Abstract
Purpose
Our aim is to examine the gender performance of Patient-Reported Outcome Measurement Information System Physical Function (PROMIS-PF) scores among patients undergoing minimally invasive transforaminal lumbar fusion (MIS TLIF).
Methods
A prospectively collected surgical dataset was retrospectively assessed for eligible patients from March 2015–June 2019. We included patients if they underwent primary MIS TLIF procedures on one or two vertebral levels. We collected baseline demographics, perioperative characteristics, and PROMIS-PF scores for each subject at pre and postoperative timepoints (e.g., 6-weeks, 3-months, 6-months, and 1-year). Chi-squared analyses were utilized to assess categorical variables and a Student’s t-tests analyzed continuous variables. A linear regression was used to analyze PROMIS-PF scores from baseline through all postoperative time points. Finally, we evaluated the PROMIS PF achievement of minimal clinically important difference (MCID) among gender.
Results
192 patients were included: 77 were females and 115 were males. No significant differences were observed among gender subgroups for PROMIS-PF scores at pre- or postoperative evaluations. Compared to males, females experienced significantly greater postoperative improvement with PROMIS-PF scores at the 3-month assessments, though no significant gender differences were observed during later follow-up evaluations at 6-months or one year. Females were observed to have significant PROMIS-PF score improvement from their preoperative evaluation to each postoperative score. Males were assessed to have statistically significant postoperative (e.g., at 3-months, 6-months, and 1-year) PROMIS-PF score improvement from their preoperative PROMIS-PF scores. There were no significant differences among gender in achieving MCID at any postoperative time interval.
Conclusion
Among gender, we observed no statistically significant difference in PROMIS-PF scores during the pre- or postoperative evaluations. Additionally, with no difference in the rate of achieving PROMIS-PF MCID postoperatively, this study established that both genders should experience similar functional outcomes following MIS TLIF.
Keywords: Minimally invasive spine surgery, Gender, MIS TLIF, Patient-reported outcome measurement information system, Physical function, PROMIS PF
1. Introduction
The Patient-Reported Outcome Measurement Information System (PROMIS) is becoming widely implemented to evaluate patient health status and wellbeing in a variety of surgical and nonsurgical settings.1,2 The National Institutes of Health (NIH) initially created the PROMIS set of instruments based Computer Adaptive Testing (CAT) as well as item response theory. The goal of PROMIS was to improve on previously developed patient reported outcome measures (PROM) by developing a time-effective survey that could be remotely administered for patients either at home or in clinic. The physical function (PF) and disability version of PROMIS can be used for patients independent of disease state.3,4 Compared to numerous earlier PROMs, PROMIS offers advantages due to its ability to gather a comprehensive patient health profile in a timely and efficient manner.
PROMIS instruments offer several domains that can be utilized to evaluate mental, physical or social patient health statuses. Nonetheless, the PROMIS PF domain is an important outcome measurement within spine surgery because of its validated assessment of coordination, mobility, and strength. While the PROMIS PF metric is validated for use in many clinical settings, there are still questions regarding its ability to evaluate outcomes within specific patient populations undergoing spine surgery operations.
Patient characteristics including age, insurance status, and diabetes status have previously been associated with poor postoperative outcomes. However, gender differences may also have implications on surgical recovery.5 Biological differences between men and women can have a significant influence on disease manifestation and treatment outcomes, especially within the realm of degenerative spinal conditions.6, 7, 8 Gender has previously been associated with differences in the development of spinal pathology as well as pain perception and functional impairment.10, 11, 12, 9 Thus, significant attention has been given to the study of gender-related influences of spinal conditions, with the goal of developing targeted prevention, diagnostic, and treatment strategies. We sought to evaluate pre- and postoperative PROMIS PF scores among gender in order to identify potential differences in lumbar fusion postoperative recovery. Our null hypothesis was that, among patients of both genders, there would be no difference between the mean pre- and postoperative PROMIS scores of either gender.
