Lowest Instrumented Vertebra Selection in Adolescent Idiopathic Scoliosis With Concomitant Spondylolysis

Abstract

Study Design

Retrospective Cohort Study.

Objectives

Adolescent idiopathic scoliosis (AIS) with a concomitant pars defect poses the surgical challenge of balancing stress avoidance at the lytic segment, deformity correction, and mobility preservation. Data on lowest instrumented vertebra (LIV) selection are limited. This study aimed to identify a safe LIV in posterior spinal fusion (PSF) to minimize pain and slip progression.

Methods

Retrospective review of AIS patients (10-18 years) with spondylolysis or spondylolisthesis who underwent PSF (2016-2023) with ≥ 2-year follow-up. Variables included demographics, curve characteristics, Meyerding grade, LIV selection, and mobile segments between LIV and lytic level. Primary outcome was back pain (VAS). Secondary outcomes included slip progression, subjacent curve, mechanical complications, and revision. Between-group comparisons used Mann–Whitney U; regression assessed effects of mobility preservation and subjacent curvature on pain.

Results

Of 462 AIS patients, 29 met inclusion criteria (mean age 15.5 ± 1.5 years; 24% spondylolisthesis). Fusion ended at or above L3 in 76% and below in 24%. Follow-up VAS pain was higher in patients with <3 mobile segments between LIV and lytic level (4.5 ± 1.4 vs 2.8 ± 1.5; P = .003) and in fusions extending below L3 (5.0 ± 1.3 vs 3.0 ± 1.4; P = .004). Regression showed each additional mobile segment decreased pain (β = −0.77, P = .001), while greater subjacent curvature increased pain (per 10°, β = 0.92, P = .043). Two patients progressed to grade 1 slip; three were indicated for revision with distal junctional failure or persistent pain.

Conclusions

In AIS with coexisting spondylolysis, selecting LIV proximal to L3 minimizes pain while preserving mobile segments, without excessive slip progression.

Keywords

adolescent idiopathic scoliosis spondylolysis spondylolisthesis lowest instrumented vertebra fusion levels

Introduction

Adolescent idiopathic scoliosis (AIS) is a structural, multi-dimensional deformity of the spine. It is reported to affect approximately 3-5% of adolescents and often requires surgical intervention when curves progress beyond 45-50°.^1,2 Posterior spinal fusion (PSF) remains the standard of care for achieving deformity correction, spinal stabilization and improved quality of life.^3-7 One of the most important determinants of surgical outcome is the appropriate selection of fusion levels, with the objective of achieving deformity correction while preserving the maximum number of mobile segments, particularly in the lumbar spine, to optimize long-term spinal health.^8-10

Spondylolysis, a defect in the pars interarticularis most commonly at the L5-S1 level, and spondylolisthesis, defined as anterior translation of a vertebral body, are often asymptomatic but may influence spinal biomechanics, sagittal alignment, and postoperative outcomes.^11-14 AIS is reported to coexist with spondylolysis or isthmic spondylolisthesis in about 7% of patients with AIS and presents a unique subset of spinal deformity patients.⁴ When present in the lower lumbar spine, the coexistence of these conditions with AIS adds complexity to surgical planning, particularly in determining the distal extent of fusion.¹⁵ Surgeons are faced with a decision to either extend the fusion, including the pathological segment, or preserve motion at the lumbosacral junction, potentially risking future instability or symptomatic progression.^11,16,17 This consideration is especially relevant in Lenke type 5 and 6 curves with a low apex.^1,11,15 Traditionally, the lowest instrumented vertebra (LIV) in AIS is chosen based on strategic vertebrae identified on radiographs, such as the stable vertebra (SV), last touched vertebra (LTV), and last substantially touched vertebra (LSTV).^8-10,17-21 However, these guidelines may not apply when spondylolysis or spondylolisthesis is present at or near the potential LIV.^11,22,23 In such cases, concerns include postoperative progression of the lytic defect or listhesis, increased mechanical stress at adjacent segments, and a heightened risk of pseudarthrosis or instrumentation failure.^4,24,25

