The effect of spinal instrumentation particulate wear debris. an in vivo rabbit model and applied clinical study of retrieved instrumentation cases.
METHODS
The current study was undertaken to determine if the presence of spinal instrumentation wear particulate debris deleteriously influences early osseointegration of posterolateral bone graft or disrupts an established posterolateral fusion mass.


OBJECTIVE
Using an in vivo animal model, the first phase (basic science) of this study was to evaluate the effect(s) of titanium wear particulate on a posterolateral spinal arthrodesis based on serological, histological and immunocytochemical analyses. The second phase (clinical) was to perform the same analysis of soft tissue surrounding spinal instrumentation in 12 symptomatic clinical patients.


BACKGROUND
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 II, n=20). Group I underwent a posterolateral arthrodesis (PLF) at L5-L6 using tricortical iliac autograft or tricortical iliac autograft plus titanium particulate. Group 2 all received iliac autograft at the initial surgery and were reoperated on after 8 weeks and treated with PLF exposure alone or titanium particulate. Postoperative analysis included serological quantification of systemic cytokines. Postmortem microradiographic, immunocytochemical and histopathological assessment of the intertransverse fusion mass quantified the extent of osteolysis, local proinflammatory cytokines, osteoclasts and inflammatory infiltrates. Clinical aspect of study: Over the last 2 years, 12 patients more than 0.4 years after spinal instrumentation presented with painful paraspinal inflammation. At surgical exploration, the cultures were negative for infection and the surrounding soft tissue was examined for cytokine reactions. There was loosening of implants and osteolysis in the location of the wear debris in 8 of 12 patients.


RESULTS
Basic science phase: serological analysis of systemic cytokines indicated no significant differences in cytokine levels (p>.05) between the titanium or autograft treatments. Immunocytochemistry indicated increased levels of local cytokines: TNF-alpha at the titanium-treated PLF sites at both time periods (p<.05). Osteoclast cell counts and regions of osteolytic resorption lacunae were higher in the titanium-treated versus autograft-alone groups (p<.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. Clinical aspect: Eleven of 12 clinical cases demonstrated elevated TNF-alpha levels and an increased osteoclastic response in the vicinity of wear debris caused by dry frictional wear particles of titanium or stainless steel. Osteolysis most commonly involved loose transverse connectors. Resection of the wear debris and surrounding fibroinflammatory glycocalyx resulted in resolution of clinical symptoms in all 12 cases.


CONCLUSIONS
Titanium particulate debris introduced at the level of a spinal arthrodesis elicits a cytokine-mediated particulate-induced response favoring proinflammatory infiltrates, increased expression of intracellular TNF-alpha, increased osteoclastic activity and cellular apoptosis. This is the first basic scientific study and the first clinical study demonstrating associations of spinal instrumentation particulates wear debris and increased cytokines and increased osteoclastic activity. Osteolysis is the number one cause of failure of orthopedic implants in the appendicular skeleton. Spinal surgeons need to increase their awareness of this destructive process.
Cunningham
Bryan W
BW
Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Union Memorial Hospital, 201 East University Parkway, Baltimore, MD 21218, USA. bcspine@aol.com
Orbegoso
Carlos M
CM
Dmitriev
Anton E
AE
Hallab
Nadim J
NJ
Sefter
John C
JC
Asdourian
Paul
P
McAfee
Paul C
PC
D000135:Acid Phosphatase / Q000378:metabolism; D000328:Adult; D000818:Animals; D017209:Apoptosis; D016723:Bone Remodeling; D002452:Cell Count; D016207:Cytokines / Q000097:blood; D019276:Glycocalyx; D006801:Humans; D007085:Ilium / Q000637:transplantation; D018836:Inflammation Mediators / Q000097:blood; D008297:Male; D008854:Microscopy, Electron; D009192:Myelography; D009984:Orthopedic Fixation Devices / Q000009:adverse effects*; D010010:Osteoclasts / Q000201:enzymology / Q000473:pathology; D010014:Osteolysis; D010587:Phagocytosis; D011475:Prosthesis Failure; D011817:Rabbits; D012086:Reoperation; D013116:Spinal Cord / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D013193:Stainless Steel; D013997:Time Factors; D014025:Titanium; D014182:Transplantation, Autologous; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D016207:Cytokines; D018836:Inflammation Mediators; D014409:Tumor Necrosis Factor-alpha; D013193:Stainless Steel; D014025:Titanium; D000135:Acid Phosphatase