Authors

1. John Alex Sielatycki MD – Center for Sports Medicine and Orthopaedics, Chattanooga Orthopaedic Group
2. Tyler Metcalf MS IV – The Ohio State University College of Medicine
3. Grant Chudik OMS II – The Ohio University Heritage College of Medicine
4. Clinton J. Devin MD – Department of Orthopaedic Surgery, Vanderbilt University School of Medicine
5. Jenna Jarrell MS IV – American University of the Caribbean School of Medicine
6. Scott Dean Hodges DO – Center for Sports Medicine and Orthopaedics, Chattanooga Orthopaedic Group
7. Marissa Koscielski, MS – University of Cincinnati College of Medicine

Abstract

Study Design: Narrative Review

Objective: This narrative review provides an overview of the current trends in lumbar fusion with a focus on analyzing literature related to incidence, clinical outcomes, measuring outcomes, predictors of success, adjacent level degeneration, and cost effectiveness.

Methods: A literature search utilizing PubMed (Medline) and Google Scholar was performed using the terms “lumbar fusion”, “incidence of lumbar fusion”, “lumbar fusion outcomes”, “lumbar fusion clinical outcomes”, “lumbar fusion success”, “lumbar fusion adjacent segment disease”, and “lumbar fusion cost effectiveness”.  The clinically relevant articles were grouped into the following categories: incidence, clinical outcomes, measuring outcomes, predictors of success, adjacent segment degeneration, and cost effectiveness.

Results: The rates of fusion have increased for elderly patients as well as for more complex spinal disorders. Lumbar fusion has shown improved results over decompression alone or nonoperative treatment, but at an increased cost.  Over time, the cost difference is decreased due to the increased need for revision surgeries in the decompression only group.  Minimally invasive techniques as well as lumbar disc arthroplasty have yielded decreased complications, hospital stay and return to work time with similar or improved clinical outcomes when compared to either open techniques or lumbar fusion, respectively.

Conclusions: An improved surgical option could utilize both the concepts of disc arthroplasty as well as minimally invasive techniques to minimize complications and optimize outcomes. It is possible that a spinal arthroplasty device that addresses both the intervertebral disc as well as the facet joints could provide improved benefits as compared to the current disc replacement and facet replacement devices currently utilized.

Keywords: Spine, Fusion, Review, Spinal, Disorders, Lumbar, Degeneration, Surgery

Introduction

Lower back pain is one of the most common complaints heard by primary care physicians and is a leading cause of disability. It is also amongst the most expensive medical issues with an annual cost of more than $50 billion.¹ There has been a 54% increase in years lived with disability due to back pain between 1990-2015.^2,3 Fortunately, the majority of cases are self-limited and respond well to conservative treatment including medications, physical therapy, chiropractic, and injections. For refractory cases, surgery is a potential option. The indications for surgery and the type of surgery varies based on the patient’s complaints and underlying pathology and imaging results. Lumbar fusion has been utilized for more than one hundred years and has become a common treatment option for patients with intractable back pain failing conservative treatment options. It is considered the gold standard for treatment of refractory degenerative disc disease.^4,5 There are many variations of lumbar fusion based on approach, use of instrumentation and other implants, and use of grafting materials that are beyond the scope of the current review. One of the main criticisms of spinal fusion is the potential risk of adjacent level degeneration. This has led to the development of artificial disc replacement devices in an attempt to decrease the forces applied to the adjacent levels following fusion.

Advancements in minimally invasive techniques and disc arthroplasty have had good success rates to date and have been able to limit some of the risks and complications associated with lumbar fusion. The purpose of this paper is to review the incidence of lumbar fusion including trends of use, evaluate clinical and radiographic outcomes following lumbar fusion, identify predictors of success or failure, and evaluate cost effectiveness of traditional lumbar fusion to both minimally invasive techniques and to lumbar disc arthroplasty. Finally, we will conclude with a discussion on the ideal components of implants for the future.

Methods

A literature search to identify the clinically relevant publications on lumbar spinal fusion, utilizing PubMed (Medline) and Google Scholar was completed. The search terms/phrases included “lumbar fusion”, “incidence of lumbar fusion”, “lumbar fusion outcomes”, “lumbar fusion clinical outcomes”, “lumbar fusion success”, “lumbar fusion adjacent segment disease”, and “lumbar fusion cost effectiveness”. Only English language, peer-reviewed articles, published between 2009-2019 were reviewed. Articles that were applicable to clinical practice were chosen and the references of these articles were screened for additional publications that matched the inclusion criteria. Retrospective and prospective studies, meta-analyses, and systematic reviews were included in this review. The clinically relevant articles on lumbar fusion were chosen and grouped into the following categories: incidence, clinical outcomes, measuring outcomes, predictors of success, adjacent segment degeneration, and cost effectiveness. These categories were reviewed and are presented separately in this narrative.  The study design, outcome measures, outcome criteria (if applicable), and study findings of the publications in these categories and are summarized in Tables 1, 2, 3, 4, 5, and 6.

Background/Incidence

Buser et al. performed a retrospective review of Medicare and Humana insurance databases in an attempt to identify current trends in degenerative spinal conditions and their associated treatments.⁶ The Medicare database revealed an insignificant 18.5% increase in lumbar fusion procedures (p=0.0595) between 2006 and 2011. Elderly patients had the greatest relative increase in lumbar fusion rates (p<0.0001) with a 13% increase for those 80-84 and 11% increase for those over 84. The incidence of nonoperative procedures decreased significantly by 16.4% (p<0.0001). Analysis of the Humana database also showed an increase in the incidence of lumbar degenerative disorders but did not show an increase in the rate of lumbar fusion.

Raad et al. performed a retrospective database review of 20,279 patients aged 40-64 years who had undergone surgery for lumbar stenosis from 2010-2014.⁷ The overall incidence of surgery decreased during the study period with a high in 2011 and 2012 of 1.8 per 1000 and a low of 1.2 per 1000 in 2014. There was, however, a significant increase in the proportion of fusion as compared to decompression alone (OR 1.08, p<0.001). The proportion of more complex fusions (>2 levels or combined approach) also increased during the study period (OR 1.4). There was increased likelihood of postoperative medical complications (OR 1.11, p=0.013) and discharge to a skilled facility (OR 1.11, p=0.005) over time. Additionally, patients undergoing fusion had higher rates of complications (1.9% vs 1.2 %, p<0.001) and discharge to skilled facilities (2.5% vs 1.4%, p<0.001) as compared to patients undergoing decompression alone. There were geographical variances identified with patients being more likely to undergo fusion in the Midwest and South as compared to the Northeast or West (p<0.001). Mean hospital payments increased significantly each year for all patients by a mean of $1633 per year (p<0.001), and they were significantly greater for fusion patients ($48,000 vs $35,000, p<0.001). The authors stated that it was unclear what had led to the increase in more complex fusion surgeries during the study period but hypothesized that it could have been related to financial incentives, influence of opinion leaders and marketing of new surgical devices. Limitations of the study included being retrospective, lack of standardization of surgery type or patient selection.

