Already one of the most common procedures, knee replacement surgeries are expected to grow 673% by 2030. By that time, more than 3.5 million people will undergo knee replacement each year. Patients with osteoarthritis opt for knee replacement to relieve pain and improve their knee range of motion (ROM). Enjoying these benefits, though, requires some work.
After surgery, you'll work toward knee ROM milestones. To meet these, you'll complete exercises at home and at therapy. Importantly, you'll need to work on these exercises through the pain. Improving knee ROM after surgery requires dedication to painful work, but the benefits are worth the effort.
What Is Full Range of Motion for a Knee?
The normal knee is involved in five main movements. These include:
. Flexion, or bending
. Extension, or straightening
. Adduction, or moving toward the center of the body
. Abduction, or moving away from the center of the body
. Rotation, or twisting in and out
Recovering from knee replacement requires regaining the full range of these movements. However, the term "knee range of motion"—and specific measurements of your progress—focus mostly on flexion and extension.
Knee range of motion is measured in degrees of flexion. A fully extended knee will measure 0º of flexion. Meanwhile, a fully bent knee will measure 135º of flexion.
Even otherwise healthy patients vary in their ability to match these measurements. This means that as you recover from surgery, you should not necessarily target these measures of full flexion and extension. Rather, you should evaluate your progress by your own ROM measures before surgery.
You should also evaluate your progress by your ability to carry out daily activities. In general, knee flexion measures in the range of 105º-110º enable the completion of many necessary activities. Reaching 125º and higher permits additional activities that involve intense bending.
The following measures offer a general guide to the flexion required for daily activities:
. 65º for walking
. 70º for retrieving an object from the ground
. 85º for climbing stairs
. 95º for getting up from a seated position
. 105º for tying your shoelaces
. 115º+ for sitting cross-legged or riding a bike
. 125º+ for most other activities
What Causes Limited Range of Motion in the Knee Before Surgery?
Prior to surgery, your knee range of motion will be limited by pain, swelling, and misalignment. Studies show that 80% of patients with osteoarthritis experience a limited ROM.
Most patients opt for knee replacement when the inflammation of osteoarthritis produces pain, swelling, and stiffness that cannot be managed by conservative measures. Severe osteoarthritis also involves deterioration of the bones in the knee joint. This deterioration can cause deformities, which further limit knee ROM.
What Causes Limited Range of Motion in the Knee After Surgery?
Knee replacement surgery removes the inflamed and damaged joint. In doing so, it aims to relieve pain and swelling and improve ROM. In the days, weeks, and even months after surgery, though, you will continue to experience some degree of pain and swelling. Pain and swelling are the body's response to the trauma of the surgery. With time and rehab, they will lessen.
Besides pain and swelling, another factor that limits knee range of motion after surgery is scar tissue. Scar tissue is also part of the body's response to trauma. During knee replacement, the surgical incision must cut through skin, muscle, ligaments, tendons, and other soft tissues. As these tissues heal, they form scar tissue.
Scar tissue is thicker and more fibrous than healthy tissue. Thus, scar tissue is more inflexible as well. Some patients form more scar tissue than others. More invasive procedures also tend to cause more scar tissue.
Fortunately, you can work through the pain, swelling, and scar tissue of your surgery to improve your knee ROM. For most patients, this means completing sometimes intensive physical therapy. The most important factor to limit scar tissue formation is movement. The longer you remain immobile after surgery, the more likely scar tissue is to form.
Approximately 6% of knee replacement patients develop a condition called stiff knee syndrome, or arthrofibrosis, after surgery. These patients may need other interventions, including additional surgery, to regain full knee range of motion.
How Long Does It Take to Get Full Range of Motion After Knee Replacement?
After recovering from knee replacement, the vast majority of patients see significant improvements in their ROM. In fact, most patients achieve flexion greater than 110º after surgery. This degree of flexion, remember, is sufficient for most daily activities.
Again, though, every patient and every knee is different. Furthermore, some studies report even more promising results with patients achieving flexion of 128º-130º after surgery. Still, the important measure of your progress remains your ability to go about your daily routine more easily than you did before surgery.
So how quickly can you expect to see improvements in your knee ROM?
Your doctor and physical therapist will monitor your progress over three stages. Overall, you can expect to achieve your maximum post-surgery ROM within 6 months of the procedure.
Stage One (0 to 2 Weeks)
Your recovery will begin immediately after surgery. This means beginning to move and beginning knee exercises shortly after your procedure. The longer you are immobile, the greater your risk of complications, including arthrofibrosis.
You'll spend at least some portion of stage one in the hospital or a rehab facility. There, you'll begin physical therapy to break up scar tissue, reduce swelling, and improve ROM.
This process will involve some pain. However, your therapists will help you identify and manage normal post-surgery pain. They will also monitor you for signs of complications.
During your hospital stay, you might also use a continuous passive motion (CPM) machine to keep your joint moving even when you are resting. Historically, use of these devices was actually quite common. In recent years, though, they've declined in popularity. This is because studies show they don't produce significant improvements in ROM or other aspects of a patient's recovery.
By the end of stage one, you can expect to achieve 65º-90º of flexion. This range of motion will let you get up from a seated position. It will also let you walk without assistance. With this ROM, you should, finally, be able to navigate some stairs with support.
Stage Two (2-6 Weeks)
By this time, you'll be home from the hospital or rehab facility. And with a goal of 115º of flexion, you'll be well on your way to regaining your normal routine. With 115º, you'll be able to move normally and sit down without assistance. Eventually, you'll even be to reach for items on the ground and tie your shoes.
Outpatient and at-home physical therapy exercises remain key to your continued recovery during this time.
