Many of the inherent complications affiliated with a conventional anterior or posterior surgery are avoidable with the XLIF (XLIF®, NuVasive, Inc., San Diego, CA, USA) approach [25, 30–32]. The literature has cited decreased blood loss, quicker recovery, and lower costs as advantages of a lateral surgery [10, 32, 33]. Isaacs et al. [32] reported an operative time of 177.9 min or 57.9 min per level. The length of stay averaged 2.9 days for unstaged surgeries and 8.1 days for staged procedures. Estimated blood loss was minimal (≤100 mL) for the majority of patients (62.5 %), while nine patients did lose up to 300 mL. In comparison, results from traditional procedures have reported a much higher blood loss [34, 35]. Daubs et al. [34] demonstrated a mean blood loss of 2,056 mL (300–5,500). However, the average number of levels was twice that of Isaacs et al. [32] (4.4 levels vs. 9 levels).

Tormenti et al. [36] reported improved VAS (visual analog scale) scores for both the combined XLIF and posterior and posterior-only groups. The scores improved from 8.8 to 3.5 and 9.5 to 4.0 for the combined and posterior-only groups, respectively. These scores were not statistically significant between groups. The average follow-up period was 10.5 and 11.5 months for the combined and posterior-only groups, respectively. Unfortunately, the sample sizes were very small for each group (8 = combined and 4 = posterior only), and VAS scores for only six of the eight patients in the combined group were available.

Phillips et al. [37] demonstrated significantly better ODI (Oswestry Disability Index), VAS back and leg, SF-36 MCS (36-Item Short Form Health Survey Mental Component Summary), and SF-36 PCS (36-Item Short Form Health Survey Physical Component Summary) scores between presurgery and 2-years postsurgery (p < 0.001). Additionally, a high percentage of patients (85 %) were very satisfied with their outcomes and 86 % declared they would be willing to do the procedure again. Although the sample size was fairly large, only 77 % of the patients were accessible at the 24-month follow-up.

Previous literature has demonstrated a revision rate for pseudarthrosis ranging from 0 to 19 % for anterior plus posterior and posterior-only traditional approaches in deformity patients [38–42]. In contrast, Phillips et al. [37] showed a 2 % revision rate when pseudarthrosis was diagnosed. This small percentage of revision surgeries noticed after XLIF (XLIF®, NuVasive, Inc., San Diego, CA, USA) agrees with prior studies who have reported high rates of fusion success [25, 28, 43, 44]. The authors believed that the high rate of fusion with XLIF (XLIF®, NuVasive, Inc., San Diego, CA, USA) procedures most likely indicates the capacity to accomplish a complete discectomy and place a large cage within the disc space packed with more abundant bone graft within the interbody cage on the apophyseal ring of the end plate, as compared to transforaminal lumbar interbody fusion (TLIF) or posterior lumbar interbody fusion (PLIF) surgeries. However, due to poor radiographic visualization, 10 % of patients were not able to be assessed for fusion, and at the latest follow-up of 12 months (range: 12–36 months), 58 % had a solid fusion, 39 % had a partial fusion, and 3 % showed no consolidation. Additionally, 8 % of patients demonstrated nonfusion at ≥1 level. The length of follow-up for the fused patients as compared to the nonfused patients was not provided in this study. Also, 10.6 % of the patients were documented as smokers. Smoking has been shown to affect outcomes and fusion [45, 46]. The authors did state that fusion status was influenced by fixation method. Thus, solid bridging was greater in those with bilateral pedicle screw supplementation compared to those with either a stand-alone XLIF (XLIF®, NuVasive, Inc., San Diego, CA, USA), lateral supplementation, or unilateral pedicle screw fixation.

Isaacs et al. [32] reported 14 major complications for 13 (12.1 %) of the 107 patients, 2 of which were classified as major medical and 12 were categorized as major surgical. Overall, 21 surgical complications occurred in 16 patients, 9 of which were minor, and 16 medical complications among 11 patients, 14 of which were minor. There were no infections with stand-alone XLIF (XLIF®, NuVasive, Inc., San Diego, CA, USA) as well as when posterior instrumentation was completed minimally invasively. However, three early reoperations ensued due to deep wound infections, which were related to the open posterior instrumentation approach. Prior minimally invasive studies have demonstrated fewer infections compared to published rates for traditional open techniques [47–49]. Furthermore, it was shown that patients with open posterior fixation had both a significantly higher incidence of any complication (p = 0.02) as well as a major complication (p = 0.04) compared to individuals with percutaneous posterior fixation. In a subsequent publication, Phillips et al. [37] reported that 13 patients needed a supplementary surgical procedure. Reasons for the additional surgeries included pseudarthrosis, treatment at adjacent segments, and posterior-only procedures.

