Updates on the current concepts to prevent thoracolumbar proximal junctional kyphosis and failure: a narrative review

Introduction

Adult spinal deformity (ASD) is a complex condition that often involves severe malalignment in multiple planes resulting in significant pain and disability. Currently, approximately 30 million adults in the United States are affected by ASD, and this number is projected to increase in the coming years (1). Treating ASD is challenging and while surgical management has been shown to improve quality of life and provide better outcomes compared to nonoperative care, it is associated with a high complication rate (2-4). In fact, up to 70% of patients undergoing surgery experience complications with proximal junctional kyphosis (PJK) being one of the most concerning (4). PJK affects up to 48% of patients and can lead to reoperation in as many as 25% of cases (5-9).

PJK was initially defined by Glattes et al. as a sagittal Cobb angle of 10° or more between the upper instrumented vertebrae (UIV) and the superior endplate two levels above or as a change of at least 10° from the preoperative measurement (10,11). Although PJK is primarily identified through imaging, its clinical relevance remains a topic of debate. Some studies suggest that radiographic PJK does not always correlate with worse patient reported outcome measures (PROMs) while others such as the findings by Kim et al. show that PJK can negatively affect pain scores on the Scoliosis Research Society (SRS) scale (12,13). These mixed results suggest that radiographic forms of PJK may range from a mild and asymptomatic condition to a severe problem that requires revision surgery.

The term proximal junctional failure (PJF) was introduced to describe the more severe end of the PJK spectrum. Unlike PJK, PJF is defined by both clinical and radiographic criteria. PJF is defined radiographically by Lafage et al. as a proximal junctional angle (PJA) greater than 28° or by an increase of 22° or more from baseline (14). Clinically, it is characterize by symptomatic PJK that requires revision surgery (15). In addition to its impact on patient’s health and recovery, PJF also carries significant financial costs. Theologis et al. estimated that 57 revision surgeries for PJF resulted in direct costs exceeding $3 million (16).

Given the high revision rates and substantial impact of PJK and PJF, efforts to prevent these complications have become a priority. Several recent reviews have provided an overview of the variety of techniques and strategies used to prevent PJK in ASD patients. Specifically, Chatelain et al. and Arora et al. highlighted many of the risk factors, such as sarcopenia, poor bone mineral density (BMD), or altered sagittal alignment that can contribute to the risk for PJK and some of the potential prevention strategies, with Arora paying particular attention to the many possible intraoperative prophylactic techniques (17,18). While these articles provide a useful overview of key risk factors for PJF and strategies for prevention, they do not address the variety of definitions for PJK and PJF, the challenge of defining clinically versus radiographically significant PJK, or provide an overview of newer classification systems. Additionally, there are several newer prevention strategies, such selection of the landing zone, that are not adequately described. As such, this review aims to provide the latest updates to definitions, classifications, and our understanding of PJK and highlight newer strategies to prevent the development of PJK and PJF to ultimately improve outcomes for patients with ASD. We present this article in accordance with the Narrative Review reporting checklist (available at https://asj.amegroups.com/article/view/10.21037/asj-24-62/rc).

Methods

A detailed search of electronic databases, including PubMed and Scopus was conducted to identify peer-reviewed articles on PJK (Table 1). The search strategy included the following keywords “adult spinal deformity”, “ASD”, “proximal junctional kyphosis”, “PJK”, “proximal junctional failure”, “PJF”, “definition”, “classification”, “risk factors”, “prevention”, “prophylaxis”, “surgical planning”, “patient optimization”, and “alignment” (Table S1). These terms were combined using Boolean operators (“AND”, “OR”) to improve the search results and maximize identification of relevant literature. Articles were restricted to those published in English.

Articles published between July 2005 and November 2024 were included, with a focus on updated definitions and improved understandings of PJK as well as newer prevention techniques. Eligible studies included peer-reviewed journal articles, expert reviews, case studies, and editorials. Exclusion criteria included an emphasis on unrelated conditions, incomplete data, or non-human studies.

Current understandings and definitions of PJK

Since the original definition of PJK by Glattes et al., several alternative definitions have been proposed to better predict its clinical significance (10). Bridwell et al. suggested raising the threshold for PJK to 20° due to a lack of correlation between the original definition and clinical outcomes (19). However, even with this adjusted threshold, no statistically significant relationship between PJK and PROMs was found (19). In 2023, Lovecchio et al. proposed a new definition of PJK and defined it as an angle between UIV−1 and UIV+2 of ≤−28° with a change of ≤−22°. While this definition had the highest positive predictive value (PPV) for PJF and was associated with the highest revision rates, its PPV and sensitivity remained low which highlighted the need for more precise definitions (20).

