Approximately one-third of the current United States population older than 70 years suffers from diagnosed spinal degeneration. 1 An increase of 62% was seen in the volume of elective lumbar fusions in the United States between 2004 and 2105. 2 Increasing life expectancy combined with a preference for an active lifestyle is expected to increase the size of the elderly population seeking surgical care for degenerative pathology of the spine. Minimally invasive techniques have been reported to decrease intraoperative blood loss and injury to the surrounding tissues, and this may be particularly beneficial in the elderly. 3–9
Lumbar fusion is a more invasive procedure compared to decompression alone because it frequently involves instrumentation and placement of an interbody cage. 10–12 Patients, especially the elderly, naturally have queries regarding its outcomes, speed of recovery, and the risk-benefit ratio. Although these questions cannot always be answered accurately, an appropriate explanation as part of surgical counseling can help in setting realistic expectations in terms of outcomes.
Transforaminal lumbar interbody fusion (TLIF) is regarded as a workhorse technique for the treatment of degenerative conditions of the lumbar spine. 13 Although various studies have been previously conducted to assess the outcomes of minimally invasive TLIF (MI-TLIF) in the elderly, 13–18 only a few have reported minimum clinically important difference (MCID) achievement rates, 17,18 and none have reported the time taken to achieve MCID, return to activities, and discontinue opioids postoperatively. Therefore, the purpose of this comparative study was to fill this gap in the literature by assessing the MCID achievement, return to activities, and opioid discontinuation, in addition to analyzing the improvement in patient-reported outcome measures (PROMs), fusion rates, and complication/reoperation rates in patients ≥ 70 years old following MI-TLIF.
Methods
Study Design and Patient Population
This was an institutional review board–approved retrospective cohort study that was exempt from the informed consent requirement. Patients who underwent primary single-level MI-TLIF (Qureshi-Louie class 2) 19 for the treatment of degenerative conditions of the lumbar spine between April 2017 and February 2021 and who had a minimum of 1-year follow-up were included. Revision and multilevel surgeries were excluded. Surgeries were performed by fellowship-trained spine surgeons with practices dedicated mainly to minimally invasive spine surgery. The included patients were divided into 3 groups based on age: < 60 years, 60–69 years, and ≥ 70 years.
Surgical Technique
MI-TLIF was performed as previously described in the literature, 20–27 by using a tubular retractor with unilateral facetectomy, preparation of the disc space, interbody cage placement, and a bilateral percutaneous pedicle screw construct.
Data Collection
The following data were collected and managed using REDCap (Research Electronic Data Capture) 28,29 hosted at Weill Cornell Medicine Clinical and Translational Science Center, supported by the National Center for Advancing Translational Science of the National Institutes of Health (award no. UL1 TR002384), as follows.
- 1.Preoperative: demographics (age, sex, body mass index [BMI], age-adjusted Charlson Comorbidity Index [CCI], American Society of Anesthesiologists [ASA] class) and PROMs (visual analog scale [VAS] for back and leg pain, Oswestry Disability Index [ODI], and 12-Item Short-Form Health Survey Physical Component Summary [SF-12 PCS]).
- 2.Operative: operative time, estimated blood loss (EBL), and complications.
- 3.Postoperative: postoperative length of stay (LOS), PROMs, return to work and driving, discontinuation of opioids, complications/reoperations, and fusion rates. Data were collected at the postoperative time points of 2 weeks, 6 weeks, 12 weeks, 6 months, 1 year, and 2 years, and two postoperative time points (early [< 6 months] and late [≥ 6 months]) were defined for analysis. Fusion status was assessed on the 1-year postoperative CT scan as described previously in the literature.30 Fusion was defined as bony bridging from endplate to endplate within the cage as well as lateral to the cage.
