Application of a Novel Porous Tantalum Implant in Rabbit Anterior Lumbar Spine Fusion Model: In Vitro and In Vivo Experiments
Spinal fusion surgeries aim to achieve stability and decompression in degenerative, traumatic, or deformative spinal conditions. However, challenges such as pseudarthrosis (5–35% incidence) and limitations of bone graft materials persist. Autologous bone remains the gold standard but carries risks of donor-site morbidity and limited availability. Allografts and synthetic substitutes face issues like immune rejection, poor biodegradability, or inadequate mechanical properties. Porous tantalum has emerged as a promising alternative due to its biocompatibility, osteoconductivity, and mechanical similarity to bone. This study evaluates a novel porous tantalum implant synthesized via chemical vapor deposition (CVD) and 3D-knitted wire frameworks for lumbar interbody fusion in rabbits, comparing its performance to autografts and discectomy controls.
Material and Methods
Porous Tantalum Implant Fabrication
The porous tantalum implants (Ning Xia Orient Tantalum Industry Co. Ltd, China) were cubic (2.5–3.0 mm dimensions) with interconnected pores averaging 500 μm in size. The structure featured a diamond-like lattice formed by CVD-deposited tantalum on a knitted wire framework, achieving 86.8% porosity. Scanning electron microscopy (SEM) revealed rough surfaces and open-pore architecture conducive to bone ingrowth. Energy-dispersive X-ray spectroscopy confirmed pure tantalum composition without contaminants. The Young’s modulus (0.6 GPa) closely matched human bone.
In Vitro Biocompatibility Testing
Bone marrow-derived mesenchymal stem cells (BMSCs) from rabbits were cultured on porous tantalum. Cell proliferation and toxicity were assessed using Cell Counting Kit-8 (CCK-8) assays. SEM evaluated cell adhesion and morphology. Leachates from tantalum implants were tested for cytotoxicity by comparing BMSC viability to controls.
In Vivo Surgical Model
Twenty-four New Zealand rabbits underwent anterior discectomy at L3–L4, L4–L5, and L5–L6 levels. Each level was randomized into three groups:
- Control: Discectomy only.
- Autograft: Discectomy + autologous iliac crest bone.
- Tantalum: Discectomy + porous tantalum implant.
Rabbits were sacrificed at 2, 4, 6, and 12 months postoperatively (n = 6 per timepoint). Neurologic function was monitored using a standardized scoring system (0–4).
Radiographic and Histologic Evaluation
Micro-computed tomography (micro-CT) assessed fusion using the Brantigan-Steffee criteria:
- Denser bone in fusion area.
- No radiolucency at implant-bone interfaces.
- Trabecular bridging.
Fusion index scores (0–3) were assigned per Bridwell’s grading. Histologic sections stained with toluidine blue and hematoxylin-eosin evaluated bony bridging, osteonecrosis, and inflammatory responses.
Results
In Vitro Outcomes
CCK-8 assays showed no toxicity, with similar absorbance values between tantalum leachates and controls (1.25 ± 0.06 vs. 1.23 ± 0.04, P = 0.545). SEM images revealed BMSCs adhering to tantalum surfaces with spindle-like morphology, forming continuous layers and infiltrating pores (Figure 8).
Surgical Outcomes
All rabbits recovered without neurologic deficits (score = 0). One case of incision infection and one abdominal hernia resolved with treatment.
Radiographic Fusion
- Control Group: No fusion (score = 0 at all timepoints).
- Autograft Group: Scores increased from 1.11 ± 0.68 at 2 months to 2.89 ± 0.32 at 12 months (P < 0.001).
- Tantalum Group: Scores rose from 1.11 ± 0.32 at 2 months to 2.83 ± 0.38 at 12 months (P < 0.001), with no significant difference versus autograft at 12 months (P = 0.709).
Micro-CT demonstrated progressive fusion:
- 2 Months: Radiolucent zones around implants (non-union).
- 4 Months: Partial fusion with new bone formation.
- 6 Months: Trabecular bridging (partial fusion).
- 12 Months: Complete fusion with overgrown bridging bone (Figure 4D).
Histologic Analysis
At 12 months:
- Control: Fibrous tissue filled intervertebral spaces (non-union).
- Autograft: Continuous bony bridges with cartilage formation and endochondral ossification (Figure 6B).
- Tantalum: Trabecular bone infiltrated implant pores, forming direct bone-implant contact without degradation, osteolysis, or inflammation (Figure 6C, 7B).
Discussion
Biocompatibility and Osteoconductivity
The porous tantalum’s high porosity (86.8%) and interconnected pores facilitated BMSC adhesion, proliferation, and osteogenic differentiation. Rough surfaces enhanced cell anchoring, while the absence of toxic leachates confirmed biocompatibility. These findings align with prior studies showing tantalum’s ability to stimulate osteoblast activity.
Fusion Performance
Both autograft and tantalum groups achieved 100% histologic fusion at 12 months, surpassing PEEK and titanium cages, which often exhibit fibrous encapsulation. The tantalum implant’s mechanical properties (elastic modulus ≈ bone) likely reduced stress shielding, promoting physiologic load distribution and bone remodeling.
Comparative Advantages Over Existing Materials
- Autografts: Tantalum eliminated donor-site morbidity while matching fusion rates.
- Allografts/Xenografts: No immune rejection risks.
- PEEK/Titanium: Tantalum’s osteoconductivity and radiolucency (vs. titanium) improved fusion assessment.
Limitations and Future Directions
While biomechanical testing was omitted to preserve histologic samples, future studies should evaluate load-bearing capacity. Long-term human trials are needed to confirm clinical efficacy and address potential late complications.
Conclusion
This novel porous tantalum implant demonstrated excellent biocompatibility, osteoconductivity, and fusion efficacy in a rabbit lumbar model. Its performance paralleled autografts, with complete bony integration and no adverse reactions. The customizable porosity and mechanical properties position it as a promising alternative for spinal interbody fusion, potentially reducing pseudarthrosis rates and improving patient outcomes.
doi.org/10.1097/CM9.0000000000000030
Was this helpful?
0 / 0