Abstract
-
Objective
To determine the role of dynamic hip joint coverage in maintaining postoperative sagittal balance in adult spinal deformity (ASD) patients following S2-alar-iliac (S2AI) fixation.
-
Methods
A total of 224 ASD patients who underwent S2AI fixation were enrolled. Patients were stratified into 2 groups based on pre-to-post (from preoperative to postoperative) changes in femoral head coverage (ΔFHC): change group (group C) and noncoverage change group (group NC). Group C was further subdivided according to FHC recovery during follow-up into rebound (group C-R) and nonrebound (group C-NR) groups. Clinical outcomes and radiographic parameters of hip and spinopelvic alignment were assessed preoperatively, at the initial postoperative standing, and at the 2-year follow-up.
-
Results
Compared to group C, patients in group NC demonstrated a higher incidence of sagittal imbalance-related mechanical complications at 2-year follow-up, with a greater tendency for sagittal imbalance progression (p=0.013), a larger post-to-follow-up change in sagittal vertical axis (ΔSVA) (p=0.029), and a higher incidence of proximal junctional kyphosis (PJK) (p=0.031). Although there was no significant difference in PJK incidence between group C-NR and group C-R (p=0.845), group C-NR showed a greater tendency for postoperative sagittal imbalance aggravation (p=0.025), with a significantly larger ΔSVA during follow-up (p=0.002). The optimal cutoff values for predicting postoperative sagittal imbalance aggravation were 3.5% for pre-to-post ΔFHC (area under the curve [AUC]=0.694) and 1.8% for post-to-follow-up ΔFHC (AUC=0.713).
-
Conclusion
Dynamic postoperative changes in hip joint coverage, characterized by the FHC, are associated with postoperative sagittal balance maintenance. Patients with limited pre-to-post and post-to-follow-up changes in the FHC demonstrate compromised hip joint compensatory capacity, thereby increasing the risk of postoperative sagittal imbalance-related mechanical complications.
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Keywords: Hip joint coverage, Adult spinal deformity, Hip compensation, Sagittal balance, S2AI fixation, Proximal junctional kyphosis
INTRODUCTION
The hip joint, which serves as a crucial connection between the trunk and lower extremities, has garnered increasing attention from both hip and spine surgeons in recent years for its compensatory capacity to counteract spinal sagittal imbalance [
1-
7]. Deterioration of sagittal imbalance due to aging or adult spinal deformity (ASD) triggers compensatory adaptations in the hip joint, such as femoral head retroposition [
4,
8-
11]. Tang et al. [
12] further demonstrated that optimal femoral head coverage (FHC) and hip mobility were restored in patients with hip joint degeneration or dysplasia who underwent total hip arthroplasty (THA), causing a gradual improvement in sagittal alignment in some patients with preoperative sagittal imbalance, highlighting the crucial role of the hip joint in tuning sagittal balance. In patients with ASD and severe sagittal decompensation, a long spinal fusion to the pelvis is necessary for sagittal balance restoration [
10,
13,
14].
ASD surgery is classically associated with a high complication rate, particularly postoperative aggravation of sagittal imbalance and even proximal junctional kyphosis (PJK) [
15-
19]. Although pelvic retroversion, spinal extension, and hip joint flexion collectively contribute to sagittal balance compensation, fixation-related restrictions on pelvic and spinal mobility during long fusion limit their range of motion, thereby necessitating compensation for the hip joint [
4-
9,
20-
22]. Recent investigations into the hip-spine relationship have revealed that long spinal fusion, particularly S2-alar-iliac (S2AI) fixation, significantly alters hip joint biomechanics [
2,
23-
26], resulting in suboptimal hip joint coverage and subsequent progressive hip pain or hip osteoarthritis (OA), which may further increase the risk of sagittal imbalance [
27,
28]. These alterations were dynamic and persisted throughout the follow-up period [
2,
3]. Theoretically, hip joints exhibiting different compensatory changes in coverage postoperatively demonstrate varying capacities to reconstitute a new hip-spine relationship and maintain long-term sagittal balance [
4,
8]. To the best of our knowledge, whether alterations in hip joint coverage following long spinal fusion to the pelvis affect the compensatory capacity of the hip joint has not yet been investigated, and its potential influence on the maintenance of postoperative sagittal balance remains unknown.
Because S2AI fixation alters the sacroiliac-hip positional relationship, it may restrict the compensatory mechanisms by which the hip joint maintains sagittal balance. Therefore, this study aimed to investigate the dynamic changes in hip joint coverage from preoperative to postoperative (pre-to-post) and from postoperative to follow-up and to determine their role in maintaining postoperative sagittal balance in ASD patients with S2AI fixation.
MATERIALS AND METHODS
1. Study Design and Population
This retrospective study included ASD patients who underwent long-segment posterior fusion to the sacrum with S2 iliac fixation between January 2016 and November 2023. Additionally, 35 patients who underwent S1 iliac screw (IS) fixation were included. The inclusion and exclusion criteria are shown in
Fig. 1.
Demographic information such as age, sex, and fusion segments was collected. Preoperative, initial postoperative erect, and 2-year follow-up standing posteroanterior and lateral radiographs of the spine were obtained. All full-spine standing radiographs were obtained using a standardized positioning protocol with no mixed cases: patients stood upright in a comfortable, natural position with feet shoulder-width apart. A dedicated support bar was placed in front of each patient to standardize hand placement and maintain consistent upper limb positioning, which minimized potential bias in FHC measurement caused by interpatient variations in center of gravity shift. Patients were explicitly instructed not to apply force on the bar to avoid altering their sagittal alignment or pelvic–hip orientation.
Twelve radiographic spinopelvic parameters and 5 hip parameters independent of pelvic rotation and tilt were evaluated29 (
Fig. 2;
Table 1). Spinopelvic radiographic parameters were measured using validated software (Surgimap, Nemaris, USA). Hip2Norm (2007, Switzerland) was used to measure hip parameters according to previous literature (
Figs. 2 and
3) [
30]. Two experienced surgeons independently measured all radiographic parameters, and the mean values were used for the analysis.
In this study, we used the FHC directly simulated by Hip-2Norm to represent the 3-dimensional acetabular coverage of the femoral head, reflecting the spatial relationship between the acetabulum and femoral head. The physiologic-range change in femoral head coverage (ΔFHC) partially reflects an individual’s functional postural adaptability [
30,
31]. Patients with a pre-to-post ΔFHC in the upper quartile were defined as group C (change), while those in the lower quartile were defined as group NC (noncoverage change).
