Blount's Disease

DefinitionBlounts

 

Progressive varus deformity of knees

- secondary to abnormality of medial upper tibial physis

- localised varus & internal rotation deformity

 

Infantile form 

- onset 1-3 years / bilateral

 

Adolescent form 

- onset > 6 years / unilateral

- 5 times less common

- M:F

- presents 8 - 14 years

 

Epidemiology

 

Africans / African Americans / West Indians

 

Associations

 

Female

Obesity

FHx

Early walking

 

Aetiology

 

Unknown / Multifactorial

 

Familial

- no consistent inheritance pattern

-  ? related to tendency to obesity 

 

Mechanical

- most likely due to abnormal compression on medial side of proximal tibial physis

- causes retardation of growth

-  ? traumatic role

 

Pathology

 

Posteromedial disordered endochondral ossification 

- dense islands of hypertrophied chondrocytes

- acellular areas of dense fibrocartilage in resting zone

- abnormal groups of capillaries

 

Fragmented physis

 

Clinical

 

Infantile presents at 12-36/12 

 

Bilateral & symmetrical

- bowing noted when commence walking

- associated internal tibial torsion due to fibular tethering normal ER of tibia with growth

- continuum between physiological vara & Blount's (infantile may be severe physiological vara) 

- varus should resolve by the age of 2

 

Examination

 

Milestones / height & weight percentiles

 

Knee ROM 

 

Measure of Genu Varum & Tibial torsion

 

Ligamentous Laxity

 

X-ray

 

Indications

- severe genu varum

- rapidly worsening

- height < 25th percentile

- marked asymmetry

- FHx

 

Findings

- localised deformity at proximal tibia

 

Metaphyseal - Diaphyseal Angle

 

Blounts Metaphyseal Diaphyseal Angle

 

Technique

- line drawn perpendicular to axis of tibia 

- line drawn through medial & lateral beaks of metaphysis

- Blount's > 11°

- physiologic bow legs < 11°

 

Measurements

- 11° is arbitrary cut off where Blount's is more likely

- 16o definite

 

Medial Physeal Slope

 

Blounts Medial Physeal Angle

 

Technique

- line through medial physis & line through lateral physis

 

Measurements

- significant if > 60°

- prognostic of progression

 

CT

 

Used to identify presense of physeal bar

 

Langenskiold Classification

 

Stage I: Beak 2-3 years

- irregular metaphyseal ossification

- medial metaphyseal beaking

 

Stage II: Saucer 2-4 years

- saucer shaped defect in medial metaphyseal beak

- medial epiphyseal wedging

 

Stage III:  Step 4-6 years

- saucer deepens into step 

- medial epiphysis irregular

 

Stage IV: Bent plate 5-10 years

- growth plate inclined distally at medial side

- i.e. epiphysis extends down over meta beak

 

Stage V: Double epiphysis 9-11 years

- Xray appearance of severe posteromedial depression

 

Stage VI: Medial physis ossified 10-13 year

- medial physeal closure

 

Blounts Langenskiold Type VI

 

DDx

 

Physiological varus

Metaphyseal dysplasia / achondroplasia

Ricket's

Trauma / Tumour / Infection

OI

JRA

 

Physiological Varus

- symmetrical involvement

- normal growth plate

- medial bowing of proximal tibia & distal femur

- metaphyseal-diaphyseal angle < 11°

 

Rickets

- short stature, osteopaenic

- widened physes / cupped metaphyses 

- distal Femur Flared too

- may have coxa vara

- hypophosphataemic most common

 

Renal Osteodystrophy

 

Metaphyseal Chondrodysplasia

- widened metaphysis, cupped physis

- similar to rickets

- mild short stature

- may have coxa vara as well

 

Focal fibrocartilagenous dysplasia 

- generalised abnormality or focal deformity in tibia

 

OI

 

Trauma

Infection

Tumor

 

NHx

 

Progresses to severe OA by early adulthood

- metaphyseal-diaphyseal angle >11° --> likely to progress

- medial-physeal slope >60° likely to progress

- Philadelphia sign: lateral subluxation of tibial epiphysis 

- if restore normal valgus should have good outcome

 

Need to manage child before they develop a bar (i.e. end stage of growth plate injury)

 

Management Infantile Type

 

Algorithm

 

Depends on

- age of child

- stage of disease

 

1.  <2 years 

 

Observe

 

2.  2 - 3 years & Medial Physeal Angle < 60°

 

KAFO Single Medial upright 

- free ankle with no knee hinge

- flexion limited

- knee cuff pulls it into valgus

 

Full-time bracing successful > 50%

 

3. Age > 3 years / Progression in Brace / Medial Physeal Angle > 60° 

 

Aim

- correct varus and internal rotation deformity

 

Options

 

A.  Lagenskiold I - IV

- osteotomy

- guide growith

 

B.  Lagneskiold V / VI

- take down bar and osteotomy or

- epiphysiolysis + medial metaphseal osteotomy

 

Langenskiold Stages I-IV Surgical Management

 

1.  Osteotomy

 

Aim

- restore alignment

- deformity reversible

- if restore physiological valgus (7o) then resolution is usual for I & II / possible for III & IV 

 

Type of osteotomy

 

A.  Opening / closing wedge

B.  "Smiley" upside down dome

C.  Oblique osteotomy

- Rab biplanar oblique osteotomy

- fix with single screw

 

Osteotomy Technique

 

Performed distal to TT

- closing wedge simplest but upside down dome has least shortening

- must osteotomise fibula

- usually want to correct IR deformity at same time

- must release anterior compartment to prevent compartment syndrome

- desired valgus & ER achieved

- fixation with K wires or screw

- POP post operatively

 

Recurrence after osteotomy

 

1. Obese

2. > Stage III

3. Medial physeal slope > 60°

4. Age

- > 5 y = 76%  

- < 5 y = 31%

 

2.  Guided growth / 8 plate

 

Now common mechanism of treating condition

 

3.  Osteotomy and external fixation

 

Langenskiold Stages V & VI 

 

Issue

 

Irreversible

- need to address physis as well as osteotomy

- usually total physiodesis

- overcorrection 10°

 

Surgery 

- must do fibula osteotomy as well

- usually perform total physeodesis of ipsilateral side

- always perform fasciotomy

- may need to realign epiphysis in severe forms with large medial-physeal slope

- consider epiphysiodesis of other side to address LLD

 

Options

 

1.  Medial Metaphyseal Elevation Osteotomy

 

Indications

- Grade V

 

Blounts Elevation

 

2.  Physeal Bridge Resection (physeolysis) + Osteotomy

 

Indications

- Grade VI

- bridge < 30% of physis

 

Technique

- excise bar where CT shows a bridge

- Insert fat into defect

 

3.  Lateral Hemi-epiphysiodesis + osteotomy

 

Indications

- grade VI

- bridge > 30%

 

Technique

 

All need fibula osteotomy

All need prophylactic compartment release

 

Complications

 

Compartment syndrome - must prophylactic release

Recurrence of varus - usually secondary to physeal bar

LLD

OA

 

Adolescent Type

 

Management

 

Wait till skeletal maturity, then HTO