Patients with spondylolysis have been reported to score significantly lower on health-related quality-of-life measures, such as the Scoliosis Research Society Outcomes Questionnaire (SRS-22), compared to age-matched controls and AIS patients without spondylolysis.²⁶ Despite this, the biomechanical consequences of sparing vs including the pathological segment during fusion, for patients with co-existent pathologies, remain incompletely described. Finite element modeling (FEM) and biomechanical studies suggest that long spinal fusions shift loads to adjacent levels, including the lumbosacral junction, manifested by increased facet forces and altered motion, potentially exacerbating instability at a pre-existing defect.^27-30 However, the clinical significance of these theoretical findings, particularly in asymptomatic patients, remains unclear, and whether such biomechanical stresses translate into worse outcomes has yet to be firmly established.

While each pathology has been well studied in isolation, literature addressing their concurrence is limited. No standardized guidelines exist for determining the distal fusion level when a pars defect or low-grade spondylolisthesis is present, and the decision to stop above or include the pathological segment is often based on surgeon preference rather than robust evidence. Existing studies are largely retrospective, anecdotal, and heterogenous in terms of pathology severity, fusion strategy and follow-up duration, making comparisons difficult. This study aims to address these gaps by evaluating the outcome of PSF in AIS patients with concurrent spondylolysis or low-grade spondylolisthesis, with a specific focus on identifying a safe choice of LIV that minimizes symptom progression and slip advancement. By directly examining radiographic, mechanical, and patient-reported outcomes in this under-studied subgroup, it seeks to provide evidence-based guidance where current surgical decision-making is largely driven by anecdote and individual experience.

Methods

This institutional review board–approved, single-center, retrospective study reviewed all patients who underwent posterior spinal fusion for AIS with coexisting spondylolysis or low-grade spondylolisthesis between 2016 and 2023. This included patients aged 10-18 years with a minimum follow-up of 2 years. For all patients, preoperative assessment included orthogonal plain radiographs. In cases where spondylolysis was uncertain, computed tomography (CT) or magnetic resonance imaging (MRI) was reviewed for confirmation.

Data Collection and Outcome Measures

Demographic data, curve characteristics (magnitude and location), instrumented levels, Meyerding Grade, and the number of mobile segments between the LIV and the spondylolytic level were recorded. A mobile segment was defined as the smallest functional spinal motion unit, two adjacent vertebrae and the intervening disc-facet complex, that remained unfused and therefore preserved physiologic motion. An LIV at L2, for example, preserves three mobile segments above an L5-S1 spondylolysis (L2-L3, L3-L4, and L4-L5). The primary outcome was back pain severity measured using the Visual Analog Scale (VAS). Secondary outcomes included progression of slip, degree of subjacent curve postoperatively, occurrence of mechanical complications, and the need for revision or additional surgery.

Statistical Analysis

Data were analyzed using STATA version 17 (StataCorp, College Station, TX). Continuous variables were summarized as mean ± standard deviation or median with interquartile range, while categorical variables were expressed as frequency and percentage. Between-group comparisons used chi-square tests for categorical variables and independent t-tests or Mann–Whitney U tests for continuous variables, depending on distribution. A linear regression model was applied to assess the independent effects of LIV level and the number of unfused mobile segments between the LIV and the spondylolytic level on outcomes, particularly low back pain and degree of subjacent curve postoperatively. Statistical significance was set at P < .05.

Results

Patient Demographics and Preoperative Characteristics (Table 1 and Table 2)

During the study period, 462 patients underwent posterior spinal fusion for AIS. Of these, 29 patients (mean age 15.5 ± 1.5 years; range, 13-18 years) met the inclusion criteria and had a minimum follow-up of 2 years. The mean body mass index (BMI) was 20.76 ± 1.7 (males: 21.5 ± 1.3; females: 20.8 ± 1.8). Mean thoracic kyphosis measured 11.9 ± 3.6 (males: 10.2 ± 2.9; females: 12.4 ± 3.7). At baseline, 31% (9/29) of patients demonstrated a pre-existing mental health disorder and 7% (2/29) were opioid dependent. One patient had a history of thalassemia (Tables 1 and 2).

Table 1.

