Dr. Kevin Yip

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

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Posteromedial Bow of the Tibia

Basics
Description
  • Posteromedial bowing of the tibia is an angulation of the lower leg noticed at birth.
  • The foot typically is in a calcaneovalgus position.
  • The angulation of leg is secondary to a deformity in the tibia.
  • In most children, the angle gradually corrects itself during growth.
  • The limb-length discrepancy persists and increases proportionately during growth.
Epidemiology
  • This condition is rare.
  • Noticed at birth
  • Occurs equally in males and females
Risk Factors
No risk factors are known.
 
Genetics
No Mendelian pattern is known.
 
Etiology
  • Unknown, but thought to be secondary to intrauterine positioning
  • May also represent an inborn error in physeal growth
  • Unlikely to be the result of fracture because of the proportionate shortening that follows
Associated Conditions
No known associated conditions
 
Diagnosis
Signs and Symptoms
  • At birth, the ankle is dorsiflexed, and the foot is in the calcaneovalgus position.
    • An obvious bow is present in the distal part of the tibia posteromedially.
  • The condition is painless.
  • The condition is almost always unilateral.
History
No history of gestational abnormality or birth trauma
 
Physical Exam
  • Perform a complete examination of the lower extremity.
    • The leg appears shortened below the knee.
  • Measure the leg length bilaterally.
  • Measure the range of foot dorsiflexion, plantarflexion, inversion, and eversion.
  • The foot is calcaneovalgus.
  • Check for active function of all ankle muscles.
Tests
Lab
None is needed.
 
Imaging
  • Plain radiographs reveal the deformity.
  • Angulation of the tibia may be up to 60°.
  • Tibial bone may be normal or thickened.
  • No internal cystic change is seen.
Pathological Findings
  • All muscles, tendons, and tissues are within normal limits, although the anterolateral muscles are underdeveloped.
  • Only the bone is abnormal, with thickening and bowing.
Differential Diagnosis
  • Tibial fracture
  • Fibular hemimelia
  • Calcaneovalgus foot (similar foot position)
  • Congenital pseudarthrosis and NF, which are associated with anterolateral bow
Treatment
General Measures
  • This condition often resolves spontaneously with growth, so initial treatment is watchful waiting.
  • Residual deformity may be up to 6-8° of angulation and limb length inequality of up to 5 cm at maturity.
    • Usually, it is much less.
  • Patients with a projected limb-length inequality of >2 cm at skeletal maturity should be candidates for epiphysiodesis or limb lengthening, depending on the degree of discrepancy and their preference for a major versus minor procedure.
  • Casting, bracing, and stretching provide no benefit in most cases.
  • In some extreme cases, a splint may be helpful in placing the foot flat to allow walking.
  • No activity restrictions are necessary.
  • A heel lift may benefit some patients with large limb-length inequalities.
Special Therapy
Physical Therapy
Physical therapy is not indicated.
 
Surgery
  • Epiphysiodesis of the contralateral tibial epiphysis is the most common procedure.
    • Performed near adolescence, long after the bow has straightened
  • Residual angulation of the tibia is sometimes problematic (5-10% of patients).
  • Osteotomy of the tibia is used to correct the angulation.
  • Tibial lengthening procedures are used rarely.
Follow-up
Prognosis
  • Prognosis is generally good.
  • No long-term sequelae occur as long as lengths are corrected.
Complications
  • Limb-length inequality:
    • The main complication
    • Thought to be secondary to damage to physis by asymmetric forces as a result of bowing
    • Is correctable by surgery
Patient Monitoring
  • Obtain radiographic measurements of limb lengths (scanogram) by age 5 years, so they can be plotted onto a growth curve.
  • Usually, growth inhibition remains proportionate.
  • Radiographic measurement allows for prediction of final discrepancy and determination of the need for future surgery.
Miscellaneous
Codes
ICD9-CM
736.89 Posteromedial bowing of the tibia
 
Patient Teaching
  • Educate the family about the benign course of the disease.
  • Bowing should correct itself over the 1st few years.
  • Impress on the family that the patient must be followed throughout growth to assess limb lengths, angulation, and the need for surgery.
FAQ
Q: Could posteromedial bow be the result of a fracture in utero?
A: No, because the discrepancy in length increases proportionately in patients with posteromedial bow, whereas in patients with fracture, the discrepancy decreases slightly because of the overgrowth phenomenon.
 
Q: Is casting or bracing helpful in speeding resolution?
A: No evidence suggests that it does. The only role for bracing is in children who have such malposition of the foot that a brace improves function.
 
Q: What percentage of children with posteromedial bow require surgery?
A: More than 1/2 of children require epiphysiodesis near maturity for leg-length equalization. Fewer than 1/4 require treatment of the angulation.

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