Effect of the Hybrid Screw Insertion Technique Using Pedicle and Laminar Screws at the Upper Instrumented Vertebra for Preventing Proximal Junctional Kyphosis

Abstract

Study Design

Retrospective comparative study.

Objective

To evaluate whether a hybrid screw insertion technique (one pedicle screw and one laminar screw) at the upper instrumented vertebra (UIV) preserves vertebral trabecular architecture and reduces the incidence of proximal junctional kyphosis (PJK) compared with conventional bilateral pedicle screw fixation in adult spinal deformity (ASD) surgery.

Methods

From March 2023 to August 2024, 89 patients who underwent ASD surgery using the hybrid screw insertion technique and had a minimum follow-up of 12 months were retrospectively reviewed. The control group consisted of 78 patients who underwent ASD surgery using conventional UIV fixation, performed by the same surgeon during an 18-month period of identical duration immediately preceding the study period. The incidences of PJK and PJF within the first postoperative year were compared between the two groups.

Results

Baseline demographic characteristics and preoperative and postoperative spinopelvic parameters were comparable between the two groups, except for preoperative lumbar lordosis, which was greater in the hybrid screw group. During the first postoperative year, the incidence of PJK was lower in the hybrid screw group than in the control group (16.9% [15/89] vs. 35.9% [27/78], p = 0.005). No significant difference was observed in the incidence of PJF. Multivariate analysis identified hip bone mineral density, postoperative L1PA, and the use of the hybrid screw insertion technique as independent predictors of PJK.

Conclusions

The hybrid screw insertion technique may reduce the risk of PJK in ASD surgery by preserving vertebral trabecular architecture at the UIV compared with the conventional method.

Keywords

adult spinal deformity hybrid screw insertion technique upper instrumented vertebra proximal junctional kyphosis

Introduction

The incidence of proximal junctional kyphosis (PJK) remains significant, ranging from 17% to 40%, and remains an unresolved issue in adult spinal deformity (ASD) surgery.^1-4 The upper instrumented vertebra (UIV) is known to be the most vulnerable site for PJK, and several strategies have been proposed to reinforce this weak point, including cement augmentation at the UIV and avoiding bicortical pedicle screw fixation.^5-9 Although various approaches have been introduced to mitigate PJK, an effective solution has yet to be established.

Vertebral strength is proportional to the relative amount of vertical trabeculae.¹⁰ Furthermore, the biomechanical competence of vertebral trabecular bone is influenced not only by its amount but also by the continuity of the trabecular lattice.¹¹ In trabecular bone biomechanics, maximum support is achieved when trabecular elements are completely connected.¹² Considering these previous findings and the fact that PJK frequently occurs due to fractures of the UIV, it is presumed that preserving more trabeculae within the UIV compared with conventional surgery may help reduce the incidence of PJK.

In conventional ASD surgery, instrumentation of the upper instrumented vertebra (UIV) is typically achieved through bilateral pedicle screw fixation. However, bilateral pedicle screws inevitably violate the trabeculae on both sides of the vertebral body. In this study, we hypothesized that by fixing one side of the UIV with a pedicle screw and the other with a laminar screw, the hybrid screw insertion technique could preserve more of the vertebral body trabeculae compared with the conventional method, thereby enhancing the mechanical resistance of the UIV to PJK. In this study, we aimed to compare the incidence of PJK, as well as postoperative outcomes, between patients who underwent the hybrid screw insertion technique at the UIV and those who received the conventional bilateral pedicle screw fixation in ASD surgery.

Methods

Study Design

This study was conducted through a retrospective analysis of prospectively collected data, targeting patients treated for ASD at a single spinal center in a tertiary care teaching institution. This study was approved by the Institutional Review Board of the hospital where it was conducted (B-2506-976-102). The study was reported in accordance with the STROBE guidelines.

The study group consisted of patients who underwent ASD surgery using the hybrid screw insertion technique between March 2023 and August 2024. The inclusion criteria were as follows: (1) age > 50 years; (2) underwent surgical treatment for symptomatic degenerative spinal deformities, including lumbar kyphosis and thoracolumbar scoliosis; and (3) subjective disability attributable to ASD. Exclusion criteria comprised the following: (1) the presence of other spinal pathologies impairing ambulation, such as thoracic and/or cervical myelopathy; (2) peripheral vascular disease; (3) syndromic or neuromuscular disorders; (4) serious uncontrolled medical comorbidities, including sepsis or malignancy, that could lead to disability or adversely affect the overall medical condition; (5) other uncontrolled chronic conditions that might influence study outcomes, such as endocrine disorders, metabolic disease, kidney disease, or rheumatoid arthritis; and (6) psychiatric disorders, including dementia, intellectual disability, severe substance abuse, or alcohol addiction. To minimize selection bias, the control group included all consecutive, eligible patients who underwent conventional UIV fixation by the same surgeon during an identical 18-month period (August 2022–February 2023), without selective inclusion.

