Minimally Invasive Anterior Longitudinal Ligament Release for Anterior Column Realignment

Anterior Column Release: With Great Lordosis Comes Great Risk of Complications-A Case Series

STUDY DESIGN

Retrospective review.

OBJECTIVE

We sought to characterize complications associated with anterior column release (ACR).

SUMMARY OF BACKGROUND DATA

Correction of positive sagittal imbalance was traditionally completed with anterior column grafts or posterior osteotomies. ACR is a minimally invasive technique for addressing sagittal plane deformity by restoring lumbar lordosis.

METHODS

We conducted a retrospective review of consecutive patients who underwent ACR in a prospectively kept database at a tertiary care academic center from January 2012 to December 2018. The prespecified complications were hardware failure (rod fracture, hardware loosening, or screw fracture), proximal junctional kyphosis, ipsilateral thigh numbness, ipsilateral femoral nerve weakness, arterial injury requiring blood transfusion, bowel injury, and abdominal pseudohernia.

RESULTS

Thirty-eight patients were identified. Thirty-five patients had ACR at L3-4, 1 had ACR at L4-5, and 1 patient had ACR at L2-3 and L3-4. Eighteen patients (47.4%) had one of the prespecified complications (10 patients had multiple). Ten patients developed hardware failure (26.3%); 8 patients (21.1%) had rod fracture, 4 (10.5%) had screw fracture, and 1 (2.6%) had screw loosening. At discharge, rates of ipsilateral thigh numbness (37.8%) and hip flexor (37.8%)/quadriceps weakness (29.7%) were the highest. At follow-up, 6 patients (16.2%) had ipsilateral anterolateral thigh numbness, 5 (13.5%) suffered from ipsilateral hip flexion weakness, and 3 patients (5.4%) from ipsilateral quadriceps weakness. Arterial injury occurred in 1 patient (2.7%). Abdominal pseudohernia occurred in 1 patient (2.7%). There were no bowel injuries observed.

CONCLUSIONS

ACR is associated with a higher than initially anticipated risk of neurological complications, hardware failure, and proximal junctional kyphosis.

Early Experience with Prone Lateral Interbody Fusion in Deformity Correction: A Single-Institution Experience

Background/Objectives: Lateral spine surgery offers effective minimally invasive deformity correction, but traditional approaches often involve separate anterior, lateral, and posterior procedures. The prone lateral technique streamlines this process by allowing single-position access for lateral and posterior surgery, potentially benefiting from the lordosing effect of prone positioning. While previous studies have compared prone lateral to direct lateral for adult degenerative diseases, this retrospective review focuses on the outcomes of adult deformity patients undergoing prone lateral interbody fusion. Methods: Ten adult patients underwent single-position prone lateral surgery for spine deformity correction, with a mean follow-up of 18 months. Results: Results showed significant improvements: sagittal vertical axis decreased by 2.4 cm, lumbar lordosis increased by 9.1°, pelvic tilt improved by 3.3°, segmental lordosis across the fusion construct increased by 12.2°, and coronal Cobb angle improved by 6.3°. These benefits remained consistent over the follow-up period. Correlational analysis showed a positive association between improvements in PROs and SVA and SL. When compared to hybrid approaches, prone lateral yielded greater improvements in SVA. Conclusions: Prone lateral surgery demonstrated favorable outcomes with reasonable perioperative risks. However, further research comparing this technique with standard minimally invasive lateral approaches, hybrid, and open approaches is warranted for a comprehensive evaluation.

Oblique anterior column realignment with a mini-open posterior column osteotomy for minimally invasive adult spinal deformity correction: illustrative case

BACKGROUND

Adult spinal deformity (ASD) occurs from progressive anterior column collapse due to disc space desiccation, compression fractures, and autofusion across disc spaces. Anterior column realignment (ACR) is increasingly recognized as a powerful tool to address ASD by progressively lengthening the anterior column through the release of the anterior longitudinal ligament during lateral interbody approaches. Here, we describe the application of minimally invasive ACR through an oblique antepsoas corridor for deformity correction in a patient with adult degenerative scoliosis and significant sagittal imbalance.

