Differences in Clinically Important Physical Function Improvement in Workers’ Compensation Population

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

doi:10.14444/8186

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Table 1

Unmatched patient baseline demographics.

Characteristic	Total (n = 634)	Non-WC (n = 374)	WC (n = 260)	P Value^a
Age, mean ± SD	50.8 ± 11.7	53.9 ± 11.7	46.4 ± 10.0	<0.001
Gender				<0.001
Female	37.9% (240)	48.7% (182)	22.3% (58)
Male	62.1% (394)	51.3% (192)	77.7% (202)
Ethnicity				<0.001
White	66.3% (420)	79.4% (297)	47.5% (123)
Nonwhite	33.7% (213)	20.6% (77)	52.5% (136)
Body mass index				0.003
<30 kg/m²	51.9% (328)	56.8% (212)	44.8% (116)
≥30 kg/m²	48.1% (304)	43.1% (161)	55.2% (143)
Smoking status				<0.001
Nonsmoker	80.8% (512)	86.1% (322)	73.0% (190)
Smoker	19.2% (122)	13.9% (52)	26.9% (70)
Diabetic status				0.976
Nondiabetic	88.8% (563)	88.8% (332)	88.9% (44)
Diabetic	11.2% (71)	11.2% (42)	11.1% (4)
American Society of Anesthesiologists Score				0.742
<2	82.8% (521)	83.2% (308)	82.2% (213)
≥2	17.2% (108)	16.7% (62)	17.8% (46)
Charlson Comorbidity Index Score				0.001
≤1	24.9% (154)	19.9% (73)	32.1% (81)
>1	75.1% (464)	80.1% (293)	67.9% (171)

Data presented as % (n) unless otherwise indicated. Boldface indicates statistical significance.
aP value calculated using χ ² test or Student’s t test.
WC, workers’ compensation.

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Table 2

Matched patient baseline demographics.

Characteristic	Total (n = 121)	Non-WC (n = 92)	WC (n = 29)	P Value^a
Age, mean ± SD	53.5 ± 9.4	54.6 ± 9.7	50.0 ± 7.4	0.023
<50 y	34.7% (42)	31.5% (29)	44.8% (13)
50–64 y	62.0% (75)	64.1% (59)	55.2% (16)
<65 y	3.3% (4)	4.3% (4)	0.0% (0)
Gender				0.044
Female	36.4% (44)	41.3% (38)	20.7% (6)
Male	63.6% (77)	58.7% (54)	79.3% (23)
Ethnicity				<0.001
White	78.5% (95)	87.0% (80)	51.7% (15)
Nonwhite	21.5% (26)	13.0% (12)	48.3% (14)
Body mass index				0.437
<30 kg/m²	54.5% (66)	56.5% (52)	48.3% (14)
≥30 kg/m²	44.5% (55)	43.5% (40)	51.7% (15)
Smoking status				0.078
Nonsmoker	88.4% (107)	91.3% (84)	79.3% (23)
Smoker	11.6% (14)	8.7% (8)	20.7% (6)
Diabetic status				0.423
Nondiabetic	90.1% (109)	91.3% (84)	86.2% (25)
Diabetic	9.9% (12)	8.7% (8)	13.8% (4)
American Society of Anesthesiologists Score				0.794
<2	84.3% (102)	84.8% (80)	82.8% (24)
≥2	15.7% (19)	15.2% (14)	17.2% (5)
Charlson Comorbidity Index Score				0.331
≤1	23.6% (29)	26.1% (24)	17.2% (32)
>1	76.4% (92)	73.9% (68)	82.8% (12)
Duration of symptoms				0.005
<6 mo	20.4% (22)	19.5% (16)	23.1% (6)
6 mo to 1 y	21.3% (23)	14.6% (12)	42.3% (11)
>1 y	58.3% (63)	65.9% (54)	34.6% (9)
Time to surgery, mo, mean ± SD, mo (n)	4.9 ± 10.4 (114)	4.7 ± 11.4 (92)	5.9 ± 4.1 (22)	0.628

Data provided as % (n) unless otherwise indicated. Boldface indicates statistical significance.
aP value calculated using χ ² test or Student’s t test.
WC, workers’ compensation.

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Table 3

Perioperative characteristics.

