Genu Valgum (Knock Knees)

What genu valgum looks like

Stand with your knees together and look at your feet. With genu valgum, the inner ankle bones cannot touch. "Valgum" describes the lower leg angling outward from the knee, so the knees point toward each other.

Doctors measure:

• Intermalleolar distance: the gap between the inner ankle bones with the knees touching. Under about 8 cm (3 inches) is usually within normal limits for a young child.
• Tibiofemoral angle: the angle between the thigh bone and shin bone. A few degrees of valgus is normal in adults; children aged 3 to 4 often have 10 to 15 degrees.

People with knock knees may walk with the feet apart, swing the legs outward, or brush the knees together. Many also have flat feet, because the alignment shifts weight to the inner foot.

Normal development: when knock knees are expected

This pattern happens in almost all children. If your toddler's legs worry you, the bowlegged or knock-kneed page explains the normal range and the signs that need a check. Bowing, the opposite shape, is covered under genu varum.

Causes of abnormal knock knees

In children

• Physiological (normal) valgus that is exaggerated: more common in children with excess weight.
• Rickets: soft bones from vitamin D or calcium deficiency, or inherited phosphate-wasting rickets. Clues are wide wrists, delayed walking, poor growth and bone pain.
• Growth plate injury: a fracture or infection near the knee can cause one side to grow faster or slower. A fracture of the upper shin in young children (Cozen's phenomenon) can cause the leg to drift into valgus over the next year.
• Obesity: extra weight on the outer knee slows growth there, and the deformity can worsen.
• Skeletal dysplasias and genetic conditions: for example multiple epiphyseal dysplasia, Morquio syndrome and Ellis-van Creveld syndrome.
• Other: kidney disease affecting bone, neuromuscular conditions, and tumors such as multiple hereditary exostoses.

In adults

• Osteoarthritis of the outer knee: wear of the lateral compartment lets the knee collapse inward. More common in women and in people with rheumatoid arthritis.
• Rheumatoid or inflammatory arthritis.
• Old fractures around the knee that healed with angulation.
• Persisting childhood valgus.

Problems knock knees can cause

Mild knock knees cause no problems. More marked genu valgum can lead to:

• knee pain on the inner side from stretched ligaments, or at the front from kneecap strain (patellofemoral pain)
• kneecap instability or dislocation, because the kneecap is pulled outward
• an awkward gait, tripping and tiring easily
• self-consciousness in teenagers
• in the long term, uneven loading of the outer knee and earlier knee arthritis

How genu valgum is diagnosed

A doctor watches you walk, measures ankle distance and knee angles, checks for one-sidedness, leg length differences and flat feet, and plots the child's height. Further tests are done when the pattern is abnormal:

• Standing full-length leg X-ray: measures the mechanical axis (a line from hip to ankle) and identifies where the deformity lies, in the thigh bone, shin bone or both.
• Blood tests: calcium, phosphate, alkaline phosphatase, vitamin D and kidney function if rickets is suspected.
• Genetic evaluation for suspected skeletal dysplasia.

Genu valgum treatment

Children

• Observation: normal developmental knock knees need nothing. Special shoes, braces and exercises do not change bone alignment and are not recommended.
• Treat the cause: vitamin D and calcium for nutritional rickets; specialist treatment for inherited rickets. Legs often straighten as bones heal.
• Weight management in children with obesity.
• Guided growth (hemiepiphysiodesis): for significant knock knees after about age 8 to 10, while the child is still growing. A small plate or screws placed on the inner side of the growth plate slows growth on that side so the leg gradually straightens, usually over 12 to 18 months. The plates are then removed. This is a small operation with quick recovery.
• Osteotomy: cutting and realigning the bone, for teenagers who have finished growing or severe deformity.

Adults

• Exercises and physical therapy: strengthening the hip abductors and quadriceps can ease pain and improve control. They do not straighten the bone.
• Pain relief, weight loss and bracing: an "unloader" brace can reduce pressure on the outer knee.
• Distal femoral osteotomy: realigns the thigh bone to shift weight off a worn outer compartment in younger, active adults.
• Total knee replacement: corrects the alignment in people with advanced osteoarthritis.

Frequently asked questions

At what age do knock knees go away?

Knock knees are usually most noticeable around age 3 to 4 and gradually straighten by age 7 to 8. A slight inward angle persists into adulthood and is normal. Knock knees that are still marked after age 8, or getting worse, should be checked by a doctor.

Can knock knees be corrected in adults?

Exercises can improve strength and knee pain but cannot change bone shape. Significant genu valgum in adults is corrected with an osteotomy, which cuts and realigns the bone, or with a knee replacement if arthritis is advanced. Treatment is usually offered for pain or function, not appearance alone.

What causes knock knees?

In young children, it is a normal stage of growth. Abnormal knock knees can result from rickets (vitamin D deficiency), a growth plate injury or fracture, obesity, or genetic bone conditions. In adults, it is usually caused by arthritis of the outer knee or an old fracture.

Do exercises fix genu valgum?

No exercise reshapes the bones. Strengthening the hips and thighs can improve how the knee tracks, reduce pain and help walking. In children, normal knock knees correct with growth, and exercises, braces or special shoes do not speed this up.

Is genu valgum serious?

Usually not. Most cases in children are normal and resolve. It is worth assessing when it is one-sided, severe, persists past age 8, or comes with short stature, pain or bone problems. In adults, it can speed up wear of the outer knee.