Khalifé et al. applied normative analysis to define PJAs at each thoracic level, with abnormal values set at the mean ± 2 standard deviations (21). Using this approach, 22.9% of ASD patients met the definition of PJK in comparison to 46.2% with Glattes’ definition and 8.7% with Lovecchio’s. This approach provides a more specific definition and offers valuable insights in terms of surgical planning to prevent PJK (21). Recent findings by Lafage et al. demonstrate the need for a broader understanding of PJF to account for a wider range of complications at the junctional angle (22). In their study of 185 patients with severe junctional issues, the authors identified three distinct patterns of failure at the junction: vertebral failure, disc failure, and junctional degeneration with 25% of patients demonstrating non-kyphotic junctional disease (Figure 1) (22). This broader definition of proximal junctional disease is useful in identifying patients at risk of suboptimal clinical outcomes that might be overlooked using traditional definitions.

Figure 1 Examples of Lafage’s modes of failure at the proximal junction. (A) Vertebral failure at the UIV; (B) angular soft tissue failure (disc degeneration above the UIV); (C) junctional degeneration (disc collapse). UIV, upper instrumented vertebrae.

Classification systems for PJK

Efforts have also been made to classify PJK to capture its varying presentations. In 2011, Yagi et al. proposed a system that graded PJK based on the degree of junctional angle increase: Grade A (10–14°), Grade B (15–19°) and Grade C (≥20°) (23). Moreover, the causes of PJK were categorized as disc and ligamentous failure (Type 1), bone failure (Type 2), and implant/bone failure (Type 3) (23). While this classification described common presentations of PJK, it did not guide management.

To address this limitation, Hart and the International Spine Study Group (ISSG) introduced a six-component PJK severity scare (HART-ISSG PJKSS) in 2013. This classification considers factors such as neurological deficit, focal pain, instrumentation issues, changes in kyphosis/posterior ligamentous complex integrity, UIV/UIV+ fractures, and the UIV level and assigns points to each category based on the severity of the findings. A score of ≥7 out of 15 was recommended as the threshold for which the patient should undergo revision surgery (24). Studies have validated the predictive value of this system and showed the association of higher scores to worse PROMs and the need to undergo revision surgery (25,26).

In our current understanding, PJK can result from mechanical or biological factors at either a local or global level (27). Dubousset and Diebo identified three primary local mechanical causes: disruption of soft tissues at the upper level during surgical exposure, weakness of the posterior instrumentation leading to pullout, and lack of anterior vertebral body resistance to compression. Global mechanical causes are related to the displacement of the center of gravity of the head. The most common global cause is selecting an unstable UIV. Other global factors include inadequate correction such as insufficient thoracic kyphosis (TK) in long fusions for thoracic scoliosis which could pull the head backward and increase the risk of PJK. On the other hand, overcorrection, such as surgically induced hyperlordosis, can also increase the risk of PJK by inducing posterior thoracic translation triggering a compensatory PJK (Figure 2) (27).

Figure 2 Examples of a patient with a minimally translated construct and of a patient with a posteriorly translated construct. (A) Preoperative imaging. (B) At 1 year postoperatively UIV SPi =11° and UIV SVA =−3 mm in a minimally translated patient. (C) Preoperative imaging. (D) At 1 year postoperatively UIV SPi =28.3° and UIV SVA =−52 mm in a posteriorly translated patient. SPi, spino-pelvic inclination; SVA, sagittal vertical axis; UIV, upper instrumented vertebrae.

Patient risk factors and optimization as prevention

Three primary biologic causes of PJK have been identified which include aging, metabolic bone diseases, and neuromuscular pathology. Older patients often present with decreased muscle mass which compromises spinal stabilization and hence would increase the probability of malalignment of the spine which increases the risk of developing PJK (27). Metabolic bone diseases, such as osteoporosis, increase the risk of implant related complications such as cage subsidence and compression fractures both of which could lead to the development of PJK (27). For neuromuscular conditions, Glassman et al. reported that 76% of patients undergoing revision surgery for PJK had an underlying neuromuscular disorder. They further emphasized on the importance of performing a thorough neurologic evaluation prior to surgery and especially in older patients (28).

