THURSDAY, March 23 (HealthDay News) -- The thousands of Americans who undergo hip replacement surgery each year should have a full medical evaluation and get into good physical shape before the procedure, new studies affirm.

The studies also noted that two factors, older age and excess weight, affect patient outcomes after a hip replacement, revision hip replacement, or fracture-related surgical treatments.

The findings were presented Wednesday at the annual meeting of the American Academy of Orthopaedic Surgeons, in Chicago.

One study of 158 patients over age 80 who had revision hip replacement (replacement of an artificial joint) found that, within six months of the surgery, 16.5 percent of the patients experienced orthopedic complications and 15.3 percent experienced medical complications. Most of those medical complications were linked to pre-existing medical conditions.

"Although revision surgery can be as rewarding and effective in the elderly as in younger patients, octogenarians are likely to experience higher complications," study author Dr. Javad Parvizi, an associate professor of orthopedics at the Rothman Institute, Thomas Jefferson University in Philadelphia, said in a prepared statement.

This study concluded that it's important to conduct a full medical evaluation of the patients before surgery and to help them achieve optimum health.

A second study of 1,434 elderly patients who had hip fracture surgery concluded that orthopedic surgeons need to identify factors that could lead to poor patient outcomes after surgery.

"Increasing age and a greater delay to surgery, as well as a higher American Society of Anesthesiologists score -- which measures a patient's general health, coexisting conditions, length of hospital stay and risk of death -- can predict how much functional independence a patient may have after surgery," study author Dr. Raymond Klug, an orthopedic resident at the University of Illinois Medical Center in Chicago, said in a prepared statement.

A third study found that obesity impacts recovery time for patients who've had primary hip replacement. The University of Manitoba, Canada, study of 1,247 patients found that highly obese patients were 2.3 times more likely to stay in hospital more than five days and 2.6 times more likely to be discharged to a skilled nursing facility.

More information

The American Academy of Family Physicians has more about hip problems.