Abstract
Background Osteotomies are fundamental for correcting adult spinal deformity (ASD). This study sought to compare the effectiveness of anterior column realignment (ACR), pedicle subtraction osteotomy (PSO), intradiscal osteotomy (IDO), and Ponte osteotomies in achieving spinopelvic correction, clinical outcomes, and complications.
Methods A retrospective analysis of 146 patients who underwent posterior fusions for ASD correction between 2016 and 2022 was conducted. Patients with ≥1 year of follow-up were included. Patients were grouped according to the osteotomies with the most significant impact on sagittal alignment change: IDO, PSO, ACR, or Ponte. Spinopelvic parameters—including pelvic tilt (PT), pelvic incidence (PI), sacral slope (SS), lumbar lordosis (LL), PI-LL mismatch, and sagittal vertical axis (SVA)—and their changes from pre- to postoperative images were compared. Surgical and clinical variables were collected, including mechanical complications (proximal junctional kyphosis, proximal junctional failure, different types of hardware failure, estimated blood loss, packed red blood cell transfusions, and length of stay). Clinical status was measured with the Oswestry Disability Index. Revision-free survival time was analyzed using Kaplan-Meier curves, with patients followed from index surgery until revision or last follow-up, and differences between osteotomy types were assessed.
Results A total of 146 patients underwent ASD correction with IDO (n = 23), PSO (n = 21), ACR (n = 32), or Ponte (n = 70) osteotomies. Groups were comparable in age, body mass index, preoperative disability, and most spinopelvic parameters. PSO achieved the greatest sagittal correction (ΔLL = 29.7° ± 19.1°, ΔPI–LL mismatch = –24.75 ± 14.52, ΔSVA = –74.6 ± 51.6), IDO and ACR produced intermediate corrections, and Ponte produced the least. Estimated blood loss and packed red blood cell units transfused were lower in ACR and Ponte groups, corresponding to shorter instrumented constructs. Proximal junctional kyphosis occurred most frequently in ACR (31.3%) and Ponte (21.7%) groups, while the IDO group had the lowest rate (8.7%). Hardware complications were common but similar across groups, with screw pullout more frequent in ACR. Kaplan-Meier analysis of revision-free survival up to 50 months showed no significant differences among groups (Log-rank, P = 0.478), with the earliest reoperations occurring in the Ponte group, followed by the ACR and PSO groups.
Conclusions PSO achieved the greatest sagittal correction, while IDO and ACR provided intermediate correction. Although not statistically significant, IDO showed a numerically higher revision-free survival, with the earlier reoperations observed in Ponte, followed by ACR and PSO. These findings suggest a trend toward greater durability with IDO, highlighting the importance of osteotomy selection in maintaining long-term alignment.
Clinical Relevance These findings highlight the distinct corrective profiles, safety considerations, and long-term mechanical complication outcomes of four osteotomy techniques, emphasizing their clinical implications for surgical planning and decision-making.
Level of Evidence 3.
- PSO
- IDO
- ACR
- ponte
- PJK
- pedicle subtraction
- osteotomy
- intradiscal
- anterior column realignment
- proximal junctional kyphosis
- proximal junctional failure
- hardware failure
Introduction
Adult spinal deformity (ASD), defined as the presence of abnormal curvature(s) in the vertebral column,1 is usually treated with surgical correction, which relies on the proper interpretation and use of spinopelvic parameters for adequate surgical planning.2 These parameters, which include pelvic incidence (PI), sagittal vertical axis (SVA), sacral slope (SS), pelvic tilt (PT), lumbar lordosis (LL), and the mismatch between pelvic incidence and lumbar lordosis (PI-LL), serve as important goals for treatment. Extreme deviations from these parameters are strongly predictive of pain and functional disability and thus require more aggressive corrections.3–5 Originally, deformity correction was performed exclusively by manipulating the posterior elements of the vertebrae, which provided limited restoration of spinopelvic parameters.6 The evolution of spine surgery has led to the development of techniques capable of achieving more harmonious restorations7–11 through manipulation of the intervertebral space of the vertebral body. Osteotomies have significantly changed how ASD is corrected, allowing the safe resection of spinal structures in a controlled manner and enabling the reconstruction of rigid and severe deformities.
