Patient Frailty Influences Outcome After Open, But Not Minimally Invasive, Transforaminal Interbody Fusion: A Case Series of 115 Patients With Lumbar Degenerative Disease : Operative Neurosurgery

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Patient Frailty Influences Outcome After Open, But Not Minimally Invasive, Transforaminal Interbody Fusion: A Case Series of 115 Patients With Lumbar Degenerative Disease

Burke, John F. MD, PhD*; Garcia, Joseph H. MD; Safaee, Michael M. MD*; Wong, Christopher BS§; Gill, Sabraj A. BS*; Chou, Dean MD*; Mummaneni, Praveen V. MD, MBA*; Deviren, Vedat MD; Ames, Christopher P. MD*; Clark, Aaron J. MD, PhD*

Author Information
Operative Neurosurgery 24(6):p 565-571, June 2023. | DOI: 10.1227/ons.0000000000000665
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Abstract

ABBREVIATIONS:

ASD-FI
Adult Spinal Deformity Frailty Index
LL
lumbar lordosis
LOS
length of stay
MIS
minimally invasive surgery
O-TLIF
open TLIF
PI
pelvic incidence
PT
pelvic tilt
SS
sacral slope
TLIF
transforaminal lumbar interbody fusion.

Frailty has emerged as a tool to predict preoperative risk of complications after spinal surgery.1,2 Frailty is a relatively recent diagnosis that captures differences in chronological and physiological age.2 The adult spinal deformity frailty index (ASD-FI) quantifies frailty and is correlated with length of stay (LOS), major complications, and reoperation rates after adult spinal deformity surgery.3,4 These data suggest that frailty is a major predictor of recovery after surgical treatment of deformity,5 neoplasms,6 and degenerative conditions.7

Although the association between preoperative frailty and outcome has been convincingly shown for large spinal operations, it is less well studied after less complex or minimally invasive surgery (MIS). Although previous studies suggest that frailty is not strongly associated with outcome after less complex spinal surgery,8 more recent data have shown that frailty predicts complication rate9 and LOS10 after transforaminal lumbar interbody fusion (TLIF) procedures. However, whether frailty can be used to risk stratify patients to MIS vs open procedures for lumbar degenerative pathology is not known.

Pertinent to this, TLIF procedures can be performed using either open transforaminal lumbar interbody fusion (O-TLIF) or MIS-TLIF techniques.11 Several studies have directly compared MIS-TLIF vs O-TLIF in obese patients and found that MIS-TLIF is associated with reduced intra- and perioperative complications12-15; however, there is no significant difference in long-term pain reduction.16 Similarly, several systematic reviews have shown that MIS-TLIF is associated with reduced blood loss and intraoperative complications, but there is not a clear benefit of MIS-TLIF in long-term outcomes.17-21 Thus, there are currently scant objective data to guide surgical decision-making between MIS- vs O-TLIF operations.

We hypothesized that patients with high frailty scores would have an overall benefit for MIS-TLIF compared with O-TLIF, but patients with low frailty scores would have similar outcomes for these procedures. To investigate this, we used a retrospective database composed of consecutive patients undergoing MIS-TLIF vs O-TLIF.

METHODS

Patient Population

All patients were identified consecutively at a single institution for the period from June 2013 to July 2018. Inclusion criteria were TLIF surgery for lumbar degenerative pathologies. We included 1- to 3-level transforaminal interbody fusions in this retrospective review. Exclusion criteria were (1) age younger than 18 years, (2) TLIF for deformity/tumors/infections, and (3) previous surgery within 30 days. Demographic and surgical parameters were collected retrospectively. Follow-up information was collected from the initial postoperative visit (6 weeks after surgery) with at least a 2-year follow-up after surgery. After initial collection, all analyses were performed on deidentified data. Given the retrospective nature of data collection, consent and Institutional Review Board approval were not deemed necessary.

