Risk factors for knee replacement due to primary osteoarthritis, a population based, prospective cohort study of 315,495 individuals

Table 4 Crude rate and relative risk of KR due to primary OA in 161,700 Norwegian women

	No. of participants	Person-years	No. of knee replacements	KRs per 10,000 person-years (crude rate)	Multivariate adjusted RR* (95% CI)
*Body Mass Index, kg/m* ²
<21.6	40,526	489,541	35	0.7	1
21.7-23.5	39,562	477,775	73	1.5	1.93 (1.29-2.89)
23.6-26.1	40,691	491,052	177	3.6	3.92 (2.72-5.64)
> = 26.2	40,911	491,705	608	12.4	11.06 (7.83-15.62)
P (test for trend)					<0.0001
*Physical activity at work*
Sedentary	46,050	555,499	201	3.6	1
Moderate	84,368	1,017,358	498	4.9	1.18 (1.00-1.40)
Intermediate	27,744	334,751	149	4.5	1.30 (1.05-1.61)
Intensive	3,343	40,230	45	11.2	2.29 (1.65-3.18)
P (test for trend)					<0.0001
*Physical activity at leisure*
Sedentary	31,322	377,346	190	5.0	1
Moderate	113,127	113,127	624	55.2	0.99 (0.84-1.16)
Intermediate	16,204	16,204	75	46.3	0.92 (0.70-1.21)
Intensive	968	11,687	4	3.4	1.72 (0.64-4.65)
P (test for trend)					0.797
*Height*
< 161	44,123	531,632	325	6.1	1
162-165	42,320	510,399	238	4.7	1.10 (0.93-1.30)
166-169	38,461	464,179	150	3.2	0.93 (0.77-1.14)
> = 170	36,791	443,925	180	4.1	1.48 (1.23-1.80)
P (test for trend)					0.003
*Smoking*
Never smoker	65,929	794,420	526	6.6	1
Former smoker	31,174	376,055	163	4.3	0.81 (0.68-0.96)
Smoker	64,597	779,720	204	2.6	0.66 (0.56-0.78)
P (test for trend)					<0.0001

*Adjusted for age at screening, height, smoking habits, BMI and physical activity at work, and at leisure time.

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