The patients were placed in the prone position, and the target levels were exposed through a standard midline incision. Traditional pedicle screws were then inserted freehand into the planned segments. Subsequently, S2AI screws were placed under intraoperative 3-dimensional imaging and navigation using the O-arm Surgical Imaging System and Stealth Station (Medtronic, USA). In 66 patients, the upper instrumented vertebra (UIV) was instrumented with a tricortical pedicle screw. In these cases, the reference frame was repositioned to the spinous process 2 levels caudal to the UIV, and the UIV−1 pedicle was selected as the entry point for screw placement under real-time navigation. In the remaining 158 patients, pedicle screws at the intended UIV were inserted bilaterally using a freehand technique. After all screws had been placed, pedicle subtraction osteotomy was performed at the preplanned levels for correcting kyphoscoliosis. Age-adjusted PI–LL (pelvic incidence minus lumbar lordosis) served as the fundamental strategy for establishing ideal sagittal alignment in surgical planning.
4. Statistical Analysis
All analyses were performed using IBM SPSS Statistics ver. 28.0 (IBM Co., USA). Since FHC has been rarely addressed in the field of spinal deformity, this study initially employed quartile-based groupings to allow us to detect the potential associations between FHC and postoperative sagittal imbalance that might otherwise be overlooked due to the narrow range of FHC change values, by comparing Q4 (group C) and Q1 (group NC). We then further validated the clinical value of FHC in the overall cohort through Pearson correlation, multivariable logistic regression, and receiver operating characteristic (ROC) analysis. The normality of continuous variables was assessed using the Shapiro-Wilk test. Continuous variables with normal distribution were compared between the 2 groups using the t-test, whereas categorical variables were analyzed using the chi-square test or Fisher exact test. Pearson correlation analysis was performed to assess the relationship between changes in hip parameters and the progression of sagittal imbalance during follow-up. ROC curves were used to evaluate the area under the curve (AUC) for variables significantly associated with the aggravation of sagittal imbalance and PJK. The optimal cutoffs for sensitivity and specificity were determined using the Youden index. Intraclass correlation coefficients (ICCs) were calculated to assess interobserver and intraobserver reliabilities of radiographic measurements. p-values were adjusted using the Benjamini-Hochberg false discovery rate method to reduce type I errors. Statistical significance was set at p<0.05.
RESULTS
1. Cohort Characteristics
In this study, 224 patients with ASD (448 hips) who underwent S2AI fixation were recruited (
Fig. 1;
Table 2). There were 164 females and 60 males, with a mean age of 63.8±6.2 (range, 54–79) years. The average follow-up duration was 27.4±3.9 (range, 24–50) months, and the fusion region spanned an average of 10.7±2.7 (range, 7–18) levels. All radiographic parameters demonstrated good inter- and intraobserver reliability, with ICCs ranging from 0.791 to 0.992.
Of these patients, 56 (112 hips) were included in group C, and 56 (112 hips) were included in group NC. Group C had a smaller preoperative FHC (82.7±5.6 vs. 84.2±7.5, p=0.046), while other hip parameters (Lateral center-edge [LCE], acetabular index [AI], sharp angle [SA], and extrusion index [EI]) showed no statistical difference (
Table 3).
Additionally, we included 35 ASD patients who underwent IS fixation to compare the impact of different pelvic fixation techniques on the hip joint. Results showed that postoperative ΔFHC were significantly greater in the S2AI fixation group compared to the IS fixation group (2.4%±1.9% vs. 1.8%±1.7%, p=0.042).
2. Postoperative and During Follow-up Radiological Dynamic Changes Assessment in Groups C and NC
Both groups exhibited good postoperative sagittal balance restoration (
Table 4), with comparable postoperative lordosis distribution index (0.7±0.3 vs. 0.7±0.6, p=0.893). However, during follow-up, group NC had significantly higher change in sagittal vertical axis (ΔSVA) (37.1±22.8 vs. 14.4±9.8, p=0.029), change in thoracic kyphosis (ΔTK) (6.1±1.6 vs. 2.9±1.0, p=0.035), and change in proximal junctional angle (ΔPJA) (2.9±1.0 vs. 8.0±1.7, p=0.016) compared to group C. At the 2-year follow-up, group NC demonstrated both a higher PJK incidence (40.0% vs. 17.9%, p=0.031) and a greater risk of sagittal imbalance deterioration (defined as ΔSVA ≥ 50 mm, 42.9% vs. 14.2%, p=0.013) compared to group C (
Table 5). No significant differences were observed in other postoperative mechanical complications or perioperative complications between the 2 groups (
Table 4).
Regarding pre-to-post changes in hip parameters (
Table 4), Group C patients demonstrated greater ΔFHC (left: 5.9±5.0 vs. 0.3±0.1, p<0.001; right: 5.0±4.8 vs. 0.2±0.3, p<0.001) and more pronounced ΔEI (left: -2.7±1.8 vs. -0.8±0.3, p=0.025; right: -2.5±1.9 vs. -1.1±0.7, p=0.027). During follow-up, group C exhibited a rebound trend in FHC and EI, whereas these parameters remained stable in group NC. The post-to-fu ΔFHC (Left: -2.0±1.6 vs. 0.3±0.2, p=0.005; Right: -1.9±1.5 vs. 0.2±0.1, p=0.004) and ΔEI (left: -0.8±0.5 vs. 0.1±0.1, p=0.032; right: -0.6±0.5 vs. 0.3±0.1, p=0.027) were significantly greater in group C compared to group NC. No statistically significant differences were observed between the groups in pre-to-post and post-to-fu ΔLCE, ΔAI, and ΔSA (p>0.05).
Based on the significant rebound in hip parameters observed in group C during follow-up, whereas hip parameters remained stable in group NC, we further subdivided the patients in group C based on post-to-fu ΔFHC (
Fig. 1;
Table 6). Patients were categorized into group C-R (rebound, with larger post-to-fu ΔFHC, ranked among top 50% of cases in group C) and group C-NR (no rebound, with smaller post-to-fu ΔFHC, ranked in the lower 50% of cases in group C).
No significant differences were found between groups C-R and C-NR in pre-to-post changes in spinal-pelvic and hip parameters (
Table 6). However, group C-NR exhibited greater ΔSVA (35.3±19.5 vs. 6.7±5.3, p=0.002) and ΔTK (5.3±5.1 vs. 0.4±0.4, p=0.028) during follow-up, along with a higher rate of sagittal balance deterioration (6/22 vs. 2/26, p=0.025) at 2-year follow-up. No significant differences were observed between the groups in other spinopelvic parameters during follow-up or in the incidence of PJK at the 2-year follow-up. Regarding hip parameters, group C-R demonstrated greater rebound in FHC (post-to-fu ΔFHC: -2.1±1.7 vs. -0.5±0.2, p=0.022) during follow-up compared to group C-NR, while all other hip parameters showed no statistically significant differences between groups (p>0.05).
Pearson correlation analysis was performed in the entire cohort to evaluate the relationships between changes in hip parameters (pre-to-post and post-to-fu) and the progression of the PJA and SVA during follow-up (
Table 7). Pre-to-post ΔFHC demonstrated significant negative correlations with both post-to-fu ΔSVA (r=-0.413, p=0.009) and ΔPJA (r=-0.409, p=0.012), while post-to-fu ΔFHC showed a significant negative correlation only with ΔSVA (r=-0.341, p=0.041).