Demographic, radiological, and surgical variables are reported separately for patients in the O-TLIF condition and for patients in the MIS-TLIF condition. Radiographic variables were measured on standing lateral radiographs of the lumbar spine and included pelvic incidence, pelvic tilt, lumbar lordosis (LL), sacral slope, and the derived variable pelvic incidence LL, which should be less than 10° in the well-balanced spine.22 More global metrics of spinal alignment such as the sagittal vertical axis could not be measured because full-length scoliosis radiographs were not routinely obtained in this case series. This case series has been reported in line with the Preferred Reporting of Case Series in Surgery (PROCESS) Guideline. The surgical technique for the MIS-TLIF is described previously.23

The ASD-FI is a standard index of frailty that has been validated on large prospective databases of patients undergoing deformity surgery.24 It ranges from 0 to 1, is calculated based on 40 binary variables that reflect the patient's medical comorbidities, and can be calculated retrospectively from the medical chart.2 Although there are several methods of calculating frailty, the ASD-FI has been externally validated on a large prospectively collected cohort of spinal surgical patients.3,4 In addition, the ASD-FI is disease-specific—it is tailored to the spinal surgery population. Thus, although the ASD-FI has been developed for deformity surgery, it is the most specific measure of frailty that applies to the spinal degenerative population. To calculate the ASD-FI, all variables that met criteria for inclusion were recorded as binary, and the mean score of all such binary variables was calculated, resulting in a frailty index continuously ranging from 0 to 1. Patients with scores of >0.3 were considered severely frail.

Our statistical approach was separated into 3 sections: univariate analysis, multivariable analysis, and post hoc analysis. In general, our strategy was to broadly test all measured variables across both outcome measures (presence of revision surgery and discharge to a location other than home) in the univariate analysis. We compared binary variables using Fisher's exact test and continuous variables using a t-test. Then, we included the variables that trended to be significant (P < .1) in a multivariate logistic regression. The multivariate analysis was run separately for both outcome measures. Significance was reported using odds ratios and 95% CI for the multivariate analysis. Finally, in our post hoc analysis, we specifically examined the relation among frailty, outcome, and open vs MIS TLIF to better understand the interaction between these clinically salient variables. All significance thresholds were set to 0.05. All analyses were conducted using MATLAB (version 2018b, The MathWorks).

RESULTS

One hundred fifteen patients met inclusion criteria, of whom 44 underwent an MIS-TLIF procedure and 71 underwent an O-TLIF procedure. The indications for surgery are listed in Table 1. The patient demographic information is given in Table 2. There were no differences between the O-TLIF group and the MIS-TLIF groups in the number of levels fused, the presence of previous surgery, the frailty index, the percentage of female patients, and preoperative lumbosacral radiographic parameters. However, there was a trend for the MIS-TLIF group to have a larger percentage of comorbidities (P < .10). There was also a significant age difference between the groups, with the O-TLIF group being older. The percentage of patients older than 75 years was 2.3% (1/44) in the MIS group and 11.3% (8/71) in the O-TLIF group. The O-TLIF group also had a significantly longer LOS than the MIS-TLIF group.

TABLE 1. - Indications for Surgery
Indication for surgery N Percentage (%)
Spondylolisthesis 79 68.7
Severe disk disease ± facet cyst 18 15.7
Recurrent disk disease 9 7.8
Scoliosis (fractional curve) 6 5.2
Previous arthrodesis (ASD/PSA) 3 2.6
ASD, adjacent segment disease; N, the number of patients in each group; PSA, pseudarthrosis.
The indications for surgery are sorted by prevalence.

TABLE 2. - Patient Demographic and Radiographic Information
Variables O-TLIF MIS-TLIF P-value
N 71 44
Demographic information
 Age, y 62.3 (12.1 SD) 53.6 (12.1 SD) <.0003
 Perc of female 49.3% 56.8% .4345
Frailty index 0.2 (0.2 SD) 0.3 (0.2 SD) .6866
 Number of levels 1.2 (0.4 SD) 1.4 (0.6 SD) .1400
 >3 comorbidities 14.1% 27.3% .0806
 Previous surgery 28.2% 15.9% .1317
Radiographic information
 PI 55.9 (12.3 SD) 51.7 (11.6 SD) .0687
 LL 48.4 (14.6 SD) 46.8 (14.0 SD) .5630
 PI-LL 7.5 (14.1 SD) 4.9 (16.8 SD) .3661
 PT 21.7 (9.8 SD) 19.4 (11.4 SD) .2567
 SS 34.7 (9.6 SD) 32.3 (8.6 SD) .1760
Surgical information
 Perc of revision 28.2% 11.4% .0337
 LOS 4.5 (1.5 SD) 3.0 (1.6 SD) <.0001
 Perc. of discharge to a location other than home 28.2% 13.6% .0702
LL, lumbar lordosis; LOS, length of stay; MIS-TLIF, minimally invasive surgery-transforaminal lumbar interbody fusion; N, the number of patients in each group; O-TLIF, open TLIF; Perc, percentage; PI, pelvic incidence; PT, pelvic tilt; SS, sacral slope.