OBSERVATIONS

A 65-year-old female with a prior history of L4-5 transforaminal lumbar interbody fusion and morbid obesity presented with refractory, severe low-back and lower-extremity pain. Preoperative radiographs showed significant sagittal imbalance. Computed tomography showed a healed L4-5 fusion and a vacuum disc at L3-4 and L5-S1, whereas magnetic resonance imaging was notable for central canal stenosis at L3-4. The patient was treated with a first-stage L5-S1 lateral anterior lumbar interbody fusion with oblique L2-4 ACR. The second-stage posterior approach consisted of a robot-guided minimally invasive T10-ilium posterior instrumented fusion with a mini-open L2-4 posterior column osteotomy (PCO). Postoperative radiographs showed the restoration of her sagittal balance. There were no complications.

LESSONS

Oblique ACR is a powerful minimally invasive tool for sagittal plane correction. When combined with a mini-open PCO, substantial segmental lordosis can be achieved while eliminating the need for multilevel PCO or invasive three-column osteotomies.

Moderate sagittal plane deformity patients have similar radiographic and functional outcomes with either anterior or posterior surgery

PURPOSE

This study aimed to compare the functional and radiographic outcomes of two surgical interventions for adult spinal deformity (ASD): anterior lumbar interbody fusion with anterior column realignment (ALIF-ACR) and posterior approach using Smith-Peterson osteotomy with transforaminal lumbar interbody fusion and pedicle screw fixation (TLIF-Schwab2).

METHODS

A retrospective cohort study included 61 ASD patients treated surgically between 2019 and 2020 at a single tertiary orthopedic specialty hospital. Patients were divided into two groups: Group 1 (ALIF-ACR, 29 patients) and Group 2 (TLIF-Schwab2, 32 patients). Spinopelvic radiographic parameters and functional outcomes were evaluated at 3, 6, and 12 months postsurgery.

RESULTS

Perioperative outcomes favored the ALIF-ACR group, with significantly smaller blood loss, shorter hospital stay, and operative time. Radiographic and functional outcomes were similar for both groups; however, the ALIF-ACR group did have a greater degree of correction in lumbar lordosis at 12 months. Complication profiles varied, with the ALIF-ACR group experiencing mostly hardware-related complications, while the TLIF-Schwab2 group faced dural tears, wound dehiscence, and proximal junctional kyphosis. Both groups had similar revision rates.

CONCLUSION

Both ALIF-ACR and TLIF-Schwab2 achieved similar radiographic and functional outcomes in ASD patients with moderate sagittal plane deformity at 1-year follow-up. However, the safety profiles of the two techniques differed. Further research is required to optimize patient selection for each surgical approach, aiming to minimize perioperative complications and reoperation rates in this challenging patient population.

Prone position lateral interbody fusion-a narrative review

Background and Objective

Lateral access lumbar interbody fusion is an increasingly popular procedure that allows for anterior column support through discectomy, endplate preparation, and interbody insertion. This procedure was initially described and performed with the patient in the lateral decubitus position. This would typically be followed by repositioning the patient to the prone position for pedicle screw fixation. Increasingly common is the lateral access lumbar interbody fusion in the prone position. This narrative review seeks to summarize the available literature on advantages, disadvantages, and unique features of the prone position lateral access lumbar interbody fusion.

Methods

We performed a narrative review of articles published up to 01 November 2022 through a PubMed search. The search terms "prone lateral spine surgery" and "lateral approach spine surgery" AND "prone position" were used. Articles not available in English were excluded. The search result abstracts were independently reviewed by 2 authors and 28 full text articles were reviewed. Both reviewing authors were orthopedic surgery chief residents.

Key Content and Findings

There are several unique advantages as well as disadvantages to the prone position lateral interbody fusion. Some advantages include ease of placing pedicle screws, simultaneous posterior and lateral access, greater ease in achieving segmental lumbar lordosis, and a relatively safer positioning of the psoas muscle, lumbar plexus, and abdominal structures. Disadvantages include more difficulties with exposure and retraction, as well as visualization, positioning and ergonomics of surgery.