Surgical Procedure

All procedures were performed by a single surgeon to ensure consistency in the surgical technique across all cases. After the patients were positioned prone in the operating room, lateral radiographs were used to calculate the pelvic incidence-lumbar lordosis mismatch. Based on the measurements, the required correction angle, osteotomy type, and fusion length were determined. T10 was selected as the UIV because of its biomechanical stability associated with the presence of true ribs. Given the high risk of L5–S1 pseudoarthrosis, iliac screw fixation was routinely performed as part of standard practice. Dual-rod constructs are routinely implemented to prevent rod breakage.

In the study group, a pedicle screw was inserted on the right side of the UIV, while a laminar screw was inserted on the left side (Figure 1). Preoperative CT was used to plan the trajectory, width, and length of the laminar screw (Figure 2). Laminar screws with a diameter of approximately 4.5–5.5 mm were typically used. In the control group, conventional bilateral pedicle screw insertion was performed at the UIV. To minimize time-related bias, all surgical procedures were performed identically between the study and control groups except for the UIV screw insertion technique. In both groups, gradual kyphotic contouring was applied to the proximal rod to reduce the risk of PJK. In addition, the interspinous and supraspinous ligaments were preserved to maintain the proximal posterior tension band. Unicortical fixation was also routinely performed at the UIV in both groups.

Figure 1.

Postoperative radiograph of a patient who underwent adult spine deformity (ASD) surgery with the hybrid screw insertion technique applied at the upper instrumented vertebra (UIV)

Figure 2.

(A) Preoperative CT was used to plan the laminar screw trajectory at the UIV and to measure the appropriate screw size. (B) Postoperative CT demonstrates appropriate insertion of the laminar screw at the upper instrumented vertebra (UIV) along the planned trajectory

Measurements and Outcomes

Baseline Characteristics

Baseline data included factors known to influence the development of PJK and Proximal junctional failure (PJF), such as age, sex, Charlson Comorbidity Index (CCI), body mass index (BMI), hip bone mineral density (BMD), preoperative and immediate postoperative spinopelvic parameters, and spinopelvic parameters at 1 year postoperatively. All radiographic assessments were performed using biplanar stereo-radiographic full-body imaging (EOS, Paris, France).

Primary Outcomes: PJK and PJF Rates

The primary outcomes were the 1-year postoperative rates of PJK and PJF following ASD surgery. In accordance with the standard definition, PJK was defined as a proximal junctional sagittal Cobb angle ≥ 10° between the lower endplate of the UIV and the upper endplate of UIV+2, along with an increase of ≥ 10° compared with the preoperative angle. PJF was defined as the need for revision surgery due to a vertebral fracture at the UIV or UIV+1, subluxation between the UIV and UIV+1, failure of fixation, or the development of a neurologic deficit.

Secondary outcome: patient-reported outcomes (PROs)

The secondary outcome was the change in PROs 1 year postoperatively. PROs included the visual analog scale (VAS) for back pain, Oswestry Disability Index (ODI), and EuroQol-5 Dimensions (EQ-5D). The VAS for back and leg pain uses a 10-cm line ranging from 0 (“no pain”) to 10 (“disabling pain”). The ODI is a self-report questionnaire consisting of 10 items that assess functional impairment due to back pain, with scores ranging from 0 to 100.¹³ The EQ-5D evaluates health-related quality of life (HRQOL) on a scale of 0 to 1, where 1 represents perfect health.¹⁴

Hounsfield Unit Measurement

Because the trabecular bone density of the UIV may influence the development of PJK and PJF, the preoperative Hounsfield unit (HU) of the UIV was measured on computed tomography (CT) scans.^15,16 HU measurements were performed using a previously established method.¹⁷ Regions of interest (ROIs) were placed at three levels on axial CT images obtained as parallel to the vertebral endplates as possible: immediately below the superior endplate, at the mid-vertebral body, and immediately above the inferior endplate. The ROIs were drawn to include only cancellous bone while avoiding cortical bone, osseous abnormalities, and voids such as vascular channels. The mean HU value of the three measurements was used for analysis.

