Effect of Titanium Particulate on Development and Maintenance of a Posterolateral Spinal Arthrodesis

†Orthopaedic Biomechanics Laboratory, Union Memorial Hospital and ‡Scoliosis and Spine Center, Baltimore, Maryland, USA; *Institute of Human Virology, University of Maryland Biotechnology Institute, Baltimore, Maryland, USA; ** Orthopaedic Research Laboratory, Rush University, Chicago, Illinois, USA

PURPOSE: The effect of unintended wear particulate, resulting from motion at implant interconnections, on local spinal and systemic tissues remains a clinical concern. 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, based on serological, histological and immunocytochemical analyses using an in-vivo model.

METHODS: Thirty-four New Zealand White rabbits were randomized into two groups based on post-operative time periods of three-weeks (Group I: n=14) and four months (Group II: n=20). Each animal in Group I underwent a posterolateral arthrodesis (PLF) at L5-L6 using the following techniques: (1) tricortical iliac autograft [2g] (n=7) or 2) tricortical iliac autograft [2g] + 200mg titanium particulate (n=7). Group II animals all received iliac autograft at the initial surgery and were re-operated on after eight-weeks and treated with the following (1) PLF exposure alone (n=10) or 2) 200mg titanium particulate at PLF site (n=10) to determine the effects of titanium on an established fusion mass. The titanium particles (<5MM in diameter) were shown to be free of endotoxin by limulus assay prior implantation. Post-operative analysis included serological quantification systemic cytokines (IL-1, IL-2, IL-6, TNF-a and PGE2) at weekly intervals. Post-mortem immunocytochemical histopathological assessment the intertransverse fusion mass quantified level local pro-inflammatory cytokines, osteoclasts inflammatory infiltrates.

RESULTS: Serological analysis of the systemic cytokines in Group I treatment indicated no significant differences in cytokine levels (p>0.05) between the titanium or autograft treatments. Immunocytochemistry indicated increased levels of local cytokines - TNF-a at the titanium treated PLF sites. Based on serial histologic PLF sections prepared using trichrome stain, osteoclasts cell counts and regions of osteolytic resorption lacunae were higher in the titanium treated versus autograft alone groups (p<0 .05). Tartrate-resistance acid phosphatase staining (TRAP) indicated definitive evidence of multi-nucleated giant cells containing phagocytized titanium particles and foci local inflammatory changes in treated sites.

CONCLUSIONS: Titanium particulate debris introduced at the level of a spinal arthrodesis appears to elicit a cytokine-mediated particulate-induced response favoring increased osteoclastic activity and pro-inflammatory infiltrates. The presence of titanium particulate debris, secondary to motion between spinal implants, may serve as the impetus for late-onset inflammatory / infectious complications and osteolysis of an established posterolateral fusion mass in the clinical setting.