The appearance of legs bending backward when standing, often called “swayback knees,” is medically known as Genu Recurvatum. This posture occurs when the knee joint extends past its natural, straight alignment, forcing the lower leg into hyperextension. This deviation places abnormal stress on the knee structures. Understanding this issue is crucial for addressing the underlying causes and preventing long-term consequences.
What Defines Hyperextended Knees
Normal knee alignment means the thigh bone (femur) and shin bone (tibia) form a perfectly straight line (zero degrees of extension). Genu Recurvatum is defined as the knee extending backward more than five degrees beyond this neutral position. This excessive backward bending makes the leg appear to lock back, placing the knee joint’s center of gravity in front of the joint axis.
The severity of the condition is measured using a goniometer, which quantifies the exact degree of hyperextension. Mild cases involve only a slight backward curve, while more pronounced instances show a significant “bowing” effect. In this locked-back position, the knee does not rely on muscle activity for stability, instead hanging passively on the ligaments and joint capsule.
Underlying Causes and Contributing Factors
The ability of the knee to hyperextend is rooted in structural and functional elements that compromise joint stability. A frequent cause is inherent ligamentous laxity, meaning the ligaments surrounding the knee are naturally looser than typical. This can be a genetic trait, sometimes associated with generalized joint hypermobility or connective tissue disorders like Ehlers-Danlos syndrome.
Muscle imbalance is another contributor, particularly weakness in the hamstrings, glutes, and calf muscles. These groups dynamically control the knee’s terminal extension, and their weakness can fail to prevent the joint from snapping into a hyperextended position. For instance, strong quadriceps combined with weak hamstrings can pull the joint backward without sufficient counter-stabilization.
Previous trauma is a common acquired cause, where an injury, such as a sprain or tear of the anterior or posterior cruciate ligaments, leaves the joint structurally unstable. Even after healing, the damaged or stretched ligaments may no longer provide the necessary restraint to prevent backward movement. Furthermore, issues in skeletal alignment, such as an excessive anterior slope of the tibia, can make a person anatomically predisposed to hyperextension.
Immediate Symptoms and Associated Risks
Individuals with Genu Recurvatum may experience a range of immediate symptoms, often starting with discomfort and instability around the knee joint. Pain is common, sometimes described as a sharp, pinching sensation in the front of the knee or a dull ache in the posterior aspect. Many report a feeling that the knee is “giving out” or an inability to trust the joint when bearing weight, which is related to poor proprioceptive control—the body’s sense of joint position.
Chronic, uncorrected hyperextension creates abnormal loading patterns and long-term risks. Standing with the knees locked back forces the posterior joint capsule and ligaments to bear the body’s weight, leading to overstretching and chronic strain. This mechanical stress accelerates wear and tear on the cartilage surfaces, increasing the risk of developing premature osteoarthritis. It also elevates the susceptibility to acute injuries, such as meniscus tears, because the joint is already positioned at its end range of motion.
Corrective Management and Treatment
Management of Genu Recurvatum primarily focuses on conservative, non-invasive strategies aimed at restoring muscular control and joint stability. Physical therapy (PT) is the first-line treatment and involves targeted exercises to strengthen the muscles that dynamically stabilize the knee. This includes intensive work on the hamstrings and gluteal muscles, which act as a natural brake to prevent the knee from moving past neutral alignment.
PT programs also incorporate proprioceptive training to improve the body’s awareness of the knee’s position in space, helping to break the habit of locking the joint. In addition to muscle strengthening, gait re-education is performed to consciously shift the center of gravity forward, encouraging a slight bend in the knee when standing. For cases where muscle control is severely lacking or the structural laxity is significant, external support may be provided through specialized bracing or custom orthotics.
Surgical intervention is considered only in rare circumstances, typically reserved for cases resulting from severe trauma or underlying bony deformities. These procedures might involve complex ligament reconstruction or an osteotomy (a bone-cutting procedure to alter the angle of the tibia). Most individuals successfully manage the condition through dedicated muscle strengthening and consistent habit modification, ensuring the knee is supported by muscle rather than passively held by ligaments.