Conclusions

Prone position lateral interbody fusion is an increasingly prevalent and useful surgical technique with several advantages and disadvantages when compared to lateral interbody fusion in the lateral decubitus position. There are several surgical indications and goals for which prone lateral interbody fusion may provide significant benefit when compared to other interbody fusion techniques.

A Modified Anterior Column Realignment With Partial Anterior Longitudinal Ligament Release in Oblique Lateral Interbody Fusion

STUDY DESIGN

Retrospective radiological analysis.

OBJECTIVE

To demonstrate the radiological outcome after a modified anterior column realignment (mACR) with partial anterior longitudinal ligament (ALL) release in oblique lateral interbody fusion (OLIF).

SUMMARY OF BACKGROUND DATA

Anterior column realignment (ACR) remains a powerful sagittal correction technique in minimally invasive adult spinal deformity surgery and is often combined with posterior column osteotomy (PCO) to achieve more lordosis. OLIF is ideal for ACR because the anterior-to-psoas corridor typically involves the anterolateral half of the disk.

METHODS

This study included 112 operated disk levels of 101 consecutive patients who underwent OLIF between L2-L3 and L4-L5 using a 12° lateral cage. The mACR was performed at 73 (65.2%) levels with 30% to 50% sectioning of the ALL. Each operated level was grouped according to the mACR and additional PCO as: (1) no mACR, OLIF only (n=39); (2) mACR with no PCO (n=18); (3) mACR with grade 1 PCO (n=27); (4) mACR with grade 2 PCO (n=22); or (5) mACR with grade 3 PCO (n=6).

RESULTS

At the last follow-up, the mean disk lordotic angles were 10.9±2.9°, 12.6±3.0°, 13.3±3.9°, 16.7±3.2°, and 16.8±2.4° in the no mACR, mACR with no PCO, mACR with grade 1 PCO, mACR with grade 2 PCO, and mACR with grade 3 PCO groups, respectively ( P <0.001). The mean increases in disk lordotic angle were 5.8±4.1°, 12.1±6.1°, 13.5±8.7°, 15.8±6.7°, and 17.9±6.2° in each group, respectively ( P <0.001).

CONCLUSIONS

ACR can be performed with partial ALL release under direct vision in OLIF without deep dissection into the ventral disk space. The mACR in OLIF is a simple, safe, and effective technique for anterior column lengthening.

LEVEL OF EVIDENCE

4.

Radiographic and MRI evidence of indirect neural decompression after the anterior column realignment procedure for adult spinal deformity

OBJECTIVE

The anterior column realignment (ACR) procedure, which consists of sectioning the anterior longitudinal ligament/annulus and placing a hyperlordotic interbody cage, has emerged as a minimally invasive surgery (MIS) for achieving aggressive segmental lordosis enhancement to address adult spinal deformity (ASD). Although accumulated evidence has revealed indirect neural decompression after lateral lumbar interbody fusion (LLIF), whether ACR serves equally well for neural decompression remains to be proven. The current study intended to clarify this ambiguous issue.

METHODS

A series of 36 ASD patients with spinopelvic mismatch, defined as pelvic incidence (PI) minus lumbar lordosis (LL) > 10°, underwent a combination of ACR, LLIF, and percutaneous pedicle screw (PPS) fixation. This "MIS triad" procedure was applied over short segments with mean fusion length of 3.3 levels, and most patients underwent single-level ACR. The authors analyzed full-length standing radiographs, CT and MRI scans, and Oswestry Disability Index (ODI) scores in patients with minimum 1 year of follow-up (mean [range] 20.3 [12-39] months).

RESULTS

Compared with the preoperative values, the radiographic and MRI measurements of the latest postoperative studies changed as follows. Segmental disc angle more than quadrupled at the ACR level and LL nearly doubled. MRI examinations at the ACR level revealed a significant (p < 0.0001) increase in the area of the dural sac that was accompanied by significant (p < 0.0001) decreases in area and thickness of the ligamentum flavum and in thickness of the disc bulge. The corresponding CT scans demonstrated significant (all p < 0.0001) increases in disc height to 280% of the preoperative value at the anterior edge, 224% at the middle edge, and 209% at the posterior edge, as well as in pedicle-to-pedicle distance to 122%. Mean ODI significantly (p < 0.0001) decreased from 46.3 to 26.0.

