A method for treating back pain by stabilizing the sacroiliac joint. The method includes fusing a sacrum bone to an ilium bone or otherwise mechanically immobilizing the sacroiliac joint by inserting at least two implants into voids formed within or between the articular surfaces of each sacroiliac joint of a patient without substantially distracting the joint. The voids are arranged within each joint at either a converging orientation or a diverging orientation. A kit containing the implants and tools required to insert the implants into the joint are also described.