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There have been a multitude of studies attempting to identify the relationship between gender and postoperative outcomes; however, few studies have examined how this relationship may affect outcomes after anterior lumbar interbody fusion (ALIF) surgery. We aim to better characterize the impact that self-reported gender may have on patient reported outcome measures (PROMs) and achievement rates of minimum clinically important difference (MCID) after ALIF.
Methods
A retrospective database of a single spine surgeon was searched for patients who had undergone single-level ALIF. Indications for surgery including acute trauma, infection, or malignancy were excluded. The population was separated into cohorts by self-reported gender, female or male. PROMs were recorded and compared within groups to their preoperative baselines and between groups. MCID achievement rate was compared between groups.
Results
140 patients were identified for this study, with 68 patients self-identifying as female gender. The male gender cohort was found to have a significantly greater prevalence of hypertension (p = 0.018). Both cohorts showed significant improvement during at least one or more postoperative time points for each evaluated outcome measure (p ≤ 0.048, all). No significant difference in mean PROM scores was noted between cohorts at any time point for any measured outcome. The female gender cohort had significantly greater MCID achievement rates for visual acuity scale (VAS) back pain overall and at the 6-month time point (p ≤ 0.043, both). The female gender cohort also had significantly greater achievement of MCID at the 1-year time point for VAS leg pain (p = 0.017).
Conclusion
Both female and male gender cohorts demonstrated significant improvement in all outcomes measured at one or more postoperative time points. Postoperative outcomes did not differ by gender. MCID achievement was more common in female patients. Female patients may experience more tangible clinical improvement after ALIF compared to male patients.
Sociodemographic characteristics, especially sex, have been demonstrated to influence outcomes following surgical intervention across an array of fields. In search of better understanding as to how sex plays a role in outcomes following surgery, a multitude of literature comparing differences between male and female sex has been reported with contrasting results. These studies, including specialties ranging from pancreatic to orthopaedic surgery, have posited varying outcomes with several studies finding women to have inferior results or higher complication rates compared to men,
Persistent racial and sex disparities in outcomes after coronary artery bypass surgery: a retrospective clinical registry review in the drug-eluting stent era.
Does patient sex influence cartilage surgery outcome? Analysis of results at 5-year follow-up in a large cohort of patients treated with Matrix-assisted autologous chondrocyte transplantation.
Patient-reported outcome scores and rate of return to sport after hip arthroscopic surgery: a sex-based comparison in professional and collegiate athletes.
As a result, our understanding of the impact that sex has on surgical outcomes is nuanced and unable to be generalized to different surgical subspecialties. However, the impact that sex has on outcomes following surgery can be significant. In a randomized review of studies published by six prominent orthopaedic surgery journals over a one-year period, Gianakos et al. (2020) reported 39% of studies that included gender analysis in a multivariable analysis demonstrated differences in outcomes regarding sex.
As a result, Gianakos et al. (2020) argued for the need to better understand differences between outcomes as influenced by sex in orthopaedic surgery to promote equitable healthcare for male and female patients.
The current published studies regarding the effect of gender on outcomes following lumbar surgery utilizing homogenous populations and techniques are sparse. In order to better understand the effect that gender may have on patients undergoing lumbar spine surgery, this study seeks to evaluate the potential relationship between self-reported gender and outcomes following anterior lumbar interbody fusion (ALIF) (Fig. 1, Fig. 2).
Fig. 140 year old male undergoing ALIF at L5/S1. A: Preoperative anterior-posterior (AP) [left] and lateral [right] films. B: 6-week postoperative AP [left] and lateral [right] films.
Fig. 247 year old female undergoing ALIF with posterior instrumentation at L5/S1. A: Preoperative AP [left] and lateral [right] films. B: 6-week postoperative AP [left] and lateral [right] films.
Following acquisition of patient consent and Institutional Review Board approval (ORA #14051301), patients who had undergone single-level ALIF were retrospectively searched in a prospectively maintained registry from a single academic spine surgeon. Patients missing information regarding gender or with surgical indication including infection, trauma, or malignancy were excluded. Patients were divided into two cohorts by gender: female or male.
