A retrospective comparative study of mortality and causes of death among patients with metal-on-metal and metal-on-polyethylene total hip prostheses in primary osteoarthritis after a long-term follow-up

Table 4 Observed number of cancer deaths (Obs) and standardised mortality ratio (SMR) and rate ratio (RR) with 95% confidence intervals of patients with metal-on-metal and metal-on-polyethylene total hip prostheses stratified by number of postoperative years.

Follow-up time, completed years	Metal-on-metal prosthesis (n = 579)			Metal-on-polyethylene prosthesis (n = 1585)
	Obs	SMR	95% CI‡	Obs	SMR	95% CI	RR	95% CI
0 to 1	2	0.35	0.04-1.27	3	0.14	0.03-0.41***	2.51	0.21 -21.94
2 through 9	29	0.92	0.62-1.32	77	0.78	0.61-0.96*	1.19	0.74 - 1.85
10 through 19	43	1.19	0.86-1.59	89	0.84	0.67-1.02	1.42	0.96 - 2.07
20+	19	0.84	0.50-1.30	33	0.89	0.61-1.24	0.95	0.51 - 1.71
Total	93	0.97	0.78-1.18	202	0.76	0.66-0.87***	1.27	0.98 - 1.63

ISSN: 1471-2474