A torn anterior cruciate ligament (ACL) requires surgical reconstruction to restore stability and function to the knee joint. A frequent complication following this surgery is stiffness, medically termed arthrofibrosis. Arthrofibrosis restricts the knee’s ability to achieve full extension (straightening) or full flexion (bending). This stiffness arises from an excessive buildup of scar tissue within the joint, which restricts normal movement. Early intervention is the most effective strategy for management.
Immediate Post-Operative Management
The foundation for preventing severe stiffness is laid immediately after surgery, typically within the first one to four weeks. Controlling the inflammatory response is paramount, as swelling and pain directly inhibit the muscles responsible for moving the knee, leading to limited mobility and scar tissue formation. The R.I.C.E. protocol—Rest, Ice, Compression, and Elevation—is a fundamental tool in managing this initial inflammation. Consistent application of ice for 15 to 20 minutes several times a day, alongside keeping the leg elevated above the heart, helps to reduce fluid accumulation in the joint space.
Effective pain management is another immediate priority because high pain levels make it difficult to perform the necessary range of motion exercises. Patients should take prescribed or over-the-counter pain medications regularly as advised by their physician to ensure they can participate in early rehabilitation. Early, gentle movement, often initiated by a physical therapist, is also introduced to prevent the formation of dense scar tissue.
A primary goal in this phase is to achieve full knee extension, or zero degrees, as quickly as possible. Early passive range of motion exercises, such as gentle heel slides performed while lying down, help to maintain the available motion without stressing the newly reconstructed ligament. Restoring full straightening early is considered the single most important factor in the initial recovery to avoid a permanent limp and to prepare the leg for later strengthening exercises.
Targeted Range of Motion Restoration Techniques
Once the initial post-operative pain and swelling subside, usually around four weeks, the focus shifts to more deliberate and aggressive techniques to restore the full arc of motion. These targeted exercises are designed to push the limits of the knee’s movement, distinguishing them from the gentle, maintenance-focused movements of the first few weeks. Regaining full extension is prioritized because even a slight deficit of three to five degrees can negatively impact long-term function and walking mechanics.
Specific techniques for restoring extension often involve using gravity to assist the stretch. The prone hang exercise requires the patient to lie on their stomach with the surgical knee positioned off the edge of a bed or table, allowing the lower leg to hang freely with a weight applied just above the ankle. Another technique is the heel prop, where the patient lies on their back and rests the heel of the affected leg on a rolled towel or bolster, letting the knee relax into a straight position for an extended period. These low-load, long-duration stretches are important for slowly lengthening the contracted tissues in the back of the knee.
Restoring knee flexion, or bending, is addressed progressively after extension is secured. Passive techniques involve using external force to increase the bend, such as heel slides with a towel or strap assist, where the patient pulls their heel toward their buttocks. Another effective passive stretch is the use of a stationary bike, which provides controlled, repetitive, and low-impact motion to warm up the joint and gradually increase the bend. The key difference between active and passive stretching is that active movement uses the patient’s own muscles, while passive stretching uses gravity, another limb, or a therapist to gently push the joint further.
Seated flexion stretches are utilized to push the flexion range. For this stretch, the patient sits with their foot on the floor and gently slides their buttocks forward on the chair, which increases the bend in the knee. These range of motion exercises should be performed frequently throughout the day, rather than in a single, intense session, as gentle repetition is more effective at breaking down scar tissue and improving flexibility. These techniques are continued for months, aiming for a full range of motion, which is 0 degrees of extension and 135 degrees of flexion.
Addressing Persistent Stiffness
When knee stiffness persists or plateaus despite months of consistent, intensive physical therapy and home exercise, a consultation with the orthopedic surgeon is necessary to consider more aggressive medical or surgical options. This persistent loss of motion indicates a significant accumulation of dense, fibrous scar tissue that cannot be overcome with rehabilitation alone. The first-line surgical intervention considered is Manipulation Under Anesthesia (MUA).
MUA involves the surgeon gently but forcefully bending and straightening the knee while the patient is fully unconscious under general anesthesia. The goal of this procedure is to mechanically break up the internal scar tissue, or adhesions, that are physically blocking the joint’s movement. The procedure is often combined with an arthroscopic lysis of adhesions (LOA).
Lysis of adhesions is a minimally invasive surgical procedure where a camera (arthroscope) and small instruments are inserted into the knee joint. The surgeon then visually identifies and removes the restrictive scar tissue that has formed around the graft and within the joint capsule. Following these surgical interventions, intensive physical therapy is immediately restarted to preserve the motion gained during the procedure and prevent the recurrence of scar tissue.