Therefore, recent efforts have focused on optimizing these factors especially bone health as a strategy to prevent PJK and PJF. In fact, studies have demonstrated that pre-existing low BMD is a significant risk factor for PJK. Yagi et al. further identified that a BMD less than −1.5 is associated with a greater risk of developing PJF (23,29,30). As part of prevention strategies, Kim et al. showed that a 3-month preoperative treatment with teriparatide resulted in significantly lower rates of PJF and improved PROMS compared to a 3-month treatment with denosumab in osteoporotic patients (31). This suggests that preoperative management of bone health is vital part for high risk patients (31).

Frailty, and more specifically sarcopenia, has been identified as a significant risk factor for PJK and PJF. Moreover, older age is also frequently reported as a risk factor, likely due to its association with increased frailty (32). Several tools including the ASD-Frailty Index and the Risk Analysis Index can help identify patients at risk. In a 2022 study, Eleswarapu et al. found that low psoas cross-sectional area measured on computed tomography (CT) or magnetic resonance imaging (MRI) strongly predicted PJK and PJF with thresholds of less than 12 cm² for men and less than 8 cm² for women (33). Preoperative optimization of frail patients typically involves nutritional management and prehabilitation exercises to strengthen the muscles most important for recovery. These interventions aim to address malalignment and poor stabilization caused by reduced muscle mass during the postoperative period (27,34). Recently, the ReActive8 Trial has investigated the use of implantable neurostimulation to treat chronic low back from multifidus muscle degeneration (35). Following 2 years of treatment, 76% of participants experienced clinically significant improvements in self-reported measures of pain and disability, suggesting that neuromodulation is effective at improving muscle quality and neuromuscular control (36). While the initial study was conducted in nonoperative patients, these finding may potentially have broader implications for PJK prevention and spine surgery generally if neuromodulation can be used to improve muscle quality and ultimately spine stabilization.

At the other extreme, a body mass index (BMI) of over 25 kg/m² has also been associated with an increased risk of PJK (37,38). While it may be unrealistic to expect all patients to achieve a BMI below 25 kg/m² prior to surgery, it is important to recognize this risk factor in order to better council the patient. Weight loss however minimal may in fact reduce the risk of PJK along with other surgical complications.

Diebo et al. recently identified preoperative self-reported loss of balance and gait disturbance potential risk factors for PJK (39). In their study, 212 patients were about a history of recent balance loss or gait disturbances. Those reporting imbalance had 2.2 times higher odds of developing PJK within 2 years and nearly double the rates of PJF compared to those without imbalance (34.00% vs. 17.92%) (39). These findings align with Glassman et al.’s findings that 76% of PJK patients had an undiagnosed neurologic disorder and hence emphasizes the importance of a thorough physical examination and functional testing in managing ASD, and ultimately in preventing PJK (28). While additional research is needed to determine how to optimize this patient population, recognizing these risk factors is an important step to better select surgical candidates in order to minimize complications.

Preoperative planning and sagittal alignment for PJK/PJF prevention

The prevention of PJK and PJF starts with careful preoperative planning. Recent research has highlighted the importance of defining both ideal segmental alignment and patient-specific correction targets during surgical correction. In 2018, Lafage et al. found that while overall lumbar lordosis correction was similar in patients with and without PJK, those with PJK patients experienced reduced segmental lordosis from L4–S1 and relied on increased lordosis at more cranial levels to achieve correction (40). This challenges the current belief that the majority of lordosis should come from the lower lumbar spine and emphasizes that both the magnitude and distribution of correction are critical to prevent the development of PJK (41).

The amount of correction required to prevent PJK may vary significantly between patients. To address this, Lafage et al. introduced the sagittal age-adjusted score (SAAS) which compares postoperative sagittal alignment to ideal age-adjusted alignment values for pelvic incidence-lumbar lordosis (PI-LL), pelvic tilt (PT), and T1 pelvic angle (TPA). Valuably, the use of age specific alignment goals means this classification system is more patient specific than some other alignment systems which use static alignment thresholds. For each of the three parameters, a point value of −2 to 2 is assigned depending on if a patient is under, over, or appropriately corrected to age-adjusted targets. The SAAS score is calculated by adding the points from each of the parameters. A score of −2 or less means the patient was under corrected and a score greater than 2 means the patient was overcorrected. Scores of −1 to 1 are considered as matched correction to age (42). Higher SAAS scores were found to be associated with increased incidences of PJK and worse PROMs, emphasizing the need to individualize alignment goals (42). Similarly, Protopsaltis et al. further demonstrated that correcting patients to normative alignment rather than age-adjusted functional alignment resulted in higher rates of PJF with no improvements in PROMS and hence further support the need for tailored correction targets (43).

