Anterior Column Realignment Through Open Pre-posterior Release-Anterior-Posterior Fusion Versus Hybrid Minimally Invasive-Anterior-Posterior Fusion for Dynamic Sagittal Imbalance of the Spine

Abstract

Study Design

Retrospective comparative study.

Objectives

To investigate the clinical and radiological outcomes after anterior column realignment (ACR) through pre-posterior release-anterior-posterior surgery (PAP) and minimally invasive surgery -lateral lumbar interbody fusion (MIS-LLIF) using hybrid anterior-posterior surgery (AP).

Methods

A total of 91 patients who underwent ACR with long fusions from T10 vertebra to the sacropelvis with a follow-up period of at least 2 years after corrective surgery for adult spinal deformity were included and divided into two groups by surgical method: AP and PAP. AP was performed in 26 and PAP in 65 patients. Clinical outcomes and radiological parameters were investigated and compared. A further comparison was conducted after propensity score matching between the groups.

Results

The more increase of LL and decrease of PI-LL mismatch were observed in the PAP group than in the AP group postoperatively. After propensity score matching, total operation time and intraoperative bleeding were greater, and intensive care unit care and rod fracture were more frequent in the PAP group than in the AP group with statistical significance. Reoperation rate was higher in PAP (29.2%) than in AP (16.7%) without statistical significance.

Conclusions

PAP provides a more powerful correction for severe sagittal malalignment than AP procedures. AP results in less intraoperative bleeding, operation time, and postoperative complications. Therefore, this study does not suggest that one treatment is superior to the other.

Level of Evidence

III.

Keywords

adult spinal deformity anterior column realignment lateral lumbar interbody fusion spinopelvic alignment complications

Introduction

Surgical correction of adult spinal deformity (ASD) with severe dynamic sagittal imbalance (DSI) is challenging for spine surgeons.¹ The primary goal of all surgical strategies is to restore sagittal and coronal balance. In particular, sagittal balance has been demonstrated to be closely associated with health-related quality-of-life outcomes in the treatment of ASD.² Recently, advanced sagittal correction of ASD has been introduced, such as pre-posterior release-anterior-posterior instrumentation (PAP) as a combined approach (anterior column realignment, ACR)^3-5 and hybrid technique (ACR and posterior, AP) using minimal approach (lateral lumbar interbody fusion, LLIF) and open posterior instrumentation.^6,7 ACR through PAP has conventionally invasive approaches, which have limited utility for severe spectrum of sagittal plane deformity.⁸ Additionally, PAP is an extensive surgery and is associated with a large amount of intraoperative blood loss and significant complications rates.^2,8 Thus, ACR through hybrid minimal invasive surgery (MIS) has been introduced to mitigate surgical morbidity and related complications. However, not all patients may be candidates for hybrid surgery because MIS-LLIF with incomplete anterior release for ACR and without pre-posterior release may lead to relative under-correction of severe forms of sagittal imbalance of the spine. Nonetheless, both AP and PAP approaches might show a higher correction rate than posterior instrumentation alone for severe DSI.^3,6,9,10

To the best of our knowledge, there is a paucity of literature on the direct comparison between the two surgical procedures with the same fusion level, similar age and diagnosis. Therefore, this study aimed to evaluate and compare the clinical and radiological outcomes and complications of two different surgical procedures for the correction of ASD with DSI.

