Risk Factors for Failing to Reach a Minimal Clinically Important Difference Following Minimally Invasive Lumbar Decompression

Elliot D.K. Cha; Conor P. Lynch; Cara E. Geoghegan; Caroline N. Jadczak; Shruthi Mohan; Kern Singh

doi:10.14444/8176

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Table 1

Patient baseline characteristics.

Characteristic	% Total (n = 811)
Age (mean ± SD)	44.6 ± 13.6
Gender % (n)
Female	29.9% (243)
Male	70.1% (568)
BMI
<30 kg/m²	60.4% (483)
≥30 kg/m²	39.6% (317)
Smoking Status
Nonsmoker	83.2% (675)
Smoker	16.8% (136)
Diabetes
Diabetic	5.8% (47)
Nondiabetic	94.2% (764)
ASA score
<2	34.5% (232)
≥2	65.5% (440)
Ageless CCI
<1	58.8% (440)
≥1	41.2% (308)
Insurance
Non-WC	69.4% (563)
WC	30.6% (245)
Operative length (min)	45.7 ± 15.0
EBL (mean ± SD; mL)	31.4 ± 14.2
LOS (mean ± SD; h)	5.7 ± 6.6
Operative technique
Laminectomy	17.9% (144)
Discectomy	11.5% (92)
Laminectomy + discectomy	70.6% (567)
Number of operative levels
Single	81.7% (663)
Multilevel	18.3% (148)
Spinal pathology
HNP	77.1% (625)
Central stenosis	61.2% (496)
Foraminal stenosis	33.9% (275)

ASA, American Society of Anesthesiologists; BMI, body mass index; CCI, Charlson Comorbidity Index; EBL, estimated blood loss; HNP, herniated nucleus pulposus; LOS, length of stay; WC, workers’ compensation.

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Table 2

Improvement of outcome measures.

Outcome measure	n	Mean ± SD	P value^a
VAS back
Preoperative	712	6.27 ± 2.45	<0.001
6 wk	594	2.78 ± 2.57	<0.001
12 wk	321	3.05 ± 2.83	<0.001
6 mo	221	3.20 ± 2.92	<0.001
1 y	121	3.27 ± 2.89	<0.001
VAS leg
Preoperative	476	6.17 ± 2.57	<0.001
6 wk	377	2.87± 2.80	<0.001
12 wk	216	2.93 ± 2.87	<0.001
6 mo	164	3.12 ± 2.92	<0.001
1 y	120	2.77 ± 2.90	<0.001
ODI
Preoperative	494	42.2 ± 17.6	<0.001
6 wk	391	25.0 ± 18.2	<0.001
12 wk	226	24.8 ± 20.8	<0.001
6 mo	170	31.9 ± 77.5	0.054
1 y	120	23.0 ± 20.8	<0.001
SF-12 PCS
Preoperative	446	31.7 ± 7.91	<0.001
6 wk	288	38.2 ± 10.1	<0.001
12 wk	168	41.1 ± 10.9	<0.001
6 mo	146	40.7 ± 11.2	<0.001
1 y	141	42.3 ± 10.9	<0.001
PROMIS PF
Preoperative	304	36.3 ± 6.8	<0.001
6 wk	212	42.7 ± 8.4	<0.001
12 wk	124	45.6 ± 10.1	<0.001
6 mo	111	43.4 ± 9.8	<0.001
1 y	101	45.5 ± 10.1	<0.001

Boldface indicates statistical significance.
aP values calculated difference from baseline values using paired t test.
ODI, Oswestry Disability Index; PROMIS PF, patient-reported outcomes measures information system physical function; SF-12, 12-item short form; VAS, visual analog scale.

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Table 3

Bivariate analysis achievement for VAS back.

