 10 cases on axial CT images with passable clinical results. Regenos spacers lowered the risk of early dislocation after implantation and facilitated bone bonding due to infiltration of surrounding tissue. However, the deformation and absorption was observed at high rates because of their insufficient mechanical strength, we need to require a longer term follow-up to more clearly evaluate their adverse impact in clinically.