Methods

Data Collection

This study was performed after obtaining approval from the Institutional Review Board (IRB) of Kyung Hee University Hospital at Gangdong (approval number: KHNMC- 2020-12-021). Written informed consent was obtained from all the participants. Among the various ASD diseases, patients diagnosed with DSI between May 2012 and July 2019 were included in this retrospective study. The inclusion criteria were as follows: (1) age >65 years at the index surgery; (2) DSI without major coronal imbalance; (3) ACR with proximal fusion level to T10 and distal to the sacropelvis using bilateral iliac screws; (4) posterior two-rod instrumentation; and (5) patients who underwent anterior lumbar interbody fusion (ALIF) or minimally invasive lateral lumbar interbody fusion (LLIF) with insertion of three or more cages from L1-L5, and/or posterior lumbar interbody fusion (PLIF) or ALIF for L5-S1. In the AP group, L5-S1 fusion was performed using oblique lateral interbody fusion if cage insertion was accessible. However, 23 patients (4 patients in the AP group and 19 patients in the PAP group) who were ineligible for assessment due to follow-up loss before postoperative 2 years were excluded. All patients underwent two-staged surgery. The AP group underwent ACR through hybrid MIS-LLIF without pre-posterior release followed by open posterior instrumentation, whereas the PAP group underwent open pre-posterior release first, and then ACR and open posterior instrumentation were performed simultaneously in the second stage surgery. However, grade 2 Schwab posterior osteotomies¹¹ during posterior release in the PAP group and posterior instrumentation in the AP group were performed at the segments based on the degree of fixed regional and global malalignments. (Figure 1) Finally, 91 patients who met the inclusion criteria were enrolled. Subsequently, all included patients were divided into two groups according to the surgical procedures. Additionally, a further comparison was conducted after propensity score (PS) matching between the groups. (Figure 2)

Figure 1.

Diagram of the surgical procedures of the AP and PAP approaches.

Figure 2.

Flow diagram showing the selection of patients ACR: Anterior column realignment, PAP: Pre-posterior release, anterior and posterior instrumentation, MIS-LLIF: Minimally invasive surgery-lateral lumbar interbody fusion, AP: Anterior surgery and posterior instrumentation, ALIF: Anterior lumbar interbody fusion, LLIF Lateral lumbar interbody fusion, OLIF: Oblique lumbar interbody fusion, UIV: Uppermost instrumented vertebra, PI: Posterior instrumentation.

Radiographic Assessment

Radiographic measurements were performed by two independent spine fellows who did not participate in either surgery at the preoperative, the immediate postoperative, and the regular postoperative outpatient visits (3, 6, 9 months, 1-, 2-year and the final follow-up), respectively. Radiographic measurements included the standard sagittal spinopelvic parameters. Pelvic tilt (PT), sacral slope (SS), and pelvic incidence (PI) were measured. Spinopelvic parameters such as lumbar lordosis (LL), thoracic kyphosis (TK), C7 sagittal vertical axis (C7SVA), T1 pelvic angle (T1PA), proximal junctional angle (PJA), and sagittal Cobb angle between the caudal endplate of the uppermost instrumented vertebra (UIV), cephalad endplate of UIV+2, and postoperative lordosis distribution index (LDI, [L4 S1 lordosis/L1 S1 lordosis] x100) were measured at each time point.

Proximal junctional kyphosis (PJK) was defined as a PJA >20° and ≥20° greater than the preoperative measurement without any bone or instrumentation failures, based on previous studies.^12,13 Proximal junctional failure (PJF) was considered as patients presenting with symptoms and radiographs showing the followings: fractures at UIV or UIV+1, junctional subluxation, and failure of UIV fixation. Failure of metallic fixation was defined as the pullout or dislodgment of screws from rods and fractures of the screws or rods. Reoperations due to mechanical complications, such as PJK/PJFs or rod fractures (RF), were also recorded.

Clinical Assessment

Clinical data collected from the medical records included age at the time of index surgery, sex, body mass index (BMI), medical comorbidities, smoking history, lowest T-score of bone mineral density (BMD), Charlson comorbidity index (CCI)¹⁴ and previous history of spinal surgery. Surgery-related data included the surgical techniques.

Statistical Analysis

IBM SPSS Version 21.0 software (IBM Corporation, Armonk, NY, USA) was used for all the statistical analyses. Numerical data are presented as mean ± standard deviation (SD). Continuous data were analyzed using student’s t-test, and categorical data were analyzed using Fisher’s exact test. Statistical significance was set at P < .05.

