Why bow legs and knock knee lead to arthritis?

Basics

Bow legs (genu varum) is condition when legs have deformity outward of natural legs position.

Knock knee (genu valgum) is condition when legs have deformity inward of natural legs position.

Arthritis means a disorder of the knee joint, generally implying early joint surface damage.

Leg axis is conventional axis that shows how the body weight distributes among leg joints.

Articular cartilage is a type of dense connective tissue. It can supply smooth surfaces for the movement of articulating bones.

First of all bow legs (genu varum) and knock knee (genu valgum) are deformities that are not only cosmetic defects. They also lead to knee-joint move abnormality that after a number of years result to arthritis.

We find out that normal body weight distribution is when the leg axis go straight through femoral head, center of the knee-joint and center of articulation of foot. In this case the body weight distribute naturally and articular cartilage of knee-joint have equal weight distribution at full surface. There is natural position of knee-joint that allows to save the articular cartilage in health during years.

What is happen when a person have bow legs or knock-knee? As you could imagine that legs axises go still straight through femoral head and center of articulation of foot but do not go through center of the knee-joint. So body weight distribution change and regarding the knee-joint one part of the knee have more loading than another. If bow legs there is more loading of inner part of knee-joint and if knock knee there is more loading of outer part of knee-joint. So articular cartilage of knee-joint have different weight distribution at surface that leads to its attrition in the part where the loading is maximum. In time the articular cartilage attrition leads to arthritis and a person feels pain in knee-joints. Appearance of arthritis usually happen after years in elderly age but sometimes it is happen in middle age. It depends on individual health of each person.

The only way to protect yourself from appearance of knee-joint arthritis is the surgery for bow legs and knock-knee correction. With the surgery the leg axis become natural position so articular cartilage of knee-joint get equal weight distribution at full surface and keeps its health in years. Also there is a cosmetic effect that lets a person feels himself or herself more comfortable around other people.