Journal
JOURNAL OF BONE AND JOINT SURGERY-AMERICAN VOLUME
Volume 97A, Issue 12, Pages 1003-1010Publisher
LIPPINCOTT WILLIAMS & WILKINS
DOI: 10.2106/JBJS.N.01311
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Funding
- Orthopaedic Research and Education Foundation
- AO Spine Foundation
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Background: Cigarette smoking inhibits bone-healing and leads to increased rates of pseudarthrosis. However, the mechanisms behind these effects are controversial. Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin)-a cigarette smoke constituent and potent activator of the aryl hydrocarbon receptor (Ahr)-negatively impacts bone quality and osteoblast differentiation. We hypothesized that activation of the Ahr by dioxin would inhibit bone morphogenetic protein (BMP)-2-mediated spinal fusion in a rat arthrodesis model. Methods: Female Long-Evans rats were pretreated with dioxin or vehicle in six weekly doses, followed by bilateral posterior lumbar spinal fusion across the L4-L5 transverse processes using recombinant human BMP (rhBMP)-2. Treatments continued until sacrifice at four weeks postoperatively. A third group was treated with dioxin for six weeks, followed by a recovery period of four elimination half-lives to assess the reversible effects of dioxin exposure on spinal fusion capacity. Bone formation and fusion capacity were evaluated using fusion scoring, radiography, micro-computed tomography, and histologic analysis. Results: Fusion scores for dioxin-treated and dioxin-recovery rats were significantly lower than those for controls. Although fusion rates were also significantly reduced in dioxin-treated animals relative to controls (50% versus 100%, respectively), rates were not significantly reduced in dioxin-recovery animals (80%). Conclusions: Dioxin treatment significantly inhibited spinal fusion in a rat arthrodesis model, and a prolonged cessation of dioxin exposure facilitated only a partial recovery of bone-healing capacity. This finding indicates that, although the effects of dioxin are persistent, an extended recovery from exposure could potentially restore bone regeneration in vivo.
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