Results

Patients Demographic Data

A total of 91 patients who met the inclusion criteria were enrolled, of whom 26 underwent MIS-LLIF ACR followed by posterior surgery (AP group) (Figure 3) and 65 underwent posterior release-ACR-posterior surgery (PAP group) (Figure 4). The mean age was 69.7 ± 5.2 without statistically significant difference between the two groups, and 88 of the 91 patients were female. The mean follow-up period was 51.5 ± 18.4 in the PAP group, and 39.7 ± 26.4 (P = .041) in the AP group. Mean CCI was .7 ± .9 in the AP and .6 ± .8 in the PAP group without significant difference. Although the mean age was not different between the two groups, AP group had greater BMI (26.1 ± 3.3 m/kg² vs 24.6 ± 2.1 m/kg², P = .044) and lower T-score of BMD (−2.5 ± .8 vs −1.9 ± 1.3, P = .010) than PAP group (Table 1). After PS matching, only follow-up period between the groups was different (Table 2).

Figure 3.

Sequential radiographs of a 71-year-old female patient with degenerative sagittal imbalance who underwent MI-LLIF using hybrid anterior-posterior surgery (AP group). (A) Preoperative whole spine standing lateral radiograph (B) Postoperative 1-year whole spine standing lateral radiograph (C) Postoperative 5-year follow-up showing stable maintenance of fused construct with slightly increased C7 sagittal vertical axis.

Figure 4.

Sequential radiographs of a 69-year-old female patient with degenerative sagittal imbalance who underwent pre-posterior release with ACR and posterior instrumentation (PAP group) (A) Preoperative whole spine standing lateral radiograph showing major sagittal deformity. (B) Postoperative 3 months’ whole standing lateral radiograph showing a restoration of global sagittal alignment. (C) Postoperative 2 years’ whole spine standing lateral radiograph showing aggravated global sagittal alignment due to nonunion with rod fracture at L3-L4 level. (D) After revision surgery (additional bone graft and change of rod), sagittal malalignment was restored.

Table 1.

Demographic Data in AP Group Versus PAP Group.

	AP Group (n = 26)	PAP Group (n = 65)	P
Age (years)	71.0 ± 6.3	69.2 ± 4.6	NS
Body mass index (kg/m²)	26.1 ± 3.3	24.6 ± 2.1	.044
Bone mineral density (T-score)	−2.5 ± 0.8	−1.9 ± 1.3	.010
Charlson comorbidity index	.7 ± 0.9	.6 ± 0.8	NS
Follow-up period (months)	51.5 ± 18.4	39.7 ± 26.4	.041

NS, not statistically significant.

Student’s t test was performed.

Table 2.

Demographic Data in AP Group Versus PAP Group After Propensity Score Matching.

	AP Group (n = 24)	PAP Group (n = 24)	P
Age (years)	71.6 ± 6.3	71.7 ± 4.1	NS
Body mass index (kg/m²)	25.4 ± 2.5	25.0 ± 1.9	NS
Bone mineral density (T-score)	−2.5 ± 0.9	−2.7 ± 0.9	NS
Charlson comorbidity index	.8 ± 0.9	.7 ± 1.0	NS
Follow-up period (months)	51.2 ± 18.5	30.3 ± 15.2	<.001

NS, not statistically significant.

Student’s t test was performed.

Perioperative Complications

The perioperative complications between the two groups are shown in Table 3. Not surprisingly, the operative time was significantly longer and the estimated blood loss was significantly higher in the PAP group than in the AP group. Superficial infection developed in 2 patients in the AP group and three in the PAP group without statistical significance. All superficial infections developed after posterior instrumentation, but none developed an infection after the anterior approach. Neurologic deficits due to nerve root injury during the posterior approach developed in 1 (3.8%) in the AP group and five patients (7.7%) in the PAP group. Four patients improved spontaneously at 6 months postoperatively, but two patients did not improve until the final follow-up. Major medical complications developed in six patients (23.1%) in the AP group and 14 patients (21.5%) in the PAP group, without statistical significance. The incidence of other perioperative complications, including surgery-related and medical complications, was similar between the groups (Table 3). After PS matching, total operation time and intraoperative bleeding were greater and intensive care unit care was more frequent in the PAP group than the AP group (Table 4).