Multivariable logistic regression analysis demonstrated that pre-to-post ΔFHC was a factor influencing the occurrence of PJK at the 2-year follow-up (
Table 8). Both pre-to-post ΔFHC and post-to-fu ΔFHC were identified as risk factors for the aggravation of sagittal imbalance at the 2-year follow-up (
Table 8). ROC analysis revealed that the cutoff value of pre-to-post ΔFHC for determining the occurrence of PJK or aggravation of sagittal imbalance at the 2-year follow-up was 3.5% (AUC=0.694), while the cutoff value of post-to-fu ΔFHC for determining aggravation of sagittal imbalance at the 2-year follow-up was 1.8% (AUC=0.713) (
Fig. 4).
All patients showed significant postoperative improvement in visual analogue scale (VAS) back pain scores, which remained stable during follow-up (
Table 9). However, VAS leg pain scores significantly increased in group NC during follow-up (2.1±1.1 vs. 2.8±1.4, p=0.031) and were significantly higher compared to group C at 2-year follow-up (2.1±1.7 vs. 2.8±1.4, p=0.039).
DISCUSSION
The hip joint plays a crucial role in compensating for sagittal imbalance [
4,
7-
9]. In patients with ASD and long spinal fusion to the pelvis, the restricted range of motion of the pelvis and spine necessitates compensation from the hip joint [
6,
22,
24]. While recent evidence has demonstrated that corrective surgery for ASD, especially S2AI fixation, can significantly affect hip joint biomechanics and lead to changes in hip joint coverage, the relationship between these secondary alterations and the maintenance of postoperative sagittal alignment remains underinvestigated [
2,
24]. Our study provides new evidence that dynamic postoperative changes in hip joint coverage following S2AI fixation play a beneficial role in maintaining sagittal balance in patients with ASD. Patients with limited compensatory changes in hip joint coverage experienced a higher incidence of sagittal imbalance-related mechanical complications at the 2-year follow-up, underscoring the necessity of a comprehensive hip-spine relationship evaluation post-S2AI fixation.
Secondary hip joint alterations after S2AI fixation have emerged as a significant concern in recent years [
1,
3,
28]. Studies have suggested that these changes can substantially modify the hip joint coverage and elevate mechanical stress across the joints in patients with ASD, potentially compromising multiple aspects of joint function, including articular tribology, wear patterns, and biomechanical stability [
23-
26]. Moreover, some patients may experience the progression of postoperative hip degeneration or acetabular fractures, leading to substantial deterioration of health-related quality of life [
25,
26,
28]. However, the critical question of whether these secondary alterations impair the hip joint compensatory capacity and subsequently contribute to postoperative sagittal imbalance remains unclear. Previous studies have demonstrated that changes in hip joint coverage in patients with ASD occur not only after S2AI fixation, but also persist dynamically throughout follow-up [
2,
3]. Therefore, this study focused on coverage-related hip parameters to investigate the relationship between dynamic postoperative changes and the postoperative progression of sagittal imbalance in patients with ASD.
Using FHC directly simulated by Hip2Norm [
30] software on posteroanterior radiographs of the spine to represent hip joint coverage, our study found that patients with lower pre-to-post ΔFHC (group NC) demonstrated significantly greater ΔSVA and ΔPJA during follow-up. Moreover, the NC group showed higher rates of PJK and aggravation of sagittal imbalance at the 2-year follow-up (
Table 4). These findings suggest that patients in group NC may have insufficient hip compensatory capacity to accommodate the newly reconstructed spinal alignment, resulting in suboptimal postoperative hip-spine alignment and a tendency toward postoperative sagittal imbalance. Compared to group C patients, when achieving similar intraoperative sagittal correction, the limited compensatory capacity of the distal hip joint in group NC patients may cause concentrated mechanical stress from a positive sagittal imbalance in the proximal region, increasing the incidence of mechanical complications such as PJK. Moreover, our present study suggests that dynamic postoperative changes in FHC may represent a response to intraoperative pelvic tilt (PT) correction and its subsequent loss during follow-up. Intraoperatively gained PT correction reflects only part of the overall realignment restoration, specifically pelvic-spinal alignment; however, the hip joint may undergo compensatory adaptations following PT correction to accommodate the significant sagittal reconstruction and maintain global hip-pelvic-spinal alignment, presenting as immediate postoperative increase in FHC. Our present study also found that patients in the NC group experienced a mean PT loss of 11.7° during follow-up, compared to 8.2° in group C. We hypothesize that patients with poorer hip compensatory capacity undergo greater pelvic compensation to maintain sagittal balance throughout the follow-up period. Future studies should further investigate the combined mechanisms by which hip and pelvis interact to maintain optimal global sagittal alignment.
When group C was further subdivided into group C-NR and group C-R based on FHC rebound during follow-up (
Table 6), no significant difference in PJK incidence was observed between the 2 subgroups at the 2-year follow-up. However, group C-NR demonstrated a significantly greater ΔSVA (35.3±19.5 vs. 6.7±5.3, p=0.002) and an increased risk of sagittal deterioration (6/22 vs. 2/26, p=0.025). This suggests that the reconstruction of the hip-spine relationship represents a dynamic process rather than a static immediate postoperative phenomenon. In patients with strong hip compensatory capacity, postoperative realignment induces temporary biomechanical changes that normalize over time (manifesting as dynamic hip coverage alterations). Initial compensatory adequacy may not ensure optimal long-term hip-spine alignment, as progressive sagittal imbalance can develop despite good early compensation if hip compensatory capacity deteriorates due to S2AI fixation in some patients. This dynamic nature is exemplified in group C-NR, where a significant increase in VAS leg pain from the 3-month to the 2-year follow-up may indicate progressive hip joint degeneration secondary to S2AI fixation (
Table 9), potentially compromising the compensatory capacity during follow-up. Kozaki et al. [
32] further conceptualized postoperative hip joint degeneration as an adjacent segment disease following spinal fusion, emphasizing the necessity of long-term hip evaluation. Our results also showed greater postoperative FHC changes with S2AI versus IS fixation, likely due to the hip joint bearing increased stress as the adjacent segment to S2AI fixation.
Further correlation analysis between dynamic FHC changes and sagittal imbalance during follow-up revealed that post-to-fu ΔSVA was significantly negatively correlated with both pre-to-post and post-to-follow-up ΔFHC, while ΔPJA showed significant negative correlation with pre-to-post ΔFHC (
Table 7). Multivariable analysis identified pre-to-post ΔFHC as an independent predictor of PJK, while both pre-to-post and post-to-fu ΔFHC were potential risk factors for sagittal imbalance aggravation at 2-year follow-up (
Fig. 5). ROC analysis revealed that the cutoff value of pre-to-post ΔFHC for determining the occurrence of PJK or aggravation of sagittal imbalance at the 2-year follow-up was 3.5%, while the cutoff value of post-to-fu ΔFHC for determining aggravation of sagittal imbalance at 2-year follow-up was 1.8% (
Fig. 4). These findings further confirm that among the studied hip coverage parameters, the FHC serves as a superior indicator of sagittal compensatory capacity in patients with ASD following S2AI fixation, with postoperative dynamic changes closely associated with sagittal imbalance compensation capacity.
