Lumbar Fusion and Fixation
Mechanical instability of the spine may result from a several causes, including degenerative disease, trauma, or cancer. If the degree of instability is excessive the structural integrity of the spine will be compromised. This decreased stability can produced pain during normal activities, a condition known as mechanical low back pain. The pain is typically confined to the lower back, hips, and thighs. Conservative measures are designed to re-establish stability by strengthening compensatory structures such as the muscles of the lower back and abdominal wall. If a significant degree of instability exists or conservative measures fail, the structural integrity of the spine is restored through a spinal stabilization surgery. The operative procedure, known as a fusion and fixation, is intended to eliminate the movement across the unstable portion of the spine and reduce the production of pain. Fixation provides immediate spinal stability through the implantation of metallic screws, known as pedicle screws, connected by metallic rods. Long-term stability is achieved through the growth of a bony bridge between the unstable bones, known as a fusion.
The procedure is performed under general anesthesia. A midline incision is made in the lower back overlying the area of instability. Soft tissue is dissected off the back of the spine to expose the unstable spinal segments. A lumbar laminectomy is typically performed to decompress the neural elements, as described in the lumbar laminectomy section. Once the neural elements are free, the spinal stabilization procedure is performed. The bone to create the fusion is harvested from the iliac crest (a part of the hip bone) through the same or separate incision. Using bony landmarks, fluoroscopy or a Stereotactic Navigational System, the entry site and trajectory of the pedicle screws is identified and the screws are inserted. These advanced imaging techniques allow more accurate screw insertion. The harvested bone is then transplanted across the unstable spinal segments. The pedicle screws are then connected with metallic rods providing immediate stability. The operative site is then sutured closed in multiple layers.
Course of Treatment
Patients are admitted for several days following surgery. Pain control is initially achieved with intravenous medications, eventually changing to oral analgesics. Ambulation is encouraged on the day following surgery. Patients are evaluated by physical therapy and taught maneuvers to decrease their post-operative pain during normal activities. Activity is limited to ambulation until the initial follow-up visit, at four to six weeks. Activity is then increased as tolerated. Formal physical therapy for lower back strengthening and range of motion is not initiated until approximately three months following surgery. Patients are intermittently evaluated with lower back X-rays during the follow-up period to monitor the progression of bone fusion.