CONCLUSIONS

The CT-based data showing vertebral column lengthening across the entire ACR segment with an increasingly greater degree anteriorly suggest that the corrective action of ACR relies on a lever mechanism, with the intact facet joints acting as the fulcrum. Whole-segment spine lengthening at the ACR level reduced the disc bulge anteriorly and the ligamentum flavum posteriorly, with eventual enlargement of the dural sac. ACR plays an important role in not only LL restoration but also stenotic spinal canal enlargement for ASD surgery.

Management of severe adult spinal deformity with circumferential minimally invasive surgical strategies without posterior column osteotomies: a 13-year experience

OBJECTIVE

To evaluate the mid- to long-term clinical outcomes of circumferential minimally invasive surgery (CMIS) without posterior column osteotomies for severe adult spine deformity (ASD) correction.

METHODS

All patients with a minimum of 2-year follow-up undergoing staged CMIS correction of ASD from January 2007 to July 2018 were identified. All included patients had fusion of 3 or more interbody levels that spanned the L5-S1 junction. Only patients with severe deformity, Coronal Cobb > 50° or at least one SRS-Schwab ++ sagittal modifier (SVA > 95 mm, or PI-LL > 20, or PT > 30) were included. All complications were noted.

RESULT

136 patients met inclusion criteria; mean age of patients was 63.6 years (21-85, SD 13.7). The mean follow-up was 82.8 months (24-159, SD 36.6). The mean number of levels fused was 7 (3-16, SD 3). A total of 40 (29.4%) major complications were noted at final follow-ups: 2 (1.4%) intra-operative, 12 (8.9%) peri-operative (≤ 6 weeks from index), 26 (19.1%) post-operative (> 6 weeks from index). There was a total of 53 (40.0%) minor complications. Seven (5.1%) patients who developed radiographic proximal junctional kyphosis. Three patients (2.2%) developed proximal junctional failure. There were 8 (5.9%) cases of pseudarthrosis. Five of these occurred in patients undergoing AxiaLIF. All patients experienced improvements in patient-perceived outcomes (VAS, TIS, ODI, and SRS-22) and radiographic parameters at last follow-up when compared to pre-op (p < 0.05).

CONCLUSION

Rates of complications with CMIS correction of severe ASD are lower than published rates of complications seen with open ASD correction. Specifically, the incidence of catastrophic complications is lower. Furthermore, CMIS is associated with significant improvements in clinical and functional outcomes, low rates of pseudarthrosis and proximal junctional kyphosis. Therefore, in the appropriately selected patient, CMIS may be an excellent alternative approach to addressing severe ASD.

Are Minimally Invasive Spine Surgeons or Classical Open Spine Surgeons More Consistent with Their Treatment of Adult Spinal Deformity?

OBJECTIVE

Spine surgeons have a heuristic sense of how to surgically restore alignment and address adult spinal deformity (ASD) symptoms, but consensus on the extent of treatment remains unclear. We sought to determine the variability of surgical approaches in treating ASD.

METHODS

Sixteen spine surgeons were surveyed on treatment approaches in 10 select ASD cases. We repeated the survey with the same surgeons 4 weeks later, with cases ordered differently. We examined the variability in length of construct, use of interbody spacers, osteotomies, and pelvic fixation frequency.

RESULTS

Treatment approaches for each case varied by surgeon, with some surgeons opting for long fusion constructs in cases for which others offered no surgery. There was no consensus among surgeons on the number of levels fused, interbody spacer use, or anterior/posterior osteotomies. Intersurgeon and intrasurgeon variability was 48% (kappa = 0.31) and 59% (kappa = 0.44) for surgeons performing minimally invasive surgery (MIS) versus 37% (kappa = 0.21) and 47% (kappa = 0.30) for those performing open surgery. In the second-round survey, 8 of 15 (53%) surgeons substantially changed the construct length, number of interbody spacers, and osteotomies in at least half the cases they previously reviewed. Surgeons performing MIS versus open surgery were less likely to extend constructs to the pelvis (42.5% vs. 67.5%; P = 0.02), but construct length was not correlated with whether a surgeon performed MIS or open surgery.

