Impact of Body Mass Index on Postsurgical Outcomes for Workers’ Compensation Patients Undergoing Minimally Invasive Transforaminal Lumbar Interbody Fusion

Madhav R. Patel; Kevin C. Jacob; Frank A. Chavez; Justin T. DesLaurier; Hanna Pawlowski; Michael C. Prabhu; Nisheka N. Vanjani; Kern Singh

doi:10.14444/8309

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Table 1

Patient demographics.

Characteristic	Nonobese (n = 116)	Obese I (n = 70)	Severe + Morbid (n = 61)	P Value^{^a}
Age, y, mean ± SD	45.7 ± 18.7	45.7 ± 9.3	47.8 ± 10.2	0.315
Gender, % (n)				0.037
Female	20.16% (25)	14.9% (11)	31.9% (23)
Male	79.8% (99)	85.1% (63)	68.9% (49)
Ethnicity, % (n)				0.163
African American	12.2% (15)	24.7% (18)	19.4% (14)
Asian	2.4% (3)	0.0% (0)	0.0% (0)
Hispanic	30.9% (38)	27.4% (20)	27.8% (20)
White	49.6% (61)	48.0% (35)	50.0% (36)
Other	4.9% (6)	0.0% (0)	2.8% (2)
Diabetic status, % (n)				0.113
Nondiabetic	94.9% (114)	84.8% (65)	81.9% (59)
Diabetic	0.0% (0)	12.2% (9)	18.1% (13)
Smoking status, % (n)				0.584
Nonsmoker	72.6% (90)	74.0% (54)	79.2% (57)
Smoker	27.4% (34)	26.0% (19)	20.8% (15)
Blood pressure, % (n)				<0.001
Normotensive	79.7% (98)	60.3% (44)	47.2% (34)
Hypertensive	20.3% (25)	39.7% (29)	52.8% (38)
ASA score, % (n)				<0.001
≤2	92.7% (114)	77.8% (56)	69.0% (49)
>2	7.3% (9)	22.2% (16)	31.0% (22)
Charlson Comorbidity Index score, % (n)				0.063
<1	37.9% (44)	33.8% (23)	21.4% (15)
≥1	62.1% (72)	66.2% (45)	78.6% (55)
Insurance type, % (n)
Medicare/Medicaid	0.0% (0)	0.0% (0)	0.0% (0)
Workers’ compensation	100% (124)	100% (74)	100% (72)
Private	0.0% (0)	0.0% (0)	0.0% (0)

Abbreviation: ASA, American Society of Anesthesiologists.
Note: Boldface indicates statistical significance.
↵a P value calculated using χ² analysis or Student’s t test.

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Table 2

Perioperative characteristics.

Characteristic	Nonobese (n = 116)	Obese I (n = 70)	Severe + Morbid (n = 61)	P Value^{^a}
Spinal pathology, % (n)
Degenerative spondylolisthesis	37.9% (47)	36.5% (27)	41.7% (30)	0.798
Isthmic spondylolisthesis	19.4% (24)	16.2% (12)	20.8% (15)	0.763
Recurrent herniated nucleus pulposus	29.0% (36)	23.0% (17)	22.2% (16)	0.480
Scoliosis	0.8% (1)	2.7% (2)	0.0% (0)	0.270
Operative time, min, mean ± SD	120.0 ± 34.3	125.3 ± 27.6	140.1 ± 48.4	<0.001
Estimated blood loss, mL, mean ± SD	56.2 ± 27.8	51.7 ± 22.2	60.3 ± 30.3	0.160
Length of stay, h, mean ± SD	46.1 ± 27.2	49.4 ± 29.6	53.0 ± 30.9	0.282
Day of discharge, % (n)				0.097
POD 0	13.3% (16)	10.0% (7)	5.6% (4)
POD 1	30.8% (37)	27.1% (19)	35.2% (25)
POD 2	30.0% (36)	35.7% (25)	22.5% (16)
POD 3	18.3% (22)	18.6% (13)	29.6% (21)
POD 4	2.5% (3)	0.0% (0)	4.2% (3)
POD 5	0.0% (0)	0.0% (0)	1.4% (1)
POD 6	0.0% (0)	2.9% (2)	0.0% (0)
POD 7	0.0% (0)	0.0% (0)	1.4% (1)

Abbreviation: POD, postoperative day of discharge.
Note: Boldface indicates statistical significance.
↵a P value calculated using χ² analysis or Student’s t test.

