Everything you need to know about knee replacements

A power drill whirs noisily—shavings curl from the bit as it bores a precise hole. Cement oozes from a caulking gun to join two surfaces. A hammer whacks repeatedly on metal. Behind the workers, a busy crew shares measurements and part sizes.

It's the sounds of renovation, but it's not a new kitchen. In a hospital in Philadelphia, a medical team led by orthopaedic surgeon Dr Matthew Austin is replacing a knee joint. It's his fifth surgery of the day.

Three hours after surgery wraps up, Ralph Gabriel, then 69, the construction-business owner upon whom those tools whirred and banged, is awake and joking with his family. He didn't want surgery. But years of tile installation had destroyed his right knee, creating constant pain. ''You have to have the will to get it done," Gabriel says.

The human knee is particularly vulnerable to wear. Every step, every jump, every crossing of the legs, puts stress on the joint. When you combine the active lifestyle of the over-50 population and longer life spans, it's no wonder that an increasing number of people are experiencing knee pain. There are many short-term remedies, such as weight loss, physical therapy, injections and supplements, but for a perpetually painful or arthritic knee, the go-to solution is to replace it.

Ask your surgeon about his or her outcomes, complication rates, infection rates and re-admissions. Don't settle for an answer from your surgeon citing national averages: you want their rate. The number should be around two per cent or lower.

Put simply, an artificial knee works as a multidirectional hinge that connects the bottom of your femur (the upper leg bone) to the tibia (the shinbone). To install it, surgeons remove damaged cartilage and bone and connect the artificial knee to your bones. The surgery takes about an hour and is done with the patient under local or general anesthesia.

Doctors can choose from more than 150 sizes and variations of artificial knees. Most are made with polished titanium or a cobalt-chrome alloy, plus high-grade plastics, and can last for decades. For most patients, the type of implant is probably irrelevant, many experts say. “The key is to trust that your surgeon is familiar with the device being used,” says Dr Stephen Kelly, a joint-replacement surgeon at New England Orthopaedic Surgeons in Springfield, Massachusetts.

Few would dispute that knee replacements are generally safe and, in most cases, appropriate. But not all doctors are convinced that replacement is the best answer for many patients.

One study looked at the level of patient-reported pain and knee function, along with X-ray evidence of arthritis, in people who got total knee-­replacement surgery. The conclusion: About a third of the procedures were "inappropriate" using a standard classification system developed in Spain.

A 2015 follow-up study found that surgeries classified as inappropriate yielded little or no benefit in relieving pain or improving function. That is, patients with mildly bad knees had much less to gain from knee-replacement surgery than those with severe pain or bone-on-bone arthritis did.

“You don't leap out of bed afterward,” says Dr Nortin M. Hadler, who is emeritus professor of medicine at the University of North Carolina at Chapel Hill. “In addition to the inevitable risks of surgery, you have months of rehab ahead of you.”

Keep in mind these four important concerns before you schedule your knee replacement.

1. There is no clear standard
Surprisingly, there are no definitive criteria to determine whether you should undergo surgery, explains Daniel Riddle, a professor of physical therapy at Virginia Commonwealth University. Doctors assess three variables: pain, limits on daily activities, and visible evidence of bone damage. Only the last of the three can be measured objectively.

Ask your doctor to gauge how your symptoms compare with those of others, using a standardised scale that can be compared with research. The Knee Injury and Osteoarthritis Outcome Score is one example. "I'd want to know if my symptoms are considered mild, moderate, or severe, and what I can expect a year from now,” Riddle says.

2. Expectations vary
In one European study, 93 per cent of patients were generally satisfied five years after surgery. But most also reported that they had expected more. Only one-third of those who considered sports important were pleased with their results.

And about 20 per cent of patients will have long-term pain, suggests one study. Ralph Gabriel, now 73, is one of them. Post-surgery, he has been in constant pain, he says, and nothing he has tried so far—extensive physical therapy, electrical stimulation, over-the-counter painkillers—has helped.

Ask your surgeon detailed questions, specific to your daily activities, about what you should expect after surgery. Most surgeons say you may have to forgo high impact hobbies (such as singles tennis), because they could prematurely shorten implant life.

3. Recovery takes time
"You have to work hard to get better from this operation," Dr Kelly says. That means six to eight weeks of rehabilitation and physical therapy to regain range of motion and rebuild muscles and ligaments that stabilise and support the knee.

Even with modern rehab techniques, one study found that a third of patients didn't have measurable improvements in pain six months after surgery. Another found that one in eight patients still had moderate to severe pain one year on. In the latter study, however, almost all patients felt satisfied with their operations five years out.Dr Kelly recommends that anxious patients visit a physical therapist before surgery to discuss rehab.

Research suggests that you'll do best with a surgeon who does more than 50 knee-replacement operations a year. High- and low-volume surgeons had similar results on pain relief, one study found. But surgeons who do six or fewer knee replacements a year in low-­volume hospitals may be less skilled at the soft tissue fine-tuning needed to achieve normal motion and full function. In that same study, patients of low-volume surgeons were twice as likely to score poorly on function measures such as being able to fully extend their knees two years on.

4. Risks are small but serious
The odds of having a major complication from knee-replacement surgery are relatively low. Few people assume they'll be among the fraction of those who have more serious complications such as blood clots. "That's why discussion about risks needs to be more substantial than simply signing a consent form," Riddle says. "You need to have a detailed conversation with your GP."

The earlier you discuss possible complications with your GP, the better, Dr Hadler says. "Once the mindset is, 'I need this,' you don't hear the risk, you hear the benefit," he says."

Scientists are looking for better solutions that improve outcomes for knee-replacement surgery or bypass it with less invasive procedures. Here are some options that have emerged.

Patient-Specific Instruments: digital imaging creates tailor- made instruments that surgeons use just once to guide cuts and implant placement so they better match and preserve a patient’s anatomy. “It makes the operation shorter and more efficient,” says Dr Steven Haas, chief of knee service at the Hospital for Special Surgery in New York.

“Partial” Surgeries: surgeons switch out just one part of the knee for an implant, leaving healthy cartilage, bone, and ligaments intact on the rest of the knee. Recovery tends to be quicker. “The trade-off is that partial knee replacements fail at a significantly higher rate than total knee replacements, " Dr Haas says.

Robotic Surgery: robotic systems can help surgeons position implants more precisely and consistently. “The surgeon controls the tool, and the robot keeps him from going outside the area he wants to cut,” says Jeremy Suggs, engineering manager at the ECRI Institute, a Philadelphia nonprofit that independently researches medical devices. Doctors most often use robotic systems for partial knee replacements that require extra precision to preserve ligaments.

Arthroscopic Procedures: people get “scoped” in a procedure called partial meniscectomy. It entails a surgeon going into the knee through a “keyhole” incision, to trim and smooth jagged edges of torn meniscus, a layer of cartilage that cushions bones in the joint. Some studies, however, have found that this procedure produces no better results than sham surgery in which orthopaedists scope the knee but don’t fix anything.

“That’s made a lot of surgeons cautious about recommending arthroscopy for patients with arthritis of the knee," says Dr Craig Della Valle, an orthopedic surgeon and chief of adult reconstructive surgery at Rush University Medical Center.

Whether the balance of risk and reward steers you toward knee­replacement surgery depends on many factors, but it ultimately comes down to your tolerance for one type of discomfort over another.

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