Characteristic	Total (n = 121)	Non-WC (n = 92)	WC (n = 29)	P Value^a
Spinal pathology
Degenerative disc disease	55.3% (67)	53.3% (49)	62.1% (18)	0.405
Degenerative spondylolisthesis	65.4% (70)	61.9% (52)	78.3% (18)	0.144
Isthmic spondylolisthesis	24.3% (26)	28.6% (24)	8.7% (2)	0.049
Operative time, min, mean ± SD	124.5 ± 23.5	123.9 ± 23.2	126.1 ± 24.9	0.663
Estimated blood loss, mL, mean ± SD, mL	48.5 ± 25.2	48.5 ± 24.3	48.3 ± 28.3	0.962
Length of stay, h, mean ± SD	29.2 ± 18.7	29.4 ± 19.7	28.8 ± 15.4	0.877
Day of discharge				0.310
POD 0	19.0% (23)	18.5% (17)	20.7% (6)
POD 1	61.2% (74)	63.0% (58)	55.1% (16)
POD 2	15.7% (19)	13.0% (12)	24.1% (7)
POD 3	4.1% (5)	5.5% (5)	0.0% (0)

Data provided as % (n) unless otherwise indicated. Boldface indicates statistical significance.
aP value calculated using either χ ² test or Student’s t test.
POD, postoperative day; WC, workers’ compensation.

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Table 4

Postoperative improvement of outcomes between groups.

Patient-Reported Outcome Measures	Non-WC, Mean ± SD (n)	P Value^a	WC, Mean ± SD (n)	P Value^a	P Value^b
VAS back
Preoperative	6.0 ± 2.6 (92)	–	6.7 ± 2.2 (29)	–	0.297
6 wk	3.3 ± 2.6 (83)	<0.001	5.1 ± 2.0 (25)	0.001	0.001
12 wk	2.6 ± 2.2 (76)	<0.001	5.3 ± 2.5 (24)	0.004	<0.001
6 mo	2.5 ± 2.4 (75)	<0.001	5.3 ± 2.5 (25)	0.007	<0.001
1 y	2.2 ± 2.4 (48)	<0.001	4.7 ± 2.7 (13)	0.147	0.004
VAS leg
Preoperative	5.3 ± 3.0 (92)	–	5.0 ± 3.0 (29)	–	0.475
6 wk	2.5 ± 2.5 (83)	<0.001	4.1 ± 2.7 (25)	0.188	0.012
12 wk	1.9 ± 2.4 (77)	<0.001	3.6 ± 2.7 (24)	0.032	0.004
6 mo	1.6 ± 2.5 (75)	<0.001	3.4±2.5 (25)	0.044	<0.001
1 y	1.9 ± 2.9 (48)	<0.001	4.1 ± 2.7 (13)	0.223	0.002
ODI
Preoperative	35.8 ± 13.9 (92)	–	45.1 ± 15.6 (29)	–	0.003
6 wk	28.5 ± 18.1 (84)	<0.001	46.6 ± 17.3 (25)	0.696	<0.001
12 wk	22.4 ± 15.8 (78)	<0.001	43.5 ± 14.3 (24)	0.439	<0.001
6 mo	15.7 ± 13.6 (76)	<0.001	39.1 ± 18.9 (25)	0.088	<0.001
1 y	15.7 ± 18.7 (48)	<0.001	30.3 ± 21.3 (13)	0.071	0.009
SF-12 PCSy
Preoperative	32.4 ± 8.0 (88)	–	27.4 ± 6.6 (27)	–	0.001
6 wk	34.0 ± 9.2 (77)	0.138	26.3 ± 6.0 (22)	0.319	0.001
12 wk	38.1 ± 10.6 (68)	0.001	27.5 ± 5.7 (23)	0.775	<0.001
6 mo	42.9 ± 11.0 (62)	<0.001	28.3 ± 7.0 (18)	0.581	<0.001
1 y	43.1 ± 10.8 (54)	<0.001	30.8 ± 10.1 (15)	0.401	<0.001
PROMIS-PF
Preoperative	36.4 ± 4.9 (92)	–	32.6 ± 5.3 (29)	–	0.001
6 wk	38.2 ± 6.9 (77)	0.017	33.7 ± 5.5 (21)	0.444	0.004
12 wk	42.2 ± 6.4 (62)	<0.001	37.2 ± 6.3 (18)	0.043	0.005
6 mo	45.3 ± 6.7 (63)	<0.001	39.2 ± 7.3 (16)	<0.001	0.003
1 y	47.2 ± 8.2 (57)	<0.001	39.0 ± 8.5 (12)	0.022	0.004

Boldface indicates statistical significance.
aP value was calculated using paired t test.
bP values calculated using Mann-Whitney U test.
ODI, Oswestry Disability Index; PROMIS-PF, Patient-Reported Outcome Measurement Information System physical function; SF-12, 12-Item Short Form Physical Component Summary; VAS, visual analog scale; WC, workers’ compensation.

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Table 5

Effect of duration of symptoms and time to surgery on outcomes.

