Bow legs (varus knee): causes, symptoms and treatment

What are bow legs?

Bow legs, also called O-legs, varus knee or genu varum, curve outwards between the hip and the ankle. When you stand with your ankles together, a gap remains between the knees.

Slight bowing is normal in toddlers and usually straightens as they grow. This page is about adolescents close to the end of growth and adults, in whom the alignment no longer corrects itself.

Why alignment matters for the knee

In a straight leg, the load line (mechanical axis) from the hip to the ankle runs close to the centre of the knee. With bow legs it shifts towards the inner side, so the inner cartilage and meniscus carry more of the body weight with every step.

Over time, this extra load can contribute to wear of the cartilage on the inner side of the knee, known as medial knee osteoarthritis. Wear can in turn increase the bowing.

Possible causes

• A natural build, often on both sides
• Wear of the inner knee (medial osteoarthritis)
• Loss of the inner meniscus after an injury or operation
• A fracture that healed in a bowed position
• Childhood conditions such as Blount disease or rickets
• Loose or injured ligaments

Typical symptoms

• Pain on the inner side of the knee, especially after walking, standing or sport
• Swelling or stiffness after activity
• A shorter walking distance
• Visible bowing when standing

Some people with bow legs have no symptoms. Treatment decisions depend on complaints, measurements and the condition of the joint, not on appearance alone.

How bow legs are assessed

An orthopaedic specialist examines the knee and the whole leg. A long X-ray of both legs taken while standing shows the load line and allows the angles of the thigh bone and shinbone to be measured. This shows where the deformity lies, often in the upper shinbone (tibia).

An MRI scan can show the condition of the cartilage, meniscus and ligaments. Together, these findings guide the choice of treatment and the planning of any correction.

Treatment options

Without surgery

Weight management, physiotherapy and muscle strengthening, activity changes, pain relief, insoles or an unloading brace can ease the symptoms. They do not change the alignment of the bone.

Realignment osteotomy (HTO)

When the bowing lies in the upper shinbone and the joint is still worth preserving, a high tibial osteotomy changes the angle of the bone and moves the load line away from the inner knee. Your own knee is kept.

UniPlasty

UniPlasty is a gradual opening-wedge HTO: the correction is made step by step after surgery with a temporary external fixator and can be fine-tuned on standing X-rays.

Knee replacement

When wear affects the whole joint, a partial or total knee replacement may be more suitable.