Posterior Spinal Fusion (AIS)

Posterior spinal fusion is an operation performed through the back to straighten a scoliosis curve and then permanently join the affected vertebrae into one solid, balanced column. It is a single procedure — there is no need to operate through the chest or the abdomen — which is one of the reasons it is the workhorse of scoliosis surgery. Anchors, most commonly pedicle screws, are placed into the vertebrae on both sides; two contoured rods are used to derotate and straighten the spine; and bone graft is laid so that, over the following months, the instrumented segments knit together. The metalwork holds the correction while the bone heals; the fusion itself is what makes the result permanent.

Posterior spinal fusion is the easiest and most reliable of the operations I use, and for many curves it is all that is needed. I tend to choose it on its own for the smaller curves that are more flexible — curves that will straighten well from the back without needing the front of the spine to be released or supported first. When a curve is very large, very stiff, or has a particular sagittal shape that needs addressing, I may add other steps (described on the related pages), but for the flexible curve in the braceable-to-moderate range that has crossed the threshold for surgery, a well-planned posterior fusion does the job in a single operation.

Some of the most important decisions in this operation are made before I ever pick up an instrument: where to start the fusion and, especially, where to stop it. My guiding principle here follows directly from my two aims. I want a spine that is balanced in both planes, and I want to achieve that while fusing as little of the spine as possible — because every mobile segment I can leave un-fused is movement preserved for life. In particular, I try to preserve as many lumbar segments as I can. Keeping the fusion short and high, where the curve pattern allows it, protects the flexibility of the lower back and is associated with better long-term function and self-image. This is why curve classification and careful assessment of the curve's behaviour matter so much: they tell me which curves will let me perform a shorter, selective fusion and still leave the whole spine balanced.

Modern pedicle-screw constructs allow a genuinely three-dimensional correction. As well as pulling the curve towards the midline, they let me derotate the apex of the curve directly, which improves both the rotational and the coronal correction. Because scoliosis is a three-dimensional deformity — a side-to-side curve, a rotation, and a change in the normal front-to-back profile — I pay close attention to the sagittal plane throughout. Powerful screw corrections can tend to flatten the thoracic spine, and restoring a healthy thoracic kyphosis and lumbar lordosis is an explicit part of my reduction strategy, not an afterthought. Throughout the operation the nerves are monitored, and the correction is checked against the goal of a balanced, level spine.

Segmental all-pedicle-screw posterior fusion is the established standard for adolescent idiopathic scoliosis, and the evidence is strong. It reliably achieves large coronal corrections — commonly in the region of 70 to 80 percent of the main curve — and direct vertebral derotation improves apical rotation beyond older techniques. Selective fusions that deliberately spare the lower curve produce spontaneous improvement of the unfused segment and keep the lumbar spine stable over the very long term, with studies following patients to 20 years, and shorter fusions are associated with better function and self-image scores. The literature also documents the tendency of powerful posterior constructs to reduce thoracic kyphosis, which is exactly why sagittal restoration is treated as a core aim. Long-term series report durable correction and quality-of-life scores approaching those of the general population.

Recovery follows a well-trodden path. There is usually a hospital stay of several days, with active pain relief and help to get up and walk, often within a day or two. Many young people are struck by how much taller and more even they stand once the curve is corrected. Strenuous activity, heavy lifting and contact sport are limited for a period of months while the fusion becomes solid, and a graded return to school and normal life is guided by the team. The fused part of the spine will feel stiff, because those levels are now joined, but the rest of the spine — and, where I have been able to preserve them, the lower lumbar segments — continue to move. The spine is followed up over the long term.

• —Suk SI, et al. Direct vertebral rotation: three-dimensional correction with segmental pedicle screw fixation in AIS. (PMID 14752361)
• —Lenke LG, et al. Lenke classification system of adolescent idiopathic scoliosis: treatment recommendations. (PMID 15948478)
• —Classifications in Brief: the Lenke classification for adolescent idiopathic scoliosis. (PMC6259994)
• —Cheung KM, Luk KD. Selection of fusion levels in AIS using fulcrum-bending prediction: a prospective study. (PMID 18794761)
• —Correlation of lowest instrumented vertebra with spinal mobility and HRQoL after posterior spinal fusion for AIS. (PMID 31361270)
• —Lumbar curve is stable after selective thoracic fusion for AIS: a 20-year follow-up. (PMID 21971127)
• —Thoraco-lumbar selective fusion in AIS with Lenke C modifier curves: 10-year analysis. (PMID 28547576)
• —Sagittal plane analysis of selective posterior thoracic fusion: all pedicle screw vs hybrid instrumentation. (PMID 24979229)
• —Effect of direct vertebral body derotation on the sagittal profile in AIS. (PMC3252432)
• —Very long-term outcomes after posterior spinal fusion with pedicle screws for thoracic AIS. (PMID 33030700)
• —Posterior correction of thoracic AIS with pedicle screws: minimum 10-year follow-up. (PMC3555635)
• —Long-term outcomes of spinal fusion in AIS: a literature review. (PMC11536752)
• —Increased risk of thoracic hypokyphosis after posterior spinal fusion in AIS with thoracic double curve. (PMID 36645436)