Genu valgum is the medical term for knock-knees, a condition where the knees angle inward and touch or nearly touch each other while the ankles remain apart. A small degree of inward knee angle is normal in adults (about 5 to 7 degrees), but genu valgum refers to an alignment beyond that typical range. In most young children, knock-knees are a completely normal phase of leg development that resolves on its own. When the alignment persists or worsens past a certain age, it can affect how the knee joint bears weight and increase the risk of joint problems over time.
Why Most Children With Knock-Knees Don’t Need Treatment
Children’s legs go through a predictable pattern of alignment changes as they grow. Knock-knees first become noticeable around age 2 and reach their peak between ages 3 and 4, when the angle can be as high as 8 to 10 degrees of valgus. At that age, anywhere from 2 degrees of bowleg to 20 degrees of knock-knee falls within the normal range. From there, the legs gradually straighten, settling into a stable adult alignment of 5 to 7 degrees by age 7.
Most children under 6 who are evaluated for knock-knees actually have this normal, physiologic version. It resolves spontaneously without braces, exercises, or any intervention. The key distinction is what happens after age 7: if the inward angle hasn’t decreased by then, or if it’s getting worse, the condition is considered pathologic genu valgum rather than a passing developmental phase.
What Causes Pathologic Genu Valgum
When knock-knees don’t follow the normal developmental timeline, an underlying cause is usually responsible. The possibilities differ depending on whether both legs are affected or just one.
Bilateral genu valgum (both legs) can result from metabolic bone diseases like rickets, which weakens bones through vitamin D or phosphorus deficiency. Skeletal dysplasias, a group of genetic conditions affecting bone and cartilage growth, are another cause. Certain rare storage diseases that cause abnormal buildup of substances in the body can also lead to progressive knock-knee deformity.
Unilateral genu valgum (one leg) is most often caused by injury. Fractures near the growth plate of the upper tibia can trigger uneven bone growth on one side, pulling the knee into a valgus position. This is sometimes called the Cozen phenomenon, where increased blood flow during fracture healing causes the inner part of the bone to overgrow. Bone tumors, infections, and prior radiation therapy are less common causes.
How Genu Valgum Affects the Knee Over Time
When the knee angles inward beyond its normal range, it shifts how body weight is distributed across the joint. Instead of loading evenly, more pressure falls on the outer (lateral) compartment of the knee. This uneven loading accelerates wear on the cartilage and meniscus on that side.
Research from two large longitudinal studies found that even mild valgus malalignment significantly raises the risk of lateral knee osteoarthritis. People with just 1 to 3 degrees of excess valgus had roughly 2 to 3.5 times the odds of their existing knee arthritis progressing. At 3 degrees or more, the risk of developing new cartilage damage on MRI was nearly 6 times higher. Meniscal damage on the outer side of the knee was over 4 times more likely in people with valgus alignment above 3 degrees. These risks apply to adults living with uncorrected alignment over years and decades.
Beyond osteoarthritis, the altered alignment increases stress on the anterior cruciate ligament (ACL). The inward knee position creates a stronger lateral pull from the quadriceps muscles, which places the ACL under greater strain during activities like cutting, jumping, or pivoting.
How Severity Is Measured
The simplest screening tool is the intermalleolar distance: the gap between your inner ankle bones when your knees are touching. A larger gap suggests a greater degree of knock-knee. However, recent international consensus among orthopedic specialists moved away from using this measurement alone to make surgical decisions.
The preferred assessment involves a full-length standing X-ray of both legs. From this image, surgeons measure the mechanical axis, an imaginary line from the center of the hip to the center of the ankle. In a well-aligned leg, this line passes through or near the center of the knee. In genu valgum, it falls to the outer side. Treatment is generally considered when the mechanical axis deviates more than 10 millimeters from center, the angle exceeds 10 degrees, or the intermalleolar distance is greater than 8 centimeters.
Treatment for Children and Adolescents
For children whose knock-knees are pathologic and not resolving, the most common surgical option is guided growth. This minimally invasive procedure involves placing a small plate on one side of the growth plate near the knee, which temporarily slows growth on that side while the other side continues growing. Over months, the leg gradually straightens. It works because children’s bones are still actively growing, and it’s most effective when performed roughly 1 to 2 years before the growth plate is expected to close, typically between ages 14 and 16 depending on the child. The procedure is indicated for deformities under about 11 degrees.
Because it relies on remaining growth, timing matters. If the deformity is identified too late or the growth plates have already fused, guided growth won’t work, and more involved surgical correction becomes necessary.
Treatment for Adults
Adults with symptomatic genu valgum don’t have active growth plates, so correction requires a different approach. Distal femoral osteotomy is a joint-preserving surgery where the surgeon cuts the lower thighbone and realigns it to shift weight-bearing back toward the center of the knee. This unloads the damaged lateral compartment and can delay or prevent the need for a knee replacement.
Recovery follows a fairly predictable timeline. Patients are typically limited to partial weight-bearing for the first 5 to 6 weeks, then gradually progress to full weight-bearing by 6 to 12 weeks. Returning to sports takes considerably longer, ranging from about 8 to 17 months across published studies.
Can Exercise Correct Knock-Knees?
Strengthening exercises targeting the hip and lower leg muscles are frequently recommended for people with knock-knee alignment, particularly athletes. The logic is that stronger hip stabilizers (especially the gluteus medius) can help control the knee’s inward drift during movement. In practice, the evidence is limited. One randomized controlled trial found that a 6-week program targeting the gluteus medius and lower leg muscles in young football players did not significantly reduce knee valgus angles or improve dynamic balance.
This doesn’t mean exercise is useless. Strengthening the muscles around the hip and knee can reduce symptoms, improve functional stability, and protect against injury even if it doesn’t change the underlying bone alignment. For structural genu valgum caused by bone deformity rather than muscle weakness, exercise alone won’t straighten the legs. The distinction matters: dynamic valgus (the knee collapsing inward during movement due to poor muscle control) can improve with training, while structural valgus (the bones themselves are angled) requires surgical correction if it’s causing problems.