Schoenfeld et al. performed a retrospective review of the Medicare claims database from 2009-2014 to evaluate the changes in use of lumbar fusion following the formation of Accountable Care Organizations (ACOs).⁸ This study considered the pre-ACO period from 2009-2011 and the post-ACO period 2012-2014. When analyzing the use of lumbar fusion regardless of condition, institutions that would form ACOs showed an increase in the use of lumbar fusion from 50% in 2009-2011 to 54% in 2012-2014. For those institutions not forming an ACO the use of fusion increased from 52% in 2009-2011 to 59% in 2012-2014. The difference in use of fusion in ACOs versus non-ACOs was -2.6% (p=0.13). When performing a subgroup analysis for only patients with lumbar stenosis, ACOs had a decrease in the use of lumbar fusion from 31% in 2009-2011 to 29% in 2012-2014, and non ACOs increased the use of fusion from 31% in 2009-2011 to 35% in 2012-2014. The difference in use of fusion for lumbar stenosis in ACOs versus non-ACOs was -5.8% (p=0.03). Other factors associated with the use of fusion included Hispanic vs whites (OR 1.17, p=0.01), older age (OR 0.97 for each year, p<0.001), increased comorbidities (OR 0.97 for each increase in Charleston score, p<0.001) and male gender (OR 0.55, p<0.001). The authors reported that the use of ACOs had a significant reduction of the use of lumbar fusion for Medicare patients with stenosis (p=0.03) and that this could be an indication of further reductions in lumbar fusions in the future. Limitations of the study include being retrospective, lack of standardization of surgical technique, and since the Medicare database was used the results are based on those 65 or older and may not apply to all other age groups equally.

Kim et al. performed a retrospective database analysis of all Korean patients that underwent surgery in 2003 and 2008 for degenerative lumbar spondylolisthesis.⁹ There was a minimum 5-year follow-up. The overall number of surgeries nearly doubled in 2008 (47,316 vs 93,032). The percentage of patients receiving decompression with fusion in 2003 was 31.13% but increased to 91.54% in 2008. The reoperation rate in 2003 was 6.2% and in 2008 was 8.1%. It had been thought that decompression and fusion would decrease the need for reoperation, thus justifying the larger surgery. However, the results of the current study did not support this hypothesis. The authors concluded that despite a large increase in the percentage of lumbar spondylolisthesis patients receiving fusion, there was not an associated benefit of reduced reoperation rates. Limitations in this study included being retrospective and lack of either clinical or radiographic outcomes data.  

Martin et al. performed a retrospective National Inpatient Sample database analysis of patients undergoing elective lumbar spinal fusion from 2004 to 2015.¹⁰ The number of fusion procedures increased from 122,679 (60.4 per 100,000 US adults) in 2004 to 199,140 (79.8 per 100,000) in 2015 with the largest increased noted in patients over 65 years of age. The majority of the increase was attributed to cases of spondylolisthesis or scoliosis, but 42.3% of the elective fusions in 2015 were for disc degeneration, recurrent herniation and stenosis. However, the number of fusions performed for disc degeneration and recurrent herniation decreased during the final 3 years of the study. The authors noted that the strongest evidence for effectiveness of lumbar fusion is for cases of deformity, which correlated with the greatest increase in fusion utilization in the current study. There remains debate over the use fusion in cases of spondylolisthesis without clinical instability. A limitation of the current study was that, given its retrospective nature, it was not able to identify more specific surgical indications in terms of clinical or radiographic findings that led to fusion in cases of spondylolisthesis.  

Bronson et al. performed a retrospective analysis of lumbar fusion patients enrolled in the Bundled Payments for Care Initiative (BCPI) programs to determine length of stay, discharge location, and cost as compared to a baseline group.¹¹ A total of 350 patients were enrolled in the BCPI program and compared to a control group of 518 patients. The length of stay was decreased in the BCPI group (4.58 vs 5.13 days, p=0.009). There was no difference in terms of readmission for the two groups. There was an increase in the utilization of discharge home with home health in the BCPI group. As a whole, there was no change in the cost between the two groups. However, in a subgroup analysis of patients with DRG 460 (TLIF and PLIF patients) the cost were found to increase in the BCPI group ($51,105 vs $45,934, p=0.001). During the study period the institution had an increase in the number of more complex cases during the BCPI enrollment as compared to the control group (45% vs 23%, p<0.001). The authors warned that there could be a financial disincentive for surgeons to take on more difficult cases or use newer and more expensive technology. It was additionally argued that adjustments need to be made to existing DRGs to better anticipate the cost of each episode of care.

Kha et al. performed a retrospective National Inpatient Sample database analysis to determine trends of octogenarians undergoing lumbar spine fusion.¹² The study group consisted of 17,471 patients from 2004 through 2013 with a mean age of 82.7 years. The total number of fusions increased over time from 1144 to 2061. While most patients were female, the percentage of females decreased (68.2% to 57.5%, p<0.0001). The proportion of patients with at least 2 comorbidities increased (706 vs 1427, p<0.0001). The mean length of stay decreased (6 vs 4.5 days, p<0.0001). The total hospital cost increased ($58,471 vs $111,235, p<0.0001). The authors concluded that there has been a significant increase in lumbar fusions in octogenarians with a decreased length of stay, but there has been an increase in the associated hospital cost. The limitations of the study include being retrospective, lack of data on clinical outcomes or complications, and lack of standardization of patient selection or surgical technique.

Clinical Outcomes

Shen et al. performed a meta-analysis of five randomized controlled trials to assess the clinical outcomes of 438 patients with lumbar spinal stenosis treated with lumbar decompression with or without fusion.¹³ Combined data from these studies revealed no significant differences for the two surgical groups for either patient satisfaction (p=0.53) or for Oswestry Disability Index scores (p=0.71). Values for operative time (p=0.002), blood loss (p<0.0001), and length of hospital stay (p=0.007) were significantly greater for fusion patients as compared to decompression alone. There was no significant difference for reoperation rate between the two groups. This study did not provide data related to cost, complications, ambulatory ability, or ability to work. The major limitation of this analysis was the heterogeneity of the included studies. There was no standardization among inclusion criteria, evaluation of preoperative or postoperative signs of instability, surgical technique, or duration of follow-up. As a result, this analysis provides only weak evidence for the benefits of decompression alone over fusion for patients with lumbar stenosis.

Koenders et al. performed a meta-analysis to study the effects of primary lumbar spinal fusion for degenerative lumbar spinal disorders on leg and back pain as well as disability.¹⁴ The study groups included patients with spinal stenosis, spondylolisthesis, disc herniation, and discogenic back pain. The final analysis studied 25 studies and excluded randomized controlled trials. Overall, visual analog scale (VAS) for back pain reduced from 64 to 20 at 24-month follow-up. VAS for leg pain decreased from 70 to 17. Oswestry Disability Index (ODI) decreased from 44.8 to 17.3. This study shows that lumbar fusion can be very effective in the treatment of a variety of degenerative lumbar disorders by decreasing back and leg pain and disability for up to 24 months. A sensitivity analysis was performed that showed a prolonged improvement in the leg pain but that back pain and disability increase at longer-term follow-up. The authors suggested that the longer-term results for back pain and disability might be more questionable; however, they also noted that there was a high risk of bias in the associated studies and the results should be interpreted with caution. Further limitations of the study included the treatment of a wide variety of lumbar complaints. It is certainly possible, for example, that differences in outcome could exist following fusion for spondylolisthesis versus discogenic disease. There was also no exclusion based on the type of lumbar fusion or approach performed or number of levels fused. Additionally, there was a wide variation in outcomes measures reported in the 25 studies reviewed, limiting the data available for each outcome measure.  