Table 3.

Perioperative Complications in AP Group Versus PAP Group.

	AP Group (n = 26)	PAP Group (n = 65)	P
Surgery-related complications
Total operation time (min)	413.4 ± 59.7	591.9 ± 84.9	<.001^a
Estimated blood loss (mL)	792.7 ± 154.4	1976.9 ± 826.5	<.001^a
Intensive care unit care	15.4% (n = 4)	23.1% (n = 15)	NS^b
Neurologic compromise	3.8% (n = 1)	7.7% (n = 5)	NS^b
Surgical site infection (superficial)	7.7% (n = 2)	4.6% (n = 3)	NS^b
Medical complications
Pulmonary complications	7.7% (n = 2)	4.6% (n = 3)	NS^b
Ileus	11.5% (n = 3)	15.4% (n = 10)	NS^b
Deep vein thrombosis/Pulmonary thromboembolism	3.8% (n = 1)	1.5% (n = 1)	NS^b

NS, not statistically significant.

^aStudent’st test was performed.

^bChi-square test was performed.

Table 4.

Perioperative Complications in AP Group Versus PAP Group After Propensity Score Matching.

	AP Group (n = 24)	PAP Group (n = 24)	P
Surgery-related complications
Total operation time (min)	404.4 ± 62.0	604.7 ± 84.6	<.001^a
Intraoperative bleeding (mL)	781.7 ± 155.6	2225.0 ± 890.6	<.001^a
Intensive care unit care	12.5% (n = 3)	41.7% (n = 10)	.049^b
Neurologic compromise	4.2% (n = 1)	16.7% (n = 4)	NS^b
Surgical site infection (superficial)	8.3% (n = 2)	4.2% (n = 1)	NS^b
Medical complications
Pulmonary complications	8.3% (n = 2)	4.2% (n = 1)	NS^b
Ileus	11.5% (n = 3)	16.7% (n = 4)	NS^b
Deep vein thrombosis/Pulmonary thromboembolism	4.2% (n = 1)	0% (n = 0)	NS^b

NS, not statistically significant.

^aStudent’s t test was performed.

^bChi-square test was performed.

Radiological Outcomes

The radiographic results are presented in Table 5. Postoperatively, all global and regional sagittal parameters improved in both groups. The mean preoperative LL in the AP group was 7.3 ± 22.8° and −10.4 ± 24.6° (- indicates kyphosis) in the PAP group, with statistical significance (P = .002). The postoperative mean LL increased to 38.0 ± 9.1° in the AP and 52.2 ± 12.5° in the PAP group, respectively, with statistical difference (P < .001). Mean PI-LL improved from 43.8 ± 24.2° to 13.1 ± 11.3° in AP group and from 67.5 ± 26.2° to 4.6 ± 14.0° in PAP group. The PAP group showed greater improvement than AP group in the postoperative PI-LL mismatch (P = .009). The mean SVA decreased from preoperative 14.0 ± 8.4 cm to postoperative 2.6 ± 4.1 cm in the AP group and from 18.8 ± 9.6 cm to 2.7 ± 3.4 cm in the PAP group. However, there was no significant difference between the two groups in terms of postoperative SVA. At the final follow-up, all sagittal parameters, except LL (P = .008) and PJA (P = .047), were not significantly different between the two groups.

Table 5.

Comparison of Radiological Outcome Between AP and PAP Groups.

