Passive knee flexion refers to the bending of the knee joint when an external force, rather than the individual’s own muscles, generates the movement. This motion is a component of comprehensive joint mobility assessments.
Understanding Passive Knee Flexion
A therapist, caregiver, or even a machine provides the necessary force to move the leg during passive knee flexion. As the knee bends, the shin bone (tibia) moves relative to the thigh bone (femur), involving a natural rotation. The normal range for passive knee flexion can extend up to 150 degrees, though it often reaches around 135 degrees during assessment.
Purpose of Passive Knee Flexion
Passive knee flexion plays a significant role in rehabilitation and recovery, particularly after injuries or surgeries involving the knee. A primary goal is to maintain or improve the knee’s range of motion, which can become restricted due to swelling, pain, or scar tissue formation. Restoring adequate knee flexion, around 120-125 degrees, is important for daily activities like sitting, walking, and climbing stairs. Early and consistent passive movement helps prevent joint stiffness, reduces contractures, and aids in decreasing post-operative swelling. It also contributes to improved circulation around the joint, supporting the healing process.
Applying Passive Knee Flexion
Passive knee flexion is commonly applied through various methods in clinical and home settings. A physical therapist or caregiver may manually bend the individual’s knee, providing gentle pressure within pain limits. Another method involves continuous passive motion (CPM) machines, which gently and continuously move the knee through a set range without active muscle engagement. For self-application, an individual might use a towel or strap looped around the foot to gently pull the heel towards the buttocks while sitting, allowing the knee to bend.
Passive Versus Active Knee Motion
The distinction between passive and active knee motion lies in the source of the movement. Active knee motion occurs when an individual uses their own muscles, such as the hamstrings, to bend or straighten the knee. In contrast, passive knee motion relies entirely on an external force, meaning the individual’s muscles remain relaxed. If a therapist moves your leg, it is passive motion; if you bend your own knee using your thigh muscles, it is active motion. Understanding this difference is important in rehabilitation because passive movements can initiate motion when active movement is limited by pain, weakness, or surgical restrictions, gradually progressing towards active engagement as recovery advances.
Key Considerations and Precautions
When performing passive knee flexion, proceed with caution and under professional guidance, especially following surgery or injury. Movement should remain within a comfortable range and never be forced beyond mild discomfort. Avoid pushing into pain, as this could cause further damage or hinder recovery. Ensure the individual’s muscles remain relaxed during the movement. Adhere to specific post-surgical instructions from a surgeon or therapist regarding the allowed range of motion, as certain procedures may have temporary limitations on flexion.