Makanji et al. performed a systematic review of the literature to assess fusion rates, complications and clinical success following various lumbar fusion techniques.¹⁵ They evaluated the period from 2000-2015 and compared results to a prior study period from 1980-2000.¹⁶ The current analysis included 160 studies with 8599 patients. The various fusion techniques utilized included noninstrumented posterolateral fusion (5.9%), instrumented posterolateral fusion 34.3%, anterior lumbar interbody fusion (7.3%), circumferential fusion 10.2%, transforaminal or posterior lumbar interbody fusion (32.7%), lateral interbody fusion (5.9%), and minimally invasive fusion (21.6%). The combined fusion rate for all studies was 88.5%. The use of interbody fusion techniques achieved greater rates of fusion with PLIF, TLIF and LLIF each having significantly greater fusion rates as compared to instrumented posterolateral fusion alone. Minimally invasive techniques also had a significantly greater odds ratio for fusion as compared to open techniques. Instrumented posterolateral fusion had significantly greater odds ratio of fusion as compared to noninstrumented posterolateral fusion. Clinical success was defined by a greater than 50% improvement in ODI and was achieved in 52.5% of the patients.¹⁷ The lowest rate of clinical success was found with LLIF (25.6%) and the highest with minimally invasive PLIF (95.8%). There were significantly greater rates of clinical success when using biologics and minimally invasive techniques. As a whole, the complication rate was 14%, and the lowest rates were found with minimally invasive TLIF (7.8%). The highest complication rates were found with LLIF (22.9%). Limitations of the study included a lack of standardization of fusion success criteria and overall heterogeneity among studies.

Purvis et al. performed a prospective cohort study of 146 patients with lumbar stenosis and spondylolisthesis that underwent lumbar decompression and fusion from January 2015 through August 2016 with complete 1-year outcomes data.¹⁸ Patients that did not achieve a minimal important difference (MID) in outcomes measures in the early follow-up period within 3 months had less likelihood of achieving MID at the 1-year follow-up for physical health (OR 0.33), back pain (OR 0.30), leg pain (OR 0.14) and disability (OR 0.11). The authors concluded that patients were likely to achieve maximum benefits by three months after lumbar fusion, and if they have not experienced MID by three months, they should consider other diagnostic or treatment options.

Vail et al. performed a retrospective database analysis of 73,176 patients with spondylolisthesis who received either decompression or decompression with fusion from 2007-2014.¹⁹ Patients receiving fusion were more likely to have a 30-day readmission (OR 1.15, p=0.04) but less likely to undergo revision surgery (OR 0.66, p<0.01). These results different from those previously reported by Shen et al. and Kim et al. ^9,13 Length of stay was approximately one day longer in patients with fusion (p<0.01). The use of opiates was significantly higher during the initial two months postoperatively for the fusion patients (p<0.01), but this difference normalized after the two-month time point. The index cost associated with fusion was significantly greater (p<0.01); however, the subsequent cost beyond the index procedure were lower in the fusion group. At a two-year follow-up the subsequent cost savings for fusion had only partly offset the higher index cost, leaving the fusion patients with overall cost approximately $10,000 higher than the decompression group (p<0.01). Limitations of the study included being retrospective, lack of clinical or radiographic outcomes and lack of standardization of surgical selection or treatment criteria.

Mattei et al. Performed a retrospective study comparing lumbar disc arthroplasty to ALIF for patients with lumbar disc disease at a single center between 2007-2010.²⁰ A total of 80 patients (30-disc replacement and 50 control ALIF patients) were included. Disc replacement patients had significantly lower VAS pain scores and ODI compared to ALIF patients at follow-up from 6-weeks to 1 year. Disc replacement patients returned to work an average of 65 days earlier than ALIF patients (p=0.011). The authors concluded that disc replacement led to improved pain and disability scores and quicker return to work as compared to ALIF patients.

Bai et al. performed a meta-analysis of 14 RCTs comparing lumbar disc replacement versus lumbar fusion.²¹ Disc replacement had significantly improved ODI, VAS, SF-36, patient satisfaction, overall success, reoperation rates, reduced operative time, shortened hospital stay, and decreased complications as compared to fusion patients. Charges were significantly lower in the 1-level group but equivalent in the 2-level group.

Park et al. performed a meta-analysis of minimally invasive versus open lumbar fusion and evaluated nine prospective cohort studies.²² The minimally invasive group had significantly greater ODI improvements (p=0.0003), lower infection rates (OR 0.3, p=0.02), less blood loss (p<0.0001), shorter hospital stay (p<0.0001), but had longer operative time (p<0.0001) and increased radiation exposure (p<0.0001). The authors concluded that the minimally invasive approach was more effects than open fusion in terms of functional improvement, infection, blood loss and hospital stay.

Irimia et al. performed a prospective, multicentric and observational study to compare health-related quality of life following lumbar spine fusion versus total hip and total knee arthroplasty.²³ Results at 6-months, 1-year, and 2-years each showed significant improvement in terms of general wellbeing and physical function for lumbar fusion, total knee and total hip arthroplasty. The improvement was statistically similar for each of the three groups. Results from total hip and total knee arthroplasty are widely considered to be successful surgeries. This was an important study showing similar results of lumbar fusion as compared to hip and knee arthroplasty.

Measuring Outcomes After Lumbar Fusion

Minimum clinical important difference (MCID) is a widely accepted concept that defines a threshold of clinical efficacy to help researchers and clinicians interpret clinical results. Three patient reported outcomes (PRO): the Oswestry Disability Index and numeric rating scales for leg and back pain, are the primary endpoints used to measure if a lumbar spine surgery has achieved the benchmark of success. ^24,25,26 Numerous studies have been dedicated to determining the most accurate and statistically sound classification criteria for clinical efficacy. These studies have produced a spectrum of results due to lumbar spine surgery intrasample variability. The magnitude and statistical intricacy of MCID research is beyond the scope of this paper. However, the five highly regarded studies presented aim to provide statistically sound thresholds for varying classifications of clinical success.  

Copay et al., completed a retrospective analysis of prospectively collected patient reported outcome measures after lumbar spine surgery to analyze the anchor-based and distribution-based methods frequently used to define MCID.²⁷ Additionally, the study aimed to establish a statistically viable MCID for ODI, a leg pain score, a back pain score and the physical component score from SF-36. The patient sample was composed of 454 lumbar spine surgery patients from the Lumbar Spine Study Group that had complete preoperative and 1-year postoperative data. Numerous calculations were completed to determine the minimum detectable change (MDC) in this patient sample was statistically the MCID. The MCID for ODI was -12.8 points, -1.6 points for leg pain, -1.2 points for back pain, and -4.9 points for the physical component score. One limitation of this study is the sensitivity to sample variability in the distribution-based analyses to determine MDC. Since this study included all lumbar spine surgeries and a spectrum of pathologies, the authors postulate the MCID would be different for each of these subgroups.

Parai et al., completed a retrospective review of Swespine data to statistically define the MCID for lumbar degeneration surgeries.²⁸ The sample of lumbar spine surgery patients was composed of 31,314 patients with lumbar disc degeneration, 53,043 with lumbar spinal stenosis and 14,375 with degenerative disc disease. Performing the McNemar test, the minimum important difference at one and two years postoperatively was calculated using the Back Visual Analog Score, Leg Visual Analog Score, Oswestrey Disability Index and EQ-5D index. Results suggested the MIC was a statistically appropriate definition of MCID for the lumbar spinal stenosis subgroup with a 14-point reduction in ODI, 27-point reduction in leg pain and 29-point reduction in back pain. For lumbar herniated disc, a 22-, 39-, and 20-point reduction for ODI, leg pain and back pain respectfully and a 16-,23-, 39- point reduction for these same metrics in the degenerative disc disease subgroup. In the spinal stenosis group, 54% of patients achieved MCID for ODI at 2 years, 51% for leg pain and 41% for leg pain. The sample of this study strengthens these analyses. However, the authors acknowledge that the significance of clinical differences between PROs at 1 year and 5 years is not well understood.

