Surgical management of LOIS

Indication

Can change the underlying spinal shape and the cosmetic appearance.

A curve of less than 40° is unlikely to require surgical treatment on the grounds of poor cosmesis.

Aim

To prevent progression

Minimising the future risk of increasing deformity

Formation of a stable and well-balanced spine

While preserving as many motion segments as possible.

Maximum safe cosmetic correction

Cosmetic correction defined as

Level shoulders
Centralisation of the trunk with balanced waist creases
Correction of spinal axial rotation to reduce the rib or loin prominence.

Improving cardiopulmonary function

only in very severe curves

Fusion levels

Info from AO spine, Baghdadi 2023)

Lenke’s orginal theorem. Now surgeons are trying to save levels therefore this is slowly going out of fashion

At least fuse all structural curves from the upper End vertebrae to the lower End vertebrae).
Avoid ending the fusion at the apex of kyphosis.

Mod_2_Determination_of_instrumentation_levels_in_AIS_M_Loibl.pdf

2375.8KB

Trobisch 2013

Lenke Curve Type	Description	Selective Thoracic Fusion	Upper Instrumented Vertebra	Lower Instrumented Vertebra
1	Main thoracic	Yes. Lumbar fusion is optional in modifier C curves with significant rotation.	T2 for preoperative left shoulder elevation, T3 for preoperative level shoulders, T4 for preoperative left shoulder depression	Vertebra merely touching the CSVL for modifier A curves. Proximal stable vertebra (ie, at the distal end of the thoracic curve) for modifier B and C curves.
2	Double thoracic	Yes. Lumbar fusion is optional in modifier C curves with significant rotation.	T2	Vertebra merely touching the CSVL for modifier A curves. Proximal stable vertebra (ie, at the distal end of the thoracic curve) for modifier B and C curves.
3	Double major	Not in most cases. Optional in select curves without significant lumbar rotation with the thoracic curve being much more severe and rigid.	T2 for preoperative left shoulder elevation, T3 for preoperative level shoulders, T4 for preoperative left shoulder depression	Distal EV. Can fuse to the vertebra proximal to the EV if EV–1 crosses the midline on convex bending radiograph and shows significantly reduced rotation. Rarely below L3, but mild postoperative disk wedging can occur. Sometimes L4 if a level disk is to be achieved.
4	Triple major	No	T2	Distal EV. Can fuse to the vertebra proximal to the EV if EV–1 crosses the midline on convex bending radiograph and shows significantly reduced rotation. Rarely below L3, but mild postoperative disk wedging can occur. Sometimes L4 if a level disk is to be achieved.
5	Thoracolumbar/lumbar	Selective lumbar fusion is optional if rib hump deformity is not a concern	Upper EV. Should not be at the apex of the thoracic kyphosis.	Distal EV. Can fuse to the vertebra proximal to the EV if EV–1 crosses the midline on convex bending radiograph and shows significantly reduced rotation. Rarely below L3, but mild postoperative disk wedging can occur. Sometimes L4 if a level disk is to be achieved.
6	Thoracolumbar/lumbar (main thoracic)	No	T2 for preoperative left shoulder elevation, T3 for preoperative level shoulders, T4 for preoperative left shoulder depression	Distal EV. Can fuse to the vertebra proximal to the EV if EV–1 crosses the midline on convex bending radiograph and shows significantly reduced rotation. Rarely below L3, but mild postoperative disk wedging can occur. Sometimes L4 if a level disk is to be achieved.

Upper vertebral fusion level

Decision made

Based on

Prevent postoperative shoulder imbalance or T1 Tilt

General

Shoulder balance is an important post-operative outcome measure from a cosmetic standpoint, especially in adolescents.
T1 tilt and shoulder balance are key independent variables for Lenke types 1 and 2 curves
Shoulder balance improves years after fusion, regardless of whether or not level shoulders are achieved at the time of surgery

due to patient’s own compensatory mechanism

If MSB is restored, the LSB will improve, but if the MSB is not corrected, the improvements in LSB are unpredictable.
Average individual without AIS may have up to 1 cm of shoulder imbalance, which is neither noticed nor causes symptoms.