Characteristic	Failed MCID (%)	RR	95% CI	P value^a
Overall	28.2%	–	–	–
Age
18–50 y	61.8%	Reference
>50 y	38.2%	1.1	(0.9–1.5)	0.176
Gender
Male	68.6%	0.9	(0.7–1.2)	0.563
Female	31.4%	Reference
BMI
<30 kg/m²	58.3%	Reference
≥30 kg/m²	41.7%	1.1	(0.9–1.3)	0.455
Smoking status
Nonsmoker	79.9%	Reference
Smoker	20.1%	1.2	(0.9–1.6)	0.103
Diabetes
Nondiabetic	93.8%	Reference
Diabetic	6.2%	1.1	(0.7–1.7)	0.806
Ageless CCI
<1	51.2%	Reference
≥1	48.3%	1.4	(1.1–1.7)	0.007
ASA score
<2	32.6%	Reference
≥2	67.4%	1.1	(0.8–1.4)	0.526
Insurance
Non-WC	61.1%	Reference
WC	38.9%	1.4	(1.1–1.6)	0.001
Operative length
<50 min	69.0%	Reference
≥50 min	31.0%	0.9	(0.8–1.0)	0.185
EBL
<50 mL	50.0%	Reference
≥50 mL	50.0%	1.1	(0.9–1.3)	0.411
Operative levels
Single	71.7%	Reference
Multilevel	28.3%	1.4	(1.2–1.7)	0.001
Operative technique
Laminectomy	20.1%	0.9	(0.7–1.3)	0.945
Discectomy	-	-	-	-
Laminectomy + discectomy	74.3%	1.2	(0.9–1.5)	0.148
Spinal pathologies
HNP	76.9%	0.9	(0.7–1.3)	0.858
Central stenosis	63.0%	1.1	(0.8–1.3)	0.508
Foraminal stenosis	31.7%	0.9	(0.7–1.1)	0.432

Boldface indicates statistical significance.
aP value calculated using Poisson regression.
ASA, American Society of Anesthesiologists; BMI, body mass index; CCI, Charlson Comorbidity Index; EBL, estimated blood loss; HNP, herniated nucleus pulposus; RR, relative risk; VAS, visual analog scale; WC, workers’ compensation.

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Table 4

Bivariate analysis achievement for VAS leg.

Characteristic	Failed MCID (%)	RR	95% CI	P value^a
Overall	20.7%	–	–	–
Age
18–50 y	57.5%	Reference
>50 y	42.5%	1.4	(1.1–1.8)	0.015
Gender
Male	72.0%	1.1	(0.8–1.5)	0.530
Female	28.0%	Reference
BMI
<30 kg/m²	59.0%	Reference
≥30 kg/m²	41.0%	1.1	(0.8–1.4)	0.692
Smoking status
Nonsmoker	81.0%	Reference
Smoker	19.0%	1.2	(0.8–1.6)	0.369
Diabetes
Nondiabetic	92.9%	Reference
Diabetic	7.1%	1.3	(0.75–2.1)	0.389
Ageless CCI
<1	49.0%	Reference
≥1	51.0%	1.5	(1.2–1.9)	0.005
ASA score
<2	36.3%	Reference
≥2	63.7%	0.9	(0.7–1.3)	0.646
Insurance
Non-WC	64.9%	Reference
WC	35.1%	1.2	(0.9–1.5)	0.081
Operative length
<50 min	66.7%	Reference
≥50 min	33.3%	0.9	(0.9–1.0)	0.051
EBL
<50 mL	91.1%	Reference
≥50 mL	8.9%	1.9	(1.4–2.6)	0.001
Operative levels
Single	72.0%	Reference
Multilevel	28.0%	1.7	(1.3–2.3)	0.001
Operative technique
Laminectomy only	28.1%	1.6	(1.2–2.0)	0.001
Discectomy only	-	-	-	-
Laminectomy + discectomy	71.0%	0.6	(0.5–0.8)	0.001
Spinal pathologies
HNP	69.1%	0.6	(0.5–0.9)	0.003
Central stenosis	70.2%	1.5	(1.1–2.0)	0.008
Foraminal stenosis	40.5%	1.3	(1.1–1.7)	0.042

Boldface indicates statistical significance.
aP value calculated using Poisson regression.
ASA, American Society of Anesthesiologists; BMI, body mass index; CCI, Charlson Comorbidity Index; EBL, estimated blood loss; HNP, herniated nucleus pulposus; RR, relative risk; VAS, visual analog scale; WC, workers’ compensation.

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Table 5

Bivariate analysis achievement for ODI.