CONCLUSIONS

Spinal deformity surgeons lack consensus on the optimal surgical approach for treating ASD. Classifying surgeons as performing MIS or open surgery does not mitigate this variability.

Safe dissection and complication avoidance for L1–2 interbody placement via a lateral access approach

The lateral access approach for L1–2 interbody placement or other levels at or near the thoracolumbar junction may be difficult without proper knowledge and visualization of anatomy. Specifically, understanding where the fibers of the diaphragm travel and avoiding injury to the diaphragm are paramount.

The video can be found here: https://stream.cadmore.media/r10.3171/2022.3.FOCVID2221

Expandable Lateral Lumbar Cages With Integrated Fixation: A Viable Option for Rostral Adjacent Segment Disease

BACKGROUND

Adjacent segment disease (ASD) above a previous posterior lumbar instrumented fusion can be managed with minimally invasive lateral lumbar interbody fusion. Earlier procedures with stand-alone lateral cages risked nonunion, and lateral cages with separate lateral plates risked lumbar plexus injury and vertebral fracture. We investigated clinical and radiographic outcomes of an expandable lateral titanium interbody cage with an integrated lateral fixation (eLLIFp) device as a stand-alone treatment for symptomatic ASD above a previous posterior lumbar fusion and performed a comparative cost analysis of eLLIFp to alternative operations for ASD.

METHODS

In this prospective, observational study, patients with ASD above 1-, 2-, 3-, or 4-level instrumented posterior fusions underwent surgery with lateral expandable titanium cage(s) with an integrated lateral plate with single screws into each adjacent vertebra from August 2017 to August 2019. Multimodality intraoperative neural monitoring was performed. Patient-reported outcomes, computed tomography outcomes, and total costs were analyzed.

RESULTS

A total of 33 patients received 35 eLLIFp cages. All clinical outcomes improved significantly. The eLLIFp cages added 2.2° segmental lordosis and 2.7 mm posterior disc height. Interbody fusion rate was 94% at 12 months. There were 2 neurologic complications (6%): 1 patient reported transient anterior thigh numbness and 1 had mild persistent L4 radiculopathy. No cage subsidence, cage migration, screw loosening, or vertebral fracture occurred. No revision lateral surgery, posterior decompression, or supplemental posterior fixation was required. The total eLLIFp cost (AU$19,715) was lower than the cost for all other procedures.

CONCLUSIONS

eLLIFp provided a minimally invasive, low morbidity, cost-effective, and robust alternative to traditional posterior construct extension surgery for rostral lumbar ASD in selected patients with 1- to 2-level stenosis and minimal deformity.

CLINICAL RELEVANCE

Traditional ASD treatment involves substantial risks and expense. eLLIFp should be considered a safe, effective, and lower cost alternative to posterior construct extension surgery.

LEVEL OF EVIDENCE: 2

Patient outcomes after circumferential minimally invasive surgery compared with those of open correction for adult spinal deformity: initial analysis of prospectively collected data

OBJECTIVE

Circumferential minimally invasive spine surgery (cMIS) for adult scoliosis has become more advanced and powerful, but direct comparison with traditional open correction using prospectively collected data is limited. The authors performed a retrospective review of prospectively collected, multicenter adult spinal deformity data. The authors directly compared cMIS for adult scoliosis with open correction in propensity-matched cohorts using health-related quality-of-life (HRQOL) measures and surgical parameters.

METHODS

Data from a prospective, multicenter adult spinal deformity database were retrospectively reviewed. Inclusion criteria were age > 18 years, minimum 1-year follow-up, and one of the following characteristics: pelvic tilt (PT) > 25°, pelvic incidence minus lumbar lordosis (PI-LL) > 10°, Cobb angle > 20°, or sagittal vertical axis (SVA) > 5 cm. Patients were categorized as undergoing cMIS (percutaneous screws with minimally invasive anterior interbody fusion) or open correction (traditional open deformity correction). Propensity matching was used to create two equal groups and to control for age, BMI, preoperative PI-LL, pelvic incidence (PI), T1 pelvic angle (T1PA), SVA, PT, and number of posterior levels fused.