Therefore, this study hypothesizes that dynamic changes in the FHC following S2AI fixation in patients with ASD serve as a valuable indicator of the hip joint’s sagittal compensatory capacity, offering potential clinical value in determining preoperatively which patients will compensate with their FHC versus not. Patients with smaller pre-to-post ΔFHC may have inferior hip compensatory ability, leading to a higher risk of mechanical complications like PJK during follow-up (
Figs. 6A and
7A–
C). Although patients with higher pre-to-post FHC but smaller post-to-fu FHC may have a lower PJK risk, their hip compensatory capacity might gradually diminish owing to fusion-related hip degeneration, resulting in sagittal imbalance deterioration, and their risk of PJK development during extended follow-up remains unknown (
Figs. 6B and
8A–
C). Conversely, patients maintaining both high pre-to-post and post-to-follow-up ΔFHC demonstrate good hip compensatory capacity, responding well to sagittal reconstruction and maintaining a favorable hip-spine relationship, thus preserving sagittal balance during long spinal fusion follow-up (
Figs. 5A–
D and
6C). This hypothesis aligns with the perspective of Yagi et al. [
19], which suggests that restricted hip range of motion diminishes sagittal compensatory capacity, potentially leading to a significant positive sagittal imbalance. Similarly, Diebo et al. [
28] reported continuous SVA progression in patients with ASD and hip OA after deformity correction, which is consistent with our findings.
This study has several limitations. First, the cutoff values in this study only represent physiologically acceptable changes in FHC, while the upper limit remains undetermined because it was a single-center retrospective study with a limited sample size. Second, the VAS leg pain domain may not accurately distinguish between radiculopathy-related and hip-related leg pain. A more precise evaluation of hip degeneration requires advanced imaging such as hip joint computed tomography and magnetic resonance imaging, which provide more accurate assessment of FHC and degeneration while avoiding posture-related evaluation bias [
33,
34]. Additionally, as this study focused on physiological hip joints, excluding patients with Kellgren-Lawrence grade ≥3 or prior THA may have resulted in selection bias. Third, owing to the retrospective nature of the study, radiographic analysis was limited to 3 time points: preoperative, initial postoperative erect, and 2-year follow-up (minimum 2 years). More frequent dynamic assessments over a longer period, combined with minimum clinically important difference-based categorization rather than quartile-based grouping, would better elucidate the progression of sagittal malalignment. Specifically, it would be valuable to explore whether patients with isolated SVA progression during follow-up would subsequently develop PJK and whether this deterioration correlates with progressive hip joint degeneration. Finally, the limited cohort size prevented more precise matching of variables such as pelvic compensatory capacity and LL. Future large-scale case-matched studies are warranted to further elucidate the mechanistic interplay between hip joint compensation and sagittal balance maintenance, as well as to determine the clinical utility of preoperative FHC thresholds for surgical planning. Additionally, whether preoperative ΔFHC changes between weightbearing/non-weightbearing positions or other postural variations can be used to assess the remaining hip joint compensatory capacity in ASD patients is also a direction worth investigating [
31,
35].
CONCLUSION
In conclusion, the dynamic changes in hip joint coverage following S2AI fixation in ASD patients contribute favorably to maintaining postoperative sagittal balance, which can be assessed through pre-to-post ΔFHC and post-to-fu ΔFHC. Patients with limited postoperative dynamic changes in the FHC may exhibit compromised hip joint sagittal compensatory capacity, increasing the risk of postoperative sagittal imbalance aggravation. These findings highlight the compensatory capacity of the hip joint to counteract sagittal imbalance and provide insights for hip and spine surgeons.
NOTES
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Conflict of Interest
The authors have nothing to disclose.
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Funding/Support
This work was supported by the National Natural Science Foundation of China (No. 82272545), fundings for Clinical Trials from the Affiliated Drum Tower Hospital, Medical School of Nanjing University (2022-LCYJ-MS-22), and the Jiangsu Provincial Medical Innovation Center of Orthopedic Surgery (No. CXZX202214).
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Author Contribution
Conceptualization: DL, JL, YQ, ZZ, ZL; Data curation: DL, YX, ZH; Formal analysis: DL, JL, YX, ZH; Funding acquisition: YQ, ZL; Methodology: DL, JL, YX, ZH, YQ, ZZ, ZL; Project administration: YQ, ZZ, ZL; Visualization: DL, JL, YX; Writing – original draft: DL; Writing – review & editing: DL, JL, ZL.
Fig. 1.Flowchart showing the criteria for patient recruitment and grouping of patients according to pre-to-post (from preoperative to postoperative) and post-to-fu (from postoperative to follow-up) changes in femoral head coverage (FHC). S2AI, S2-alariliac; ΔFHC, changes in FHC; group C, change group; group NC, noncoverage change group; group C-R, C rebound group; group C-NR, C nonrebound group.
Fig. 2.Schematic illustration shows the investigated radiographic parameters (see
Table 1 for definitions). Coronal parameters: (A) Cobb angle, angle between the upper and lower endplates of the vertebrae at the apex of the curve; coronal balance distance (CBD), horizontal distance between the C7 plumb line (C7PL) and the center sacral vertical line (CSVL). Sagittal parameters: (B) Thoracic kyphosis (TK), Cobb angle between T5 and T12; sagittal vertical axis (SVA), horizontal distance between the vertical line from the midpoint of C7 and the posterior upper endplate of S1; (C) PJA, the angle between the inferior endplate of upper instrumented vertebra (UIV) and the superior endplate of UIV+2; lumbar lordosis (LL), Cobb angle between L1 and S1; proximal LL, Cobb angle between L1 and L4; distal LL, Cobb angle between L4 and S1. Hip parameters: (D) Femoral head coverage (FHC), The craniocaudal coverage of the femoral head by the acetabulum. (E) Sharp angle, angle formed by a horizontal line and a line connecting the caudal tip of the teardrop to the lateral edge of the acetabulum. (F) Extrusion index (EI), percentage of femoral head not covered by the acetabulum (A) relative to the total diameter of the femoral head (A+B). (G) Lateral centeredge (LCE) angle, angle formed by the longitudinal pelvic axis and a line connecting the center of the femoral head with the lateral edge of the acetabulum. (H) Acetabular index (AI), angle formed by a horizontal line and a line connecting the most medial point of the sclerotic zone of the acetabular roof with the lateral edge of the acetabulum.