Osteotomies can be classified according to their extent of resection into 6 anatomic grades.12 Grades 1 and 2 are used to correct sagittal spinal alignment by exclusive resection and detachment of posterior column elements, such as facet joints, ligamentum flavum, and laminae.13 Smith-Peterson and Ponte osteotomies (Figure 1D) enable an increase in flexibility, which allows redistribution of sagittal angulations.14 Pedicle subtraction osteotomies (PSOs; Figure 1B) are classified as Schwab grade 3 osteotomies. They require complete resection of the pedicles, lamina, and articular processes and a wedge osteotomy in the vertebral body.15 PSO can shorten the posterior and middle spinal columns by using the anterior cortex of the vertebral body as a fulcrum.16 More recently described is the intradiscal osteotomy (IDO; Figure 1A), also classified as Schwab 3.17 The term IDO refers to the targeted release of a fused intervertebral space using bilateral disc entry and sequential disruption of the fusion mass. IDO allows restoration of segmental motion, realignment, and preparation of the disc space for intervertebral interbody cage implantation.18 The procedure begins with a laminectomy at the index level to expose the posterior elements and facilitate access to the fusion mass. The superior and inferior facets are completely removed to visualize the exiting nerve roots. Fluoroscopy is used to accurately identify the fused disc space. Bilateral entry into the fused disc is then performed using chisels and sequential shavers or osteotomes. The anterior longitudinal ligament (ALL) is then released using intradiscal distractors and chisels to achieve adequate distraction and restore disc height. Finally, expandable interbody cages are placed to maintain anterior column stability. By preserving the pedicles, IDO allows for screw fixation, which may reduce the incidence of pseudarthrosis.
Schematic illustrations of 4 spinal deformity correction osteotomy techniques: (A) Intradiscal osteotomy performed at 2 levels; (B) single-level pedicle subtraction osteotomy; (C) anterior column realignment with release of the anterior longitudinal ligament and placement of a hyperlordotic interbody cage; (D) 2-level Ponte osteotomies.
Motivated by a search for less invasive approaches, minimally invasive alternatives have also been described. These alternatives avoid disruption of posterior tensional elements by using the lateral transpsoas retroperitoneal route and achieve sagittal correction by releasing the ALL. Anterior column realignment (ACR; Figure 1C) is described as a less invasive method to achieve restoration of focal kyphotic deformity.19 Allegedly, this technique’s preservation of the posterior tensional bands protects from junctional complications.20
The identification of the most appropriate osteotomy to correct ASD or its combination is an individualized and multifactorial decision. The type of deformity, magnitude of the curve, stiffness, bone density, operative goals, and surgeon’s experience all significantly influence preoperative planning.14 The relative rate of postoperative complications associated with each technique is also an important consideration. Given the heterogeneity of posterior approaches, amount of resected bone, and surgical techniques used for ASD correction, we sought to compare their ability to correct spinopelvic parameters and clinical outcomes, including surgical, nonsurgical, and mechanical complications, such as proximal junctional kyphosis (PJK), proximal junctional failure (PJF), and hardware failure (HF). To our knowledge, no prior study has documented such associations; thus, we aim for our findings to help guide the selection of the most appropriate approach and osteotomy technique for ASD correction.
Methods
Study Design and Inclusion and Exclusion Criteria
We retrospectively analyzed a prospectively collected database maintained with all consecutive patients undergoing surgical correction of ASD between January 2016 and December 2022 at our institution. The study included patients older than 18 years with a diagnosis of ASD who underwent surgical correction. Patients were included if they fulfilled a minimum follow-up time of 1 year. Inclusion criteria involved a minimum uppermost instrumented vertebra (UIV) at L2 and a lowermost instrumented vertebra (LIV) in the sacrum or ilium. We excluded patients for whom no osteotomies were performed.
Groups were defined by the most structurally significant osteotomy performed. Four groups were considered: IDO, PSO, ACR, and Ponte, and each patient was assigned to a single group representing the highest-order osteotomy performed. Notably, Ponte osteotomies frequently co-occurred within the IDO, PSO, and ACR groups, given that they facilitate additional flexibility thanks to detachment and added flexibility of the posterior column at adjacent segments. Patients were assigned exclusively to the Ponte group only when no higher-grade osteotomy (ie, PSO, ACR, or IDO) was performed. Patients with co-occurrence of PSO, ACR, or IDO were excluded to isolate the effect of specific techniques better.