Statistical Analysis

Descriptive statistics were used to summarize the participant characteristics. To assess group homogeneity in terms of demographic and baseline variables, t-test, chi-square test, and Fisher’s exact test were used as appropriate. Continuous variables were analyzed using an independent t-test, with results reported as mean ± standard deviation. Categorical variables were compared using the chi-square test or Fisher’s exact test. The incidences of PJK and PJF were compared using chi-square or Fisher’s exact test. Repeated measures analysis of variance was used to compare changes in PROs 1 year postoperatively.

We first performed a univariate analysis to identify risk factors associated with PJK, followed by a multivariate analysis including variables with a p-value < 0.25 to evaluate the effect of the intervention. For the univariate analysis of risk factors associated with PJK, categorical variables were compared using the chi-square or Fisher’s exact test, whereas continuous variables were analyzed using t-tests to compare the means between the PJK and non-PJK groups. Multivariate analysis was conducted using binary logistic regression to identify independent predictors of PJK. Multicollinearity was assessed using Variance Inflation Factors (VIF), with a VIF < 5 indicating no significant multicollinearity.

All statistical analyses were performed using SPSS software (version 27.0; IBM Corp., Armonk, NY, USA). Statistical significance was set at a two-sided p-value < 0.05.

Results

Participants

Between March 2023 and August 2024, the hybrid screw insertion technique was applied in 89 patients who underwent ASD surgery and met the inclusion criteria (hybrid screw group). Seventy-eight patients who underwent ASD surgery in the 18-months period before the start of the study (August 2022 to February 2023), in whom bilateral pedicle screw fixation was performed at the UIV using the conventional method, and who met the inclusion criteria were assigned to the control group. There were no significant differences in baseline demographic characteristics between the two groups. In addition, hip BMD and preoperative UIV HU values were comparable between the groups. Regarding pre-operative spinopelvic parameters, the study group demonstrated a significantly greater preoperative lumbar lordosis compared with the control group (hybrid screw group: 6.96 ± 23.98° vs. control group: –0.36 ± 19.84°, p = 0.035). There were no significant differences between the two groups in the immediate postoperative spinopelvic parameters or the spinopelvic parameters at 1 year postoperatively (Table 1).

Table 1.

Characteristics of Participants in the Study

	Hybrid screw (N=89)	Control (N=78)	P-value
Age (years)	72.8±7.2	72.4±5.8	0.661
Female, n (%)	76 (85.4)	71 (91.0)	0.263
CCI	1.03±0.70	0.82±0.96	0.101
BMI (kg/m2)	25.30±3.72	26.17±4.00	0.151
Hip BMD (g/cm²)	0.70±0.14	0.67±0.14	0.117
UIV HU	120.09±65.21	115.61±52.47	0.631
Composite alignment, n (%)			0.217
Isolated coronal deformity (Type T, L or D + SVA <4cm)	57 (64.0)	51 (65.4)
Isolated coronal deformity (Type N + SVA >4cm)	14 (15.7)	6 (7.7)
Mixed coronal and sagittal deformity (Type T, L or D + SVA >4cm)	18 (20.2)	21 (26.9)
Preoperative Spinopelvic Parameters
TK (°)	15.29±15.67	13.60±15.16	0.512
PT (°)	33.42±12.92	32.68±11.36	0.698
PI (°)	53.00±11.63	51.44±12.73	0.409
LL (°)	6.96±23.98	-0.36±19.84	0.035 *
PI-LL (°)	46.29±24.83	50.78±22.52	0.225
SVA (mm)	166.11±79.33	147.79±87.08	0.159
Immediate Postoperative Spinopelvic Parameters
TK (°)	26.42±12.36	27.36±10.01	0.806
PT (°)	27.36±10.01	25.09±9.20	0.132
PI (°)	53.04±9.62	52.13±10.96	0.569
LL (°)	39.63±13.92	40.77±10.21	0.554
PI-LL (°)	13.52±12.80	11.43±13.31	0.305
SVA (mm)	47.43±35.89	36.42±38.58	0.059
L1PA	10.16±7.71	11.33±7.33	0.330
One-Year Postoperative Spinopelvic Parameters
TK (°)	22.76±13.48	23.86±11.53	0.628
PT (°)	27.16±10.05	24.59±8.57	0.094
PI (°)	51.35±11.26	50.10±10.26	0.477
LL (°)	35.35±12.59	37.36±12.98	0.330
PI-LL (°)	16.00±11.76	12.73±13.39	0.109
SVA (mm)	63.68±38.34	53.80±44.74	0.142

*indicates statistical significance.

