Posterolateral Lumbar Fusion

Overview

Posterolateral lumbar fusion is a surgery that permanently joins two or more vertebrae in the lower back so they heal into a single, stable segment of bone. The surgeon approaches the spine from the back, exposes the transverse processes (the small wing-like bone projections on each side of the vertebrae) along with the facet joints, and roughens their surface so they will accept bone graft. Bone graft material is packed along this posterolateral gutter, outside the spinal canal, and over the following months the graft knits the transverse processes of adjacent vertebrae into one continuous piece of bone.

To hold the spine still while that healing takes place, most posterolateral fusions are reinforced with pedicle screws placed into the vertebral bodies and connected by rods, sometimes called instrumented fusion. This hardware acts like an internal cast, keeping the segment rigid from the moment of surgery so the bone graft is not disrupted by motion. Posterolateral fusion is frequently combined with a decompression procedure, such as a laminectomy or partial facetectomy, performed at the same operation to relieve pressure on compressed nerve roots before the segment is stabilized.

When it's recommended

This procedure is generally reserved for patients whose back or leg symptoms come from a segment of the spine that is unstable or likely to become unstable, and who have not gotten adequate relief from an extended course of nonsurgical care such as physical therapy, activity modification, and injections. Common reasons to add fusion include degenerative or isthmic spondylolisthesis where one vertebra has slipped forward on the one below, flexion-extension X-rays showing abnormal movement between two vertebrae, and cases where a decompression alone would remove enough supporting bone and ligament to destabilize the segment.

Fusion may also be recommended after a prior decompression surgery that has led to recurrent instability, or when significant low back pain, not just leg pain, is a dominant part of the symptom picture. The decision to fuse, and how many levels to include, is individualized based on imaging, the pattern of symptoms, bone quality, and overall health, and is made jointly between the patient and surgeon.

How it works

Under general anesthesia, the patient is positioned face down and a midline incision is made over the affected levels. The surgeon exposes the posterior elements of the spine, including the transverse processes and facet joints, and places polyaxial pedicle screws into the vertebral bodies at each level using anatomic landmarks and fluoroscopic X-ray guidance to confirm safe positioning. Titanium or cobalt-chromium rods are then contoured to match the natural curve of the lower back and locked into the screw heads on each side, rigidly connecting the instrumented levels.

If nerve compression is present, the surgeon performs the decompression at this point, removing portions of bone or ligament pressing on the nerve roots or spinal canal. The bony surfaces of the transverse processes and facet joints are then decorticated, meaning their outer surface is roughened to expose bleeding bone, which encourages new bone to form. Bone graft, which may come from the patient's own hip or from the bone removed during decompression, supplemented with donor bone or bone-graft substitute, is packed along this prepared surface. The incision is then closed in layers, and over the following months the graft matures into solid bone connecting the transverse processes.

Preparing for the procedure

Before surgery, expect a preoperative visit covering medical clearance, a review of current medications (blood thinners and certain supplements are typically stopped in advance), and imaging to confirm the surgical plan. Patients who smoke are strongly encouraged to quit well before surgery, since smoking significantly reduces the chance that the bone graft will successfully fuse. Optimizing nutrition, blood sugar control, and bone density where relevant also supports healing.

On the day of surgery, patients are asked to fast beforehand and to arrange for someone to drive them home after discharge, since this is an inpatient procedure typically requiring a hospital stay of one to a few days. It helps to plan ahead for practical recovery needs, such as arranging help at home, setting up a recliner or firm bed for sleeping, and removing trip hazards, before the day of surgery.

Recovery and aftercare

Most patients get up and walk with assistance within a day of surgery, and hospital discharge typically follows within one to a few days once pain is controlled and basic mobility is safe. A back brace may be recommended for the first several weeks to support the healing segment. Physical therapy usually begins with gentle walking and gradually introduces core-stabilizing exercises, with bending, twisting, and heavy lifting restricted for a period of weeks to months while the bone graft matures.

Full bony fusion generally takes several months to about a year, though pain and function often improve well before the bone has completely healed, since the pedicle screws and rods provide stability in the meantime. Follow-up visits include periodic X-rays or CT scans to confirm that the graft is fusing as expected. Most patients gradually return to desk work within a few weeks and to more physical activities and driving once cleared by their surgeon, typically over one to three months.

Risks and considerations

As with any spine surgery, posterolateral fusion carries risks including infection, bleeding, a tear in the covering of the spinal cord (dural tear), and injury to a nerve root. Reported fusion rates with pedicle screw instrumentation are generally favorable, with many series reporting solid union in roughly 90 percent or more of patients, though pseudarthrosis, meaning the bone fails to fully fuse, and hardware problems such as screw loosening or rod breakage can still occur and sometimes require revision surgery.

Because a fused segment no longer moves, adjacent-segment degeneration, extra wear at the disc and joints above or below the fusion, can develop over years and occasionally requires further treatment. Other general surgical risks include blood clots in the legs (deep vein thrombosis), which can travel to the lungs, and the risks of general anesthesia. Not every patient achieves complete relief of pain, and some have persistent symptoms afterward. Your surgeon will weigh these risks against your expected benefit based on your specific anatomy and health.