Characteristic	Failed MCID (%)	RR	95% CI	P value^a
Overall	26.8%	–	–	–
Age
18–50 y	53.7%	Reference
>50 y	46.3%	1.6	(1.3–2.0)	0.001
Gender
Male	26.7%	1.2	(0.9–1.5)	0.231
Female	73.3%	Reference
BMI, kg/m²
<30	60.3%	Reference
≥30	39.7%	1.0	(0.7–1.3)	0.974
Smoking status
Nonsmoker	82.5%	Reference
Smoker	17.5%	1.1	(0.8–1.4)	0.731
Diabetes
Nondiabetic	93.5%	Reference
Diabetic	6.5	1.1	(0.7–1.8)	0.622
Ageless CCI
<1	46.9%	Reference
≥1	53.1%	1.6	(1.3–2.1)	0.001
ASA score
<2	30.8%	Reference
≥2	69.2%	1.2	(0.9–1.6)	0.241
Insurance
Non-WC	69.1%	Reference
WC	30.8%	1.0	(0.8–1.3)	0.725
Operative length
<50 min	68.7%	Reference
≥50 min	31.3%	0.9	(0.8–1.0)	0.158
EBL
<50 mL	91.6%	Reference
≥50 mL	8.4%	1.1	(0.7–1.6)	0.472
Operative levels
Single	72.8%	Reference
Multilevel	27.2%	1.7	(1.3–2.1)	0.001
Operative technique
Laminectomy only	27.4%	1.5	(1.1–1.9)	0.001
Discectomy only	-	-	-	-
Laminectomy + discectomy	71.3%	1.0	(0.8–1.3)	0.796
Spinal pathologies
HNP	70.1%	0.6	(0.5–0.9)	0.003
Central stenosis	73.7%	1.8	(1.4–2.3)	0.001
Foraminal stenosis	41.9%	1.4	(1.1–1.7)	0.003

Boldface indicates statistical significance.
aP value calculated using Poisson regression.
ASA, American Society of Anesthesiologists; BMI, body mass index; CCI, Charlson Comorbidity Index; EBL, estimated blood loss; HNP, herniated nucleus pulposus; ODI, Oswestry Disability Index; RR, relative risk; WC, workers’ compensation.

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Table 6

Bivariate analysis achievement for SF-12 PCS.

Characteristic	Failed MCID (%)	RR	95% CI	P value^a
Overall	22.2%	–	–	–
Age
18–50 y	58.9%	Reference
>50 y	41.1%	1.3	(1.1–1.7)	0.035
Gender
Male	32.2%	0.9	(0.7–1.2)	0.451
Female	67.8%	Reference
BMI
<30 kg/m²	57.1%	Reference
≥30 kg/m²	42.9%	1.1	(0.9–1.5)	0.306
Smoking status
Nonsmoker	83.3%	Reference
Smoker	16.7%	0.9	(0.7–1.4)	0.967
Diabetes
Nondiabetic	94.4%	Reference
Diabetic	5.6%	0.9	(0.5–1.7)	0.877
Ageless CCI
<1	53.2%	Reference
≥1	46.8%	1.3	(0.9–1.6)	0.085
ASA score
<2	34.0%	Reference
≥2	66.0%	1.0	(0.7–1.4)	0.888
Insurance
Non-WC	70.6%	Reference
WC	29.4%	1.1	(0.8–1.4)	0.663
Operative length
<50 min	74.4%	Reference
≥50 min	25.6%	0.7	(0.5–0.9)	0.025
EBL
<50 mL	93.0%	Reference
≥50 mL	7.0%	0.9	(0.6–1.3)	0.720
Operative levels
Single	80.0%	Reference
Multilevel	20.0%	1.1	(0.8–1.5)	0.486
Operative technique
Laminectomy only	21.3%	1.2	(0.9–1.5)	0.076
Discectomy only	-	-	-	-
Laminectomy + discectomy	77.3%	0.8	(0.7–1.0)	0.096
Spinal pathologies
HNP	75.0%	0.7	(0.6–1.0)	0.050
Central stenosis	76.1%	2.0	(1.5–2.8)	0.001
Foraminal stenosis	50.0%	1.9	(1.5–2.5)	0.001

Boldface indicates statistical significance.
aP value calculated using Poisson regression.
ASA, American Society of Anesthesiologists; BMI, body mass index; CCI, Charlson Comorbidity Index; EBL, estimated blood loss; HNP, herniated nucleus pulposus; RR, relative risk; SF-12, 12 item short form; WC, workers’ compensation.

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Table 7

Bivariate analysis achievement for PROMIS PF.