Data Collection, Definition of Variables, and Radiographic Assessment
Data were collected from medical records as part of a standardized protocol. Collected data included patients’ age, body mass index (BMI), length of stay (LOS), pre- and postoperative Oswestry Disability Index (ODI), pre- and postoperative radiographs, surgical variables such as number of instrumented levels, type, number, and level of osteotomies, and number of treated levels. Estimated blood loss (EBL) was recorded as the total EBL for the entire procedure; for cases performed in multiple stages, EBL was calculated as the sum of EBL, while for single-stage procedures, it corresponded to the EBL of the single surgery. In addition, transfused packed red blood cells intraoperatively and postoperatively were recorded. Mechanical complications were tracked, including PJK and PJF with days to diagnosis, as well as HF events such as screw and rod fractures, screw pullouts, pseudarthrosis, and revision-free time (days).
Medical complications included rhabdomyolysis, deep vein thrombosis (DVT), urinary tract infection (UTI), pneumonia, pulmonary embolism (PE), wound infection, and dehiscence. Rhabdomyolysis was defined as a creatine phosphokinase level >2000 U/L.
Preoperative and postoperative radiographic measurements included PT, PI, SS, LL, PI-LL mismatch, and SVA. Measurements were performed using Surgimap software (version 2.3.2.1, Nemaris Inc., New York, NY, USA) on preoperative and immediate postoperative 36-inch standing scoliosis films. PI was defined as the angle between a line perpendicular to the sacral endplate midpoint and a line connecting this point to the femoral head axis. PT was measured as the angle between a vertical line through the femoral heads and a line connecting the sacral endplate midpoint to the femoral heads. SS was defined as the angle between the superior sacral endplate and the horizontal. LL was calculated as the Cobb angle from the superior endplate of L1 to the superior endplate of S1. PI-LL mismatch was calculated as the difference between PI and LL. SVA was measured as the horizontal distance from the C7 plumb line to the posterior superior corner of S1.
Mechanical Complications
Records were systematically reviewed to determine the occurrence of mechanical complications. PJK was defined as an abnormal kyphotic angulation at segments adjacent to the UIV, while PJF was described as a progressive process within the spectrum of PJK, marked by structural failures at the posterior ligament complex, vertebral body fractures, or vertebral subluxation.21 We assessed pseudarthrosis, defined as a failure of bony fusion, which may coexist with or contribute to HF and results in persistent motion at the intended fusion site. HF events were identified from clinical records and corroborated with radiological images. The time to mechanical complication was calculated from the day of surgery to the first radiological imaging that identified such a complication, with data collected as the number of days to the complication. The revision decision was based on clinical and radiological variables and was made according to each treating surgeon’s preference.
Surgical Techniques
Patients underwent a posterior midline approach for spinal fusion, with a minimum UIV at L2 or higher and LIV at S1, iliac bolts, or S2AI. Patients could undergo Ponte (Figure 2), PSO (Figure 3), or IDO (Figure 4) during posterior correction. Operative plans were based on clinical and radiological findings, including the severity of the deformity. The correction objective was to obtain a sagittal and coronal balance. The decision to perform a specific osteotomy technique was made by the senior surgeon on a case-by-case basis, considering the rigidity of the curve, the magnitude of sagittal and coronal malalignment, bone quality, and the patient’s overall clinical status. In general, Ponte osteotomies were preferred for flexible curves requiring modest correction, IDO for moderate to large deformities with fixed thoracolumbar curves,9 PSO for a rigid or severe sagittal imbalance not correctable with lesser techniques, and ACR (Figure 5) for cases where anterior column lengthening was necessary to achieve the planned correction. In the case of ACR, a lateral approach was performed, retroperitoneal access was obtained, and the ALL was dissected and cut. The placement of hyperlordotic cages was performed according to the goals of the desired correction. Lateral cases required posterior fixation either through open or percutaneous placement of pedicle screws.
