Knee flexion describes the bending motion of the knee joint, bringing the lower leg closer to the thigh. This movement is a fundamental part of nearly every physical activity. From getting out of bed to walking, sitting, and reaching for objects, knee flexion allows for necessary joint articulation.
Measuring Knee Range of Motion
The range of motion in the knee is assessed by measuring its ability to bend and straighten, known as flexion and extension. Full knee extension is typically considered 0 degrees, representing a completely straight leg. Flexion, the bending movement, is measured in degrees from this extended position. For a healthy adult knee, the typical range of motion extends from 0 degrees of extension to approximately 135 to 145 degrees of flexion.
Clinicians commonly use a tool called a goniometer to accurately measure knee joint angles. This device features a central pivot point aligned with the knee’s axis of rotation, and two arms that align with the bones of the thigh and lower leg. By positioning the goniometer and moving the knee through its full range, healthcare professionals can determine the precise angle of flexion and extension. This objective measurement helps in evaluating joint health and tracking progress during rehabilitation.
Required Angles for Everyday Movements
Daily activities demand varying degrees of knee flexion. Simple actions like walking require approximately 60 to 75 degrees of knee flexion, allowing the foot to clear the ground during the gait cycle. This relatively modest bending enables efficient forward progression.
More complex movements, such as ascending or descending stairs, necessitate greater knee flexion, typically around 80 to 90 degrees. This increased bend accommodates the change in elevation and provides stability. Getting in and out of a standard chair also requires a significant amount of knee flexion, generally falling within the range of 90 to 115 degrees.
Activities that involve bending down, such as picking an object off the floor or tying a shoe, demand even more knee flexion. These actions often require approximately 75 to 115 degrees of knee bend to lower the body. The ability to achieve these specific angles directly influences a person’s independence and ease in performing routine tasks.
Causes of Reduced Knee Flexion
Reduced knee flexion can stem from various underlying issues, often involving pain, swelling, or stiffness within the joint. Traumatic injuries are a common cause of limitation. Ligament tears, including ACL tears, meniscal tears, or fractures, can lead to instability, swelling, and muscle guarding.
Post-surgical complications also contribute to limited knee flexion. After procedures like a total knee replacement or ACL reconstruction, scar tissue can form around the joint, a condition known as arthrofibrosis. This excessive scar tissue, along with inflammation and inadequate rehabilitation, can impede the knee’s ability to bend fully.
Chronic conditions also result in reduced knee motion over time. Degenerative joint diseases such as osteoarthritis cause cartilage breakdown, bone spur formation, and joint space narrowing, leading to stiffness and pain that limit motion. Inflammatory conditions like rheumatoid arthritis, gout, or infectious arthritis also contribute to stiffness and decreased range of motion due to inflammation and joint damage.