Smoking affects the rate and quality of bone healing. Animal studies indicate a reduction in the quantity and quality of bone at osteotomy sites.106 Studies using the Ilizarov device demonstrate that a nonsmoker can make 1 cm of bone in two months, however a smoker requires three months to make 1 cm of bone, with a 90 percent failure of complete bony union at the osteotomy site.112 Fractures of the tibia that occur in smokers also require a longer mean time for clinical union with an increase in the rate of delayed union.59 Animal studies have indicated a tendency for bone resorption at fracture ends with subsequent interference in bone healing.62
Arthrodesis is also adversely affected by smoking. In a study of ankle arthrodesis, Cobb found the risk for nonunion in smokers to be 3.75 times that of nonsmoking controls. Brown found a 40 percent rate of pseudarthrosis in lumbar spinal fusion compared to an 8 percent rate in nonsmokers.18 Hanley and Levy also demonstrated a higher failure rate among smokers in a review of fusions for spondylolisthesis.39
There are many possible explanations for these findings. At the cellular level, nicotine has been found to be toxic to the osteoblast, and may also interfere with calcitonin. Hydrogen cyanide interferes with cellular metabolism and carbon monoxide interferes with oxygen transport. Oxygen levels have been measure at the fusion site, and as predicted, a significant decrease in pO2 among smokers has been demonstrated.13 As a result of these and other studies, heavy smoking is now considered to be a relative contraindication for spinal fusion.
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