Dr. Kevin Yip

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

Featured on Channel NewsAsia

Blount Disease

Basics
Description
  • Bowing of the legs can be a normal stage of growth for infants and toddlers.
    • This phase is called physiologic bowing and resolves spontaneously by approximately 2 years of age.
    • The vast majority of children presenting with bowed legs have this benign physiologic state.
  • More rarely, bowed legs may be pathologic.
    • The most common cause of this condition is Blount disease.
    • It is an abnormality of the proximal tibial growth plate secondary to overload.
    • It causes progressive varus alignment of the knees (bowed legs) in children or adolescents.
  • Classification:
    • Infantile form: Presents in children 0-4 years old
    • Juvenile form: Presents at >4-9 years of age in obese children
    • Adolescent form: Presents in children >10 years old; has excellent prognosis with surgery
  • Synonyms: Infantile tibia vara (0-4 years); Juvenile tibia vara (>4-9 years); Adolescent tibia vara (10-16 years); Pathologic bowlegs
General Prevention
  • Weight control
  • Extremely early standing or walking should not be encouraged.
  • Early bracing sometimes is effective.
Epidemiology
Incidence
  • Infantile tibia vara is the most common cause of pathologic bowing in young children and accounts for <1% of all bowed legs.
  • The juvenile form is much less common: Only 60 reports in the literature in the United States.
  • The adolescent form is becoming more commonly recognized.
Prevalence
  • The infantile form is more common in girls.
  • The juvenile or adolescent form is more common in boys.
  • The disorder is more common in African American children than those of other races.
Risk Factors
  • African American ethnicity
  • Obesity
  • Early age of walking
  • Varus greater on the tibial than the femoral side is a risk factor for infantile and juvenile Blount disease.
Genetics
  • No genetic pattern has been proved.
  • More likely, patients inherit a body habitus that predisposes them to the disorder.
Pathophysiology
  • The growth plate shows islands of densely packed cartilage cells with more hypertrophy than normal, islands of almost acellular fibrous cartilage, and abnormal groups of capillaries.
  • Biopsy is not indicated.
Etiology
Decreased growth of the proximal medial tibial growth plate (physis) causes varus angulation (bowing) and internal rotation of the proximal tibia secondary to weight-related overload of this portion of the growth plate.
 
