Simultaneous prone transpsoas interbody fusion and osteotomies for severe deformity correction: multi-institutional retrospective review

Introduction

The rapidly aging population and increasing life expectancy are driving a rise in the prevalence of adult spinal deformity (ASD) in the United States (1). By 2060, an estimated 91.5 million Americans, 23% of the population, will be 65 years of age or older, placing them at the highest risk for ASD (1). With this increasing burden, the need for effective, patient-centered treatment options to address the unique challenges posed by this condition is urgent.

Management of ASD most often involves restoration of alignment and neural decompression of the spine. Minimally invasive spine surgery (MISS) has revolutionized the management of ASD with substantial pain relief, improvements in function, and excellent safety (2). However, patients with severe ASD are often challenging to treat with circumferential MISS approaches unless performed by a surgeon proficient in advanced MISS (3). Further, patients with significant sagittal plane abnormalities, such as those meeting minimally invasive spinal deformity revision 2 (MISDEF2) class IV criteria who may require more than 10 segments of instrumentation, are not candidates for MISS (3). In addition, these patients often have prior instrumentation that requires revision or multiple existing fused levels including L5–S1, which necessitates an open anterolateral approach (4). Such cases often involve complex, multi-stage surgeries with intraoperative position changes to achieve adequate deformity correction (5,6). While multistage surgeries effectively correct deformity, they are fraught with significant drawbacks. Prolonged operating room time carries greater risks, particularly for elderly patients (7-9). Furthermore, these complex, multi-position surgeries are associated with longer hospital stays, higher costs, and less favorable patient-centered outcomes (10,11). These challenges highlight the need for innovative surgical strategies to mitigate the drawbacks of traditional approaches.

The prone transpsoas (PTP) lumbar interbody fusion has emerged as a promising alternative that leverages the anatomical advantages of the prone position while enabling lateral access for placement of larger interbody implants without intraoperative repositioning (12). Not only does this approach minimize operative time, but also the posterior procedures can be smoothly executed without any compromise on the grounds of safety or efficiency by the surgeons (10,13-15). As repositioning is not necessary with the PTP approach, the operative team can easily gain access for posterior instrumentation, often required in extensive ASD correction. Similarly, posterior column procedures such as pedicle subtraction osteotomies (PSO) and posterior column osteotomies (PCO) can be performed concurrently at the same levels or different levels of lateral interbody fusion, allowing for greater deformity correction. However, there is a paucity of literature evaluating this combination of surgical approaches. In this study, we examine the radiographic and clinical outcomes of 15 patients with severe ASD treated using the novel trajectory of the PTP approach coupled with osteotomies. We present this article in accordance with the STROBE reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-25-123/rc).

Methods

Study design and setting

This retrospective, multicenter cohort study aimed to evaluate pre- to postoperative changes in patients with severe ASD treated with PTP and osteotomies. The study was conducted at three academic medical centers in the United States: Duke University, Wright State University, and New York University Langone Health. Data from patients who underwent surgery between July 2024 and November 2024 were collected from electronic medical records. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. As this was a retrospective study, approval by the Duke University Institutional Review Board was waived. However, all participating hospitals were informed and agreed to the study. Informed consent was waived in this retrospective study.

Patient selection

Patients were eligible for inclusion if they were at least 18 years of age at the time of surgery and had ‘severe’ ASD, defined by meeting MISDEF2 Class III or IV criteria (3). Class III includes patients with pelvic incidence-lumbar lordosis (PI-LL) mismatch over 30°, as well as increased pelvic tilt (PT) and sagittal vertical axis (SVA). Class IV includes those who (I) underwent a revision or revision-extension of a pre-existing fusion of 5 or more levels, including L5–S1; or (II) required 10 or more levels of instrumentation. All included patients underwent PTP lumbar interbody fusion with concomitant PCO or PSO. Exclusion criteria included incomplete clinical or radiographic records or absence of follow-up data.