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Table 3

Impact of BMI on PROMs and follow-up completion.

PROM	Nonobese (mean ± SD)	Obese I (mean ± SD)	Severe + Morbid (mean ± SD)	P Value^{^a}	P Value^{^b}	P Value^{^c}
VAS back						0.339
Preoperative	6.7 ± 2.0	7.3 ± 1.9	7.1 ± 1.7	0.114	0.897
6 wk	4.8 ± 2.2	5.3 ± 2.2	5.5 ± 2.2	0.068	0.536
12 wk	4.6 ± 2.4	5.6 ± 2.2	5.5 ± 2.1	0.007	0.944
6 mo	4.7 ± 2.6	5.3 ± 2.1	5.1 ± 2.6	0.388	0.992
1 y	5.2 ± 2.8	4.5 ± 2.7	5.1 ± 2.8	0.812	0.893
2 y	3.3 ± 2.6	6.3 ± 2.2	6.7 ± 2.9	0.026	0.990
VAS leg						0.186
Preoperative	5.3 ± 2.9	6.4 ± 2.9	6.6 ± 2.1	0.051	0.993
6 wk	4.4 ± 3.3	4.1 ± 3.3	5.5 ± 2.6	0.168	0.168
12 wk	3.9 ± 3.0	4.5 ± 2.5	4.8 ± 2.5	0.388	0.825
6 mo	3.5 ± 2.7	4.3 ± 2.6	4.9 ± 2.8	0.099	0.521
1 y	3.7 ± 3.0	3.7 ± 3.5	4.6 ± 2.8	0.629	0.870
2 y	2.5 ± 2.6	5.3 ± 3.4	5.1 ± 2.7	0.100	0.968
Oswestry Disability Index						0.056
Preoperative	44.2 ± 15.1	53.9 ± 13.9	55.6 ± 15.0	0.008	0.928
6 wk	47.5 ± 17.4	51.8 ± 16.1	52.2 ± 17.2	0.372	0.827
12 wk	39.5 ± 15.6	51.5 ± 10.8	46.8 ± 16.5	0.003	0.790
6 mo	35.0 ± 19.8	43.7 ± 13.7	45.6 ± 18.2	0.015	0.727
1 y	38.7 ± 24.3	39.6 ± 22.1	46.6 ± 20.8	0.409	0.539
2 y	27.1 ± 21.1	49.0 ± 13.6	47.6 ± 21.1	0.076	1.000
12-Item Short Form physical composite score						0.081
Preoperative	28.3 ± 6.3	30.6 ± 13.2	25.8 ± 4.8	0.090	0.103
6 wk	29.7 ± 7.1	25.5 ± 7.5	25.5 ± 5.1	0.057	0.959
12 wk	29.6 ± 6.6	29.8 ± 8.9	27.3 ± 6.8	0.513	0.483
6 mo	31.9 ± 8.5	31.0 ± 8.2	30.4 ± 6.3	0.817	0.933
1 y	31.2 ± 11.8	32.6 ± 11.7	33.3 ± 9.2	0.819	0.944
2 y	38.0 ± 14.2	29.3 ± 5.8	29.5 ± 12.0	0.227	0.916
PROMIS-PF						0.303
Preoperative	35.2 ± 6.4	32.7 ± 4.1	30.1 ± 4.7	0.021	0.910
6 wk	33.4 ± 6.7	31.2 ± 3.9	31.4 ± 3.8	0.616	0.992
12 wk	39.2 ± 6.7	38.1 ± 7.7	31.8 ± 2.6	0.011	0.050
6 mo	40.4 ± 7.1	39.3 ± 8.6	36.6 ± 6.7	0.542	0.662
1 y	39.6 ± 9.7	41.3 ± 8.1	37.9 ± 6.4	0.640	0.613
2 y	38.6 ± 11.6	33.7 ± 6.5	36.5 ± 8.2	0.683	0.875

