There are always risks with any surgery and older age does factor into those risks. Researchers say the most important risk factor is health. Older adults in good health have a very low risk of death after knee replacement.
To put this into numbers, a large study from Canada reported death in 1.5 percent of adults over 80 years old having a total hip replacement. This figure was even less (1.09 percent) after total hip replacement.
It's true that the number of older adults (80 years old and older) who die from complications of hip or knee replacement is higher than in younger adults (less than 80 years old). The main difference is the presence of other diseases. Heart disease, low or high blood pressure, diabetes, and cancer are just a few examples of conditions that put an older adult at greater risk of death after total hip or knee replacement.
Talk to your mother's doctor about your concerns. Knowing the status of her general health may help ease your mind.