Is it Necessary to Fuse? A Propensity Score-Matched Analysis of One- Versus Two-Level Fusions With Multilevel Decompression

Abstract

Study Design

Retrospective cohort study.

Objective

In patients with multilevel degenerative lumbar pathology, the decision to extend fusion across all decompressed levels remains a subject of debate. While fusion provides stability in cases of instability or deformity, its necessity for adjacent levels without specific fusion indications is unclear. This study evaluates whether decompression alone at levels without clear fusion indications can achieve similar outcomes compared to spanning the entire decompression with fusion.

Methods

The present study is a retrospective cohort study. Patients who underwent one-level decompression and fusion with 2 level decompression (SLF) were propensity score matched with patients who underwent two-level decompression and fusion (DLF) for degenerative conditions of the lumbar spine. Patient-reported outcome measures (PROMs), complication rates, revision surgeries, and recovery kinetics were compared between the cohorts.

Results

After propensity score matching a total of 43 SLF patients were compared with 43 DLF patients. Early follow-up (<6 months) showed significantly higher SF-12 PCS scores in the SLF group (P = .042) and greater achievement of VAS-leg MCID (88.9% vs 59.4%, P = .012). Long-term outcomes (≥6 months) demonstrated no significant differences in ODI, VAS-back, VAS-leg, or SF-12 PCS scores between groups. There were no differences in intraoperative or perioperative complications. The postoperative complication rate was significantly higher in the DLF group (25.6% vs 7%, P = .019) including 4 DLF patients that underwent revision surgery while no SLF patients required revision during their follow up time.

Conclusion

SLF resulted in similar long-term outcomes compared to DLF with fewer revisions and adjacent segment symptoms. These findings suggest that “saving” a fusion level in cases without a specific fusion indication at the adjacent level may be warranted to optimize longevity of the construct. Further research is necessary to refine patient selection for fusion levels in degenerative lumbar disease.

Keywords

fusion decompression multi level PROMs outcomes

Introduction

Degenerative lumbar pathology is a leading cause of disability, often requiring surgical intervention when conservative management fails. Lumbar fusion is commonly performed to provide stability, alleviate pain, and improve function in patients with conditions such as lumbar stenosis, spondylolisthesis, and degenerative disc disease.¹ While single-level fusion with decompression is a well-established treatment, the decision to extend the fusion to a second level remains controversial.² The balance between achieving adequate decompression and maintaining spinal mobility is a critical consideration for both surgeons and patients.

One previous study examined the clinical outcomes of single- vs multi-level fusion utilizing a large national database finding multi-level fusion was associated with increased 90-day complications.² However, the literature still lacks robust and granular comparisons of outcomes between one-level and two-level fusion in patients with comparable surgical indications. Given the potential for increased surgical morbidity with additional levels of fusion, it becomes important to understand the impact of two-level fusion on perioperative outcomes, complication rates, and long-term recovery compared to one-level fusion. As such, the purpose of the present study is to compare clinical outcomes in patients with multilevel degenerative lumbar pathology who underwent one-level lumbar decompression and fusion with decompression alone at the adjacent level vs patients who underwent two-level lumbar fusion and two-level decompression.

Methods

Study Design and Patient Selection

This is a retrospective cohort study conducted after approval by the Institutional Review Board (IRB number 2018-1599) with informed consent obtained from all included patients. Patients who underwent primary one-level decompression and fusion with second-level laminectomy for adjacent level pathology (SLF) or two-level decompression and fusion (DLF) for surgical management of degenerative lumbar pathology between 2017 and 2024 with at least 1-year follow-up were identified from a prospectively maintained institutional surgical registry. Exclusion criteria included surgical indications of trauma, infection, or malignancy, as well as revision surgeries, skip-level fusions, non-instrumented fusions, and decompression-only procedures. Additionally, patients with “absolute” indications for two-level fusion such as 2 levels of instability were excluded from the DLF fusion group. The “first level” was defined as the fused level in SLF patients and the level with the primary fusion indication in DLF patients. The “second level” was defined as the adjacent level decompression in SLF patients or the level without instability or other specific fusion indication in DLF patients.

