Bow Legs and Knock Knees
Patient information for parents and carers — Dr Christopher Spelman, Orthopaedic Surgeon
Overview
Bow legs (genu varum) and knock knees (genu valgum) describe the way the legs are aligned at the knees. In bow legs the knees are wide apart when the ankles are together; in knock knees the knees touch while the ankles are apart. A degree of each is a completely normal part of childhood development, and most children need only reassurance and observation.
Normal development
The alignment of a child’s legs changes predictably as they grow. Toddlers are naturally bow-legged, straightening out at around age two. Legs then typically pass through a knock-kneed phase, often most noticeable between about three and four years of age, before gradually settling towards adult alignment by around seven years. Because this pattern is so consistent, most “bow legs” and “knock knees” are physiological (normal) and resolve on their own without treatment.
When to seek assessment
Certain features suggest the alignment may not simply be part of normal development and warrant assessment:
Alignment that is only on one side (asymmetry)
Alignment that is severe, or worsening rather than improving with age
A child who is much shorter than expected for their age
Alignment that persists beyond the expected age of resolution
A family history of bone conditions, or other health concerns
Causes to consider
When the alignment is outside the normal pattern, an underlying cause may be present. These include Blount’s disease (a growth-plate disorder of the shin bone), rickets or other conditions affecting bone metabolism, previous injury or infection of a growth plate, and some skeletal conditions. Identifying these is the purpose of assessment.
Assessment and treatment
Assessment involves examining the legs, observing the child walking and, where needed, measuring the alignment. X-rays are used if an underlying cause is suspected, and blood tests are occasionally required (for example, to check for rickets). The great majority of children need only reassurance and periodic review. Where a genuine deformity persists or is due to an underlying condition, treatment addresses that condition and, occasionally, uses a guided-growth procedure to gently correct the alignment as the child grows; more severe deformity is rarely corrected with an osteotomy.
Outcomes and what the evidence shows
Studies mapping normal leg alignment across childhood confirm that the tibiofemoral angle follows a predictable path from bow-legged in infancy, through a knock-kneed phase, to adult alignment, with physiological knock knees of up to around 11 degrees being within normal limits. This normal developmental pattern is why most cases need no treatment – identifying the small number that fall outside it is the purpose of assessment.
Complications
Physiological bow legs and knock knees resolve without any lasting problem and have no complications. The considerations relate to genuine deformity and its treatment:
Persistent deformity from an underlying condition – if a cause such as Blount’s disease or rickets is missed, the deformity can progress and, over the long term, place uneven load on the knee.
Guided-growth complications – if a corrective guided-growth procedure is used, the alignment can occasionally be over- or under-corrected, and there can be “rebound” of the deformity after the plate is removed, sometimes needing further treatment.
Hardware issues – prominence of, or irritation from, the small plate and screws, which are usually removed once alignment is corrected.
Osteotomy risks – where a bone-cutting procedure is required for severe deformity, the usual risks of healing, hardware and (rarely) nerve irritation apply.
Summary
Bow legs and knock knees are usually a normal, self-correcting part of growing up and need only reassurance. Assessment is aimed at spotting the minority with an underlying cause or a deformity outside the normal range, which can be treated effectively – often with a minor guided-growth procedure – when needed.