Demographic and Radiographic Characteristics of Included Patients With AIS and Spondylolysis

ID	Age	Sex	Lenke type	PT cobb	MT cobb	TL/L cobb	Level of pars lesion	Olisthesis	Meyerding grade	SV	LTV	LSTV	Levels instrumented	No. of stages	Segments between LIV and pars lesion	Post-op subjacent curve (⁰)	Revision indicated
1	16	F	2	36	52	-	L5S1	Y	1	L2	L1	L2	T2-L1	1	4	32	Y
2	15	M	1	-	99	-	L6S1	Y	1	L3	L2	L3	T3-L3	2^a	3	26	Y
3	13	F	4	38	93	72	L5S1	Y	2	L4	L3	L4	T2-L4	3^a	1	12	N
4	13	F	1	-	57	-	L5S1	N	0	L2	L1	L2	T2-L1	1	4	8	N
5	13	F	1	-	63	-	L5S1	N	0	L3	L1	L2	T5-L2	1	3	26	Y
6	14	F	3	-	75	54	L4L5	N	0	L3	L2	L3	T4-L3	1	1	13	N
7	15	F	5	-	-	66	L5S1	N	0	L4	L3	L3	T4-L4	1	1	12	N
8	16	M	1	-	80	-	L5S1	N	0	L2	L1	L2	T4-L2	2^a	3	14	N
9	17	F	3	-	70	62	L5S1	N	0	L4	L2	L3	T5-L4	1	1	11	N
10	18	F	5	-	-	75	L5S1	N	0	L3	L2	L3	T5-L3	1	2	13	N
11	18	F	1	-	66	-	L5S1	N	0	L2	T12	L1	T5-L1	1	4	15	N
12	14	F	5	-	-	60	L5S1	N	0	L4	L2	L3	T5-L3	1	2	14	N
13	15	F	1	-	59	-	L5S1	Y	1	L2	T12	L1	T5-L1	1	4	8	N
14	16	M	5	-	-	62	L5S1	N	0	L4	L2	L3	T5-L4	1	1	8	N
15	15	F	1	-	77	-	L5S1	N	0	L2	L1	L2	T4-L2	1	3	11	N
16	18	F	1	-	51	-	L5S1	N	0	L2	T12	L1	T5-L1	1	4	6	N
17	14	F	2	48	54	-	L5S1	N	0	L3	L1	L2	T2-L2	1	3	6	N
18	16	F	1	-	62	-	L5S1	N	0	L3	L1	L2	T4-L2	1	3	8	N
19	15	F	2	48	55	-	L5S1	N	0	L3	L1	L2	T2-L2	1	3	14	N
20	17	M	1	-	50	-	L5S1	N	0	L2	L1	L2	T5-L1	1	4	6	N
21	17	F	1	-	57	-	L5S1	N	0	L2	L1	L2	T5-L1	1	4	6	N
22	16	F	5	-	-	86	L5S1	Y	1	L3	L1	L2	T5-L3	1	2	6	N
23	18	F	1	-	74	-	L5S1	N	0^b	L2	L1	L1	T4-L1	1	4	12	N
24	15	F	1	-	88	-	L5S1	Y	1	L2	L1	L2	T4-L2	1	3	4	N
25	14	M	6	-	54	76	L5S1	N	0	L3	L2	L3	T3-L4	1	1	6	N
26	16	F	3	-	80	56	L5S1	N	0^b	L3	L1	L3	T3-L3	1	2	6	N
27	17	F	1	-	92	-	L5S1	N	0	L2	L1	L1	T4-T12	2^a	5	8	N
28	15	M	1	-	68	-	L5S1	N	0	L2	T12	L1	T4-L1	1	4	8	N
29	16	F	3	-	70	62	L6S1	Y	1	L4	L2	L3	T3-L4	1	2	6	N

^aPosterior release + Pegs, HGT, followed by PSF; PT proximal thoracic, MT main thoracic, TL/L thoracolumbar/lumbar, SV stable vertebra, LTV last touched vertebra, LSTV last substantially touched vertebra, LIV Lowest instrumented vertebra, Y yes, N no.