Surgical Indications

The decision to fuse one vs both levels was made at the discretion of the attending surgeon based on radiographic and clinical findings. All patients included in the study had multilevel degenerative lumbar pathology, with the primary surgical indication defined at the first level. Fusion at the first level was indicated in the presence of instability (as defined by dynamic flexion-extension radiographs), degenerative spondylolisthesis with significant translation, angulation, or deformity, and cases where decompression alone would cause iatrogenic instability. The second (adjacent) level was decompressed in all patients due to the presence of significant central, foraminal, or subarticular stenosis causing radicular symptoms or neurogenic claudication. However, in patients in the SLF cohort, this level did not meet criteria for fusion due to the absence of overt instability or deformity. In contrast, patients in the DLF cohort underwent fusion at both levels despite the absence of classic fusion criteria at the second level. These cases were typically based on the surgeon’s clinical judgment, considerations of construct stability, or concern for disease progression at the adjacent level. Patients with “absolute” indications for two-level fusion were excluded from the analysis to ensure that comparisons were made between groups with similar clinical and radiographic profiles at the second level.

Data Collection

Data were collected and managed using REDCap (Research Electronic Data Capture)^3,4 hosted at Weill Cornell Medicine Clinical and Translational Science Center supported by the National Center For Advancing Translational Science of the National Institute of Health under award number: UL1 TR002384. The following data was collected from patients’ electronic medical records:

1. Patient Demographics: age, gender, race, body mass index (BMI), insurance type, age-adjusted Charlson Comorbidity Index (CCI), and American Society of Anesthesiologists (ASA) Classification, and surgical indications (central stenosis, subarticular stenosis, foraminal stenosis, unstable/stable spondylolisthesis) at each level.

2. Preoperative X-ray Measurements: Spinopelvic parameters including total lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS) were all measured. Additionally, on the AP view, the patients’ maximum coronal lumbar Cobb angle was measured.

3. Surgical and perioperative details: Surgical approach (minimally invasive [MIS], open), interbody usage (yes/no), operative time, estimated blood loss (EBL), and intraoperative/perioperative complications.

4. PROMs: Oswestry Disability Index (ODI) Visual Analog Scale, (VAS) back and leg, and 12-Item Short Form Survey Physical Component Score (SF-12 PCS) were collected at 2 weeks, 6 weeks, 12 weeks, 6 months, 1 year, and 2 years after the surgery. Two postoperative timepoints - early (<6 months) and late (≥6 months) - were defined for analyses.^5-7 Minimal clinically important difference (MCID) achievement was defined as a decrease in ODI by 12.8, VAS-back by 1.2, VAS-leg by 1.6, and SF-12 PCS by 4.1 at any postoperative time point compared with the preoperative baseline as previously defined by Copay et al.⁸ Patient acceptable symptom state achievement (PASS) was defined as an absolute postoperative ODI less than 25.2 as defined by Shahi et al.^9,10

5. Return to activities/Recovery kinetics: Patients who were driving and working preoperatively were asked if they had begun driving and working again at every follow-up until they returned to each activity. Patients who took opioids postoperatively were asked the date of cessation, if applicable.

6. Postoperative complications: Symptoms and treatment of postoperative surgical complications and adjacent level pathology. Instances of revision surgery and reason for revision were recorded.

Patient Matching and Statistical Methods

To minimize selection bias and ensure comparability between SLF and DLF patients, we performed both nearest-neighbor matching (NNM) and propensity score matching (PSM) using key demographic and clinical variables. Matching variables included age, CCI age-adjusted score, BMI, sex, ASA classification, race, insurance type, surgical approach (MIS vs open), and interbody usage. First, NNM was conducted based on Euclidean distance, pairing SLF and DLF patients in a 1:1 ratio. The assessment of standardized mean differences (SMDs) demonstrated a suboptimal balance between cohorts. To improve matching quality, PSM was implemented using a logistic regression model to estimate propensity scores, predicting the probability of undergoing a SLF based on the same matching covariates. DLF patients were then matched 1:1 and 1:2 to SLF patients using a caliper width of 0.2 standard deviations of the logit-transformed propensity score without replacement. Post-matching SMD analysis confirmed a superior balance with 1:1 PSM compared to 1:1 NNM or 1:2 PSM, supporting its selection as the preferred method (Figure 1).

