By Mr Ahmed-Ramadan Sadek, Neurosurgeon · Last reviewed October 2026 · 7 min read

What is a lumbar interbody fusion?

Between each pair of vertebrae in your lower back lies a disc, a shock-absorbing cushion with a soft centre and a strong outer wall. When a disc wears out, or a vertebra has slipped, the affected segment can become a source of ongoing pain or allow nerves to be squeezed.

In an interbody fusion, the surgeon clears out the disc and fills the space with a cage. This is a hollow spacer made of titanium, carbon fibre or a strong plastic called PEEK, sized to fit snugly and packed with bone graft. The graft may be your own bone, a synthetic bone substitute or donor bone. Over time your body grows new bone through it. the British Association of Spine Surgeons (BASS) describes this as a process of about 6 to 12 months, after which the two vertebrae act as one.

Who is it for?

Fusion may be suggested for degenerative disc disease, degenerative spondylolisthesis, spondylolytic spondylolisthesis, or repeated disc prolapses. It is usually considered only after non-surgical treatment has been tried thoroughly. Deciding to go ahead is a personal choice, best made after weighing the possible benefits against the risks and the alternatives with your surgeon.

The two approaches

TLIF: transforaminal lumbar interbody fusion (from the back)

You lie face down and the surgeon makes a cut in the middle of your lower back. The muscles on one side are moved aside and one facet joint (a small joint at the back of the spine) is removed to open a doorway to the disc. Surgeons usually choose the side where your leg pain is, so the trapped nerve can be checked and freed at the same time. The disc is cleared back to the bony end plates and the cage and graft are inserted, with extra graft laid along the side of the spine. If both legs are affected, the other nerve can be freed too, sometimes through a small tube.

TLIF is almost always combined with pedicle screws: screws placed into each vertebra and linked by rods. They act like internal scaffolding while the bone heals, and are normally left in place afterwards. A related operation, PLIF, works from both sides of the back.

ALIF: anterior lumbar interbody fusion (from the front)

You lie on your back and the surgeon makes a cut in your tummy. The bowel stays inside its protective sac (the peritoneum), which is gently moved to one side. The major blood vessels that cross the lower spine are then carefully eased out of the way, sometimes with help from a vascular surgeon. A window is cut in the front of the disc, the disc is removed and a cage with graft is pushed in. Some cages are secured with screws or blades anchored in the neighbouring vertebrae. If your own bone is needed for graft, the surgeon can harvest it from the rim of the pelvis through a separate small cut.

How do they differ?

	TLIF	ALIF
Way in	Through the back	Through the abdomen
Back muscles	Moved aside on one side	Left undisturbed
Freeing a trapped nerve	Can be done in the same operation	Not done directly; may need a separate back procedure
Main structures at risk	Nerve roots and their lining (dura)	Large blood vessels, nerves controlling some automatic body functions, bowel
Screws and rods	Usually used	Cage may be screwed in; back screws sometimes added

Your surgeon will recommend an approach based on your symptoms, which level is involved, any previous surgery, your build and general health. Sometimes both are combined. BASS notes that expected results are broadly similar whichever route is used.

Before your operation

• Stop smoking. Nicotine is the factor that most reduces the chance of fusion. BASS advises stopping ideally 2 to 3 months before, and surgery may be postponed if you have not.
• Tell your team about any blood thinners (for example aspirin, warfarin, clopidogrel or rivaroxaban) and anti-inflammatories, which may need stopping.
• BASS advises women to stop oestrogen-containing medicines, such as HRT or the combined pill, four weeks ahead of the operation to reduce the clot risk.
• Arrange for someone to take you home, as you should not drive or use public transport at first.

After surgery and recovery

You will wake in the recovery area with a drip and possibly a wound drain, usually removed the next day. A physiotherapist will help you get up, walk and manage stairs. According to BASS, most people go home 1 to 2 days after either operation. Pain should ease steadily, though irritated nerves may take eight weeks or longer.

• You can usually shower after 48 hours, keeping the dressing dry; avoid baths for two weeks.
• Driving: typically not for at least four weeks, and only once you can do an emergency stop.
• Work: around four weeks off, or up to eight for physical jobs.
• Lifting: avoid heavy loads for the first few weeks and possibly up to three months.
• Flying: BASS suggests avoiding flights for six weeks, and long-haul for up to three months.

Walk little and often. It helps your circulation, reduces stiffness and lowers the risk of clots.

Risks and complications

The figures below are from the BASS patient booklets on TLIF and ALIF. They are approximate; your surgeon will talk through your own risks.

Risks of both approaches

Risk	Approximate frequency (BASS)
Superficial wound infection	Up to 4 in 100
Deep wound infection	Fewer than 1 in 100
Blood clot in the leg or lung (DVT or PE)	Fewer than 1 in 700
Bones fail to fuse (non-union)	Up to 5 in 100
Cage or implant moves	Up to 2 in 100; about 1 in 100 need another operation
Death from injury to major vessels or organs	About 1 in 10,000
Fatal complication of general anaesthetic	About 1 in 250,000

Both approaches can also cause bleeding, pressure injuries from positioning, ongoing pain and, rarely, worse symptoms. In extremely rare cases, bleeding into the spinal canal or a moving cage can damage the nerves and cause paralysis or loss of bladder and bowel control.

Additional TLIF risks (BASS)

• Nerve root injury: under 1 in 100 for a first operation, rising to up to 10 in 100 for repeat surgery
• Tear in the dura (the nerve lining): fewer than 5 in 100; a further operation for a persistent leak is needed in less than 0.05%
• Screws in the wrong position: 2 in 100, which can injure a nerve; screws or rods can occasionally break months later
• Nerve pain from scar tissue, and very rarely loss of sight linked to positioning face down

Additional ALIF risks (BASS)

• Injury to the large blood vessels: up to 15 in 100, less often in experienced hands. Most tears are repaired straightforwardly, but very rarely bleeding can be life-threatening.
• Retrograde ejaculation in men, where semen passes back into the bladder: under 1 in 100. It does not cause impotence but can affect fertility, and may recover over months to a year.
• Paralytic ileus, where the bowel temporarily stops working, causing bloating and constipation: about 11 in 100.
• A warm feeling in the leg on the side of the surgery, which may fade or may be permanent.

Further reading

• BASS patient booklet: Transforaminal Lumbar Interbody Fusion
• BASS patient booklet: Anterior Lumbar Interbody Fusion
• NHS: Treatments for back pain
• Spinemathema: Degenerative disc disease

This guide is general information and is not a substitute for advice about your own situation. Please speak to your GP or specialist.