Surgical technique

All procedures were performed under general anesthesia with the patient in a prone “Superman” position on an open Jackson table. Neurophysiological monitoring was employed in all cases. The patient was secured around the chest and lower hips against lateral movement while leaving the skin overlaying the psoas and lumbar spine accessible. Standard preoperative procedures, including skin preparation and draping, ensue. Anatomical reference points over the skin may be marked at this point, such as the anterior and posterior borders of the target vertebral levels. Accessing the anterior column is then carried out and thoroughly described in the literature (14). Due to the involvement of multiple surgeons, there is some variation in specific surgical techniques, including the approach to anterior column access and instrumentation. However, all patients in this study underwent simultaneous PSO or PCO while in the prone position. The posterior instrumentation and osteotomies were typically performed first to mobilize the segment, followed by the PTP lumbar interbody fusion. The selection of osteotomy type (PCO vs. PSO) was based on preoperative planning, with PSO reserved for more sagittal deformities requiring greater correction (>30°) and PCO used for moderate corrections or to address coronal imbalance and facet fusion.

Outcomes

De-identified data were collected from institutional electronic health records using standardized forms. Variables included demographic, surgical/perioperative parameters, clinical outcomes, and radiographic outcomes. Demographic data included age, sex, body mass index (BMI), comorbidities, smoking status, and surgical history. Perioperative details included operative levels, laterality, duration of surgery, estimated blood loss, and fluoroscopy exposure. Data about final cage height and lordosis, as well as length of hospital stay and any complications during the follow-up period, were also collected. Postoperative hardware integrity and fusion were assessed using full-length standing and flexion-extension X-rays taken during postoperative and follow-up clinic visits.

Pre- and post-operative patient-reported outcome measures (PROMs) assessed included Oswestry Disability Index (ODI) and Visual Analogue Score for back (VAS-B) and leg (VAS-L) pain. Radiographic spinopelvic parameters were also measured pre- and post-operatively using standing X-rays and included segmental lordosis (SL) at the operative levels, pelvic incidence (PI), PT, lumbar lordosis (LL), PI-LL mismatch, SVA, T1 pelvic angle (TPA), coronal Cobb angle, and thoracic kyphosis (TK). In addition, SL was measured throughout the lumbar spine. Postoperative clinical and radiographic outcomes were measured at a single time point representing the latest follow-up time point available, with a mean follow-up of 13.9±8.9 months. No intermediate time points were analyzed.

To minimize selection bias, all eligible patients during the study period who met inclusion criteria were consecutively reviewed. Measurement bias was reduced by using standardized radiographic assessment protocols and trained reviewers. No formal sample size calculation was performed due to the retrospective nature of the study. All eligible patients within the study period were included to maximize statistical power.

Statistical analysis

Continuous variables were reported as mean ± standard deviation (SD) and range, and categorical variables as frequencies and percentages. Data normality was assessed using the Shapiro-Wilk test. As this study evaluated a single cohort without a control group, all analyses focused on pre- to postoperative changes within the same patients. Pre- and postoperative comparisons for normally distributed PROMs and radiographic parameters were assessed using paired t-tests.

Spearman’s rank coefficients were calculated to assess relationships between changes in radiographic and PROMs. Correlation strength was interpreted as follows: 0–0.3 (weak), 0.31–0.6 (moderate), 0.61–0.8 (strong), and 0.8–1.0 (very strong). Clinical significance was assessed using published minimum clinically important difference (MCID) thresholds: ODI (12.8), VAS-L (1.6), and VAS-B (1.2) (16). All analyses were performed using R Statistical Software v4.2.2, with statistical significance defined as a two-tailed P value <0.05.