Figure 1.

Standardized Mean Difference (SMD) Plot Before and After Matching

Statistical analyses were conducted to compare differences between the 2 matched groups. Normally distributed continuous variables between groups were compared with a paired t-test or a 2-tailed independent sample t-test when appropriate. Non-normally distributed variables were compared with a Mann-Whitney U test rather than an independent sample t-test. Continuous variables were reported as mean ± standard deviation (SD) if normally distributed or median [IQR] when non-normally distributed. Categorical variables were compared between groups with a χ2 test or a Fisher exact test when the number of subjects was less than 10. All continuous and categorical variables were noted as mean (SD) and n (%), respectively. Statistical analyses were performed using Python (version 3.11.8, Python Software Foundation with a Jupyter environment). Statistical significance was set at P < .05.

Results

After applying exclusion criteria, a total of 136 patients were included, of which 43 underwent one-level fusion with decompression and 93 underwent two-level fusion (Figures 1 and 2). Following propensity score matching (1:1), the final cohort of 43 SLF patients was compared with 43 DLF patients. Baseline demographics and radiographic characteristics were similar between the groups (P > .05 for all, Table 1). There were no significant differences in surgical approach - 51.2% of SLF cases and 55.8% of DLF cases were performed using an open approach (P = .665). Interbody devices were utilized at similar rates in both cohorts (81.4% vs 83.7%; P = .776).

Figure 2.

Patient Selection Flowchart

Table 1.

Baseline Demographics, Radiographic, and Surgical Comparison of the Groups

Variable	1-Level fusion	2-Level fusion	P-value
N	43	43
Age	66.81 (8.89)	67.37 (10.34)	.789
Gender
Male	51.2%	55.8%	.829
Female	48.8%	44.2%	.829
BMI	28.97 (4.28)	29.11 (4.74)	.884
ASA
I	4.7%	4.7%	.883
II	67.4%	72.1%
III	27.9%	23.3%
CCI	3.16 (1.66)	3.33 (1.70)	.655
Race
White	76.7%	74.4%	.798
Asian	4.7%	0.0%
Black	14.0%	14.0%
Other/Unknown	4.6%	11.6%
Insurance
Private	53.5%	51.2%	.317
Medicare/Medicaid	41.8%	34.9%
Other	4.7%	13.9%
Baseline radiographs
PT	23.71 (7.52)	23.10 (10.43)	.756
PI	57.29 (11.70)	55.05 (12.80)	.405
SS	33.55 (8.13)	33.90 (8.46)	.844
LL	−45.94 (12.19)	−38.86 (28.55)	.145
Coronal cobb	6.55 (7.69)	7.31 (7.67)	.650
Open vs MIS surgery
Open	51.2%	55.8%	.665
MIS	48.8%	44.2%	.665
Interbody usage	81.4%	83.7%	.776

The most common indications for surgery were foraminal stenosis (overall: 61.6%, SLF: 58.1%, DLF: 65.1%) and central stenosis (overall: 58.1%, SLF: 65.1%, DLF: 51.2%) at the first level. The presence of spondylolisthesis was common at the first level, with 79.1% of the overall cohort presenting with this pathology, of which 45.3% (SLF: 41.9%, DLF: 48.8%) were deemed unstable on upright, flexion-extension radiographs. At the second level, foraminal stenosis was less common (37.2% in both groups), and spondylolisthesis was infrequent (overall: 11.6%, SLF: 7%, DLF: 16.3%) with no cases deemed unstable. Details of surgical indications can be found in Figure 3.

Figure 3.

Indications for Surgery at Both Levels

At early follow-up (<6 months), both groups demonstrated significant improvement in ODI, and VAS-back and leg were comparable to baseline values (Tables 2 and 3). However, only SLF patients saw a significant improvement compared to their baseline for SF-12 PCS (SLF: P = .004, DLF: P = .069). The SLF fusion group demonstrated significantly higher SF-12 PCS scores at early follow-up (37.35 vs 33.08, P = .042) (Tables 2 and 3, and Figure 4). Furthermore, a significantly higher proportion of patients in the SLF group achieved MCID for VAS-leg at early follow-up (88.9% vs 59.4%, P = .012) (Figure 5). By late follow-up (≥6 months), there were no significant differences between groups in ODI, VAS-back, VAS-leg, SF-12 PCS, or MCID/PASS achievement (Tables 2 and 3, and Figures 4 and 5).

