When instability or deformity runs across more than one lumbar level, the segments are decompressed and joined together into a single stable column. It is a large operation, and the aim is to fuse the spine in the right shape, so you can stand upright without straining.
TLIF: Transforaminal Lumbar Interbody Fusion. Licensed patient-education animation, ViewMedica.
A single-level fusion treats one worn-out level. A multilevel fusion treats a spine that can no longer hold its own shape, where several segments have slipped, tilted or collapsed.
The operation has three parts. The nerves are decompressed wherever they are being squeezed. The segments are realigned, which does the most to decide how you feel a year later. And the whole construct is held with screws and rods while the bone grows across and makes the fusion permanent.
The screws and rods hold everything still and in the right position for the months it takes the bone to heal. The fusion itself is the bone that grows across.
Multilevel instrumented lumbar fusion. Posterior and lateral views of a multi-segment construct with pedicle screws and contoured rods, interbody cages at the treated levels, and the restored lumbar lordosis shown against the pre-operative alignment.
Problems where instability or deformity runs across several levels.
A common sign is being able to stand straight for only a few minutes before needing to hold onto something, or finding yourself looking at the ground when you walk. The spine is no longer balanced, and the muscles do the work instead until they tire.
A healthy lower back curves forward. That curve is what balances the head and torso over the pelvis, so standing upright costs almost nothing in muscular effort. As discs collapse at several levels the curve flattens, the torso drifts forward, and staying upright becomes work the muscles have to do all day.
This is why a multilevel fusion is planned on standing full-length X-rays as well as an MRI. The MRI shows what is compressing the nerves; the standing X-rays show the shape of the spine and how the body has compensated, for example with the pelvis tilted back, the knees slightly bent or the upper back flattened.
A fusion that leaves the spine flat locks in the posture the patient came in with. So the rods are shaped, the cages are chosen for the curve they hold, and stiff areas are released, all so the fusion sets in the natural shape of the spine.
Each extra level adds operating time and blood loss, stiffens more of the lower back and puts more load on the segments at either end of the fusion. Those end segments are where adjacent segment disease shows up years later.
The length of the fusion is not set by how much of the spine looks worn on the scan, because a lot of the wear seen on imaging causes no symptoms. The fusion covers the levels that are unstable or deformed, plus any that must be crossed to end it at a healthy level, and no more.
Where the fusion ends is planned carefully, because ending on a level that is itself unstable is one of the recognized ways a long fusion fails.
Standing full-length films, flexion and extension views, MRI and usually CT. The alignment targets and the intended top and bottom of the construct are decided before the day of surgery.
Prone on a frame that lets the abdomen hang free and allows the lordosis to be set by the table. A CT scan is taken in the operating room so the navigation works from your spine in that position.
The nerves are freed at every level where they are compressed: in the central canal, in the lateral recesses and out through the foramina. Because the levels are being fused, the joints can be taken as far as the decompression requires.
At levels where height and lordosis have to be restored, the disc is removed and a cage is placed. This is where most of the correction comes from, and it also puts graft in the disc space, which is the most reliable place for a fusion to take.
Pedicle screws are placed under CT-based navigation, with robotic guidance where it suits the case. The path is planned on the images and the robot holds the guide to it, which helps most in a rotated, scoliotic spine where the usual landmarks are least reliable.
Rods contoured to the planned alignment are seated and the correction is brought about against them. Bone graft is laid along the decorticated surfaces to fuse. Final imaging confirms every screw and the alignment achieved before closing.
Spinal cord and nerve monitoring runs throughout. When the alignment is being changed across several levels, the monitoring shows straight away whether the nerves are tolerating the correction.
Multilevel instrumented fusion. Navigated screw placement across a rotated segment, interbody cages restoring height and lordosis, and the correction brought about against contoured rods.
A multilevel fusion is a major operation, and it is only recommended when the alternative is worse. In practice this means:
These are reasons to be certain the operation is needed before going ahead.
Figures are general ranges from the surgical literature and cannot be guaranteed for any one person. Recovery after a multilevel fusion varies more between patients than after a shorter fusion, because the fusions themselves vary so widely, from two levels to seven. Always follow the instructions you are given after your own operation.
Whether this is the operation, and how much of the spine it would need to span, is decided on standing full-length X-rays alongside the MRI. Bring any imaging and any operative reports from previous spine surgery.