Scoliosis Surgery for Adolescents: Spinal Fusion and Risks

Scoliosis surgery corrects the curve and fuses the corrected segment so that it cannot progress. Today the standard operation for adolescent idiopathic scoliosis is posterior spinal fusion with pedicle screws at every involved level, two rods and bone graft. It is offered for curves beyond 40 to 45 degrees, and the risk of neurological injury after surgery is less than 1%.

Dr. Manoj Miglani, Principal Director Orthopaedics, Fortis Flt. Lt. Rajan Dhall Hospital, Vasant Kunj, New Delhi, India, set out who needs the operation, how the fusion levels are chosen, how the instrumentation evolved to its present form, the place of anterior surgery and growth-friendly tethering, and the complication rates families should expect. When to choose observation or a brace instead is covered in the article on scoliosis treatment thresholds, and the condition as a whole in the complete guide to adolescent idiopathic scoliosis.

Which adolescents need scoliosis surgery?

Dr. Miglani operates on two groups of adolescents:

• Skeletally immature children with curves of more than 40 to 45 degrees and a clinically obvious deformity. These curves are likely to progress to a severe deformity, and a brace is unlikely to stop them.
• Skeletally mature adolescents whose curve already exceeds 45 degrees, causes a clinical problem, and who want the deformity corrected.

Earlier correction is better. The more severe a curve becomes, the harder it is to correct, the greater the morbidity and the higher the chance of complications. Left alone, curves over 45 degrees in growing children progress, and in adult life they can cause back and leg pain, nerve compression and, once beyond 70 to 80 degrees, restriction of heart and lung function.

The modern operation: posterior fusion with pedicle screws

The principle is to correct the deformity and fuse the spine so that it cannot progress again. Combined anterior and posterior approaches, or anterior surgery alone, were used more widely in the past. The leading technique now is posterior fusion:

1. Pedicle screws are placed at all levels of the involved vertebrae, on both sides. A pedicle is the strong bony bridge between the back of the vertebra and its body.
2. Two rods, one on each side, are attached to the screws.
3. Correction is achieved by compressing the convex side and distracting the concave side in a controlled way.
4. Derotation manoeuvres correct the rotation of the vertebral bodies, especially near the apex of the curve (the most rotated vertebra, at its centre).
5. Fusion is achieved with bone graft and local bone, so the corrected segment heals into a single solid unit.

Why pedicle screws changed outcomes

Dr. Miglani explained that pedicle screws hold all three columns of the vertebra, from the posterior elements through the pedicle into the vertebral body. That three-column grip makes the construct rigid enough to withstand the corrective forces and creates a solid fixation, with less chance of non-union or pseudarthrosis (a failed fusion that leaves a false joint). Another practical gain is that patients do not need a brace after surgery.

Planning the spinal fusion: which levels to include

Choosing where the fusion starts and stops is the core of surgical planning. Dr. Miglani assesses:

• The apex and extent of the deformity, meaning how many levels the curve involves.
• Any local kyphosis within the curve.
• Shoulder levels. Broadly, if the higher shoulder is on the convex side of the thoracic curve, the fusion extends up to the fourth thoracic vertebra (T4). If the higher shoulder is on the concave side, the fusion must go higher, to about T1 or T2.
• The tilt of the fourth lumbar vertebra (L4), which helps decide whether the fusion must extend lower, even to the pelvis with fixation into the ilium.
• Lumbar alignment and how correctable the lumbar curve is.
• The relationship between the thoracic and thoracolumbar curve angles.
• Coronal balance, judged by whether the seventh cervical vertebra (C7) is shifted sideways relative to the sacrum, together with the translation and rotation of the apical vertebra.

Each of these shapes a plan that is specific to the individual curve. The bending X-rays taken at diagnosis, described in the article on scoliosis diagnosis, supply much of this information.

How scoliosis instrumentation evolved

Dr. Miglani traced the history of scoliosis implants to explain why today's construct looks the way it does. Each generation solved a problem left by the one before.

The Harrington rod

The Harrington system stretched out the concave side of the curve. Hooks were placed in the uppermost and lowermost vertebrae of the curve, and a ratcheted rod between them was used to distract the concavity. The approach had two major shortcomings. It did not correct the rotational deformity, so the ribs remained prominent and the concavity was only partly corrected. And because the correction relied on distraction, it also stretched the spinal cord, with a high risk of complications including neurological deficit.