Associated Conditions
Obesity
 
Diagnosis
Signs and Symptoms
  • Patients with infantile tibia vara usually present between 14 and 40 months of age with increasingly bowed legs (usually bilateral involvement).
  • Adolescent presentation also involves progressive varus deformity (bowing), but many of these patients also have medial knee pain and often only 1 leg is affected.
  • If untreated, the infantile form may progress to become severe.
  • The juvenile and adolescent forms rarely become as severe.
  • Some internal tibial torsion usually is present along with the bowing.
Physical Exam
  • Record the patient’s height, weight, and percentiles.
  • The finding of short stature suggests rickets or a skeletal dysplasia.
  • Note the location of any pain.
  • Record the gap between the medial sides of the knees and check knee ROM and ligamentous laxity.
  • Assess tibial torsion by the thighfoot angle.
  • Perform a routine knee examination, observe gait, and measure the foot progression angle (angle of the feet with the direction of walking).
Tests
Lab
  • Testing is indicated if rickets is suspected.
  • In Blount disease, calcium, phosphorus, alkaline phosphatase, and renal function tests are all normal.
Imaging
  • Radiography:
    • Appropriate radiographs: A long leg AP view of the tibia and femur to evaluate the tibiofemoral angle and mechanical axis.
    • The radiograph should show the whole limb from the hip to the ankle, and it should be a true AP view of the knee.
    • The metaphyseal-diaphyseal angle differentiates Blount disease and physiologic varus:
      • <11° is physiologic varus.
      • >16° indicates Blount disease.
      • Values between 11° and 16° signify a risk of potential Blount disease.
    • Reveals a medial physeal bar (disappearance of the growth plate with metaphysisepiphysis fusion) in more advanced disease
  • CT or MRI:
    • Can be useful in delineating the physeal damage that later may form a bar.
    • Patients with adolescent Blount disorder show less deformation of the epiphysis and rarely form a bar, but they usually have some deformity on the femoral as well as on the tibial side
Differential Diagnosis
  • Physiologic bowed legs
  • Hypophosphatemic rickets
  • Trauma to metaphysis or growth plate
  • Osteochondroma
  • Metaphyseal chondrodysplasia
  • Focal fibrocartilaginous dysplasia
Treatment
General Measures
  • Children <3 years old who present with Blount disease may be braced, preferably with a long brace from the hip to the ankle that is locked at the knee.
  • Full-time bracing (22 hours a day) puts a corrective valgus stress on the knee (more knock-kneed) and decreases the stress on the medial physis.
    • If bracing is begun when the deformity is mild, this treatment allows the growth plate to catch up the growth medially.
  • If the patient is being braced, full weightbearing is encouraged.
  • If bracing fails to correct the deformity, or if a patient >3 years old presents with moderate to severe deformity, an osteotomy is needed.
  • If osteotomy is performed, the patient is kept nonweightbearing until healing (8-12 weeks) of the osteotomy; then full weightbearing can be resumed.
  • Hemiepiphysiodesis is also an alternative in juveniles if the deformity is moderate.
Activity
  • No activity restriction on unbraced patients
  • Bracing restricts participation in sports.
Special Therapy
Physical Therapy
  • Does not help improve knee varus
  • Crutch training after osteotomy
  • Regaining knee ROM after osteotomy
Surgery
  • Osteotomy (cutting and realigning the proximal tibia) will decrease the stress on the medial physis and can allow healing.
  • If a physeal bar has formed:
    • An osteotomy often is combined with completion of the closure of the proximal tibial physis.
    • The whole growth plate should be fused to prevent the lateral portion of the growth plate from causing recurrent varus; patients with advanced cases may have a secondary deformity of the distal femur and/or the distal tibia.
  • If substantial leg-length inequality develops, it may be treated by lengthening the short limb or by growth plate closure of the longer limb.
  • Adolescent Blount disease may be treated with tethering (stapling) of the lateral sides of the growth plate to allow the bone to correct itself.
  • In more advanced cases, osteotomy of the tibia and/or the femur is needed.
Follow-up
Prognosis
  • Because the recurrence rate is higher in patients treated after 4 years of age (70-75%) than in patients treated before age 4 (20-30%), early osteotomy (before age 4) should be performed if bracing is not successful.
  • Patients with late treatment or incomplete treatment have an increased risk of arthritis of the knee.
Complications
  • Recurrence of deformity leads to abnormal limb alignment and degenerative arthritis.
  • Limb-length inequality may result.
  • Postosteotomy complications include neurovascular complications and compartment syndrome.
Patient Monitoring
  • Patients should be followed until skeletal maturity.
  • The interval between visits is determined by the severity of the disease.
 
Miscellaneous
Codes
ICD9-CM
732.4 Blount’s disease
Patient Teaching
  • The patient’s family must understand the benefit of regular monitoring and weight reduction.
  • If they elect to use bracing in patients with infantile Blount disease, the braces must be worn 22 hours a day to exert their corrective effect on growth.
FAQ
Q: How can Blount disease be distinguished from physiologic bowing of the tibia?
A: They can be distinguished by the metaphyseal-diaphyseal angle in young children (<3 years old) being >11° and by the shape of the tibial deformation in older children.
 
Q: What is the cause of Blount disease?
A: The cause is overload of the medial growth plate of the upper tibia.
 
Q: Is surgery always necessary?
A: Surgery is recommended for all patients who are symptomatic or who have varus of >10°.
 
Q: Does adolescent Blount disease develop from infantile Blount disease?
A: No, adolescent Blount disease develops spontaneously in older-aged children than does infantile Blount disease.

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