A lumbar fusion done from the side, without going through the back muscles or the abdomen. A large cage is placed across the strong rim of the vertebra, restoring the collapsed disc height, which opens the spaces where the nerves exit without entering the spinal canal. The approach passes through the psoas muscle, which is the source of the temporary thigh symptoms this operation is known for.
XLIF Lateral Lumbar Interbody Fusion. Licensed patient-education animation, ViewMedica.
The direction a fusion takes to reach the disc decides much of what the operation involves for the patient. From behind, the back muscles are moved and the nerve root is held aside. From the front, the great vessels have to be worked around. From the side, the disc is reached through the space behind the abdominal contents, and the only thing in the way is the psoas muscle.
Coming in from the side exposes the disc across its whole width, so the cage can be large, spanning from one side of the vertebral rim to the other and resting on the dense bone at the edge. A larger cage on stronger bone can hold the disc height without sinking into the vertebra.
Lateral interbody cage in position. Coronal view of the cage spanning the vertebral rim from side to side, with the disc height restored and the neural foramina opened above and below.
When a disc collapses, the vertebrae above and below settle toward each other and the openings the nerves leave through get shorter. The ligament at the back of the canal, no longer held taut, buckles inward. Much of what shows on the scan as stenosis comes from that settling.
Restoring the height reverses this. Lifting the segment back up tightens the ligament so it flattens out of the canal, and lengthens the foramen so the nerve has room again. The nerve is decompressed without the canal being opened, so no bone is removed from over it and no scar forms against it.
That works when the compression is soft and comes from collapse. It does not work when the compression is fixed:
Where indirect decompression will not be enough, a different operation is used, or this one is combined with a direct decompression from behind. This is decided on the MRI before surgery.
Degenerative levels that have lost height, where the anatomy in front and behind is suitable for the corridor. It is particularly useful where several adjacent levels need treating, because each one is reached through the same approach.
From L1–L2 down to L4–L5. L5–S1 cannot be reached from the side, because the iliac crest is directly in the way and the nerves of the lumbar plexus lie across the disc at that level.
When the bottom level needs treating too, the lateral approach is used for the levels it suits and L5–S1 is done through a different approach under the same anesthetic, usually ALIF from the front or TLIF from behind. Using two approaches in one operation is common.
L4–L5 can be reached in most patients, but a high iliac crest can block it. Whether it is available in a given case is measured on the pre-operative imaging.
The corridor to the disc runs through the psoas muscle, and the nerves of the lumbar plexus run through the psoas as well. The muscle is spread apart without being cut and the nerves are mapped continuously during the approach, but the surgeon is working very close to them.
Continuous neuromonitoring is used throughout the approach for this reason. Directional EMG shows the surgeon in real time where the nerves are relative to the instruments, so the path is opened away from them.
The patient is turned onto their side and secured, and the table is used to open the space between the ribs and the pelvis. Imaging confirms a true side view of the target disc before an incision is made, because the whole approach depends on coming in square to the disc.
A small incision in the flank. The plane behind the abdominal contents is entered bluntly, so the abdominal cavity itself is never opened, and the psoas muscle is identified.
A dilator is advanced through the muscle while stimulating continuously. The response tells the surgeon which direction the plexus lies in and how far away it is; the retractor is docked where the readings are safe.
The disc is removed across its full width and the endplates are cleaned back to bleeding bone without breaking through them, since they are what the cage will rest on.
A trial establishes the height that restores the segment without over-distracting it. The cage, packed with graft, is seated across the vertebral rim so it bears on the dense bone at both edges.
Many constructs are supplemented with pedicle screws placed percutaneously through small posterior incisions, often under navigation or robotic guidance. Whether that is required depends on stability, bone quality and the number of levels.
Lateral lumbar interbody fusion. The retroperitoneal corridor, the transpsoas docking under neuromonitoring, discectomy and endplate preparation, and the cage seated across the rim with the foramen opening as height is restored.
For most patients the alternative is MIS TLIF, which reaches the same disc from behind.
Both are minimally invasive and Dr. Zaidi performs both. Which is better depends on the level, the kind of stenosis and your own anatomy. See how the approach is chosen.
Figures are general ranges from the surgical literature and cannot be guaranteed for any one person. Recovery varies with the number of levels treated, whether posterior fixation was added, bone quality and general health. Always follow the instructions you are given after your own operation.
This is decided on imaging: the height of your iliac crest, where the nerves of the lumbar plexus lie, and whether your stenosis is the kind that restoring disc height relieves. Please bring any MRI or CT you already have.