Table 2. Association between status as a baggage handler and cumulative years as a baggage handler and meniscal lesions.

Copenhagen Airport Cohort, 1994–2012.

Model	Cases	Person-years	IR	IRR, unadjusted (95%CI)	IRR,adjusted1 (95% CI)
1. Baggage handler
No	3,243	949,530	341.5	0.55 (0.49–0.62)	0.64 (0.52–0.80)
Yes	277	44,583	621.3	1.00 (ref)	1.00 (ref)
p-value				< .0001	< .0001
2. Baggage handler years, categorical
Non baggage handler	3,243	949,530	341.5	0.61 (0.49–0.76)	0.79 (0.60–1.04)
0.1–2.9 years	86	15,371	559.5	1.00 (ref)	1.00 (ref)
3.0–9.9 years	107	15,242	702.0	1.25 (0.94–1.67)	1.38 (1.04–1.83)
10.0–19.9 years	66	9,882	667.9	1.19 (0.87–1.65)	1.40 (1.01–1.94)
20.0+ years	18	4,087	440.4	0.79 (0.47–1.31)	1.02 (0.61–1.71)
p-value (df = 4)				< .0001	0.0003
p-value (only baggage handlers, df = 3)				0.15	0.16
3. Baggage handler years, linear2
Baggage handler
No				0.51 (0.43–0.61)	0.66 (0.52–0.83)
Yes				1.00 (ref)	1.00 (ref)
Continuous linear (per 5 years)				0.96 (0.88–1.04)	1.01 (0.93–1.10)
p-value				0.29	0.76
4. Baggage handler years, linear spline2
Baggage handler
No				0.71 (0.53–0.94)	0.95 (0.68–1.34)
Yes				1.00 (ref)	1.00 (ref)
Continuous linear 0–4.9 years (per 5 years)				1.70 (1.15–2.52)	1.91 (1.29–2.84)
p-value				0.0079	0.0012
Continuous linear 5+ years (per 5 years)				0.84 (0.75–0.95)	0.88 (0.78–1.00)
p-value				0.0063	0.043
p-value of no difference between linear slopes				0.035	0.020

Abbreviations: IR, incidence rate per 100,000 person-years; IRR, incidence rate ratio.

¹ Adjusted for age, calendar year, use of baggage lifter, use of baggage belt loader, educational level and pre-employment knee injuries.

² Also adjusted for baggage handler (yes/no).