Statistical Analysis
Differences in demographics and operative variables between the 3 groups were analyzed with the 1-way ANOVA/Kruskal-Wallis and chi-square tests. PROMs were analyzed for improvements following surgery. Paired t-tests were performed to analyze the changes in postoperative VAS back, VAS leg, ODI, and SF-12 PCS compared to the preoperative baseline. One-way ANOVA tests were performed to assess the differences between the 3 groups in preoperative PROMs and the magnitude of improvement. The proportion of patients achieving MCID for these PROMs was calculated. The following MCID-threshold values were used: 12.8 for ODI, 1.2 for VAS back, 1.6 for VAS leg, and 4.9 for SF-12 PCS. 31 Time to MCID achievement was calculated. The percentage of patients returning to activities and discontinuing opioids and the average time to do so were analyzed. Significance was defined at p ≤ 0.05, and IBM SPSS version 25 (IBM Corp.) was used to perform all analyses.
Results
Demographic, Operative, and Perioperative Variables
A total of 147 patients (age < 60 years: 62 patients, 60–69 years: 47 patients, ≥ 70 years: 38 patients) were included. Significant differences between the 3 groups were seen in age-adjusted CCI (0.8 vs 2.7 vs 4, p < 0.001) and ASA class (p = 0.006). No significant difference was seen in sex, BMI, operative time, EBL, and postoperative LOS (Table 1).
Comparison of demographic and operative variables between the 3 groups
| Group 1, <60 Yrs | Group 2, 60–69 Yrs | Group 3, ≥70 Yrs | p Value | ||||
|---|---|---|---|---|---|---|---|
| Overall | Group 1 vs 3 | Group 1 vs 2 | Group 2 vs 3 | ||||
| No. of pts | 62 | 47 | 38 | ||||
| Age (in yrs) | 47.9 ± 8.74 | 64.38 ± 3.19 | 74.65 ± 5.38 | ||||
| Sex | 0.479 | ||||||
| Female | 34 (54.8%) | 21 (44.7%) | 17 (44.7%) | ||||
| Male | 28 (45.2%) | 26 (55.3%) | 21 (55.3%) | ||||
| BMI (in kg/m2) | 28.32 ± 5.9 | 29.14 ± 8.02 | 27.03 ± 5.1 | 0.33 | |||
| Age-adjusted CCI | 0.75 ± 0.78 | 2.7 ± 0.97 | 4.02 ± 1.38 | <0.001 | <0.001 | <0.001 | <0.001 |
| ASA class | 0.006 | ||||||
| I | 12 (19.3%) | 1 (2.1%) | 1 (2.6%) | ||||
| II | 48 (77.4%) | 40 (85.1%) | 34 (89.5%) | ||||
| III | 2 (3.2%) | 6 (12.7%) | 3 (7.9%) | ||||
| Op time (in mins) | 106.93 ± 36.48 | 126.42 ± 109.05 | 111.26 ± 57.38 | 0.091 | |||
| EBL (in mL) | 63.15 ± 103.77 | 61.38 ± 42.61 | 58.16 ± 43.75 | 0.949 | |||
| Postop LOS (in hrs) | 40.52 ± 28.8 | 35.83 ± 22.02 | 32.9 ± 19.91 | 0.301 | |||
Pts = patients.
Values are shown as the number of patients (%) or the mean ± SD unless otherwise indicated. Boldface type indicates statistical significance.
Improvement in PROMs
No significant difference was found between the 3 groups in any of the PROMs at the preoperative and the early (< 6 months) and late (≥ 6 months) postoperative time points. Each of the 3 groups showed significant improvements in all PROMs at both time points compared to the preoperative baseline (Table 2).