Tormenti et al. [36] demonstrated an unusually high number of complications including bowel perforations, incidental durotomy, pleural effusions, pulmonary embolism, ileus, junctional kyphosis, and a wound infection. By the 11.5-month follow-up, no infections or indications of hardware failure were seen. The authors noted the nature of the scoliotic spine greatly enhances the risk of complications to the intra- and retroperitoneal anatomy. Additionally, the very small sample size should be taken into consideration when interpreting these results. Despite these results [36], traditional approaches do seem to report much higher complication rates than minimally invasive techniques. For instance, Pateder et al. [50] reported a complication rate as high as 45 % for deformity patients that underwent traditional surgery, and Fujita et al. [35] demonstrated rates up to 66 %.

Compared to traditional procedures, the fewer complications documented for lateral surgeries are likely due to the method of the lateral approach. The lateral technique is able to circumvent several of the related complications seen with open anterior surgeries, since the abdominal vasculature, ureter, and peritoneal cavity are not manipulated [37]. Along those lines, the prevalence of perioperative complications is reduced when walking and mobility occurs early after surgery [51]. Thus, patients who undergo a minimally disruptive lateral surgical procedure are more likely to have a shorter length of hospital stay and therefore ambulate more rapidly following surgery [37].

The lateral or XLIF (XLIF®, NuVasive, Inc., San Diego, CA, USA) approach has both anatomical access advantages and disadvantages [12]. One of those disadvantages is the risk of injuring the lumbar plexus due to the transpsoas exposures [12]. As a result, it makes sense that motor and sensory weaknesses will be seen after an assortment of advances through the psoas muscle [32]. The addition of neural monitoring has helped guard these neural elements [12]. However, unlike motor elements, the lateral femoral cutaneous nerve (LFCN) or sensory elements are not identifiable by electromyogram (EMG) [12].

Isaacs et al. [32] reported that 33.6 % (36 patients) of their sample had some amount of lower extremity weakness. The majority (29 patients) of those patients had isolated hip weakness, which as most likely the result of the placement of the retractors in the muscle to allow entry to the spine; and this was significantly associated with length of surgery (p = 0.03). That is, patients with weakness had a longer surgery time compared to patients without weakness. However, for 86.2 % of these patients, the weakness was temporary. Only seven patients had deficits that were categorized as a serious surgical complication either due to the weakness not being resolved within 6 months or the weakness declined more than two grades.

Tormenti et al. [36] reported two motor radiculopathies and six thigh paresthesias/dysesthesias. One patient had sustained motor radiculopathy at the 3-month follow-up, while the other resolved by two months postoperatively. At the latest follow-up, sensory radiculopathies had resolved in five of the six patients.

It appears that the XLIF (XLIF®, NuVasive, Inc., San Diego, CA, USA) approach is a promising substitute to conventional approaches for treating adult deformity patients. Typically, these individuals are older with multiple medical comorbidities, which make them poor candidates for traditional open fusion procedures. Thus far, the trend in the literature has demonstrated significant improvements in treatment characteristics, clinical and radiographic assessments, as well as the occurrence of fewer complications in individuals who have undergone a minimally invasive XLIF (XLIF®, NuVasive, Inc., San Diego, CA, USA) approach in comparison to patients who underwent traditional surgeries [32, 33]. However, high-level evidence-based data is still needed to further clarify the effectiveness of the lateral technique for the adult deformity population.

The minimally invasive lateral approach has become a steadily popular approach to treating degenerative conditions including spondylolisthesis and fusion of the anterior column and provide indirect foraminal decompression [28, 52, 53]. Due to the increasing number of XLIFs (XLIF®, NuVasive, Inc., San Diego, CA, USA) performed each year, anticipated complications and their predictive determinants, as well as patient and procedural extenuating factors, need to be further identified and distinguished. Although the minimally invasive lateral technique has its benefits over conventional open procedures, there still seems to be some ambiguity about the total risk posed by this approach [54].