Characteristic	Failed MCID (%)	RR	95% CI	P value^a
Overall	17.0%	–	–	–
Age
18–50 y	18.5%	Reference
>50 y	81.5%	0.89	(0.7–1.1)	0.363
Gender
Male	43.5%	1.1	(0.9–1.4)	0.309
Female	56.5%	Reference
BMI
<30 kg/m²	46.7%	Reference
≥30 kg/m²	53.3%	1.4	(1.1–1.7)	0.002
Smoking status
Nonsmoker	87.0%	Reference
Smoker	13.0%	0.9	(0.6–1.3)	0.817
Diabetes
Nondiabetic	79.3%	Reference
Diabetic	20.7	1.2	(0.9–1.5)	0.099
Ageless CCI
<1	3.3%	Reference
≥1	96.7%	1.5	(0.7–3.5)	0.332
ASA score
<2	63.0%	Reference
≥2	37.0	1.1	(0.9–1.3)	0.487
Insurance
WC	84.8%	Reference
Non-WC	15.2%	1.1	(0.9–1.4)	0.508
Operative length
<50 min	43.5%	Reference
≥50 min	56.5%	1.1	(0.9–1.3)	0.508
EBL
<50 mL	50.0%	Reference
≥50 mL	50.0%	1.1	(0.9–1.3)	0.411
Operative levels
Single	71.7%	Reference
Multilevel	28.3%	1.4	(1.2–1.7)	0.001
Operative technique
Laminectomy only	23.3%	1.3	(0.9–1.8)	0.077
Discectomy only	–	–	–	–
Laminectomy + discectomy	75.4%	0.8	(0.6–1.1)	0.147
Spinal pathologies
HNP	46.7%	0.8	(0.6–0.9)	0.015
Central stenosis	10.9%	1.2	(1.0–1.5)	0.094
Foraminal stenosis	15.2%	1.3	(1.0–1.7)	0.088

Boldface indicates statistical significance.
aP value calculated using Poisson regression.
ASA, American Society of Anesthesiologists; BMI, body mass index; CCI, Charlson Comorbidity Index; EBL, estimated blood loss; HNP, herniated nucleus pulposus; PROMIS PF, patient-reported outcomes measures information system physical function; RR, relative risk; WC, workers’ compensation.

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Table 8

Multiple regression analysis for MCID achievement.

Outcome Measure	RR	95% CI	P value^a
VAS Back
Insurance	1.7	(1.2–2.3)	0.001
VAS Leg
Age	1.0	(0.9–1.0)	0.512
Ageless CCI	1.6	(1.1–2.3)	0.024
EBL	3.3	(1.3–8.5)	0.010
HNP	0.5	(0.3–0.9)	0.032
ODI
Age	1.1	(1.0–1.0)	0.032
Ageless CCI	2.2	(1.4–3.5)	0.001
EBL	1.0	(0.9–0.9)	0.001
Smoking status	0.7	(0.4–1.3)	0.282
Operative length	0.9	(0.9–1.0)	0.772
Central stenosis	1.2	(0.7–1.9)	0.415
Foraminal stenosis	1.5	(0.9–2.3)	0.099
SF-12 PCS
Age	1.0	(0.9–1.0)	0.103
Gender	0.9	(0.6–1.3)	0.522
BMI	1.2	(0.8–1.7)	0.451
Ageless CCI	1.6	(0.9–2.6)	0.056
EBL	1.2	(0.5–2.5)	0.627
Smoker status	0.7	(0.4–1.3)	0.318
Operative length	1.1	(0.7–1.8)	0.551
HNP	0.5	(0.3–0.8)	0.016
Foraminal stenosis	0.6	(0.4–1.0)	0.063
Laminectomy	2.5	(0.5–11.5)	0.252
PROMIS PF
Gender	0.9	(0.6–1.5)	0.931
BMI	1.1	(0.8–1.7)	0.480
Diabetes	0.4	(0.1–1.3)	0.140
Insurance	2.0	(1.1–3.8)	0.022
EBL	4.5	(1.1–17.6)	0.027
No. of operative levels	1.3	(0.8–1.9)	0.287

Boldface indicates statistical significance.
aP value calculated using LASSO logistical regression model.
BMI, body mass index; CCI, Charlson Comorbidity Index; EBL, estimated blood loss; HNP, herniated nucleus pulposus; RR, relative risk; VAS, visual analog scale.