Improvement in PROMs compared to the preoperative values at the early (< 6 months) and late (≥ 6 months) postoperative time points
| <60 Yrs | 60–69 Yrs | ≥70 Yrs | p Value | |
|---|---|---|---|---|
| VAS back | ||||
| Preop | 5.83 ± 2.99 | 5.86 ± 2.57 | 4.84 ± 3.18 | 0.247 |
| Early | 2.95 ± 2.68 (p < 0.001) | 2.68 ± 2.35 (p < 0.001) | 1.8 ± 2.07 (p < 0.001) | 0.098 |
| Late | 2.61 ± 2.79 (p < 0.003) | 2.4 ± 2.31 (p < 0.001) | 2.14 ± 2.67 (p = 0.003) | 0.753 |
| VAS leg | ||||
| Preop | 5.25 ± 3.33 | 5.98 ± 3.04 | 5.56 ± 3.01 | 0.561 |
| Early | 2.17 ± 2.54 (p < 0.001) | 2.1 ± 2.55 (p < 0.001) | 1.88 ± 2.19 (p < 0.001) | 0.863 |
| Late | 2.16 ± 3.03 (p < 0.001) | 1.87 ± 2.55 (p < 0.001) | 1.59 ± 2.08 (p < 0.001) | 0.653 |
| ODI | ||||
| Preop | 39.52 ± 17.04 | 33.26 ± 17.54 | 37.07 ± 19.27 | 0.256 |
| Early | 23.57 ± 19.21 (p < 0.001) | 21.31 ± 16.74 (p = 0.001) | 18.86 ± 15.5 (p < 0.001) | 0.475 |
| Late | 17.90 ± 18.28 (p < 0.001) | 13.53 ± 13.9 (p < 0.001) | 17.6 ± 16.83 (p < 0.001) | 0.454 |
| SF-12 PCS | ||||
| Preop | 32.87 ± 10.33 | 34.11 ± 9.69 | 33.88 ± 8.56 | 0.82 |
| Early | 38.74 ± 11.28 (p = 0.001) | 40.31 ± 10.54 (p = 0.007) | 39.79 ± 9.83 (p = 0.005) | 0.79 |
| Late | 43.38 ± 12.39 (p < 0.001) | 47.24 ± 10.7 (p < 0.001) | 40.42 ± 11.46 (p = 0.008) | 0.096 |
Boldface type indicates statistical significance.
Comparison of the Magnitude of Improvement in PROMs Between the 3 Groups
No significant difference was found between the groups in the magnitude of improvement in any of the PROMs at either time point (Table 3).
Comparison of the magnitude of improvement in PROMs between the 3 groups at the early (< 6 months) and late (≥ 6 months) postoperative time points
| <60 Yrs | 60–69 Yrs | ≥70 Yrs | p Value | |
|---|---|---|---|---|
| VAS back | ||||
| Early | −2.94 ± 3.47 | −3.35 ± 3.18 | −2.79 ± 3.14 | 0.754 |
| Late | −2.66 ± 3.69 | −3.28 ± 3.3 | −2.29 ± 3.58 | 0.540 |
| VAS leg | ||||
| Early | −3.22 ± 3.5 | −3.88 ± 3.7 | −3.45 ± 3.5 | 0.697 |
| Late | −2.64 ± 3.61 | −3.88 ± 3.63 | −3.83 ± 3.54 | 0.227 |
| ODI | ||||
| Early | −16.78 ± 17.94 | −12.93 ± 21.74 | −17.58 ± 21.04 | 0.581 |
| Late | −18.78 ± 17.46 | −18.89 ± 17.68 | −16.82 ± 21.13 | 0.867 |
| SF-12 PCS | ||||
| Early | 6.2 ± 12.78 | 6.11 ± 11.94 | 5.97 ± 10.69 | 0.997 |
| Late | 9.31 ± 14.06 | 13.17 ± 10.96 | 6.37 ± 11.6 | 0.134 |
MCID Achievement
Although the MCID achievement rates for VAS leg and ODI were similar for the 3 groups, they were comparatively lower in the ≥ 70-year-old patient group for VAS back at the early and late time points (55% and 48% vs 65%–76%) and SF-12 PCS at the late time point (46% vs 64% and 74%) (Table 4). Although time to MCID achievement for ODI and SF-12 PCS was similar (approximately 4 months) in the 3 groups, it was comparatively greater in the ≥ 70-year-old patient group for VAS back (2.5 months vs 1.2 and 1.5 months) and VAS leg (1.8 months vs 0.9 and 1.2 months) (Table 5) (Fig. 1).