Results

Case example

This patient was a 60-year-old female who presented with severe low back and anterior right thigh pain. She had a past surgical history of L4–S1 fusion with revision and extension to L3 secondary to adjacent segment disease. A lower extremity neurologic exam was unremarkable. However, she had a preoperative ODI of 78 and 10 out of 10 pain for both VAS-B and VAS-L. Preoperative magnetic resonance imaging (MRI) demonstrated adjacent segment degeneration with spondylolisthesis and severe central canal stenosis at L2–3 (Figure 1). Preoperative standing X-ray showed evidence of iatrogenic flatback with previous L3–S1 instrumentation as well as adjacent segment disease of L2–3 and L3–4 pseudoarthrosis (Figure 1B,1C). As the patient had exhausted conservative management, we proceeded with fusion from T10 to pelvis with PTP at L2–3, PSO at L4, and PCO at L2–3. The procedure was completed in approximately ten hours with 2L of blood loss. The patient was discharged home on postoperative day 4. On follow-up, her LL increased to 43°, her PI-LL mismatch decreased to 17°, and her SL increased to 14°. In addition, her postoperative ODI score decreased to 6, while her VAS-B and VAS-L scores decreased to 6 and 3 out of 10, respectively.

Figure 1 Pre- and post-operative imaging of a 60-year-old female with severe low back and anterior right thigh pain. (A) Preoperative sagittal MRI demonstrating adjacent segment degeneration at L2–3 with spondylolisthesis and severe central canal stenosis. (B) Comparison of pre- and postoperative lateral standing radiographs showing prior L3–S1 instrumentation and improvement of lumbar lordosis and PI-LL mismatch. (C) Comparison of pre- and postoperative AP standing radiographs showing prior L3–S1 instrumentation and extension up to T10 and down to the pelvis. AP, anteroposterior; LL, lumbar lordosis; MRI, magnetic resonance imaging; PI-LL, pelvic incidence-lumbar lordosis.

Demographic information

A total of 15 patients across the three participating institutions met the inclusion criteria and were included in this retrospective analysis (Table 1). The mean age of the cohort was 64.4±9.6 years. Of the patients included, 9 (60%) were male and 6 (40%) were female. Comorbid conditions were present in several patients with hypertension being the most common (10, 60%), followed by diabetes (4, 26.7%) and cardiac disease (3, 20%). One patient (6.7%) had chronic kidney disease. Regarding smoking history, 1 patient (6.7%) was a current smoker, while 7 (46.7%) were former smokers, and 7 (46.7%) had never smoked. Prior spine surgery was reported in 9 patients (60%).

Pre-operative diagnoses included isthmic and degenerative spondylolisthesis, adjacent segment disease, degenerative disc disease, canal stenosis, and flat back syndrome. For osteotomies, 7 patients (46.7%) underwent PCO alone, while 6 patients (40.0%) underwent PSO alone, with 2 patients (13.3%) undergoing both PCO and PSO during the same operation. The mean skin-to-skin operative time was 477.1±143.4 minutes with a mean estimated blood loss of 984.6±610.3 mL. Each surgery involved a mean of 6.1±2.2 operative levels, including 3.1±2.9 PTP levels and 2.6±1.7 osteotomy levels. Osteotomies were most commonly performed between L2 and L4, and PTP most commonly encompassed L2 and L3. The mean cage height was 11.1±3.4 mm, with a mean cage lordosis of 15.1±8.5 degrees. The surgical approach was left-sided in 9 cases (60%) and right-sided in 6 (40%). The average length of hospital stay was 7.4±3.4 days. The mean follow-up time was 13.9±8.9 months.

Perioperative and postoperative complications

Postoperative complications were observed in several patients (Table 2).

Among PCO patients (n=8), 2 (25%) experienced transient transpsoas weakness and 1 (12.5%) had anterior thigh numbness, all resolving within six months. One PCO patient (12.5%) developed incisional drainage treated with antibiotics. Among PSO patients (n=7), 1 (14.3%) had anterior thigh numbness resolving within six months, 1 (14.3%) experienced wound dehiscence requiring revision, and 1 (14.3%) had urinary retention. One PSO patient (14.3%) with underlying cerebral palsy suffered a perioperative non-ST-elevation myocardial infarction (NSTEMI). One patient (6.7%) developed proximal junctional kyphosis (PJK) at 1 year follow-up. All patients demonstrated radiographic fusion with intact hardware.