Correction of the deformity will elevate the shoulder to the opposite of the apex of the main curve.

Therefore, when the apex of the major curve and the elevated shoulder are on the same side, a lower UIV (T4-5 for Lenke 1, 3, and 6, and T3 for Lenke 2, 4) is appropriate.

If T1 tilt and shoulder balance would worsen with correction of the main curve (e.g., both tilted right, leading to left shoulder elevation), then the upper thoracic curve should be included in the fusion.

If T1 tilt and shoulder balance are in opposite directions, partial inclusion of the thoracic curve (e.g., T2 or T3) may be possible

Example:

Assume it is a right sided curve-which is the most common; otherwise vice versa

Right shoulder high fuse to T4

When the apex of the major curve and the elevated shoulder are on the same side, a lower UIV (T4-5 for Lenke 1, 3, and 6, and T3 for Lenke 2, 4)
When the apex of the major curve is opposite to the elevated shoulder, go higher (T2-3 for Lenke 1,3, and 6, and T2 for Lenke 2, 4).
In Lenke 5, UIV = UEV, unless it coincides with the apex of the kyphosis.

Left shoulder high fuse to T2

Proximal curve progression

Skeletal Maturity: Skeletal immaturity (indicated by open triradiate cartilage) is a risk factor for proximal adding on

Proximal junctional kyphosis (PJK)

PJK can occur in a substantial number of cases (up to 27%), though often it is only a radiographic finding, with long-term implications that are unknown.

Structural vs nonstructural PT curves

For nonstructural PT curves, some studies suggest that including them in the fusion offers no added radiographic advantage, especially if shoulder balance is not a specific concern

Not based on

Motion preservation is less of a factor for the UIV

As the thoracic spine is inherently rigid due to the rib cage and sternum
Unlike the distal fusion levels,

Lenke et al. (1994) criteria for PT curve inclusion:

Curve magnitude >30° OR
Inability to correct below 25° on side bending OR
Apical rotation ≥ Nash-Moe grade 1 OR
Apical vertebral translation (AVT) >1 cm OR
Elevation of the left shoulder or T1 tilt into the concavity of the PT curve OR
Location of the transitional vertebra between the two thoracic curves at T6 or lower

Decision table

Lenke type	Recommendation	Notes
1, 3, 6	Right shoulder high: T4 Shoulders level: T4 Left shoulder high: T3	• Do not stop at the apex of PT (stop > 1 level above or below apex) • Do not stop at the apex of the kyphosis • Shoulder balance improves regardless of the UIV, given a reasonable MSB • Use a temporary right rod in Lenke 2
2, 4	T2 (T3 acceptable if shoulders level or right shoulder up)	ㅤ
5	UEV or UEV + 1	Fuse MT if TL kyphosis present ensuring UIV is not at the apex of the thoracic kyphosis

PT, proximal thoracic curve; MT, main thoracic curve; TL, thoracolumbar; UEV, upper end vertebra; SV, stable vertebra; LTV, last touched vertebra; LSTV, last substantially touched vertebra; LIV, lower instrumented vertebra; UIV, upper instrumented vertebra

Lower vertebral fusion level

General

Farther the LIV is from the CSVL, the risk of coronal decompression higher
Fusion to the SV will lead to an unnecessarily long fusion

Improved curve correction
Reduced postoperative immobilisation time
Preserved motion segments using shorter fusions

In lumbar fusions: Multiple theories (none conclusive)

Harrington “stable zone”

Area between two lines erected vertically from the lumbosacral joints.
The LIV within this zone was acceptable

There is substantial disagreement between surgeons when identifying the NV.
Fusing down to the NV, i.e., the most proximal vertebra caudal to the main curve with no rotation.

Newton

The vertebrae “last touched” by the CSVL caudal to the major curve could be used to determine the appropriate LIV

Dubousset

LIV = NV
Flexible disc (>10 deg) between planned fused and not fused spine
Absence of kyphosis between supra-jacent and infra-jacent disc (on lateral view)

Use Suk Classification to decide.

