Trends and geographic variations in major surgery for degenerative diseases of the hip, knee, and spine.

Although Medicare rates for surgery to treat degenerative diseases of the hip, knee, and spine are highly variable among hospital referral regions (HRRs), the relative risk for surgery within a region is constant from year to year-a large majority of the variation in surgery in 2000--01 is "explained" by the variation in rates in 1992--93. The within-region constancy in rates for highly variable procedures (the "surgical signature") is illustrated for South Florida HRRs. Involving the patient in choice of treatments (shared decision making) and outcomes research are promising strategies for reducing unwarranted regional variation and local constancy in surgery risk.