Table 2.

Comparison of PROMs at Early and Late Follow-Up.

PROM	Time point	1-Level fusion	2-Level fusion	P-value
ODI	Preop	39.62 (16.59)	40.71 (15.55)	.770
	<6m	24.44 (15.5)	30.16 (17.68)	.147
	<6m	<0.001	<0.001	.147
	≥6m	19.51 (17.18)	21.8 (18.28)	.605
	≥6m	<0.001	<0.001	.605
VAS-back	Preop	6.09 (2.41)	6.5 (2.4)	.462
	<6m	2.18 (2.15)	2.71 (2.56)	.339
	<6m	<0.001	<0.001	.339
	≥6m	2.03 (2.31)	2.1 (2.09)	.906
	≥6m	<0.001	<0.001	.906
VAS-leg	Preop	6.22 (2.54)	6.03 (3.22)	.781
	<6m	1.77 (2.32)	2.71 (2.6)	.109
	<6m	<0.001	<0.001	.109
	≥6m	2.94 (2.99)	1.97 (2.51)	.163
	≥6m	<0.001	<0.001	.163
SF12-PCS	Preop	30.34 (8.87)	29.88 (7.02)	.822
	<6m	37.35 (8.74)	33.08 (7.17)	.042
	<6m	0.004	0.069	.042
	≥6m	41.19 (9.84)	39.43 (8.68)	.496
	≥6m	<0.001	<0.001	.496

Bold denotes statistical significance.

Table 3.

Change in PROMs at Early and Late Follow-Up

PROM	1-Level fusion <6m	2-Level fusion <6m	P-value	1-Level fusion ≥6m	2-Level fusion ≥6m	P-value
ODI	−16.02 (16.58)	−11.42 (15.54)	.229	−21.00 (16.82)	−19.09 (16.55)	.652
VAS-back	−4.33 (2.79)	−3.72 (2.96)	.384	−4.08 (2.46)	−4.32 (2.70)	.718
VAS-leg	−4.75 (2.95)	−3.09 (3.81)	.052	−3.05 (3.38)	−4.33 (3.43)	.151
SF12PCS	7.11 (11.95)	3.43 (9.97)	.210	11.17 (11.73)	10.56 (10.95)	.852

Figure 4.

(A-D) Change in PROMs at Various Follow-Up Time Points. Bold denotes statistical significance.

Figure 5.

(A-E) MCID and PASS Achievement at Early and Late Follow-Up

Both SLF and DLF patients returned to driving and working at comparably high rates. Patients in both cohorts similarly discontinued narcotics within a few weeks after surgery (Table 4).

Table 4.

Recovery Kinetics Comparing Patients in SLF and DLF Groups

	1-Level fusion	2-Level fusion	P-value
Return to driving (1 level - 15, 2 level - 28)
Percentage	86.7%	89.3%	.798
Days	25 [15-44]	29 [19-54]	.631
Return to working (1 level - 10, 2 level - 16)
Percentage	80%	81.3%	.937
Days	19.5 [12.5-41.5]	30 [18-62]	.424
Discontinue narcotics (1 level - 22, 2 level - 27)
Percentage	86.4%	81.5%	.646
Days	18.5 [8-51.5]	13 [5-19]	.234

Surgical details were not significantly different between the groups, in terms of operative time and EBL (P > .05 for both) (Table 5). All intraoperative complications noted in both groups were durotomies, 6 in the SLF and 1 in the DLF group, although this difference did not achieve statistical significance (P = .307). Patients experienced similar lengths of stay and rates of perioperative medical complications (P > .05 for both). Postoperatively, the complication rate was higher in the DLF cohort compared to the SLF cohort (25.6% vs 7%, P = .019). 4 patients in the DLF group were revised for pseudarthrosis (n = 2) or cage subsidence (n = 2), while there were no revisions in the SLF cohort at follow-up. For adjacent segment disease (ASD), 3 SLF patients developed symptoms and radiographic signs of ASD compared to 7 patients in the DLF group.

