Minimally Invasive Approaches to Adult Spinal Deformity Correction

Abstract

The management of adult spinal deformity has undergone a transformative shift with the emergence of minimally invasive approaches. Traditionally, the correction of complex spinal curvatures necessitated extensive open surgeries to perform the osteotomies and instrumentation, contributing to long and high-risk operations. However, the advent of minimally invasive techniques has ushered in a new era of patient-centric care. These innovative approaches entail smaller incisions, reduced tissue disruption, and advanced navigational tools that in many instances yield satisfactory and comparable results. The benefits are manifold: decreased blood loss, shorter hospitalizations, faster recovery times, and improved patient satisfaction. This chapter highlights the profound impact of these techniques on patient outcomes and healthcare systems. Nonetheless, challenges remain. Surgeons must navigate a steep learning curve, and there are limitations in addressing severe deformities through minimally invasive means. Rigorous patient selection and meticulous preoperative planning are pivotal to achieving success.

1. Introduction

Adult spinal deformity (ASD) is a spectrum of diseases involving both lumbar and thoracic regions and consisting of adult degenerative scoliosis, degenerative sagittal plane deformities, and iatrogenic spinal deformities [1, 2]. Given that number of geriatric patients over 65 in the United States is expected to double by 2050 compared to 2010, and there is evidence that shows the overall prevalence of ASD in older patients is close to 68%, proper attention and appropriate interventions should be taken into account before it causes major burdens and disabilities to the patients [3, 4]. Based on the severity of the disease, patients may experience a spectrum of symptoms such as axial or radicular pain, claudication, walking disturbance, and symptoms of spinal stenosis [2, 5, 6]. Different treatment options are available for patients with ASD. Conservative therapy, including physical therapy, medications, and a combination of interventional pain procedures has been the first line of treatment [7, 8, 9]. Surgery could be reserved for those refractories to conservative management and those with worsening deformity, significant neurological deficits and symptoms disrupting patients’ activities of daily living [4, 10, 11, 12]. Open techniques to correct the deformity have been in practice for decades with good results; however, there is a growing body of evidence and interest in the minimally invasive surgery (MIS) techniques nowadays [13]. In a study by Lak et al., a review of 350 cases of adult degenerative scoliosis revealed that open surgery and MIS showed comparable improvement in outcomes of patients. However, better outcome was associated with open surgery and better safety outcomes with MIS [14]. Another study by Dangelmajer et al. reported no significant difference in the complication rates between the open surgical approach and MIS [15]. Current evidence could not draw a solid conclusion regarding the superiority of MIS vs. open surgery techniques, and recent studies emphasize individualized surgical planning for each patient [16]. In this chapter, we will delve into the application of MIS for ASD, patient selection (i.e., an algorithm to decide which patients are a better fit for MIS or hybrid vs. open), advantages and disadvantages of MIS vs. open techniques, different MIS techniques, and possible future advances.

2. Definitions

Before proceeding, some definitions and indexes should be reviewed.

2.1 Coronal cobb angle (CCA)

The angle between two lines perpendicular to the lines extending from the superior (cephalic spine body) and inferior (caudal) endplates of the most tilted spine vertebral bodies [17].

2.2 Pelvic incidence-lumbar lordosis (PI-LL) mismatch

Pelvic incidence (PI) is defined as an angle between a line drawn from the middle of the head of the femoral bone to the midpoint of sacrum superior endplate and a line perpendicular to the middle of the sacral endplate [18]. Lumbar lordosis (LL) is traditionally determined by the Cobb angle between the upper endplates of the first lumbar (L1) and either the lower endplate of L5 or the upper endplate of S1 [19]. The discrepancy between PI and LL, referred to as PI-LL mismatch or discordance, is correlated with the patient’s quality of life (QoL), and a mismatch of more than 10 degrees suggests misalignment as it is an indicator of maladaptation of the lumbar region to the pelvic anatomy [20].

2.3 Sagittal vertical Axis (SVA)

The term SVA refers to the measurement of the horizontal distance between two points on lateral full-body standing X-rays. C7-S1 SVA refers to the distance between the posterior superior part of S1 endplate and a plumb line drawn from the center of C7 [21], assessing in accordance with the upper thoracic to the pelvis. To take neck posture into account, C2 and Cranial Center of Gravity (CCoG) SVAs are proposed, measuring the distance between the posterior superior part of S1 endplate and a plumb line passing through the middle of C2 vertebral body and external auditory meatus, respectively [20]. It has been found that these indexes are associated with pain and QoL of patients [22].