Suk et al. hypothesised that derotation manoeuvres might bring cephalad vertebrae into the stable zone, allowing shorter fusions

L3 vs. L4 decision:

If possible try to stop at L3 in Lenke type 3 and 4 to preserve lumbar motion segments:

In thoracic fusions, SV, LTV, and LSTV are often safe choices for the LIV.

Successful derotation and coronal balance of the LIV are important determinants of long-term success.

To achieve this, the larger the lumbar curve, the more distal the LIV should be.
For example, if a Lenke 1C is to undergo STF, SV + 1 provides better control over lumbar curve derotation.

Do not fuse to

L5 level because

Cochran found increase incidence of low back pain with fusion to L5, and to a lesser extent L4.
Puts too much stress on the L5/S1 disc can cause ASD

Pelvis

it is almost never required to fuse to the pelvis in idiopathic scoliosis

Lenke type	Recommendation	Notes
1, 2, Selective thoracic fusion in 3	Lumbar modifiers A/B: SV or SV-1 (Usually T11-12) Lumbar modifier C: LTV (Usually T12-L1)	• Watch out for the Lenke 1AR (A Main thoracic major curve with a right-tilted lumbar apex modifier "A,”): LTV or LSTV decreases the risk for adding on • The goal is a derotated, level LIV
4, 5, 6	L3 if: -at least one level below the lumbar apex and, -L3-4 disk opens to the concave side on bending films Otherwise, L4	• Patient/family are counselled regarding the risks and benefits of L3 vs. L4 as the LIV, and a shared, informed decision is made

Selective fusion

Definition: Fusion of either the thoracic or thoracolumbar/lumbar curve ONLY when the associated compensatory curve crosses the midline.

More applicable for skeletal matured spine

Immature spine → more potential to grow → inc. risk of post op decompensation.

Spontaneous correction

Compensatory, nonstructural curvature can achieve up to 70% spontaneous correction with no instrumentation, following instrumentation of the structural curvature. Thus, the major curve must be identified first
Spontaneous coronal curve correction

Occurs in

53% to 70% for non-instrumented lumbar curves
36% to 41% for non-instrumented thoracic curves.

Factors influencing this correction include

Surgical approach (anterior or posterior)
Skeletal maturity
Compensatory curve flexibility
Sex
Instrumentation
Surgical technique.

Spontaneous axial correction (derotation)

Occurs in

49% for non-instrumented lumbar curves
26% for non-instrumented thoracic curves.

Pros:

Preserving motion segments

Especially important in the lumbar spine.

Shorter operative time
Less bleeding

Cons:

Coronal or sagittal imbalance
Adding on
Coronal decompensation

Selective thoracic fusion (STF)

Definition: as the fusion of only the main thoracic curve in patients with a Lenke 1–3 curve and a lumbar C modifier.

Criteria for selective thoracic fusion (STF): Fischer 2011

Category	Criteria	Notes
Curve type	Lenke 1-4, lumbar modifier C	Lumbar modifiers A and B are generally treated with STF regardless of other criteria
Clinical parameters	Older age	Younger patients (especially with an open triradiate cartilage) have a greater risk for decompensation
ㅤ	Right trunk shift	Pre-operative left trunk shift is a risk factor for decompensation
ㅤ	Rib prominence > lumbar prominence	ㅤ
Radiographic measures	Thoracic to lumbar Cobb angle ratio	Ratio > 1.2 is favorable
Coronal plane	Thoracic to lumbar Apical vertebral translation ratio	Ideally, a smaller, less rotated, less shifted, and more flexible lumbar curve compared to the major thoracic curve
ㅤ	Curve flexibility	ㅤ
ㅤ	Small-moderate lumbar curve size	Lumbar curves > 50-60 degrees are unlikely to correct completely with STF
Sagittal plane	T10-L2 kyphosis < 10	Regional kyphosis is a strong predictor of postoperative DJK
ㅤ	Lordotic disk below the LIV	ㅤ

Selective lumbar fusion (SLF)

Definition: when the thoracic curve is left unfused in a Lenke 5 or 6 curve.

