Genu recurvatum refers to a condition where the knee joint extends beyond its normal straightened position. It is often described as “back knee” or a “hyperextended knee.” This condition can affect one or both knees and can vary in its degree of severity, from a subtle bend to a pronounced backward angle.
Underlying Musculoskeletal Issues
The stability of the knee joint relies on its surrounding ligaments. When these ligaments are overly loose or stretched, a condition known as ligamentous laxity, they may not adequately restrict the knee’s backward movement. This can allow the knee to hyperextend beyond its typical range of motion, contributing to genu recurvatum.
Generalized joint hypermobility, where individuals possess more flexibility in many joints, also plays a role. Conditions such as Ehlers-Danlos syndrome or benign joint hypermobility syndrome exemplify systemic causes where widespread ligamentous laxity can predispose an individual to genu recurvatum.
Structural abnormalities in the tibia or femur can also influence knee alignment. Specific angles or rotations of these bones, such as tibial torsion, may predispose the knee to hyperextension. These bone deformities can be present from birth, representing congenital factors that influence the joint’s mechanics from an early age.
The joint capsule, a fibrous sac enclosing the knee joint, helps provide stability. If this capsule becomes weakened or stretched over time, it can contribute to increased joint instability. This allows for greater backward movement of the knee, facilitating the development or progression of genu recurvatum.
Neurological Conditions and Muscle Imbalances
The muscles surrounding the knee play a role in its stability and controlled movement. Weakness in specific muscle groups, such as the quadriceps or hamstrings, can lead to the knee “locking back” into hyperextension. This occurs as the body compensates for insufficient muscle support, using the hyperextended position for stability during standing or walking.
Neurological impairments can affect the control of leg muscles, contributing to genu recurvatum. Conditions like stroke, cerebral palsy, or post-polio syndrome can result in muscle imbalances or spasticity. These disruptions can cause muscles to pull the knee into a hyperextended position, disrupting normal joint mechanics.
Spinal cord injuries or peripheral nerve damage can interrupt signals between the brain and leg muscles. This disruption can lead to a loss of muscle control or strength, making it challenging to maintain proper knee alignment. The affected limb may then exhibit genu recurvatum due to insufficient muscular support.
Impaired proprioception, the body’s awareness of its position, can affect knee control. If the brain receives inaccurate information about knee alignment, it can lead to improper muscle activation patterns. This lack of precise joint position awareness contributes to difficulty maintaining a stable knee, promoting hyperextension.
Acquired Factors and Injury
Severe knee injuries represent a significant acquired cause of genu recurvatum, as they can compromise the inherent stability of the joint. Traumatic events like significant ligament tears, such as a severe anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL) injury, can directly lead to increased laxity within the knee. Knee dislocations or fractures around the joint can also disrupt the structural integrity, predisposing the knee to hyperextension.
In some instances, complications following knee surgeries can contribute to altered joint mechanics and subsequent genu recurvatum. Procedures involving ligament reconstruction or joint replacement, while aiming to restore function, can sometimes result in an imbalance of forces or residual instability. If the surgical outcome leads to excessive joint slackness or improper alignment, the knee may develop a tendency to hyperextend.
Chronic biomechanical stress, often stemming from long-term abnormal gait patterns or improper posture, can gradually impact knee stability. Repetitive stress on the knee joint over time can lead to a stretching of the surrounding soft tissues, including ligaments and the joint capsule. This cumulative effect can incrementally increase joint laxity, contributing to the development of genu recurvatum.
Degenerative changes within the knee, such as those seen with age-related wear and tear or conditions like osteoarthritis, can also influence joint mechanics. While less common, advanced stages of osteoarthritis can sometimes lead to bone loss or changes in joint surfaces that alter alignment. These alterations can, in specific cases, result in a hyperextended knee as the joint attempts to find a new compensatory position for stability.