Study DesignA rabbit model for lumbar intertransverse process spine arthrodesis was utilized, with blind evaluation of the control and experimental animals.ObjectivesTo establish an animal model for motion-induced nonunion of lumbar intertransverse process spine arthrodesis and to determine if there was an early time period during which excessive motion at the arthrodesis site was deleterious to fusion.Summary of Background DataMost previously reported animal models for nonunion of lumbar spine arthrodesis do not use intertransverse process fusion and do not allow variable control of the nonunion-inducing factor.MethodsForty-two adult New Zealand white rabbits underwent posterolateral intertransverse process spine arthrodesis with autogenous iliac crest graft. Rabbits in the experimental group (n = 23) underwent a lifting protocol to produce motion at the arthrodesis site; those in the control group (n = 12) remained undisturbed in their cages. Arthrodeses were assessed radiographically and manually to determine if fusion had occurred.ResultsLifted rabbits exhibited a 13% fusion rate compared to a 50% fusion rate in controls. Rabbits lifted during only the first 2 postoperative weeks exhibited a fusion rate that was significantly less (P= 0.03) than that of controls.ConclusionsA small animal model for motion-induced nonunion of lumbar intertransverse process spine arthrodesis has been established. With respect to excessive motion as a promoter of nonunion in spine arthrodeses, the early postoperative time period appears critical.