2.4 Coronal vertical Axis (CVA)

Similar to SVA, CVA is measured on an anterior-posterior full-body standing X-rays. The most commonly used is C7-S1 CVA, as the distance measured between the midpoint of S1 endplate and a vertical plumb line passing through the midpoint of C7 vertebral body.

2.5 Pelvic tilt (PT)

PT is an angle between a vertical line drawn from the center of the head of the femoral bone and another line from the head of the femoral bone to the middle part of the superior endplate of S1. This term refers to the orientation of the pelvis in relation to the femoral head. Like previous measurements, it is correlated with the QoL and health condition of patients [20, 23].

Of note, these are only a few of several other measurements related to surgical planning for ASD patients. Readers are referred to other chapters or references for a full review of these.

3. Background, emergence, and development of MIS techniques

While initially developed and implemented in the 1990s to perform thoracic and lumbar discectomy and laminectomy in limited series [24, 25], the development of tubular retraction systems advanced the field of minimally invasive spine surgery [26, 27]. As MIS became more popular, conventional fusion techniques were implemented in MIS, initially including pedicle screw fusion (MIS-PSF), Transforaminal Lumbar Interbody Fusion (MIS-TLIF), and Posterior Lumbar Interbody Fusion (MIS-PLIF) [28, 29, 30]. Overall, these techniques were associated with decreased blood loss and pain and accelerated recovery time [31, 32, 33]. Later, newer MIS techniques were developed for fusion, such as Anterior Lumbar Interbody Fusion (ALIF), trans-psoas Lateral Lumbar Interbody Fusion (MIS-LLIF/TP), anterior-to-psoas Oblique Lumbar Interbody Fusion (MIS-OLIF/ATP), and trans-Kambin Oblique Lateral Lumbar Interbody Fusion (MIS-OLLIF) [34, 35]. Overall, these new approaches let surgeons access the spinal bodies from various angles [36].

With the development of advanced fusion techniques, MIS has been routinely implemented in deformity correction, either as MIS-alone techniques or combined with open techniques (hybrid approaches). To gain better global sagittal balance, Anterior Column Release (ACR) is added to anterolateral approaches. The goal is to release the anterior longitudinal ligament (ALL) and place a hyperlordotic interbody cage, to gain more sagittal correction. Currently, there is a growing trend toward less invasive procedures, and MIS techniques for ASD are rapidly progressing. These techniques are trying to achieve a higher success rate, fewer adverse events, faster recovery times, and provide better correction and alignment rates.

4. Overview of MIS techniques for ASD correction

4.1 Interbody fusion techniques

The utilization of interbody devices stands as a pivotal component within the realm of MIS deformity correction. In this context, the benefits extend beyond the fundamental aspects of load sharing and the enhancement of fusion rates—rationales commonly associated with their application in spinal surgery at large. As executing multi-level and higher-grade osteotomies through MIS means remains the main challenge, thereby a significant portion of the curve correction should be obtained through interbody devices. Consequently, the meticulous selection of the appropriate interbody technique stands as a pivotal cornerstone of surgical planning.

Various factors play a role in the choice of interbody fusion route: 1) past surgical history (spine, abdominal, and vascular): anterolateral approaches are riskier in those with multiple abdominal and vascular surgeries; 2) degree of correction needed: better sagittal and coronal correction obtained through anterolateral approaches; 3) need for direct decompression (as opposed to indirect decompression only): generally needed for those with severe canal stenoses, direct decompression is better achieved through posterior approaches; and 4) higher body mass indexes (generally more than 35–37) make anterolateral approaches less doable.

4.1.1 Posterior interbody fusion techniques

Including two techniques (PLIF and TLIF), their main advantages include: single approach surgery (i.e., no need to reposition), ability to be performed at any lumbosacral level, absence of anatomical restrictions, and providing direct decompression (added to indirect). However, their biggest disadvantage of MIS deformity surgery is that they provide less restoration of lumbar lordosis per level, compared to anterolateral approaches. Moreover, their ability to correct coronal curves is very limited, making them a less suitable option for these curves. With the advent of expandable devices, there are some hopes to provide better sagittal correction, but their use so far has been limited mostly to short-segment fusions and has not been an integral part of deformity correction. Lastly, their smaller size provides a smaller device-endplate contact surface area, making proper deformity correction less achievable.