Luque rods and sublaminar wiring

The next step held each vertebra individually, using Luque rods with wires passed under the lamina (the bony arch at the back of the spinal canal). This was better than the Harrington system, but passing wires beneath the lamina risked injury to the dura (the membrane covering the spinal cord), cerebrospinal fluid leaks and neurological deficit. It still could not control rotation properly, the fixation was not solid enough for large corrections, and it could not be used where a laminectomy was needed, because the lamina must be intact for the wires.

The Cotrel-Dubousset system

The Cotrel-Dubousset (CD) system introduced the principle of segmental correction with double rods, and its descendants are the constructs used worldwide today. The original CD system relied substantially on hooks; current practice has largely dropped hooks in favour of pedicle screws at most levels, double rods, controlled compression and distraction, and derotation near the apex.

Anterior surgery and growth-friendly tethering

Posterior instrumentation is used for the large majority of cases worldwide, but anterior surgery still has a place.

Anterior instrumentation

In anterior surgery the spine is approached from the front. The discs are removed and screws placed in the vertebral bodies are compressed to correct the curve at the apex. For longer curves this is sometimes combined with posterior instrumentation. The advantages are better correction through an anterior release of the spine, smaller and more cosmetic scars, and the involvement of fewer vertebrae. Dr. Miglani noted that for thoracolumbar curves the anterior route is often said to be preferable, because a posterior correction would need fixation across many more levels than an anterior derotation, which corrects the spine well. Anterior instrumentation is now used much less, probably because of approach-related issues.

Vertebral body tethering

A newer anterior technique avoids fusion altogether. Known as anterior vertebral body tethering, it uses screws placed in the vertebral bodies near the apex of the curve, joined by a flexible cord on the convex side. The cord restrains growth on the convex side while the concave side continues to grow, so the spine keeps growing, is not fused, and the curve corrects gradually. It suits flexible curves that correct on the bending films. Tethering is generally reserved for children with growth remaining, and its long-term results are still being established.

What are the risks of scoliosis surgery?

Dr. Miglani was direct that nothing is 100% safe, but that the complication rates of adolescent scoliosis surgery are low, similar to other routine operations and lower than those of adult spinal deformity correction. The figures he gave:

Superior mesenteric artery syndrome is a narrowing of the angle between the aorta and the superior mesenteric artery that can compress the duodenum after a spine is straightened, causing vomiting and feeding difficulty. It is usually managed without surgery.

Neuromonitoring as the safety net

Dr. Miglani routinely uses intraoperative neuromonitoring, which tracks spinal cord and nerve function electrically throughout the operation, when correcting deformities, especially curves of more than 60 to 70 degrees. The system stays on for the whole procedure, and his team checks it after every screw and after every corrective manoeuvre. He credits this practice with keeping his neurological complication rate below 1%, including nerve root injuries. For a fuller account of how monitoring and other safeguards fit together, see Dr. S. K. Rajan's guide to spine surgery safety.

Late infection around implants

Any metal implant in the body carries a lifelong possibility of becoming infected from a systemic infection elsewhere. Dr. Miglani stressed that the risk with scoliosis implants is no higher than with any plate, nail or rod used for a fracture. It is present, but it is not specific to scoliosis surgery.

Why centre volume matters

His final point was about where surgery is done. Centres that perform these operations in high volume have lower complication rates and better results, and the surgery becomes more cost-effective. For patients travelling for treatment, the number of deformity corrections a team performs each year is a meaningful selection criterion. The cost of scoliosis correction surgery can be reviewed separately, and complex or previously operated curves are discussed in Dr. Puneet Girdhar's article on revision spine surgery and neglected deformity. Spinal tuberculosis, scoliosis correction and children's spine surgery are covered in Dr. S. K. Rajan's article on spinal TB surgery and children's spines.

Questions from attending doctors on heredity, follow-up intervals and exercises are answered in the Live Discussion from this masterclass. More about Dr. Miglani's spine and deformity practice is on his doctor profile, and related topics are on the orthopaedics specialty hub.