In 2001, approximately 122,000 lumbar fusions were performed in the U.S. On a population basis, this represented a 220% increase from 1990 in fusions per 100,000. The slope of the rising rate increased in 1996, when fusion cages were approved. From 1996 to 2001, the number of lumbar fusions increased over 113%, compared with 13-15% for hip replacement and knee arthroplasty. Rates of lumbar fusion rose most rapidly among patients aged 60 and above. In this group, rates increased 230% over the decade, compared with 180% among adults aged 40-59, and 120% among adults under age 40. The proportion of all lumbar operations involving a fusion increased for all diagnoses