Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Genu Varum (Bowed legs)

Basics
Description
  • The knee goes through normal phases of changing alignment in childhood: Genu varum (bowed legs) is physiologic in infants and young children up to 2 years of age, and its appearance is maximal at 12-18 months of age.
  • Bowing is most obvious when children start walking.
  • It may be combined with internal tibial torsion, which makes it appear more pronounced.
  • Bowing may seem greater with weightbearing.
  • This condition usually resolves by 2 years of age and changes to physiologic genu valgum (knock-knee).
  • Tibia vara (Blount disease) (see Blount Disease chapter), rickets, fibrocartilaginous dysplasia of the proximal tibia, and other genetic disorders can cause pathologic genu varum.
Epidemiology
  • Physiologic (normal) bowing is ~1,000 times more common than pathologic bowing (e.g., Blount disease).
  • It occurs equally in boys and girls.
Risk Factors
Family history
Genetics
  • Some causes of bowed legs are familial:
    • Blount disease
    • Renal rickets
    • Skeletal dysplasia
Etiology
  • Bowing is an imbalance between the load and growth plate development.
  • It may be caused by:
    • Overweight
    • Rickets
    • Skeletal dysplasia
  • Physiologic causes: Normal growth patterns of the femoral and tibial growth plates include a period of normal varus in early infancy.
  • Pathologic causes:
    • Tibia vara (Blount disease)
    • Rickets (nutritional or renal)
    • Achondroplasia
    • Epiphyseal and metaphyseal dysplasias
    • Focal fibrocartilaginous dysplasia
  • In most of these conditions, the varus results from inability of the growth plate to respond normally to load.
Associated Conditions
  • Early walker
  • Heavy weight
Diagnosis
Signs and Symptoms
  • Parental concern about the appearance of the legs is the most common reason for the presentation of children.
  • The patient should be pain free; if pain exists, another cause should be sought.
  • Genu varum may develop spontaneously in the overweight adolescent who previously had straight legs (adolescent Blount disease), and it usually requires treatment.
History
If a patient has physiologic bowing, the parents should start to notice improvement after the 2nd birthday.
 
Physical Exam
  • Obtain a medical, family, and developmental history.
  • Determine the patient’s height and weight percentiles.
  • Estimate the angulation of the knee.
  • Check the rotation of the tibia and femur.
  • To monitor the patient’s progress, document the distance between the medial surfaces of the knees (intercondylar distance).
Tests
Lab
  • In routine cases, tests are not indicated if varus appears mild and physiologic.
  • If metabolic causes are suspected, serum calcium, phosphate, alkaline phosphatase, 1,25-vitamin D, and creatinine levels may be measured.
Imaging
  • Radiographic evaluation of bowed legs in children <18 months old should be reserved for asymmetric bowing or for patients suspected of having a pathologic condition other than benign physiologic varus.
  • A single AP radiograph of the lower extremity from hip to ankle on a standing film is the most appropriate 1st imaging study; care should be taken that the knee is pointing straight ahead.
  • Widening of physis suggests rickets; delayed ossification of the distal femoral and proximal tibial epiphyses may be a result of excessive pressure on 1 side of the knee.
  • The femorotibial angle and the metaphyseal-diaphyseal angle of the tibia should be measured.
  • If the metaphyseal-diaphyseal angle is <11°, physiologic bowing is assured.
  • If the metaphyseal-diaphyseal angle is >16°, the child has Blount disease.
  • If the metaphyseal bowing in the femur is equal to or greater than that in the tibia, the bowing is more likely to be physiologic.
Differential Diagnosis
  • Achondroplasia
  • Rickets
  • Infantile or adolescent Blount disease
  • Metaphyseal or epiphyseal dysplasia
Treatment
General Measures
  • Physiologic conditions:
    • Physiologic bowing always resolves without treatment; bracing is not needed
    • At <18 months of age, follow-up examination and imaging are needed to differentiate physiologic bowing from tibia vara (may be difficult).
  • Pathologic conditions:
    • Rickets or other metabolic bone disease:
      • The underlying disease is treated, with osteotomy reserved for those patients with persisting varus after treatment.
    • Achondroplasia and epiphyseal or metaphyseal dysplasia:
      • The patient may need surgical treatment, depending on the degree of deformity.
    • Tibia vara (Blount disease):
      • Brace treatment is appropriate for children <3 years old; a knee-ankle-foot brace may be used for walking.
      • If the patient is >4 years of age, osteotomy is recommended.
Special Therapy
Physical Therapy
  • Not necessary for physiologic bowing
  • Not an effective treatment for pathologic varus
Surgery
  • Many different types of osteotomy are available for correcting varus deformity, including dome, oblique, closing wedge, or opening wedge osteotomy.
  • The tibia or the femur may require surgery, depending on the site of the deformity.
  • Physeal bar resection or hemiepiphysiodesis may be indicated for some cases.
Follow-up
Prognosis
  • Physiologic genu varum has an excellent prognosis for spontaneous improvement.
  • The prognosis of pathologic genu varum varies.
  • Knee pain and worsening of the bow are likely in adulthood if the deformity is >10-15°.
Complications
  • Untreated genu varum may cause pain on the medial part of the knee and eventual arthritis during adulthood.
  • Adolescent genu varum may be painful.
  • Complications occasionally seen from surgery may include:
    • Infection
    • Compartment syndrome
    • Recurrence of deformity
    • Growth disturbance
Patient Monitoring
  • The frequency of follow-up varies, depending on the individual surgeon or pediatrician.
  • Physiologic bowing does not need frequent follow-up unless the condition is not improving; resolution is a slow process and may take a year.
  • Pathologic bowing needs more prolonged follow-up.
Miscellaneous
Codes
ICD9-CM
736.42 Genu varum
 
Patient Teaching
  • Parents should be told that physiologic genu varum will resolve spontaneously and slowly; if it is not starting to improve at least by 2-3 years of age, additional evaluation is needed.
  • No restriction on activity is recommended.
  • Exercises do not help genu varum resolve.
FAQ
Q: Do infant jumper devices contribute to bowed legs?
A: No evidence suggests that they do. The children are supported in these devices, so the load on the legs is controlled.
 
Q: When should a child with bowing be referred to a specialist?
A: If the bowing gets worse after 18 months or persists after the 2nd birthday.

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