Table 5.

Operative and Postoperative Complications in SLF and DLF Fusion Cohorts.

Variable	1-Level fusion	2-Level fusion	P-value
Operative time (minutes)	214.33 (68.12)	238.05 (84.88)	.157
EBL	236.86 (212.96)	216.51 (195.03)	.645
Length of stay (hours)	67.27 (46.07)	67.58 (52.08)	.977
Intraoperative complications	6 (14%) - durotomy	1 (2.3%) - durotomy	.307
Perioperative complications	12 (27.9%) - PONV x4, foot drop x1, small bowel obstruction x1, anemia requiring transfusion x2, POUR x3, respiratory distress x1	8 (18.6%) - cardiac event x1, anemia requiring transfusion x2, delirium x1, POUR x2, PONV x1, ileus x1	.209
Postoperative complications/Revisions	3 (7%)	11 (25.6%)	.019
Complications requiring revision surgery	0 (0%)	4 (9.3%) - pseudarthrosis x2, cage subsidence x2
Complications not requiring revision surgery	3 (7%) - ASD symptoms x3	7 (16.3%) - ASD symptoms x6, proximal junctional kyphosis x1

Bold denotes statistical significance.

Discussion

Patients with multilevel degenerative disease of the lumbar spine often have several points of pathologic compression contributing to pain and disability. In these patients, decompression with or without fusion is often considered. In the present analysis, we included patients who underwent surgery for 2 levels of degenerative disease treated with two-level decompression with concomitant two-level fusion vs two-level decompression with only single-level fusion. Using propensity score matching, our findings support the notion that sparing patients that additional fusion level may provide similar or superior clinical outcomes and may mitigate the long-term risk of future surgeries associated with longer fusion constructs.

SLF patients demonstrated similar PROMs at the early time point for ODI, VAS-back, and VAS-leg. However, SLF patients had significantly higher SF12-PCS at this early time point (specifically at 12 weeks and 6 months) compared to DLF patients. Rates of VAS-leg MCID achievement were also higher among the SLF cohort. Importantly, however, the recovery kinetics and long-term PROMs were not different between the 2 groups. Taken together, SLF patients likely experience a faster improvement in disability compared to DLF patients but ultimately achieve similar long-term outcomes. While both decompression and fusion are generally thought to improve patient symptoms, specific indications for various degenerative pathologies of the lumbar spine have been the subject of much of the recent literature.¹¹ The present study adds to the existing body of literature by demonstrating that in patients indicated for single-level fusion with multilevel pathology, spanning the fusion across all decompressed levels results in similar clinical outcomes as decompression alone at the adjacent level. Given the overall similarity in long-term results, future research should focus on identifying patient-specific characteristics that may influence early recovery trajectories and optimizing perioperative management strategies to enhance functional outcomes for both SLF and DLF patients.

Our study found no significant differences in operative time, blood loss, or perioperative complications between the cohorts, noting the likely similar “invasiveness” of the surgical procedures themselves. Many studies comparing the “cost,” in terms of added surgical risk of fusion vs decompression alone, have demonstrated a marginally increased complication profile among fusions.^11,12 In patients already undergoing one-level fusion and already having the “hit” associated with that particular surgical intervention, it is possible that the second level, whether decompression alone vs decompression and fusion, does not make much of a difference regarding complications in the perioperative period. Interestingly, Ratnasamy et al in a PearlDiver database study comparing three-level decompression plus fusion with three-level decompression and one-level fusion found significantly elevated rates of postoperative medical and surgical adverse events in the three-level decompression plus fusion cohort.² Each additional level of fusion may add some inherent intra- and perioperative risk, and this is something that should be considered when formulating and executing a surgical plan.