4.1.2 Anterolateral interbody fusion techniques

One of the first non-posterior interbody approaches devised, ALIF, might not conventionally be considered MIS by all. However, advent of newer retracting systems, avoidance of cutting posterior lumbar muscles, and retroperitoneal trajectories, make it an ideal MIS technique. Primarily used at L5-S1 and L4-L5, it has a wider range of available lordotic and hyper-lordotic options, making it a strong tool for the restoration of segmental lordosis and sagittal balance. Also, it is more efficient in providing coronal restoration than the posterior options. ALIF also allows for resection of ALL and sometimes posterior longitudinal ligament (PLL), adding to its deformity correction potential. The inclusive disadvantage of the technique is a risk of vascular injuries and safe access being limited to L4-S1.

LLIF/TP can be safely performed in most upper and mid-lumbar levels (L1-L2 to L2-L4), but also at L4-L5, though with some difficulty due to the anatomy of iliac crest. Availability of a wide range of lordotic and hyper-lordotic options, providing a large device-endplate contact surface area, and adding bilateral endplate coverage to the benefits, it is a strong option for sagittal correction and by far the strongest interbody option to restore coronal curves. The main disadvantage is, however, the risk of direct or more commonly retraction injury to lumbar plexus nerves [37, 38].

The anatomic limitations of ALIF and LLIF/TP, paved the way for the advent of OLIF/ATP approach [39]. Always a left-sided approach which uses the corridor between psoas muscle and aorta/left common iliac artery at L1-L5 and the corridor between right and left common iliac arteries (like ALIF) at L5-S1, it has a lower risk of lumbar plexus injury compared to LLIF and lower risk of vascular injury compared to ALIF (although more than LLIF) [38, 40]. In terms of deformity correction, they are strong tools in both sagittal and coronal curve correction (comparable to LLIF). Moreover, their anatomic approach makes ALL release more accessible than LLIF, adding to the benefit.

Regardless of the choice, all MIS interbody options are valuable integral parts of MIS deformity correction. A meta-analysis of a total of 18 studies and 732 ASD patients undergoing deformity correction showed that all-posterior MIS options were associated with shorter operative times compared to lateral. MIS lateral options (LLIF and OLIF) were superior to MIS and open posterior options in terms of blood loss and length of hospital stay. Both MIS options resulted in similar fusion rates, and functional and radiological outcomes, compared to open [41].

4.2 Anterior column release techniques

Although MIS is reported to be effective in improving the global sagittal and coronal alignment, its efficacy is less than open techniques for the correction of severe imbalances, especially if only relies on interbody devices to correct the deformity [42]. These limitations led to the development of new techniques, including Anterior Column Release (ACR) [43]. Mostly done as a part of a lateral trans-psoas or oblique anterior-to-psoas approach to perform complete discectomy and release of the ALL, followed by placement of a hyper-lordotic (20–30°) interbody device, ACR enables surgeons to achieve similar effectiveness as open surgery through an MIS approach [42, 44]. The primary reports showed promising effects, although these results were limited by the small sample size of studies [45].

As ACR is relatively new, long-term data on its complication profile and efficacy is still missing. However, early data exploring the efficiency of ACR performed as a part of LLIP/TP has been very promising, and 20–30° of sagittal correction, 10–15° of coronal correction, and 5–10° of PT correction has been achieved through ACR alone. More importantly, the complications are less, especially in terms of blood loss (average ~ 50 mL) compared to open osteotomy techniques including pedicle subtraction osteotomy (PSO) and vertebral column resection (VCR), which are traditionally associated with a substantial blood loss (occasionally even up to 1–2 L). All these earlier results have been achieved through a combination of LLIF/TP and ACR. However, ACR is achievable through an OLIF/ATP (and potentially ALIF), as both approaches provide excellent access to ALL. The main complication after ACR, like other anterolateral approaches, has been reported to be anterior thigh weakness and numbness, which in most cases fully resolves within 1–2 years after surgery. This complication can be further reduced and avoided with various modifications, including minimization of retraction time, limiting the exposure, employment of neuromonitoring, flexing hips and knees, and not breaking the surgical table [46, 47, 48, 49]. In general, ACR has been reported to obtain similar radiographic results compared to open osteotomy counterparts, with significantly less estimated blood loss and similar overall complication rates.

