When your knees bend backward beyond straight, the medical term is genu recurvatum, also called knee hyperextension. A knee at full extension sits at roughly 0 degrees. Anything beyond that, where the joint visibly curves backward, crosses into hyperextension territory, and extension greater than 5 degrees is the threshold most clinicians use to diagnose genu recurvatum.
What Genu Recurvatum Looks Like
If you stand with your legs straight and your knees push past the locked position so your lower leg angles backward, that’s the classic appearance. Some people notice it in photos or mirrors, where the leg forms a slight backward “C” curve at the knee rather than a straight line. Others first become aware of it when a coach, physical therapist, or doctor points it out. The degree matters: a few degrees of hyperextension is relatively common and may cause no problems at all, while more severe cases (15 degrees or beyond) can cause visible deformity and functional issues.
Why It Happens
There’s no single cause. Genu recurvatum can develop from loose ligaments, muscle weakness, bone alignment problems, or a combination of all three.
On the ligament side, the structures that normally stop the knee from extending too far can be stretched or torn. An anterior cruciate ligament (ACL) tear, for example, removes one of the knee’s main stabilizers and can allow backward drift over time. General ligament laxity, where connective tissue throughout the body is naturally stretchier than average, is another common factor.
Muscle imbalances play a significant role too. Weak hip extensors (the glutes) or a weak quadriceps can change how forces travel through the knee during walking and standing, allowing it to snap backward rather than staying controlled at full extension. A difference in leg length can also shift mechanics enough to cause hyperextension on one side.
In children, genu recurvatum occasionally appears at birth as a congenital condition, linked to the positioning of the baby in the womb or to growth plate abnormalities. In these cases, treatment usually begins early and often corrects successfully.
Connective Tissue and Hypermobility Disorders
Knees that bend backward are one of the hallmark signs of generalized joint hypermobility, the kind often associated with hypermobile Ehlers-Danlos syndrome (hEDS) and hypermobility spectrum disorders. In the diagnostic criteria for hEDS, knee hyperextension greater than 10 degrees on each side counts as a specific finding. People with these conditions have connective tissue that’s stretchier than normal throughout the body, so hyperextending knees typically show up alongside other flexible joints: elbows that bend past straight, thumbs that touch the forearm, fingers that bend far backward.
If your knees go back and you also notice you’re unusually flexible in multiple joints, bruise easily, have soft or stretchy skin, or deal with chronic joint pain, it’s worth exploring whether a hypermobility condition is the underlying cause. Not everyone with hyperextended knees has a connective tissue disorder, but it’s one of the more common explanations when the flexibility is widespread.
Neurological Causes
Genu recurvatum is also common after a stroke or in people with cerebral palsy. When the brain’s control over leg muscles is disrupted, the balance of forces around the knee changes. Muscle spasticity (where certain muscles are constantly tight) and weakness in opposing muscles can push the knee into hyperextension during walking. In stroke patients specifically, knee recurvatum during gait is a well-recognized problem that affects walking stability and speed.
Symptoms and Long-Term Effects
Mild hyperextension often causes no symptoms. Many people live with slightly hyperextended knees their entire lives without pain or functional problems. When genu recurvatum does cause issues, the most common complaints are knee pain (typically at the back of the joint), a feeling of instability or the knee “giving way,” and difficulty controlling the knee during activities like walking downstairs or landing from a jump.
People with more pronounced hyperextension often develop an altered walking pattern. Instead of the knee bending smoothly through each step, it snaps backward at the moment the foot hits the ground, creating a stiff, lurching gait. Over time, this abnormal movement pattern puts extra stress on cartilage, ligaments, and the joint capsule at the back of the knee. The concern with longstanding, uncorrected genu recurvatum is that it can accelerate cartilage breakdown and lead to osteoarthritis earlier than it might otherwise develop.
Proprioception, your body’s sense of where your joints are in space, also tends to be poor at the end range of knee extension in people with this condition. That reduced awareness makes it harder to catch the knee before it hyperextends, which feeds a cycle of repeated overextension and gradual stretching of the joint structures.
Treatment Without Surgery
For most people, genu recurvatum is managed without surgery. The approach depends on what’s driving the hyperextension.
Strengthening exercises are the foundation. Building up the hamstrings (the muscles behind the thigh) helps actively resist backward movement of the knee. Strengthening the glutes and hip muscles improves overall leg alignment during walking and standing. Equally important is training the quadriceps to activate in a controlled way so they stabilize the knee at full extension without pushing it past that point. Proprioceptive training, exercises that challenge your balance and joint awareness, helps your body learn to recognize and correct hyperextension before it happens.
Bracing and orthotics offer external support when muscle training alone isn’t enough. Ankle-foot orthoses (lightweight braces worn inside the shoe and along the lower leg) can redirect ground forces so the knee is less likely to snap backward. For more severe cases, a knee-ankle-foot orthosis provides direct mechanical limits on how far the knee can extend. Heel lifts are sometimes added to fine-tune the alignment.
For people whose hyperextension stems from muscle spasticity after a stroke, targeted injections to relax overactive calf or thigh muscles can reduce the forces pushing the knee backward. These injections are often combined with bracing for the best results, and in many cases this combination is enough to avoid more invasive treatment.
When Surgery Is Considered
Surgery becomes an option when genu recurvatum is severe, painful, and hasn’t responded to conservative treatment. The general threshold is hyperextension greater than 15 degrees, recurrent knee instability, or a failed ligament reconstruction. The most common surgical approach involves cutting the shinbone just below the knee and repositioning it to change the angle of the joint surface. This corrects the backward slope that allows the knee to hyperextend. The goal is to prevent ongoing pain and slow the progression of arthritis in the joint.
Recovery from this type of bone realignment surgery typically involves a period of limited weight-bearing followed by months of physical therapy to rebuild strength and range of motion. It’s generally reserved for cases where the structural problem is in the bone itself, such as after a fracture that healed in the wrong position, rather than for people whose hyperextension comes from loose ligaments or hypermobility alone.
Living With Hyperextended Knees
If you’ve noticed your knees bend backward, the most practical thing you can do is pay attention to your knee position during everyday activities. Standing with a slight “micro-bend” in the knees rather than locking them fully straight takes pressure off the back of the joint. During exercise, especially activities involving jumping, squatting, or landing, consciously avoiding that final snap into hyperextension protects the ligaments and cartilage over time.
For people who are generally hypermobile, a consistent strengthening program focused on the muscles surrounding the knee is the single most effective long-term strategy. The joint itself may always have more range than average, but strong muscles act as dynamic stabilizers that keep the knee from reaching its end range during normal movement.