Total knee arthroplasty (TKA), or total knee replacement, successfully relieves pain and restores function in an arthritic joint. While most people improve significantly, a small percentage experience persistent stiffness, limiting the ability to fully bend or straighten the knee. This restricted range of motion hinders daily activities like climbing stairs or sitting comfortably. Understanding the causes and the approach to resolving stiffness is the first step toward regaining full mobility.
Why Knee Stiffness Develops After Replacement Surgery
The primary reason for persistent stiffness is arthrofibrosis, characterized by excessive scar tissue formation within the joint. The body interprets surgical trauma as an injury, triggering an overzealous healing response that deposits thick, fibrous bands around the prosthesis. These scar tissue bands physically restrict the smooth movement of the joint surfaces, preventing the knee from achieving full range of motion.
Inadequate initial range of motion (ROM) is closely linked to scar tissue formation. If a patient does not aggressively move the joint immediately after surgery, the scar tissue matures and contracts in a shortened position, making later stretching difficult. Less common causes involve technical factors, such as component malpositioning or incorrect sizing, which mechanically block movement. Other contributors include infection or heterotopic ossification (the growth of excessive bone outside the normal skeleton).
Patient-Driven Strategies: Physical Therapy and Home Exercise
The cornerstone of treating post-operative stiffness is a consistent regimen of physical therapy and home exercises. The goal is to apply controlled force to the joint, lengthening the restrictive scar tissue without causing a new inflammatory response. Dedication to the exercise program, often involving two to three sessions daily, is the most powerful tool a patient has in the first few months after TKA.
Specific exercises focus on regaining both flexion (bending) and extension (straightening). For flexion, the heel slide is common: the patient lies on their back and slowly pulls the heel toward the buttocks, often using a strap or towel for assistance. For extension, the patient performs a static quadriceps set, pushing the back of the knee down against a rolled towel to achieve full straightening.
A stationary bicycle is an effective tool, providing a low-impact, rhythmic way to work on range of motion. Adjusting the seat height so the knee is only slightly bent at the bottom of the pedal stroke allows for gradual, sustained movement against minimal resistance. The principle of low-load, prolonged stretching is important: the patient holds a gentle stretch for an extended period (often 20 to 30 seconds) rather than using quick, forceful movements.
Managing pain and swelling is important for a successful rehabilitation program, as discomfort inhibits a patient’s willingness to exercise fully. Using ice or over-the-counter anti-inflammatory medications before or after exercise helps dampen the inflammatory response and allows for more productive stretching. Consistent compliance with the physical therapy schedule and daily home exercises provides the best chance of breaking down initial scar tissue before it becomes chronic.
Physician-Led Treatments for Unresolved Stiffness
When aggressive conservative treatment fails to achieve functional range of motion (stiffness persisting beyond three to six months), physicians recommend active interventions. The first-line procedure for early, stubborn stiffness is a Manipulation Under Anesthesia (MUA). This outpatient procedure involves putting the patient to sleep so the orthopedic surgeon can manually and forcefully bend and straighten the knee, fracturing the restrictive scar tissue bands.
The MUA procedure is most successful when performed early, generally within three months of the initial surgery, while the scar tissue is immature. Immediately following manipulation, the patient begins an aggressive physical therapy protocol to maintain the newly gained motion before the body forms new scar tissue. If stiffness is chronic, severe, or if a previous MUA was unsuccessful, the next step may be an arthroscopic lysis of adhesions.
This surgical procedure involves inserting a small camera and instruments into the knee joint to visualize and excise the thick, fibrous scar tissue. The surgeon uses specialized tools to cut away the bands mechanically impeding joint movement in areas like the suprapatellar pouch and the joint gutters. Lysis of adhesions is often combined with an MUA during the same session to maximize motion improvement. In rare cases where stiffness is caused by component malposition or a loose implant, revision surgery may be necessary to correct the mechanical problem and replace the prosthetic components.