The effects of dexamethasone on bone fusion in an experimental model of posterolateral lumbar spinal arthrodesis

Object. The use of corticosteroid agents during the healing phase after spi nal arthrodesis remains controversial. Although anecdotal opinion suggests that corticosteroids may inhibit bone fusion, such an effect has not been s ubstantiated in clinical trials or laboratory investigations. This study wa s undertaken to delineate the effect of exogenous corticosteroid administra tion on bone graft incorporation in an experimental model of posterolateral lumbar fusion. Methods. An established. well-validated model of lumbar intertransverse pro cess spinal fusion in the rabbit was used. Twenty-four adult New Zealand wh ite rabbits underwent L5-6 bilateral posterolateral spinal fusion in which autogenous iliac crest bone graft was used. After surgery, the animals were randomized into two treatment groups: a control group(12 rabbits) that rec eived intramuscular injections of normal saline twice daily and a dexametha sone group (12 rabbits) that received intramuscular dexamethasone (0.05 mg/ kg) twice daily. After 42 days, the animals were killed and the integrity o f the spinal fusions was assessed by radiography, manual palpation, and bio mechanical testing. In seven (58%) of the 12, control rabbits, solid posterolateral fusion was achieved. In no dexamethasone-treated rabbits was successful fusion achieve d (p = 0.003). Tensile strength and stiffness of excised spinal segments we re significantly Lower in dexamethasone-treated animals than in control ani mals (tensile strength 91.4 +/- 30.6 N and 145.3 +/- 48.2, respectively, p = 0.004; stiffness 31.4 +/- 11.6 and 45.0 +/- 15.2 N/mm, respectively, p = 0.02). Conclusions. The corticosteroid agent dexamethasone inhibited bone graft in corporation in a rabbit model of single-level posterolateral lumbar spinal fusion, inducing a significantly higher rate of nonunion, compared with tha t in saline-treated control animals.