2.2 Data collection
Demographics and perioperative characteristics were collected for both cohorts. Demographics collected included age, body mass index (BMI), ethnicity, presence of diabetes, active smoking, and hypertension, American Society of Anesthesiologists (ASA) score, Charlson Comorbidity Index (CCI) score, and insurance provider variant (Medicare/Medicaid versus Workers’ Compensation versus Private). Perioperative characteristics included spinal pathology, level of fusion, operative time, estimated blood loss, length of stay, acute postoperative visual analog scale (VAS) pain, postoperative narcotic consumption, and postoperative day of discharge. Patient-reported Outcome Measures (PROMs) were collected preoperatively and at 6 weeks, 12 weeks, 6 months, and 1 year postoperatively. PROMs collected included Patient-reported Outcomes Measurement Information System Physical Function (PROMIS PF), 12-item Short Form Physical Component Score (SF-12 PCS), VAS back, VAS leg, and Oswestry Disability Index (ODI).
2.3 Statistical analysis
All statistical analysis was performed utilizing Stata 16.0 (StataCorp LP, College Station, TX) with a p-value <0.050 used to determine significance. Continuous variables were compared between cohorts via independent t-tests. Chi-square tests were utilized to compare categorical variables between cohorts. Differences in mean PROM scores between the preoperative period and each postoperative period were compared within groups via paired sample t-tests. Absolute arithmetic differences in PROM scores between the preoperative stage and each postoperative period were calculated and compared to literal values for to assess for achievement of minimal clinically important differences (MCID) for each PROM. The literature values used to assess MCID achievement are as follows: 4.5 for PROMIS PF, 2.5 for SF-12 PCS, 2.1 for VAS back, 2.8 for VAS leg, and 14.9 for ODI.
Utility of minimum clinically important difference in assessing pain, disability, and health state after transforaminal lumbar interbody fusion for degenerative lumbar spondylolisthesis.
Minimum clinically important difference in pain, disability, and quality of life after neural decompression and fusion for same-level recurrent lumbar stenosis: understanding clinical versus statistical significance.
One-hundred and forty patients were identified for the study, with 68 female patients and 72 male patients included. Cohort demographics did not significantly differ with the exception of hypertension, which was more prevalent among male patients (38.9% versus 20.6%, p = 0.018) (Table 1). A large majority of patients underwent fusion at L5-S1 (82.9%) (Table 2). There were no significant differences between cohorts regarding spinal pathology, fusion level, operative time, estimated blood loss, length of stay, or acute postoperative pain or narcotic consumption (Table 2).
Table 1Patient demographics.
Characteristic
Total (n = 140)
Female Gender (n = 68)
Male Gender (n = 72)
∗p-value
Age (mean ± SD, years)
50.2 ± 12.1
49.7 ± 12.2
50.6 ± 12.1
0.639
BMI (mean ± SD, kg/m2)
30.9 ± 6.5
31.2 ± 6.9
30.5 ± 6.2
0.530
Ethnicity
0.991
African-American
12.9% (18)
11.8% (8)
13.9% (10)
Asian
2.9% (4)
2.9% (2)
2.8% (2)
Hispanic
7.9% (11)
8.8% (6)
6.9% (5)
White
75.0% (105)
75.0% (51)
75.0% (54)
Other
1.4% (2)
1.5% (1)
1.4% (1)
Diabetic Status
0.166
Non-Diabetic
87.1% (122)
91.2% (62)
83.3% (60)
Diabetic
12.9% (18)
8.8% (6)
16.7% (12)
Smoking Status
0.754
Non-Smoker
81.3% (113)
82.4% (56)
80.3% (57)
Smoker
18.7% (26)
17.7% (12)
19.7% (14)
Blood Pressure
0.018
Normotensive
70.0% (98)
79.4% (54)
61.1% (44)
Hypertensive
30.0% (42)
20.6% (14)
38.9% (28)
ASA score
0.745
≤2
12.7% (17)
13.6% (9)
11.8% (8)
>2
87.3% (117)
86.4% (57)
88.2% (60)
CCI Score (mean ± SD)
1.73 ± 1.6
1.5 ± 1.3
1.9 ± 1.8
0.934
Insurance Type
0.837
Medicare/Medicaid
7.2% (10)
6.0% (4)
8.3% (6)
Workers' Comp
23.0% (32)
22.4% (15)
23.6% (17)
Private
69.8% (97)
71.6% (48)
68.1% (49)
BMI = Body Mass Index; ASA = American Society of Anesthesiologists; CCI = Charlson Comorbidity Index; SD = Standard Deviations; Workers' Comp = workers' compensation.