Although a consensus on absolute change values for MCID has not been reached for lumbar spine surgery, MCID is widely accepted as threshold metric and classification system for clinical success. Glassman et al. performed a retrospective review of prospectively collected patient reported outcomes and quality of life measures at baseline and one year following lumbar arthrodesis to define substantial clinical benefit (SCB).29 SF-36, ODI and leg pain and back pain scores from 357 patients were analyzed using receiver operating characteristic curve analysis. The SCB was defined by net change, percent change and raw score at one year for each outcome measure. For SF-36, SCB was defined as a 6.2-point or 19.4% or >35.1-point raw score. For ODI, 18.8-point or 36.8% improvement or <31.3 raw score. For leg pain and back numeric rating scales, an improvement of 2.5 points or a raw score <3.5 points or a 38.8% improvement for leg pain and 41.4% improvement for back pain respectfully was determined to achieve substantial clinical benefit. The three achievement criteria are a limitation of the study as it will produce intrasample variability of SCB achievement rates in future clinical studies.

Copay et al. and Parai et al. determined MCID values in patients with a wide range of lumbar pathologies, subsequent surgical subpopulations and baseline scores.^24,25 The variance in MCID thresholds in the literature suggest that absolute change values are not a reliable or accurate classification of success.^30,31 Asher et al., performed a retrospective analysis of the Quality Outcomes Database lumbar module, a surgical spine registry, to determine if a percent reduction was a statistically sound and clinically relevant way to define MCID.32 The registry included patients undergoing elective lumbar spine surgery for lumbar degeneration, adjacent segment disease and pseudoarthrosis between January 2012 and March 2018 at 74 sites in the United States. Exclusion criteria was comprised of age <18 years and surgical indications of infection, tumor, or trauma. Demographic characteristics, ASA grade, surgical procedure and patient reported outcomes (ODI, Leg pain, Back pain, and satisfaction) were collected at baseline. The patient reported outcomes were also collected at 3 and 12 months postoperative. 23,280 patients were segmented into having met or unmet a ≥30% change in disability and pain scores. A 30% reduction threshold was chosen based on the work of Osteo et al. that suggested a 30% reduction in back pain is a meaningful improvement.³³ The MCID absolute change score criteria outlined in the aforementioned studies by Copay et al., Parai et al., and Glassman et al. were compared to the 30% reduction MCID. 69.9% of patients achieved a 30% decrease in ODI from baseline, which was significantly higher than the percentage satisfying the MCID for each absolute change threshold. Only 67.1% of fusion patients achieved 30% reduction in ODI, which was significantly lower than the 67.9% (p=0.007) achieving a 12.8-point decrease and significantly higher than the 14-point (65.7%, p<0.001) and 20-point (54.3%, p<0.001) decrease thresholds. Using 30% as the MCID threshold for ODI, NRS leg pain and back pain was a better predictor of patient satisfaction than the absolute change values (p<0.001). The 30% reduction in ODI, leg pain, and back predicted satisfaction at 12-months with an accuracy of 77%, 70% and 73% respectfully. Additionally, the largest AUROC differences, which were found in the minimally disabled or bed-bound disability categories statistically favored the 30% reduction over absolute change scores. A similar trend was noted in the NRS back and leg pain scores, also favoring the 30% threshold. The authors concluded that a 30% threshold for was similar or better than absolute change values to accurately define MCID. Limitations to this study included SF-36 data being unavailable in this patient sample to use as an anchor. Future studies will need to include a physical function and general health metric to validate that a 30% reduction is a reliable MCID classification strategy.

MCID by definition is the minimum floor for clinically meaningful result. In an observational cohort study, Crawford et al. measured the number of patients in a sample from the Quality Outcomes Database that achieved a best outcome one year following lumbar arthrodesis.³⁴ The literature on substantial clinical benefit, willingness to undergo the same operation, minimum clinical important difference, and acceptable symptom state suggests that best outcomes following lumbar spine surgery were defined as ODI ≤20 and pain NRS ≤2 and patients that achieve best outcomes will not likely require further medical care.^34,36,26 74 of 396 (19%) patients satisfied the best outcomes threshold at one year. Patients in the best outcomes group were more likely to have a preoperative diagnosis spondylolisthesis or disc herniation than the patient group that did not achieve the minimal symptom state (p=0.001). Additionally, the minimum symptom state group had a lower preoperative ODI (43 to 56, p=0.0×00) and back pain (6.5 to 7.5, p=0.000), were older in age (62 to 57, p=0.001) and had fewer operated levels (1.25 to 1.47, p=0.005). The authors suggest that the best outcomes threshold will not be achieved by the majority of patients and only a small percentage of lumbar spinal fusion patients will be “cured”. Limitations of this study include the single center study design and absence of physical function scores and comorbidity data.  

Predictors of Success

Chan et al. performed a retrospective review of patients from the Quality Outcomes Database who had undergone surgery for grade I spondylolisthesis between July 2014 and December 2015.³⁷ Patients were included if they received either 1- or 2-level decompression or fusion for grade I spondylolisthesis and had North American Spine Society satisfaction data for 12 months postoperatively. Patients that answered “1” or “4” on the satisfaction survey represented the most and least satisfied groups and were compared in this study. The study group consisted of 477 patients, of which 255 (53.5%) were most satisfied and 26 (5.5%) were least satisfied. Based on a multivariate analysis, female gender was the only factor independently associated with the most satisfaction (p=0.02). When the data was separated into a subgroup analysis consisting of fusion only patients, female gender remained the only factor independently associated with the most satisfaction (p=0.02). There was no significant association with patient satisfaction identified for ASA class, smoking, psychiatric comorbidity, or employment status. Limitations in this study included its retrospective nature, lack of standardization of surgical technique or patient selection and relatively short follow-up period of 12 months.

In a similar study by the same group, Mummaneni et al. analyzed the Quality Outcomes Database for patients undergoing surgery for grade I spondylolisthesis between July 1, 2014, and June 30, 2016.³⁸ Patients were included if they received either 1- or 2-level decompression or fusion for grade I spondylolisthesis and had North American Spine Society satisfaction data for 2 years postoperatively. Score of either 1 or 2 were considered satisfied, and scores of either 3 or 4 were considered not satisfied. The analysis included 502 patients.  Decompression alone was performed in 113 (22.5%), and fusion was performed in 389 (77.5%). Patient satisfaction was achieved in 412 (82%) patients but not in 90 (18%) patients. There were no differences in patient satisfaction based on gender, ethnicity, BMI, education status or type of insurance. Satisfied patients were more likely to have worker’s compensation (p=0.006) and be employed and working (p=0.001). There were no significant differences regarding patient satisfaction based on history of prior surgery, diabetes, coronary artery disease, anxiety, depression, and osteoporosis. Based on a multivariate analysis, the most important predictors of patient satisfaction were employment, fusion, and age. The authors concluded that the addition of fusion was likely to increase the patient satisfaction rate for treatment of grade I spondylolisthesis. Limitations of the study included being a retrospective analysis, and lack of standardized surgical technique or patient selection. Interestingly, there were differences noted in the current study as compared to the prior study by Chan et al.²⁴ It is possible that this is related to the larger patient and increased follow-up period in the current study.

