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Different Fusion Approaches for Single-level Lumbar Spondylolysis Have Similar Perioperative Outcomes

Gala, Raj J. MD*; Bovonratwet, Patawut BS*; Webb, Matthew L. MD; Varthi, Arya G. MD; Daubs, Michael D. MD§; Grauer, Jonathan N. MD*

doi: 10.1097/BRS.0000000000002262

Study Design. Retrospective cohort study

Objective. The aim of this study was to compare perioperative adverse events for patients with lumbar spondylolysis treated with transforaminal lumbar interbody fusion (TLIF), posterior spinal fusion (PSF), combined anterior and posterior fusion (AP fusion), or anterior lumbar interbody fusion (ALIF).

Summary of Background Data. Previous cohort studies have shown similar long-term outcomes for different surgical approaches for this indication, but potential differences in 30-day perioperative adverse events have not been well characterized.

Methods. The present study uses data extracted from the American College of Surgeons National Surgical Quality Improvement Database. Patients undergoing fusion with different approaches for lumbar spondylolysis were identified. Propensity score matching was utilized to account for potential differences in demographic and comorbidity factors. Comparisons among perioperative outcomes were then made among the propensity score-matched study groups.

Results. Of 1077 cases of spondylolysis identified, 556 underwent TLIF, 327 underwent PSF, 108 underwent AP fusion, and 86 underwent ALIF. After propensity score matching, there were no differences in the rates of any of the 30-day individual adverse events studied and no differences in the aggregated groupings of any adverse event, serious adverse event, or minor adverse event. There was a significantly increased operative time in the AP fusion group, but there were no differences in hospital length of stay or readmission rates.

Conclusion. Because perioperative adverse event rates were similar, even with a slightly longer operative time in the AP fusion group, these findings suggest that surgeon preference and long-term outcomes are better used to determine the recommendation of one surgical approach over another for single level fusions for lumbar spondylolysis.

Level of Evidence. 3

*Department of Orthopaedics and Rehabilitation, Yale School of Medicine, New Haven, CT

Department of Orthopaedic Surgery, Hospital of the University of Pennsylvania, Philadelphia, PA

Midwest Orthopaedics at Rush, Rush University Medical Center, Chicago, IL

§Division of Orthopaedic Surgery, University of Nevada School of Medicine, Las Vegas, NV.

Address correspondence and reprint requests to Jonathan N. Grauer, MD, Department of Orthopaedics and Rehabilitation, Yale School of Medicine, 47 College St, New Haven, CT 06510; E-mail:

Received 7 March, 2017

Revised 12 April, 2017

Accepted 19 April, 2017

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

Relevant financial activities outside the submitted work: board membership, grants, expert testimony.

Spondylolysis, a defect in the pars intra-articularis, can lead to spondylosis, instability, and spondylolisthesis. This can be associated with lumbar back pain and/or lower extremity symptoms. The initial treatment of this condition is nonoperative with multiple modalities including physical therapy, activity modification, anti-inflammatory medications, and possibly injection.1 Surgery may be considered if there is lack of improvement with nonoperative options, progression of spondylolisthesis, or neurologic deficit.2,3

When surgery is considered for this condition, it is notable that there is no clear consensus regarding the optimal surgical approach for patients with spondylolysis with or without low-grade spondylolisthesis.2,4–6 Fusion options include transforaminal lumbar interbody fusion (TLIF), posterior spinal fusion (PSF), circumferential combined anterior posterior fusion (AP fusion), and anterior lumbar interbody fusion (ALIF).5 Various studies and reviews have evaluated outcomes achieved with these varying surgical approaches.6–16

TLIF is preferred by some because it can be done through a single posterior approach. It has the further advantages of direct decompression of the foramen on the side of the approach and indirect elevation of both foramen by restoration of disc height with the interbody technique. It affords both posterior and interbody fusion surface areas and avoids an anterior approach to the spine.17–19

PSF alone can be done for low-grade spondylolisthesis, and as with other techniques may be coupled with a decompression.1,13 This avoids the anterior approach and more extensive interbody work of TLIF. Disadvantages include limited ability to reduce slips or restore lumbar lordosis, owing to lack of anterior column support. There is also concern of lesser fusion surface area.20

Other spine surgeons advocate for ALIF with posterior instrumented fusion (AP fusion) for spondylolytic spondylolisthesis. For those facile with the anterior approach to the lumbar spine, AP fusion has the advantage of an anterior exposure for placement of a larger interbody device than can be achieved from posterior,21 greater restoration of lordosis, and indirect decompression of the foramen.2,4,22 Performing ALIF alone is an option,15,23,24 but many find that the addition of posterior instrumentation is beneficial in the setting of spondylolysis.25–27

As with any surgical decision, the question of relative advantages and risks must be considered. Recently published reviews5 and guideline articles2 have attempted to analyze and compare the clinical outcomes for surgical treatment of low-grade isthmic spondylolisthesis. The general conclusions were that clinical outcomes are similar among all surgical approaches, with conflicting evidence whether one approach is superior to another. In terms of cost-effectiveness, the North American Spine Society work group reported insufficient evidence to deem one surgical treatment method superior than another.2

If clinical outcomes are similar among surgical options for spondylolysis, knowledge of perioperative adverse event rates might be something to sway decision-making. The purpose of the present study was to compare the rates of perioperative adverse events among TLIF, PSF, AP fusion, and ALIF for patients with spondylolysis. The American College of Surgeons National Surgical Quality Improvement Program (NSQIP) was utilized to perform a retrospective review of prospectively collected 30-day perioperative outcomes.