Abbreviations: BMI, body mass index; PROM, patient-reported outcome measures; PROMIS-PF, Patient-Reported Outcome Measurement Information System physical function; VAS, visual analog scale.
Note: Boldface indicates statistical significance.
↵a P values calculated using linear regression of PROMs by BMI.
↵b P values calculated using post hoc pairwise comparisons of adjusted means to compare PROMs between obese I and severe + morbid cohorts.
↵c P values calculated using linear regression of follow-up completion by BMI.

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Table 4

Impact of body mass index on MCID achievement.

PROM	6 wk	12 wk	6 mo	1 y	2 y	Overall
VAS back	n = 89	n = 85	n = 82	n = 16	n = 8	n = 146
Nonobese	43.4% (56)	44.7% (38)	45.1% (37)	12.5% (2)	37.5% (3)	45.9% (67)
Obese I	31.5% (28)	31.7% (27)	29.3% (24)	43.8% (7)	37.5% (3)	27.4% (40)
Severe + morbid	23.6% (21)	23.5% (20)	25.6% (21)	43.8% (7)	25.0% (2)	26.7% (39)
P value^a	0.425	0.279	0.783	0.106	0.184	1.000
VAS leg	n = 31	n = 30	n = 38	n = 13	n = 9	n = 59
Nonobese	38.7% (12)	40.0% (12)	44.7% (17)	30.8% (4)	33.3% (3)	39.0% (23)
Obese I	38.7% (12)	30.0% (9)	29.0% (11)	38.5% (5)	22.2% (2)	28.8% (17)
Severe + morbid	22.6% (7)	30.0% (9)	26.3% (10)	30.8% (4)	44.4% (4)	32.2% (19)
P value^a	0.323	0.830	0.701	0.646	0.866	0.424
Owestry Disability Index	n = 19	n = 24	n = 39	n = 15	n = 5	n = 50
Nonobese	31.6% (6)	29.2% (7)	38.5% (15)	6.7% (1)	20.0% (1)	34.0% (17)
Obese I	26.3% (5)	25.0% (6)	25.6% (10)	40.0% (6)	0.0% (0)	24.0% (12)
Severe + morbid	42.1% (8)	45.8% (11)	35.9% (14)	53.3% (8)	80.0% (4)	42.0% (21)
P value^a	0.640	0.339	0.823	0.053	0.230	0.023
12-Item Short Form physical composite score	n = 16	n = 20	n = 17	n = 19	n = 11	n = 48
Nonobese	50.0% (8)	40.0% (8)	52.9% (9)	31.6% (6)	45.5% (5)	37.5% (18)
Obese I	25.0% (4)	30.0% (6)	29.4% (5)	26.3% (5)	36.4% (4)	33.3% (16)
Severe + morbid	25.0% (4)	30.0% (6)	17.7% (3)	42.1% (8)	18.2% (2)	29.2% (14)
P value^a	0.445	0.891	0.484	0.587	0.631	0.409
PROMIS-PF	n = 8	n = 9	n = 14	n = 13	n = 7	n = 26
Nonobese	75.0% (6)	66.7% (6)	50.0% (7)	23.1% (3)	42.9% (3)	38.5% (10)
Obese I	25.0% (2)	33.3% (3)	28.6% (4)	30.8% (4)	28.6% (2)	30.8% (8)
Severe + morbid	0.0% (0)	0.0% (0)	21.4% (3)	46.2% (6)	28.6% (2)	30.8% (8)
P value^a	0.096	0.076	0.376	0.571	0.927	0.723

Abbreviations: MCID, minimum clinically important difference; PROM, patient-reported outcome measure; PROMIS-PF, Patient-Reported Outcome Measurement Information System physical function.
Note: Boldface indicates statistical significance.
↵a P values calculated using χ² analysis.