^bProgressed from Spondylolysis to Grade 1 Spondylolisthesis at follow-up; †Halo-gravity traction (HGT) followed by Posterior Spinal Fusion (PSF).

Table 2.

Summarized Demographic and Radiographic Characteristics of Included Patients With AIS and Spondylolysis

Age in years	15.5 ± 1.5
Mean ± SD (range)	(13-18)
Sex (M/F)	6/23
Body mass index	20.8 ± 1.7
Mean ± SD (range)	(18.4-24.3)
Lenke types, n (%)
Type 1	15 (52)
Type 2	3 (10)
Type 3	4 (14)
Type 4	1 (3)
Type 5	5 (17)
Type 6	1 (3)
Preoperative cobb angle	65.3 ± 14.5
mean ± SD (range)	(36-99)
Level of pars lesion, n (%)
L4-L5	1 (3)
L5-S1	26 (90)
L6-S1	2 (7)
Spondylolisthesis, n (%)	7 (24)
Progression of slip^a, n (%)	2 (7)
LIV selection methodology^b, n (%)
SV	13 (45)
LTV	5 (17)
LSTV	18 (62)
LSTV = SV	13 (45)
LIV location, n (%)
At or above L3	22 (76)
L4	7 (24)
Post-operative subjacent curve	11.2 ± 6.6
mean ± SD degrees (range)	(4-32)
Revision (received or indicated), n (%)	3 (10)

^aProgressed from Spondylolysis to Grade 1 Spondylolisthesis at follow-up.

^bSV stable vertebra, LTV last touched vertebra, LSTV last substantially touched vertebra.

LSTV = SV: the selected LSTV corresponds with the selected SV.

Pre-operatively, 76% of patients had spondylolysis and 24% had low-grade spondylolisthesis. Across the cohort, there were 39 curves with a mean pre-operative Cobb angle of 65.3 ± 14.5° (Figure 1). Lenke type 1 main thoracic curves were most common (52%). Twenty-three patients had Lenke types 1-4 curves, while isolated thoracolumbar/lumbar curves occurred in 6 patients.

Figure 1.

Distribution of curve magnitudes

Lowest Instrumented Vertebra Selection (Table 1 and Table 2)

The last substantially touched vertebra (LSTV) was selected as the LIV in 18 patients, the last touched Vertebra (LTV) in 5, and the stable vertebra (SV) in 13. The LSTV corresponded to the SV in 13 patients. In six patients, the LIV was one level above the pars defect. Sixteen patients had fixations ending proximal to L3, six had L3 as the LIV, and seven had L4. Four patients underwent a staged correction with posterior releases and/or halo traction prior to definitive fusion.

Postoperative Outcomes and Complications (Table 2 and Table 3)

Overall, 76% (22/29) of patients had fusion ending at or above L3, and 24% (7/29) extended below. Follow-up low back pain was significantly higher in patients with <3 mobile segments between the LIV and the lytic level (VAS: 4.5 ± 1.4 vs 2.8 ± 1.5; P = .003), and in those with fusion extending below L3, compared to fusions ending at or above this level (5.0 ± 1.3 vs 3.0 ± 1.4; P = .004).

Progression of lysis to Meyerding grade 1 slip occurred in two patients (Table 3). The average postoperative subjacent lumbar curve measured 11.2 ± 6.6°. On univariable linear regression, each additional mobile segment was associated with a 0.77-point decrease in follow-up VAS pain (β = −0.77, 95% CI −1.18 to −0.36, P = .001), while greater subjacent lumbar curvature was associated with higher follow-up pain (per 10° increase; β = 0.92, 95% CI 0.07-1.77, P = .043). On multivariable regression, including both number of mobile segments and subjacent curvature, each remained a significant predictor of follow-up VAS pain (per segment added: β = −0.81, 95% CI −1.18 to −0.44, P = .0002; per 10° increase: β = 1.02, 95% CI 0.37-1.67, P = .006).

Table 3.

