Spinal fusion surgery involves adding bone graft to an area of the spine to set up a biological response that causes the bone to grow between two vertebral elements and thereby stop the motion of the segment.
Instrumentation provides temporary stability of the spine until a bridge of bone connects the vertebrae together (fusion).
The decision to perform these procedures is based on three factors:
Posterior lumbar fusion has traditionally been performed through a midline or paraspinous approach. In a midline approach the muscles over the spine are elevated from the bone allowing decompression of nerves, placement of graft, and instrumentation. A paraspinous exposure requires two parallel incisions on either side for the same purposes.
Decompression of the spinal canal can be performed at one or more levels including removal of herniated discs and other pressure on the spinal nerves.
Following decompression, instrumentation can be attached to the vertebrae to provide stability, correct deformity, and maintain a particular alignment until a fusion develops. These implants usually consist of hooks or screws attached to bone and connected by rods or plates. The surface of the spine is removed (decorticated) and bone graft laid on this surface. Bone graft is commonly obtained from the pelvis through the same or sometimes a separate incision. The decorticated surfaces then grow to the graft and form a solid bar of bone much like a fracture heals. Ultimately, this provides the stability needed and prevents further progression of deformity, etc… Banked bone (allograft) or bone substitutes have generally been shown to be inferior to the patients own bone (autograft) in developing a solid fusion posteriorly. Early reports using Bone Morphogenic Protein are encouraging and may increase fusion success rates in the future, which at present may at best be between 85 to 95% when instrumentation is used.
The anterior lumbar interbody fusion (ALIF) is similar to the posterior lumbar interbody fusion (PLIF), except that in the ALIF the disc space is fused by approaching the spine through the abdomen instead of through the back.
Some ALIF procedures will be done using a minilaparotomy (one small incision) or with an endoscope (a scope that allows the surgery to be done through several one-inch incisions), this allows better visualization and can be done with a minimal amount of postoperative. The results with either procedure are equivalent and the type of approach used depends on which procedure suits the patient’s particular circumstances.
Sometimes, both a lumbar interbody fusion and a posterolateral gutter fusion will be performed and both the front and back of the spine will be fused.
This procedure is usually done for patients with a high degree of spinal instability (e.g. fractures), or in revision surgery (if the initial fusion did not set up), although some surgeons do prefer the anterior/posterior fusion as a primary spinal fusion technique.
Fusing both the front and back provides a high degree of stability for the spine and a large surface area for the bone fusion to occur. The disc may be approached either as an ALIF or as a PLIF, and the back part of the spine is fused with a posterolateral gutter fusion, which involves placing bone graft in the posterolateral portion of the spine (a region just outside the spine).
Over the last 10 years many medical specialties, including orthopedics, neurosurgery, cardiology, gastroenterology, and radiology, have made incredible advances in the diagnosis and treatment of many conditions. Many of these advances have been made possible by using fiberoptic video cameras and specially designed tools to perform surgery and diagnostic tests with much smaller incisions, less damage to the surrounding tissue, and faster recovery times. Most people are familiar with this type of technology in the form of “arthroscopic” surgery, which allows orthopedic surgeons to look inside joints like the knee and operate through very small incisions with a minimal amount of pain, scarring, and trauma to the muscles that move the knee. Minimally invasive surgical techniques have become the standard of care in the treatment of many conditions that affect the joints, heart, and GI tract.
The technology behind minimally invasive surgery is now being applied to spine surgery, where it holds the promise of allowing surgeons to accomplish their surgical goals while providing patients with less post-operative pain, shorter recovery times, and easier rehabilitation than after conventional “open” spine surgery.
Several technological advances are making these developments possible, most notably specialized instrumentation systems for video assisted thoracoscopic and laparoscopic spine surgery, new instruments and tools for percutaneous spine surgery, and technologies for advanced surgical navigation.
These enabling technologies such as advanced surgical navigation tools and specialized instrumentation allow surgeons to place pedicle screw instrumentation, and bone grafts in the vertebral bodies of the spine with small, percutaneous incisions.