Table 2.

Risk for revision surgery in the four stages of endoprosthesis introduction

Stage of introduction	Hazard ratio*	95% confidence interval
Group A (operations 1–15)	1.48	1.14–1.91
Group B (16–30)	0.97	0.71–1.33
Group C (31–50)	0.85	0.61–1.17
Group D (51–100)	1.14	0.93–1.40
Group E (over 100)	1.00

* Adjusted with all factors that are listed in Table 1.