Bow Legs and Knock Knees

Bow legs will naturally straighten as the child grows. If bowing continues to persist, further diagnosis may be needed to find out the causes.

Abnormal alignment of the lower limbs can be very worrying for parents and is indeed a common question posed. It is largely physiological and resolves spontaneously as the child grows.

Physiological bow legs (Varus) are very common in the child younger than 2 years of age. The Salenius Curve describes the natural history of how varus/ bow legs are present at birth and proceed to a neutral alignment at 24 months, before becoming in valgus(knock knees) at the age of 3, and then moving to the adult mild valgus(normal) alignment by the age of 6-7.

bow legs
Figure 1. Salenius Curve

While bow legs are mostly physiological, there are conditions in which it may not be normal. This is important as the treatment and prognosis are different.

Most newborns are bowed with 10-15 degrees angulation and as they begin to stand and walk it appears more prominent. Presentation is typically after standing at 12 months to 24 months. There are no other significant findings.

Although there is an expected pattern of change as described above, variations of the norm may occur. However it is prudent to give Bowing after 2 years of age, a second look to exclude other causes.

Persistent, asymmetrical bowing would warrant radiological investigation.

Other causes of Bowing:

1) Blount’s disease (Tibia Vara)

This occurs when there’s growth delay at the inner aspect of the tibial growth plate. It is dichotomised into infantile (2 to 5 years) and adolescent (more than 10 years).

Infantile Blount’s cause is undetermined but could be due to overloading in the child with a genetic predisposition. It is seen in overweight children and early walkers.

X-rays complement physical examination and help in making the diagnosis. Early diagnosis allows for best outcome and treatment may entail off-loading as well as bracing.

Surgery is indicated only after failure of conservative management after the child’s 4th birthday.

Adolescent Blount’s may also be due to excessive loads on a predisposed patient, but the disease behaves differently. It is less common and affects the femur (thigh bone) as well as the leg bone (tibia). It tends to occur on one side, and conservative management usually fails.

Surgical management involves fusing of the outer aspect of the growth plates or making bone cuts (osteotomy) to realign the bones

2) Trauma

Trauma can cause angulation, growth plate damage, leading to deformities. This is especially the case in the thigh bone (femur).

Deformities causing or predicted to cause deformities are treated surgically. Bars may form in the growth plate, necessitating excision in order for normal growth to occur (especially when there are at least 2 years of growth remaining ). Bone cuts are often done in tandem for realignment.

In cases where the growth arrest is sufficiently large, with less than 2 years left of growth, early closing of the growth plate is an option.

3) Skeletal Dysplasias (eg achondroplasia)

The child has bowlegs associated with a short stature at less than 5th Percentile. There are associated characteristic facial appearances and body habitus.

Indication for surgical intervention depends on the form and function and symptoms.

4) Metabolic diseases

An example of these is Rickets, and it is associated with short stature with limb deformities occurring on multiple planes. The growth plate is abnormal and widened.

Medical management is the first line and may resolve the issue if instituted early enough. Surgery is only indicated once there has been a plateau in limb correction after medical stabilisation of the disease.

Knock Knees (Genu Valgum)

Physiologic knock knees are usually apparent after the age of 2 as seen in the Salenius curve.

The maximum “deformity” is seen at 3-4 years of age before it settles into the more adult alignment. Bracing is not required and indeed is poorly tolerated by children of this age.

Metabolic disease such as renal rickets (osteodystrophy) and skeletal dysplasia can also cause knock knees which are bilateral.

The unilateral knock knee may occur due to damage to the growth plate from trauma or infection.

Valgus of the knee that keeps increasing beyond the age of 7 is not physiologic and needs to be investigated. It may require surgical management if deformity keeps increasing and is associated with pain.

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