Preoperative (A and B) and postoperative (C and D) radiographs of a patient who underwent T9–pelvis posterior instrumented fusion with bilateral iliac screws, L2–L3 and L3–L4 interbody fusion, L5–S1 interbody fusion, multiple Ponte osteotomies (L1–L4), and cement augmentation at T9, T10, L1, and S1. Abbreviations: LL, lumbar lordosis; PI, pelvic incidence; PI-LL, pelvic incidence and lumbar lordosis mismatch; PT, pelvic tilt; SS, sacral slope; SVA, sagittal vertical axis.
Preoperative (A and B) and postoperative (C and D) radiographs of a patient undergoing T10–pelvis posterior instrumented fusion, L4 pedicle subtraction osteotomy, L1–L2 posterior lumbar interbody fusion with cage and allograft/autograft, laminectomies, and decompressions at L3–L5, prior hardware removal, and final multirod construct placement. Abbreviations: LL, lumbar lordosis; PI, pelvic incidence; PI-LL, pelvic incidence and lumbar lordosis mismatch; PT, pelvic tilt; SS, sacral slope; SVA, sagittal vertical axis.
Preoperative (A and B) and postoperative (C and D) radiographs of a patient with fixed sagittal imbalance and prior lumbar fusion who underwent multilevel posterior-only revision with hardware removal, Ponte and intradiscal osteotomies at L3–S1, interbody fusion using allograft and autograft, and T11-pelvis posterior instrumented fusion. Abbreviations: LL, lumbar lordosis; PI, pelvic incidence; PI-LL, pelvic incidence and lumbar lordosis mismatch; PT, pelvic tilt; SS, sacral slope; SVA, sagittal vertical axis.
Preoperative (A and B) and postoperative (C and D) radiographs of a patient undergoing anterior column realignment at L3–L4, osteotomies and release of the anterior longitudinal ligament, placement of hyperlordotic interbody cages with allograft, and posterior T10–pelvis fusion with decortication and allograft placement. Abbreviations: LL, lumbar lordosis; PI, pelvic incidence; PI-LL, pelvic incidence and lumbar lordosis mismatch; PT, pelvic tilt; SS, sacral slope; SVA, sagittal vertical axis.
Statistical Analysis
Statistical analyses were conducted using IBM SPSS Statistics version 30.0.0.0 (IBM Corp., Armonk, NY). Descriptive statistics, including frequency distributions and summary measures, were calculated for all variables. Continuous variables were reported as mean ± SD, and categorical variables as frequencies with percentages. Group comparisons were performed using analysis of variance, with Levene’s test assessing the assumption of homogeneity of variances. For variables with equal variances, Tukey’s test was applied, and for variables with unequal variances, the Games-Howell test was used. Categorical variables were compared using χ² test. Revision-free survival among the 4 osteotomy groups was evaluated using Kaplan-Meier analysis, with survival curves compared via the log-rank (Mantel-Cox) test. A P value < 0.05 was considered statistically significant.
Results
Patient Population
A total of 146 patients were included. Exclusions were made for fusions not extending to the required UIV or LIV, procedures requiring a combination of 2 Schwab grade ≥3 osteotomies, lack of follow-up ≥1 year, and incomplete radiographic assessment. Patients were stratified into 4 groups based on the highest-grade osteotomy performed: 23 IDO (15.8%), 21 PSO (14.4%), 32 ACR (21.9%), and 70 Ponte (47.9%).
Baseline Demographics
The mean age was 63.88 years (±9.17), and the mean BMI was 29.85 (±5.57), corresponding to a BMI category of overweight. The mean LOS was 9.09 ± 4.42 days. The mean number of vertebral levels fused was 8.58 ± 2.89.
Comparison of Groups: Age, BMI, Sex Distribution, LOS, and Number of Fused Levels
Groups did not differ significantly in age, BMI, LOS, discharge disposition, or preoperative ODI (Table 1). Sex distribution differed significantly accross the four groups (P = 0.002), driven by a larger proportion of women in the Ponte group (62.9%). When excluding the Ponte group, differences among the IDO, PSO, and ACR groups were not significant (P = 0.740). Instrumented levels differed across groups (P = 0.003), with ACR patients having shorter constructs than IDO and Ponte patients (P = 0.001 and 0.005), and although not significant, shorter than PSO (P = 0.092). Postoperative disability scores and changes in ODI were similar across groups (P = 0.300 and 0.294, respectively), and most patients were discharged home.