Average Pain Level Compared by Number of Segments Between LIV and Pars Lesion

No. of mobile segments	Patients (N)	VAS pain level,mean (SD)
1	6	5.2 (1.3)
2	5	3.6 (0.9)
3	8	3.1 (1.7)
4	9	2.7 (1.3)
5	1	2

At the final follow-up, two patients experienced distal junctional failure that would require revision. One patient with persistent severe low back pain underwent subsequent isolated fusion of the spondylolisthesis. Notably, two of the patients with significant post-operative complications carried a mental health diagnosis.

Discussion

Patient Demographics and Clinical Characteristics

This study examined the clinical and radiographic outcomes of PSF in AIS patients with coexisting spondylolysis or low-grade spondylolisthesis. Our findings contribute to an evolving understanding of how fusion level selection and other surgical considerations influence postoperative outcomes in this distinct population. Although prior studies report a prevalence of approximately 7% among AIS patients, unpublished data from our center showed a higher concurrence rate of 11.5%.^11,15

Demographic data revealed a male-to-female ratio of 1:4, mirroring the well-documented higher prevalence of AIS among adolescent females.^1,2,31 Approximately 30% of this cohort carried a mental health diagnosis, a rate lower than in other reports but still representing a significant psychosocial burden.^31-33 Notably, two patients with chronic opioid use and one with thalassemia further highlight the complex medical and psychosocial factors that may complicate postoperative pain and recovery. While these three patients may represent isolated cases, their presence emphasizes the need for thorough preoperative evaluations, such that a tailored perioperative management strategy might optimize outcomes.³⁴

Radiographic Characteristics and Curve Patterns

Spondylolysis was located at L5-S1 in 90% of patients, consistent with the established anatomical predilection for this region.^35-37 The predominance of Lenke type 1 curves in our cohort reflects the general AIS population but also may suggest that thoracic-dominant curves lead to specific loading patterns in the lower lumbar spine that unmask or exacerbate latent spondylolysis.^1,2 These biomechanic relationships warrant further exploration.

Fusion Level Selection and Postoperative Outcomes

For our cohort, touched vertebrae—whether LSTV or LTV—were chosen in about 70% of cases while the LSTV corresponded to the SV in nearly half. Regardless, LIV selection followed standard radiographic principles for AIS, as strategically chosen vertebrae have been shown to significantly correlate with favorable postoperative outcomes.^8,9,18

Interestingly, we found that patients had significantly higher follow-up low back pain when fewer than three mobile segments separated the LIV from the spondylolytic level. On both univariable and multivariable regression, each additional preserved segment was associated with about a 0.8-point reduction in follow-up VAS pain. This suggests that proximity of the fusion construct to a pathological vertebra may increase stress concentration, predisposing to symptomatic degeneration or progression at adjacent segments. These findings align with prior concerns about accelerated adjacent segment degeneration distal to the LIV in long fusions.^38-40 Although some reports found no difference in outcomes regardless of the number of unfused segments between the LIV and the spondylolytic level,⁴ our data indicate that maintaining adequate mobile segments below the fusion is clinically relevant in this population.

In this cohort, patients whose fusion extended below L3 had significantly higher follow-up low back pain compared with those whose constructs ended at or above this level. Although an LIV at or proximal to L3 preserves at least two mobile segments, our earlier finding indicated that having fewer than three mobile segments between the LIV and the lytic level was associated with comparatively greater postoperative pain. These observations are not contradictory; rather, they reflect a graded relationship in which each additional preserved segment confers incremental symptomatic benefit. Consequently, selection of L2 vs L3 involves considerations beyond pain mitigation alone, including curve behavior, alignment goals, and the capacity to achieve durable coronal and sagittal balance. While L3 may remain appropriate in selected patients (particularly when neutral alignment, coronal balance, and sufficient tilt correction are achieved), our findings indicate that, when feasible, stopping at L2 offers a more favorable long-term symptom profile by maximizing the buffer of distal mobile segments. Accordingly, for AIS patients with concomitant spondylolysis, L2 may represent the more optimal distal fusion level, provided that global alignment objectives can be reliably met.

