Anterior Instrumented Fusion (AIS)

Anterior instrumented fusion is an operation performed from the front of the spine to correct and fuse a scoliosis curve. For a thoracolumbar or lumbar curve, I typically reach the spine through the side, entering through the bed of the tenth rib. The discs across the curve are then removed thoroughly — a radical discectomy — and the spine is corrected and instrumented from the front, with structural support placed into the emptied disc spaces. It is performed as a single procedure. The appeal of the anterior approach for these particular curves is that it works directly on the front column of the spine, which is exactly where the shape of the lumbar spine is set.

I use anterior instrumented fusion mainly for flexible thoracolumbar curves. The reason comes back to my second aim — restoring alignment in the sagittal plane. When the discs are removed and the segment is compressed to correct the curve, there is a natural tendency for that part of the spine to lose its normal forward curve, its lordosis. To prevent that, and in fact to actively rebuild a normal lumbar profile, I use interbody cages placed into the disc spaces. Those cages hold the height at the front of the spine and set the segmental alignment I want, so that the lower back is left with a healthy lordosis rather than flattened. Restoring normal lumbar alignment in this deliberate, controlled way is one of the real strengths of the anterior approach for these curves.

There is a further advantage that matters a great deal to me: the anterior approach usually allows me to fuse one fewer level than a posterior operation would for the same curve. Because I am working directly on the curve from the front, I can often stop the fusion one segment higher and still leave the spine balanced. Every lumbar segment preserved is movement kept for life, and keeping the lowest instrumented level higher may help protect the discs below from wear over the years. This level-saving, combined with the controlled restoration of lordosis, is why I favour the anterior route for suitable thoracolumbar and lumbar curves.

The evidence supports anterior instrumented fusion as an excellent option for flexible thoracolumbar and lumbar (Lenke type 5) curves. It reliably achieves large corrections of the main curve, comparable to posterior surgery, while consistently fusing roughly one level fewer — a difference confirmed in meta-analyses and matched comparisons. Because a thorough discectomy tends to kyphose the segment, the literature is clear that restoring lordosis depends on structural anterior support such as interbody cages, and biomechanical studies confirm that cages markedly increase the stability of the construct and help set the desired lordosis. Dual-rod anterior systems with interbody support have largely eliminated the small risk of non-union and rod problems seen with older single-rod constructs, and long-term series following patients twelve to twenty-three years show durable correction. Head-to-head studies find anterior and posterior approaches give broadly comparable outcomes, with the anterior approach favouring shorter fusions.

Because the operation involves the front of the spine, and often the chest cavity is entered, a temporary drain may be used for a short time and breathing is supported and monitored closely in the early days. Beyond that, recovery resembles other spinal fusions: a hospital stay of several days, active pain relief, help to get up and move as soon as it is safe, and a graded return to normal life over the following months while the fusion becomes solid. Strenuous activity and contact sport are limited during that healing period. The fused segment will feel stiff, but keeping the fusion short preserves as much lower-back movement as possible, which is much of the point of choosing this approach. The spine is followed up over the long term.

• —Anterior surgery for adolescent idiopathic scoliosis (review). (PMC3566254)
• —Prospective outcomes of dual-rod instrumented anterior spinal fusion in AIS: comparison with single-rod constructs. (PMID 16985460)
• —Prospective outcomes and complications of single solid-rod anterior spinal fusion in AIS. (PMID 11547193)
• —Single- versus dual-rod anterior instrumentation of thoracolumbar curves in AIS. (PMID 26687125)
• —Long-term outcomes of anterior dual-rod instrumentation for TL/L curves in AIS: 12–23 year follow-up. (PMID 23595075)
• —Anterior solid dual-rod instrumentation and fusion for flexible TL/L deformities in AIS. (PMC12088289)
• —Retrospective analysis of anterior correction and fusion for AIS TL/L scoliosis: preserving mobile segments and trunk balance. (PMC2899232)
• —Anterior versus posterior approach in Lenke 5C AIS: meta-analysis of fusion segments and radiological outcomes. (PMC4940871)
• —Anterior versus posterior selective fusion in AIS: systematic review and meta-analysis. (PMID 29309975)
• —Anterior dual rod versus posterior pedicle fixation for Lenke 5C AIS: matched case analysis. (PMID 27927296)
• —Anterior spinal fusion for thoracolumbar scoliosis: radiographic, clinical and pulmonary outcomes. (PMID 20864850)
• —Mini-open anterior instrumentation with diaphragm sparing for thoracolumbar idiopathic scoliosis. (PMID 21181213 / PMC3030707)
• —Reducing the kyphosis effect of anterior short TL/L scoliosis correction with an autograft fulcrum effect. (PMC7903709)