Fig. 3.Illustration of Hip2 Norm: On the anteroposterior xray, the following anatomical landmarks are labeled: red crosses indicate the inferior margins of the teardrops as the horizontal reference; the green point indicates the sacrum, and the red point indicates the symphysis; the blue and yellow circles represent the acetabulum and the femoral head, respectively; the blue and red dashed lines outline the acetabular rim contour. After these markings are completed, the Hip2Norm software automatically calculates a simulated three-dimensional femoral head coverage based on the x-ray images.
Fig. 4.Receiver operating characteristic (ROC) curve for using pre-to-post and po-to-fu ΔFHC as predictors of sagittal imbalance progression after adult spinal deformity surgery using S2AI screws. ΔFHC, changes in femoral head coverage; S2AI, S2-alar-iliac.
Fig. 5.A 64-year-old female patient from group C exhibited a pre-to-post ΔFHC of 9.6% (>3.5%, A) and a post-to-follow-up ΔFHC of 7.7% (>1.8%, B-D), indicating robust hip compensatory capacity to accommodate the reconstructed hip-spine alignment. She demonstrated a progressive improvement in sagittal alignment from the immediate postoperative period through the 3-year follow-up (B, postoperative, SVA=101.55 mm; C, 3-month-postoperative, SVA=80.76 mm; D, 3-year-postoperative, SVA=33.84 mm). FHC, femoral head coverage; ΔFHC, changes in FHC; SVA, sagittal vertical axis.
Fig. 6.Schematic diagram illustrating hypothesized patterns of hip joint sagittal compensation following S2AI fixation across groups: (A) Noncoverage change group (group NC): limited preoperative hip compensatory capacity impairs adaptation to reconstructed hip-spine alignment, resulting in increased risk of sagittal malalignment progression (ΔSVA≥50 mm) and proximal junctional kyphosis (PJK) during follow-up. (B) Nonrebound coverage change group (group C-NR): progressive decline in hip compensatory capacity due to pelvic-anchored long spinal fusion. Despite no significant PJK risk at 2-year follow-up, sagittal malalignment progression was observed. (C) Rebound coverage change group (group C-R): adequate hip compensatory capacity enables successful adaptation to sagittal reconstruction, maintaining optimal hip-spine relationship and stable sagittal alignment throughout follow-up. S2AI, S2-alar-iliac; group C, change group; group NC, noncoverage change group; group C-R, C rebound group; group C-NR, C nonrebound group; SVA, sagittal vertical axis; PJA, proximal junctional angle.
Fig. 7.A 63-year-old female patient from group NC exhibited minimal pre-to-post (0.9%<3.5%, A) and post-to-follow-up (0.2%<1.8%, B and C) changes in FHC, indicating limited hip compensatory capacity. At 2-year follow-up (C), she developed severe PJK with a PJA of 26° and ΔPJA of 22°. Group NC, noncoverage change group; FHC, femoral head coverage; PJK, proximal junctional kyphosis; PJA, proximal junctional angle.
Fig. 8.A 69-year-old male patient from group C-NR exhibited a pre-to-post ΔFHC of 4.3% (>3.5%, A) and a post-to-follow-up ΔFHC of 0.4% (<1.8%, B and C), indicating initially adequate hip compensatory capacity that may have been depleted following S2AI fixation, rendering the hip unable to effectively adapt to the substantially reconstructed hip-spine relationship. Although PJK did not occur, the patient experienced sagittal imbalance aggravation during follow-up (C). Group C-NR, C nonrebound group; FHC, femoral head coverage; S2AI, S2-alar-iliac; PJK, proximal junctional kyphosis; PJA, proximal junctional angle.
Table 1.Definitions of the spinal-pelvic and hip radiographic parameters
Table 1.
|
Parameter |
Definitions |
|
Spinal-pelvic |
|
|
Pelvic incidence (PI) |
Angle formed by a line connecting the center of the femoral head to the center of the upper endplate of S1 and a perpendicular line from the upper endplate of S1 |
|
Pelvic tilt (PT) |
Angle formed between a vertical line and a line connecting the femoral head axis to the midpoint of the upper endplate of S1 |
|
Sacral slope (SS) |
Angle formed by the horizontal line and the upper endplate of S1 |
|
Cobb angle |
Angle between the upper and lower endplates of the vertebrae at the apex of the curve |
|
Sagittal vertical axis (SVA) |
Horizontal distance between the vertical line from the midpoint of C7 and the posterior upper endplate of S1 |
|
Coronal balance distance (CBD) |
Horizontal distance between the C7 plumb line and the center sacral vertical line |
|
Thoracic kyphosis (TK) |
Cobb angle between T5 and T12 |
|
Lumbar lordosis (LL) |
Cobb angle between L1 and S1 |
|
Lordosis distribution index (LDI) |
L4–S1 lordosis/L1–S1 lordosis (LL) × 100% |
|
Proximal LL |
Cobb angle between L1 and L4 |
|
Distal LL |
Cobb angle between L4 and S1 |
|
PI–LL |
PI minus LL |
|
PJA |
The angle between the inferior endplate of upper instrumented vertebra (UIV) and the superior endplate of UIV+2 |
|
Hip |
|
|
Femoral head coverage (FHC) |
The craniocaudal coverage of the femoral head by the acetabulum |
|
Lateral center-edge (LCE) angle |
Angle formed by the longitudinal pelvic axis and a line connecting the center of the femoral head with the lateral edge of the acetabulum |
|
Acetabular index (AI) |
Angle formed by a horizontal line and a line connecting the most medial point of the sclerotic zone of the acetabular roof with the lateral edge of the acetabulum |
|
Sharp angle |
Angle formed by a horizontal line and a line connecting the caudal tip of the teardrop to the lateral edge of the acetabulum |
|
Extrusion index (EI) |
Percentage of femoral head not covered by the acetabulum (A) relative to the total diameter of the femoral head (A+B) |
Table 2.Basic characteristics of adult spinal deformity patients
Table 2.