Similarly, on both univariable and multivariable regression, each 10° increase in subjacent lumbar curve postoperatively was associated with nearly a 1-point increase in follow-up VAS pain. For patients in this study with reported complications, there was rapid progression of the lumbar curve below the LIV over the follow-up period (≥24 months). In principle, residual deformity may alter biomechanics and increase paraspinal fatigue, effects compounded by compromised posterior elements at the lumbosacral junction in the setting of spondylolysis.^41,42 This reiterates the importance of curve correction, alignment below the fusion level, and overall global balance on clinical outcomes.^10,43

In our cohort, two patients developed persistent pain and worsening coronal deformity following distal anchor failure (unilateral pedicle screw fracture) (Figures 2 and 3). This typically results from fatigue failure secondary to persistent motion across an unfused segment (pseudoarthrosis), a high strain environment (spondylolysis) or increased mechanical demands on the implants (repetitive micromotion at the screw-rod junction leading to loosening and eventual fatigue fracture). This underscores the significance of robust distal fixation in patients with underlying lumbosacral instability. Surgeons should exercise caution when relying on distal anchors at or adjacent to the lumbosacral junction in the presence of spondylolisthesis. Observation with regular follow-up visits, or a revision of the distal anchors and bone grafting to achieve a solid arthrodesis may suffice without attempt at fusion of the spondylolisthesis.

Figure 2.

16-year-old female; (A/B) Pre-op AP and lateral, (C) In-traction AP, (D/E) immediate post-op AP and lateral (T2 – L1 PSF), (F/G) 3 years post-op AP and lateral, and (H/I) 4 weeks post-op fusion of L5S1. Note the anchor failure at right L1 with pedicle screw fracture and worsening subjacent deformity

Figure 3.

16-year-old male; (A) Pre-op lateral view showing pars fracture and L5S1 grade 1 spondylolisthesis, (B/C) pre-op AP and lateral views, (D) post Halo, (E/F) immediate post-op views (T2 – L2 PSF) and (G/H) 5 years post-op views. Note the increasing deformity below the LIV as well as right LIV anchor failure at L2

Another patient with fixation extending to L4, who had persistent pain, maintained stability without subsequent anchor failure (Figure 4). While the trade-off is loss of distal mobility, consideration of extending fixation to L4 (or lower) may be warranted when concomitant spondylolisthesis threatens distal anchor integrity. This case was a 1AL type deformity with minimal L4 tilt, and stopping fixation at L3 may have provided adequate correction of the curve, including the subjacent lumbar deformity.

Figure 4.

13-year-old female; (A/B) Pre-op lateral view showing pars fracture and L5S1 grade 2 spondylolisthesis, (C/D) Pre-op AP and Lateral views, (E) post halo-pegs and ponte osteotomy, (F/G) immediate post-op views (T2 – L4 PSF) and (H/I) 3 years post-op views. Note the deformity below L4 remains the same and the slip is stable

Long-Term Considerations

Although spinal fusion remains the gold standard for the treatment of AIS, there are reports and concerns about the long-term effect on the lower non-fused segments, particularly regarding degeneration and consequent back pain.⁴⁴ AIS patients who have undergone fusion may experience earlier onset low back pain compared to the general population.⁴⁵ This risk is further elevated when the fusion extends below L3, especially if horizontalization of L3 or L4 is not achieved.^38,40,43 These observations contextualize our findings, highlighting the importance of strategic LIV selection to minimize postoperative pain and long-term degeneration. Given the elevated risk of anchor-related complications in this subset, patients and families should be counseled regarding the potential need for revision, and the implications for lumbar mobility and overall spine health.

Comparison With Prior Literature

The broader literature on LIV selection for AIS reflects ongoing debate. Some studies suggest radiographic and clinical outcomes are unaffected by LIV choice, while others report superior long-term functional outcomes when the distal fusion stops at or above the L3 vertebra. Li et al found no difference between stopping at L3 vs L4 in Lenke type 5C patients, yet supported L3 as the ideal choice, particularly for younger individuals, to favor preservation of motion. Toyone et al proposed that horizontalization of L3 could limit distal degeneration and prevent long term subjacent segment failure.^39,43,46 These studies reinforce the principles that, even in lumbar curves (Lenke 5 and 6, including type C modifiers), fusion should stop as far as feasible from the lytic segment to maximize motion and that overall spine health after a fusion depends on achieving global balance.⁴⁷

