Abstract Purpose of study: Increased fracture rates among osteoporotic patients in proximity to instrumentation and prosthetic joint replacements is well documented in the literature. The authors have recently described burst fractures of the caudal end-instrumented lumbar vertebrae in adult patients treated with an instrumented fusion for scoliosis. The purpose of this study was to describe traumatic sacral spondylolisthesis (TSS), which is a newly recognized complication resulting from the surgical management of adult deformity after instrumentation to the sacrum, and to suggest possible treatment options. Methods used: Review of four patients with symptomatic spinal deformities and osteoporosis who were treated with surgical intervention. Each patient subsequently developed an insufficiency fracture and olisthesis of S1. of findings: Four patients averaging 60 years of age (range, 36 to 78 years) underwent a combined anterior and posterior spinal fusion to the sacrum averaging 9 levels (range, 3 to 13). Preoperative diagnoses included degenerative spondylolisthesis (n=2), degenerative scoliosis (n=1) and Charcot spine (n=1). Insufficiency fractures of the sacrum resulting in a traumatic S1 spondylolisthesis was documented an average of 7 weeks postoperatively in these patients (range, 5 to 12). Minor trauma resulting from a fall was documented in two patients. Two patients did not have a clear history of significant trauma associated with the onset of symptoms. Anterior olisthesis of the proximal S1 fragment varied from 20% to 100%. Three patients did not progress, and one patient with a 40% olisthesis progressed to a spondyloptosis. Intermittent urinary incontinence with urgency as a result of high-grade stenosis was identified in a patient with traumatic spondyloptosis. All patients had significant pain. One patient presented with the hallmark clinical posture of a high-grade spondylolisthesis. The two patients with spondyloptosis elected surgical intervention. One of these patients developed incontinence and underwent decompression, partial reduction and extension of the fusion to the ilium. Another patient underwent extension of the fusion to the ilium without reduction. The remaining two patients were treated nonoperatively. All patients demonstrated clinical improvement at most recent follow-up. Relationship between findings and existing knowledge: Combined anterior and posterior fusion may create stress risers at adjacent levels. In the osteoporotic patient this may result in insufficiency fractures. Sacral insufficiency fractures as a consequence of spinal instrumentation have not been previously described. These fractures may present with painful instability and symptoms of neurologic compression similar to that seen in high-grade developmental spondyloptosis. Overall significance of findings: In the osteoporotic patient preoperative consideration should be given to constructs that are shorter and that preserve a distal buffer zone between the lowest instrumented vertebrae and the sacrum. In addition, decreasing the stiffness of the constructs may help to decrease the magnitude of stress transferred to the adjacent vertebral levels or the sacrum. Developing a plan of treatment for a patient with TSS of S1 must take into consideration the degree of displacement, neurologic symptoms and the general health and goals of the patient. Nonsurgical treatment is appropriate for patients who cannot tolerate a significant spinal reconstruction to the ilium or the potential significant blood loss that could result from disimpaction and realignment of the fracture. Nonoperative care consisting of an extended period of bedrest has resulted in acceptable outcome. However, the risks of prolonged bed rest in the elderly is not benign. Surgical intervention to perform reduction and stabilization is an attractive, definitive option for patients who are physiologically robust. The benefit of surgical repair is the ability to decompress the neural elements and achieve rapid mobilization. Disclosures: No disclosures. Conflict of interest: No conflicts.