Demand for knee replacement surgery rises steadily in the US

The number of total knee replacements done each year in the US increased by 161.5% from 1991 to 2010, say researchers⇑. An ageing population is partly to blame, although obesity and expanding indications for surgery may also have contributed. Rates of primary knee replacement operations per capita doubled (from 31.2/10 000 to 62.1/10 000), and rates of revision operations went up by 59.4% during the same period (from 3.2/10 000 to 5.1/10 000).

The trends emerged from administrative data kept by Medicare, federally funded healthcare for adults aged 65 years or more. Other notable findings include a significant drop in length of stay (from eight days to 3.5 days for primary procedures; P<0.001), which was accompanied by a significant rise in readmissions to hospital within a month of discharge (from 4.2% to 5%; P<0.001). Being older, sicker, and male were all associated with a higher risk of readmission in adjusted analyses.

Postoperative mortality hasn’t changed much since 1990, although the researchers noticed a worrying increase in wound infections after a revision arthroplasty (from 1.4% (95% CI 1.3% to 1.5%) to 3.0% (2.9% to 3.1%); P<0.001).

By 2010, Medicare was paying for just over 250 000 primary and revision procedures each year. Overall demand is projected to reach 3.5 million procedures a year by 2030, says a linked editorial (p 1266). Knee replacement surgery is cost effective, but with such high numbers, containing costs (while maintaining quality of care) has to be a government priority. Options already being considered include restructuring reimbursements, controlling the use of new expensive implants, and establishing joint replacement registers to help compare the multitude of implants now available.