Radiographic outcomes

Comparison of pre- and postoperative radiographic outcomes showed significant improvement across several parameters (Table 2). Both PT and PI exhibited minimal changes with non-significant differences from 21.5±10.5° to 21.9±9.9° [t(14)=−0.21, P=0.84] and 58.0±8.3° to 60.1±8.3° [t(13)=−1.11, P=0.29], respectively (Table 3). LL showed a significant improvement postoperatively, increasing from a preoperative mean of 22.2±17.5° to 47.0±12.7° [t(14)=−3.85, P=0.002]. PI-LL mismatch also showed a significant improvement, decreasing from a preoperative mean of 35.9±19.1° to 15.7±9.2° postoperatively [t(14)=3.64, P=0.003]. Similarly, SVA significantly improved, decreasing from a preoperative mean of 73.5±52.3 to 43.6±29.9 mm postoperatively [t(13)=2.50, P=0.03]. TPA decreased significantly from a preoperative mean of 23.6±10.3° to 19.1±8.4° [t(11)=2.41, P=0.03]. Additionally, the coronal Cobb angle significantly improved from a preoperative mean of 11.8±6.6° to 8.9±5.0° [t(13)=2.46, P=0.03].

SL varied by spinal level (Table 2). At the L1–L2 level, SL decreased from a preoperative mean of 8.0±5.5° to 4.5±4.1°. Although there was a downward trend, this change did not reach statistical significance [t(7)=2.08, P=0.08]. A similar pattern was observed at L2–L3, where SL non-significantly decreased from 11.3±5.0° preoperatively to 6.8±4.7° postoperatively [t(9)=2.03, P=0.07]. At the L3–L4 level, SL increased from a preoperative mean of 9.7±4.6° to 10.7±8.8°, but this change was not significant [t(7)=−0.82, P=0.44]. At both the L4–L5 level and L5–S1, the mean SL remained relatively unchanged, increasing slightly from 16.7±5.6° to 17.1±10.5° at L4–L5 [t(7)=−0.96, P=0.37] and from 19.6±11.0° to 19.1±13.0° [t(7)=−0.74, P=0.49].

Patient-reported outcomes

Postoperative functional and pain outcomes demonstrated significant improvement (Table 4). The mean ODI decreased from 54.1±16.8 preoperatively to 29.5±18.5 postoperatively [t(10)=5.43, P<0.001]. Similarly, the mean VAS-B and VAS-L showed significant reductions. The mean VAS-B score improved from 8.1±1.2 preoperatively to 4.2±2.5 postoperatively [t(10)=5.61, P<0.001], while the mean VAS-L score decreased from 7.9±1.3 to 3.7±2.7 [t(10)=6.59, P<0.001].

Correlational analyses

Correlational analyses revealed a range of relationships between radiographic and PROMs (Table 5). SL at L2–L3 demonstrated moderate to strong negative correlations with ODI (r=−0.6239), VAS-B (r=−0.6640), and VAS-L (r=−0.7157). Conversely, L3–L4 showed a moderate positive correlation with ODI (r=0.6407) but only very weak correlations with VAS-B (r=0.0746) and VAS-L (r=0.1445). Both L4–L5 and L5–S1 showed very weak to weak correlations between postoperative change and PROMs.

LL exhibited a moderate positive correlation with VAS-B (r=0.4302) and a weak positive correlation with VAS-L (r=0.3708), though its correlation with ODI was very weak (r=−0.2268). Coronal Cobb angle had a weak positive correlation with ODI (r=0.2938) and a moderate positive correlation with VAS-L (r=0.4533), while its correlation with VAS-B was negligible (r=0.0276). PI, PT, PI-LL mismatch, SVA, and TPA all had very weak to weak correlations with changes in VAS-B, VAS-L, and ODI scores.