O’Connell et al. performed a retrospective analysis of a national database of patients from 2007 and 2014 and identified 60,597 patients who had undergone lumbar fusion, and 4985 of those patients had a diagnosis of depression.³⁹ There was a greater percentage of female patients in the group with preoperative depression as compared to the no depression group (71.7% vs 55.6%, p<0.001). Patients with preoperative depression were significantly more likely to have received a multilevel fusion (72.3% vs 66.0%, p<0.001). Mean cumulative dose in MME was significantly greater in patients with depression (8761.6 vs 4042.4, p<0.001), as was chronic postoperative opiate use (31.8% vs 18.4%, p<0.001). Opiate cessation at 6-12 months was significantly lower for depressed patients (44.1% vs 57.9%, p<0.001). There were significantly greater rates of complications (14.2% vs 12.2%, p<0.001), revision fusion (15.3% vs 12.5%, p<0.001), 30-day readmission (6.7% vs 4.8%, p<0.001), and mean cost at 2-years ($94,150 vs $80,257, p<0.001). Even after controlling for demographic and comorbidity variables and for preoperative opiate use, a preoperative diagnosis of depression was associated increased risk of complications (OR 1.14), revision surgery (OR 1.15) and 30-day readmission (OR 1.19). The authors recommended that preoperative depression should be evaluated prior to lumbar fusion, and as it is a potentially modifiable condition should be addressed prior to fusion when possible.

Sivaganesan et al. performed a retrospective database review of 33,674 patients who had undergone elective lumbar spine surgery.⁴⁰ Of those, 2079 (6.15%) had a 90-day readmission for either medical or surgical complications. A multivariable logistic regression analysis identified an increased risk of medical readmission for patients with increased age (p<0.001), male gender (p=0.03), higher ASA score (p<0.001), diabetes (p=0.04), CAD (p=0.002), African American vs Caucasian (p=0.02) fusion (p=0.003), increased number of levels (p<0.001), anterior or combined approach (p=0.007), unemployed due to disability (p=0.04), higher baseline ODI (p=0.002), and smoking (p=0.04). Surgical readmissions were more likely in patients with higher BMI (p=0.0002), higher ASA score (p=0.016), female gender (p=0.0345), African American vs Caucasian (p=0.026), severe depression (p=0.0331), increased number of levels (p=0.0082), anterior approach (p=0.0261), and higher ODI (p<0.001). The most common variables for both medical and surgical readmission were increased number of levels, anterior approach, higher ASA grade, and baseline ODI. Limitations of the study increased being retrospective, lack of standardization of surgical technique or patient selection, and lack of consistency for readmission criteria.

Wagner et al. conducted a prospective study undergoing lumbar decompression with or without fusion for degenerative lumbar disorders.⁴¹ The study included 180 patients with 3- and 12-month follow-up data including psychological assessment. Clinical outcomes measures were significantly improved at both 3 and 12 months postoperatively (p<0.001) with no difference based on fusion being performed. Patients with depression had significantly lower EuroQol 5D (0.58 vs 0.36, p<0.001) and ODI scores (35.5 vs 51.9, p<0.001) preoperatively, but by 12 months postoperatively these patients had significant improvements equal to those without preoperative depression. The authors concluded that preoperative testing for psychological conditions should be included; however, these results should not be used to exclude patients from proceeding with lumbar surgery. With appropriate perioperative psychological treatment, depressed patients can achieve the same benefits of surgery in terms of quality of life and functional ability as those without depression. Limitations of this study include a lack of standardizing for specific lumbar disorder or treatment performed.

Zakaria et al. performed a prospective study on the effectiveness of using the Patient Health Questionnaire-2 (PHQ-2) as a predictor of depression for patient satisfaction, return to work and change in ODI at 2 years following a lumbar fusion.⁴² The study included 8585 patients undergoing lumbar fusion between January 2015 and June 2018. A score of at least 3 is considered positive for depression.⁴³ Patients with a positive PHQ-2 score were more likely to be smokers, have used opiates for at least 3 months, have had prior spine surgery, have a history of anxiety or depression, and be less likely to be ambulatory (p<0.001). Patients with a positive PHQ-2 had higher rates of readmission at 30-days, increased length of stay, and increased likelihood of discharge to a skilled facility.  In terms of clinical follow-up, patients with a positive PHQ-2 were less likely to be satisfied and less likely to return to work at 90 days, 1 year or 2 years (p<0.001). There was no association with positive PHQ-2 and adverse events postoperatively. When evaluating postoperative depression, 37.5% patients had a positive PHQ-2 score preoperatively, but that decreased to 20% up to 2 years postoperatively (p<0.001) suggesting that treatment of the somatic pain could improve the sense of well-being. The authors concluded that the presence of preoperative depression was associated with increased length of stay, and decreased patient satisfaction and return to work following lumbar fusion. Identifying these patients prior to surgery and maximizing preoperative and perioperative treatment of depression is necessary to improve results following lumbar fusion. Limitations of the study included lack of standardization for patient selection or surgical treatment performed.

Turcotte et al. performed a retrospective outcomes study of 1966 patients to determine if the Centers for Medicare and Medicaid Services Hierarchical Condition Category (CMS HCC) score was a predictor of readmission and reoperation following inpatient spine surgery.⁴⁴ The CMS HCC is utilized to calculate anticipated risk and adjust capital payments made for Medicare Advantage patients. Lumbar fusion was performed in 592 of the patients, and in this subgroup analysis CMS HCC score was found to be predictive of hospital length of stay (p=0.002). Additionally, the rate of readmission was nearly doubled with each increase in CMS HCC quartile (OR 1.88, p=0.011). Return to surgery rate after lumbar fusion was nearly tripled with each increase in CMS HCC quartile (OR 3.27, p=0.002). The authors concluded that the CMS HCC was an effective tool for predicting increased length of stay, readmission and reoperation following lumbar fusion procedures. Limitations of the study include being retrospective and a lack of standardization of patient selection or surgical technique.

Patel et al. performed a retrospective database analysis of 130 patients undergoing primary single-level minimally invasive TLIF to determine if the Patient-Reported Outcomes Measurement Information System, Physical Function (PROMIS PF) score is predictive of postoperative pain and narcotic consumption or of long-term patient reported outcomes.⁴⁵ PROMIS PF scores were grouped as mild disability (score 40-50), moderate disability (score 30-39), and severe disability (score 20-29). Patients with increased levels of disability had higher VAS pain scores and narcotic consumption on postoperative day 0 and day 1. Additionally, patients with higher levels of disability based on PROMIS PF scores had lower PROMIS PF, ODI, SF-12 PCS and worse VAS pain score at 6 weeks, 3 months, 6 months, and 12 months postoperatively. The authors concluded that the preoperative PROMIS PF score was a reliable predictor of both short-term and long-term outcomes following minimally invasive TLIF. This study was limited by being retrospective, and all patients were treated by a single surgeon. There was also no data regarding preoperative or post-discharge narcotic usage.