Several other alignment systems have been proposed with varying ability to predict PJK. The Roussouly system describes 4 types of spinal curvatures and encompasses a variety of parameters, including the inflection point, sacral slope, upper and lower arcs of lordosis, and TK (44). The decision for which spinal type would be the ideal correction is guided by a patient’s PI (45). Several articles have shown that patients that were not corrected to their ideal Roussouly type were at significantly increased risk for mechanical complications, including PJK and PJF as well as revision surgery (45-47). The SRS-Schwab classification was later proposed in an attempt to improve classifications of spinal malalignment and includes the coronal curve type and three sagittal modifiers, PI-LL mismatch, sagittal vertical axis (SVA), and PT. Using the SRS-Schwab modifiers and alignment cutoffs, Park et al. assigned scores based on the severity of the sagittal imbalance with a maximal score of 2 for each category (48). A total score of 2 or less was considered mild imbalance, a score of 3–4 moderate imbalance, and 5–6 was considered severe imbalance. This study found that there was no statistically significant difference in rates of PJK, PJF, or revision surgery between patients when classified by the SRS-Schwab system. Using a similar SRS-Schwab scoring system, Wang et al. was able to show that the SRS-Schwab system was capable of predicting mechanical complications, including PJK; however, there was no statistically significant difference in rates of mechanical complications between groups (49). In contrast, the Global Alignment and Proportion (GAP) Score was shown to be both predictive of mechanical complications and there was a statistically significant difference in the incidence of mechanical complications between groups. GAP uses relative pelvic version, relative lumbar lordosis, lordosis distribution index, and relative spinopelvic alignment to calculate a combined score that can then be used to classify patients as proportioned, moderately proportioned, or severely disproportioned (50). In contrast to the findings of Wang, Lord et al. found that there was no correlation between PJK and GAP (50). The conflicting results emphasize the challenge of developing an alignment system that can reliably predict the risk for PJK. Additionally, few articles report on exclusively PJK and instead focus on mechanical complications more generally, making it challenge to reliably evaluate the predictive ability of these systems in relation to the development of PJK.

With the rapid development of machine learning models and the existing limitations of current classification systems to predict PJK, there is growing interest in using artificial intelligence (AI) to predict the risk of PJK in ASD patients. Recently, Lee et al. developed an online calculator using the random forest model to predict PJK after ASD surgery. Parameters in the calculator included the type of deformity, age, BMI, SRS curve pattern, SRS PI-LL modifier, SRS global balance modifier, PI, and postoperative PJA. The model used in the calculator exhibited an area under the receiver operating curve of 0.76 with high accuracy and specificity for predicting PJK (51). Johnson et al. developed three different models using either a support vector machine or convolutional neural networks and variable combinations of radiographic parameters, clinical data, or preoperative MRIs. Johnson’s third model using thoracic MRIs was able to predict PJK with a sensitivity of 73.1% and specificity of 79.5% (52). While these models appear promising, ongoing research is required to demonstrate their value clinically.

Upper and lower instrumented vertebrae (LIV) selection, the landing zone concept

The choice of UIV and LIV is imperative to achieve alignment targets and reduce mechanical complications. In 2023, Yao et al. compared LIV placements at L4/L5 versus S1/Ilium and found that fusions to S1/Ilium provided better sagittal alignment but were associated with higher PJK incidences (53). In terms of UIV selection, lower thoracic fusions have been associated with higher incidences of PJK whereas upper thoracic fusions are associated with an increased risk of severe PJF (54). For these reasons, Ohba et al. proposed criteria for UIV selection based on changes in TK from standing to supine or prone positions recommending UIV placement if supine ΔTK surpasses 18.5° and prone ΔTK surpasses 11.5° (55). Frailty also plays a significant role as Onafowokan et al. reported that severely frail patients had fewer significant PJK or PJF complications when the UIV was positioned above the thoracolumbar junction (56).

In 2024, Diebo et al. introduced the concept of selecting a high-quality landing zone (UIV−1 to UIV+2) as part of preoperative surgical planning for PJK prevention (57). They found that patients with preoperative listhesis at the landing zone or a spino-pelvic inclination (SPi) at the UIV above 15° had significantly higher PJK rates at 2 years, with the highest rates observed in patients with both conditions (45.5%) (57). This study challenges the traditional dichotomous thinking of upper vs. lower thoracic UIV and focuses on selecting proper landing zone for UIV selection. This highlights the importance of evaluating and optimizing the entire landing zone to reduce the risk of PJK effectively.