|
Variable |
S2AI group (N = 224) |
IS group (N = 35) |
|
Age (yr) |
63.8 ± 6.2 |
63.6 ± 7.1 |
|
Sex, female:male |
164:60 |
27:8 |
|
Follow-up (mo) |
27.4 ± 3.9 |
29.5 ± 2.5 |
|
Fusion segments |
10.7 ± 2.7 |
9.1 ± 2.5 |
|
Instrument type at UIV, TPS: traditional pedicle screws |
66:158 |
0:35 |
|
UIV |
|
|
|
Above T8 |
68 (30.4) |
10 (28.6) |
|
T8–10 |
108 (48.2) |
16 (45.7) |
|
Below T10 |
48 (21.4) |
9 (25.7) |
|
Spinal-pelvic radiographic data |
|
|
|
PI (°) |
48.9 ± 12.2 |
50.1 ± 13.5 |
|
PT (°) |
30.3 ± 9.3 |
29.2 ± 7.4 |
|
SS (°) |
18.5 ± 12.3 |
20.9 ± 8.1 |
|
Cobb angle (°) |
40.1 ± 18.5 |
45.3 ± 18.3 |
|
SVA (mm) |
69.5 ± 56.8 |
71.2 ± 41.2 |
|
CBD (mm) |
19.8 ± 15.2 |
16.9 ± 10.2 |
|
TK (°) |
15.7 ± 5.4 |
17.2 ± 11.3 |
|
LL (°) |
17.1 ± 8.8 |
16.6 ± 12.1 |
|
Proximal LL (°) |
-5.4 ± 1.6 |
-3.9 ± 2.1 |
|
Distal LL (°) |
22.5 ± 15.1 |
20.5 ± 2.4 |
|
LDI |
1.5 ± 0.7 |
1.2 ± 0.9 |
|
PI–LL (°) |
31.9 ± 18.4 |
33.5 ± 17.9 |
|
Hip radiographic data |
|
|
|
FHC (%) |
|
|
|
Left |
83.8 ± 7.3 |
82.9 ± 5.6 |
|
Right |
82.5 ± 6.7 |
82.1 ± 7.5 |
|
LCE angle (°) |
|
|
|
Left |
35.1 ± 7.7 |
32.1 ± 6.5 |
|
Right |
34.7 ± 7.5 |
33.2 ± 7.1 |
|
AI (°) |
|
|
|
Left |
8.9 ± 6.0 |
8.2 ± 3.7 |
|
Right |
8.9 ± 6.4 |
8.5 ± 4.9 |
|
SA (°) |
|
|
|
Left |
37.8 ± 5.4 |
35.4 ± 8.2 |
|
Right |
37.8 ± 4.3 |
36.0 ± 7.7 |
|
EI (%) |
|
|
|
Left |
15.4 ± 7.0 |
16.1 ± 6.4 |
|
Right |
15.1 ± 6.7 |
16.9 ± 6.0 |
Table 3.Comparisons of basic characteristics between groups C and NC
Table 3.
|
Variable |
Group C (N = 56) |
Group NC (N = 56) |
p-value |
|
Age (yr) |
63.5 ± 6.1 |
65.4 ± 5.0 |
0.188 |
|
Sex, female:male |
47:9 |
44:12 |
0.835 |
|
Follow-up (mo) |
25.4 ± 3.2 |
24.8 ± 2.7 |
0.704 |
|
Spinal-pelvic parameters |
|
|
|
|
PI (°) |
50.8 ± 12.8 |
49.0 ± 13.2 |
0.602 |
|
PT (°) |
31.2 ± 8.3 |
30.3 ± 10.7 |
0.763 |
|
SS (°) |
19.8 ± 12.4 |
18.7 ± 14.4 |
0.771 |
|
Cobb angle (°) |
41.9 ± 17.4 |
35.0 ± 16.1 |
0.123 |
|
SVA (mm) |
68.8 ± 51.9 |
62.0 ± 48.5 |
0.435 |
|
CBD (mm) |
20.3 ± 16.0 |
14.6 ± 11.3 |
0.528 |
|
TK (°) |
13.8 ± 10.9 |
17.1 ± 15.7 |
0.403 |
|
LL (°) |
16.9 ± 15.7 |
18.2 ± 16.8 |
0.785 |
|
Proximal LL (°) |
-5.6 ± 1.1 |
-4.4 ± 1.5 |
0.754 |
|
Distal LL (°) |
22.6 ± 17.6 |
22.7 ± 16.8 |
0.972 |
|
LDI |
1.8 ± 1.3 |
1.7 ± 0.8 |
0.910 |
|
PI–LL (°) |
33.9 ± 15.5 |
30.8 ± 20.7 |
0.522 |
|
Hip parameters |
|
|
|
|
Bilateral FHC (%) |
82.7 ± 5.6 |
84.2 ± 7.5 |
0.046 |
|
Bilateral LCE (°) |
35.4 ± 8.5 |
35.0 ± 8.1 |
0.550 |
|
Bilateral AI (°) |
8.3 ± 6.5 |
7.3 ± 7.0 |
0.577 |
|
Bilateral SA (°) |
38.1 ± 5.3 |
37.9 ± 5.9 |
0.887 |
|
Bilateral EI (%) |
14.7 ± 5.7 |
13.9 ± 8.2 |
0.687 |
Table 4.Comparison of variations in parameters between groups C and NC following S2AI fixation and during follow-up
Table 4.
|
Variable |
Pre-to-post
|
During follow-up
|
p-value |
|
Group C (N = 56) |
Group NC (N = 56) |
Group C (N = 56) |
Group NC (N = 56) |
|
Spinal-pelvic parameters |
|
|
|
|
|
|
ΔPT (°) |
-13.7 ± 9.2 |
-10.6 ± 9.4 |
8.5 ± 6.3 |
11.3 ± 11.4 |
0.238†, 0.267‡
|
|
ΔSS (°) |
5.2 ± 1.2 |
9.5 ± 1.7 |
-2.5 ± 7.6 |
-1.0 ± 14.8 |
0.111†, 0.306‡
|
|
ΔSVA (mm) |
-43.6 ± 16.0 |
-32.4 ± 15.0 |
14.4 ± 9.8 |
37.1 ± 22.8 |
0.321†, 0.029‡
|
|
ΔCBD (mm) |
-18.1 ± 14.2 |
-3.4 ± 2.0 |
-1.3 ± 0.7 |
-2.3 ± 1.2 |
0.074†, 0.790‡
|
|
ΔTK (°) |
7.8 ± 1.1 |
9.1 ± 2.0 |
2.9 ± 1.0 |
6.1 ± 1.6 |
0.652†, 0.035‡
|
|
ΔLL (°) |
17.5 ± 13.7 |
20.0 ± 16.9 |
-4.0 ± 3.3 |
-8.1 ± 6.1 |
0.519†, 0.099‡
|
|
ΔLDI |
-1.7 ± 1.6 |
-0.5 ± 0.4 |
-0.1 ± 0.1 |
-0.3 ± 0.2 |
0.347†, 0.131‡
|
|
ΔPI–LL (°) |
-26.3 ± 13.1 |
-20.0 ± 17.3 |
9.0 ± 7.3 |
8.4 ± 7.4 |
0.114†, 0.753‡
|
|
ΔPJA |
- |
- |
2.9 ± 1.0 |
8.0 ± 1.7 |
0.016‡
|
|
Hip parameters |
|
|
|
|
|
|
Bilateral ΔFHC (%) |
|
|
|
|
|
|
Left |
5.9 ± 5.0 |
0.3 ± 0.1 |
-2.0 ± 1.6 |
0.3 ± 0.2 |
< 0.001†, 0.005‡
|
|
Right |
5.0 ± 4.8 |
0.2 ± 0.3 |
-1.9 ± 1.5 |
0.2 ± 0.1 |
< 0.001†, 0.004‡
|
|
Bilateral ΔLCE (°) |
|
|
|
|
|
|
Left |
1.8 ± 1.1 |
0.8 ± 0.1 |
-1.0 ± 0.2 |
1.5 ± 1.3 |
0.296†, 0.195‡
|
|
Right |
2.0 ± 1.9 |
1.0 ± 1.1 |
-0.8 ± 0.2 |
1.6 ± 1.2 |
0.282†, 0.207‡
|
|
Bilateral ΔAI (°) |
|
|
|
|
|
|
Left |
-0.7 ± 0.4 |
-0.4 ± 0.4 |
0.8 ± 0.2 |
0.4 ± 0.3 |
0.721†, 0.766‡
|
|
Right |
-0.8 ± 0.9 |
-0.6 ± 0.3 |
0.7 ± 0.8 |
0.5 ± 0.5 |
0.772†, 0.639‡
|
|
Bilateral ΔSA (°) |
|
|
|
|
|
|
Left |
-0.8 ± 0.9 |
0.9 ± 0.7 |
0.6 ± 0.6 |
0.5 ± 0.4 |
0.609†, 0.971‡
|
|
Right |
-0.7 ± 0.7 |
0.3 ± 0.2 |
0.2 ± 0.1 |
0.1 ± 0.1 |
0.613†, 0.862‡
|
|
Bilateral ΔEI (%) |
|
|
|
|
|
|
Left |
-2.7 ± 1.8 |
-0.8 ± 0.3 |
-0.8 ± 0.5 |
0.1 ± 0.1 |
0.025†, 0.032‡
|
|
Right |
-2.5 ± 1.9 |
-1.1 ± 0.7 |
-0.6 ± 0.5 |
0.3 ± 0.1 |
0.027†, 0.027‡
|
Table 5.Comparison of surgical details and complications between groups C and NC
Table 5.