	AP Group (n = 26)	PAP Group (n = 65)	P
Preoperative
PI (°)	52.7 ± 12.2	56.8 ± 9.6	NS
PT (°)	33.2 ± 12.0	37.5 ± 11.2	NS
SS (°)	19.7 ± 13.2	21.9 ± 12.7	NS
LL (°)	7.3 ± 22.8	−10.4 ± 24.6	.002
TK (°)	14.8 ± 15.3	10.7 ± 14.3	NS
SVA (cm)	14.0 ± 8.4	18.8 ± 9.6	NS
T1PA (°)	33.4 ± 12.8	41.4 ± 12.0	NS
PJA (°)	−.1 ± 5.6	2.5 ± 8.3	NS
PI-LL (°)	43.8 ± 24.2	67.5 ± 26.2	<.001
Postoperative
PT (°)	23.1 ± 12.1	23.2 ± 11.6	NS
SS (°)	28.0 ± 10.4	33.7 ± 9.2	.015
LL (°)	38.0 ± 9.1	50.2 ± 8.9	<.001
ULL (°)	11.2 ± 6.8	15.5 ± 6.7	.023
LLL (°)	26.7 ± 4.8	34.7 ± 4.3	<.001
LDI (%)	71.5 ± 12.4	69.1 ± 9.6	NS
TK (°)	29.0 ± 14.8	29.0 ± 14.8	NS
SVA (cm)	2.6 ± 4.1	2.7 ± 3.4	NS
T1PA (°)	20.5 ± 10.5	11.0 ± 2.2	.001
PJA (°)	7.3 ± 8.8	13.0 ± 10.5	.001
PI-LL (°)	13.1 ± 11.3	4.6 ± 14.0	.009
Final follow-up
PT (°)	26.7 ± 9.5	25.1 ± 10.6	NS
SS (°)	26.5 ± 8.4	32.2 ± 10.1	NS
LL (°)	33.3 ± 13.7	46.6 ± 13.2	.008
ULL (°)	8.0 ± 6.3	13.5 ± 6.7	<.001
LLL (°)	25.3 ± 4.9	32.8 ± 4.3	<.001
LDI (%)	75.9 ± 10.6	70.2 ± 9.8	NS
TK (°)	32.3 ± 16.8	33.3 ± 13.9	NS
SVA (cm)	7.1 ± 4.4	6.5 ± 4.6	NS
T1PA (°)	27.1 ± 9.4	21.7 ± 11.9	NS
PJA (°)	11.3 ± 9.3	15.7 ± 9.5	.047
PI-LL (°)	11.4 ± 9.0	10.5 ± 16.7	NS

-: kyphotic angle.

Student’s t test was performed.

NS, not statistically significant.

Mechanical Complications and Reoperations

Postoperative mechanical complications were summarized in Table 6. Mechanical complications developed in 50 of 91 patients (54.9%). Of these 50 patients, 15 patients developed in the AP group and 35 patients in the PAP group. Among them, PJF developed in 5 patients (19.2%) in the AP group and 17 (26.2%) in the PAP group. Although immediate postoperative sagittal balance had improved, sagittal decompensation without PJK/PJFs developed at the final follow-up: C7 SVA >5 cm in 9 patients (34.6%) in the AP group, and in 2 patients (3.1%) in the PAP group with statistically significant difference (P < .001). RFs were more frequent in the PAP group (16 patients, 24.6%) than in the AP group (1 patient, 3.8%) with a statistical significance (P = .034). After PS matching, sagittal imbalance without PJK/PJF and rod fracture were also statistically different (Table 7). The total reoperation rate did not differ between the two groups (Tables 6 and 7). However, 7 patients underwent reoperation for RF in the PAP group (Figure 3), but no patients underwent reoperation for RF in the AP group. The major cause of reoperation in the AP group was PJFs (4 patients) and that in the PAP group was RFs with nonunion in 7 patients. Among the patients undergone reoperation, two underwent reoperation in each group for recurrent PJFs.

Table 6.

Postoperative Mechanical Complications and Reoperation in AP Group Versus PAP Group.

