Knock knees, also known as genu valgum, is a type of knee alignment seen when a child (or adult) stands up straight with their knees together, but their feet and ankles stay apart. The opposite type of alignment, called bow legs (genu varum), is when someone stands with their feet and ankles together, and there is a gap between the knees.
Knock knees are usually assessed by directly measuring the angle of the shin bone to the thigh bone (tibiofemoral angle) or by measuring the distance between the ankles (intermalleolar distance). Sometimes photographs or x-rays can be taken to calculate these measures.
Knock knees (and bow legs) are a normal part of a child’s growth and development. The classic pattern of changes at the knee with age in Caucasian children is bow legs at birth, straightening out at two years, going into knock knees at four years, and straightening out between six to 11 years.
What causes pathological knock knees
Pathological knock knees can occur in some neurological conditions, such as cerebral palsy or spina bifida, as a result of the altered muscle pull on the bones.
So pathological knock knees may be one of the early signs of an underlying disorder. Bone diseases resulting from poor mineralisation, such as rickets, may present through large knee angles during childhood. When pathological knock knees are seen in combination with short stature and other bone and joint misalignment, a skeletal dysplasia or metabolic bone disorder may be the cause.
Obesity during adolescence is also associated with more severe knock knees, and is more commonly seen in children with flat feet and those with hypermobile (overly flexible) joints.
Do they have to be treated?
It is usually parental concern for the way a child looks when standing or walking that sparks initial review by a health professional. Children presenting with physiological knock knees do not require treatment or ongoing monitoring, as they will grow out of it with time.
Conservative treatments may be beneficial such as exercises and weight loss programs to reduce obesity and improve knee movement in children, or knee braces and foot orthoses for painful osteoarthritis associated with knock knees in adults. However, these interventions require more scientific evidence to support their use as there currently isn’t much.
Those with severe or worsening pathological knock knees might need orthopaedic surgery to correct their knee alignment, particularly in the presence of persistent pain or disability, regardless of the underlying cause.