Regaining the ability to bend the knee, known as knee flexion, is the most important goal following knee surgery. Flexion is necessary for fundamental daily functions, including walking, sitting down comfortably, and navigating stairs. The rehabilitation process focuses on restoring this range of motion (ROM) to ensure the knee can move freely. This effort requires consistent, controlled work to overcome the body’s natural response to surgery.
Establishing the Timeline for Flexion
The speed and extent of initial knee movement depend heavily on the specific procedure performed, such as a total knee replacement or ligament reconstruction. Before attempting any flexion exercise, receiving clearance from your surgeon and physical therapist is mandatory to protect the surgical site. The general protocol divides recovery into an immediate postoperative phase and an active phase.
The immediate phase often focuses on gentle, controlled passive motion, where the leg is moved without using the surrounding muscles. This early movement is emphasized to combat arthrofibrosis, a common complication involving the formation of dense scar tissue that can limit joint mobility. Delaying movement allows this stiff tissue to develop, making later attempts at bending the knee more difficult.
For patients who have undergone a total knee replacement, there are measurable benchmarks for progress. A common target is to achieve approximately 90 degrees of flexion by the end of the first week post-surgery. This progresses to about 100 degrees within two to three weeks, approaching 110 to 120 degrees by the six-week mark. Adhering to the prescribed physical therapy schedule is the most effective way to meet these targets.
Primary Exercises for Regaining Knee Bend
The foundation of regaining flexion involves a progression from passive to active range of motion exercises. Passive range of motion (PROM) means an external force, like your arm or a strap, moves the joint, while active range of motion (AROM) means you use your own muscles. The most foundational exercise is the heel slide, which can be performed in either the supine (lying on your back) or seated position.
To perform a supine heel slide, lie on your back and slowly drag the heel of the operative leg toward your buttocks, bending the knee as far as comfort allows. Aim for a deep but tolerable stretching sensation, holding the peak of the bend for about five seconds before slowly returning the leg to the starting position. This exercise should be repeated for two to three sets of 10 to 20 repetitions, multiple times throughout the day.
As your strength improves, you can transition to using tools for a more controlled passive stretch. A towel or belt can be looped around the foot, allowing you to use your arms to gently pull the foot closer to your hip while sitting or lying down. This technique provides leverage to achieve a deeper bend than possible with leg muscles alone, applying controlled tension to the forming scar tissue. Push the knee into the point of uncomfortable stretch, but never sharp pain.
A seated knee bend can be performed by sitting in a chair with your foot on the floor and gently sliding it back underneath the chair as far as possible. Using the non-operative foot to hook under the ankle of the surgical leg and gently push it backward provides a powerful form of PROM. Hold the maximum stretch for 30 to 60 seconds, repeating five times per session.
In the later stages of recovery, stationary cycling becomes a beneficial exercise for improving dynamic flexion. Start with the seat positioned high to limit the required bend and focus on partial, slow revolutions at a low resistance. As mobility increases, the seat can be gradually lowered, forcing the knee to flex further with each complete rotation. Cycling is a low-impact, high-repetition activity that warms the joint and promotes fluid movement.
Managing Pain While Increasing Range of Motion
Increasing knee flexion involves stretching healing tissues and scar tissue, which causes discomfort. Managing this pain is not about eliminating it entirely, but reducing it enough to allow for productive exercise sessions. A common strategy is to schedule pain medication to align with your therapy sessions.
Taking prescribed pain relievers approximately 30 to 45 minutes before starting exercises ensures the medication is active when you begin stretching. This pre-emptive approach can lower the pain threshold, allowing you to achieve a greater range of motion during the session. Consult with your care team to confirm the appropriate timing for your specific medications.
Applying heat to the knee before starting exercises can prepare the joint for movement. Heat increases blood flow and helps to loosen the surrounding muscles and soft tissues, making them more pliable for stretching. Conversely, applying ice immediately after your session reduces the inflammation and swelling that the stretching may have caused.
Simple techniques such as controlled breathing can help you tolerate the discomfort of deeper stretches. As you ease into the peak of the stretch, slowly exhaling can relax the muscles and nervous system, permitting a slightly greater degree of flexion. Focusing on a slow, steady exhalation prevents the tendency to tense up, which restricts movement.
Recognizing Critical Limits and When to Seek Help
While discomfort is expected during flexion exercises, recognizing the difference between a productive stretch and a potential complication is important for safety. Short-term goals, such as reaching 90 degrees of flexion, are necessary for common tasks like sitting in a chair. Long-term goals often target 110 to 120 degrees, which allows for more demanding activities like descending stairs.
Contact your surgeon or physical therapist immediately if you experience sudden, sharp pain during an exercise, as this can indicate a serious issue. Excessive swelling that does not subside with elevation and ice is a warning sign, suggesting internal irritation or bleeding. A fever or increasing redness and warmth around the incision site are symptoms of a potential infection and require immediate medical attention.
A critical limit is reached if you fail to make measurable progress in range of motion over two consecutive weeks despite diligently following the physical therapy protocol. If the knee motion stalls, often remaining below 70 degrees of flexion, your care team may discuss further intervention. In some cases, manipulation under anesthesia (MUA) might be required, where a surgeon gently forces the knee to bend while you are unconscious to break up scar tissue.