Spine · Procedure

Lateral Lumbar Interbody Fusion (LLIF or XLIF): Fusion Through the Side

Lateral lumbar interbody fusion reaches the front part of the lower spine through a small incision on your side. It places a large spacer in the disc space to restore height and alignment while the bones heal together. You may also hear it called XLIF, DLIF, or a lateral or transpsoas fusion.

At a glance

The disc is reached through the side of the body, with the back muscles left largely undisturbed.
A large spacer can restore disc height, which may widen the openings for nerves and improve alignment.
Temporary thigh or groin numbness, pain, or hip weakness on the operated side is common and usually improves.
It is often combined with screws placed through small incisions in the back.

Why a lateral fusion may be considered

A lateral fusion may be considered for spinal stenosis, a slipped vertebra (spondylolisthesis), a degenerated disc with instability, curvature of the spine (degenerative scoliosis), or a problem at a level next to a previous fusion. Like any fusion, it treats a stability or alignment problem; the operation is chosen because limiting movement at a specific level is expected to help you.

Restoring the height of a collapsed disc can enlarge the openings where nerves leave the spine. This is called indirect decompression. When nerve pressure is severe or caused by bone or a large disc fragment, a direct decompression may still be needed. A published review describes the conditions treated with this approach.

Comparing it with other choices

For many nonurgent conditions, options include physical therapy, suitable medicines, activity changes, selected injections, or watchful waiting. Surgical alternatives include a decompression without fusion, a fusion from the back (TLIF or PLIF), or a fusion through the abdomen (ALIF). Each approach reaches the disc from a different direction and has its own tradeoffs.

The lateral approach is best suited to certain levels. The lowest level of the spine (L5-S1) is usually blocked by the pelvis and is treated another way. Blood vessel and nerve anatomy on your imaging also guide whether the side approach is safe for you. Ask why this approach fits your anatomy and goals.

How the operation works

Under general anesthesia, you lie on your side. Using X-ray guidance, the surgeon makes a small incision on the flank and passes gently through the space behind the abdominal lining to reach the side of the spine. The path usually goes through or beside the psoas muscle, which runs along the spine near the nerves to the leg.

Nerve monitoring is used during the approach to help the team avoid the nerves of the lumbar plexus. The disc is removed and a spacer filled with bone graft is placed across the disc space. Depending on your bone quality and the problem being treated, the spacer may be supported by a plate on the side or by screws and rods placed through small incisions in the back, sometimes in the same operation. NICE reviews the technique and its evidence.

Understanding benefits and limits

Potential advantages include a large spacer, small incisions, limited disturbance of the back muscles, and less blood loss for many patients. The goals are improved leg symptoms, better alignment, and a stable segment while the bones fuse.

As with any fusion, relief is not guaranteed, nerves that were already damaged may not fully recover, and neighboring levels can wear over time. Bone healing takes months. Discuss which symptoms are most likely to improve in your case.

Material risks

General risks include infection, bleeding, blood clots, anesthesia complications, nonunion (the bones not joining), implant problems, persistent pain, and the need for more surgery.

Risks specific to the side approach include numbness, burning, or pain in the front of the thigh or groin and weakness in lifting the leg at the hip on the operated side. These symptoms are common in the first weeks and usually improve, but a small number of patients have lasting weakness. Rare risks include injury to bowel, blood vessels, the ureter, or the nerves that control leg strength, and a hernia or bulge at the flank incision. A large multicenter study reports how often these problems occur.

What to address beforehand

Review your medical conditions, nicotine use, bone health, and all medicines and supplements, including blood thinners, with the team. Ask whether a bone density test is needed. Stopping smoking and other nicotine improves the chance of a solid fusion.

Plan for help at home with meals, errands, and transportation for the first weeks. Ask whether you will have one operation or two stages, and how many incisions to expect.

Recovery

Many patients walk the same day or the day after surgery. Expect soreness at the side incision and, often, thigh or groin symptoms on that side. Hip flexor weakness can make climbing stairs or lifting the leg into a car harder for a while; tell the team so physical therapy can help. Lifting, bending, driving, and return to work follow an individual plan. Fusion continues to mature over several months. AAOS explains fusion healing. The fusion recovery guide on this site also applies.

Go to the nearest emergency department for new or worsening leg weakness, new numbness around the genitals or anus, new trouble starting or passing urine, or loss of bladder or bowel control. Seek urgent care for a swelling abdomen, severe abdominal pain, fever, or a draining incision. Call 911 for chest pain, breathing trouble, or collapse. The NHS describes warning signs that need emergency care.

Questions for your care team

Which levels will be treated, and why is the side approach a good fit for my anatomy?
Will I also need screws in the back, and will that be the same day?
How likely are thigh numbness or hip weakness for me, and how will we manage them?
How will we judge whether the fusion has healed?

Sources and further reading

These sources support the general information on this page. Instructions from other institutions may differ from your own care plan.