RESULTS

A total of 154 patients (77 underwent open procedures and 77 underwent cMIS) were included after matching for age, BMI, PI-LL (mean 15° vs 17°, respectively), PI (54° vs 54°), T1PA (21° vs 22°), and mean number of levels fused (6.3 vs 6). Patients who underwent three-column osteotomy were excluded. Follow-up was 1 year for all patients. Postoperative Oswestry Disability Index (ODI) (p = 0.50), Scoliosis Research Society-total (p = 0.45), and EQ-5D (p = 0.33) scores were not different between cMIS and open patients. Maximum Cobb angles were similar for open and cMIS patients at baseline (25.9° vs 26.3°, p = 0.85) and at 1 year postoperation (15.0° vs 17.5°, p = 0.17). In total, 58.3% of open patients and 64.4% of cMIS patients (p = 0.31) reached the minimal clinically important difference (MCID) in ODI at 1 year. At 1 year, no differences were observed in terms of PI-LL (p = 0.71), SVA (p = 0.46), PT (p = 0.9), or Cobb angle (p = 0.20). Open patients had greater estimated blood loss compared with cMIS patients (1.36 L vs 0.524 L, p < 0.05) and fewer levels of interbody fusion (1.87 vs 3.46, p < 0.05), but shorter operative times (356 minutes vs 452 minutes, p = 0.003). Revision surgery rates between the two cohorts were similar (p = 0.97).

CONCLUSIONS

When cMIS was compared with open adult scoliosis correction with propensity matching, HRQOL improvement, spinopelvic parameters, revision surgery rates, and proportions of patients who reached MCID were similar between cohorts. However, well-selected cMIS patients had less blood loss, comparable results, and longer operative times in comparison with open patients.

Complication rate evolution across a 10-year enrollment period of a prospective multicenter database

OBJECTIVE

Adult spinal deformity is a complex pathology that benefits greatly from surgical treatment. Despite continuous innovation, little is known regarding continuous changes in surgical techniques and the complications rate. The objective of the current study was to investigate the evolution of the patient profiles and surgical complications across a single prospective multicenter database.

METHODS

This study is a retrospective review of a prospective, multicenter database of surgically treated patients with adult spinal deformity (thoracic kyphosis > 60°, sagittal vertical axis > 5 cm, pelvic tilt > 25°, or Cobb angle > 20°) with a minimum 2-year follow-up. Patients were stratified into 3 equal groups by date of surgery. The three groups' demographic data, preoperative data, surgical information, and complications were then compared. A moving average of 320 patients was used to visualize and investigate the evolution of the complication across the enrollment period.

RESULTS

A total of 928/1260 (73.7%) patients completed their 2-year follow-up, with an enrollment rate of 7.7 ± 4.1 patients per month. Across the enrollment period (2008-2018) patients became older (mean age increased from 56.7 to 64.3 years) and sicker (median Charlson Comorbidity Index rose from 1.46 to 2.08), with more pure sagittal deformity (type N). Changes in surgical treatment included an increased use of interbody fusion, more anterior column release, and a decrease in the 3-column osteotomy rate, shorter fusion, and more supplemental rods and bone morphogenetic protein use. There was a significant decrease in major complications associated with a reoperation (from 27.4% to 17.1%) driven by a decrease in radiographic failures (from 12.3% to 5.2%), despite a small increase in neurological complications. The overall complication rate has decreased over time, with the lowest rate of any complication (51.8%) during the period from August 2014 to March 2017. Major complications associated with reoperation decreased rapidly in the 2014-2015. Major complications not associated with reoperation had the lowest level (21.0%) between February 2014 and October 2016.

CONCLUSIONS

Despite an increase in complexity of cases, complication rates did not increase and the rate of complications leading to reoperation decreased. These improvements reflect the changes in practice (supplemental rod, proximal junctional kyphosis prophylaxis, bone morphogenetic protein use, anterior correction) to ensure maintenance of status or improved outcomes.

