The effect of titanium particulate on development and maintenance of a posterolateral spinal arthrodesis -: An in vivo rabbit model

Study Design. The current study was undertaken to determine if the presence of titanium wear particulate deleteriously influences early osseointegration of posterolateral bone graft or disrupts an established posterolateral fusion mass. Objectives. Using an in vivo animal model to evaluate the effect(s) of titanium wear particulate on a posterolateral spinal arthrodesis based on serologic, histologic, and immunocytochemical analyses. Summary of Background Data. The effect of unintended wear particulate resulting from micromotion between the interconnection mechanisms in spinal instrumentation remains a clinical concern. Methods. Thirty-four New Zealand White rabbits were randomized into two groups based on postoperative time periods of 2 months (Group 1, n=14) and 4 months (Group 2, n=20). Group 1 underwent a posterolateral arthrodesis at L5-L6 using tricortical iliac autograft or tricortical iliac autograft + titanium particulate. Group 2 received iliac autograft at the initial surgery and were reoperated on after 8 weeks and treated with posterolateral arthrodesis exposure alone or titanium particulate. Postoperative analysis included serologic quantification of system cytokines. Postmortem microradiographic, immunocytochemical, and histopathologic assessment of the intertransverse fusion mass quantified the extent of osteolysis, local pro-inflammatory cytokines, osteoclasts, and inflammatory infiltrates. Results. Serologic analysis of systemic cytokines indicated no significant differences in cytokine levels (P>0.05) between the titanium or autograft treatments. Immunocytochemistry indicated increased levels of cytokines (tumor necrosis factor-alpha) at the titanium-treated posterolateral arthrodesis sites at both time periods (P<0.05). Osteoclast cell counts and regions of osteolytic resorption lacunas were higher in the titanium-treated versus autograft alone groups (P<0.05), and the extent of cellular apoptosis was markedly higher in the titanium-treated sites at both time intervals. Electron microscopy indicated definitive evidence of phagocytized titanium particles and foci of local, chronic, inflammatory changes in the titanium-treated sites. Conclusion. Titanium particulate debris introduced at the level of a spinal arthrodesis elicits a cytokine-mediated particulate-induced response favoring pro-inflammatory infiltrates, increased expression of intracellular tumor necrosis factor-alpha, increased osteoclastic activity, and cellular apoptosis. The presence of titanium particulate debris, secondary to motion between spinal implants, may serve as the impetus for late-onset inflammatory-infectious complications and long-term osteolysis of an established posterolateral fusion mass in the clinical setting.