	AP Group (n = 26)	PAP Group (n = 65)	P
PJK/PJF	19.2% (n = 5)	26.2% (n = 17)	NS^a
UIV fracture	15.4% (n = 4)	9.2% (n = 6)
UIV+1 fracture	0% (n = 0)	4.6% (n = 3)
Both UIV and UIV+1 fracture	0% (n = 0)	4.6% (n = 3)
UIV screw pull-out	0% (n = 0)	1.5% (n = 1)
PJK	3.8% (n = 1)	6.2% (n = 4)
Sagittal imbalance without PJK/PJF	34.6% (n = 9)	3.1% (n = 2)	<.001^b
Rod fracture	3.8% (n = 1)	24.6% (n = 16)	.034^b
Unilateral	0% (n = 0)	6.2% (n = 4)
Bilateral	3.8% (n = 1)	18.5% (n = 12)
Reoperation	15.4% (n = 4)	18.5% (n = 12)	NS^b
PJK/PJF	15.4% (n = 4)	7.7% (n = 5)
Rod fracture	3.8% (n = 1)	10.8% (n = 7)

NS, not statistically significant.

^aChi-square test was performed.

^bFisher’s exact test was performed.

Table 7.

Postoperative Mechanical Complications in AP Group Versus PAP Group After Propensity Score Matching.

	AP Group (n = 24)	PAP Group (n = 24)	P
PJK/PJF	20.8% (n = 5)	29.2% (n = 7)	NS^a
Sagittal imbalance without PJK/PJF	37.5% (n = 9)	4.2% (n = 1)	.010^a
Rod fracture	4.2% (n = 1)	33.3% (n = 8)	.023^a
Reoperation	16.7% (n = 4)	29.2% (n = 7)	NS^a

NS, not statistically significant.

^aFisher’s exact test was performed.

Clinical Outcomes

The clinical outcomes are summarized in Table 8. Preoperative VAS and ODI scores were similar between the two groups. However, the VAS score for back pain was higher in the PAP group than in the AP group at the final follow-up (4.1 ± 2.7 vs 2.8 ± 1.8, P = .047). The ODI at the final follow-up was similar between the two groups.

Table 8.

Comparison of Clinical Outcomes.

	AP Group (n = 26)	PAP Group (n = 65)	P
Preoperative
VAS for back pain	5.5 ± 1.2	6.3 ± 2.2	NS
ODI	48.5 ± 25.0	55.0 ± 17.8	NS
Final follow-up
VAS for back pain	2.8 ± 1.8	4.1 ± 2.7	.047
ODI	31.8 ± 10.4	35.3 ± 21.2	NS

VAS, Visual analogue scale; ODI, Oswestry disability index. NS, not statistically significant.

Student’s t test was performed.

Discussion

Generally, it is accepted that PAP showed superior radiological outcomes compared with AP for surgical correction because AP through MIS LLIF with a small surgical window could be fundamentally limited to adequate exposure of the anterior longitudinal ligament (ALL) due to the risk of vascular injury.^3-5 However, each surgical procedure has its own merits and demerits.^9,15,16 ACR by MIS-LLIF was not suitable for the treatment of sagittal imbalance greater than 7 cm of SVA, and open approaches, including three-column osteotomies, were recommended.⁸ PAP is a valuable complement to other realignment techniques for severe sagittal plane deformities and was the most effective at the lower lumbar spine using hyperlordotic cages.^17,18 Akbarnia et al¹⁹ also suggested that fixed deformities required more extensive surgery and were relative contraindications to ACR without posterior osteotomies.

In our study, both groups showed an SVA of >10 cm (average, 14 cm vs 18.8 cm) and PI-LL mismatch greater than 40° with PT greater than 30° preoperatively. A significant improvement in spinopelvic alignment was observed after surgical correction in the both groups. However, the PAP group showed greater improvement in spinopelvic parameters (SS, LL, T1PA, and PI-LL) compared with those of the AP group. In particular, postoperative LL (38.0° ± 9.1° vs 52.2° ± 12.5°, P < .001) and PI-LL (13.1° ± 11.3° vs 4.6° ± 14.0°, P = .009) significantly improved more in the PAP group. In PAP, it was thought that the segments became more mobile during anterior surgery (LLIF) by performing posterior muscle dissection and grade 2 Schwab osteotomy in on-involved segments, so that it could be inserted with lesser damage to the bony endplates or a larger size could be inserted during cage insertion, and which resulted in more gain of disc space height. This suggests that PAP provides a more powerful correction for sagittal imbalances.

