Table 2.

Repeated ASD Rates and Time Periods.

	Non-ASD	First ASD	Second ASD	Third ASD
Numbers	910	90 (9%)	11 (1.1%)	4 (0.4%)
Average age (years)	67	66	67	65
ASD period (years)		4.7	3.5	1.5

Abbreviation: ASD, adjacent segment disease.