Discussion

Severe ASD is a complex, debilitating condition characterized by spinal malalignment, scoliosis, and/or kyphosis. In severe ASD patients, these deformities have considerable sagittal and coronal imbalances that may result in substantial pain and functional impairment (11,17). Recent studies comparing less invasive methods to ASD correction with traditional open surgery suggest comparable improvement in spinopelvic parameters with fewer perioperative complications and better patient-reported outcomes. While MIS and open surgery show comparable results for coronal Cobb angle correction, open surgery tends to provide greater improvement in LL and PT (18,19). However, MIS is also associated with less intraoperative blood loss and shorter hospitalizations (20). While both approaches are associated with significant improvements in patient-reported pain and disability, MIS patients often report lower postoperative pain and have reduced opioid consumption (20,21). For complications, MIS may have lower rates of surgical site infection and neurological deficits compared to open surgery (22). While corrective surgery for ASD can result in significant pain relief and improved function, patients with severe deformities typically require open approaches, conferring an increased risk of intraoperative and postoperative complications (23). Our findings demonstrate the potential of the hybrid PTP approach with osteotomy to provide deformity correction in complex cases typically not amenable to other MISS techniques.

Compared to traditional staged surgery, the PTP approach offers several advantages. First, PTP maintains operative efficiency by avoiding the requirement of patient repositioning. By avoiding repositioning, this technique reduces operative time and anesthesia exposure and, subsequently, decreases complication rates and hospital stays, which are key considerations in the elderly ASD population (24). Furthermore, this approach allows the operative team to perform simultaneous anterior and posterior column procedures while avoiding a position change. While studies of PTP specifically for ASD are in their infancy and limited to case series, these early studies show modest coronal and sagittal deformity correction in mild to moderate ASD with significant improvements in LL, PI-LL mismatch, and SVA (5,15,25,26). These improvements extend to clinical improvement, with consistent improvement in patient-reported pain and disability (15,26). Similarly, undergoing osteotomies, including PCO and PSO, is associated with significant increases in LL and decreases in disability and pain (27-30). In this study, patients underwent simultaneous PTP and osteotomy for severe deformity correction. To the authors’ knowledge, this is the first study to evaluate this combined approach. We observed positive radiographic changes in LL, PI-LL mismatch, and SVA, in addition to TPA and coronal Cobb with a relatively low observed complication profile.

Clinically, the difference between pre- and postoperative ODI exceeded the established MCID by two-fold. Postoperative changes in VAS-B and VAS-L scores also exceeded MCID by two to threefold. When assessing for correlational relationships between PROMs and radiographic outcomes, there were moderate to strong correlations between postoperative increases in SL at L2–L3 and reductions in back and leg pain and disability scores. These findings are unsurprising, as numerous studies have shown how loss of LL contributes to pain and disability in ASD patients (31-33).

In the present study, we found nonsignificant changes in PT. While PT often changes following spine deformity correction, there are instances where this is not the case. Deformity patients often demonstrate pelvic retroversion, even when high PI is accounted for with overcorrection of lordosis. Passias et al. [2023] previously reported that upwards of 24.9% of ASD patients may exhibit pelvic nonresponse, where patients fail to correct PT despite achieving more ideal spinal alignment (34). Prabhakar et al. [2024] also reported that patients with more severe sagittal imbalance undergoing fusions over four levels often require a greater change in C2 pelvic angle to achieve an appropriate change in PT (35). Given the high PT and comparatively high rate of pelvic nonresponse in deformity patients, it is possible that some of these patients were unable to achieve adequate correction. We also found nonsignificant increases in SL of the upper lumbar spine at L1–L2 and L2–L3. These findings are not surprising given that PSOs at or above L3 predominantly increase lordosis in the upper lumbar spine and were common in our sample (36). The observed decrease in SL at L1–L2 and L2–L3 may reflect a redistribution of lordosis following major correction in the lower lumbar spine, as the spine adapts to achieve global sagittal balance. However, a concern of MIS approaches to deformity correction is the potential for lordotic maldistribution in the lumbar spine, which is associated with an increased risk of revision surgery (37). As this new potential approach to deformity surgery is further studied, careful attention should be paid to lordosis distribution.