We next performed several univariate analyses to determine which variables were associated with the 2 outcome variables: the need for subsequent revision surgery and discharge to a location other than home (Table 3). Regarding the need for revision surgery, higher frailty (P = .0007), the presence of previous surgery (P = .0278), and the percentage of patients undergoing O-TLIF (P = .0337) were all significantly associated with a greater rate of revision surgery. Regarding the likelihood of discharging to a location other than home, higher age (P = .0019), higher frailty (P < .0001), and the presence of 3 or more comorbidities (P = .0224) were all significantly associated with a greater risk of revision surgery. In addition, patients undergoing O-TLIF compared with MIS-TLIF trended to have a greater probability of discharging to a location other than home (P = .0702).

TABLE 3. - Univariate Comparisons
Variables Revision surgery Discharge other than home
Revision No revision P Home Not home P
N 25 90 89 26
Demographic information
 Age, y 61.4 (13.1 SD) 58.2 (12.7 SD) .2799 56.9 (12.6 SD) 65.7 (10.9 SD) .0019
 Perc. of female 52.0% 52.2% .9843 53.9% 46.2% .4848
Frailty index 0.4 (0.1 SD) 0.3 (0.2 SD) .0007 0.25 (0.1 SD) 0.41 (0.2 SD) <.0001
 Number of levels 1.3 (0.5 SD) 1.3 (0.5 SD) .9840 1.28 (0.5 SD) 1.27 (0.5 SD) .9151
 >3 comorbidities 24.0% 17.8% .4841 14.6% 34.6% .0224
 Previous surgery 18.9% 40.0% .0278 25.8% 15.3% .2684
Radiographic information
 PI 54.0 (14.3 SD) 54.3 (11.6 SD) .9124 53.7 (12.2 SD) 56.4 (11.9 SD) .3174
 LL 46.0 (17.8 SD) 48.3 (13.3 SD) .4745 48.2 (14.1 SD) 46.4 (15.2 SD) .5739
 PI-LL 8.1 (14.8 SD) 6.1 (15.3 SD) .5574 5.5 (15.2 SD) 10.0 (14.8 SD) .1818
 PT 22.3 (9.7 SD) 20.4 (10.7 SD) .4404 20.4 (10.7 SD) 22.3 (9.4 SD) .4078
 SS 32.3 (11.4 SD) 34.2 (8.6 SD) .3566 33.7 (9.0 SD) 34.2 (10.3 SD) .8261
Surgical information
 Perc. of MIS-TLIF 20.0% 43.3% .0337 42.7% 23.1% .0702
LL, lumbar lordosis; MIS-TLIF, minimally invasive surgery-transforaminal lumbar interbody fusion; N, the number of patients in each group; Perc, percentage, PI, pelvic incidence; PT, pelvic tilt; SS, sacral slope.
Univariate comparisons for the patients who underwent revision surgery vs no revision surgery are shown in the left, and univariate comparisons for those who were discharged to a location other than home vs not are shown on the right. Comparisons are shown for demographic information, radiographic information, and surgical information.

We next used the variables that trended toward significance (P < .1) in the univariate analysis as predictors in a multiple regression model to predict the 2 outcome variables: the need for subsequent revision surgery and discharge to a location other than home (Table 4). Specifically, age, frailty, the presence of previous surgery, the approach (O-TLIF vs MIS-TLIF), and the presence of 3 or more comorbidities were used as predictors. In both cases, only frailty was independently associated with both reoperation (odds ratio 8.1, 95% CI 2.5-26.1, P = .0005) and discharge to a location other than home (odds ratio 3.9, 95% CI 1.2-12.7, P = .0239).

TABLE 4. - Multivariate Analysis

Prediction variable
Revision rate Discharge nonhome rate
OR (95% CI) P OR (95% CI) P
Age 0.99 (0.95-2.75) .2208 1.04 (0.99-1.10) .0761
>3 comorbidities 0.47 (0.12-1.04) .7240 1.73 (0.43-6.91) .4378
MIS 0.36 (0.11-1.86) .2833 0.36 (0.10-1.28) .1148
FI > 0.3 8.07 (2.49-26.10) .0005 3.90 (1.19-12.72) .0239
Previous surgery 2.58 (0.85-7.75) .0910 0.26 (0.07-1.01) .0523
FI, frailty index; MIS, minimally invasive surgery; OR, odds ratio.
The univariate variables that trended to be significant (P < .1) were included as predictors in a multivariate logistic regression to predict the presence of subsequent revision surgery (left) and discharge to a location other than home (right). The OR, 95% CI of the OR, and the P-value of each predictor in the model are shown.