Gender differences have been evaluated by other researchers as a potential contributing factor for adverse patient events and worse patient survey scores following spinal surgeries, though we were unable to find any investigations that used the PROMIS PF instrument to evaluate possible differences in clinical outcomes among gender.10,13,14 Furthermore, to our knowledge, the vast majority of investigations that have assessed gender differences among lumbar spine surgery populations have found significant gender differences at final times of follow-up. Therefore, the goal of our investigation was to evaluate potential gender differences in postoperative recovery among patients undergoing minimally invasive transforaminal lumbar fusion (MIS TLIF). MIS TLIF is a common spine surgery that is typically used to treat conditions such as degenerative disc disease, spondylolisthesis, and recurrent disc herniation. The aim of our study is to identify possible gender differences in pre- and postoperative outcomes following MIS TLIF through an analysis of PROMIS PF instrument scores.
2. Methods
2.1. Study population
We conducted this study after obtaining approval from our Institutional Review Board (ORA# 14051301). A prospectively collected surgical registry of patient records was assessed for eligible patients from March 2015 to June 2019. Eligible patients were those who received a primary, one- or two-vertebral level MIS TLIF procedure for degenerative spinal pathology. Patients were removed from this study if they had incomplete preoperative PROMIS PF evaluations. All spine surgeries in this study were performed at one academic hospital system by the senior author.
2.2. Collection of patient records
Patients were organized into subgroups by gender. We recorded demographic variables for all patients, including age (at date of surgery), body mass index ([BMI], kg/m2), history of diabetes, insurance status, smoking status, diabetes mellitus, and comorbidity burden. Comorbidity burden was represented with the Charlson Comorbidity Index (CCI) value after excluding the age component. Removing the CCI age component allowed for the independent evaluation of comorbidity without over-representing either variable. Preoperative spinal pathologies were assessed including herniated nucleus pulposus, degenerative disc disease, isthmic spondylolisthesis, degenerative spondylolisthesis, and foraminal stenosis. Perioperative variables included number of fusion levels, operative duration (in minutes, from skin incision to closure), estimated intraoperative blood loss (EBL), postoperative length of stay (in hours), and discharge day. We novelly evaluated PROMIS PF scores that were collected prior to surgery, and again postoperatively at 6-weeks, 3-months, 6-months, and at 1-year clinic visits. Finally, we summarized studies relevant to this investigation according to their assessed outcome instruments and noted their overall findings with regard to gender differences.
2.3. Statistical analysis
Our statistical calculations and analysis were conducted with StataSE® 16.0 for Mac (StataCorp LLC, College Station, Texas). We used Chi-squared and Student’s t-tests, as appropriate, to compare baseline demographic variables and perioperative characteristics by gender. We evaluated potential improvement with a paired t-test to compare PROMIS PF scores from preoperative to postoperative time points within each gender. A linear regression was used to compare PROMIS PF scores among gender at each timepoint. Achievement rate of the PROMIS PF score minimal clinically important difference (MCID) was evaluated by gender at each timepoint using chi-squared analysis. MCID values for PROMIS PF = 8.0 were derived from Hung et al 2018.15 Statistical significance was set at p < 0.050.
3. Results
After selection, 192 MIS TLIF patients were included in our study. 77 (40.1%) patients were females and 115 (59.9%) were male. Evaluation of baseline demographics and spinal pathologies revealed no statistically significant differences among gender (Table 1). We observed no statistically significant difference among gender when assessing perioperative variables such as day of discharge, EBL, hospital length of stay, operative time duration, or number of involved operative levels (Table 2). The cohort had 180 patients that underwent an elective single-level procedure and 12 patients who underwent a two-level operation. Although not significantly different, EBL approached statistical significance between genders (Male 48.5 ml vs Female 63.1 ml, p = 0.051). There was no statistically significant difference among gender in PROMIS PF score at any of the evaluated timepoints (Table 3). PROMIS PF scores were not significantly different than males at preoperative and all postoperative timepoints. Although, females experienced significantly more improvement in postoperative PROMIS PF scores when compared to males at the 3-month timepoint (7.6 vs 4.2; p = 0.016).