Consistent with these observations and as previously discussed, our cohort demonstrated a statistically significant increase in follow-up low back pain among patients whose fusion extended below L3. Although this association reached significance, paired with our results showing statistically greater pain when maintaining less than three mobile segments, the generalizability of these findings should be interpreted cautiously given the small sample size and single-center nature of this cohort. Patients with spondylolysis are also reported to have lower SRS-22 scores compared to controls and AIS cohorts.²⁶ Biomechanical studies suggest that fusions extending into the lower lumbar spine increase stress and motion at unfused segments, particularly in the presence of pre-existing structural abnormalities such as spondylolysis.^27-30 While fusions below L3 may offer mechanical stability, our findings reinforce the concern that longer constructs increase load transfer to lytic or unstable segments, contributing to postoperative pain and degeneration.^40,44,45

Limitations

This study is limited by its retrospective design, single-center cohort, relatively small sample size and lack of long-term follow-up. The minimum follow-up of 24 months, while sufficient for short-term outcomes, does not capture the full trajectory of adjacent segment degeneration or the durability of fusion constructs. Advanced imaging such as CT or MRI was not universally obtained preoperatively and may have underestimated the prevalence of asymptomatic spondylolysis. Additionally, pain outcomes were based on relatively subjective patient-reported measures, which lack multidimensional assessment and are susceptible to variability in individual pain perception.

Future work should further refine the relationship between distal alignment and postoperative symptoms by specifically analyzing preoperative, immediate postoperative, and follow-up angulation of L3 and L4 in patients whose LIV was selected at either of these levels. Such an analysis may clarify how distal segment orientation and horizontalization influence postoperative mechanics and distal junctional loading. In addition, evaluating whether preoperative curve magnitude independently predicts long-term postoperative health-related quality of life would enhance the clinical applicability of these findings by helping to identify patients at higher risk for persistent symptoms despite structurally successful fusion.

Conclusion

This study offers valuable insights into the relationship between fusion levels and postoperative outcomes in AIS patients with concurrent spondylolysis. The LIV can be safely selected above the pars defect, where choosing to stop proximal to L3 appears to minimize pain at follow-up. In addition, the LSTV or SV (particularly with Lenke 3, 4, 5 and 6 curves) may serve as safe LIV choices. Surgical planning should prioritize correction of a distal compensatory curve via horizontalization or reduced angulation of L3/L4 when selected as LIV, and should favor a safe biomechanical buffer between the fusion construct and the lytic segment.

These findings emphasize three key considerations for clinical practice: (1) thorough preoperative assessment, including psychosocial and medical comorbidities; (2) recognition of curve type and lumbar loading patterns that may influence the manifestation or progression of pars defects; and (3) judicious LIV selection with preservation of mobile segments, balancing stability with mobility, and restoration of global alignment. Prospective studies with larger cohorts and longer follow-up are needed to refine fusion strategies and optimize outcomes in this complex patient population.

Footnotes

ORCID iDs

Mutaleeb A. Shobode

Anirejuoritse Bafor

Kirsten Tulchin-Francis

Allen Kadado

Ethical Considerations

The study was conducted in accordance with the Declaration of Helsinki and was approved by the IRB of Nationwide Children’s Hospital (no. 2280) on April 11, 2022, with the need for written informed consent waived.

Author Contributions

Mutaleeb Shobode, MBBS: Conceptualization, Data Acquisition, Interpretation, Writing–Original Draft, Review & Editing. Josiah Wolf, MD: Data Acquisition, Curation, Analysis, Interpretation, Writing–Review & Editing. Asahi Murata, MPH: Data Analysis, Interpretation, Writing–Review & Editing. Anirejuoritse Bafor, MBBS: Writing–Review & Editing. Kirsten Tulchin-Francis, PhD: Conceptualization, Data Analysis. Walter P. Samora, MD: Conceptualization, Resources. Reid C. Chambers, DO: Conceptualization, Resources, Writing–Review & Editing. Allen Kadado, MD: Conceptualization, Data Interpretation, Review & Editing, Supervision.

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 datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.*

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