Values are represented as mean±SD and n (%).

Abbreviations: CCI, Charlson comorbidity index; BMI, Body mass index; BMD, Bone mineral density; UIV, Upper Instrumented Vertebra; HU, Hounsfield unit; TK, Thoracic kyphosis; PT, Pelvic tilt; PI, Pelvic incidence; LL, Lumbar lordosis; SVA, Sagittal vertical axis.

Primary Outcomes: PJK and PJF Rates

One year after ASD surgery, the PJK rate was significantly lower in the hybrid screw group than in the control group (hybrid screw group, 16.9% vs. control group, 35.9%; p = 0.005). No significant difference was observed in the PJF rate between the two groups (hybrid screw group, 4.5% vs. control group, 11.5%; p = 0.090) (Figure 3).

Figure 3.

The rate (the proportion of PJK or PJF occurrence in each group) of PJK and PJF in the hybrid screw insertion technique group and the control group

Secondary Outcome: PROs

One year after ASD surgery, both groups showed significant improvements over time in VAS scores for back and leg pain, ODI, and EQ-5D (p < 0.05). In the EQ-5D, the hybrid Screw group showed a statistically significant improvement in outcomes compared with the Control group (p = 0.048). However, there were no statistically significant differences in the other measures. (VAS score for back pain, p = 0.703; VAS score for leg pain, p = 0.319; ODI, p = 0.159) (Figure 4).

Figure 4.

Patient-reported outcomes (PROs) at the follow-up assessments (baseline, 3 months, 6 months, and 12 months)

Multivariate Analysis of Risk Factors for PJK

The following variables related to PJK were evaluated using univariate analysis: age, sex, CCI, BMI, hip BMD, preoperative and postoperative spinopelvic parameters, and hybrid screw insertion technique. Only the variables associated with PJK p-value < 0.25 were included in the multivariate analysis (Table 2).

Table 2.

Univariate Analysis of Risk Factors Associated With Proximal Junctional Kyphosis

Variables	Non-PJK (N= 124)	PJK (N=43)	p-value
Age (years)	72.2±7.0	73.8±5.3	0.150 †
Female, n (%)	107 (86.3)	40 (93.0)	0.241 †
CCI	0.94±0.83	0.93±0.86	0.972
BMI (kg/m2)	25.61±3.89	26.00±3.84	0.566
Hip BMD (g/cm²)	0.71±0.14	0.62±0.11	<0.001 *
Pre-op UIV HU	121.66±61.21	107.71±53.89	0.187 †
Pre-op spinopelvic parameters
TK (°)	14.47±15.74	14.31±14.55	0.957
PT (°)	33.22±12.19	32.66±12.29	0.795
PI (°)	52.23±12.40	52.39±11.51	0.941
LL (°)	3.99±22.96	2.34±20.89	0.678
PI-LL(°)	47.92±25.20	49.73±19.48	0.668
SVA (mm)	162.42±83.89	143.35±81.04	0.198 †
Post-op spinopelvic parameters
TK (°)	25.79±10.76	27.32±13.78	0.511
PT (°)	25.65±9.42	28.11±10.26	0.152 †
PI (°)	52.44±10.66	53.09±9.07	0.723
LL (°)	40.14±12.88	40.25±10.57	0.960
PI-LL(°)	11.80±11.91	14.65±15.83	0.218 †
SVA (mm)	41.93±38.87	43.06±33.64	0.865
L1PA	9.97±7.51	12.72±7.35	0.042 *
Hybrid screw	74 (59.7)	15 (34.9)	0.005 *

*indicates statistical significance.

†was included in the multivariate analysis with a p-value< 0.25.

Values are represented as mean±SD and n (%).

Abbreviations: CCI, Charlson comorbidity index; BMI, Body mass index; BMD, Bone mineral density; TK, Thoracic kyphosis; PT, Pelvic tilt; PI, Pelvic incidence; LL, Lumbar lordosis; SVA, Sagittal vertical axis; Pre-op, Preoperative; Post-op, Postoperative.