MCID achievement rates at the early (< 6 months) and late (≥ 6 months) postoperative time points
| <60 Yrs | 60–69 Yrs | ≥70 Yrs | |
|---|---|---|---|
| VAS back | |||
| Early | 68.6% | 75.7% | 54.8% |
| Late | 65.2% | 67.6% | 48.1% |
| VAS leg | |||
| Early | 62.7% | 75.7% | 64.5% |
| Late | 58.7% | 64.7% | 70.4% |
| ODI | |||
| Early | 62.7% | 51.4% | 51.6% |
| Late | 63.8% | 61.8% | 59.3% |
| SF-12 PCS | |||
| Early | 54.9% | 56.8% | 54.8% |
| Late | 63.8% | 73.5% | 46.4% |
Time to MCID achievement for PROMs
| <60 Yrs | 60–69 Yrs | ≥70 Yrs | |
|---|---|---|---|
| VAS back | 1.2 mos | 1.5 mos | 2.5 mos |
| VAS leg | 0.9 mos | 1.2 mos | 1.8 mos |
| ODI | 4.1 mos | 4.2 mos | 3.7 mos |
| SF-12 PCS | 4.4 mos | 4.2 mos | 3.8 mos |
Graph showing time in months (y-axis) to MCID achievement for PROMs.
Return to Activities and Discontinuation of Opioids
Overall, 98% of patients who had previously driven returned to driving (average 19 days), 80% of previously working patients returned to work (average 18 days), and 97% of patients discontinued opioid use postoperatively (average 10 days). No significant difference was seen between the groups (Table 6).
Percentage of patients returning to driving/working and discontinuing opioid use postoperatively and the average time to achieve it
| <60 Yrs | 60–69 Yrs | ≥70 Yrs | p Value | |
|---|---|---|---|---|
| Return to driving | 100%, 21 days | 96%, 19 days | 96%, 16 days | 0.329, 0.142 |
| Return to work | 81%, 21 days | 74%, 14 days | 86%, 16 days | 0.754, 0.253 |
| Opioid discontinuation | 98%, 12 days | 93%, 7 days | 93%, 10 days | 0.479, 0.212 |
The p values are for comparisons of percentage of patients and number of days, respectively.
Fusion Rates
Evidence of fusion could be assessed in only 70 of 147 patients due to the unavailability of postoperative CT scans for the remaining individuals. There was no significant difference between the groups in the fusion rates (age < 60 years: 89.3%, 60–69 years: 86.4%, ≥ 70 years: 85%; p = 0.901).
Complications/Reoperations
The groups showed no significant difference in complication/reoperation rates (Table 7). No surgery-related mortality was reported in any of the groups.
Complication and reoperation rates in the 3 groups
| Complication | <60 Yrs | 60–69 Yrs | ≥70 Yrs |
|---|---|---|---|
| Intraop | 0 | 1 (2.1%) durotomy | 0 |
| Immediate postop | 6 (9.7%) | 2 (4.2%) | 3 (7.9%) |
| 4 urinary retention | 2 urinary retention | 1 urinary retention | |
| 2 nausea/vomiting | 2 nausea/vomiting | ||
| Reops | 7 (11.3%) | 1 (2.1%) | 2 (5.2%) |
| 1 screw revision | 1 ASD | 1 pseudarthrosis | |
| 3 pseudarthrosis | 1 ASD | ||
| 1 ASD | |||
| 1 painful hardware | |||
| 1 SSI | |||
| Other complications | 3 (4.8%) minor wound complication | 3 (6.4%) minor wound complication | 1 (2.6%) minor wound complication |
ASD = adjacent-segment disease; SSI = surgical site infection.
Discussion
This study evaluated the impact of age on the outcomes of MI-TLIF. The analysis reveals that patients > 70 years of age had lower rates of MCID achievement for back pain and physical function, and took longer to achieve MCID for back pain and leg pain. However, age was not significantly associated with the overall degree of improvement in PROMs, return to activities, discontinuation of opioids, fusion rates, and complication/reoperation rates.