However, in our study, the PAP group had higher incidence of RF than the AP group did. RFs, either unilateral or bilateral, were identified in 16 patients (24.6%) in the PAP group and in one patient (3.8%) in the AP group (P = .034). Nevertheless, the overall incidence (18.7%) of RF was similar to 12% to 47% in other reports.^20,21 Based on these results, patients in the PAP group had larger sagittal deformity (7.3° ± 22.8° in AP vs −10.4° ± 24.6°in PAP) preoperatively, which eventually required more forceful correction of LL leading to RF. It is considered that excessive removal of the ALL and the posterior bony structures to obtain desirable LL consequently resulted in the instability of the fusion construct and the lack of posterior bony fusion area. In addition, the posterior rods should be customized to bear the newly surgically obtained LL. In biomechanical studies,^22-24 it was demonstrated that rod contouring could significantly reduce the yield strength of the rods. Thus, sacrificing ALL and overcorrection with rod contouring may be major contributors to the RF development. Despite more frequent mechanical complications, the corrective power was better in the PAP. Therefore, if there is an additional effort to reduce mechanical complications, this method can be used carefully. Other studies have suggested the use of multi-rod technique²⁵ or the use of cobalt-chrome rod²⁶ as alternative solution to reduce RF.

With regard to the relationship between PJK/PJFs and correction rate, moderate PJK was observed with undercorrection and severe PJK with overcorrection of the sagittal balance.²⁷ The highest incidence of PJK/PJFs was also reported in patients with overcorrection beyond age-adjusted sagittal alignment.^28,29 In our study, overall, 22 (24.2%) patients developed PJK or PJF. The incidence of PJK/PJFs in this study at the age of 65 years was similar to that reported previously.^12,29,30 However, the PAP group had a higher tendency for PJK/PJF, with an incidence of 17 patients (26.2%) in the PAP group than in five (19.2%) in the AP group, although the difference was not statistically significant. The higher incidence of PJK/PJF in the PAP group may be explained by larger LL correction. Not only the amount of corrected LL, however, the effect of LDI on PJK has been investigated by several researchers and its impact on the occurrence of PJK is still in ongoing debate in recent studies.^31-33 We further measured and compared the postoperative LDI, and which was not statistically different between the two groups. (Table 5) It was thought that it was intended to improve the lower lumbar lordosis (L4-S1 lordosis) to create physiological curves during surgery in the both groups, and this has not been clarified in this study. In recent studies,^34-37 moreover, methods for evaluating bone strength for each vertebral body have been introduced such as HU (Hounsfield Units) values and VBQ (Vertebral Body Quality) scores, and which are thought to help quantitatively analyze the preoperative bone quality of UIV or UIV+1 level causing PJF by bony failure. In this study, however, since not all patients had preoperative computed tomography (CT) or magnetic resonance imaging (MRI) including the segments above UIV, the assessment of HU or VBQ was not performed. It would have been better study if those methods were added to distinguish the cause of PJF or PJK in each group.

However, sagittal imbalance with an increase of more than 5 cm at the final follow-up compared to postoperative SVA was noted in 9 patients (34.6%) in the AP group and 2 patients (3.1%) in the PAP group, with statistical significance (P < .001). Park et al³⁸ reported postoperative sagittal imbalance would develop without PJK/PJFs that were associated with less correction of sagittal alignment and degeneration of the paravertebral muscles, resulting in the hip joint serving as the center of rotation. Therefore, these results could explain the relatively higher incidence of sagittal imbalance without PJK/PJFs in patients in the AP group resulting from less correction of sagittal alignment than in the PAP group.

