TABLE 2.

Factors Associated With the Likelihood of a Worker Receiving an Early MRI for Low Back Sprain/Strain

	Unadjusted		Model 1		Model 2
	IRR	95% CI	IRR	95% CI	IRR	95% CI
Demographics
Age (at injury)
<24 yr	0.56	0.37–0.83	0.84	0.57–1.24	0.81	0.55–1.19
25–34 yr	0.76	0.59–0.98	0.93	0.73–1.18	0.91	0.71–1.15
35–44 yr	1.00	Reference	1.00	Reference	1.00	Reference
45–54 yr	1.04	0.83–1.32	0.95	0.77–1.17	0.97	0.78–1.21
>55 yr	0.82	0.58–1.15	1.00	0.72–1.39	0.85	0.61–1.18
Sex
Female	1.00	Reference	1.00	Reference	1.00	Reference
Male	1.25	1.02–1.00	1.43	1.12–1.82	1.24	0.98–1.58
Race
White	1.00	Reference	1.00	Reference	1.00	Reference
Nonwhite	0.73	0.58–0.91	0.78	0.61–1.00	0.83	0.64–1.07
Ethnicity
Non-Hispanic	1.00	Reference	1.00	Reference	1.00	Reference
Hispanic	0.88	0.68–1.14	1.33	1.00–1.76	1.37	1.02–1.83
Education
Less than high school	0.88	0.65–1.19	0.86	0.64–1.15	0.90	0.67–1.22
High school diploma/GED	1.00	Reference	1.00	Reference	1.00	Reference
Some college	0.92	0.75–1.14	0.84	0.70–1.02	0.83	0.68–1.00
College degree	0.74	0.50–1.10	0.79	0.54–1.16	0.77	0.53–1.13
Household income ($)
<30,000	1.00	Reference	1.00	Reference	1.00	Reference
30,000–45,000	1.24	0.98–1.58	1.07	0.85–1.35	1.09	0.85–1.38
45,001–70,000	1.36	1.07–1.73	1.11	0.85–1.43	1.10	0.85–1.43
>70,000	1.41	1.03–1.93	1.39	1.01–1.90	1.25	0.90–1.74
Marital status
Married	1.00	Reference	1.00	Reference	1.00	Reference
Living with partner	0.98	0.75–1.29	1.09	0.84–1.42	1.04	0.80–1.36
Divorced	1.07	0.84–1.35	1.04	0.83–1.29	1.10	0.88–1.39
Other	0.69	0.51–0.95	0.84	0.63–1.14	0.76	0.56–1.02
Health characteristics
BMI
Normal, <25	1.00	Reference	1.00	Reference	1.00	Reference
Overweight, 25–29	1.16	0.92–1.46	1.06	0.86–1.32	1.09	0.87–1.35
Obese, 30–34	1.23	0.94–1.60	1.10	0.85–1.41	1.17	0.91–1.50
Very obese, >34	1.37	0.99–1.90	1.07	0.79–1.46	1.19	0.87–1.63
Health in year before injury
Excellent	1.00	Reference.	1.00	Reference
Very good	0.88	0.69–1.12	0.80	0.61–1.05
Good	0.90	0.70–1.16	0.88	0.67–1.17
Fair/poor	0.98	0.70–1.36	0.88	0.62–1.24
SF-36 mental health score
2 SD below population mean	3.06	2.31–4.06	1.34	1.00–1.81
1–2 SD below population mean	2.61	1.98–3.43	1.24	0.94–1.64
1 SD below population mean	2.14	1.62–2.82	1.38	1.06–1.81
At or above population mean	1.00	Reference	1.00	Reference
Catastrophizing
Low (<1)	1.00	Reference	1.00	Reference
Moderate (1–2.9)	1.88	1.38–2.57	1.00	0.73–1.36
High (3–4)	3.01	2.19–4.13	1.15	0.82–1.61
Work fear-avoidance
Low (0–2.9)	1.00	Reference	1.00	Reference
Moderate (3–4.9)	1.67	1.15–2.42	1.32	0.94–1.85
High (5–5.9)	2.81	1.98–3.99	1.73	1.24–2.41
Very high (>6)	3.09	2.15–4.43	1.54	1.07–2.22
Clinical characteristics
Type of first medical visit
Primary care	1.00	Reference	1.00	Reference	1.00	Reference
Occupational medicine	1.40	0.93–2.10	1.28	0.90–1.82	1.21	0.84–1.74