Our study assessed PROMs by using the VAS for back and leg pain, ODI, and SF-12 PCS surveys, and we found significant improvements in all PROMs in all 3 groups at both early and late time points. Additionally, no significant difference could be demonstrated between the groups in the magnitude of improvement in any PROM at either postoperative time point. A recent study conducted by Goh et al. similarly demonstrated global improvement in PROMs after MI-TLIF in both the ≥ 70-year-old and < 70-year-old patient groups, with no significant difference in the magnitude of improvement between the groups. 17 Two similar studies also demonstrated good clinical outcomes following MI-TLIF irrespective of age. 13,14 These findings of comparable outcomes across age groups emphasize the advantage of the use of minimally invasive techniques for lumbar fusion in the elderly. Previously, Glassman et al. had demonstrated that following open TLIF, older patients may have worse outcomes compared to younger patients. 32 Takahashi et al. had similarly concluded that the clinical benefits of open TLIF in patients older than 70 years were limited compared to the younger patients. 33
Although the overall magnitude of improvement in PROMs did not differ across groups, a difference was noted in MCID achievement rates for back pain and physical function. Compared to their younger counterparts, a lower proportion of patients > 70 years of age achieved MCID for VAS back at the early and late time points (approximately 50% vs 65%–76%) and SF-12 PCS at the late time point (46% vs 64%–74%). Although the time to MCID achievement for disability and physical function was similar (approximately 4 months) across groups, it was comparatively longer for the ≥ 70-year-old group for back pain (2.5 months vs 1.2 and 1.5 months) and leg pain (1.8 months vs 0.9 and 1.2 months). Goh et al. had previously demonstrated no significant difference in MCID achievement rates between the ≥ 70-year-old and < 70-year-old patient groups following MI-TLIF for degenerative spondylolisthesis. 17 Another study also reported similar MCID achievement across age groups (age < 65 years, 65–74 years, ≥ 75 years), except for VAS leg at 6 weeks and 12 weeks. 18 The current study showed no significant difference between the groups in terms of return to activities and discontinuation of opioids postoperatively. No previous study had analyzed the impact of age on these variables following MI-TLIF.
The complication/reoperation rates following MI-TLIF reported in this study are similar to what has been previously described in the literature. A meta-analysis conducted by Jin-Tao et al. had shown a complication rate of 13%. 15 The current study found no major differences in the complication/reoperation rates between the 3 groups, suggesting that age independently is not a risk factor for complications following MI-TLIF. Mohan et al. similarly demonstrated no significant difference in the complication rates following MI-TLIF among 3 different age cohorts (< 65 years, 65–74 years, ≥ 75 years). 18 Patel et al. showed that although postoperative complications not affecting outcome were frequently seen in patients > 65 years of age, there was no significant difference in terms of neurological or cardiopulmonary events based on age. 14
All 3 age groups had statistically similar rates of fusion at 1 year, ranging from 85% to 90%. A meta-analysis by Wu et al. reported a mean fusion rate of 94% following MI-TLIF. 34 A retrospective cohort study by Lin et al., similar to the current study, reported a higher fusion rate in the younger age group of < 65 years (95%) versus the older age group of ≥ 65 years (85%), although their findings were not statistically significant, after single-level MI-TLIF. 13 More recently, Goh et al. demonstrated no significant difference in fusion rates based on age (87% for patients < 70 years and 90% for patients ≥ 70 years; p = 0.135). 17
This study has several limitations. It was a single-institution study, which reduces its generalizability. Patients who were lost to follow-up were not included, which introduces selection bias. There can also be an inherent bias in selecting the "healthy" older patients because some patients, especially in the ≥ 70-year-old group, might not have been medically fit to undergo a fusion procedure. The retrospective study design limits the level of evidence, but the data were prospectively collected, which mitigates recall bias. The inclusion of only 1-level MI-TLIFs limits the generalizability to multilevel surgeries and other types of lumbar interbody fusion. Variables like psychosocial factors, degree of degenerative changes, and difference in CCI between the groups may have contributed to the reported findings but were not accounted for in the analysis. The < 60-year-old cohort did not have a lower age limit, so the youngest patients may have skewed the data in that cohort. The inclusion of patients with a minimum of 1-year and a maximum of 2-year follow-up warrants future studies to assess long-term outcomes. Last, postoperative CT scans done at 1 year to assess evidence of fusion were available for only approximately half of the patients. Also, the 1-year period may not be enough to determine failure of fusion.