The following variables were included in the multivariate analysis of risk factors for PJK based on the univariate analysis: Age, sex, hip BMD, preoperative SVA, postoperative PT, postoperative PI-LL, and hybrid screw insertion technique. The VIF for all seven variables was < 5, confirming the absence of multicollinearity. The hybrid screw insertion technique at the UIV was effective in preventing PJK in multivariate analysis (odds ratio [OR], 0.354 [0.160–0.782], p = 0.010). Among the other variables, Hip BMD (OR, 0.008 [0–0.174], p = 0.002) was identified as significant risk factors in the multivariate model (Table 3).

Table 3.

Multivariate Analysis of Risk Factors Associated with Proximal Junctional Kyphosis (Binary Logistic Regression)

Variable	OR (95% CI)	p-value
Age	1.047 (0.973 – 1.127)	0.220
Sex	0.885 (0.183 – 4.284)	0.879
Hip BMD	0.006 (0 – 0.161)	0.002 *
Pre-op UIV HU	0.999 (0.991 – 1.007)	0.763
Preoperative SVA	0.996 (0.991 – 1.001)	0.135
Postoperative PT	1.012 (0.967 – 1.058)	0.613
Postoperative PI-LL	1.029 (0.996 – 1.064)	0.089
Postoperative L1PA	1.066 (1.008 – 1.126)	0.025 *
Hybrid screw	0.363 (0.160 – 0.825)	0.016 *

*indicates statistical significance.

Abbreviations: BMI, Body mass index; BMD, Bone mineral density; HU, Hounsfield unit; L1PA, L1 pelvic angle; PI, Pelvic incidence; LL, Lumbar lordosis.

Mechanism of PJF

We analyzed the mechanisms of PJF occurrence between the two groups. Three mechanisms of PJF were identified: UIV fracture, UIV+1 fracture, and screw pull-out. Among these, the rate of PJF caused by UIV fracture was significantly lower in the hybrid screw group than in the control group (hybrid screw group, 1.1% vs. control group, 9.0%; p = 0.018) (Table 4).

Table 4.

Mechanisms of Proximal Junctional Failure (PJF)

PJF mechanism	Hybrid group (N=89)	Control (N=78)	p-value
UIV fracture	1 (1.1%)	7 (9.0%)	0.018 *
UIV+1 fracture	1 (1.1%)	1 (1.3%)	0.913
Screw pull-out	2 (2.2%)	1 (1.3%)	0.654
Total	4 (4.5%)	9 (11.5%)	0.090

*indicates statistical significance.

Abbreviations: UIV, Upper Instrumented Vertebra.

Post Hoc Power Analysis

We performed a post hoc power analysis for the primary outcome (PJK rate). Assuming a two-sided alpha level of 0.05, the analysis demonstrated a statistical power of 81.1% to detect the observed difference in PJK incidence between the hybrid and conventional groups (effect size, Cohen’s h ≈ 0.22).

Discussion

Our study proposes a novel approach to reduce acute PJK by utilizing a hybrid screw insertion technique that better preserves the trabecular bone of the UIV body that resists body compression than the conventional method of bilateral pedicle screw insertion. Additionally, in multivariate analysis of PJK risk factors, the hybrid screw insertion technique was found to be significantly effective in preventing PJK. Although the overall PJF rate did not differ significantly between the two groups, a more detailed analysis of the mechanisms of PJF revealed that the rate of PJF caused by UIV fracture was significantly lower in the hybrid screw group than in the control group. This finding further supports the hypothesis that preservation of the UIV trabecular bone may reduce susceptibility to compression-related failure at the proximal junction.

In posterior long instrumented fusion procedures, such as those performed for ASD, proximal junctional problems, such as PJK and PJF, may result from stress concentration at the proximal end of the instrumentation.^18,19 Therefore, to prevent PJK and PJF, it is important to implement protective strategies that enhance resistance to compressive forces at the UIV, which is the area subjected to mechanical stress. Previous studies have reported that bicortical pedicle screw fixation during UIV may increase the risk of early compression fractures at this level.⁶ It is believed that not only the cortical bone but also the trabecular bone of the vertebral body plays a crucial role in resisting compressive forces. Reduced strength of the vertebral body against compressive forces due to the loss of trabecular bone has been observed in several previously reported cases of vertebral body fractures following pedicle screw removal, despite solid fusion.^20-22 Therefore, several strategies have been proposed to prevent PJK by augmenting the trabecular bone of the vertebral body. Cement augmentation of the UIV, which is vulnerable to PJK, has been reported in multiple previous studies as an effective method.^7,8 In our previous study, we demonstrated that injecting recombinant human BMP-2 into the UIV to augment the trabecular bone of the vertebral body significantly reduced the incidence of PJK.²³