Jain et al. performed a retrospective review of a Humana database of patients undergoing a primary one- or two-level posterior lumbar fusion for degenerative disorders from 2007-2015 to determine the postoperative effects of chronic preoperative opiate use.⁴⁶ The study analyzed 24,610 patients with a mean age of 65.5 years. Of those, 5,500 (22.3%) had chronic opiate use for greater than 6 months preoperatively. Patients with chronic opiate use had greater risk of wound complications (OR 1.19, p=0.005), new pain diagnoses within 90 days (OR 1.10, p=0.009), all cause 90-day emergency department visits (OR 1.12, p=0.003), emergency department visit for lumbar spine pain (OR 1.31, p<0.001), readmission at 90-days for all complications (OR1.15, p=0.02), chronic postoperative opiate use (OR 8.08, p<0.001), revision surgery within 1 year (OR1.33, p<0.001), and increased utilization of epidural and facet joint injections within 1 year (OR2.24, p<0.001). The presence of anxiety, depression, inflammatory arthritis, tobacco use disorder, and drug abuse/dependence were significant predictors of chronic preoperative opiate use. While chronic opiate use might not be commonly considered as an inhibitor to proper wound healing, the authors describe prior reports of impaired angiogenesis and downregulation of myofibroblasts and macrophages that cause a negative effect on early phases of wound healing.^47,48,49 Limitations in the study include being retrospective, sample group limited to those over 65 years of age, and a lack of ability to quantify the actual number of opiates consumed by patients. The authors argue that the chronic use of opiates leads to increased rates of postoperative complications, resource utilization and associated costs.

Tank et al. performed a retrospective review of the National Inpatient Sample database to analyze the effect on length of stay, cost and complications following one- and two-level lumbar fusions.⁵⁰ The analysis included 1,826,868 patients from 2003-2014, of which 7964 (0.44%) had a discharge diagnosis of opioid dependence. There was an increase in opioid dependency from 3.1 per 1000 lumbar fusions in 2003 to 7.0 per 1000 in 2014 (p=0.037). These patients had a 2.11 times greater incidence of length of stay > 5days (p<0.001). Mean cost was also significantly increased in the opioid group ($35,827 vs $29,349, p<0.001). Overall complication as well as infection, hematoma/seroma, acute posthemorrhagic anemia, device-related, and pulmonary insufficiency were significantly higher in the opioid group. Limitations of the study include being retrospective and lack of ability to determine the reason for increased length of stay.

Ukogu et al. performed a retrospective study of an American College of Surgeons database to determine the rates of complications in patients with hypoalbuminemia undergoing ALIF.⁵¹ A total of 3184 ALIF cases were identified, but only 1275 (40%) had preoperative albumin levels available. There were 53 (4.15%) of patients with an albumin level less than 3.5g/dL which was used as an indicator of malnutrition. Evaluation of the demographic variable identified that the malnourished patients had higher rates of smoking (p=0.003), chronic or active bleeding disorders (p<0.01), pulmonary comorbidities (p=0.018) and higher incidence of ASA class of 3 or greater (p=0.007) as compared to those without malnutrition. A univariate analysis identified length of stay of at least 5 days (p<0.01), wound complications (p=0.017), pulmonary complications (p=0.019), urinary tract infection (p<0.01), blood transfusion (p=0.007), sepsis (p=0.029), and readmission (p=0.039) were higher in those with malnutrition. When using a multivariate regression analysis, the presence of malnutrition was found to be an independent risk factor for increased length of stay (OR 2.56, p=0.002), urinary tract infection (OR 5.93, p=0.001), and sepsis (OR 5.35, p=0.035). Limitations of the study include being retrospective, complications were limited to the first 30 days postoperatively, and lack of other laboratory analysis that could have affected the results.

Durand et al. performed a retrospective database review from the American College of Surgeons of 22,151 patients that underwent posterior lumbar spine fusion from 2012 to 2015 to identify risk factors for 30-day reoperations.⁵² The overall reoperation rate was 3.4%. The study revealed disseminated cancer (OR 3.44, p=0.049), weight loss >10% in 6 months preoperatively (OR3.26, p=0.027), bleeding disorders (OR 1.92, p=0.049), ASA score of 3 (OR 1.46, p<0.0001), BMI 35.0-39.9 (OR 1.50, p=0.037), BMI greater 40 (OR 1.83, p<0.0001), and multilevel fusion (OR 1.24, p=0.0069) as independent risk factors for reoperation within 30 days. The most common reason for reoperation was infection. Diabetes and chronic steroid use did not achieve statistical significance. Limitations of the study include being retrospective, and lack of information on patient selection and surgical technique criteria.

Lim et al. performed a retrospective review of 217 patients who underwent open transforaminal lumbar interbody fusion from 2008 to 2012 with a two-year follow-up to determine preoperative predictors of postoperative satisfaction.⁵³ All patients had either stable lumbar stenosis or spondylolisthesis. There was significant improvement in all clinical outcomes scores at two years including ODI (59.4 vs 16.2, p<0.001), Neurogenic Symptom Score (52.8 vs 11.1, p<0.001), SF-36 PCS (36.0 vs 65.3, p<0.001), SF-36 MCS (60.7 vs 79.8, p<0.001), NPRS back pain score (6.6 vs 1.2, p<0.001), and NPRS leg pain score (6.6 vs 0.7, p<0.001). Multivariate analysis revealed that preoperative leg pain score was the only significant predictor of postoperative patient satisfaction (OR 1.331, p=0.009). Limitations of the study included being retrospective and all surgeries performed by a single surgeon.

Macki et al. performed a retrospective database analysis of the Michigan Spine Surgery Improvement Collaborative to identify predictors of patient dissatisfaction at 1 and 2 years following lumbar spine surgery.⁵⁴ Of the 5390 patients included, there was a 22% patient dissatisfaction rate at both 1 and 2 years postoperatively. At 1 year, predictors of dissatisfaction included increased BMI (RR 1.007, p<0.001), African American race vs white (RR 1.51, p<0.001), lack of high school education (RR 1.25, P=0.008), smoking (RR1.34, p<0.001), daily preoperative opioids for 6 months (RR 1.22, p<0.001), depression (RR 1.31, p<0.001), symptom duration >1 year (RR1.32, p<0.001), prior spine surgery (RR 1/32, p<0.001), and higher back pain score (RR 1.04, p=0.002). Lower rates of dissatisfaction at 1 year were predicted by independent ambulation (RR 0.90, p=0.039), higher leg pain score (RR 0.97, p=0.013), and fusion surgery (RR 0.90, p=0.014). The authors concluded that there were multiple independent risk factors for patient dissatisfaction following lumbar spine surgery. Limitations of the study included being retrospective, not being limited to a specific type of lumbar spine surgery, and lack of standardization.

Pearson et al. performed a combined prospective, randomized, controlled trial and observational cohort study of patients with degenerative spondylolisthesis comparing surgery (395 patients) versus nonoperative treatment (210 patients).⁵⁵ All subgroups improved significantly more with surgery as compared to nonoperative treatment (p<0.05). Multivariate analysis identified age 67 or less (p=0.014), female sex (p=0.01), absence of stomach problems (p=0.035), neurogenic claudication (p=0.004), reflex asymmetry (p=0.016), opioid use (p<0.001), not taking antidepressants (p=0.014), dissatisfaction with symptoms (p=0.039), anticipating high likelihood of surgical success (p=0.019) were independently associated with greater treatment effect. The authors noted several limitations in the Humana database.

Kalakoti et al. performed a retrospective observational cohort study from a Humana claims database to measure postoperative opioid usage following lumbar arthrodesis 2007 and 2015.⁵⁶ 26,553 patients undergoing ALIF, TLIF, PLIF, and PLF surgical approaches were included in the cohort. 58.3% of the patients were preoperative opioid users with an average preoperative filling rate of 28.5%. At one year postoperative, 8.6% of preoperatively opioid naïve patients and 42.4% of preoperatively opioid users continued to use opioids. The Absolute risk of remaining on narcotics at one year was in patients undergoing ALIF and PLF (RR: 5.5, 95% CI).