PJK/PJF surgical prophylaxis

Several intraoperative prophylactic techniques, such as cement augmentation and tethering, have been proposed to prevent PJK. While no consensus exists on the most effective technique or specific indications for their use, the general benefits of prophylaxis are well documented (58-60). Prophylactic UIV cement vertebroplasty is one of oldest techniques for PJK prevention; however recent studies have called its effectiveness into question. In a sample of 39 patients that underwent two-level prophylactic vertebroplasty, Raman et al. reported that 28.2% of patients developed PJK suggesting this technique is not effective for decreasing the incidence of PJK (61). Han et al. similarly found that 2-level prophylactic vertebroplasty was not effective in preventing the development of PJK and further reported that it was not effective in reducing the incidence of PJF or proximal junctional fracture (62). The recent, largely negative results of vertebroplasty have encouraged the development of newer prophylactic techniques to more effectively reduce the incidence of PJK.

As an alternative to cement augmentation, Park et al. investigated the impact of human bone morphogenetic protein-2 (rhBMP-2) combined with beta-tricalcium phosphate (β-TCP) injection at the UIV on PJK development. Patients who received rhBMP-2 at the UIV had significantly lower rates of PJK compared to the control group (12.0% vs. 35.7%) as well as an increase in Hounsfield unit measurements from preoperative values to one year after surgery (63).

Recent prevention techniques have focused on modifying the surgical construct by using hooks, screws, or flexible rods at the UIV. In 2021, Cazzulino et al. proposed using hooks at the UIV to create a “Soft Landing Zone” providing a more gradual transition between the rigid fusion and non-instrumented levels (64). With this technique, the average change in PJA was 8° and nearly 60% of patients experienced a PJA change of less than 10°. However, Bourghli et al. recently compared prophylactic screws to hooks for PJK prevention in ASD and found no significant difference between the two with both cohorts showing PJK/PJF rates of approximately 25% (65). Additionally, Tsutsui et al. found that the incidence of PJK was actually significantly higher in patients that received transverse process hooks as prophylaxis in comparison to patients that received pedicle screws and further that PJK with transverse process hook was associated with UIV or UIV+1 fracture (66). Ultimately the results of hook prophylaxis for PJK prevention are mixed, but there is potential for this to be a useful technique.

Early evidence suggests that flexible rods that allow for small degrees of flexion and extension at the proximal junction of a long fusion may significantly reduce PJK incidences. However, this approach has yet to be extensively studied (67). A recent study introduced a hybrid screw technique in which a pedicle screw is placed on one side of the UIV and a laminar screw on the other to improve resistance to compression at the upper end of the construct (68). Patients that underwent fusion with this hybrid construct experienced significantly lower rates of PJK and PJF compared to the control group (0.0% vs. 31.7%). While these results are promising, larger studies are needed to validate the effectiveness of this technique.

Tethering at the UIV similarly aims to reduce the abrupt transition between the rigid construct and the flexible upper segments herein minimizing the stresses that contribute to PJK and PJF (59). This technique typically involves threading a strong tape through the spinous processes of UIV+1 and UIV+2 before applying tension and attaching the tape to the proximal end of the construct. There is significant variability in how tethering systems are applied but the overall findings are encouraging (69). The initial evidence in favor of prophylactic tethering was provided by Bess et al. in their 2017 study in which using finite analysis the authors were able to show that in long instrumented spine constructs, tethers created a gradual transition in range of motion and adjacent segment stress between instrumented and non-instrumented segments and that this technique was more effective than segmental pedicle screws or transverse process hooks (70).

From Bess’s initial analysis, significant attention has been dedicated towards determining the ideal tethering configuration to reduce the incidence of PJK. Iyer et al. showed that tethering reinforcement at the UIV+1 and UIV−1 without crosslinking was largely ineffective and reported a comparable incidence of PJK in those with and without tethering prophylaxis (71). Buell et al. similarly showed that one-level tethering did not lead to a statistically significant reduction in PJK; however tethering at the UIV+1 with the addition of crosslinking augmentation at lower levels did (72). Based on the low impact of short tethering segments, current recommendations are in favor of two to three level tethering in a ligamentous augmentation fashion, often with the addition of crosslinking (73). Using their ligament augmentation technique at the UIV−1, UIV, and UIV+1, Safaee et al. reported significantly lower rates of reoperation for PJF (3.3% vs. 15.6%) in patients that had been prophylactically tethered (74). Building on the initial findings of Buell, Rabinovich et al. reported that at 2-year follow-up, patients that received tethering at the UIV+1 as well as crosslink tethering at UIV−1 and UIV−2 had significantly lower rates of PJK in comparison to patients without tethering and no patient in this cohort required revision for PJK (75). Tethering appears to be emerging as an effective intervention for PJK prevention; however, ongoing research will be required to determine the ideal configuration and amount of tension in the augmentation to maximize clinical outcomes.

