Associations between biomarkers of bone and cartilage turnover, gender, pain categories and radiographic severity in knee osteoarthritis

Table 3 Estimated effect of baseline characteristics on uCTX-II biomarker level

Descriptive variable	Univariate		Multivariate		Multivariate		Multivariate
Descriptive variable	Estimate (95% CI) %	p value	Estimate (95% CI) %	p value	Estimate (95% CI) %	p value	Estimate (95% CI) %	p value
WOMAC pain (per 10 points)	5.5 [3.3;7.7]	< 0.001	2.2 [0.2;5.2]	0.03	–	–	–	–
WOMAC WB pain (per 10 points)	5.4 [3.2; 7.6]	< 0.001	–	–	2.2 [0.2;4.2]	0.03	–	–
WOMAC NWB pain (per 10 points)	3.1 [1.3;4.9]	< 0.001	–	–	–	–	1.3 [− 0.3;2.9]	0.11
Age (per year)	1.0 [0.4;1.6]	< 0.001	0.5 [0.1;0.9]	0.02	0.6 [0.0;1.2]	0.02	0.6 [0.0;1.2]	0.01
BMI (per 1 kg/m²)	1.2 [0.6;1.8]	< 0.001	0.8 [0.2;1.4]	0.02	0.7 [01;1.3]	0.03	0.8 [0.0;1.6]	0.02
Female sex	47.6 [38.0;57.2]	< 0.001	41.7 [32.7;50.7]	< 0.001	41.4 [32.4;50.4]	< 0.001	41.7 [32.7;50.7]	< 0.001
KL (per KL grade)	18.5 [14.8;22.2]	< 0.001	14.8 [11.0;18.5]	< 0.001	14.6 [10.9;18.3]	< 0.001	15.1 [11.4;18.8]	< 0.001

Effects of baseline body mass index, sex, the sum of Kellgren-Lawrence grade of the non-target and the target knee and WOMAC pain to the baseline uCTX-II value, in percent and in univariate and multivariate analyses. WOMAC pain and sub-categories are calculated as the sum of both knees, normalised to 0–100 and analysed as the sum of the five pain sub-score questions, and as composites of weight-bearing (WB) pain or non-weight-bearing (NWB) pain. As the category “WOMAC pain” contains variables also included in “WOMAC WB pain” and “WOMAC NWB pain”, one multivariate model per each of these groups is performed. The parameter estimates and the standard error of estimate from the regression analyses are back-transformed in the presentation of the outcome of the regression analyses whereby the estimated effect and the confidence interval of the baseline characteristics will be given in the unit of percentage of the biomarker value. p values < 0.05 were considered significant and highlighted in italics. WOMAC Western Ontario and McMaster Universities Osteoarthritis Index, BMI body mass index, KL Kellgren-Lawrence, uCTX-II urine C-telopeptide of cross-linked collagen type II

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