Lateral Lumbar Interbody Fusion (LLIF / XLIF)

What it is and why we do it

A lateral lumbar interbody fusion, often called LLIF or XLIF, is a way of fusing one or more levels of the low back through the side of the body instead of the back. Through a small incision in the flank, I pass between the abdominal muscles, across the space beside the kidney, and gently through the psoas muscle to reach the disc. The worn disc is removed and replaced with a wide spacer filled with bone graft. The spacer restores the height of the disc space, which opens the tunnels where the nerves exit, and holds the level still while the bone fuses.

I use this approach for a collapsed, worn disc with leg pain or a slip at the levels from the upper lumbar spine down to L4-L5, for adult scoliosis, and for a worn level next to an old fusion, where going through the scarred back muscles again would be hard on the patient. It does not reach L5-S1, where the pelvis is in the way. For that level I use a front approach or a back approach.

What happens during surgery

You lie on your side under general anesthesia. Using X-ray guidance, I make a small incision over the disc, pass a series of gradually larger tubes to the disc, and open a retractor. Nerve monitoring is running the whole time, because the nerves that go to the leg pass through the psoas muscle, and the monitor tells me exactly where they are. I remove the disc, prepare the bone, and place the spacer. Depending on your spine, I may add a plate on the side, or screws in the back through small incisions, to make the level stable. The incision is usually about 3 to 5 centimeters.

Your recovery

Most people go home the next day, some the same day, and some after two nights when screws are also placed from the back. Walking starts the day of surgery. Because no back muscles were cut, the back is usually not very sore. The most common complaint is a sore or weak front of the thigh, or numbness in the thigh or groin, on the side of surgery. This comes from stretching the psoas muscle and the nerves in it. It is expected, and in most people it fades over days to weeks. Rarely it lasts longer.

Activity and restrictions

Walk often, several short walks a day. For about six weeks, avoid bending at the waist, lifting more than 10 to 15 pounds, and twisting. Driving usually resumes once you are off narcotic pain medicine and can turn comfortably, often in two to three weeks. Desk work often restarts in two to four weeks. Heavier work and sports wait until the fusion is forming, which I check with X-rays. Nicotine in any form slows fusion and raises the risk of needing another surgery; stopping before and after surgery truly matters.

The science: for the curious

The idea behind the lateral approach is indirect decompression: when a collapsed disc space is restored to its normal height, the ligaments behind it tighten and the nerve tunnels open, without any bone being removed around the nerves. The wide spacer rests on the strong rim of the vertebra, which lowers the chance of it sinking into the bone and gives a large surface for fusion. The trade-off is the path through the psoas muscle, which is why nerve monitoring, careful placement of the retractor, and limiting the time the retractor is open are the heart of the technique. For the right level and the right patient, this approach gives a strong fusion with less blood loss and a faster early recovery than the same fusion done from the back.

Learn more

OrthoInfo, Spinal Fusion: orthoinfo.aaos.org (opens in a new tab)

Society for Minimally Invasive Spine Surgery, Patient resources: smiss.org (opens in a new tab)

This handout is general education about this procedure and does not replace the specific plan, risks, and consent discussion we have together. Your own situation may differ: if anything here does not match what we talked about, what we talked about wins, so please ask me.