A Total Knee Replacement (TKR) is a procedure designed to alleviate chronic pain and restore function to a severely damaged knee joint. Regaining sufficient knee flexion, or bending, is necessary for performing everyday tasks, such as sitting comfortably in a chair, climbing stairs, or getting into a car. A knee that lacks sufficient bend—generally aiming for 120 degrees or more—significantly limits mobility and quality of life. Restoring this range of motion requires consistent effort and a dedicated progression through various physical therapy techniques.
Foundational Daily Flexion Exercises
Immediate post-operative rehabilitation focuses on gentle, active-assisted exercises to promote early mobility without stressing the healing joint. These foundational movements are performed multiple times throughout the day, relying on simple mechanics and gravity.
The Heel Slide involves the patient lying on their back and slowly sliding the heel of the operated leg toward the buttocks, bending the knee as far as comfort allows. Using a strap or towel looped around the foot allows for a controlled, assisted pull into deeper flexion.
Seated Knee Flexion uses a stable chair for leverage and control. The patient sits with the operated foot flat on the floor and slowly slides the foot backward, allowing the knee to bend under the seat. To increase the stretch, the patient can gently scoot their body forward on the chair.
A Continuous Passive Motion (CPM) machine may be introduced early on. This device mechanically moves the knee joint through a pre-set range of motion while the patient is resting, which helps prevent stiffness and encourages the joint to maintain movement.
Utilizing Equipment and Mechanical Assistance
Once the initial pain and swelling subside, rehabilitation progresses to techniques that use mechanical assistance and gravity to push the limits of the newly gained range of motion.
The stationary bicycle is a highly effective, controlled, low-impact method for increasing flexion. Patients should adjust the seat height so that the knee is only slightly bent at the bottom of the pedal stroke, preventing excessive force on the joint. Initially, patients may need to rock the pedal back and forth or use the non-operated leg to drive the motion if the operated knee cannot yet complete a full revolution.
The Wall Slide is a gravity-assisted technique where the patient lies on their back with their heels resting on a wall. By slowly allowing the operated foot to slide down the wall, gravity gently pulls the knee into increased flexion. Holding the foot in the deepest part of the bend helps to stretch the posterior capsule and surrounding soft tissues.
Prone Hangs are used to increase knee extension. The patient lies face down with the feet hanging off the end of a bed. Achieving full extension is important for normal gait and indirectly helps with flexion by ensuring the quadriceps mechanism is not restricted.
Addressing Physical Barriers to Flexion
Progress in regaining flexion is often stalled by physical factors, primarily post-operative pain and swelling. High levels of inflammation inhibit muscle function and physically block the joint from moving through its full range.
Consistent application of the R.I.C.E. principles—Rest, Ice, Compression, and Elevation—is necessary to manage this inflammatory response. Icing the knee for 20-minute intervals several times a day helps reduce swelling, making the mechanical act of bending the knee less painful and restricted.
Scar tissue formation is a natural part of the healing process, but excessive or tethered scar tissue can restrict movement. This tissue can bind together the layers of skin, fat, and fascia, limiting the necessary glide required for full flexion. Once the incision is fully healed, gentle scar mobilization techniques are applied, involving light pressure and moving the skin in various directions over the underlying tissue. This manual manipulation encourages healthier tissue remodeling and prevents the scar from adhering to deeper structures.
Medical Strategies for Stalled Progress
If recovery plateaus despite consistent and aggressive physical therapy, medical intervention may be necessary. The typical window for achieving functional flexion is within the first 6 to 12 weeks following the surgery. If a patient’s knee flexion remains significantly limited (less than 80 to 90 degrees) by the end of this period, the surgeon may recommend a procedure known as Manipulation Under Anesthesia (MUA).
During an MUA, the patient is placed under general or spinal anesthesia, ensuring complete muscle relaxation and eliminating pain. The surgeon then applies a controlled, forceful movement to the knee to physically break up the internal scar tissue, or arthrofibrosis, that is restricting the joint. Performing this manipulation within 12 weeks of the TKR yields better final range-of-motion outcomes.
Following the MUA, immediate and intensive physical therapy is required to maintain the newly acquired range, often involving the use of a CPM machine, as the scar tissue will quickly attempt to re-form.