As noted in this section there are numerous potential factors that can affect perioperative and postoperative results. While there is some discrepancy in the literature, these studies do provide some level of guidance on which patients might have more complications with surgery. Some of these factors can be treated or optimized prior to elective surgery. In cases of neurologic deficit or other urgencies, optimization might not be possible. In those cases, it is useful for the surgeon to discuss and document the increased potential for risk with the patients prior to surgery.

Adjacent Level Degeneration

Spinal fusion was developed in an attempt to restore spinal stability, maintain normal alignment, and reduce pain in affected spinal segments. A common criticism of spinal fusion is the potential to develop adjacent level degeneration. The theory is that by eliminating segmental motion through fusion, the adjacent spinal segments will take on an increased biomechanical demand to maintain normal motion. These increased forces and motion are thought to cause the adjacent segments to wear at a faster rate than if an adjacent level fusion had not been performed. While from a purely mechanical standpoint it would appear obvious that eliminating motion at a level will increase the demands at the neighboring levels, however, the concept is complicated by the effects of natural history. If the patient already has one or more levels with sufficient degenerative changes to warrant a fusion, what is the likelihood of developing degenerative changes at the adjacent level even without performing the fusion? This is even more of an issue when the level adjacent to the fusion had some early pre-existing degenerative changes at the time of the primary fusion that might not yet have warranted surgery. Also, when investigating these concepts, it is crucial to differentiate between adjacent level degeneration versus adjacent level disease. Adjacent level degeneration merely refers to degenerative changes that may or may not warrant treatment and, in some cases, remains asymptomatic. Adjacent level disease refers to cases where the degeneration has advanced to become symptomatic, and treatment is being considered. These concepts have been extensively studied in both the cervical and lumbar spine.  

To limit the risk of adjacent level degeneration, spinal arthroplasty devices have been developed. There have been a wide variety of designs, but the central focus has been to maintain as close to normal motion and kinematics as possible at the surgical level to minimize the effects on the adjacent levels. This is similar to the history of treatment for hip and knee pathology. Each of these was historically treated with fusion in severe cases. However, the developments and advancements in hip and knee arthroplasty has made these techniques some of the most successful surgeries performed and drastically limited the indications for hip or knee fusion.  

Wang et al. performed a systematic review of the literature in an attempt to determine whether lumbar motion preserving devices reduce the risk of adjacent segment pathology compared to fusion surgery.⁵⁷ Only two randomized controlled trials met the inclusion criteria for the current study^.58,59 When the two studies were pooled there were a total of 456 patients. The relative risk of clinical adjacent segment pathology treated surgically for arthroplasty patients versus fusion patients was 5.9 (p=0.02). The authors concluded that while the risk of clinical adjacent level pathology requiring surgery is likely greater following fusion than arthroplasty, the risk is still low. As a result, they graded their strength of statement as weak.

Lawrence et al. performed a systematic review of the literature to determine incidence of adjacent level pathology following lumbar fusion and to determine potential risks factors.⁶⁰ A total of five studies met the final criteria for the current study.^61-65 Based on their review, the authors concluded that the risk of developing clinical adjacent segment pathology after lumbar fusion occurs at a mean annual incidence of 0.6-3.9%. Patients over 60 years or those with pre-existing facet or disc degeneration may have an increased risk, and the risk may be greater after multilevel fusion and when performing a laminectomy adjacent to a fusion. Each of these statements was graded as a strong strength of statement. A limitation of this study was the wide variety of indications for fusion ranging from degenerative disc disease to kyphosis and scoliosis. There was also a range in number of levels addressed from single level to multiple level thoracolumbar fusions. Additionally, the majority of the included studies were retrospective cohorts.

Lee et al. performed a systematic review of the literature to determine whether indications for surgery were a risk for the development of adjacent segment pathology.⁶⁶ Three studies were included in the analysis for spinal fusion being performed for degenerative disease.^67-69 The authors found insufficient evidence in the literature to determine whether the indication/reason for fusion affects the risk of adjacent level pathology in the lumbar spine.

Lee et al. performed a systematic review to determine the population risk of radiographic degeneration and the risk of adjacent segment pathology among patients who receive and don’t receive (but were eligible for) fusion.⁷⁰ The authors concluded adjacent segment pathology may occur at a higher rate than the rate of natural spinal pathology and factors such as biomechanical effect of fusion may accelerate pathologic changes. The strength of the statement was weak.

Furunes et al. performed a controlled, randomized trial on the development of adjacent level disc degeneration following lumbar disc replacement versus nonoperative treatment.⁷¹ The study group consisted of 69 patients with disc replacement and 52 patients treated nonoperatively. At an 8-year follow-up there was no significant difference between the 23 (40%) of the nonoperative group and 29 (42%) of the disc replacement group who developed increased levels of adjacent level disc disease. This could include increased Modic changes, development of high intensity zone, decreased nucleus signal, decreased disc height, worsened disc contour, or increased of herniation. A multiple linear regression analysis found no significant associated between increased levels of adjacent level disc disease and clinical outcomes in those treated nonoperatively (p=0.85) or with disc replacement (p=0.50). The authors concluded there were no significant differences in the development of radiographic signs of adjacent level disc degeneration following disc replacement versus nonoperative treatment at 8-years. The also concluded there was no association between the development of radiographic signs of adjacent level degeneration and clinical outcomes.

In a consensus statement from the First Annual Lumbar Total Disc Replacement Summit, Gornet et al. produced a list of their recommendations as summarized in Table 7.⁷² They concluded that while there is no single strategy for diagnosing symptomatic lumbar degenerative disc disease, a combination of clinical history, physical examination, MRI findings (decreased disc height, presence of annular tears, signs of disc degeneration, central disc herniation, and endplate changes), provocation discography, response to diagnostic and therapeutic spinal injections, and failure of conservative therapy is sufficient for the appropriate diagnosis of discogenic pain. From the same summit additional consensus statement were adopted by Janssen et al. and are summarized in Table 8.⁷³ 

Cost Effectiveness

Previous studies have shown significant advantages of minimally invasive technique in terms of less muscle damage, less blood loss, shorter length of stay, fewer complications and faster return to work.^74-77 As a result, Vertuani et al. performed a systematic review and meta-analysis to develop a health economic model comparing the cost of minimally invasive versus open lumbar fusion in Italy and the United Kingdom.⁷⁸ The cost effectiveness of the minimally invasive approach was determined by the incremental cost per quality-adjusted life-year gained. The total cost savings per procedure in Italy was 973 Euro and was 1666 Euro in the United Kingdom. There was an improvement of 0.04 quality-adjusted life-years over two-years. Most of the cost saving associated with the minimally invasive approach was related to a shorter hospital stay, reduced blood loss, and fewer complications. The authors concluded that the minimally invasive approach provided, not only improved clinical results, but also cost savings. Limitations of the study included analyzing retrospective studies and restriction of cost analysis to hospital cost alone.

Djurasovic et al. performed a retrospective database analysis of patients undergoing either a minimally invasive midline lumbar interbody fusion using cortical fixation or a traditional open TLIF to compare cost effectiveness.⁷⁹ There were 214 patients in the study (181 underwent the minimally invasive approach and 33 had an open TLIF). Total direct cost was $2493 less in the minimally invasive group, but this did not reach statistical significance (p=0.073). The minimally invasive group did have significantly lower cost related to blood transfusion (p=0.015), surgical supplies (p<0.001), hospital room and board (p<0.001), pharmacy (p=0.010), laboratory (p=0.004), and physical therapy (p=0.009). There were no significant differences in clinical outcomes between the two groups. The authors concluded that the minimally invasive approach produced similar clinical outcomes with a trend toward decreased total cost. Study limitations include being retrospective, and lack of standardization on patient selection.