Postoperative prevention strategies

While successful PJK prevention is highly dependent on patient optimization and intraoperative techniques, there are several postoperative strategies as well that may be useful in preventing the development of PJK and PJF. Given that poor bone quality is a risk for PJK, aggressive management with bisphosphonates, teriparatide, and other pharmaceuticals aimed at improving bone quality should continue in the postoperative period (17). Because frailty and disruption of posterior musculature have both been shown to be risk factors for PJK, postoperative muscle strengthening through physical therapy and rehabilitation may be a useful strategy in preventing PJK. Physical therapy has been shown to improve disability scores and improve function and disability after spinal fusion surgery, but there is limited research evaluating the direct impact of muscle strengthening on PJK prevention (76). There is some evidence to suggest that postoperative bracing may also be useful in reducing a patient’s risk for PJK. Shahi et al. found that patients that used a hyperextension brace for 6 weeks following surgery had significantly lower rates of PJK at 1-year follow-up in comparison to non-braced patients (77). In contrast, Lord et al. and Crawford et al. found no statistically significant difference in rates of PJK between patients that were braced postoperatively and those that were not (50,78). Given the mixed findings and limited literature specifically evaluating postoperative PJK prevention strategies, this will likely be a valuable area of future research.

Limitations

This review of PJK faces several potential limitations. Included studies vary significantly in methodology, sample population, and in how PJK or PJF is defined. This variability makes it challenging to draw widely generalizable conclusions or recommendations regarding PJK prevention. Additionally, many studies report on all mechanical complications, including PJK, rather than exclusively PJK creating further difficulty in evaluating various classification systems or prevention strategies. Another significant limitation is varying quality of evidence due to methodological flaws, such as small samples sizes or non-randomized designs. These flaws may limit the relevance of the findings. Finally, while postoperative prevention strategies are discussed, few studies provide specific evaluations of the impact of these interventions on PJK prevention. Despite these limitations, this narrative review provides an updated and comprehensive overview of major PJK prevention strategies during the preoperative, intraoperative, and postoperative phases. Additionally, this review discusses the various definitions of PJK and PJF as well as the predictive value of various classification systems in relation to PJK and the potential future role of AI in refining these predictions.

Conclusions

Mild PJK is a common radiographic finding with an unclear impact on clinical outcomes following ASD surgeries. However, in severe cases it can progress to PJF leading to significant pain, disability and the need for revision surgery. In recent years, growing attention has been directed toward better defining, understanding, and preventing PJK. To date, efforts have primarily focused on patient optimization, preoperative planning, segmental alignment, and surgical prophylaxis. Successful PJK prevention will likely require a multifactorial approach that combines these strategies to achieve optimal clinical and radiographic outcomes while minimizing mechanical complications following ASD surgery (Table 2).

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the Guest Editors (Mark J. Lambrechts and Munish C. Gupta) for the series “Adult Spinal Deformity: Principles, Approaches, and Advances” published in AME Surgical Journal. The article has undergone external peer review.

Reporting Checklist: The authors have completed the Narrative Review reporting checklist. Available at https://asj.amegroups.com/article/view/10.21037/asj-24-62/rc

Peer Review File: Available at https://asj.amegroups.com/article/view/10.21037/asj-24-62/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://asj.amegroups.com/article/view/10.21037/asj-24-62/coif). The series “Adult Spinal Deformity: Principles, Approaches, and Advances” was commissioned by the editorial office without any funding or sponsorship. A.H.D. reports that he receives royalties from Spineart, Stryker, and Medicrea, consulting fees from Medtronic, research support from Alphatec, Medtronic, and Orthofix, grant from Medtronic, and fellowship support from Medtronic. B.G.D. is CEO and shareholder at Spinal Alignment Solutions and receives consulting fees from Clariance, SpineVision, Medtronic, and Spineart. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from patients for the publication of this study and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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