Chiropractor	0.58	0.45–0.75	0.53	0.42–0.66	0.52	0.41–0.65
Surgeon	1.53	0.96–2.43	1.78	1.08–2.92	1.51	0.95–2.42
Emergency room	1.05	0.82–1.33	0.90	0.72–1.13	0.98	0.78–1.22
Other	1.15	0.62–2.12	1.17	0.66–2.09	1.24	0.67–2.32
Work characteristics
Offered job accommodation
Yes	1.00	Reference	1.00	Reference	1.00	Reference
No	1.47	1.21–1.78	1.13	0.94–1.35	1.40	1.17–1.68
More than 1 previous compensable back claims
Yes	1.34	1.08–1.65	1.12	0.91–1.36	1.15	0.94–1.42
No	1.00	Reference	1.00	Reference	1.00	Reference
Job satisfaction
Not at all	0.79	0.50–1.27	0.66	0.43–1.00
Not too satisfied	0.95	0.67–1.36	0.84	0.60–1.17
Somewhat satisfied	1.07	0.88–1.30	1.09	0.91–1.30
Very satisfied	1.00	Reference	1.00	Reference
Industry
Natural resources	0.62	0.33–1.15	0.70	0.40–1.24	0.65	0.37–1.15
Construction	1.24	0.93–1.64	1.13	0.86–1.48	1.26	0.96–1.64
Manufacturing	1.51	1.08–2.10	1.39	1.02–1.89	1.39	1.01–1.90
Trade/transportation	1.00	Reference	1.00	Reference	1.00	Reference
Management	1.22	0.91–1.63	1.26	0.97–1.64	1.22	0.93–1.60
Education/health	1.01	0.74–1.39	1.15	0.83–1.58	1.16	0.83–1.61
Hospitality	1.01	0.72–1.41	1.11	0.83–1.47	1.15	0.85–1.56
Physical demands at work
Light	1.00	Reference	1.00	Reference	1.00	Reference
Medium	1.21	0.91–1.62	1.14	0.88–1.48	1.17	0.90–1.53
Heavy	1.16	0.85–1.58	1.02	0.76–1.37	1.17	0.87–1.57
Very heavy	1.56	1.17–2.07	1.23	0.93–1.62	1.44	1.09–1.91
Injury characteristics
Health status at the time of interview
Excellent	1.00	Reference	1.00	Reference
Very good	0.97	0.74–1.26	1.06	0.79–1.41
Good	1.06	0.81–1.38	0.98	0.73–1.31
Fair/poor	1.05	0.75–1.46	1.01	0.70–1.44
Pain intensity the last week
Low/no pain (1–3)	1.00	Reference	1.00	Reference
Mild (4–6)	2.54	1.79–3.60	0.86	0.62–1.20
Moderate/major pain (7–9)	2.88	2.08–3.99	0.92	0.67–1.26
Roland-Morris disability questionnaire score
≤6	1.00	Reference	1.00	Reference
7–12	4.09	2.25–7.43	2.98	1.63–5.46
13–18	7.43	4.25–12.98	4.63	2.54–8.42
≥18	12.00	6.94–20.76	5.87	3.16–10.89
Medical record documented injury severity rating
Mild sprain/strain and/or minor physical examination findings	1.00	Reference	1.00	Reference	1.00	Reference
Major sprain/strain evidenced by substantial immobility	1.88	1.41–2.49	1.49	1.13–1.95	1.87	1.42–2.47
Evidence of radiculopathy or reflexes absent	4.50	3.63–5.59	3.04	2.44–3.79	4.55	3.67–5.64

All covariates listed are included in model 1. Model 2 does not adjust for health in year before injury, SF-36 mental health score, catastrophizing, fear-avoidance, job satisfaction, health status at the time of the interview, pain intensity, or Roland-Morris disability questionnaire score.

IRR indicates incident rate ratio; CI, confidence interval; SF-36, 36-Item Short Form Health Survey; BMI, body mass index; GED, general education diploma; SD, standard deviation.