Conclusions
Although patients > 70 years of age may be less likely to achieve MCID for back pain and physical function and may take longer to achieve MCID for back and leg pain compared to their younger counterparts, they show an overall significant improvement in PROMs, a similar likelihood of returning to activities and discontinuing opioids, and comparable fusion and complication/reoperation rates following MI-TLIF.
Disclosures
Dr. Sheha reported personal fees from TheraCell outside the submitted work. Dr. Iyer reported personal fees from Stryker Corp., Healthgrades, and Globus Medical, Inc., outside the submitted work; ownership interest in HS2, LLC; and research support from Innovasis. Dr. Qureshi reported ownership/equity/investment in Tissue Differentiation Intelligence; he also reported personal fees from the following: Stryker K2M (royalties from intellectual property, designer, consultant); SpineGuard, Inc. (consultant); Globus Medical, Inc. (royalties from intellectual property, speakers’ bureau, consultant); Simplify Medical, Inc. (clinical event committee); AMOpportunities (honoraria); Surgalign (consultant); Viseon, Inc. (research support [either personally or through the Hospital for Special Surgery], consultant); HS2, LLC (ownership/equity/investment); LifeLink.com Inc. (medical or scientific advisory board membership); Spinal Simplicity, LLC (medical or scientific advisory board membership); and Contemporary Spine Surgery (editorial board) outside the submitted work. Dr. Qureshi also reported the following. North American Spine Society (NASS)—1) Political Engagement Committee member, 2) Payor Policy Review Committee member, 3) SpinePAC Advisory Committee member, and 4) CME Committee member. Annals of Translational Medicine (ATM)—Editorial Board. Hospital Special Surgery Journal—Editorial Board/Senior Associate Editor (2021–2024). Society of Minimally Invasive Spine Surgery (SMISS)—1) Program Committee member, 2) 2018 Annual Meeting Program chair, 3) Board of Directors (2021–2024), 4) Professional Society member of Directors/Trustees/Governors/Managers, member at large, or committee member. Lumbar Spine Research Society (LSRS)—1) Website Committee member (2020–2022), 2) Professional Society member of Directors/Trustees/Governors/Managers, member at large, or committee member. Cervical Spine Research Society (CSRS)—1) Publications Committee member (2019–2022), 2) Professional Society member. Minimally Invasive Spine Study Group Board of Directors—Treasurer. Association of Bone and Joint Surgeons (ABJS)—1) Program Committee member, 2) Professional Society member. International Society for the Advancement of Spine Surgery (ISASS)—1) Education Committee, 2) Program Committee, 3) 2021 Annual Meeting Program chair, 4) Professional Society member.
Author Contributions
Conception and design: Qureshi, Shahi, Shinn, Araghi, Sheha, Dowdell, Iyer. Acquisition of data: Qureshi, Shahi, Song, Araghi, Melissaridou, Sheha, Dowdell. Analysis and interpretation of data: Shahi, Dalal, Shinn, Song, Araghi, Melissaridou, Sheha, Dowdell, Iyer. Drafting the article: Shahi, Dalal, Song, Araghi. Critically revising the article: Qureshi, Shahi, Dalal, Shinn, Dowdell, Iyer. Reviewed submitted version of manuscript: Qureshi, Shahi, Dalal, Song, Sheha, Dowdell, Iyer. Approved the final version of the manuscript on behalf of all authors: Qureshi. Statistical analysis: Shahi, Shinn, Dowdell. Administrative/technical/material support: Qureshi. Study supervision: Qureshi, Sheha, Dowdell, Iyer.
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