Postoperatively, we found significantly elevated rates of complications in the DLF cohort, with an overall complication rate of 25.6% compared to 7%. Specifically, 4 patients in the DLF group required revision (2 for pseudarthrosis and 2 for cage subsidence) while none of the patients in the SLF group required revision during their follow-up time. Furthermore, 7 DLF patients developed radiographic ASD compared to 3 in the SLF group, although neither of these cohorts have undergone revision surgery to date. Several previous studies have demonstrated the correlation between ASD and length of fusion constructs.^13-17 In a recent meta-analysis by Burch et al, 55 studies were analyzed to determine risk factors for reoperation due to ASD. One of the findings in this study was a significantly higher rate of ASD in patients with longer fusion constructs.¹⁸ These findings are also supported by Ratnasamy et al’s analysis.² While the PearlDiver database studies are generally limited by a lack of granularity, they similarly found that 5-year revision-free survival was significantly lower for those undergoing three-level decompression with concomitant three-level fusion. Considering all of this, we can acknowledge the risks associated with longer fusions, which may in turn make “sparing” a fusion level a reasonable surgical consideration in treating these patients.

This study has several limitations. Firstly, this is a retrospective study, and understanding each patient’s disease history depended on each surgeon’s documentation practices. To that end, the selection of single vs two-level fusion depended on surgeon preference and individual practices. By extension, each surgeon had their own surgical decision-making algorithm leading to a final operative plan for each patient, which may introduce bias unaccounted for in the analysis.¹⁹ This study was also limited by a relatively low number of patients after propensity score matching and the single-institution nature of the study also serves to limit the external validity of the results. Finally, the study may have been limited by follow-up time, given complications such as adjacent segment disease can develop more than many years after the index surgery.²⁰ Future studies with longer-term follow-up may provide more insight to appreciate the long-term sequelae of the early postoperative trends that were observed in the present study. These factors should certainly be considered when interpreting our findings, however, the findings in this study remain novel and provide insight into how we may be able to “do less” and achieve similar outcomes in our lumbar degenerative patient cohort.

Conclusion

To our knowledge, this is the first analysis to compare outcomes of one- and two-level fusions in patients with multiple levels of degenerative lumbar pathology. We found both surgical approaches had largely similar long-term clinical outcomes with single-level fusion patients achieving better early functional scores. In the long term, we found an elevated risk of revision surgery and radiographic adjacent segment disease among two-level fusion patients.

Footnotes

ORCID iDs

Tejas Subramanian

Mihir Dekhne

Tomoyuki Asada

Tarek Harhash

Adin Ehrlich

Kasra Araghi

Austin C. Kaidi

Gregory S. Kazarian

Pratyush Shahi

Kyle Morse

Francis C. Lovecchio

Sheeraz Qureshi

Sravisht Iyer

Funding

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

Declaration of Conflicting interest

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Sheeraz Qureshi has the following disclosures: AMOpportunities: Other financial or material support; Annals of Translational Medicine: Editorial or governing board; Association of Bone and Joint Surgeons: Board or committee member; Cervical Spine Research Society: Board or committee member; Contemporary Spine Surgery: Editorial or governing board; Globus Medical: IP royalties; Paid consultant; Paid presenter or speaker; Hospital Special Surgery Journal: Editorial or governing board; HS2, LLC: Stock or stock Options; International Society for the Advancement of Spine Surgery (ISASS) - Program Committee member: Board or committee member; Lifelink.com: Other financial or material support; Lumbar Spine Research Society: Board or committee member; Minimally Invasive Spine Study Group: Board or committee member; North American Spine Society: Board or committee member; Simplify Medical, Inc.: Other financial or material support; Society of Minimally Invasive Spine Surgery (SMISS) - Program Committee member: Board or committee member; Spinal Simplicity: Other financial or material support; SpineGuard, Inc.: Paid consultant; Stryker: IP royalties; Paid consultant; Surgalign: Paid consultant; Tissue Differentiation Intelligence: Stock or stock Options; Viseon, Inc.: Paid consultant; Research support. Sravisht Iyer has the following disclosures: Globus Medical: Paid presenter or speaker; Stryker: Paid presenter or speaker; Vertebral Columns/International Society for the Advancement of Spine Surgery (ISASS): Editorial or governing board. All other authors have no conflicts of interest to disclose.

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Kawakami

Tsuji

, et al. Adjacent segment disease after posterior lumbar interbody fusion: based on cases with a minimum of 10 years of follow-up. Spine (Phila Pa 1976). 2015;40(14):E831-841. doi:10.1097/BRS.0000000000000917