Traditional open techniques, which involve extensive muscle dissection and retraction in a posterior-only approach, are accompanied by high complication rates, with 43.2% to 78.1% of patients experiencing complications, most commonly rod breakage, dural tear, radiculopathy, and PJK (38,39). We found a relatively favorable complication profile. Four patients experienced transient lower extremity weakness and paresthesias, all of which resolved without intervention. Two patients developed wound complications, both of which were managed successfully. One patient, with underlying cerebral palsy but no known cardiac disease, suffered a perioperative type 1 NSTEMI, attributed to spontaneous coronary plaque rupture. Additionally, one case of radiographic PJK was noted at 1-year follow-up. Although our findings are overall encouraging, our average follow-up period of 13.8 months may be insufficient to capture delayed complications such as PJK, which tend to manifest over longer periods. Extended longitudinal surveillance will be essential to fully assess the durability and long-term safety of this approach.

PTP with simultaneous osteotomy may offer improvement in radiographic and clinical outcomes with fewer osteotomies, as the significant lordosis obtained from large interbody cages in the prone position reduces the corrective demand on the posterior column. This allows the surgeon to achieve substantial correction with more focal, strategic osteotomies. For example, patients with severe ASD often require multiple osteotomies. Nasto et al. [2024] found that patients undergoing Ponte osteotomy for adult scoliosis required an average of 7.5 osteotomies to achieve adequate correction (40). Comparatively, in our hybrid approach, patients underwent an average of 2 to 3 osteotomies. Unfortunately, despite the promising results of MISS, not all deformity patients are candidates. In a recent spinal deformity complexity checklist developed by Anand et al. [2023], patients with severe spinal deformities, long fusion constructs, and prior fusion or existing hardware were considered more challenging to treat with MISS (41). As all of the patients in this study met MISDEF2 Class III and IV criteria, all of our patients likely would have been considered challenging to treat with MISS. However, our findings raise the possibility that patients with severe ASD could be treated with PTP in conjunction with osteotomy in a hybrid approach.

Limitations

While the strengths of the present study lie in its multicenter design, this study has several important limitations. The retrospective design introduces inherent risks of selection bias and information bias. The limited sample size reduces statistical power and limits generalizability bias. The multicenter design, while increasing diversity, may also introduce additional variability in surgical technique and patient management. Furthermore, the absence of a control group in this study precludes definitive conclusions regarding superiority over other surgical techniques and limits the ability to account for potential confounding factors. Although average follow-up exceeded 12 months, this may not be sufficient to assess long-term complications such as adjacent segment disease, nonunion, or rod fractures. Lastly, our findings are hypothesis-generating and should be validated in future prospective studies with larger, matched cohorts and long-term follow-up to better determine which patients may benefit most from this approach.

Conclusions

The results of the present study demonstrate that the PTP approach combined with posterior osteotomy may offer a safe, efficient, and effective surgical option for patients with severe ASD. This hybrid approach demonstrated promising radiographic correction and improvements in patient-reported disability and pain in this limited cohort, suggesting it may represent a potential alternative to traditional open techniques. However, further studies with larger sample sizes and extended follow-up periods are needed to validate these findings before this approach can be considered for broader use in complex ASD management.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-25-123/rc

Data Sharing Statement: Available at https://jss.amegroups.com/article/view/10.21037/jss-25-123/dss

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-25-123/prf

Funding: This work was supported by funding from the International Spine Study Group Foundation in the form of payment to Duke University.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-25-123/coif). K.D.T. serves as an unpaid editorial board member of Journal of Spine Surgery from December 2024 to December 2026. K.D.T. also reports receiving consulting fees from SI-Bone and LifeNet Health. C.C. receives research and consulting fees from Alphatec. C.I.S. reports funding from the International Spine Study Group Foundation, as well as grant support from the Department of Defense and National Institutes of Health; he also receives royalties and consulting fees from Nuvasive, Medtronic, and SI-Bone, holds stock or stock options in Nuvasive and Proprio, and serves as president of the Cervical Spine Research Society. D.A.B. receives consulting fees from Medtronic. M.M.A. receives consulting fees from BrainLab, Spinal Elements, Arthrex, Globus, and TrackX. The other authors have no 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. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. As this was a retrospective study, approval by the Duke University Institutional Review Board was waived. However, all participating hospitals were informed and agreed to the study. Informed consent was waived in this retrospective study.

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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