|
Variable |
Group C (N = 56) |
Group NC (N = 56) |
p-value |
|
Surgical details |
|
|
|
|
Fusion segments |
10.8 ± 2.1 |
10.2 ± 2.9 |
0.867 |
|
Instrument type at UIV |
|
|
0.690 |
|
Tricortical pedicle screw: traditional pedicle screws |
16/40 |
14/42 |
|
|
UIV |
|
|
|
|
Above T8 |
16 (28.6) |
17 (30.4) |
0.750 |
|
T8–10 |
28 (50.0) |
25 (44.6) |
0.412 |
|
Below T10 |
12 (21.4) |
14 (25.0) |
0.541 |
|
PSO segment |
|
|
0.890 |
|
T12 |
2 (3.6) |
3 (5.4) |
|
|
L1 |
15 (26.8) |
16 (28.6) |
|
|
L2 |
7 (12.5) |
7 (12.5) |
|
|
L3 |
5 (8.9) |
4 (7.1) |
|
|
L4 |
2 (3.6) |
1 (1.8) |
|
|
L5 |
1 (1.8) |
0 (0) |
|
|
Complications |
|
|
|
|
PJK |
10 (17.9) |
22 (40.0) |
0.031‡
|
|
Sagittal imbalance aggravation†
|
8 (14.2) |
24 (42.9) |
0.013‡
|
|
Rod breakage |
3 (5.3) |
2 (3.8) |
0.980‡
|
|
S2AI screw loosening |
7 (12.5) |
5 (7.0) |
0.679‡
|
|
Intercostal neuralgia |
4 (7.1) |
5 (8.9) |
0.981‡
|
|
Incision infection |
3 (5.4) |
3 (5.4) |
> 0.999‡
|
|
Pseudarthrosis |
2 (3.6) |
1 (1.8) |
0.991‡
|
Table 6.Comparison of variations in parameters between group C-R and group C-NR following S2AI fixation and during follow-up
Table 6.
|
Variable |
Pre-to-post
|
During follow-up
|
p-value |
|
Group C-R (N = 28) |
Group C-NR (N = 28) |
Group C-R (N = 28) |
Group C-NR (N = 28) |
|
Spinal-pelvic parameters |
|
|
|
|
|
|
ΔPT (°) |
-13.3 ± 11.1 |
-13.2 ± 6.0 |
9.7 ± 6.8 |
6.7 ± 5.7 |
0.989†, 0.264‡
|
|
ΔSS (°) |
4.7 ± 11.1 |
5.6 ± 10.5 |
-2.5 ± 1.4 |
-2.2 ± 1.9 |
0.836†, 0.922‡
|
|
ΔSVA (mm) |
-54.3 ± 48.4 |
-64.6 ± 54.9 |
6.7 ± 5.3 |
35.3 ± 19.5 |
0.661†, 0.002‡
|
|
ΔCBD (mm) |
-22.6 ± 17.6 |
-10.9 ± 26.6 |
-1.2 ± 0.7 |
-2.6 ± 1.8 |
0.380†, 0.835‡
|
|
ΔTK (°) |
7.6 ± 7.1 |
8.9 ± 10.9 |
0.4 ± 0.4 |
5.3 ± 5.1 |
0.756†, 0.028‡
|
|
ΔLL (°) |
14.9 ± 11.4 |
24.2 ± 15.8 |
-2.3 ± 1.9 |
-7.3 ± 5.3 |
0.116†, 0.144‡
|
|
ΔProximal LL (°) |
10.5 ± 10.6 |
22.2 ± 16.5 |
4.3 ± 3.3 |
-2.1 ± 1.8 |
0.077†, 0.103‡
|
|
ΔDistal LL (°) |
4.2 ± 3.4 |
2.5 ± 19.6 |
-6.6 ± 1.9 |
-5.1 ± 1.6 |
0.803†, 0.743‡
|
|
ΔLDI |
-0.5 ± 0.4 |
-0.7 ± 0.5 |
-0.1 ± 0.1 |
0.8 ± 0.3 |
0.978†, 0.065‡
|
|
ΔPI–LL (°) |
-24.0 ± 10.2 |
-29.1 ± 11.9 |
7.9 ± 6.3 |
11.8 ± 8.2 |
0.240†, 0.189‡
|
|
ΔPJA |
- |
- |
0.6 ± 0.4 |
6.3 ± 5.4 |
0.073‡
|
|
PJK |
|
|
|
|
|
|
Occurred:not occurred |
- |
- |
7:21 |
5:23 |
0.845§
|
|
Sagittal imbalance aggravation |
|
|
|
|
|
|
Occurred:not occurred |
- |
- |
2:26 |
6:22 |
0.025‡
|
|
Hip parameters |
|
|
|
|
|
|
Bilateral FHC (%) |
4.9 ± 4.1 |
6.2 ± 4.8 |
-2.1 ± 1.7 |
-0.5 ± 0.2 |
0.560†, 0.022‡
|
|
Bilateral LCE (°) |
1.5 ± 1.4 |
2.7 ± 2.3 |
-1.1 ± 1.4 |
-0.9 ± 1.2 |
0.432†, 0.897‡
|
|
Bilateral AI (°) |
-0.7 ± 0.2 |
-1.5 ± 0.8 |
-0.1 ± 0.4 |
1.7 ± 1.7 |
0.516†, 0.385‡
|
|
Bilateral SA (°) |
-0.1 ± 0.1 |
0.5 ± 0.2 |
2.6 ± 1.5 |
-1.9 ± 1.3 |
0.205†, 0.216‡
|
|
Bilateral EI (%) |
-1.7 ± 2.6 |
-2.7 ± 2.3 |
-0.9 ± 0.8 |
-0.5 ± 0.3 |
0.333†, 0.625‡
|
Table 7.Pearson correlation analysis of aggravation of sagittal imbalance during follow-up and changes in hip parameters
†
Table 7.