Table 1.
Baseline characteristics by gender.
| Characteristic | Male (N = 115) | Female (N = 77) | †p-value∗ |
|---|---|---|---|
| Age (Mean ± SD) |
50.6 ± 11.0 |
53.2 ± 10.7 |
0.105 |
| Smoking Status (n) | 0.053 | ||
| Non-smoker | 92.2% (106) | 83.1% (64) | |
| Smoker |
7.8% (9) |
16.9% (13) |
|
| Diabetes Status (n) | 0.900 | ||
| Non-diabetic | 93.0% (107) | 93.5% (72) | |
| Diabetic |
7.0% (8) |
6.5% (5) |
|
| BMI Category (n) | 0.576 | ||
| Non-Obese (<30 kg/m2) | 53.0% (61) | 57.1% (44) | |
| Obese (≥30 kg/m2) |
47.0% (54) |
42.9% (33) |
|
| Insurance (n) | 0.177 | ||
| Medicare/Medicaid | 1.7% (2) | 5.2% (4) | |
| Private/Workers’ Compensation |
98.3% (113) |
94.8% (73) |
|
| Ageless CCI (Mean ± SD) |
0.8 ± 0.9 |
1.0 ± 1.1 |
0.099 |
| Spinal Pathologies | |||
| Herniated Nucleus Pulposus | 18.3% (21) | 10.4% (8) | 0.135 |
| Degenerative Disc Disease | 46.1% (53) | 54.6% (42) | 0.251 |
| Isthmic Spondylolisthesis | 19.1% (22) | 26.0% (20) | 0.338 |
| Degenerative Spondylolisthesis | 54.8% (63) | 58.4% (45) | 0.710 |
| Foraminal Stenosis | 47.8% (55) | 59.7% (46) | 0.105 |
SD = Standard Deviation; CCI = Charlson Comorbidity Index; BMI = Body Mass Index.
∗Boldface indicate statistical significance.
†p-value was calculated for each category using chi square analysis (categorical) or student’s t-test (continuous).
Table 2.
Perioperative characteristics by gender.
| Characteristic | Male (N = 115) | Female (N = 77) | †p-value |
|---|---|---|---|
| Number of Fusion Levels | 0.270 | ||
| 1-Level | 92.2% (106) | 96.1% (74) | |
| 2-Level |
3.9% (9) |
3.9% (3) |
|
| Operative Time (Mean ± SD, min) |
126.9 ± 31.2 |
129.0 ± 25.7 |
0.216 |
| Estimated Blood Loss (Mean ± SD, mL) |
48.5 ± 24.5 |
63.1 ± 73.8 |
0.051 |
| Length of Stay (Mean ± SD, hours) |
31.8 ± 20.8 |
30.4 ± 15.6 |
0.630 |
| Discharge Date (n) | 0.698 | ||
| POD 0 | 12.5% (14) | 12.0% (9) | |
| POD 1 | 54.5% (61) | 56.0% (42) | |
| POD 2 | 17.0% (19) | 21.3% (16) | |
| POD 3+ | 16.1% (18) | 10.7% (8) |
SD = Standard Deviation; POD = Postoperative Day.
†p-value was calculated for each category using multivariate linear regression (continuous) or chi square analysis (categorical).
Table 3.
