OLIF — oblique lumbar interbody fusion

Through the flank, along a corridor between the great vessels and the psoas, the muscle that flexes the hip and through which the lumbar plexus runs. By passing in front of the psoas rather than through it, handling of that nerve plexus is reduced.

Not necessarily: from a single incision in the flank, several levels can be reached, often including L5-S1. How many are treated, and in how many sittings, depends on your case and is decided during planning, not on the day.

That is the basis of indirect decompression: restoring disc height reduces the disc bulge and re-tensions the ligaments, so the canal and foramina gain calibre without removing bone. Not every stenosis responds this way; when the narrowing is caused by bone or by thickened ligament, it has to be released directly.

In the route to the disc. XLIF passes through the psoas, which is why it is done with neurophysiological monitoring; OLIF passes in front of that muscle. The goals are similar — a wide implant, height and lordosis — and what decides is each patient's anatomy and the levels to be treated.