Posterior Lumbar Fusion

What it is

Posterior lumbar fusion — also called posterolateral fusion, or PSF — stabilizes the low back with pedicle screws and rods, then lays bone graft over the transverse processes and facet joints, alongside the spine. Over months, that graft grows into a solid bony bridge between the vertebrae. The key distinction: no cage goes into the disc space. The disc itself is left alone; the fusion is built from behind, around the spine rather than through it.

This is different from interbody fusions such as TLIF or PLIF, where a cage is placed inside the disc space after the disc is removed. PSF and TLIF are both posterior lumbar fusions, but they are not the same operation — and PSF can be performed with or without an interbody device, depending on what the spine needs.

When it may be considered

PSF is generally considered when the spine needs stabilization but the disc space itself does not need reconstruction. Common situations include spondylolisthesis (a slipped vertebra that needs to be held in place), lumbar stenosis where decompression removes enough bone that the segment would be left unstable, and degenerative conditions with documented instability on flexion-extension imaging. It is also chosen when disc height is well preserved — there is nothing to restore, so there is no reason to enter the disc.

What to discuss at consultation

• Goals: stop painful motion at the unstable segment while preserving as much of the natural anatomy as possible.
• Alternatives: continued nonoperative care; decompression alone where stability is adequate; or an interbody fusion (TLIF, PLIF, ALIF, LLIF) where disc height restoration or anterior column support is needed — see TLIF / PLIF for the comparison.
• Recovery: typically a short hospital stay; walking starts the day of surgery; bending, lifting, and twisting precautions protect the construct while the graft heals over months.
• Risks: nonunion (the graft failing to form solid bone), hardware loosening, adjacent segment wear over time, and the individual risks of surgery — discussed plainly before any decision.

From Back Talk

Related reading: Lumbar Fusion Recovery: 3 Months · Spinal Fusion Myths · Why I Don't Fuse Every Back

Who is a good candidate

• Low back or leg symptoms driven by instability — for example, a spondylolisthesis that shifts on flexion-extension X-rays
• Lumbar stenosis requiring a decompression broad enough that the segment needs stabilization afterward
• Degenerative changes with mechanical back pain that worsens with activity and eases with rest — the classic instability pattern
• Disc height that is reasonably preserved, so there is nothing an interbody cage would need to restore
• Good bone quality and overall health for a fusion operation, and a clear understanding that the graft takes months to solidify

PSF treats instability, not every source of back pain. Candidacy starts with confirming that motion at the segment — not the disc, not the joints alone — is truly driving the symptoms.

What recovery actually looks like

Days 1–3. Most patients stay in the hospital briefly and walk the day of surgery. The incision runs along the midline of the low back. Bending, lifting, and twisting (BLT) precautions begin immediately to protect the screws and rods while healing starts.

Weeks 2–6. Walking tolerance is the main activity — short, frequent walks. BLT precautions stay in place. For most patients there is no formal physical therapy during this period; it is prescribed selectively, not by default.

Weeks 6–12. Activity expands as comfort allows. X-rays check that the hardware position is holding. Core activation and gentle conditioning typically begin after the early healing phase.

3–12 months. The bone graft gradually consolidates into a solid fusion mass — this is a months-long biological process, not a weeks-long one. Most patients are back toward full activities by about 3 months, with the fusion continuing to mature up to a year.

Risks and how they are minimized

The honest risks include nonunion — the graft failing to fuse into solid bone (pseudarthrosis) — hardware loosening or breakage, infection, dural tear, blood loss, and incomplete pain relief. Over the long term, the levels next to any fusion can wear faster (adjacent segment disease).

Dr. Choi minimizes these through careful patient selection (operating only when instability is confirmed), meticulous graft bed preparation, appropriate graft material for the patient's biology — including attention to modifiable factors like nicotine use, which directly impairs bone healing — and plain discussion of every risk before any decision is made.

Alternatives considered first

Most back pain improves without fusion. The standard first course is time, activity modification, and physical therapy. When leg symptoms dominate, an injection can calm an irritated nerve — Dr. Choi does not perform injections himself and refers patients to pain management colleagues for those. Decompression alone is preferred whenever the spine is stable without hardware. And when the disc space itself needs restoration — collapsed disc height, foraminal narrowing that graft alone cannot address — an interbody fusion such as TLIF / PLIF may be the better tool. Surgery earns its place when instability is documented and conservative care has run its course.

When posterolateral fusion is combined with an interbody cage

Posterolateral fusion does not have to stand alone. It is commonly combined with an interbody fusion — ALIF, LLIF, or TLIF / PLIF — for what surgeons call a circumferential or 360° fusion. The logic is straightforward: the interbody cage restores disc height and provides support through the front of the spinal column, while the pedicle screws, rods, and posterolateral graft lock down the back. Each half does what it does best, and together they give the highest fusion rates.

This combined approach is typically reserved for situations that demand it — a spondylolisthesis with significant instability, collapsed disc height with foraminal narrowing, or revision settings where a prior fusion failed to heal. It is a bigger operation than PSF alone, and it is not needed for every fusion. The honest rule is the same as always: use the smallest construct that reliably solves the problem, and add the interbody cage when the spine — not habit — calls for it.

Related procedures

TLIF / PLIF · ALIF · LLIF · Spinal fusion · Laminectomy / laminotomy · Minimally invasive surgery

Conditions this procedure treats

Spondylolisthesis · Lumbar stenosis · Lumbar degeneration