Application of a novel porous tantalum implant in rabbit anterior lumbar spine fusion model: in vitro and in vivo experiments

Abstract

Background: Some porous materials have been developed to enhance biologic fusion of the implants to bone in spine fusion surgeries. However, there are several inherent limitations. In this study, a novel biomedical porous tantalum was applied to in vitro and in vivo experiments to test its biocompatibility and osteocompatibility.

Methods: Bone marrow-derived mesenchymal stem cells (BMSCs) were cultured on porous tantalum implant. Scanning electron microscope (SEM) and Cell Counting Kit-8 assay were used to evaluate the cell toxicity and biocompatibility. Twenty-four rabbits were performed discectomy only (control group), discectomy with autologous bone implanted (autograft group), and discectomy with porous tantalum implanted (tantalum group) at 3 levels: L3-L4, L4-L5, and L5-L6 in random order. All the 24 rabbits were randomly sacrificed at the different post-operative times (2, 4, 6, and 12 months; n = 6 at each time point). Histologic examination and micro-computed tomography scans were done to evaluate the fusion process. Comparison of fusion index scores between groups was analyzed using one-way analysis of variance. Other comparisons of numerical variables between groups were made by Student t test.

Results: All rabbits survived and recovered without any symptoms of nerve injury. Radiographic fusion index scores at 12 months post-operatively between autograft and tantalum groups showed no significant difference (2.89 ± 0.32 vs. 2.83 ± 0.38, F = 244.60, P = 0.709). Cell Counting Kit-8 assay showed no significant difference of absorbance values between the leaching liquor group and control group (1.25 ± 0.06 vs. 1.23 ± 0.04, t = -0.644, P = 0.545), which indicated the BMSC proliferation without toxicity. SEM images showed that these cells had irregular shapes with long spindles adhered to the surface of tantalum implant. No implant degradation, wear debris, or osteolysis was observed. Histologic results showed solid fusion in the porous tantalum and autologous bone implanted intervertebral spaces.

Conclusion: This novel porous tantalum implant showed a good biocompatibility and osteocompatibility, which could be a valid biomaterial for interbody fusion cages.

Figure 1

The novel porous tantalum implants. (A) The outlook of cubic porous tantalum implants (length, width and height were 2.5–3.0 mm). The scanning electron microscopic images of porous tantalum in a lower magnification (B; ×85) and a higher magnification (C; ×5000).

Figure 2

The energy dispersive spectral analysis to determine the element components of the porous tantalum implant. (A) Spot (red circle) selected for the energy dispersive spectral determination. (B) Energy dispersive X-ray spectrum measured from porous tantalum. No other elements, such as chlorine as the raw material or carbon, were detected.

Figure 3

Imaging of operative lumbar spine segments of the New Zealand rabbits. (A) Post-operative lateral radiograph showing a non-radiolucent tantalum implant was implanted into the L3–L4 intervertebral space. (B) Micro-computed tomography (micro-CT) image of discectomy only space (control group) showing the appearance of the defect after discectomy in the intervertebral space. (C) Micro-CT image showing discectomy with autologous bone implanted space (autograft group). (D) Micro-CT image showing discectomy with porous tantalum implanted space (tantalum group).

Figure 4

Micro-computed tomography images of the spinal fusion performance achieved upon implantation of tantalum implants in different post-operative periods: (A) 2 months post-operatively; (B) 4 months post-operatively; (C) 6 months post-operatively; and (D) 12 months post-operatively.

Figure 5

Micro-computed tomography images of operative lumbar intervertebral spaces in the 3 different procedures at 12 months post-operatively: (A) discectomy only space (control group); (B) discectomy with autologous bone implanted space (autograft group); and (C) discectomy with porous tantalum implanted space (tantalum group). Both autograft and tantalum groups developed solid fusion with continuous bony bridge from the cranial to the caudal vertebra, while non-fusion was observed in control group. (D) The imaging fusion index scores at different post-operative time points.

Figure 6

Representative images of the stained undecalcified sections at 12 months post-operatively. (A) Control group: a clapse gap with fibrous tissue surrounding at the intervertebral space was observed (hematoxylin and eosin staining, ×50). (B) Autograft group: histologic fusion is demonstrated by continuous cranial to the caudal bony bridging with cartilage formation (triangle) and endochondral ossification (arrows) in the intervertebral space (hematoxylin and eosin staining, ×50). (C) Tantalum group: histologic fusion is demonstrated by continuous cranial to the caudal bony bridging with newly formed bone trabecular (arrows) ingrowth into the porous tantalum (hematoxylin and eosin staining, ×50).

Figure 7

Stained undecalcified sections showing new bone formation associated with osteonecrosis in (A) autograft and (B) porous tantalum interface (hematoxylin and eosin staining, ×50). Cartilage formation (triangles) and endochondral ossification (arrows) associated with necrotic bone (pentagrams) and cement lines (dovetails) representing the process of bone remodeling. No implant degradation, bone resorption or significant local inflammation response was observed in tissue adjacent to the tantalum implant.

Figure 8

Morphology of bone marrow-derived mesenchymal stem cells cultured on tantalum implant. (A) The images of scanning electron microscope showing that the cells formed a continuous layer on the surface of tantalum and grew into the pores at lower magnification (×30). (B) The cells showed irregular shapes with long spindles adhered to the surface of tantalum implant at higher magnification (×500).