MIS deformity

Categories of MIS in ASD

Direct or indirect decompression.

Circumferential MIS (cMIS)

Hybrid surgery, which typically includes an MIS anterior reconstruction followed by traditional posterior open techniques.

MISDEF (Minimally Invasive Spinal Deformity Surgery Algorithm ) -2 algorithm

Characteristic	Class I	Class II	Class III	Class IV
Primary Complaint	Significant radicular pain > Axial back pain Radiculopathy and Neurogenic claudication Main complaints stem from compression of neural elements.	Axial back pain is more dominant	Significant axial back and leg pain	Significant axial back and leg pain
Sagittal Vertical Axis (SVA)	< 6 cm positive.	May have an increased sagittal malalignment.	Increased	Increased
LL-PI Mismatch	< 10°.	10°-30°.	> 30°.	> 30°.
Pelvic Tilt (PT)	Under 25°.	Within the range of normal.	Increased.	Increased.
Coronal Cobb Angle	< 20°.	> 20°.	> 20°.	> 20°.
Thoracic Kyphosis	Not explicitly stated.	Less than 60°.	May be over 60°.	May be over 60°.
Thoracolumbar Junction Kyphosis	Not explicitly stated.	Less than 10°.	May be over 10°.	May be over 10°.
Fixed Deformity	Minimal, if any, sagittal plane deformity.	Do not have a fixed deformity.	May have fixed deformities.	May have fixed deformities.
Prior Surgery/ Hardware/ Fusion Levels	Not explicitly stated.	Not explicitly stated.	No preexisting hardware that needs to be revised; Not had more than 5 levels of prior fusion that included L5–S1.	May have had prior surgery with instrumentation that needs to be revised; OR have instrumentation of 5 levels or more of prior fusion including L5–S1.
Segments Requiring Treatment	Not explicitly stated.	Not explicitly stated.	Should not need more than 10 segments.	Require more than 10 segments to be instrumented.
Recommended Surgical Treatment/Techniques	Minimally invasive decompression with or without a focal fusion at the level of interest.	MIS multilevel fusion techniques addressing the area of lumbar deformity.	Can be treated with open techniques; Circumferential MIS (cMIS) techniques such as anterior column release may also be an option for experienced surgeons.	Open deformity surgery.
Eligibility for MIS	Yes.	Yes.	Yes, for experienced surgeons and within segment limits.	Not candidates for MIS techniques.

Some of the data from the table is a combined from MISDEF-1 and MISDEF-2

Outcomes

Radiological

MIS for ASD has shown to improve global alignment, though not to the same degree as open surgery

Due to limitations in aggressive soft tissue and osseous releases.

Maximum correction with cMIS: (over multiple levels)

Coronal Cobb angle correction: 61%
Maximum sagittal vertical axis (SVA) correction of 89 mm.

Sagittal correction of pelvic incidence and lumbar lordosis mismatch (PI-LL) within 10 degrees was only achieved if the preoperative PI-LL mismatch was 38 degrees or less.
However, patients with moderate deformities (SVA 4.5-9 cm) did show improvement in HRQOL at 2 years,

even without complete sagittal realignment.

Patient Reported Outcomes (PROs)

In ASD: Restoration of global alignment correlates with improved HRQOL metrics.
While hybrid surgery often achieved greater PI-LL change and open surgery greater SVA correction, there were no significant differences in pre- and postoperative Oswestry Disability Index (ODI) and visual analog scores (VAS) at 1 year across MIS, hybrid, and open groups.

This suggests that ideal radiographic alignment may not be the sole factor for PRO improvement.

MIS techniques may allow older, high-risk patients to undergo surgery more safely, with MCID achieved for ODI, VAS back, and leg scores.

Complication Rates:

MIS and hybrid surgery had

fewer major complications (14% vs 45%).
MIS also resulted in less blood loss and reduced need for transfusions.

Hamilton 2016 A retrospective study showed

Lower overall complication rates in MIS (31.7%) vs. open (60.3%),
Higher re-operation rates in hybrid (27%) than MIS (11.1%) and open (12%).

Cause for revision in hybrid/open was

Neurological deficits
Pseudoarthrosis in MIS

cMIS was associated with reduced ICU length of stay (0.6 days vs. 1.2 days) compared to open, with no difference in hospital LOS.

cMIS and hybrid had more interbody fusions (4.3 and 4.1 vs. 1.9).

cMIS was associated with significantly fewer levels fused (4.8 vs. 10.1) without differences in ODI and VAS scores at 2 years.

Proximal Junctional Kyphosis (PJK) and Failure (PJF):

PJK rates vary from 5% to 46%.
MIS approaches can avoid posterior soft tissue/ligamentous disruption that contributes to PJK.
Lateral Lumbar Interbody Fusion (LLIF) showed lower

PJK rates (22.4% vs. open posterior open 38.9%)
PJF rates (8.6% vs. open posterior surgery 15.3%)

ExLIF: 0%
ACR: 30%
ACR + open posterior column osteotomies (PCO): 42.9%

Risk factors for PJK/PJF include open posterior releases, upper-instrumented-vertebra in the lower thoracic spine, severity of preoperative deformity, and degree of sagittal correction.
One study found no significant differences in overall postoperative complications, major complications, PJK rates (7.3% overall), or implant failure rates (7.3% overall) between open, hybrid, and MIS approaches.

Cost-Effectiveness

Though initial costs for MIS technologies and implants can be higher, these are offset by fewer complications, reduced blood loss, decreased transfusion needs, and shorter hospital length of stay (LOS).
One study reported lower inpatient costs for MIS (US$269,807) compared to open surgery (US$391,889).
MIS showed approximately 20% reduced costs (about US$50,000) due to operating room time utilisation.
MIS was more cost-effective in 57% of cases when accounting for complication risks.

Limitations of MIS for Deformity

Limitations include inability to achieve as robust radiographic correction as open techniques for severe fixed deformities.
Steep learning curve due to non-traditional surgical corridors and reduced visualisation.
High reliance on technology (navigated instruments, modified fluoroscopy, neuromonitoring, complex instrumentation, microscopes), where failure of any component can cause delays or complications.
Surgeon experience impacts operative time and minor complication rates, with a 47% reduction observed as experience increased.

New techniques developed to bridge the correction gap include:

Anterior Column Realignment (ACR):

To release the anterior longitudinal ligament (ALL) → allowing for placement of hyperlordotic interbody cages (typically 20-30°) to correct severe sagittal imbalance.

ACR showed similar radiographic sagittal correction to pedicle subtraction osteotomies (PSO) but with lower blood loss (1.6 vs 3.6 litres).

"Mini-open" PSO:

Adapts MIS techniques to reduce collateral tissue damage while performing open 3-column osteotomies for severe deformities, showing similar sagittal deformity correction to traditional PSO.