An instrumented spinal fusion is performed in adult or pediatric patients when the spine has been weakened by degenerative conditions, deformity, trauma, tumor, or surgery. The purpose of the procedure is to restore spinal strength so that the spine can withstand normal day-to-day stresses and can also protect the spinal cord and nerves against more excessive forces that are occasionally encountered.
The basic premise of a spinal fusion is the creation of a bone “bridge” that connects strong and healthy bone above the weakened spinal segment with strong and healthy bone below it. To build this bone bridge, the surgeon places bone graft, or small pieces of bone, across the span where fusion is desired. The graft may be taken from the patient’s own body (an autograft) or from a bone bank (an allograft).
There are proteins in the human body that encourage bones to grow and fuse; they naturally assist during the healing of a fracture. These proteins, called bone morphogenic proteins (BMPs), may also be used to encourage bones to grow together after a spinal fusion. In some patients, the surgeon may use bone substitutes, bone extenders, and biologics like demineralized bone matrix or hydroxyapatite to assist in strong bone growth.
In an instrumented spinal fusion, instruments–rods, plates, screws, cages, and/or hooks–hold the bones in place while they fuse. The instruments are generally made of titanium, stainless steel, or cobalt chrome. Screws or hooks are inserted into the weakened vertebrae, as well as into adjacent healthy vertebrae. The screws or hooks serve as strong anchors to the spine. These anchors are then attached to metal rods that span the weakened segments, forming a metallic bridge. Forces can be applied to the rods to correct deformities and straighten the spine.