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Study Population

The present study used deidentified data from the NSQIP database years 2010 to 2014. An exception was granted for studies using this dataset from the Human Investigation Committee at our institution.

NSQIP prospectively gathers patient data from 517 participating hospitals and records perioperative adverse events for 30 days after surgery, regardless of hospital discharge. In contrast to the data in administrative databases that are based on reimbursement claims and have been shown to be limited,28 inconsistent,29 and fraught with errors,30 the data in this database are chart-abstracted and prospectively collected by specially trained medical professionals and high-quality data is ensured by routine auditing.31

Cases of spondylolysis were identified using International Classification of Disease, Ninth Edition code 756.11 and 756.12. Cases treated with TLIF, PSF, AP fusion, or ALIF were then identified using Current Procedural Terminology (CPT) codes. Cases treated with TLIF were identified by CPT code 22630 or 22633. Cases treated with PSF were identified by code 22612 or 22840. AP fusion cases were identified by code 22558 and included any one of 22612 or 22840. ALIF only cases were identified by code 22558 and excluding 22612 and 22840.

Single-level cases were isolated by excluding cases that had any of the CPT codes for additional levels: 22585, 22614, or 22632. Deformity cases were excluded by removing cases with CPT codes 22800, 22802, 22804, 22808, and 22810.

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Patient Characteristics and Outcomes

Demographic variables directly available from the NSQIP database include patient’ age, sex, height, weight, American Society of Anesthesiologists (ASA) classification, and comorbid factors including diabetes (those who use any pharmacologic agent to control hyperglycemia) and smoking status (those who had smoked cigarettes in the year before admission for surgery). From these, body mass index (BMI) was calculated as weight (in kilograms) divided by height squared (in centimeters). This was divided into categorical groups. ASA was used as a general health status marker.32 Diabetes33 and smoking status were used as additional controls for medical status. Operative and hospital data were additionally abstracted. These included operative time, hospital length of stay (LOS), and 30-day readmission rates.

The NSQIP database follows patients for the occurrence of individual adverse events during the first 30 postoperative days. The rate of each individual adverse outcome was determined as well as aggregated into three groups: total adverse events, serious adverse events, and minor adverse events. Serious adverse events were death, cardiac arrest, stroke/cerebrovascular accident, sepsis/septic shock, myocardial infarction, renal failure, pulmonary embolism, peripheral nerve injury, ventilator time >48 hours, unplanned intubation, or return to the operating room. Minor adverse events were deep wound infection, superficial wound infection, wound dehiscence, renal insufficiency, deep vein thrombosis/thrombophlebitis, pneumonia, urinary tract infection, or transfusion.

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Statistical Analyses

Statistical analyses were performed using STATA version 13 (StataCorp LP, College Station, TX).

Fisher exact and Pearson χ 2 tests were used to compare demographics, comorbid factors, and perioperative adverse event rates as appropriate. To account for nonrandom treatment of patients, propensity score matching was used to minimize the effects of confounding related to differences in patient populations. Propensity scoring generates a single score based on the observed covariate data to effectively match patients from different treatment groups.34 In this case, each patient treated with ALIF was matched with a nearest neighbor control with regard to age, sex, BMI, ASA class, diabetes, and smoking status.

Once patients were matched with propensity scores, adverse event rates were compared among propensity score matched patients using Fisher exact and Pearson χ 2 tests. Of the individual adverse outcomes reported by NSQIP, 12 of those were found to have an occurrence in the study population. Statistical significance was set at a two-sided alpha level of 0.05, but because the chance of finding one or more spurious significant differences in 12 tests is 49%, the level of significance for comparisons of adverse event rates for each of these 12 adverse events was adjusted to 0.004 according to Bonferroni correction.35

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Study Population

In total, 1077 patients were identified: 556 underwent TLIF, 327 underwent PSF, 108 underwent AP fusion, and 86 underwent ALIF (Table 1). The two ICD-9 codes utilized were evaluated and there were no differences among study groups before or after propensity score matching.



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Patient Characteristics

Demographic and comorbid factors are presented in Table 2. Patients who underwent TLIF tended to be older (P = 0.000) and with higher ASA class (P = 0.017), but after propensity score matching, the distribution of ages and ASA class in the compared groups were not statistically different (P = 0.993 and P = 0.861, respectively) (Table 2). The distributions of sex, obesity, diabetes, and smoking status were similar among groups before and after propensity score matching.



Operative times were slightly longer in the AP fusion group (20 minutes longer than TLIF, 34 minutes longer than PSF, and 31 minutes longer than ALIF), which remained statistically significant after propensity score matching (Table 3, P = 0.002). There were no differences in hospital length of stays and readmission rates among the separate treatment groups (Table 3).