Deformity correction is associated with a high risk of complications in elderly populations. Smith et al²⁹ noted a 78.9% complication rate in the 65-86-year-old group vs 55.4% in the 18-44-year-old group. It was not surprising that increased age was a factor associated with selecting an MIS approach, given the decreased exposure-related morbidity and perceived decreased complication risk.³⁹ Conversely, increasingly severe deformities and the need for open decompression were the main factors influencing the selection of traditional open surgery. Soroceanu et al⁴⁰ reported the incidence of mechanical complications was approximately 31.7%, with half requiring revision surgery. In our study, 20 patients (22.0%) had medical complications and 50 (54.9%) of 91 patients developed mechanical complications; of these, 16 (17.6%) of 91 patients underwent reoperation, 4 (15.4%) in the AP group, and 12 (18.5%) in the PAP group. Of those who underwent reoperation, 4 underwent reoperation due to recurrence of UIV and UIV+1 fracture in two patients in each group. Of the 17 patients with RF in both groups, seven underwent reoperation due to progression of kyphotic deformity with pseudarthrosis at the RF site in the PAP group. Our study showed that 41.2% of the patients with RF required revision surgery.

Clinically, the PAP group had higher VAS score for back pain at the final follow-up, which may be related to the higher incidence of RF and PJK/PJF. Therefore, spine surgeons should be aware that each surgical procedure has different advantages and disadvantages for the correction of ASD with DSI. Recently, the preference of our spine team was to perform AP in patients with more medical comorbidities as this study showed that the PAP group manifested more intraoperative bleeding and longer operation time (P < .001), even though major medical complications were treated without any sequelae with conservative treatment.

Several inherent limitations of this study must be acknowledged. First, this was a non-randomized, retrospective cohort study. Especially, AP group basically included very small numbers of patients. However, its strength was the reduction of possible sampling bias with the same fusion levels, similar disease entities, and similar ages for the two different surgical procedures by PS matching. Second, this study could not select the best procedure for both the surgical approaches. However, the PAP procedure showed significant improvement with statistical significance in sagittal correction, which might be recommended for pre-posterior release for severe fixed DSI with less flexibility. Preoperative evaluation of spinal flexibility would have enabled to clarify the indication of each method. Moreover, because it is thought that patients who needed larger sagittal correction belonged to the PAP group, the presence of some selection bias is considered a limitation of this study. It would have been a better study if the patient groups with equal or similar preoperative spinopelvic parameters. However, the indications for the two surgical approaches could vary according to the surgeon’s preference, magnitude of radiographic correction, and preoperative medical comorbidity.

In conclusion, PAP provides a more powerful correction for severe sagittal malalignment than AP. However, AP results in less intraoperative bleeding, operation time, and postoperative complications. Therefore, this study does not merely suggest that one treatment is superior to the other. Prior to undergoing correction surgery for ASD with severe DSI, thorough consideration of potential complications and reduction of the risks associated with mechanical complications is of paramount importance.

Footnotes

Authors’ Contributions

JA: manuscript writing, critical revision, statistical analysis; SIK: statistical analysis; YCK, KTK, and YHK: critical revision; SMK and TK: data acquisition; KYH: study concept/design, draft manuscript writing, and critical revision. All authors have read, reviewed, and approved the article.

Declaration of Conflicting Interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: The authors declare no competing interests regarding any of the materials or devices described in this article. No benefits in any form have been received or will be received from a commercial party directly or indirectly related to the subject of this study. JA, nothing to disclose; SIK, nothing to disclose; YCK, nothing to disclose; KTK, nothing to disclose; YHK, nothing to disclose; SMK, nothing to disclose; TK, nothing to disclose; KYH, nothing to disclose.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Ethical Statement

Data Availability Statement

The patients’ data were collected in Kyung Hee University Hospital at Gangdong. The datasets generated and/or analyzed during the current study are available from the corresponding author (KYH) upon reasonable request.

Statement of Human and Animal Rights

Human subjects in this study are not identifiable, such that patients’ names, initials, hospital numbers, dates of birth, or other protected healthcare information were not disclosed.

ORCID iDs

Joonghyun Ahn

Kee-Yong Ha

Young-Hoon Kim

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