A lumbar fusion approached from the side rather than through the back muscles or the abdomen. A large interbody cage is set across the strong rim of the vertebra, restoring the collapsed disc height — which opens the nerve exits without entering the spinal canal at all. The corridor passes through the psoas muscle, and that is where the temporary thigh symptoms this operation is known for come from.
Every fusion has to get to the disc somehow, and the choice of direction decides most of what the operation costs the patient. From behind, the back muscles are moved and the nerve root is retracted. From the front, the great vessels have to be worked around. From the side, neither is true: the disc is reached through the space behind the abdominal contents, and the only thing in the corridor is the psoas muscle.
What that direction buys is size. Coming in laterally exposes the disc across its whole width, so the cage that goes in spans from one side of the vertebral rim to the other and rests on the dense bone at the edge rather than the soft bone in the middle. A bigger footprint on stronger bone is what lets the cage carry 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. A good deal of what shows on the scan as stenosis is that settling.
Restoring the height reverses it mechanically. Jacking the segment back up re-tensions 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 ever being opened — no bone removed from over it, no scar left against it, nothing placed near it.
That works when the compression is soft and comes from collapse. It does not work when the compression is fixed:
Where indirect decompression is not going to be enough, the answer is not to attempt it anyway — it is a different operation, or this one combined with a direct decompression from behind. That is decided on the MRI before surgery, not during it.
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 — the iliac crest sits directly in the corridor, and the lumbar plexus has moved forward across the disc by that level. There is no technique that gets around it.
This matters when the bottom level needs treating too. In that situation the lateral approach is used for the levels it suits and L5–S1 is done through a different corridor in the same anaesthetic — usually ALIF from the front, or TLIF from behind. A construct using two approaches is normal, not a complication.
L4–L5 is reachable in most patients but not all — 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 rather than cut, and the plexus is mapped continuously during the approach, but it is being worked around at close quarters.
Continuous neuromonitoring is used throughout the approach for this reason. Directional EMG tells the surgeon where the nerves are relative to the instruments in real time, so the corridor is opened where the plexus is not, rather than where it is assumed not to be.
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 lateral view of the target disc before an incision is made — the whole approach depends on the trajectory being 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 breaching 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.
The comparison that matters for most patients is against MIS TLIF, which reaches the same disc from the other direction.
Both columns are minimally invasive and both are operations Dr. Zaidi performs. Neither is better in the abstract — the level, the kind of stenosis and the patient’s own anatomy decide it. See how the approach is chosen.
Figures are general ranges from the surgical literature, not guarantees for any individual case. Recovery varies with the number of levels treated, whether posterior fixation was added, bone quality and general health. Follow the instructions you are given after your own operation rather than these.
Whether the side is available to you is decided on imaging — the height of your iliac crest, where the plexus sits, and whether your stenosis is the kind that height restoration relieves. Bring any MRI or CT you already have.