People needing hip and knee replacements are in poorer health than ever before, with most now obese or overweight, according to a study out today.

Some 83% of all joint replacement operations last year were carried out on overweight or obese people, a figure that has been rising steadily since 2004.

Far fewer people are also regarded as fit and healthy before they go under the knife compared to five or six years ago.

Experts behind the research said the problem would get worse in future years, with obesity leading to an increased demand for new joints, particularly knees.

Last year, 47% of people needing a knee replaced were obese and 36% were overweight, according to data from the National Joint Registry (NJR) for England and Wales.

Some 6% fell into the morbidly obese category, with a body mass index (BMI) over 40.

Just 11% of people needing a new knee in 2009 were in the healthy weight range, according to more than 42,000 knee operations where BMI was known.

A similar picture emerged for hip replacements, with 40% of patients overweight, 34% obese and 3% morbidly obese.

Just 22% were in the healthy range, according to data from almost 37,000 hip replacements where BMI was known.

Today’s report said more patients were now considered in poor health than a few years ago.

Just 17% of patients were regarded as fit and healthy prior to hip surgery in 2009, compared to 37% in 2003.

More were listed as having serious diseases which are not life-threatening but which do increase the risk of complications (13% compared with 9% in 2004).

When it comes to knee replacements, the proportion regarded as fit and healthy has fallen from 31% in 2003 to 13% in 2009.

Martyn Porter, chairman of the NJR editorial board, said the trend over the past few years was towards fewer people being regarded as fit before surgery.

“We are operating on less well patients,” he said, adding the problem is predicted to get worse.

The report is based on data from almost 164,000 hip and knee replacements in 2009.

About 10% were revisions, up from 9.2% in 2008 (or 555 extra operations compared with 2008). Some 6% of knee replacement operations were revisions, up 12% on the previous year.

Of operations in 2009, 30% of patients were aged 75 or over, 35% between 65 and 74, 23% between 55 and 64 and 12% below the age of 55.