Revisiting anterior longitudinal ligament release: Are we ready for an endoscopic approach?

Anterior longitudinal ligament release is a proven method for restoring spinopelvic parameters. This technique is mostly described using either lateral or anterior approaches with paucity regarding a posterior method. This paper is the first to provide descriptive analysis of the neurovascular anatomy in the context of planning for a posterior endoscopic ALL release. A retrospective chart review was performed on patients underwent any lumbar surgery by a single surgeon. Anatomical data was obtained from pre-operative CT to describe the location of key neurovascular structures in relation to the ALL with focus on posterior approach. A total of 20 patients were included in data analysis. A posterior approach with endoscopic assistance would be feasible at L4/5 and L5/S1, where the bifurcation of the abdominal aorta has occurred with a vessel window that ranges from 18.85 mm to 33.45 mm with at least 2 mm space between the vessels and the corresponding disc spaces in the anterior-posterior dimension with slight predilection of the left side at the L5/S1 level to avoid any neurovascular structures. Our study confirmed the findings of previous studies examining the vascular anatomy associated with the lumbar spine. Interestingly, we found that direct midline would likely not be the best location for a posterior annulotomy, and that both the window between the iliac vessels as well as the distance in AP dimension between the spine and vessels increases as you descend the lumbar spine. This information will help guide future efforts to fully develop a safe and reproducible posterior endoscopic ALL release.

The minimally invasive interbody selection algorithm for spinal deformity

OBJECTIVE

Minimally invasive surgery (MIS) for spinal deformity uses interbody techniques for correction, indirect decompression, and arthrodesis. Selection criteria for choosing a particular interbody approach are lacking. The authors created the minimally invasive interbody selection algorithm (MIISA) to provide a framework for rational decision-making in MIS for deformity.

METHODS

A retrospective data set of circumferential MIS (cMIS) for adult spinal deformity (ASD) collected over a 5-year period was analyzed by level in the lumbar spine to identify surgeon preferences and evaluate segmental lordosis outcomes. These data were used to inform a Delphi session of minimally invasive deformity surgeons from which the algorithm was created. The algorithm leads to 1 of 4 interbody approaches: anterior lumbar interbody fusion (ALIF), anterior column release (ACR), lateral lumbar interbody fusion (LLIF), and transforaminal lumbar interbody fusion (TLIF). Preoperative and 2-year postoperative radiographic parameters and clinical outcomes were compared.

RESULTS

Eleven surgeons completed 100 cMISs for ASD with 338 interbody devices, with a minimum 2-year follow-up. The type of interbody approach used at each level from L1 to S1 was recorded. The MIISA was then created with substantial agreement. The surgeons generally preferred LLIF for L1-2 (91.7%), L2-3 (85.2%), and L3-4 (80.7%). ACR was most commonly performed at L3-4 (8.4%) and L2-3 (6.2%). At L4-5, LLIF (69.5%), TLIF (15.9%), and ALIF (9.8%) were most commonly utilized. TLIF and ALIF were the most selected approaches at L5-S1 (61.4% and 38.6%, respectively). Segmental lordosis at each level varied based on the approach, with greater increases reported using ALIF, especially at L4-5 (9.2°) and L5-S1 (5.3°). A substantial increase in lordosis was achieved with ACR at L2-3 (10.9°) and L3-4 (10.4°). Lateral interbody arthrodesis without the use of an ACR did not generally result in significant lordosis restoration. There were statistically significant improvements in lumbar lordosis (LL), pelvic incidence-LL mismatch, coronal Cobb angle, and Oswestry Disability Index at the 2-year follow-up.

CONCLUSIONS

The use of the MIISA provides consistent guidance for surgeons who plan to perform MIS for deformity. For L1-4, the surgeons preferred lateral approaches to TLIF and reserved ACR for patients who needed the greatest increase in segmental lordosis. For L4-5, the surgeons' order of preference was LLIF, TLIF, and ALIF, but TLIF failed to demonstrate any significant lordosis restoration. At L5-S1, the surgical team typically preferred an ALIF when segmental lordosis was desired and preferred a TLIF if preoperative segmental lordosis was adequate.