Stage Three (6 Weeks+)
By stage three of your recovery, you'll likely have been discharged from your outpatient physical therapy program. However, it's essential that you maintain your at-home exercise program. Doing so will enable you to maintain and even increase the gains you made earlier in your recovery.
Remember, most knee replacement patients achieve at least 110º-115º of flexion after surgery. Yet, many others enjoy a knee range of motion of 120º or more.
How to Improve Knee ROM
Whether you are days, weeks, or months out from your surgery, you can take steps to improve your knee range of motion. In fact, if you're reading this before your surgery, you can take steps now to promote your recovery.
Prehab: Range of Motion Exercises Before Surgery
Doing exercises before surgery—sometimes called "prehab"—can help you recover by strengthening your joint and improving flexibility.
The following prehab exercises are helpful:
. Thigh squeezes
. Side- and back-laying straight leg raises
. Seated and lying knee bends and kicks
. Stomach kickbacks
. Supported one-legged stands
Because you'll rely on assistive devices, like walkers and crutches, after your surgery, it's also wise to strengthen your arms. Prehab exercises, like chair pushups, can prepare your upper body to support your recovery.
Always talk to your doctor before beginning any new activities. With your doctor's approval, you should aim to complete two sets of these exercises each day in the weeks before your surgery. When you begin, each set should include 5-10 repetitions. As you grow stronger, you can work up to 10-15 or even 15-20 reps per set.
Rehab: Range of Motion Exercises After Knee Surgery
After surgery, it's essential to maintain and increase your activity level. Your therapist will design a program to help you do this safely. You should take advantage of as many sessions as you can. Again, though, you'll also need to commit to completing your rehab exercises at home.
Throughout the three stages of your recovery, you'll progress through four types of exercises.
Early exercises will get you and your knee moving after the procedure. Meanwhile, functional exercises will help you regain ordinary movements, like flexing and extension.
As your recovery progresses, advanced exercises will further strengthen your joint and the surrounding muscles. Finally, maintenance exercises will keep you enjoying your new joint for many years to come.
Another benefit of doing prehab is that you'll already be familiar with exercises that promote full knee ROM. Among the best exercises for improving ROM are seated and lying knee bends and kicks. After surgery, though, you'll also be dealing with increased swelling. Adding ankle pumps to your exercise regimen can improve circulation and reduce swelling.
Finally, it's important to your physical and mental well-being that you gradually return to a broader range of physical activities.
After surgery, you'll need to avoid some activities to protect your joint. These include running, high-impact aerobics, and powerlifting. However, you'll likely find renewed enjoyment in at least some of the activities you once loved. Walking, swimming, riding a bicycle, and low-resistance weight training are just some of the exercises you can look forward to as your recovery progresses.
In fact, at almost every stage in your recovery, water therapy is one of the best exercises you can do to increase your knee ROM.
Ice, Heat, Massage, and Bracing: The Complements of a Successful Rehab Program
During your rehab program, your therapist will advise you to use other measures to enhance your ROM. Before completing your exercises, you'll likely use heat to loosen up the joint and surrounding muscles. Heat and massage can also help you manage the pain that is part of your recovery. Icing your knee also helps to manage pain, reduce swelling, and improve ROM.
Finally, your physical therapist or doctor might prescribe a brace to support your knee as you complete therapy and resume normal activities.
How to Measure ROM of the Knee
We've already seen that knee range of motion is measured in degrees of flexion. A special protractor called a goniometer is used for these measurements.
A goniometer has a circle in the center with an arm extending from either side. One arm is mobile, while the other is stationary. Measuring knee range of motion requires aligning these arms and the center circle with specific points on your leg.
It's difficult to get an accurate measure of the ROM of your own knee. So your physical therapist and doctor will provide you with the best assessments of your progress. You might want to track your own progress at home, though. If so, you have a few options.
Using a Goniometer
If you have a goniometer and someone who can help you, you can measure your knee range of motion at home.
To begin, find a firm surface. Then lie on your back while the person helping you lines the goniometer up as follows:
. The center circle should line up with the midpoint of the outer knee
. The stationary arm should line up with the bony bump below the hip on the outside of the thigh
. The mobile arm should line up with the bony bump on the outside of the ankle
To measure your knee's extension, push your knee down into the floor. To measure its flexion, slide your foot back so that your knee bends as far as possible. As you move, the person helping you should ensure that the goniometer remains in place.
Using an Estimate Method (Without a Goniometer)
Most people don't have a goniometer at home. However, you can still estimate your knee ROM.
. Estimating Knee Extension
To estimate your knee extension, lie on your back on a firm surface. Use your leg muscles to push your knee into the floor. As you do, slide your hand (palm down) underneath the knee. This will be easier or harder depending on your knee ROM:
. If you can, with difficulty, slide a few fingers beneath your knee, your knee is near full extension (0º)
. If you can slide all of your fingers but not your hand beneath your knee, your knee remains around 5º flexed
. If you can slide your whole hand beneath your knee, your knee remains around 10º flexed
. Estimating Knee Flexion
Estimating knee flexion requires a ruler or tape measure and, once again, a helper. This method won't give you a measurement of knee flexion in degrees. However, it will give you a guideline to track your progress at home.
To use this method, lie on your back on a firm surface. Slide your foot back until your knee bends as far as possible. Then ask the person helping you to measure the distance between your heel and your bottom.
Using Smartphone Apps
Recently, apps that allow you to use your smartphone as a goniometer have gained popularity. These apps vary in their reliability, and some therapists view them skeptically. However, a study in the Physiotherapy Journal reports that they can be as reliable as a goniometer.
If you do measure your knee ROM at home, it's best to do so only once or twice a week. Improving your ROM takes time. Therefore, you're unlikely to see progress—and more likely to become discouraged—if you measure your ROM more frequently.
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