Demographic variables of study participants by osteotomy group.
Surgical Variables
Percutaneous screw placement (Table 2) was performed in 31.3% of ACR cases, which also had a higher frequency of staged surgical procedures (71.9%). EBL was lower in ACR patients, reaching statistical significance only vs PSO (P = 0.013), while PSO demonstrated greater EBL than Ponte (P = 0.030). UIV distribution differed among groups (P = 0.001), with T10 most frequently used in the IDO, PSO, and Ponte groups, whereas the ACR group more commonly utilized L2. Fusions crossing the thoracolumbar junction were less frequent in the ACR group (37.5%, P < 0.001). S2AI screws at the LIV were more common in the Ponte group (41.4%). Kyphoplasty at the UIV and UIV + 1 was more common in the IDO group (82.6%) and used in 42.9% of PSO and 41.4% of Ponte cases. Transverse process hooks at UIV + 1 were used in 14.3% of PSO and 7.1% of Ponte cases (P = 0.082).
Surgical variables of study participants by osteotomy group.
Transfusions
Intra- and postoperative transfusion requirements are summarized in Table 2. There was a trend toward lower intraoperative transfusion needs in the ACR (0.28 ± 1.11) and Ponte (0.70 ± 1.02) groups compared with the IDO (1.17 ± 2.14) and PSO (1.00 ± 1.33) groups, although this did not reach statistical significance (P = 0.072). Postoperative transfusion requirements were highest in PSO patients (2.15 ± 3.51) and lowest in the ACR patients (1.06 ± 1.58), with no significant difference between groups (P = 0.194). When total transfusions were analyzed, PSO patients required significantly more packed red blood cell units than ACR patients (3.00 ± 3.31, P = 0.040). Although this trend was consistent, no additional significant differences were observed.
Preoperative, Postoperative, and Changes in Spinopelvic Parameters
Preoperative PT, PI, and SS did not differ significantly among groups (Table 3). Post hoc analysis revealed that LL was significantly greater in the Ponte group when contrasted with the PSO (P = 0.024) and ACR (P = 0.038) groups, while PI-LL mismatch in the Ponte group was significantly lower than in the PSO (P = 0.002) and ACR (P = 0.028) groups. Preoperative SVA was significantly higher in PSO patients when compared with IDO (P = 0.037) and Ponte (P < 0.001) patients; other post hoc comparisons were not significant.
Radiographic variables of study participants by osteotomy type.
The PSO group consistently achieved the largest spinopelvic corrections (ΔLL = 29.71 ± 19.08, ΔPI-LL = −24.75 ± 14.52, and ΔSVA = −74.60 ± 51.62), which differed significantly from the Ponte group (ΔLL = 8.06 ± 26.11, P = 0.001; ΔPI-LL = −10.47 ± 13.83, P < 0.001; ΔSVA = −10.14 ± 53.51, P < 0.001). Although the IDO (ΔLL = 15.06 ± 18.16, ΔPI-LL = −18.75 ± 15.46, and ΔSVA = −33.91 ± 52.75) and ACR (ΔLL = 20.65 ± 20.41, ΔPI-LL = −19.89 ± 19.8, and ΔSVA = −48.57 ± 87.67) groups achieved consistently greater corrections than Ponte, these differences did not reach statistical significance (P > 0.05).
Medical Complications
Wound infections and medical complications occurred at relatively similar rates across groups, with no significant differences observed (P > 0.05; Table 4). Among specific complications, DVT was more frequent in the ACR group, while 2 (2.9%) cases of PE were reported in the Ponte group. Rhabdomyolysis was more common in Ponte patients, with an incidence of up to 27.1%. Pneumonia was diagnosed in 1 (4.3%) IDO patient and 2 (2.9%) Ponte patients, while UTI occurred in 3 (4.3%) Ponte patients. Sepsis was observed in 1 (4.8%) PSO patient. Pneumothorax was reported in 2 (6.3%) ACR patients and 2 (2.9%) Ponte patients. None of these comparisons reached statistical significance (P > 0.05).
Medical complications of study participants by osteotomy type.