Phan et al. performed a meta-analysis and cost-effectiveness analysis of patients undergoing minimally invasive versus open TLIF.⁸⁰ The final analysis included six studies accounting for 214 minimally invasive and 170 open TLIF patients. The direct hospital cost was significantly lower by a weighted mean difference of $2820 for the minimally invasive group (p<0.00001). Additionally, the minimally invasive group had significantly shorter length of stay of 1 day (p=0.02), and less blood loss by 246.4 cc (p=0.003). The authors concluded that the minimally invasive approach allowed for significant reduction in direct cost as well as reduction in length of stay and blood loss as compared to the traditional open TLIF. Limitations of the study included several studies being retrospective, potential selection bias, and lack of clinical or radiographic outcomes.

Twitchell et al. performed a retrospective cost analysis of patients undergoing a 1- or 2-level interbody fusion with either an open or minimally invasive approach.⁸¹ The study consisted of 276 patients of which 227 (82.2%) had a 1-level fusion, and 49 (17.8%) had a 2-level fusion. The open approach was used in 188 (68.1%), and the minimally invasive approach was used in 88 (31.9%). A multivariate analysis identified independent factors associated with increased cost were length of stay, number of levels and using a minimally invasive approach. The authors argued that the unexpected increased cost of the minimally invasive approach was likely related to the increased cost of supplies and implant costs. They also noted that while the difference did reach statistical significance, the actual increase in cost was relatively small at 4.7%.

To determine the cost-effectiveness of arthroplasty versus fusion, Stubig et al. conducted a prospective, observational, cohort study of 78 patients who underwent either anterior-posterior interbody fusion or total disc replacement to assess clinical and economic results.⁸² The study group consisted of 38 fusion patients and 37 arthroplasty patients from a single center in the United Kingdom from 2005 through 2008 with a minimum 2-year follow-up. The arthroplasty cohort had significantly lower rates of operative time (193.6 vs 377.4 minutes, p<0.0001), units of blood transfusion (0 vs 0.4, p=0.02), number of levels (1.1 vs 1.4, p=0.002), and hospital stay (5.2 vs 7.0 days, p=0.002). No significant differences were found in clinical outcomes of VAS leg or back pain or ODI. There were no cases of revision surgery in the arthroplasty group during the two-year follow-up period as compared to a 21.3% revision rate in the fusion group. Overall cost savings for the arthroplasty group was 33.35% as compared to the fusion group. The authors concluded that lumbar arthroplasty provided similar clinical outcomes with a significant reduction in cost, largely related to the lower rate of revision surgery encountered with the arthroplasty group. Limitations of the study included lack of patient randomization and results limited to a single center.

Levin et al. performed a retrospective cost analysis comparing one- and two-level lumbar disc arthroplasty to circumferential fusion.⁸³ The study included 53 patients (36 arthroplasty and 17 fusion) that were randomized 2:1. For patients undergoing one-level surgery there was a significantly lower charge for the disc replacement vs the fusion ($35,592 vs $46,280, p=0.0018). Operative time and blood loss were also significantly lower in the arthroplasty group.  For two-level procedures, charges were similar for the two groups ($55.524 vs $56,823, p=0.55). The operative time remained significantly lower for the arthroplasty group.

Goldstein et al. performed a systematic review to compare the clinical effectiveness and economic evaluation of patients undergoing open versus minimally invasive posterior or transforaminal lumbar interbody fusion.⁸⁴ The study analyzed 45 prior studies consisting of 3472 patients with minimally invasive fusion and 5925 patients with open fusion. There was marked variation in operative times among the studies ranging from the minimally invasive being 44.7% longer to being 63.1% shorter. Blood loss was less in the minimally invasive group by 16.1 to 88.7%. Length of stay was also shorter in the minimally invasive group by 15.0 to 64.%. There were no significant differences in radiographic evidence of fusion between the two groups. Nine of the studies reported significantly lower complications rates in the minimally invasive group, while the remaining studies showed no difference. No significant differences were identified in patient-related outcomes measures for the two groups. The economic analysis of nine studies revealed lower hospital cost/charges in the minimally invasive group ranging from 2.5 to 49.3%.^85-93 The authors concluded that use of the minimally invasive approach for TLIF provided improved blood loss and length of stay with equivalent fusion rates and clinical outcomes. These results were achieved with lower hospital cost/charges. Limitations of the study include a lack of standardization of surgical indications and reported data in the studies reviewed.

Tosteson et al. performed a cost-effectiveness analysis of lumbar surgery versus nonoperative management.⁹⁴ Adjusted total mean costs were higher for all surgically treated patients compared to nonoperative treatment. When results were compared to a prior 2-year follow-up, the cost per QUAL gained for surgery versus nonoperative treatment improved.  The improved value of surgery over time showed a better durability of surgical results versus greater continued costs with nonoperative treatments.⁹⁵

Discussion

This review has shown a trend of increased number of fusions being performed in the elderly population as well as an increase in more complex and multilevel fusions. These all come with an overall increase in costs. While there is initially a substantial increase in cost with fusion versus decompression, this difference diminishes over time due to greater durability in the fusion results and higher rates of revision surgery with decompression alone or with continued nonoperative treatment. The use of a posterior approach appeared to have improved results compared to either anterior or circumferential approaches. The use of minimally invasive techniques has brought a decrease in complications and decreased length of stay, with equal or improved clinical results. In most studies, the minimally invasive approach yielded lower cost predominantly due to the decreased length of stay and fewer complications. The use of lumbar disc replacement versus lumbar fusion has led to improved return to work rates, decreased length of stay with similar or improved clinical outcomes. The cost associated with arthroplasty appears to be less with a single level but similar for 2 levels as compared to fusion.

In an ongoing effort to achieve improved clinical results with fewer complications, fewer revision surgeries and improved cost, the ideal treatment could use these findings to create the best surgical option for patients with lumbar stenosis or stable spondylolisthesis. There is obviously no ideal treatment option for every patient with lumbar disorders. The benefits of both the minimally invasive approach and lumbar disc arthroplasty appear to be clear for the well-selected patient. They are associated with less complications, shorter length or stay and faster return to work with similar or improved clinical results.

One common limitation for lumbar disc replacement is the presence of symptomatic facet arthritis. Since each functional spinal unit is composed of the disc and two facet joints, it is common for each of these joints to wear and become symptomatic at a similar rate. While facet joint replacements have been performed, this technique has never reached popular acceptance. It is possible that a spinal arthroplasty device that addresses both the intervertebral disc as well as the facet joints could provide improved benefits as compared to the current disc replacement and facet replacement devices currently utilized. As with other joint replacements such as total knee arthroplasty and total ankle arthroplasty there are multiple joint surfaces involved. Replacement of only one of those surfaces (i.e., unicompartmental knee arthroplasty) is only beneficial in selective cases where the other joint surfaces are not affected. Another key feature of an improved device would be the ability to implant through a minimally invasive posterior approach. As noted above, the minimally invasive approach has been shown to have many advantages over the open technique as has the posterior approach over the anterior or circumferential approach. Thus, a spinal arthroplasty device which addresses all intervertebral joint surfaces and can be implanted through a minimally invasive posterior approach, may show substantial advantages moving forward.

Familiarity with the benefits and drawbacks of the various forms of instrumentation, and surgical approaches used to treat degenerative disc disease is essential for providing patients with the best possible outcome. This review outlines findings in lumbar fusion literature to inform clinicians of the recent trends in surgical approach and instrumentation.

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