|
Variable |
ΔSVA
|
ΔPJA
|
|
r |
p-value |
r |
p-value |
|
ΔFHC |
|
|
|
|
|
Pre-to-post |
-0.413 |
0.009 |
-0.409 |
0.012 |
|
Po-to-fu |
-0.341 |
0.041 |
0.201 |
0.595 |
|
ΔLCE angle |
|
|
|
|
|
Pre-to-post |
-0.201 |
0.596 |
0.314 |
0.219 |
|
Po-to-fu |
-0.172 |
0.706 |
0.225 |
0.386 |
|
ΔAI |
|
|
|
|
|
Pre-to-post |
-0.214 |
0.466 |
-0.251 |
0.242 |
|
Po-to-fu |
0.221 |
0.398 |
-0.208 |
0.576 |
|
ΔSA |
|
|
|
|
|
Pre-to-post |
0.216 |
0.414 |
0.251 |
0.242 |
|
Po-to-fu |
-0.174 |
0.695 |
0.229 |
0.375 |
|
ΔEI |
|
|
|
|
|
Pre-to-post |
0.215 |
0.451 |
0.276 |
0.225 |
|
Po-to-fu |
0.231 |
0.335 |
-0.210 |
0.485 |
Table 8.Univariate and multivariate logistic regression analyses of factors influencing the aggravation of sagittal imbalance during follow-up
Table 8.
|
Variable†
|
Univariable analysis
|
Multivariable analysis
|
|
HR |
95% CI |
p-value |
HR |
95% CI |
p-value |
|
Analysis 1‡
|
|
|
|
|
|
|
|
ΔFHC |
|
|
|
|
|
|
|
Pre-to-post |
0.746 |
0.560–0.995 |
0.037 |
0.727 |
0.539–0.981 |
0.039 |
|
Po-to-fu |
0.567 |
0.311–1.037 |
0.065 |
|
|
|
|
ΔLCE angle |
|
|
|
|
|
|
|
Pre-to-post |
1.087 |
0.917–1.289 |
0.334 |
|
|
|
|
Po-to-fu |
1.036 |
0.955–1.125 |
0.392 |
|
|
|
|
ΔAI |
|
|
|
|
|
|
|
Pre-to-post |
0.878 |
0.732–1.053 |
0.162 |
|
|
|
|
Po-to-fu |
0.840 |
0.707–0.997 |
0.047 |
0.787 |
0.650–0.953 |
0.059 |
|
ΔSA |
|
|
|
|
|
|
|
Pre-to-post |
1.271 |
0.926–1.745 |
0.137 |
|
|
|
|
Po-to-fu |
1.017 |
0.946–1.093 |
0.648 |
|
|
|
|
ΔEI |
|
|
|
|
|
|
|
Pre-to-post |
0.915 |
0.736–1.138 |
0.046 |
0.788 |
0.613–1.014 |
0.064 |
|
Po-to-fu |
1.031 |
0.876–1.213 |
0.716 |
|
|
|
|
Analysis 2§
|
|
|
|
|
|
|
|
ΔFHC |
|
|
|
|
|
|
|
Pre-to-post |
0.666 |
0.451–0.984 |
0.041 |
0.646 |
0.420–0.993 |
0.046 |
|
Po-to-fu |
0.340 |
0.134–0.863 |
0.023 |
0.332 |
0.122–0.904 |
0.031 |
|
ΔLCE angle |
|
|
|
|
|
|
|
Pre-to-post |
0.933 |
0.788–1.118 |
0.451 |
|
|
|
|
Po-to-fu |
0.956 |
0.835–1.093 |
0.509 |
|
|
|
|
ΔAI |
|
|
|
|
|
|
|
Pre-to-post |
1.099 |
0.886–1.363 |
0.391 |
|
|
|
|
Po-to-fu |
1.001 |
0.853–1.174 |
0.901 |
|
|
|
|
ΔSA |
|
|
|
|
|
|
|
Pre-to-post |
1.205 |
0.852–1.685 |
0.276 |
|
|
|
|
Po-to-fu |
0.909 |
0.730–1.134 |
0.298 |
|
|
|
|
ΔEI |
|
|
|
|
|
|
|
Pre-to-post |
0.916 |
0.727–1.154 |
0.045 |
0.822 |
0.624–1.083 |
0.163 |
|
Po-to-fu |
1.022 |
0.857–1.219 |
0.810 |
|
|
|
Table 9.Comparison of visual analogue scale (VAS) scores between groups at preoperative, 3-month postoperative, and 2-year follow-up
Table 9.
|
Domain |
Preoperative
|
3-Month follow-up
|
2-Year follow-up
|
p-value |
|
Group C |
Group NC |
p-value |
Group C |
Group NC |
p-value |
Group C |
Group NC |
p-value |
|
VAS back pain |
5.1 ± 2.3 |
5.0 ± 1.9 |
0.725 |
2.4 ± 1.1 |
2.3 ± 1.0 |
0.823 |
2.3 ± 1.8 |
2.3 ± 1.5 |
0.728 |
a***, b, c***, d |
|
VAS leg pain |
4.3 ± 2.1 |
4.2 ± 2.0 |
0.788 |
2.1 ± 1.2 |
2.1 ± 1.1 |
0.987 |
2.1 ± 1.7 |
2.8 ± 1.4 |
0.039 |
a***, b, c***, d* |
|
Domain
|
Preoperative
|
3-Month follow-up
|
2-Year follow-up
|
p-value
|
|
Group C-R
|
Group C-NR
|
p-value
|
Group C-R
|
Group C-NR
|
p-value
|
Group C-R
|
Group C-NR
|
p-value
|
|
VAS back pain |
5.0 ± 2.3 |
5.1 ± 2.2 |
0.967 |
2.4 ± 1.1 |
2.3 ± 1.2 |
0.981 |
2.3 ± 1.7 |
2.4 ± 1.9 |
0.861 |
e***, f, g***, h |
|
VAS leg pain |
4.3 ± 2.2 |
4.4 ± 2.0 |
0.935 |
2.1 ± 1.0 |
2.2 ± 1.2 |
0.912 |
1.9 ± 1.6 |
2.6 ± 1.9 |
0.121 |
e***, f, g***, h |
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