Bow-legs (genu varum) is an angular deformity at the knee where the apex of the deformity points away from the midline. Knock-knees (genu valgum) are an angular deformity at the knee where the apex of the deformity points toward the midline.

Bow-legs and knock-knees are among the most common musculoskeletal anatomic variations encountered by pediatric primary care providers and a common reason for referral to a orthopedic surgeon.

An understanding of normal physiologic development of the lower extremity is essential to the differentiation of physiologic from pathologic deformities.

• At birth, normal alignment is varus.
• As the child begins to stand and walk, the amount of varus often increases.
• Children who walk at an early age may have greater varus alignment.
• Around 18 to 24 months of age, alignment should be neutral.
• After 24 months, alignment should progress to valgus until it reaches a maximum at four years.
• After age four years, valgus alignment should decrease toward physiologic adult alignment of slight valgus to neutral.
• By age seven, a child usually has reached their adult lower-extremity alignment of slight valgus.

Causes of Bow Legs

• Physiologic bowing
• Blount disease
• Nutritional rickets and other metabolic bone diseases
• Skeletal dysplasia
• Trauma, Infection and neoplasia causing asymmetry of growth

Characteristic features of physiologic bowing

• Age between birth and two years
• Bilateral and relatively symmetric deformities
• Bowing of both femurs and tibias
• Normal stature (within two standard deviations of the mean for age and sex)
• No lateral thrust with ambulation; a lateral thrust is a brief lateral knee-joint protrusion during the stance phase of gait that suggests incompetence of the knee ligaments with increased risk of progression 
• Normal biochemistry is seen in the Bone profile

Pathologic varus 

Clinical and radiographic features distinguish physiologic from pathologic varus. Clues to pathologic varus include 

• short stature
• lateral thrust 
• asymmetry
• progression rather than improvement between birth and two years 

Presentation

• concerns about the appearance of the child’s legs
• excessive falling
• in-toeing 

History 

• Growth and development (normal in physiologic bowing)
• Onset (before or after birth? Before or after walking)
• Progression (physiologic varus improves with growth; pathologic varus worsens with growth)
• Associated complaints (pain, limp, tripping, falling, in-toeing)
• Family history (parents or siblings with similar appearance, short stature, rickets, skeletal dysplasia)
• Previous treatment (if any) and treatment response
• Risk factors for rickets (eg, calcium and vitamin D intake, sunlight exposure) 
• History of infection, trauma, or fracture (that may have caused asymmetric growth retardation or stimulation)
• caregivers’ perceptions of the deformity and concerns regarding gait, appearance, and function

Physical examination 

• Length/height – Lower-extremity malalignment and length/height less than the 3rd percentile are potential clues to a pathologic condition (eg, rickets, skeletal dysplasia)
• Weight 
• Focused examination of the lower extremities
  • Assessment of symmetry 
  • Assessment of leg length (shortening of the legs may suggest skeletal dysplasia) 
  • Determination of the site of angulation: 
  • Palpation of the epiphyses of the long bones
• Gait
• Other supportive features of Rickets

Investigations

• Radiographs- needed if Pathological varus is suspected- Better to be decided by the Orthopaedic surgeon or Paediatric endocrinologists, so the views can be decided
• Bone Profile- If suspecting Rickets, Serum Corrected Calcium levels, Phosphate levels and Alkaline Phosphatase levels are indicated
• Vitamin D levels and PTH levels- To be decided by Paediatric Endocrinologist

Indications for referral

We suggest that children with clinical features suggestive of pathologic varus be referred to a Paediatric Endocrinologist first, as Nutritional Rickets is highly prevalent in our country. 

References

1. Jamie Ferguson, Andrew Wainwright, Tibial bowing in children, Orthopaedics and Trauma, Volume 27, Issue 1,2013, Pages 30-41, ISSN 1877-1327,https://doi.org/10.1016/j.mporth.2012.11.001.,(https://www.sciencedirect.com/science/article/pii/S1877132712001789)
2. Maire-Clare Killen, Gavin DeKiewiet, Genu varum in children, Orthopaedics and Trauma, Volume 34, Issue 6,2020, Pages 369-378, ISSN 1877-1327,https://doi.org/10.1016/j.mporth.2020.09.007.(https://www.sciencedirect.com/science/article/pii/S1877132720301135)

Written By Dr. Chamidri Naotunna
Reviewed by DR. Navoda Atapattu