Impacts of chemically different surfaces of implants on a biological activity of fibroblast growth factor-2-apatite composite layers formed on the implants.

BACKGROUND: Implants coated with fibroblast growth factor-2 (FGF-2)-apatite composite layers were previously reported to enhance soft-tissue formation, bone formation, and angiogenesis around the implants owing to the biological activity of FGF-2. However, it is unclear whether the chemistries of the material and surface of implants have some impact on the retention of the biological activity of FGF-2 in FGF-2-apatite composite layers on them. Since magnitude of the impact should be evaluated for extensive application of the composite layer to coat various implants, following items were examined; (1) surface chemistries of six implants, (2) mitogenic activities of FGF-2 in FGF-2-apatite composite layers on the implants, and (3) improved synthesis method of the composite layer for retention of the mitogenic activity of FGF-2. HYPOTHESIS: The biological activity of FGF-2 in the composite layer is affected by the chemistries of the material and surface of implants. MATERIALS AND METHODS: Six commercial products of pins and screws having different surface chemistries were coated with FGF-2-apatite composite layers. The composite layers were quantitatively analyzed for calcium (Ca), phosphorus (P) and FGF-2, and also evaluated the mitogenic activities of FGF-2. Improvement of the synthesis method was then attempted using two pin products. RESULTS: Each commercial product had a chemically and morphologically characteristic surface. FGF-2-apatite composite layers were formed on all the commercial products. Although the Ca, P, and FGF-2 contents (4.7±0.9µg/mm, 2.2±0.4µg/mm, and 21.1±3.7ng/mm, respectively) and the Ca/P molar ratios (1.69±0.01) of the composite layers were almost the same, rate of retention of the mitogenic activity of FGF-2 in the composite layers significantly decreased on some pin products (3/12-4/12). The decrease in rate of retention of the mitogenic activity of FGF-2 was prevented by a two-step synthesis method to form a composite layer on a precoating with calcium phosphate (9/12-12/12). DISCUSSION: The chemistries of the implant surfaces had a significant impact on the retention of the mitogenic activity of FGF-2 in the composite layers formed on the implant. The two-step synthesis method was useful to retain mitogenic activity of FGF-2 regardless of the surface chemistries of the implants. The two-step synthesis method has potential to expand the applicability of FGF-2-apatite composite layers to a wider range of implants. LEVEL OF EVIDENCE: III, Case control in vitro study.

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.