Rarer

Criteria for selective lumbar fusion (STF): Fischer 2011

Category	Criteria	Notes
Curve type	Lenke 5-6, lumbar modifier C	ㅤ
Clinical parameters	Age	Younger patients (especially with an open triradiate cartilage) have a greater risk for decompensation
ㅤ	Left trunk shift	ㅤ
ㅤ	Left shoulder elevation	ㅤ
ㅤ	Right waistline prominent	ㅤ
Radiographic measures	TL/L to thoracic Cobb angle ratio	Ratio > 1.25 is favorable
Coronal plane	TL/L to thoracic apical vertebral translation ratio	Ideally, a smaller, less rotated, less shifted, and more flexible thoracic curve compared to the major thoracolumbar/lumbar curve
ㅤ	Curve flexibility	ㅤ
ㅤ	Thoracic curve size	Thoracic curves > 40 may not correct completely with SLF
Sagittal plane	T10-L2 kyphosis < 10	Regional thoracolumbar kyphosis is a strong predictor of postoperative PJK

Techniques (AO Spine Surgery reference)

360 vs Posterior only

The majority of scoliosis surgery is performed via a posterior approach.
Anterior surgery may be indicated for larger, stiffer curves and is usually combined with posterior fixation.
Choices regarding the precise levels of fusion will be determined by the choice of approach and the philosophy of correction.

Anterior approaches

Deformity correction

Stiff curves need some release to achieve the optimum correction.

All facets joints are released as a means of achieving interfacetal fusions.

Facets and the ligamentum flavum can be removed, as can the intervertebral discs, giving additional flexibility.

Rigid curves require a more extensive osteotomy or complete resection of the vertebral column.

Rods

AIS surgery differs substantially from adult deformity surgery, meaning desirable rod biomechanical properties may also differ.
The theory of "stress shielding" (where high-stiffness rods decrease physiological stress on bone, potentially leading to resorption) may apply to elderly populations, but has not shown clinical relevance in AIS surgery.
Stiffer constructs, minimally weakened by intraoperative contouring, likely best achieve primary objectives of curve correction and sagittal restoration.

This may explain the increasing popularity of CoCr and higher-diameter rods.

High-quality studies are needed to draw firm conclusions.

Key-Vertebral Screws Strategy (KVSS)

Li 2016.pdf

2.6 MB

Cons of Pedicle screws

Carry potential risks for soft tissue and neural injury
Increase healthcare costs

KVSS Principle: Screws are placed at important strategic points to allow curve correction while minimising screw numbers.

One set of screws bilaterally at the upper and lower ends of the fusion block.
One screw at the apical vertebra on the convex side.
One screw each on the adjacent upper and lower vertebrae on the concave side.
This strategy ensures control of the ends of the curve and its apex.
Occasionally, hooks replaced screws at the upper end due to insertion difficulty.

Outcome: (see FBCI and FBR)

KVSS provided very similar (o historical multilevel pedicle screw constructs)

Correction rates (71.2% vs 69.3%)
FBCI (119% vs 117%)

Standing coronal radiograph of a 12-year-old female patient with AIS and a main thoracic curve of 50.0 degrees from T5 to T11.

Standing sagittal alignment was 16 degrees from T5-T12.

Fulcrum bending radiograph of the patient demonstrated correction of the thoracic curve to 9.4 degrees. The fulcrum bending flexibility was 81.2%.

Immediate postoperative radiograph illustrated curve correction to 5.0 degrees. The curve correction rate was 90% and the FBCI was 110.8%.

Immediate postoperative sagittal radiograph illustrating the sagittal alignment of the patient at 27.1 degrees, which was maintained on last follow-up.

Managing Rib Hump Deformity:

Most significant cosmetic concerns in Adolescent Idiopathic Scoliosis (AIS)

Patient satisfaction after surgery is significantly impacted by the correction of the rib hump.

