High Yield Topics

Blount Disease

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Ovid: 5-Minute Orthopaedic Consult

Editors: Frassica, Frank J.; Sponseller, Paul D.; Wilckens, John H.
Title: 5-Minute Orthopaedic Consult, 2nd Edition
> Table of Contents > Blount Disease

Blount Disease
Paul D. Sponseller MD
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 (1,2) (Fig. 1).
  • 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 (2).
  • The juvenile form is much less common: Only 60 reports in the literature in the United States.
    Fig. 1. In Blount disease, the varus is focal at the upper tibia.
  • The adolescent form is becoming more commonly recognized.
Prevalence (1,2)
  • 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 (1).
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 (2).
  • 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 thigh–foot 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 (2).
Imaging
  • Radiography:
    • Appropriate radiographs: A long leg AP view of the tibia and femur to evaluate the tibiofemoral angle and mechanical axis (1–5).
    • The radiograph should show the whole limb from the hip to the ankle, and it should be a true AP view of the knee (4).
    • 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 metaphysis–epiphysis 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 (Fig. 2)
      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
    Fig. 2. Adolescent Blount disease. Note the physeal widening and relative preservation of the epiphysis of the tibia.

P.41


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 (2).
  • 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 (6,7).
  • 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 (6).
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 (5); 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%) (2), 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.
References
1. Bowen
RE, Dorey FJ, Moseley CF. Relative tibial and femoral varus AS a
predictor of progression of varus deformities of the lower limbs in
young children. J Pediatr Orthop 2002;22:105–111.
2. Schoenecker PL, Rich MM. The lower extremity. In: Morrissy RT, Weinstein SL, eds. Lovell and Winter’s Pediatric Orthopaedics, 6th ed. Philadelphia: Lippincott Williams & Wilkins, 2006:1157–1211.
3. Doyle BS, Volk AG, Smith CF. Infantile Blount disease: long-term follow-up of surgically treated patients at skeletal maturity. J Pediatr Orthop 1996;16:469–476.
4. Gordon JE, Heidenreich FP, Carpenter CJ, et al. Comprehensive treatment of late-onset tibia vara. J Bone Joint Surg 2005;87A:1561–1570.
5. Stanitski DF, Stanitski CL, Trumble S. Depression of the medial tibial plateau in early-onset Blount disease: myth or reality? J Pediatr Orthop 1999;19:265–269.
6. Gordon JE, King DJ, Luhmann SJ, et al. Femoral deformity in tibia vara. J Bone Joint Surg 2006;88A:380–386.
7. Henderson RC, Kemp GJ, Jr, Greene WB. Adolescent tibia vara: alternatives for operative treatment. J Bone Joint Surg 1992;74A:342–350.
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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