Anterior instrumented fusion for AIS

Indications

Suitable for single thoracic and lumbar deformities with flexible compensatory curves, specifically

Lenke type 1 curvatures

Degree of Scoliosis:

Surgical correction is indicated with a Cobb angle of 40 to 50 degrees.

It is ideal for single thoracic curves (Lenke type 1 A–C) with pronounced hypokyphosis (T5–12 sagittal modifier—or N).

However, it should not be applied in primarily hyperkyphotic cases (which are rare).

Lenke type 5 curvatures

Degree of Scoliosis:

Surgical correction is indicated with an angle of 35 to 40 degrees.

Patient Age:

It is generally not recommended for very young children who tend to develop hyperkyphosis during further growth due to the anterior tethering effect of the procedure.

Other Factors:

The decision also depends on the age of the patient, the expected further progression, and the cosmetic impairment (such as a rib hump).

Advantages (Pros)

Correction and Derotation:

Achieves complete correction of the deformity in all three planes with high construct stability.

Provides excellent results in coronal plane correction.
Is superior in the restoration of the sagittal profile and apical derotation.

Derotation is more effective in Lenke type 5 curves.

Allows for powerful derotation of the apical vertebrae in thoracolumbar/lumbar curves.

Offers excellent rib hump correction, which has been shown to be better than posterior correction procedures.

Fusion Length:

Fusion is shorter compared to posterior correction, which is a significant advantage, especially in lumbar segments.

To preserve mobility and distribute loads, potentially

Reducing early disc degeneration in remaining mobile segments.
Reduce low back pain

in Anterior thoracic fusion plan will be to fuse from End to End vertebrae; In posterior approaches plan will be to fuse from Stable to stable vertebrae

Stability and Outcomes:

High stability of the construct.

Maintains thoracic curve correction, leading to stable spontaneous correction of the second lumbar curve over time.

The pseudarthrosis rate decreased with improved techniques.

Physiological Restoration:

Can correct hypokyphosis and restore a physiological sagittal profile.
An aggressive anterior release with shortening of the anterior column can lead to spontaneous correction of scoliosis and restoration of thoracic kyphosis.

Disadvantages (Cons)

Pulmonary Function:

Pulmonary function is impaired postoperatively due to the opening of the chest wall.
However, pulmonary function recovers within a few months to two years, becoming comparable to preoperative values.

Hyperkyphosis Risk:

Since the anterior correction is kyphogenic (shortens the anterior column), it should not be applied in primarily hyperkyphotic cases.
There is a risk of developing hyperkyphosis during further growth in very young patients with high growth potential.

Surgical Morbidity (for Thoracoscopic approach):

While video-assisted thoracoscopic surgery aimed for reduced morbidity, some studies found blood loss and operation time to be equal or even higher compared to open thoracotomy.

Potential for Degenerative Disc Disease:

While aiming for shorter fusion, the stress on the remaining mobile segments might be higher, which may result in an increased rate of degenerative disc disease over a lifetime.

General Principles

Thoracic Curves (Lenke Type 1)

Fusion Extent:

Correction and fusion are typically performed from end vertebra to end vertebra.

For common Lenke 1 curves,

The uppermost instrumented vertebra is T5 or T6,
The lowest instrumented vertebra is T11, T12, or L1.

Patient Positioning:

The patient is placed on a hinged table (with the hinge at the curve's apex) in the lateral position, with the convexity of the curve facing upwards.

Surgical Approach:

A single skin incision is made.
A double thoracotomy is performed:

the upper incision is usually between the 4th and 5th or 5th and 6th ribs, with distal osteotomy of the rib.

The lower incision is typically four rib spaces lower

This approach provides unobstructed access to the disc spaces and a clear view of the posterior ligaments.

Disc and Rib Management:

Rib heads overlapping the discs are removed.
Depending on the severity of the rib hump, the proximal parts of the ribs may be resected.
Discs are completely removed, including the contralateral and posterior annulus, to achieve sufficient segmental mobility for correction.
In very rigid cases, the longitudinal fibres of the posterior longitudinal ligament should be partially disrupted by distraction.
Removal of discs shortens the anterior column of the spine, which helps restore a physiological thoracic kyphosis.
In severe hypokyphosis, the convex and anterior parts of the endplates should also be removed to reinforce the kyphotic effect.

Screw Insertion:

Screws are inserted into the centre of the vertebral body.
They are placed parallel to the endplates and, accounting for the rotation of each vertebra, parallel to the posterior wall.

Correction Manoeuvres:

Initial correction is achieved by setting the operating room table back to a neutral position and applying traction to the patient.
The rod is pre-bent to match the intended sagittal contour.
Further correction is achieved through a

Cantilever technique
Rotation of the pre-bent rod from scoliosis to kyphosis
Final compression.

Grafting:

A structural graft or cage may be used at the lowest fused disc space to prevent junctional thoracolumbar kyphosis.

Lumbar Curves (Lenke Type 5)

Fusion Extent:

Correction and fusion are also typically performed from end vertebra to end vertebra, commonly from T11 to L3.

Surgical Approach:

The approach used is a thoracic-phrenic-lumbotomy, which involves sectioning of the diaphragm close to the costal insertion.

Disc and Screw Management:

After resection of the discs, screws are inserted.

Correction and Stabilisation:

A pre-bent rod (contoured for the intended sagittal profile) is inserted.
Correction is achieved using a cantilever technique during rod insertion and by rotation of the pre-bent rod from scoliosis to lordosis.
Structural spacers (e.g., cages) are inserted into the debrided disc spaces.
Compression is applied via the rod.
Autologous bone or bone substitutes are added for bony fusion.

Instrumentation

Fixation can be performed with single or double rod instrumentation, as follow-up studies have shown no significant difference in outcomes between them.

Postoperative Care

Patients are typically mobilised on the first postoperative day.

A brace is not necessary.

Patients are allowed to begin well-controlled sports (e.g., jogging, swimming, bicycling) three months after surgery.

Full activity may be resumed six months after surgery.