Statistical analysis of arthroplasty data

Figures & data

Kaplan-Meier survival curves for implants A, B, and C with standard (solid line) and modified (dotted line) 95% confidence limits for implant A at 20-year follow-up. In the modified CI the number of implants still at risk at the time of interest is taken into account in the calculation of the lower confidence limit.

Table 1. Kaplan-Meier estimated survival probabilities for implants A, B, and C with standard 95% confidence interval (CI) and modified confidence interval (CI_mod) with the Peto lower confidence limit. With the CI_mod, the number of implants still at risk at the time of interest is taken into account in the calculation of the lower confidence limit

15-year survival				20-year survival
Implant	%	CI	CImod	%	CI	CImod
A	91	91–92	90–92	88	87–89	81–89
B	90	88–90	86–91	81	78–84	47–84
C	94	93–95	90–95	92	90–94	60–94

Table 2. Cox regression estimated crude and adjusted relative risk (RR) of revision comparing implant B and C with implant A. Breakdown of patient gender and age according to type of implant

			Simple Cox regression			Multiple Cox regression ^a
Implant	% males	% ≥ 70 years	RR	95 % CI	p-value	RR	95 % CI	p-value
A	29	61	1			1
B	28	64	1.08	0.98–1.19	0.1	1.05	0.95–1.16	0.3
C	27	78	0.72	0.62–0.83	< 0.001	0.80	0.69–0.93	0.003

^a Adjustment for age (≤ 59, 60–69, 70–79, ≥ 80), sex, and diagnosis (OA, other).