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. In most children, it’s a completely normal phase of leg development that peaks between ages 3 and 4 and resolves on its own by around age 7. When it persists beyond childhood or develops in adults, it can shift how weight travels through the knee joint and eventually lead to pain, gait changes, and cartilage damage.
How Knock-Knees Look and Feel
The hallmark of genu valgum is visible inward angling of the knees when standing with feet together. Doctors measure severity using the intermalleolar distance, which is simply the gap between the inner ankle bones when the knees are touching. In children between ages 3 and 7, a gap of 2.5 to 5 centimeters is considered normal. A gap above 8 centimeters is abnormal at any age.
Most people with mild knock-knees have no symptoms at all. When the alignment is more pronounced, the most common complaints are pain along the inner side of the knee or ankle, and flat feet often accompany the condition. In more severe cases, the knees may rub together during walking, the kneecap can shift outward, and the feet may turn out to compensate. Some people develop a visible sideways thrust at the knee during each step, particularly when the condition is tied to metabolic bone disease.
Why It Happens in Children
Nearly all toddlers go through a predictable sequence of leg alignment changes. Babies are typically born slightly bowlegged. By age 2, the legs begin drifting into a knock-knee position, reaching a peak angle of about 12 degrees between ages 3 and 4. After that, the knees gradually straighten to a stable, very slight inward angle by age 7. This entire process is driven by normal bone growth and requires no treatment.
The key distinction is between this physiologic (normal) knock-knee pattern and pathologic genu valgum, which worsens over time, appears on only one side, or develops outside the typical age window. Pathologic causes include rickets from vitamin D deficiency, hereditary phosphate disorders, kidney-related bone disease, and growth plate injuries from fractures or infection. When only one leg is affected, a prior injury to the growth plate near the knee is a common culprit.
The Link to Body Weight
Excess body weight places additional mechanical stress on the knees and can push them into a valgus position. Research comparing obese adults with and without knock-knees found that those with genu valgum had significantly higher BMIs on average. Studies in children tell a similar story: obese children aged 11 to 12 show a higher prevalence of knock-knees compared to their normal-weight peers. The extra load doesn’t just reveal an existing alignment issue. It can actively worsen it, because the growth plates in children’s bones respond to uneven pressure by growing asymmetrically.
Long-Term Effects on the Knee Joint
When knock-knees persist into adulthood, the misalignment shifts more of your body weight onto the outer (lateral) compartment of the knee. Over time, this uneven loading increases the risk of lateral cartilage damage and osteoarthritis. Even a relatively slight valgus alignment can be enough to cause problems, in part because the shifted forces accelerate wear on the lateral meniscus, the crescent-shaped cushion on the outer side of the knee.
Once the meniscus starts to deteriorate, the knee loses passive stability. The muscles around the joint compensate by co-contracting more forcefully, which paradoxically increases the compressive load on the already damaged compartment. This creates a cycle where alignment issues and cartilage loss reinforce each other. The pattern is similar to what happens after an ACL tear: weight-bearing contact shifts to areas of cartilage that aren’t conditioned for repetitive stress, and degeneration follows.
How It’s Diagnosed
A doctor can often identify genu valgum just by watching you stand and walk. The intermalleolar distance gives a quick bedside measurement of severity. For a more precise picture, standing X-rays of the full leg from hip to ankle let clinicians measure the mechanical axis, an imaginary line from the center of the hip to the center of the ankle. In a normally aligned leg, this line passes through or very close to the center of the knee. In genu valgum, it falls to the outer side.
Another measurement frequently used is the Q-angle, which tracks the line of pull of the quadriceps muscle relative to the kneecap. It’s measured from the front of the hip bone to the center of the kneecap, then from the kneecap down to the bump just below the knee. A wider pelvis or greater inward knee angle increases this angle, which can contribute to kneecap tracking problems and anterior knee pain.
Exercise and Physical Therapy
For mild cases and for people with a tendency toward inward knee collapse during activities like squatting and running, targeted exercise can help. The focus is on strengthening the hip abductors and external rotators, the muscles on the outer hip that resist the knee from caving inward. Weakness in these muscles allows the thigh to rotate inward and drift toward the midline during weight-bearing activities, which increases the valgus angle at the knee.
Structured corrective exercise programs have shown measurable improvements in both hip strength and knee alignment during movement. These programs typically start with isolated muscle activation exercises so you learn to engage the correct muscles before progressing to functional movements like squats and single-leg activities. Bracing and orthotic insoles may also be used in children to manage symptoms while waiting for natural correction, though evidence for bracing alone changing the underlying bone alignment is limited.
Surgical Options
Surgery is reserved for cases that don’t resolve naturally, cause significant symptoms, or show worsening alignment. The approach depends largely on age and skeletal maturity.
Guided Growth in Children
Children and adolescents who still have open growth plates near the knee can benefit from a procedure called guided growth, or hemiepiphysiodesis. A small plate is placed on the inner side of the growth plate, temporarily slowing growth on that side while the outer side continues to grow. This gradually straightens the leg over months. Most surgeons recommend performing this between ages 8 and 10 to reduce the risk of rebound (the leg drifting back after correction) and to avoid permanent damage to the growth plate. Because the plate is removed once the desired correction is achieved, the procedure is reversible and doesn’t require precise timing the way a permanent growth plate closure would.
Osteotomy in Adults
Once the bones have finished growing, correcting the alignment requires an osteotomy, where the surgeon cuts and repositions the bone to shift the mechanical axis back toward the center of the knee. For knock-knees, this is most commonly done on the lower end of the femur (thighbone). The goal is to redistribute weight more evenly across the joint and slow or prevent cartilage breakdown.
Recovery follows a predictable timeline. Physical therapy starts the day after surgery with gentle exercises and learning to walk with crutches using only partial weight on the operated leg. For the first six weeks, you’ll use crutches, wear compression stockings, and take blood thinners to prevent clots. Over the next six weeks, you transition to a single cane or crutch and begin gentle strengthening. Full recovery to normal walking without assistive devices typically takes about three months, with return to more demanding activities coming later.