TIBIA VARA (BLOUNT DISEASE)

TIBIA VARA (BLOUNT DISEASE)

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

Aetiology:
• Abnormal compression on the posteromedial aspect of the proximal tibial physis, causing retardation of growth from that area
• Or increased growth from the proximal aspect of the fibula and the lateral aspect of the proximal part of the tibia, or both.
• This multiplanar deformity consists of varus, procurvatum and internal tibial torsion.
• Additionally, distal femoral varus is commonly noted in the late-onset form.
• Blount’s disease is the most common cause of pathologic genu varum
• The Hueter Volkmann law probably explains the aetiology: Compressive forces inhibit bone growth and tensile forces stimulate bone growth at physis.

NB: Normal knee alignment progresses from 10 to 15 degrees of varus at birth to a maximum or peak valgus angulation of 10 to 15 degrees at the age of three to three and half years. Neutral femorotibial alignment is achieved when child is 14 months to 20 months old

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

Clinical features:• Generally present at fourteen to thirty-six months old for evaluation of bowlegs.
• Infantile tibia vara is found more frequently in children who are black, female, and obese and who started walking at an early age
• The infantile form is more common in girls.
• The juvenile or adolescent form is more common in boys.
• Progression to severe form is more common in infantile variety compared to juvenile and adolescent forms
• The finding of short stature suggests rickets or a skeletal dysplasia

Differential diagnosis:
• Physiological bowlegs
1. The most common cause of genu varum in this age group.
2. Their bowlegs will spontaneously resolve before the age of three.

• Hypophosphatemic rickets:
1. Short stature and genu varum are features.
2. X-rays show widening or rachitic-like changes at the physis.
3. Serum Phosphorus is low
• Metaphyseal chondrodysplasia,
• Focal fibrocartilaginous dysplasia.



Langenskold Classification
• Stage I: Irregularity of medial proximal tibial physis with varus deformity.
• Stage II: Medial tapering of epiphysis, metaphysis and slight step in the physis.
• Stage III: Sharp angular step in the medial proximal tibial metaphysis.
• Stage IV: Ossification of epiphysis into the metaphyseal step.
• Stage V: Appearance of separate medial fragment.
• Stage VI: Bony bridge formation.




This is still the most commonly employed classification system though significant interoberver variability is seen in the intermediate stages.

X-ray
• A standing full-length anteroposterior radiograph (teleoroentgenogram) of the entire length of both lower extremities with the patellae forward is crucial for a detailed analysis of frontal plane alignment
• To obtain a true AP view: no more than 60% of the proximal part of the fibula should be seen to overlap the adjacent tibia on a true anteroposterior radiograph centered at the knee, irrespective of the patient’s age


• Drennan’s metaphyseal-diaphyseal angle of more than 11 degrees warrants close observation
>16 degree: Diagnostic
• The medial physeal slope: an angle formed by the intersection of a line through the lateral aspect of the tibial physis and a line through the medial aspect of the physis
.
• The medial physeal slope is a better radiographic predictor of recurrent varus deformity following osteotomy.
• A medial physeal slope greater than 60 degrees is always associated with recurrent varus deformity after tibial osteotomy

CT scan:
 Can be useful in delineating the physeal damage that later may form a bar
 A physeal bar is not common in adolescent variety, but the deformity maybe present in both the femur and tibia

3-D CT scan: helpful for preoperative planning in children with early-onset Blount disease who present with recurrent deformities

An intraoperative arthrogram is helpful for delineating the articular surface and for evaluating dynamic instability of the knee

MRI to define intra-articular changes such as posteromedial depression of the tibial plateau and hypertrophy of the medial meniscus in children with early-onset disease
• detecting growth plate irregularities and early physeal bar formation

Treatment• Lower stages:
 Brace (KAFO) with a medial upright and droplock hinges to unload the medial compartment of the knee for children younger than thirty-six months of age with early-stage(Langenski¨old stage-I or II) Blount disease
 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
 Risk factors for failure of brace treatment include: a weight greater than the 90th percentile, varus thrust and bilateral disease
• Proximal tibial valgus osteotomy may be done if patient presents between 3 and 4 years of age and stage III or IV:
 10 degree overcorrection is recommended.
 Elevation of depressed tibial plateau must be done.
 Chemoprophylaxis with LMW Heparin maybe given if children are obese
• Stage V, VI: Excision of bar and insertion of free fat graft. An osteotomy often is combined with completion of the closure of the proximal tibial physis. Lengthening maybe performed later.
• Adolescent form: Osteotomy may be combined with hemiepiphysiodesis on the lateral side, and later lengthening of necessary