PROMIS PF scores by gender.
| PROMIS | Male (N = 115) | Female (N = 77) | †p-value∗ |
|---|---|---|---|
| PROMIS (Mean ± SD) | |||
| Preoperative | 35.5 ± 6.0 | 34.2 ± 6.2 | 0.139 |
| 6-week | 37.1 ± 6.9 | 36.0 ± 6.8 | 0.329 |
| 3-month | 40.6 ± 7.5 | 40.9 ± 7.8 | 0.833 |
| 6-month | 44.2 ± 7.5 | 42.7 ± 7.9 | 0.290 |
| 1-year |
45.3 ± 9.5 |
43.9 ± 10.0 |
0.479 |
| Postoperative Change (Postop – Preop) (Mean ± SD) | |||
| 6-week Δ | 1.3 ± 6.5 | 2.2 ± 6.7 | 0.433 |
| 3-month Δ | 4.2 ± 6.8 | 7.6 ± 8.7 | 0.016 |
| 6-month Δ | 8.5 ± 6.8 | 7.4 ± 9.1 | 0.446 |
| 1-year Δ | 9.8 ± 7.2 | 9.5 ± 8.8 | 0.873 |
SD=Standard Deviation; PROMIS PF = Patient Reported Outcomes Measurement Information System Physical Function.
Δ = Postoperative PROMIS – Preoperative PROMIS.
†p-values calculated for each category using multivariate linear regression.
∗Boldface indicate statistical significance.
Females demonstrated a statistically significant improvement over baseline PROMIS PF scores at all postoperative timepoints, beginning at six weeks, three months, six months and one year after surgery (all p ≤ 0.001, Table 4). Males had improvement in postoperative PROMIS PF scores from baseline, with significant improvement at three months, six months, and one year (all p < 0.001) but only approached significance at the six week timepoint postoperatively (p = 0.063). Ultimately, there were no differences among genders at more long term follow-up evaluations, including 6 months, or our last analyzed follow-up assessment, at one-year. Furthermore, the rate of achieving MCID for PROMIS PF was not significantly different among genders at six weeks, three months, six months and one year after surgery (Table 5). Finally, the studies relevant to gender differences among patients undergoing lumbar surgery that were reviewed in this investigation revealed that the literature is scarce with regard to PROMIS PF score analyses (Table 6).
Table 4.
Changes in PROMIS PF from preoperative baseline within each cohort.
| Male (N = 115) | †p-value∗ | Female (N = 77) | †p-value∗ | |
|---|---|---|---|---|
| PROMIS PF (Mean ± SD) | ||||
| Preoperative | 35.5 ± 6.0 | 34.2 ± 6.2 | ||
| 6-week Δ | 1.3 ± 6.5 | 0.063 | 2.2 ± 6.7 | 0.014 |
| 3-month Δ | 4.2 ± 6.8 | <0.001 | 7.6 ± 8.7 | <0.001 |
| 6-month Δ | 8.5 ± 6.8 | <0.001 | 7.4 ± 9.1 | <0.001 |
| 1-year Δ | 9.8 ± 7.2 | <0.001 | 9.5 ± 8.8 | <0.001 |
SD = Standard Deviation; PROMIS = Patient Reported Outcomes Measurement Information System.
Δ = Postoperative PROMIS – Preoperative PROMIS.
†p-values calculated for each category using a paired t-test within each gender cohort.
∗Boldface indicate statistical significance.
Table 5.
Achievement of minimal clinically important difference (MCID).
| Gender | Preop to 6wk | Preop to 3mo | Preop to 6mo | Preop to 12mo | Overall met MCID |
|---|---|---|---|---|---|
| PROMIS PF | |||||
| Female | 75.3% | 61.0% | 55.8% | 49.4% | 88.3% |
| Male | 69.6% | 67.0% | 62.6% | 53.0% | 94.8% |
| p-value | 0.384 | 0.401 | 0.349 | 0.616 | 0.102 |
PROMIS PF MCID = 8.0 value derived from Hung et al 2018.
Table 6.