4.3 Osteotomy techniques

The current use of posterior osteotomy techniques during MIS approaches is limited to “mini-open” posterior column osteotomies (PCOs) and PSOs, which are obtained through smaller-than-open incisions, periosteal dissection only at the level of osteotomies, followed by the closure of the osteotomies across the percutaneous pedicle screws and the connecting rods through a cantilever force [34, 50]. As technically not different from the open or mini-open osteotomies, these are better addressed in other chapters, but their knowledge is necessary for spine surgeons to increase the amount of correction obtained via MIS and hybrid approaches.

4.4 Posterior fusion techniques

All previously mentioned techniques should be complemented by posterior fusion. Pedicle and iliac screws are placed in a percutaneous technique in the desired levels, either spanning from the upper (mostly T3-T5) or lower (usually T9-T11) thoracic to sacropelvic region, followed by advancing two rods under the fascia to connect the screws. No different than other MIS pedicle screw placement techniques else than the number of levels included in the fusion, details of these techniques are addressed elsewhere.

4.5 Bone graft techniques

Special attention should be paid for bone graft options during MIS surgery. As MIS surgery classically does not expose posterolateral bone, the template and basis for bony fusion are significantly limited in these surgeries. Moreover, relying more on instrumentation for deformity correction and decompression provides less autograft, compared to open counterparts. As such, surgeons need to have a good knowledge base of various bone graft options and surgical techniques that improve bony fusion. These include proper preparation of endplates during interbody device placement to maximize device-endplate interaction, use of larger interbody devices (through anterolateral approaches) if possible, maximizing the number of interbodies used, harvesting as much autograft as possible (plus considering harvesting more from remote sites), and finally proper use of allografts to include all stages and properties needed for new bone formations (osteogenesis, osteo-induction, and osteo-conduction).

5. Advantages and disadvantages of MIS for patients with ASD

Due to the less invasive nature of MIS techniques, these procedures are intriguing for both surgeons and patients. The main advantages of MIS are decreased tissue dissection and disruption and, as a result, less muscle atrophy, lower risk of infection and blood loss, shorter length of hospital stay, and faster recovery of patients [13, 34, 51, 52]. Nevertheless, some points should be considered before choosing MIS techniques to treat patients with ASD. In addition to having a steeper learning curve, both surgical staff and patients may be exposed to a greater amount of radiation [53, 54, 55]. Additionally, MIS surgery may have limited effectiveness in correcting severe deformities, which makes it less suitable for such cases. However, newer techniques are being developed to address this issue [14].