∗p-value calculated using Chi-square analysis for categorical variables or Student's t-test for continuous variables.
Regarding function, female patients reported significant improvement in PROMIS PF at 6 months and 1 year (p ≤ 0.007, all) (Table 3). Male patients reported significant improvement in PROMIS PF at 12 weeks, 6 months, and 1 year time points (p ≤ 0.048, all) (Table 3). There was no significant difference in PROMIS PF score between cohorts at any period (Table 3). SF-12 PCS scores significantly improved from preoperative baseline in female patients at 12 weeks, 6 months, and 1 year periods (p ≤ 0.017, all) (Table 3). Male patients reported improved SF-12 PCS scores at 6 week, 12 week, and 6 month time points (p ≤ 0.043, all) (Table 3). SF-12 PCS did not significantly differ between groups at any period (Table 3). Regarding pain, mean VAS back scores improved for both female and male cohorts at all postoperative periods with the exception of the male cohort at 1 year (p < 0.001, all) (Table 3). VAS leg scores were significantly improved at 12 weeks and 1 year in the female cohort (p ≤ 0.014, all) (Table 3). VAS leg scores were significantly improved in the male cohort at 6 months (p = 0.011) (Table 3). There were no significant differences between cohorts at any period in mean VAS back or VAS leg scores (Table 3). ODI significantly improved from preoperative baseline for both female and male cohorts at the 12 week, 6 month, and 1 year periods (p ≤ 0.008, all) (Table 3). There was no significant difference demonstrated between cohorts in ODI at any period (Table 3). Female patients more frequently achieved MCID in VAS back at 6 months and overall (p ≤ 0.043, both) (Table 4). Female patients also more frequently achieved MCID in VAS leg at 1 year (p = 0.017) (Table 4).
Table 3Mean patient reported outcome measures.
PROM
Female Gender (mean ± SD)
∗p-value
Male Gender (mean ± SD)
∗p-value
†p-value
PROMIS PF
Preoperative
37.2 ± 5.6
–
36.0 ± 5.9
–
0.516
6-week
38.7 ± 5.3
0.952
39.3 ± 6.0
0.116
0.778
12-week
42.2 ± 7.6
0.120
43.1 ± 9.1
0.048
0.757
6-month
46.7 ± 8.1
0.007
46.4 ± 10.1
0.002
0.927
1-year
42.2 ± 8.6
<0.001
50.7 ± 9.9
0.017
0.054
SF-12 PCS
Preoperative
30.3 ± 9.6
–
30.6 ± 8.7
–
0.888
6-week
32.6 ± 6.5
0.605
34.8 ± 10.7
0.043
0.452
12-week
36.9 ± 8.2
0.017
38.9 ± 10.1
0.001
0.497
6-month
39.1 ± 10.2
0.001
38.8 ± 11.0
0.002
0.944
1-year
43.9 ± 10.9
0.009
39.9 ± 10.5
0.400
0.434
VAS back
Preoperative
7.1 ± 2.1
–
6.5 ± 2.5
–
0.141
6-week
4.0 ± 2.6
<0.001
4.1 ± 2.7
<0.001
0.903
12-week
3.4 ± 2.7
<0.001
3.7 ± 2.6
<0.001
0.545
6-month
3.0 ± 2.7
<0.001
3.4 ± 2.6
<0.001
0.424
1-year
2.8 ± 3.4
<0.001
3.5 ± 3.7
0.604
0.702
VAS leg
Preoperative
5.2 ± 2.9
–
4.2 ± 3.2
–
0.185
6-week
3.7 ± 2.7
0.050
3.6 ± 3.3
0.895
0.926
12-week
2.8 ± 2.6
0.014
2.8 ± 2.9
0.130
0.993
6-month
3.3 ± 3.2
0.089
2.1 ± 2.7
0.011
0.227
1-year
1.9 ± 2.7
0.003
3.0 ± 3.4
0.322
0.390
ODI
Preoperative
40.3 ± 13.6
–
38.8 ± 20.5
–
0.722
6-week
35.2 ± 18.6
0.280
34.3 ± 25.5
0.578
0.880
12-week
24.3 ± 17.5
<0.001
21.5 ± 13.5
<0.001
0.493
6-month
23.5 ± 18.3
<0.001
18.1 ± 17.0
0.008
0.300
1-year
26.3 ± 25.2
0.005
20.7 ± 21.0
0.004
0.582
SD = standard deviation.
