Many types of hardware are available both for the fixation of bones that are fractured and for the fixation of bones that are to be fused (arthrodesed).
For example, the human hip girdle (see FIGS. 1 and 2) is made up of three large bones joined by three relatively immobile joints. One of the bones is called the sacrum and it lies at the bottom of the lumbar spine, where it connects with the L5 vertebra. The other two bones are commonly called “hip bones” and are technically referred to as the right ilium and-the left ilium. The sacrum connects with both hip bones at the sacroiliac joint (in shorthand, the SI-Joint).
The SI-Joint functions in the transmission of forces from the spine to the lower extremities, and vice-versa. The SI-Joint has been described as a pain generator for up to 22% of lower back pain patients.
To relieve pain generated from the SI-Joint, sacroiliac joint fusion is typically indicated as surgical treatment, e.g., for degenerative sacroiliitis, inflammatory sacroiliitis, iatrogenic instability of the sacroiliac joint, osteitis condensans ilii, or traumatic fracture dislocation of the pelvis. Currently, screws and screws with plates are used for sacro-iliac fusion. At the same time the cartilage has to be removed from the “synovial joint” portion of the SI-Joint. This requires a large incision to approach the damaged, subluxed, dislocated, fractured, or degenerative joint. The large incision and removal of tissue can cause significant trauma to the patient, resulting in pain and increasing the time to heal after surgery.
In addition, screw type implants tend to be susceptible to rotation and loosening, especially in joints that are subjected to torsional forces, such as the SI-Joint. Excessive movement of the implant after implantation may result in the failure of the implant to incorporate and fuse with the bone, which may result in the need to remove and replace the failed implant.
Consequently, it would be desirable to provide an implant for bone fusion or fixation that resists rotation, can be implanted using a minimally invasive procedure, and/or that can be used to rescue a failed implant.