Of the severely frail patients who underwent revision after O-TLIF, the average LOS was 4.36 days (SD 1.95 days) and 30.8% of patients were discharged to a location other than home. There were 3 reoperations after the revision surgery in this cohort (18.7% revision rate): 1 for wound infection shortly after the revision surgery and 2 for extension of the previous fusion more than 3 years after the revision surgery.

We performed a post hoc analysis to specifically examine the relation between frailty, outcome, and MIS vs open TLIF. Figure 1 shows the percentage of each outcome (rate of revision surgery in Figure 1A and the rate of discharge to a location other than home in Figure 1B) separately for patients categorized by both O-TLIF vs MIS-TLIF and frail (ASD-FI > 0.3) and nonfrail (ASD-FI < 0.3). Frail patients undergoing O-TLIF had a higher revision surgery rate (51.72%) compared with frail patients undergoing MIS-TLIF (16.7%), nonfrail patients undergoing O-TLIF (7.5%), and nonfrail patients undergoing MIS-TLIF (7.7%). As expected, a post hoc χ2 test comparing revision surgery rate for O-TLIF vs MIS-TLIF was significant for frail patients (P = .0087) but was not significant for nonfrail patients (P = .9770). Similarly, frail patients undergoing O-TLIF had a higher rate of discharging to a location other than home (48.3%) compared with frail patients undergoing MIS-TLIF (22.2%), nonfrail patients undergoing O-TLIF (12.5%), and nonfrail patients undergoing MIS-TLIF (7.7%). The post hoc χ2 test comparing discharge location for O-TLIF vs MIS-TLIF trended toward significance for frail patients (P = .0700) but was not significant for nonfrail patients (P = .5354).

F1
FIGURE 1.:
Post hoc analysis examining interaction of frailty and open vs MIS-TLIF. A, The percentage of patients undergoing subsequent revision surgery (y-axis) is shown for 4 groups: nonfrail patients undergoing O-TLIF (far left), nonfrail patients undergoing MIS-TLIF (middle left), frail patients undergoing O-TLIF (middle right), frail patients undergoing MIS-TLIF (far right). B, Identical grouping of data demonstrating the percentage of patients discharged to a location other than home. ASD-FI, Adult Spinal Deformity Frailty Index; MIS-TLIF, minimally invasive surgery-transforaminal lumbar interbody fusion; O-TLIF, open TLIF.

Table 5 documents the reasons for revision surgery in both the O-TLIF and the MIS-TLIF groups.

TABLE 5. - Reasons for revision surgery
Reason for revision O-TLIF MIS-TLIF
ASD 7 (9.7%) 0 (0.0%)
Radiographic failure 7 (9.7%) 2 (2.8%)
Infection 3 (4.2%) 0 (0.0%)
CSF leak 1 (1.4%) 0 (0.0%)
Residual stenosis 1 (1.4%) 3 (4.2%)
ASD, adjacent segment disease; CSF, cerebrospinal fluid; MIS-TLIF, minimally invasive surgery-transforaminal lumbar interbody fusion; O-TLIF, open TLIF.
The reasons for the revision surgery in each group (O-TLIF vs MIS-TLIF) are listed. The number of patients is given in each column, and the percentage of each row is expressed relative to the number of patients in each group (O-TIF and MIS-TLIF, respectively). Radiographic failure includes proximal junctional kyphosis, worsening deformity, hardware malposition, and pseudarthrosis.

DISCUSSION

The value of the TLIF procedure can be achieved from both open vs MIS approaches, and several studies have addressed the relative merits of each approach. Hammad et al25 presented a meta-analysis comparing O-TLIF vs MIS-TLIF and found that both approaches have statistically similar long-term outcomes, with MIS-TLIF performing better regarding blood loss, LOS, and cost savings and O-TLIF performing better regarding total operative time. Ge et al26 performed a retrospective review of 275 patients and found a significant advantage of MIS-TLIF compared with O-TLIF regarding complication profile, LOS, and blood loos, but long-term outcomes were not assessed. Another recent meta-analysis of obese patients undergoing TLIF demonstrated decreased LOS, blood loss, and a lower rate of dural tears for MIS compared with open TLIF.16 Similarly, Khan et al showed that MIS TLIF was associated with decreases in LOS, blood loss, and complication relative to open TLIF, but both procedures had similar long-term outcomes.17 Overall, these data suggest that the MIS-TLIF has a better short-term complication profile, but long-term improvements in pain and fusion rates are similar for MIS and open approaches. Thus, there is often equipoise about which approach to choose for a given patient.