PROM	Coeff	95% CI	P Value^a	P Value^b	P Value^c
VAS back
Preoperative	0.7	−0.4 to 1.8	0.196	0.090	0.163
6 wk	1.8	0.7–2.9	0.002	0.006	0.003
12 wk	2.7	1.7–3.8	<0.001	<0.001	<0.001
6 mo	2.8	1.7–3.9	<0.001	<0.001	<0.001
1 y	2.5	0.9–4.1	0.002	0.054	0.005
VAS leg
Preoperative	−0.5	−1.7 to 0.8	0.480	0.548	0.539
6 wk	1.5	0.3–2.7	0.012	0.032	0.041
12 wk	1.7	0.5–2.9	0.005	0.005	0.002
6 mo	1.8	0.6–2.9	0.003	0.001	0.006
1 y	2.1	0.3–4.0	0.021	0.032	0.145
ODI
Preoperative	9.4	3.2–15.7	0.003	0.001	0.002
6 wk	18.4	10.3–26.5	<0.001	<0.001	<0.001
12 wk	21.1	13.9–28.4	<0.001	<0.001	<0.001
6 mo	23.4	16.5–30.3	<0.001	<0.001	<0.001
1 y	14.6	2.5–26.7	0.019	0.009	0.018
SF-12 PCS
Preoperative	−5.6	−9.0 to –2.2	0.002	<0.001	0.002
6 wk	−6.7	−10.9 to –2.7	0.001	0.002	0.001
12 wk	−9.8	−14.3 to –5.2	<0.001	<0.001	<0.001
6 mo	−14.7	−20.0 to 9.3	<0.001	<0.001	<0.001
1 y	−12.2	−18.3 to –6.0	<0.001	0.001	0.001
PROMIS-PF
Preoperative	−4.0	−6.3 to –1.6	0.001	0.002	0.001
6 wk	−4.5	−7.7 to –1.2	0.007	0.009	0.010
12 wk	−5.0	−8.5 to –1.6	0.005	0.012	0.010
6 mo	−6.1	−9.9 to –2.2	0.002	0.001	0.004
1 y	−8.2	−13.4 to –2.9	0.003	0.011	0.009

Boldface indicates statistical significance.
aP value was calculated using simple linear regression to determine effect of workers’ compensation status and preoperative duration of symptoms.
bP value was calculated using multiple linear regression to determine effect of workers’ compensation while accounting for duration of preoperative symptoms.
cP values calculated using multiple linear regression to determine effect of workers’ compensation status while accounting for time to surgery.
ODI, Oswestry Disability Index; PROM, Patient-Reported Outcome Measures; PROMIS-PF, Patient-Reported Outcome Measurement Information System physical function; SF-12 PCS, 12-Item Short Form Physical Component Summary; VAS, visual analog scale; WC, workers’ compensation.

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Table 6

Impact of WC on patient-reported outcome measures.

Outcome Measure	Preop—6 wk	Preop—12 wk	Preop—6 mo	Preop—1 y	Overall
VAS back
Non-WC	63.9% (53)	77.6% (59)	72.0% (54)	77.1% (37)	85.9% (79)
WC	52.0% (13)	50.0% (12)	60.0% (15)	61.5% (8)	68.9% (20)
P value^a	0.286	0.009	0.261	0.258	0.040
VAS leg
Non-WC	61.5% (51)	71.4% (57)	68.0% (52)	58.3% (28)	78.3% (72)
WC	40.0% (10)	45.8% (11)	48.0% (12)	61.5% (8)	62.0% (18)
P value^a	0.058	0.021	0.073	0.835	0.082
ODI
Non-WC	40.5% (34)	44.9% (35)	61.8% (47)	66.7% (32)	75.0% (69)
WC	24.0% (6)	16.7% (4)	36.0% (9)	46.1% (6)	43.3% (12)
P value^a	0.133	0.013	0.024	0.176	0.001
SF-12 PCS
Non-WC	33.8% (26)	52.9% (36)	69.3% (43)	75.9% (41)	73.9% (68)
WC	18.1% (4)	30.4% (7)	22.2% (4)	53.3% (8)	48.3% (14)
P value^a	0.161	0.062	<0.001	0.088	0.010
PROMIS-PF
Non-WC	15.6% (12)	37.1% (23)	50.8% (32)	57.9% (33)	59.8% (55)
WC	9.5% (2)	22.2% (4)	43.7% (7)	25.0% (3)	37.9% (11)
P value^a	0.482	0.227	0.615	0.034	0.039

The following MCID values derived from Copay et al; VAS back = 1.2, VAS leg = 1.6, ODI = 12.8; or Parker et al; SF-12 = 4.0; PROMIS MCID values derived from Hung et al PROMIS-PF = 8.0.
Data presented as % (n). Boldface indicates statistical significance.
aP value was calculated for each category using logistic regression.
MCID, minimum clinically important difference; PROMIS-PF, Patient-Reported Outcome Measurement Information System physical function; SF-12 PCS, 12-Item Short Form Physical Component Summary; VAS, visual analog scale; WC, workers’ compensation.