Gender outcome differences among patients undergoing lumbar spine surgery.
| Study Author (Year, Journal) | Outcomes | Outcome Instrument Used | Evaluation Timepoints | Conclusion | Gender difference? |
|---|---|---|---|---|---|
| Pochon (2016, European Spine Journal) |
|
|
|
|
Yes |
| Siccoli (2018, European Spine Journal) |
|
|
|
|
Yes |
| Strömqvist (2016, Spine) |
|
|
|
|
Yes |
| Strömqvist (2016, European Spine Journal) |
|
|
|
|
Yes |
| Triebel (2016, The Spine Journal) |
|
|
|
|
Yes |
COMI=Core Outcome Measures Index; EQ-5D = European quality of life 5 dimensions questionnaire; NRS=Numeric rating scale; ODI=Oswestry Disability Index; SF=Short Form; TUG = Timed Up and Go Test; VAS=Visual Analog.
4. Discussion
Since its recent introduction, PROMIS PF has been used to assess health status among patients who have undergone elective spine surgery with regard to their mobility, coordination, and physical strength. PROMIS PF can be utilized in a wide range of spinal conditions and procedures to efficiently measure the preoperative and postoperative outcomes that can be potentially influenced by various factors. Previous studies have demonstrated that, among patients undergoing elective spine surgery for degenerative lumbar pathologies, gender can be a contributing factor in the functional impairment and in the perception of pain.7,10,16, 17, 18, 19, 20 However, to our knowledge, there has been limited research that has evaluated the effects of gender on PROMIS PF outcomes observed in the setting of MIS TLIF.
Our investigation results suggest that, compared to males, female patients undergoing a primary, one- or two-level MIS TLIF procedure for degenerative spinal pathology have a similar postoperative recovery of physical function. With regard to PROMIS PF outcomes, female patients did not demonstrate significantly different pre or postoperative scores. The difference in rate of achieving MCID postoperatively also suggests that female patients are no less likely to regain their physical function and ability compared to male patients following MIS TLIF.
Our results are unique in comparison to observations in other scientific literature evaluating gender differences among patients that have undergone surgery for degenerative lumbar spine pathology. This is one of the first studies to focus on a gender comparison that assesses PROMIS PF scores. Second, while at least one other study did find genders to have equivalent improvements at their final follow-up, no intermediate timepoint comparisons among gender were assessed or compared. Our study elaborates that, although transient differences may exist among genders during postoperative recovery, both genders appear to have a nearly equivalent improvement and ultimate physical function scores at their one-year evaluations. While most studies have observed that females reported worse preoperative pain and disability both pre- and postoperatively,5,6,13,18,21, 22, 23, 24 our study only found this to be the case at one time point, relatively early in the postoperative recovery process.
Although we found no prior studies that specifically utilized the PROMIS PF to quantify and assess the postoperative course of patients based on gender, there are several investigations that have measured outcomes using analogous patient-reported outcome surveys. For instance, Pochon et al. utilized the Core Outcome Measures Index (COMI) questionnaire to assess back pain, leg pain, and functional disability in a series of 1518 patients who underwent spine surgery for degenerative spine pathologies to investigate the influence of patient gender on postsurgical outcomes.13,14 While female patients were identified to have slightly lower preoperative scores, there were no statistically significant differences in score improvement between males and females at the 1-year postoperative timepoint. Another related investigation conducted by Strömqvist et al. utilized the Swedish National Spine Register (SWESPINE) to evaluate clinical outcomes in female versus male patients following surgery for lumbar disc herniation. Again, female patients exhibited greater preoperative back and leg pain, in addition to worse preoperative functional disability as interpreted by an ODI score, but demonstrated similar improvement in all of these measures at their 1-year follow-up after surgery.