PJK and PJF
PJK events were most frequent in the ACR group (31.3%), followed by the Ponte (21.7%), PSO (19%), and IDO (8.7%) groups, though differences did not reach statistical significance (P = 0.246) (Table 5). Revision surgery for PJK was required more often in the ACR (15.6%) and Ponte (9.6%) groups (P = 0.076). PJF occurred in 1 IDO patient (4.3%) and in 5 Ponte patients (7.1%); all of these cases required revision surgery (P = 0.271).
Measured outcomes, mechanical complications, and transfusions by osteotomy group.
Hardware Failure
Hardware-related complications were common but not significantly different across groups, occurring in 17.4% of IDO, 23.8% of PSO, 40.6% of ACR, and 30% of Ponte patients (P = 0.276; Table 5). Revision surgery for HF was most frequent in the PSO group (19%, P = 0.276). Screw pullout occurred predominantly in ACR (15.6%), reaching statistical significance (P = 0.011), while screw fractures were rare and observed only in the IDO group (8.7%, P = 0.013). Rod fracture rates were similar (8.7%–15.7%, P = 0.768). Pseudarthrosis occurred in 4.3% of IDO patients and up to 9.4% of ACR patients, without significant differences (P = 0.767).
Revision-Free Survival
Kaplan-Meier analysis of revision-free survival up to 1500 days (50 months) after surgery demonstrated no significant differences among the 4 osteotomy groups (Log-rank [Mantel-Cox] χ² = 2.483, df = 3, P = 0.478; Figure 6). The IDO group maintained the most stable survival curve, with the highest probability of remaining revision free during the first 18 months postoperatively. The first reoperations occurred in the Ponte group, followed sequentially by the ACR and PSO groups. Within the first year, 1 reoperation (4.8%) was recorded in the PSO group, 2 (6.3%) in ACR, and 6 (8.6%) in Ponte (P = 0.516). This time-to-event analysis accounted for differences in follow-up durations across groups, allowing for standardized comparison of revision-free survival probabilities.
![Kaplan-Meier curves showing revision-free survival for 4 osteotomy types (IDO, PSO, ACR, and Ponte) up to 1500 d (50 mo) postoperatively. Tick marks indicate censored observations. No significant difference was observed among groups (Log-rank [Mantel-Cox] χ² = 2.483, df = 3, P = 0.478).](https://www.ijssurgery.com/content/ijss/early/2025/11/05/8810/F6.large.jpg)
Kaplan-Meier curves showing revision-free survival for 4 osteotomy types (IDO, PSO, ACR, and Ponte) up to 1500 d (50 mo) postoperatively. Tick marks indicate censored observations. No significant difference was observed among groups (Log-rank [Mantel-Cox] χ² = 2.483, df = 3, P = 0.478).
Discussion
This study is the first to our knowledge to directly compare IDO, PSO, ACR, and Ponte osteotomies in patients undergoing surgery for ASD. Patients were grouped according to the osteotomy technique used, allowing assessment of the isolated effect of Schwab ≥3 osteotomies on spinopelvic parameters (PT, PI, SS, LL, PI-LL, and SVA), clinical outcomes (disability), and complications (medical, surgical, and mechanical). Data were derived from a retrospective clinical series, and only patients with a follow-up of 12 months were included.
Our findings confirm that the severity of preoperative deformity strongly influences osteotomy selection. Patients with milder deformities were typically treated with Ponte osteotomies, which yielded modest radiographic correction, consistent with prior reports highlighting its limited corrective power.22 PSO provided the most substantial spinopelvic correction, supporting its continued role in cases requiring major sagittal realignment. IDO and ACR achieved comparable improvements, suggesting that these techniques can offer significant correction without the added risk of PSO, demonstrated by its higher requirement for transfusions. Notably, ACR constructs were generally shorter and less likely to cross the thoracolumbar junction, resulting in lower EBL. Despite these differences, discharge disposition, changes in disability scores, and rates of medical complications were similar across groups, indicating that less extensive instrumentation does not directly correlate with an added benefit in short-term functional outcomes.