Regarding the decision to pursue an open vs MIS TLIF, we note that there are occasions when O-TLIF should be pursued over MIS-TLIF. Most importantly, because O-TLIF allows for removal of posterior bony elements, O-TLIF is often preferred in cases where surgeons need to both treat degenerative pathology and restore LL. In this article, we suggest that frailty could also be used to choose between these surgical options because patients with a high frailty score exhibited worse outcomes for O-TLIF but not for MIS TLIF. In addition, our multivariate analysis revealed that frailty was an independent predictor of the need for revision surgery and discharge disposition. Thus, when patients require a TLIF, we suggest that surgeons use a metric of frailty to determine whether the open or MIS options are pursued.

One unique aspect of this database was the high percentage of revision surgery cases (28.2% for O-TLIF and 11.4% for MIS TLIF). Although these numbers seem to be high, the reported range for revision surgery after MIS-TLIF is 0.4% to 14.2%,27 with several studies reporting a revision rate larger than 10% after MIS-TLIF.28,29 For open TLIF procedures, the published range of reoperation is around 8% to 12%.26,28,30 In this study, the rate of reoperation for O-TLIF for nonfrail patients (ASD-FI < 0.3) was 7.5%, which falls slightly below this range. However, our study does show that the rate of revision surgery increases to 51.7% for patients undergoing O-TLIF surgery who are severely frail (ASD-FI > 0.3), which is the main finding of this study. Thus, the high rate of revision surgery in our series likely reflects the high rate of severely frail patients in our database.

We note that there were some baseline differences between the open and the MIS TLIF cohorts. In particular, the open cohort was older and tended to have fewer comorbidities. The lower number of comorbidities is expected because patients who are not able to tolerate an open procedure will often be offered a MIS procedure instead. Although the older age of patients in the O-TLIF cohort may seem to be less expected, a large meta-analysis comparing open and MIS TLIF procedures similarly found a trend (P < .07) that younger patients tended to have MIS compared with open procedures.31 Although it is possible that older patients have a greater probability of previous spine surgery (necessitating an open approach), we note that there were no significant differences between the presence of previous surgery in the open and the MIS cohorts. Thus, it is not entirely clear why younger patients had a higher rate of MIS-TLIF than older patients. Regardless, our multivariate analysis included age as a predictor, which allowed us to investigate the role of frailty independent of the correlation of age with MIS vs open approaches. Using frailty, we were able to show a long-term difference between the open and MIS TLIF procedures, which has not been robustly shown in previous studies.13,17,19

Limitations

Patients were identified in a retrospective fashion, and the reasons that each surgeon chose open vs MIS procedures were not known at the time of analyses. We addressed this source of bias by performing multivariate statistics; however, a prospective trial would better address this concern. We also did not control for tubular vs pedicle screw–based MIS retractor systems; ideally, it should be shown that our results hold regardless of MIS technical implementation. Another limitation is that postoperative computed tomography scans were not routinely obtained, which limited our ability to assess fusion rates across patients. Although fusion rates can be inferred from dynamic radiographs, recent research shows that computed tomography scans are the most accurate method of assessing fusion of interbody grafts.32 We therefore leave it to a future study to address the issue of how frailty affects fusion rates after lumbar TLIF.

CONCLUSION

In this article, we show that for patients who are frail and undergo an open TLIF surgery for lumbar degenerative disease, there are a higher rate of subsequent revision surgery and a higher rate of discharge to a location other than home than for patients who are frail and undergo an MIS-TLIF surgery. These data suggest that surgeons may like to pursue MIS approaches for frail patients, with all other factors being equal.

Funding

This study did not receive any funding or financial support. Praveen V. Mummaneni has grants from NREF, NIH, PCORI, ISSG, and AO Spine.

Disclosures

Dean Chou has financial relationships with Globus and Orthofix. Praveen V. Mummanei has financial relationships with DePuy Synthes, NuVasive, and Globus, is a consultant for Stryker, has stock in Spinicity/ISD, and receives book royalties from Thieme and Springer publishers. Christopher P. Ames receives royalties from Stryker, Biomet Zimmer Spine, and DePuy Synthes. Aaron J. Clark has a financial relationship with NuVasive. The other authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.

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Keywords:

Frailty; TLIF; MIS vs open

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