Imaging studies and operative records of 55 patients who had undergone lumbar pseudarthrosis repair were studied, providing a total of 85 surgically documented pseudarthroses. Preoperative imaging studies were carefully analyzed for the anatomic characteristics of the involved levels and the morphology of the fusion mass. The pseudarthroses were found to fall into four distinct morphologic categories: atrophic, transverse, shingle, and complex. The atrophic pseudarthrosis type was noted to be strongly associated with the presence of intact facet joints or spinal hardware. This retrospective analysis indicates that stress shielding provided by intact facet joints or spinal implants may contribute to graft atrophy in certain patients. The classification scheme proposed may be useful in future analyses of different fusion techniques in determining the various causes of this surgical complication.