Long-term complications varied among osteotomy groups, with PJK occurring in 21.2% of the cohort. Given its multifactorial nature,23 evaluating the timing of PJK onset is crucial. Consistent with prior reports by Lau et al,21 which indicated that up to 66% of PJK cases develop within 3 months and 80% by 18 months, we found that 38.7% of PJK cases in our cohort were diagnosed within the first 6 months, increasing to 48% within the first year and 64% by 18 months.
The relatively delayed occurrence of junctional complications in our series may reflect a combination of patient and surgery-related factors, including preoperative assessment and optimization of bone quality, addressing modifiable risk factors, and specific surgical strategies aimed at reinforcing adjacent segments. These strategies included soft landing techniques,24 careful rod contouring, and protection of the UIV and UIV + 1 using kyphoplasty or transverse process hooks when indicated.
In addition to PJK, other mechanical complications were observed, including rod fractures, screw pullout, and pseudarthrosis. Rod fractures occurred at similar rates among groups (8.7%–15.7%), while screw pullout was significantly more frequent in the ACR group, and screw fractures were observed only in IDO cases. These findings highlight that mechanical failures remain an essential consideration in ASD surgery, particularly in procedures involving greater corrective forces or longer constructs.
The use of ACR and the subsequent preservation of the posterior tension bands has been proposed to mitigate junctional complications.20 Yet, our cohort displayed a higher incidence of PJK in patients who underwent ACR (31.3%), which aligns with findings reported by Gandhi 201925 (30%). This rate rises further when HF is included (46.9%). By contrast, IDO demonstrated lower early junctional complication rates and greater durability.
The introduction of IDO18 as an alternative is promising, as it allows for Schwab 3 corrections while preserving anterior column support through interbody cages, enabling a more physiologic restoration of LL by distributing correction across multiple levels, which may also reduce junctional stress. Conversely, ACR is often performed at the upper lumbar spine (L2–L3), which can shift LL and may increase the risk of earlier junctional complications.26,27
Study Limitations
Despite the valuable insights gained from our study, some limitations must be acknowledged. First, the current minimum follow-up time was set to 1 year; however, longer follow-up times allow for higher probabilities of the appearance of mechanical complications. The retrospective nature of our analysis inherently introduces selection bias, as patient inclusion depends on pre-existing institutional data. Additionally, the study was conducted at a single center, potentially limiting the generalizability of our findings. While sex was not the primary variable of interest in this study, the Ponte group presented an imbalance that could possibly confound comparisons of this group, particularly if sex influences perioperative risk, bone quality, or surgical planning. Although we categorized patients based on a hierarchical grouping strategy, IDO, PSO, and ACR cases often required additional Ponte osteotomies, for which we did not control. This classification allowed for isolation of the osteotomy effect but limits the ability to assess the independent contribution of Ponte osteotomies when used in combination with Schwab ≥3 osteotomies. Future studies may benefit from a subgroup analysis to capture the contribution of combined osteotomy techniques better. Additionally, other unmeasured factors, such as differences in patient-specific modifiable and nonmodifiable factors, may have influenced both the choice of surgical approach and the risk of complications.
Conclusions
ACR has been traditionally considered protective against junctional complications by preserving posterior tension bands; however, our findings suggest otherwise, showing high rates of PJK and frequent early presentations. In contrast, IDO trended toward higher revision-free survival within the first 18 months, despite achieving comparable sagittal correction. The ability of IDO to preserve anterior column support, restore LL in a more anatomical distribution, and distribute correction across multiple levels may reduce mechanical stress on the construct. Taken together, these results suggest that not all osteotomies have the same long-term biomechanical impact and that IDO may represent a promising alternative to more aggressive techniques such as PSO, with the potential to optimize alignment while mitigating mechanical complications.
Footnotes
Funding The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests The authors report no conflicts of interest in this work.
Disclosures Puya Alikhani reports consulting fees from ATEC Spine, Inc. The remaining authors have nothing to disclose.
Ethical Statement This study was approved by the Ethics Committee and obtained the proper Institutional Review Board approval (No. Pro00023643). Due to the use of deidentified data and its retrospective nature, patient-informed consent was unnecessary.
- This manuscript is generously published free of charge by ISASS, the International Society for the Advancement of Spine Surgery. Copyright © 2025 ISASS. To see more or order reprints or permissions, see http://ijssurgery.com.
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