5.1 Efficacy

Acknowledging the promising nature of MIS in addressing ASD, still the biggest question is how it compares with open approaches in terms of clinical and radiographic outcomes. A systematic review and meta-analysis by Lak et al. in 2020 included four retrospective cohorts and 350 patients to compare the efficacy of open surgery vs. MIS for patients with ASD. Although the results were inconsistent among studies, open surgery resulted in a greater change of SVA and PI-LL mismatch. Regarding the change in the leg and back pain and disability, overall, there was a significant decrease in back pain, leg pain, and disability in both MIS and open surgery groups without a significant difference between the two groups [14]. Mittal et al. conducted a systematic review and meta-analysis (2023) of the outcomes of patients following open and MIS surgeries in patients with ASD. This review included 18 studies and 732 patients and divided studies into the subgroup of lateral approaches (LLIF and OLIF) and posterior approaches (PLIF and TLIF). The latter subgroup was subdivided into MIS and open surgery further. The results of meta-analyses showed that both lateral and posterior groups could significantly reduce leg pain, back pain, disability of patients (measured by Oswestry Disability Index or ODI), Cobb angle, and SVA. It is worth mentioning that the difference between lateral and posterior subgroups was not significant in the above-mentioned analyses. In terms of the total operation time, the pooled time for the lateral approach was 401 minutes (only one study), while it was 233 minutes for MIS posterior (four studies) and 380 for open posterior (four studies) approaches; the difference was not significant between posterior approaches. Five studies in the lateral approach reported only interbody fusion time, resulting in a pooled operation time of 170 minutes. The fusion rate was determined to be 97.8% (four studies) and 96.6% (six studies) in the lateral and posterior groups, respectively; these differences were not statistically significant either. Length of hospital stay was shortest in the lateral group (with a pooled rate of 4.15 days across four studies) and the longest in the posterior open surgery (13.54 days across four studies), and the difference between these groups was significant. The posterior MIS group had a pooled rate of 6.25 days across two studies. The result might indicate overall faster recovery in the MIS approach compared to open surgery. Moreover, the study investigated the complications in addition to efficacy. According to the results, lower blood loss was achieved by the posterior MIS approach compared to the open posterior approach (385 mL vs. 1325 mL, respectively). One study in the lateral group reported total blood loss (477 mL), and three others reported blood loss only during fusion (86 mL). The difference in blood loss between the lateral and open posterior approaches was found to be significant. No significant difference was noted for other complications such as durotomy, permanent neurologic and device-related adverse events, re-operation rate, and pseudoarthrosis between MIS and open approaches [41]. In a study on ASD patients in whom three-column osteotomy was not performed, post-operative ODI, Scoliosis Research Society (SRS) score, and European Quality of life (EQ-5D) scores were all comparable between circumferential MIS (cMIS) and open patients. Both versions were also equally effective in correcting CCA, PI-LL mismatch, SVA, and PT. Confirming other results, open patients had more blood loss and shorter operative times, compared with cMIS patients. Interestingly, revision rates were similar between the two groups. Of note, excluding 3-level osteotomy cases from the study leaves severe deformity cases out, considering open surgery might be more efficient in correcting severe curves [56]. Lastly, another study comparing the complication rates of open, hybrid, and MIS techniques (among 60 patients) concluded that although there was no difference in the rate of overall complications, a significantly lower rate of intraoperative complications was observed in the MIS [13]. Added to the efficacy of MIS techniques in improving clinical outcomes, global sagittal and coronal parameters, and spinopelvic parameters, they have been shown to improve fractional curves as well, resulting in clinical improvement in radiculopathy symptoms. In a study on patients with fractional curves worse than 10 degrees undergoing either open or cMIS surgeries, both groups had comparable reductions in fractional curves and leg pain after surgery [57].

Combining the benefits of both MIS (less tissue disruption, minimal blood loss, faster recovery, etc.) and open (more efficiency and greater curve correction) surgeries, hybrid procedures seem to be interesting and now widely used alternatives. In a study, hybrid procedures were shown to correct CCA better than cMIS, while they both yielded comparable results in the correction of SVA, PI-LL mismatch, PT, and sacral slope (SS). At 2 years, cMIS had better ODI scores and a greater ODI change compared to baseline, less back pain and greater VAS back pain change, compared to hybrid techniques. All these outcomes were comparable at 3 years mark between cMIS and hybrid, except leg pain, which was lower for cMIS compared to hybrid. cMIS had fewer complications overall compared to hybrid techniques, except for pseudarthrosis (i.e., higher rate in cMIS) [58].

Nonetheless, not all studies have shown comparable results for MIS vs. open. Uribe et al. conducted a multicenter study to compare the outcomes and complications of patients with ASD who underwent open, MIS, and hybrid surgery in a propensity-matched cohort, each group consisting of 20 patients. Investigating radiographic outcomes, their results showed that open and hybrid approaches were superior to MIS in terms of improving PI-LL mismatch, thoracic CCA, thoracic kyphosis, and C7-S1 SVA. However, all 3 versions were successful in improving lumbar CCA. Comparing the clinical outcomes, all these procedures could decrease back pain (using a visual analog scale (VAS)) and disability (ODI) of patients, but the results for reducing leg pain were again superior to open surgery. The hybrid surgery had the longest overall operation time, while the open surgery had the shortest time. However, the length of hospitalization was the opposite, with patients who underwent hybrid surgery staying for a shorter period compared to others [13].

As evident in these results, studies are not consistent in terms of imaging and radiographic outcomes. However, most studies conclude that at least for less severe and moderate deformities, MIS approaches are associated with comparable outcomes to open surgery. In severe cases, it can be concluded that open approaches obtain superior results. However, almost all studies agree upon the fact that MIS is associated with less blood loss, shorter hospital stays, and faster recovery.

MIS may provide additional promising outcomes in terms of proximal junction kyphosis (PJK). PJK is radiologically defined as a Cobb angle of more than 20 degrees or an increase of more than 10 degrees postoperatively cranial to the site of surgery between the upper instrumented vertebra (UIV) and the vertebra 2 levels rostral to UIV (UIV + 2). In general, 39% of patients who undergo surgery for correction of spine deformity may be affected, but not all patients will be symptomatic [59, 60]. Gandhi et al. found that the incidence of PJK after surgery for ASD was lower for MIS versions (ACR and LLIF) compared to open surgery [61].

