Blount’s Disease (BD)

Blount’s disease (BD) is an orthopedic childhood disorder characterized by outward bowing of the leg due to abnormal ossification of the medial aspect of the tibial epiphysis. Blount’s disease mostly affects children of African descent and tends to debut at approximately 1–3 years of age. Diagnosis is made by clinical findings and is confirmed by imaging. The goal of treatment is to correct the anatomy through bracing or surgical repair, according to the severity and age of the patient at diagnosis. The prognosis is excellent if treatment is promptly started.

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Definition and Epidemiology

Definition

Blount’s disease (BD) is the progressive bowing of the legs produced by abnormal ossification at the medial aspect of the tibial epiphysis.

Classification

  • Early or infantile: debuts at 1–3 years of age 
  • Late; subdivided into:
    • Juvenile form: presents at 4–10 years of age
    • Adolescent form: occurs in children older than 10 years of age

Epidemiology

  • Increased incidence in people of African descent
  • Early BD: 
    • Boys > girls 
    • Bilateral in 50% of cases 
  • Late BD:
    • Less common and less severe than the early form
    • More likely to be unilateral
  • Prevalent in areas with higher rates of obesity and vitamin D deficiency

Etiology and Pathophysiology

Etiology

The exact cause of BD is not known and is believed to be multifactorial or due to a combination of hereditary and developmental factors:

  • Genetic susceptibility 
  • Mechanical overload of the joint (associated with obesity)

Pathophysiology

  • Basis of the development of BD:
    • Excessive force
    • Altered endochondral ossification of the leg
  • Mechanical forces (obesity and early ambulation) on the medial physis of the tibia → growth retardation
  • Histological changes can be seen on the tibial growth plate:
    • Cellular hypertrophy and fibrocartilage islands
    • Signifies damaged cartilage
  • Damaged cartilage delays bone growth on the medial side → varus deformity
  • The procurvatum (backward bending of the tibia) is mainly due to the greatest inhibitory effect being on the posteromedial aspect of the tibial metaphysis.

Blount’s disease: varus deformity and backward bending of the leg

Image by Lecturio.

Clinical Presentation

  • Patients are usually overweight or obese.
  • 3-dimensional deformity:
    1. Varus (bowing)
    2. Procurvatum (backward bending of the tibia)
    3. Internal tibial rotation (resulting in in-toeing)
  • Length discrepancy in lower limbs
  • Non-tender bony protuberance at the medial aspect of the proximal tibia

Left leg with varus deformity

Image: “Blount’s disease” by Universidade de São Paulo, Faculdade de Medicina, Hospital das Clínicas, Instituto de Ortopedia e Traumatologia, São Paulo, SP, Brazil. License: CC BY 4.0, edited by Lecturio.
Table: Clinical features of early BD versus late BD
Early BDLate BD
No painPain in the tibial area
BilateralUnilateral
Significant deformityMild deformity
Associated with early ambulationAssociated with obesity

Diagnosis

The diagnosis of BD is achieved through medical history, physical examination, and confirmation via imaging studies.

Imaging

  • Long leg radiograph:
    • Varus angulation and sloping at the tibial epiphysis with asymmetrical bowing
    • Medial beaking: fragmentation of the medial epiphysis of the tibia
    • Irregular ossification and widening at the medial epiphysis
  • Magnetic resonance imaging (MRI): mostly used in cases of infantile Blount’s disease to assess extratibial tissues

Severity

Severity is based on the metaphyseal-diaphyseal angle (MDA):

  • Measures the angle formed by a line going through the metaphyseal beaks and a perpendicular line going through the longitudinal axis of the tibia. 
  • MDA > 16 degrees is diagnostic of BD.
  • MDA between 11 and 15 degrees is a probable diagnosis and warrants follow-up.

Knee X-ray shows depression of the medial tibial plateau with beaking of the posteromedial tibial physis (pink arrow).

Image: “X-ray” by US National Library of Medicine. License: CC BY 4.0

Management and Prognosis

Management

The age of the patient and the severity of the deformity determine the type of management.

  • Bracing:
    • Indicated if younger than 3 years of age
    • Only used in non-obese patients
    • Mainly worn at night
  • Surgical management:
    • Indicated in severe cases when the disease progresses despite bracing
    • Osteotomy is performed prior to the age of 4.
    • Hemiepiphysiodesis (gradual angular correction) is performed after the age of 4.
    • Fixation methods

Prognosis

  • Early infantile BD:
    • Must be treated in order to avoid permanent deformity
    • With timely treatment → excellent prognosis with rare recurrences
    • Mild form may regress spontaneously.
  • Late adolescent BD:
    • Good prognosis with treatment 
    • Less likely to have severe deformity

Differential Diagnosis

  • Physiological genu varum: Children under the age of 2 have physiological, symmetrical, painless bowing with in-toeing that spontaneously regresses with natural growth. Follow-up is usually performed to ensure that the condition does not progress further or has an underlying pathology.
  • Rickets: distortion and softening of bones due to vitamin D deficiency or resistance. Patients usually present with bowing of the legs. Can be distinguished from BD via blood work and a lack of beaking on X-ray.

References

  1. Canale, S. T. (2017). Osteochondrosis or epiphysitis and other miscellaneous affections. In F. M. Azar MD, J. H. Beaty MD & S. T. Canale MD (Eds.), Campbell’s operative orthopaedics (pp. 1175-1248.e11). https://www.clinicalkey.es/#!/content/3-s2.0-B978032337462000032X
  2. Deeney, V. F., & Arnold, J. (2018). Orthopedics. In B. J. Zitelli MD, S. C. McIntire MD & Nowalk, Andrew J., MD, Ph.D. (Eds.), Zitelli and Davis’ atlas of pediatric physical diagnosis (pp. 759-844). https://www.clinicalkey.es/#!/content/3-s2.0-B9780323393034000220
  3. Janoyer, M. (2019). Blount disease. Orthopaedics & Traumatology: Surgery & Research, 105(1), S111-S121. doi:http://dx.doi.org/10.1016/j.otsr.2018.01.009
  4. Montgomery CO, Young KL, Austen M, Jo CH, Blasier RD, Ilyas M. Increased risk of Blount disease in obese children and adolescents with vitamin D deficiency. J Pediatr Orthop. 2010;30(8):879–882. DOI:10.1097/BPO.0b013e3181f5a0b3
  5. S DMTS, De Leucio A.(2020) Blount Disease.Treasure Island (FL): StatPearls Publishing; https://www.ncbi.nlm.nih.gov/books/NBK560923/
  6. Lauren LaMont, (2019).Blount Disease (Tibia vara). Medscape. Retrieved nov 24, 2020, from https://emedicine.medscape.com/article/1250420-overview#a1

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