∗p-values calculated using paired samples t-test to determine improvement in PROMs.
†p-values calculated using Student's t-test for independent samples to compare PROMs between groups.
Safety and efficacy of anterior lumbar interbody fusion for discogenic chronic low back pain in a short-stay setting: data from a prospective registry.
However, there is little-to-no published data regarding the influence of gender on outcomes following ALIF. As Gianakos et al. (2020) posited, it is necessary to have a better understanding of the influence gender has on spine surgery to provide equitable healthcare to both female and male patients alike.
Prior studies of lumbar spine surgery outcomes have reported contrasting findings. Additionally, none of these studies reported on isolated ALIF patients. Ekman et al. (2009) reported male gender to be an independent predictor for superior outcomes following lumbar fusion for isthmic spondylolisthesis.
Similarly, Elsamadicy et al. (2017) reported significantly fewer female patients to report satisfaction following elective lumbar spine surgery along with significantly greater pain and disability present in the female cohort when compared to male patients.
Impact of gender disparities on short-term and long-term patient reported outcomes and satisfaction measures after elective lumbar spine surgery: a single institutional study of 384 patients.
Strömqvist et al. (2008) additionally reported an increased rate of analgesic utilization in female patients at 1-year follow-up after lumbar disc herniation surgery.
However, Strömqvist et al. (2008) also noted that there was no statistical significance between relative improvement or surgical satisfaction between male and female patients.
In a later epidemiological study of 15,631 lumbar disc herniation operations, this same group reported that female patients reported inferior pain scores when compared to male patients at time of surgery scheduling.
Several studies demonstrated female patients to present with inferior pain and disability scores, but reported females to improve more dramatically than male patients after lumbar spine surgery.
Women do not fare worse than men after lumbar fusion surgery: two-year follow-up results from 4,780 prospectively collected patients in the Swedish National Spine Register with lumbar degenerative disc disease and chronic low back pain.
Finally, a large collection of studies reported that female patients presented with inferior baseline outcome measure scores, but noted that these differences between genders were not significant in the postoperative periods.
In this current study, both female and male cohorts reported significant improvement at multiple postoperative time points in both PROMIS PF and SF-12 PCS scores when compared to preoperative baseline scores. There was no significant difference in physical function outcome scores found between cohorts at any period, including the preoperative stage. Additionally, there was no significant difference in MCID achievement between cohorts. These findings most closely replicate those found by Gautschi et al. (2016) who reported similar preoperative and postoperative levels of function between male and female patients undergoing intervention for lumbar degenerative disc disease.
Gautschi et al. (2016) utilized objective functional impairment (OFI) scores and subjective functional impairment (SFI) scores to compare outcomes between genders, finding the OFI scores to be similar prior to and following intervention for both cohorts.
Gautschi et al. (2016) recommended use of more objective measurements of function and disability, such as the timed-up-and-go test, to protect against reporting bias regarding these outcomes.
Further, since all patients were evaluated and operated on by a single spine surgeon, discrepancies in preoperative patient reported scores between male and female patients may be lacking as surgical selection timing may be more consistent, limiting the concern posed by Strömqvist et al. (2008).
With regard to pain, both VAS back and VAS leg scores significantly improved in the postoperative period regardless of gender. Mean scores did not significantly differ between male and female cohorts at any time period. However, female patients were more likely to achieve MCID in both VAS back and VAS leg scores. These results are most similar to those of MacLean et al. (2020) and Triebel et al. (2016), both finding female patients to improve at a greater relative increment following intervention.
Women do not fare worse than men after lumbar fusion surgery: two-year follow-up results from 4,780 prospectively collected patients in the Swedish National Spine Register with lumbar degenerative disc disease and chronic low back pain.
One potential explanation for the variation in MCID achievement rates between cohorts may be due to variation in pain scores at presentation. While not significantly different, female patients did present with higher mean VAS back (7.1 versus 6.5 in male patients) and higher mean VAS leg (5.2 versus 4.2 in male patients), which may account for the difference in MCID achievement between the two groups.
