POSTEROLATERAL LUMBAR FUSION
Posterolateral fusion is one of two main approaches to spinal fusion, a surgery designed to stop low back pain caused by painful motion of the vertebrae. One of the main differences between these two approaches is where the bone graft is laid in the spine to form the fusion.
In posterolateral fusion the graft to form the bony bridge can be placed between the transverse processes in the back of the spine. This will allow the bone to heal from the transverse process of one vertebra to the transverse process of the next vertebra.
The most common fixation technique employed in a posterolateral fusion is pedicle screw fixation. This refers to placing screws within the pedicles of each vertebral segment (bilaterally—on both sides of the spine) and connecting them to each other with a metal rod. A one level fusion would fuse two vertebrae and usually uses four screws and two rods. A two level fusion fuses three vertebrae and uses six screws and two rods
In order to obtain a fusion certain basic criteria must be present.
- A suitable graft must be available to serve as the bridge to connect the vertebra.
- An appropriate location must be present to lay the bone graft and allow it to heal to each vertebral segment on either end.
- The bed which this bone graft is being laid in must be prepared correctly and the patient must have the appropriate biology for the graft to fuse. This bed can be prepared by removing the outside covering of the bone (the cortex) and exposing a bed with better blood supply (decortication). It is important that there is contact between the bone and the bone graft and no soft tissue (e.g. muscles, ligaments) in the way.
- There must be adequate fixation to immobilize this area while the bone graft heals to the vertebral segments. This immobilization is usually provided by internal fixation with metallic screws and rods and/or interbody devices such as cages.
Patients with spinal instability in their lower back due to degenerative disc disease, spondylolisthesis or spinal stenosis that has not responded to other non-surgical treatment measures such as rest, physical therapy or medications may be recommended for spinal fusion surgery such as Posterolateral Lumbar Fusion. Patients with spinal instability may experience pain, numbness and muscle weakness in the lower back, hips and legs.
Before prescribing Posterolateral Lumbar Fusion surgery your surgeon considers various factors such as the condition to be treated, your age, health, lifestyle and your expected level of activity after the surgery. Have a complete discussion with your spinal care provider regarding the treatment options available.
In a posterolateral fusion, the surgical approach to the spine is from the back through a midline incision that is approximately three inches to six inches long.
- First, bone graft is obtained from the pelvis (the iliac crest), although some form of bone graft substitute may also be used. Most spine surgeons work through the same incision to obtain the bone graft and to perform the spinal fusion.
- Next, the harvested bone graft is laid out in the posterolateral portion of the spine. This region lies on the outside of the spine and is a very vascular area, which is important because the fusion needs blood to supply the nutrients for it to grow.
- A small extension of the vertebral body in this area (transverse process) is a bone that serves as a muscle attachment site. The large back muscles that attach to the transverse processes are elevated up to create a bed to lay the bone graft on. The back muscles are then laid back over the bone graft, creating tension to hold the bone graft in place.