Metallosis Disrupts Bone Healing in Posterolateral Spinal Fusion: in Vivo Modeling of Metal Particle Effects on Fusion Integrity.

Background: Metallosis is a known complication of joint arthroplasty, but its role in failures of spinal fusion procedures likely remains underrecognized. The release of metallic debris from implant interfaces may impair osteogenesis by triggering local inflammatory responses. To date, no in vivo models have been developed to investigate this process in the context of spinal fusion. Using a unique modelling system, we sought to determine whether high local concentrations of metal particles impair spinal fusion, and whether particle load correlates with inflammatory response.

Methods: Twelve rabbits underwent posterolateral lumbar spinal fusion using autologous iliac crest bone grafts. Six weeks postoperatively, animals received bilateral paraspinal injections of Ti/Cr/ Co alloy at high, low, or zero concentrations immediately dorsal to the graft site. At twelve weeks, specimens were euthanized, and the grafts were assessed by radiography, manual palpation, and histopathology. A custom image analysis algorithm was used to quantify metal debris in histologic sections, and inflammatory responses were evaluated. Fusion outcomes and metal burden were compared between groups using unpaired t-tests.

Results: Five of eight evaluable specimens exhibited non-fusion, most of which contained higher levels of visible metal debris than fused counterparts upon histologic analysis. Fused grafts, in contrast, demonstrated minimal particle burden and continuous trabecular bridging. Lymphocytes were found to be localized near metal particles, and fibrotic tissue was observed to replace bone at non-fused sites. No significant differences in inflammatory cell counts were observed between groups.

Conclusion: Elevated metal particle burden in the posterolateral fusion environment was associated with impaired osteogenesis and increased localized inflammation, particularly in non-fused specimens. These results establish this model's utility for investigating metallosis-driven spinal fusion failure and suggest its potential as a predictive platform for assessing particle-related risk in spinal instrumentation.

Clinical relevance: This study provides a reproducible in vivo model to explore how metallic debris may contribute to spinal fusion failure. It offers a platform for testing future interventions targeting metallosis-related complications in spinal fusion surgery.