Although we did not observe statistically significant differences among our gender subgroups during the preoperative timepoint evaluation, others have attributed preoperative differences due to hormonal changes. Possible explanations might be estrogen-related pain modulation that may play a role in causing female patients to report greater pain before and after surgery, which in turn may affect the level of physical function and ability as reported by female patients.11,17,25, 26, 27, 28, 29, 30 At least one study has suggested that men and women have different thresholds for postoperative dysfunction and pain.31 Others have hypothesized that female patients are more likely to delay when seeking surgical intervention due to concerns about the postoperative course.32,33
The differences in postoperative improvement at the 6-week and 3-month timepoints observed in our study could likely be attributed to several factors. Zhu et al. observed that male patients had worse levels of pain at postoperative time periods including 60 and 90-days.34 Although Zhu et al.‘s study was limited to cervical spine surgery, their hypotheses may be relevant in our transient observation of women attaining an earlier postoperative improvement in physical function. For example, gender differences with regard to healthcare encounters, clinical interactions, or with respect to various therapeutic effectiveness profiles might also be associated with the occurrence, degree, and positive or negative impact on gender differences in postoperative physical function.34
Particularly among investigations within lumbar spine surgery, it is clear that there is a need for further research in this area as our understanding is still lacking with regard to the causes and mechanisms by which gender influences clinical outcomes. Nevertheless, the present study suggests that gender had no clinically significant impact on MIS TLIF. Therefore, practicing spine surgeons should keep in mind while counseling patients on postoperative goals and expectations during recovery that whether they are male or female they should expect similar outcomes. This study uniquely investigates a possible association of patient gender with PROMIS PF as a measurement tool following MIS TLIF.
This study, however, is not without limitations. First, the patients of this study were all treated in one academic health system by the senior author. This may impose limits on generalizing our findings among more diverse patient populations or in different geographic locations. Another limitation of our study may have occurred due to our postoperative time duration of followup. The data in our survey was limited to 1-year due to incomplete survey completion in the latter timepoints. Additionally, the analysis in this study was primarily retrospective, and this could have influenced our results through selection bias. Likewise, information regarding the preoperative duration of symptoms was not available, which prevented us from comparing the timing of surgical presentation between genders.
Other limitations may have arisen due to possible confounders. For example, the potential predisposition of post-menopausal women to develop osteoporosis could have an influence on outcomes following lumbar spine surgery and it may have been overlooked in this investigation and could be a confounding factor in our analysis. While we attempted to use all of the information that existed within our institutional patient records, we did not explore the presence of osteoporosis within records from other institutions, or patient health records from out-of-network primary care providers. In addition, while gender is a defining human characteristic, it is nonetheless only one of many factors that could be determinant with regard to spine surgery outcomes. Given the multifactorial nature of spine surgery outcomes, we believe further studies are warranted that investigate PROMIS PF gender differences in addition to other possible outcome determinants. Furthermore, it would have been very helpful to consider our findings in the context of other instruments, such as the patient satisfaction indices.35 Adding satisfaction considerations has been successfully elaborated in the context of clinical outcomes and may have added a meaningful dimension to this study. Lastly, we did not analyze other postoperative outcomes, such as a patient’s ability to achieve their original work ability, nor did we evaluate partial regaining of work capacity. Future studies will need to evaluate gender differences with larger, more diverse populations. Further inquiries will also need to follow patients longitudinally with prospective study designs while evaluating PROMIS PF score assessments for patients with degenerative spine disease.
5. Conclusion
We evaluated gender differences by utilizing the PROMIS PF score system among patients who had undergone MIS TLIF procedures. Whether evaluated during the pre- or postoperative time periods, patients of different genders demonstrated no statistically significant difference in PROMIS PF scores. Additionally, patients of either gender achieved MCID for PROMIS PF scores at a similar rate. This study established that both genders might expect a similar recovery in physical functionality following MIS TLIF. In addition to assisting with the future counseling of patients of both genders, our study indicates that, although female patients may transiently have an accelerated postoperative improvement, patients of both genders may ultimately have equivalent benefits from MIS TLIF procedures.
Declaration of competing interest
No funds were received in support of this work. No benefits in any form have been or will be received from any commercial party related directly or indirectly to the subject of this manuscript.
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