Regaining the ability to bend the knee (flexion) is necessary for performing daily activities like walking, climbing stairs, and sitting comfortably. The goal of rehabilitation is to achieve a functional range of motion (ROM) that allows a return to normal life. Because every patient’s surgical procedure, healing rate, and protocol are unique, all exercise guidance and timelines must be superseded by the specific instructions provided by the operating surgeon and physical therapist.
Establishing the Timeline for Flexion
The timeline for introducing and progressing knee flexion exercises depends on the type of surgery performed. For procedures like a Total Knee Arthroplasty (TKA), the goal is often rapid ROM recovery to prevent arthrofibrosis. TKA patients may aim to achieve 65 to 90 degrees of flexion within the first two weeks post-operation, with a target of 115 degrees or more by six weeks.
In contrast, surgeries involving soft tissue repair, such as an Anterior Cruciate Ligament (ACL) reconstruction combined with a meniscus repair, often require a more cautious, protected phase. The surgeon may restrict active knee flexion for up to four weeks to protect the newly repaired tissue from undue stress. During this initial period, the focus is typically on managing swelling and achieving full knee extension (straightening) first. Progression is always gradual and determined by the patient’s biological healing and the absence of increased pain or swelling.
Essential Passive and Assisted Bending Techniques
The initial phase of rehabilitation relies on passive and assisted techniques. This approach protects the healing joint while gently introducing motion to prevent stiffness and scar tissue formation. One of the most common early exercises is the supine heel slide, performed by lying on the back and gently sliding the heel toward the buttocks. Using a towel, strap, or a plastic bag under the heel can reduce friction, allowing for a smoother, more controlled movement into the bend.
Another technique involves using the non-surgical leg to assist the movement. While sitting, the patient wraps the non-surgical foot underneath the surgical leg to provide a gentle, controlled pull into further flexion. The key to these passive movements is to apply a consistent, low-level stretch and hold the position for a prescribed period, often 20 to 30 seconds, to encourage tissue elongation.
If authorized by the surgeon, a Continuous Passive Motion (CPM) machine may be used to gently and repeatedly move the knee joint through a pre-set range while the patient rests. Another simple gravity-assisted technique is the passive knee dangle, where the patient sits on a high surface and allows the surgical leg to slowly bend toward the floor. This technique uses the weight of the lower leg to encourage flexion. It is typically introduced only once initial restrictions are lifted, often allowing movement up to 90 degrees in the early weeks.
Transitioning to Active Flexion Exercises
As healing progresses and the physical therapist clears the patient for more strenuous activity, the focus shifts to active flexion, where the quadriceps and hamstring muscles begin to initiate the bend. Active sitting knee flexion is a starting point, where the patient sits at the edge of a chair and actively pulls the heel back toward the chair without assistance from the other leg or a strap.
The stationary bicycle is often introduced early in the active phase, as it provides a low-impact, controlled way to cycle the knee through a range of motion. Initial use usually involves setting the seat high to minimize the required bend and only performing partial revolutions until flexibility improves. As the joint tolerates greater movement, the patient can gradually lower the seat height, which forces the knee into a deeper flexion with each pedal stroke.
Once stability and active ROM are established, the program progresses to weight-bearing activities like standing partial squats. These are performed against a wall for support, where the patient slides down into a shallow squat, ensuring the knee does not track past the toes. The depth of the squat is controlled and slowly increased over time, moving from a shallow bend to a deeper angle as comfort and strength allow.
Recognizing and Managing Pain and Stiffness
Navigating the rehabilitation process requires understanding the difference between the expected discomfort of stretching and pain that signals a potential problem. A sensation of tightness, pulling, or a dull ache during a stretch that subsides shortly after stopping the exercise is often considered “good pain.”
Conversely, any sharp, stabbing, or intense pain that causes the patient to immediately stop the exercise is considered “bad pain” and should be avoided. Pain that persists for hours after the exercise session, or a sudden, significant increase in swelling, indicates that the activity was too aggressive and needs to be scaled back. Post-exercise stiffness and swelling are managed effectively by applying ice and elevating the leg above the level of the heart.
Patients should immediately contact their medical team if they experience symptoms like a fever, redness, warmth, or discharge around the incision site, which can indicate infection. Similarly, a sudden onset of severe calf pain or tenderness may signal a blood clot and requires urgent medical evaluation. Consistent communication with the physical therapist ensures that the rehabilitation program is safely adjusted based on the knee’s daily response to the bending exercises.