Systems and methods for stabilizing the spine are provided. For stabilizing the L5-S1 junction, the system includes a plate that has a generally triangular shape with an upper node and a pair of lower nodes. The upper node has a hole through the plate to receive a screw for passage into the L5 vertebra. The lower nodes each include a hole through the plate to receive screws for passage into the S1 vertebra. The system further includes a plate having a retaining element for preventing backout of screws inserted through the plate. Instruments and methods for attaching the plate to the spinal column are also provided.