Aetiology of rib hump

Caused by the axial rotation of the scoliotic curve.

Corrective Techniques:

Surgical techniques such as simple rod derotation (SRD) and direct vertebral body derotation (DVBD) are used to correct the deformity.
DVBD utilises three-column vertebral control through segmental or en bloc manoeuvres to reduce rib prominence.

The choice between segmental and en bloc derotation techniques for DVBD does not show a significant difference in postoperative rib prominence correction.

Thoracoplasty, which involves removing pieces from several consecutive ribs, can be performed to improve the correction of the rib hump.

Role of Thoracoplasty:

Thoracoplasty improves thoracic flexibility (when done on the concave side) and enhances rib hump correction (when done on the convex side).
Convex anterior thoracoplasty provides a more predictable reduction in rib prominence because it allows for the removal of rib heads across multiple levels, which reduces the sharp gibbus of the chest wall.
The excised ribs from a thoracoplasty can be used as bone grafts for the spinal fusion.
In severe cases, thoracoplasty can be effective in reducing the risk of recurrence of rib prominence and apical vertebral rotation.

Minimally Invasive Scoliosis Surgery (MISS)

Goal:

Aims to minimise surgical trauma by using smaller incisions and muscle-sparing techniques, theoretically leading to reduced morbidity and better cosmetic outcomes.

Pros

Blood Loss:

MISS is associated with significantly lower estimated blood loss (average of 271 mL) compared to open surgery (527 mL), reducing the need for blood transfusions.

Patient Recovery: Patients undergoing MISS may experience a shorter hospital stay (5.1 days vs. 6.4 days) and less postoperative pain due to reduced soft tissue damage.

Cons

Surgical Time:

Operative time is consistently longer for MISS (average of 380 minutes) compared to open surgery (302 minutes), likely due to the technical challenges of the approach.

MISS is more technically demanding and requires specialised training.
It may be less effective for correcting large or rigid curves.

Outcomes:

Comparative analyses show that both MISS and open surgery achieve similar curve correction rates (approximately 73.2% for MISS vs. 76.7% for open surgery), with no significant difference in postoperative coronal or sagittal balance.

Risk and complications

To reduce risk

Preoperative planning

Patient blood management

Tranexamic acid
Cell salvage

Spinal cord monitoring using somatosensory evoked potential (SSEP) and motor- evoked potentials (MEPs)

neurologic event defined as drop in amplitude of > 50%
if neurologic injury occurs intraoperatively consider

Check for technical problems
Check blood pressure and elevate if low
Check hemoglobin and transfuse as necessary
lessen/reverse correction
Administer Stagnaras wake up test
remove instrumentation if the spine is stable

Complications

Neurologic injury

Paraplegia is 1:1000
Increased risk with kyphosis, excessive correction, and sublaminar wires

Pseudoarthrosis (1-2%)

Presents as late pain, deformity progression, and hardware failure
An asymptomatic pseudarthrosis with no pain and no loss of correction should be observed

Infection (1-2%)

Presents as late pain
Incision often looks clean
Propionibacterium acnes most common organism for delayed infection (requires 2 weeks for culture incubation)
attempt I&D with maintenance of hardware if not loose and within 6 months

Crankshaft phenomenon

Rotational deformity of the spine created by continued anterior spinal growth in the setting of a posterior spinal fusion

Can occur in very young patients when PSF is performed alone and the anterior column is allowed continued growth

Avoided by performing anterior diskectomy and fusion with posterior fusion in very young patients

SMA syndrome (superior mesenteric artery [SMA] syndrome)

Compression of 3rd part of duodenum due to narrowing of the space between SMA and aorta
SMA arises from anterior aspect of aorta at level of L1 vertebrae
Presents with

symptoms of bowel obstruction in first postoperative week

associated with electrolyte abnormalities
nausea, bilious vomiting, weight loss

Risk factors

Height percentile <50%; weight percentile < 25%
Sagittal kyphosis

Treat with NG tube and IV fluids

Hardware failure

0.64% to 1.37% of cases.
late rod breakage can signify a pseudarthrosis
Example instrumentation failure, rod fractures, and screw loosening
Due to

Screw-Related Complications (Pullout, Loosening, Breakout)

High Stress on Screw-Bone Interface: Many corrective techniques place enormous stress on the interface between the pedicle screw and the bone.

