Background: Only four cases of anterior arch fracture after C1 laminectomy without fusion have been previously reported. Although atlas fractures commonly occur in response to high-energy trauma, no obvious trauma that could cause the fracture was observed in these reported cases. The purpose of this study was to elucidate the biomechanical mechanism of anterior arch fracture of the atlas following C1 laminectomy and present three cases of this fracture.Methods: Three cases of fracture of the anterior arch of the atlas following C1 laminectomy were retrospectively reviewed. Three atlas models (an intact model, a laminectomy model, and a transverse ligament resected model) were created from computed tomography data of each case using a three-dimensional finite element method. Axial load was applied on the superior facet to mimic four conditions (neutral, flexion, extension, lateral bending). The distribution of von Mises stress in the anterior arch and the displacement of the posterior arch were compared among the three models.Results: In-all three cases, the anterior arch fracture Clinically occurred after C1 laminectomy despite there being no obvious inciting trauma. During the finite element analysis, increased stress was observed in all postures of the laminectomy model as compared with the intact model. The stress-concentrated location observed in the finite element model was consistent with the fracture sites that were Clinically observed. In terms of loading condition, much higher stress was observed in extension and lateral bending as compared with other postures. There were no significant differences in stress distribution between the laminectomy model and the transverse ligament resected laminectomy model.Conclusions: Stress distribution concentrates in the anterior arch after C1 laminectomy, leading to fracture of the anterior arch despite no inciting trauma. There may be more frequent occult fractures observed after C1 laminectomy than has been reported. Therefore, surgeons should recognize anterior arch fracture as a possible complication of C1 laminectomy without fusion. (C) 2016 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.