5.2 Costs

A retrospective cohort of 71 patients tried to evaluate the costs of MIS for adult degenerative scoliosis and compare it to the open technique. This study concluded that the total inpatient charges were significantly lower for the MIS group ($269 K vs. $391 K), while there were no significant differences in terms of the need for inpatient rehabilitation after hospitalization [62]. Another study by Swamy et al. compared the cost-effectiveness of MIS (12 patients) and open surgery (10 patients) for patients with adult degenerative scoliosis. This cohort reported fewer total costs for the MIS group ($83 K vs. $111 K, adjusted to Canadian dollars), while open surgery costs less in uncomplicated cases ($47 K vs. $76 K). Also, it has been reported that MIS is associated with higher quality-adjusted life years leading to the conclusion that MIS is less expensive than the open approach [63]. Chung et al. conducted a review study and confirmed previous findings on the economic aspects of spine surgery techniques, including both MIS and open surgery, without limiting the analysis to the ASD [64].

6. Case selection

With the new advancements in MIS techniques and the lack of clear superiority of one technique over the other, now surgeons (and patients) have more tools in their armamentarium to tackle this challenging disease. Instead of choosing one over the other, there have been some efforts to recommend a tailored and case-by-case approach. Despite the controversies, most authors believe that the applicability of MIS is more limited in the case of a severe sagittal imbalance or in patients with prior fusions. Although recent advances such as ACR and mini-PSO have been used to address the limitation of MIS for severe deformities in addition to keeping the minimally invasive advantages, open surgery with osteotomy might still be the preferred option in revision surgeries in patients with severe deformities [44]. Mummaneni et al. developed an MIS deformity surgery algorithm (MISDEF) to help physicians to decide whether to proceed with MIS or open surgery [65]. In this algorithm, three classes of treatments, including MIS decompression with or without fusion, decompression with interbody fusion, and open surgery with osteotomy and fusion up to the thoracic region, were introduced regardless of the health condition or age of the patients. This algorithm was revised in 2018 to include ACR, mini-open PSO, expandable cages, and hybrid techniques. In general, for non-fused or flexible spines, SVA less than 6 cm, PT < 25, PI-LL mismatch less than 10 degrees, and CCA less than 20 degrees, MIS with decompression or combined with a fusion at the listhetic level was recommended, leaving the more severe cases amenable to open surgery [34, 66].

However, more advancements have been made since the publication of these algorithms and comfort level of spine surgeons with MIS techniques has increased, making them able to handle more severe cases with MIS surgeries. More importantly, patients’ comorbidities, past surgical history (specifically abdominal and spine), and body status favor one choice over the other. In our opinion, patients needing higher degrees of sagittal curve correction (more than 50–55 degrees), fusions anticipated to go to upper thoracic, those with previous spine surgeries resulting in multi-level and long-segment fusions, history of complex abdominal and vascular surgeries, those with multi-level severe central stenosis (needing direct multi-level decompression), and those with less optimal body status (BMI > 35–37) are a better fit for open techniques. On the other hand, those with coronal-dominant curves, severe coronal imbalance, sagittal correction needs below 50–55, lack of previous spine surgeries or short-segment fusions at most, and those with a more favorable BMI are perfect fits for MIS. In patients with coronal imbalance, it is worth mentioning that the type of curve has a significant role in outcome after MIS correction, and as a result choice of MIS vs. open. Those with a balanced (less than 3 cm) C7-S1 CVA (type A) and those with a coronal malalignment (C7-S1 CVA > 3 cm) shifted toward concavity of the main lumbar curve (type B) can be successfully handled through an MIS approach. Those with a coronal malalignment shifted toward convexity of the main lumbar curve (type C) are prone to worsened coronal imbalance after addressing the fractional lumbar curve, and as such are not ideal candidates for MIS [67]. As previously noted, above and beyond all, the surgeon’s expertise and comfort level with either technique is perhaps the most critical factor in the choice of surgery.

7. Conclusions

The current era is exciting with the wealth and plethora of surgical options to address ASD. In the absence of a clear benefit of one technique over the other in most patients, modern-day surgeons and clinicians should be well aware and trained by MIS as well as open techniques to tailor their proposed treatment to patients’ needs.