Cantilever and Vertebral Translation: Both techniques can generate significant stress, requiring slow, sequential reduction with the load shared across multiple screws to minimise the risk of pullout. Surgeons must be vigilant for signs of screw pullout, especially in patients with poor bone quality or dysplastic pedicles.
In Situ Rod Contouring: This technique places significant stress on the bone-implant interface, increasing the risk of implant failure if excessive force is applied.
Excessive Rod Stiffness: Rods that are too stiff for the patient's bone quality can surpass the strength of the bone-implant interface, leading to implant pullout.

Screw Type:

Monoaxial Screws: While providing rigid fixation ideal for derotation, their fixed head design increases stress at the bone-screw interface, raising the risk of fixation failure.

Derotation Techniques:

Segmental Derotation: Applying corrective forces to individual vertebrae sequentially can risk screw breakout due to the concentration of force on single screws.
En Bloc Derotation: This technique distributes corrective forces over multiple vertebrae at once, which reduces stress on individual screws and lowers the risk of pullout.

Temporary Internal Distraction: The use of temporary distraction rods is associated with an increased risk of anchor failure, and these anchors often cannot be reused as permanent fixation points.

Rod-Related Complications (Fracture, Dislodgement)

Rod Fracture:

This is identified as a potential implant-related complication, often resulting from excessive mechanical stress or inadequate fixation.

Rod Dislodgement:

This has been reported as a specific complication in early cases of Minimally Invasive Scoliosis Surgery (MISS).

Rod Material and Diameter:

5.5 mm rods were associated with lower reoperation rates (1%) compared to 6 mm rods (6%).
Excessive rod stiffness can contribute to catastrophic failure of the construct.
Conversely, overly flexible rods, such as those made from titanium, may recoil from their contoured shape, compromising correction.

Complications Related to LIV

Postoperative Disk Wedging:

Can occur, particularly with anterior instrumentation, and its long-term effect is unknown.

Fusing to a vertebra just proximal to the horizontal disk on a bending radiograph might prevent this

Preoperative (A and B) and 1-year postoperative (C) PA radiographs of a 15-year-old girl with a 63° thoracic curve and a 48° lumbar curve. This is a double major curve (ie, Lenke type 3B). The thoracic curve bends to 52° on the right- bending radiograph (A), and the lumbar curve bends to 27° on the left-bending radiograph (B). L1 is the stable vertebra of the thoracic curve, and T12 is the lowest vertebra touching the central sacral vertical line (CSVL). L5 is the stable vertebra of the lumbar curve, and L4 is the lowest one touching the CSVL. L1 and L5 are neutral vertebrae. The horizontal disk on the left-bending radiograph is L3/4 (panel B). Clavicular height was−1.5 cm. There was no segmental kyphosis of >20°. Fusion to L3 (ie, vertebra just proximal to the horizontal disk on left-bending radiograph) likely would have prevented postoperative disk wedging.

Distal Junctional Kyphosis (DJK):

Can lead to increased mechanical stress on adjacent segments and sagittal imbalance.
Risk factors include

Ending the fusion at the EV
Preoperative DJK (thoracolumbar kyphosis >20°).

Extending instrumentation one additional level distal to the EV seems to prevent DJK, especially in patients with preoperative DJK.

Loss of Lumbar Lordosis:

Aka: Flat back syndrome
Early Fatigability and back pain due to loss of lumbar lordosis
Rare now that segmental instrumentation addresses sagittal plane deformities
Decreased incidence with rod contouring in the sagittal plane and compression/distraction techniques
Treat with revision surgery utilizing posterior closing wedge osteotomies
Anterior releases prior to osteotomies aid in maintenance of correction
Risk factors include

Iatrogenic flattening of thoracic kyphosis
High preoperative lumbar lordosis.