4.3 Disability
Both female and male cohorts reported significant improvement in mean ODI scores at the 12-week mark and all following time points when compared to preoperative baseline. Significant differences between cohorts were not observed at any period. Similarly, MCID achievement rate did not significantly vary between cohorts. As discussed in relation to our findings regarding physical function, these results are most similar to those found by Gautschi et al. (2016).
This current study has several limitations. Use of single-surgeon data, while lending strength due to homogeneity of technique, patient population, and surgical timing, limits generalizability of these findings. In similar manner, only single-level fusions were included to prevent potential confounding, yet this limits generalizability to multi-level procedures. Further, this study utilized PROMs which are collected via survey and are subject to reporting bias. An additional limitation for relying on patient surveys was selection bias, as some patients were lost to follow-up. Further, some patients may have not reached the 1-year postoperative time point, as all data were analyzed through a prospectively maintained database. This limitation may be noted as the loss of significance at the 1-year time point for SF-12 PCS, VAS back, and VAS leg in male patients. Inclusion of a variety of spinal pathologies allows for greater generalization of our conclusions; however, this limits specificity in application to a particular diagnosis. Additionally, univariate analysis can be susceptible to confounding variables that may be more accurately accounted for by multivariable analysis. Unfortunately, multivariable analysis of this data was limited due to the large collection of preoperative variables in relation to the sample size at later follow-up times, preventing fit of a reliable predictive model. With the exception of prevalence of hypertension, which is known to vary between genders,
there were no significant demographic or perioperative differences between groups save the experimental question of gender, which lends strength to the univariate analysis. Finally, more patients in the male cohort suffered from hypertension; however, this reflects the well-known increased prevalence of hypertension in males and as such may not detract significantly from our conclusions.
Independent of gender, male and female patients report significant improvement in physical function, pain, and disability outcomes following ALIF. Significant differences between cohorts regarding function, pain, or disability were not present preoperatively or at any postoperative period. Female patients were more likely to achieve MCID in VAS back and VAS leg measures. Female patients may more frequently see clinically meaningful differences in both back and leg pain following ALIF.
IRB approval
ORA #14051301.
CRediT authorship contribution statement
Timothy J. Hartman: Conceptualization, Methodology, Visualization, Formal analysis, Software, Investigation, Writing – original draft, Writing – review & editing. James W. Nie: Conceptualization, Methodology, Visualization, Formal analysis, Software, Investigation, Writing – original draft, Writing – review & editing. Keith R. MacGregor: Project administration, Data curation, Investigation, Writing – review & editing. Omolabake O. Oyetayo: Project administration, Data curation, Investigation, Writing – review & editing. Eileen Zheng: Project administration, Data curation, Investigation, Writing – review & editing. Kern Singh: Conceptualization, Methodology, Supervision, Resources, Investigation, Writing – review & editing.
Declaration of competing interest
None.
References
Sattartabar B.
Ajam A.
Pashang M.
et al.
Sex and age difference in risk factor distribution, trend, and long-term outcome of patients undergoing isolated coronary artery bypass graft surgery.
Persistent racial and sex disparities in outcomes after coronary artery bypass surgery: a retrospective clinical registry review in the drug-eluting stent era.
Does patient sex influence cartilage surgery outcome? Analysis of results at 5-year follow-up in a large cohort of patients treated with Matrix-assisted autologous chondrocyte transplantation.
Patient-reported outcome scores and rate of return to sport after hip arthroscopic surgery: a sex-based comparison in professional and collegiate athletes.
Utility of minimum clinically important difference in assessing pain, disability, and health state after transforaminal lumbar interbody fusion for degenerative lumbar spondylolisthesis.
Minimum clinically important difference in pain, disability, and quality of life after neural decompression and fusion for same-level recurrent lumbar stenosis: understanding clinical versus statistical significance.
Safety and efficacy of anterior lumbar interbody fusion for discogenic chronic low back pain in a short-stay setting: data from a prospective registry.
Impact of gender disparities on short-term and long-term patient reported outcomes and satisfaction measures after elective lumbar spine surgery: a single institutional study of 384 patients.
Women do not fare worse than men after lumbar fusion surgery: two-year follow-up results from 4,780 prospectively collected patients in the Swedish National Spine Register with lumbar degenerative disc disease and chronic low back pain.
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