Cynthia Phillips, 57, is a hardworking woman. Along with running her Atlanta gym and being a personal trainer, she took a part-time job with FedEx in May — eight months after a right total knee replacement in September 2013. Lifting and hauling packages is part of the job, and while Phillips isn’t complaining, she’s always aware of her artificial knee. Here’s why patients have the surgery, what it takes to recover and how the new knee feels a year later.

Not for everyone. Stefan Tarlow, an orthopedic surgeon who runs the Advanced Knee Care clinics in Scottsdale and Mesa, Arizona, says patients should not have this surgery unless they really need it. “One place where joint replacements go wrong is where the knee isn’t bad enough to have it done,” he says. To justify a total knee procedure, Tarlow says, a person should have significant damage and disability, and reduced range of motion. Damage could stem from a major injury from years past that’s progressed to severe arthritis. Sports injuries such as a torn anterior cruciate ligament or torn knee meniscus are common forerunners.

“People that need to have a knee replacement have pain that interferes with their usual pursuit of life, and it hasn’t responded to pills, shots, bracing and exercise,” Tarlow says. “And it’s a type of pain they cannot cope with.” These patients can’t bend or straighten their legs normally. A physical exam should show an “angulatory deformity,” he says. Patient are usually bowlegged or knock-kneed. And X-rays should show bone-on-bone changes, he adds.

Phillips was a true surgical candidate. Some 30 years ago while in the Navy, she dislocated her right knee playing basketball. Next she tore that ACL playing softball. Fast forward to last year: Her knee cartilage was destroyed, and bone was scraping on bone. Her right tibia was starting to jut outward. Instead of lunging at the gym, she was limping.

Shaping up before surgery. Patients “need to exercise daily — low-impact aerobic exercise for six weeks preoperatively to get their body in shape to help them recover,” says Tarlow, who operates at Scottsdale Healthcare Thompson Peak Hospital.

People with arthritis can “figure out a way to go for a half-hour walk,” he says. “Putting a brace on and taking Tylenol and putting ice on their knee when they get home. Kind of hiking through the pain, so to speak. Because it’s so important to exercise to get in shape for surgery.” Swimming and cycling also work.

Patients with diabetes need to get their blood sugar under control, Tarlow says, or face a higher risk of infection and wound-healing problems. Overweight people with a body mass index of 40 or more are also at an increased risk for surgery-related blood clots. “BMI under 40 seems to be the limit,” he says. “Above it, people shouldn’t have joint replacement; and below it, it’s safe.” Smokers should try to quit two to three months before surgery, he says, and keep off cigarettes for at least that long afterward.

Pain during recovery is real. Even though they’ve been warned, Tarlow says, the biggest surprise for total knee patients is how much it hurts. “The first two to four weeks are very difficult,” he says. “You’ll have trouble getting around; you won’t feel very good.”

Rehabbing the knee is a process. Recovering from knee replacement takes personal effort. “Surgery alone doesn’t make patients better,” Tarlow says. “It has to be the surgery plus them doing rehabilitation.” Most often, that involves working with a physical therapist as an outpatient for six to eight weeks, then resuming normal exercise.

Phillips says she was “blessed” with a great inpatient nurse, plus the awareness to manage her own recovery after discharge. She stationed an exercise bike in front of the TV and set the seat high enough to avoid overextending her leg. Every day she rode, she could bend her knee further. Now, to avoid being “stagnant,” she does water exercise when it’s warm, or rides her bike outdoors. She also works out with an inclined treadmill, to reduce stress on the joints.

Back to work. Regardless of occupation, the average time off work after knee replacement is nine weeks, Tarlow says. He gives his patients a range of one to three months to get back on the job.

Working with clients at her gym, Phillips says, “I can participate to a degree, but I have to be respectful of the fact that I now have an implant in my knee.”

A year is as good as it gets. “This is as good as it’s going to be,” Tarlow says. “It’s not going to feel normal.” However, “most joint replacement patients are extremely pleased with their outcome. It returns them to their life activities.” That could mean walking around the house, going for a hike or playing tennis.

Hip-replacement patients sometimes say they “forget” they have an artificial joint. But with total knee replacements, however, “it’s very rare that somebody tells you, ‘I don’t even know it’s in there,'” Tarlow says. They’ll describe feeling “a tight band” around their knees, or fatigue after walking a certain distance.

In the first six months, the knee area may still be warm or swollen. By a year past surgery, he says, “a good total knee, superficially looking at it, should look like a normal knee that has a scar on it.” After one year, implantation is working in 99 percent of cases, Tarlow says. With a 1 percent yearly failure rate, that means in 10 years, 90 percent of new knees are still functioning, and so on.

Getting used to a new knee. These days, Phillips says, she has about 70 percent mobility when bending her knee. Scarring is a limiting factor, and sometimes discomfort awakens her at night. As for FedEx, she’s learned to grasp packages differently, use tools when she can or just ask someone for help. “I’m not the youngest chicken on the market,” Phillips says. “But people have to work. We have to make a living.”

More from U.S. News

13 Things to Know Before Your Hip Replacement

Exercising After You’ve Gone Under (the Knife, That Is)

10 Changes in Surgery in 25 Years

Total Knee Replacement: the First Year originally appeared on usnews.com