The importance of trabeculae in resisting compressive forces on the vertebral body has been demonstrated in several biomechanical studies. Previous research has shown that the relative amount of vertical trabeculae is a key factor in determining vertebral strength under compression.¹⁰ Furthermore, one study reported that the strength of the trabecular bone depends not only on the amount of bone present but also on its structural continuity, highlighting that discontinuity due to perforation leads to a greater reduction in strength than an equivalent amount of loss caused by thinning alone.^11,12 Based on these findings, the conventional method of bilateral pedicle screw fixation at the UIV can be considered disadvantageous for maintaining compressive resistance at this level. Such trabecular violations may be further exacerbated when large-diameter pedicle screws are used or when loosening occurs around these screws. In contrast, our hybrid screw insertion technique, which utilizes pedicle screw fixation on only one side of the UIV, reduces the extent of trabecular bone loss and disruption of structural continuity by approximately half compared with the traditional bilateral technique. As a result, this approach significantly decreases the incidence of PJK.

As laminar screw fixation is not a commonly employed technique in the thoracolumbar spine, concerns may arise regarding its mechanical stability and technical reproducibility. However, with respect to fixation strength, a previous study analyzing laminar width in pediatric patients reported that the average laminar width at T10—the most commonly used UIV level—was 5.6 mm in children aged ≥ 8 years.²⁴ Consistent with this finding, we were able to use sufficiently large screws with diameters ranging from 4.5 mm to 5.5 mm in all cases in our study. In addition, bicortical fixation of the contralateral pars provided adequate mechanical stability. Screw pull-out occurred in only 5.61% (5/89) of patients who underwent laminar screw fixation. Given that the screw pull-out rate in the control group using bilateral pedicle screws was 3.85% (3/78), no significant difference was observed between the two groups. Regarding technical feasibility, unlike pedicles, the lamina can be readily identified based on its bony surface anatomy, making screw placement relatively straightforward. In our technique, the entry cortex is initially breached using a burr or awl, and the laminar trajectory is carefully developed using a pedicle finder under direct anatomical and tactile guidance, followed by screw insertion.

Interestingly, among the secondary outcomes (PROs), only the EQ-5D showed a significantly better outcome in the hybrid Screw group compared with the Control group. This finding is likely attributable to the multidimensional characteristics of the EQ-5D questionnaire. Unlike the spine-specific instruments, which primarily assess pain intensity or functional capacity, the EQ-5D encompasses broader domains of general health, including mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. The higher incidence of PJK in the Control group may have led to subtle postural imbalance, chronic discomfort, and cosmetic dissatisfaction, which could negatively influence patients’ perception of overall well-being.

Limitations

First, the present study compared the two groups in terms of acute PJK that developed over 1 year. PJK occurs most frequently within 2–3 months after surgery.^25-28Late-onset PJK can occasionally occur and may not have been fully captured in the results. Therefore, additional follow-ups for 1–2 years are necessary to better assess the incidence of PJK. Second, although all surgical procedures and PJK prevention strategies, except for the UIV screw insertion technique, were performed identically in the study and control groups, the potential for time-related bias remains an inherent limitation of this study. Third, although data collection was performed prospectively in a consecutive and non-selective manner, the study design was retrospective. Based on our findings, we are planning to conduct a future study with a higher level of evidence.

Conclusion

The hybrid screw insertion technique represents a promising strategy in ASD surgery as it preserves the trabecular structure of the UIV more effectively than the conventional bilateral pedicle screw fixation method, thereby contributing to a reduced incidence of PJK.

Footnotes

Acknowledgments

The authors wish to acknowledge that there are no acknowledgments to declare.

ORCID iDs

Jin-Ho Park

Sang-Min Park

Jiwon Park

Ho-Joong Kim

Ethical Considerations

This retrospective study was approved by the Institutional Review Board of Seoul National University Bundang Hospital (B-2506-976-102).

Consent to Participate

The requirement for informed consent was waived due to the retrospective nature of the study.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.*

Disclosures

The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.

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