How many people in the United States are getting knee replacements? Who is getting them?
According to the American Academy of Orthopaedic Surgeons, more than 700,000 total knee replacements are performed annually in the United States. The number is increasing each year as our population ages. Plus, more people are experiencing a sedentary lifestyle and obesity, which can make joints wear out faster. Women have higher rates of knee replacement surgery than men.
What happens during surgery?
During knee replacement surgery, all or some of the knee joint is replaced. Surgeons remove the damaged parts of the natural knee joint and replace them with artificial joint parts made of metal or plastic. During a total knee replacement, all three areas of the knee joint are replaced – the medial or inside, the lateral or outside and under the kneecap.
What should people expect after surgery?
Recovery from knee replacement is a process and not an event. While many patients experience substantial pain relief once the joint is replaced, it doesn’t happen overnight. The early weeks can be challenging, with swelling, discomfort and muscle weakness being common.
Most people regain basic function like walking and climbing stairs within a few months. But full recovery – especially regaining strength and endurance – can take six to 12 months. It’s also important to know that progress isn’t always linear. Some days will feel like setbacks.
Neuromuscular stimulation of the quadriceps doubled the speed of recovery for patients in a 2012 study. Yet it didn’t translate to changes in clinical practice. Stevens-Lapsley and her team are currently conducting a clinical trial in 30 clinics to determine how neuromuscular stimulation works in real-world practice.
Why is recovery challenging?
After surgery, patients often experience significant quadricep inhibition – a neurologic shutdown of the group of leg muscles at the front of the thigh due to pain and swelling. This leads to rapid and significant strength loss of up to 80% in the quads. It takes a lot of work to restore this function. Without intentional and progressive strengthening, the weakness can persist long after the range of motion in the knee joint returns.
Why is quadricep strength so important?
Without adequate strength in the quads, patients can struggle with everyday tasks like climbing stairs, rising from a chair or walking longer distances – even if their knee bends well. Research shows that strength deficits can persist for months or even years after surgery if not addressed. These deficits are directly tied to slower walking speeds, balance issues and reduced quality of life.
"Your rehabilitation is just as important as surgery. You should be prepared to put in sustained effort, even after formal physical therapy ends. This means consistent participation in session and at home, particularly in progressive strengthening." – Jennifer Stevens-Lapsley, PT
In 2012, you led a study on quadricep strength that demonstrated a near double speed of recovery post-surgery using neuromuscular stimulation. Could you talk more about that and how it is used today?
One way to overcome the shutdown of the quadriceps muscle is to stimulate the muscle with electrical signals. These electrical signals stimulate the nerve that interfaces with the quadricep, allowing the muscle to contract. So even though the brain is telling the nerves to shut down, neuromuscular stimulation can override this. In 2012, we used neuromuscular stimulation to nearly double the rate of recovery in terms of muscle strength and physical function.
Unfortunately, it didn’t translate to change in clinical practice, so we learned that an actionable plan is needed.
Recently, my team received funding to conduct a clinical trial of neuromuscular stimulation in 30 clinics in partnership with UCHealth and Intermountain Health. The purpose is to overcome some of the barriers associated with the implementation of the neuromuscular electrical stimulation. The 2012 study demonstrated that neuromuscular electrical stimulation works under ideal conditions where we have one-on-one interactions with participants. What we don’t know is how to get neuromuscular electrical stimulation to work in real-world healthcare systems. So that's the focus of the current study.
Could you explain how neuromuscular stimulation works more specifically for knee surgery?
In the case of knee surgery, nerves that cause the quadriceps to contract are targeted. For our study, patients will receive a small portable device prior to surgery to use once they are home from surgery. The device is light and durable with wires connected to 3-inch by 5-inch electrodes. These attach to the thigh near the knee and at the hip. Once the device is turned on, it delivers an electrical signal to stimulate the quadricep muscle. Patients use the device twice per day for 15 minutes at a time. It’s our hope to see improved recovery outcomes in patients that use neuromuscular stimulation at home, along with their prescribed physical therapies.
After knee surgery, the brain sends signals to the quadriceps to shut down, leading to rapid and significant strength loss in the quads of up to 80%.
What do you wish patients knew before getting knee surgery?
One of the most protective factors for people facing knee surgery is going into the procedure as strong and active as possible. Preoperative quadriceps strength is a strong predictor of better post-op outcomes, including faster recovery, better function and less disability. It will be helpful to work on upper body strength as well, so you can use crutches and/or a walker. You’ll need support at home post-surgery, so be sure to arrange for help.
What do you wish patients understood about recovery?
Your rehabilitation is just as important as surgery. You should be prepared to put in sustained effort, even after formal physical therapy ends. This means consistent participation in session and at home, particularly in progressive strengthening.
Everyone recovers at a different pace, and it’s common to feel tightness or experience swelling for six to 12 months after surgery, especially after activity. The function of your knee may recover quickly – meaning you can walk and be mobile independently – but feeling comfortable and confident can sometimes take up to a year.
Finally, recovery is not just physical. Mental and emotional resilience matter, too. Having realistic expectations, setting functional goals and staying engaged in the process are all key to long-term success.