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Of the adverse events recorded in this database, 12 occurred at least once in one of the treatment groups. The individual adverse events that occurred are listed in Table 4. After the level of significance was adjusted according to Bonferroni correction, there were no differences among treatment groups in the rates of any of the individual adverse events before or after propensity score matching.



The individual adverse events were aggregated into three groups: total adverse events, serious adverse events, and minor adverse events. Table 5 shows the number of patients for each aggregated adverse event group. There were no differences for any of these aggregated adverse event groups (total, serious, or minor) before or after propensity matching.



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Spondylolysis with or without spondylolisthesis can have a detrimental effect on a patient's life and contribute to significant morbidity. There are multiple surgical approaches to this problem including TLIF, PSF, AP fusion, and ALIF. There are many studies demonstrating the efficacy of a single surgical method in treating patients with low-grade spondylolisthesis.3,13–15,24–26 Comparisons between two surgical techniques have been performed, though with mostly retrospective cohort comparisons.6,8,10–12,23,27,36 Based on the data so far, meta-analyses have provided limited conclusions, with no technique showing superiority over another in terms of long-term clinical outcomes.2,4,5

In a recent systematic review of different fusion techniques for isthmic spondylolisthesis, Wang et al suggested that, although AP fusion has higher radiographic fusion rates and potentially superior clinical outcomes, this comes at the expense of longer operative time, greater blood loss, and increased perioperative complications.5 Owing to varying study methodology, however, the authors stated that it was difficult to make definitive recommendations for one treatment over another.

The analysis presented in the present study demonstrated no statistically significant differences in the rates of individual adverse events, total adverse events, serious adverse events, or minor adverse events among these surgical approaches evaluated. This was done with and without propensity score matching to account for potential differences in the likelihood that a given patient would be treated by a specific surgical method. This matching ended up being used for the increased likelihood that TLIF was more likely to be the chosen approach for older patients with higher ASA.

The findings here highlight the need to resolve the best treatment options to optimize outcomes while minimizing morbidity and costs, for the treatment of spondylolysis. It was thought that this study might find greater differences in adverse events in the perioperative period, among the surgical approaches, but this was not the case. With the importance of evidence-based medicine, consideration of longer-term outcomes may sway further decision-making. Other variables that might contribute to differences in outcomes include alignment and rate of union, which will need to be factored into the overall picture when choosing a treatment option.

There are limitations to this study. The identification of cases was based on diagnosis/procedural codes that have inherent limitation. As with all national database studies, variations in data collection and data-inclusion have been reported among the different national datasets.37,38 Furthermore, there are no orthopedic or spine-specific outcomes, and only 30 days of postoperative follow-up. With the above said, NSQIP is considered to have robust, validated data that is nationally representative and tracks patients for 30 days, which includes beyond their hospital stay.31,38

Thirukumaran et al 39 published a study in 2016 evaluating the trends in surgical management of spondylolisthesis using a different national database, the Nationwide Inpatient Sample (NIS). Their results showed a higher complication rate for combined anterior-posterior fusion surgeries. Previous articles have compared NIS and NSQIP databases, and have shown that the populations in the databases are different, as well as the recorded data.37,38,40 NIS is an administrative reimbursement database based on codes and claims submitted to payers, whereas NSQIP data are generated through risk-assessment nurses who retrospectively review patient charts. NIS data are limited to inpatient hospital stays, whereas NSQIP tracks patients for 30 days after surgery, including outpatient records. Given these differences and more, it has been said that administrative databases such as NIS may not be appropriate for evaluating the rates of adverse events.38

Overall, the present study found that TLIF, PSF, AP fusion, and ALIF for spondylolysis have similar adverse outcomes at 30-day follow-up based on retrospective review of 1077 cases in a prospectively collected national database. The only differences identified were in operative time, with the mean operative time of AP fusion 20 minutes longer than TLIF, 34 minutes longer than PSF, and 31 minutes longer than ALIF. Nonetheless, because perioperative adverse event rates were similar, these findings suggest that surgeon preference and long-term outcomes better inform the recommendation of one surgical approach or another.

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Key Points

  • Options for treating lumbar spondylolysis include TLIF, PSF, AP fusion, and ALIF.
  • Differences in 30-day perioperative adverse event rates among these surgical approaches have not previously been well characterized.
  • After propensity score matching of patients from the American College of Surgeons National Surgical Quality Improvement Program database, the present study found similar rates of adverse events among all groups, when treating this condition.
  • There was a significantly increased operative time in the AP fusion group, but there were no differences in hospital length of stay or readmission rates.
  • Because perioperative 30-day outcomes were found to be overall similar for lumbar spondylolysis, these findings suggest that surgeon preference and long-term outcomes are better used to determine the recommendation of one surgical approach over another for this condition.
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anemia requiring transfusion; anterior lumbar interbody fusion; deep vein thrombosis; myocardial infarction; posterior lumbar fusion; postoperative complications; pulmonary embolism; sepsis; spondylolisthesis; surgical site infection; transforaminal lumbar interbody fusion; urinary tract infection

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