Posteromedial Bow of Tibia

Posteromedial bow of the tibia is a benign congenital deformity characterized by posterior and medial bowing of the tibia. It is a positional deformity that typically resolves spontaneously with growth and is distinct from the pathological anterior bowing seen in congenital pseudarthrosis of the tibia (CPT).

Epidemiology:

• Incidence: Relatively common (exact incidence not well documented)
• Male to female ratio: 1:1
• Bilateral involvement: Common (50-60% of cases)
• Left and right sides: Equal distribution
• No clear genetic inheritance pattern

Pathophysiology: Posteromedial bow results from in utero positioning, causing the tibia to develop with a posterior and medial curve. The deformity is:

• Positional (not structural)
• Benign (no risk of fracture or pseudarthrosis)
• Self-correcting with growth
• Associated with calcaneovalgus foot deformity

The condition represents a spectrum from mild (barely noticeable) to severe (more pronounced), but even severe cases typically resolve.

Normal Tibial Anatomy: The tibia is normally straight in the sagittal and coronal planes. It has a triangular cross-section with anterior, medial, and lateral surfaces. The bone remodels throughout childhood in response to mechanical forces.

Posteromedial Bow Pathology: In posteromedial bow, there is:

• Posterior bowing: Tibia curves posteriorly (backward)
• Medial bowing: Tibia curves medially (toward midline)
• Combined deformity: Posteromedial direction
• Normal bone structure: Unlike CPT, bone structure is normal
• No hamartomatous tissue: Unlike CPT, no abnormal tissue present

Pathophysiology: The bowing results from:

• In utero positioning (most likely cause)
• Fetal constraint
• Normal bone that is curved due to position
• Remodels with growth and weight-bearing

Associated Findings:

• Calcaneovalgus foot (common)
• May have mild leg length discrepancy (usually resolves)
• Normal fibula (unlike CPT where fibula may be affected)

Understanding that this is a positional, benign deformity helps guide management - observation is appropriate.

History:

• Bowing noted at birth or early infancy
• May have calcaneovalgus foot noted
• Usually no pain or functional limitation
• Family history (rare but may be present)
• No history of trauma

Physical Examination:

Inspection:

• Posterior and medial bowing of tibia
• May be bilateral (50-60%)
• Calcaneovalgus foot (common association)
• Assess for other deformities

Palpation:

• Bowing is palpable
• No pseudarthrosis site (unlike CPT)
• Normal bone structure

Range of Motion:

• Ankle: May have limited dorsiflexion (calcaneovalgus)
• Knee: Usually normal
• Assess for contractures

Measurements:

• Bowing angle (clinical estimate)
• Leg length (may have mild discrepancy)
• Foot position (calcaneovalgus assessment)

Differential Diagnosis:

• Anterior bow (CPT): Pathological, associated with NF1, requires treatment
• Physiological bowing: Normal variant, resolves by age 2-3 years
• Blount disease: Proximal tibia, varus deformity
• Other congenital conditions: Rare

Key Point: Differentiate from anterior bow (CPT) - posteromedial is benign, anterior is pathological.

Radiographs:

AP and Lateral Tibia:

• Assess posteromedial bowing
• Measure bowing angle
• Evaluate bone structure (should be normal)
• Assess for any cystic changes (should be absent)
• Evaluate medullary canal (should be normal)

Full-Length Standing Radiographs:

• Measure bowing angle accurately
• Assess alignment
• Evaluate for leg length discrepancy
• Assess foot position

Key Radiographic Features:

• Normal bone structure (unlike CPT)
• Normal medullary canal (unlike CPT Type II)
• No cystic lesions (unlike CPT Type III)
• No pseudarthrosis (unlike CPT Type IV)
• Posteromedial direction (not anterior)

Ultrasound:

• Usually not needed
• May assess foot position if calcaneovalgus present

No Further Imaging Needed:

• CT/MRI not indicated (benign condition)
• Bone scan not needed
• Genetic testing not needed (no NF1 association)

Serial Radiographs:

• Follow-up at 6-12 month intervals
• Document resolution
• Usually not needed after age 3-4 years if resolved

Natural History Complications:

Rare:

• Persistent deformity (5-10% of cases)
• Mild leg length discrepancy (usually under 1cm, acceptable)
• Calcaneovalgus persistence (rare)

Surgical Complications (if surgery performed):

Early:

• Infection (rare)
• Wound healing problems
• Neurovascular injury (rare)

Late:

• Recurrence (rare)
• Stiffness
• Hardware problems

Prevention:

• Appropriate patient selection (surgery rarely needed)
• Careful surgical technique if surgery indicated
• Realistic expectations

Key Point: Complications are rare because treatment (observation) has minimal risks.

Observation Protocol (Standard):

Follow-up Schedule:

• Initial: At diagnosis
• 6 months: Clinical and radiographic assessment
• 12 months: Clinical and radiographic assessment
• 18-24 months: Clinical assessment (radiographs if needed)
• Discharge: When resolved or stable

Monitoring:

• Clinical: Assess bowing improvement
• Radiographic: Document resolution
• Functional: Assess gait, activities

After Resolution:

• No further follow-up needed
• No restrictions
• Normal activities

If Surgery Performed (Rare):

Immediate:

• Pain management
• Wound care
• Immobilization (cast)

Postoperative:

• Cast 6-8 weeks
• Protected weight-bearing
• Physical therapy
• Gradual return to activities

Functional Outcomes:

Natural History:

• 90-95% resolve spontaneously by age 2-3 years
• Remaining 5-10% have mild persistent deformity
• No functional limitations in most cases
• Excellent prognosis overall

Predictors of Resolution:

• Younger age at presentation (better)
• Mild to moderate severity (better)
• Associated calcaneovalgus (both resolve together)
• Normal bone structure (good)

Predictors of Persistence:

• Severe initial deformity (may take longer)
• Older age at presentation (less growth remaining)
• Rare cases with structural abnormality

Quality of Life:

• Excellent in most cases
• No activity limitations after resolution
• No long-term sequelae
• Normal function

Long-term:

• Most have no residual deformity
• Mild leg length discrepancy may persist (usually under 1cm, acceptable)
• No increased fracture risk
• Normal function

Healthcare System:

• Posteromedial bow management typically involves pediatric orthopedic centers
• Public hospital system provides comprehensive care
• Usually managed in outpatient setting
• Private options available for follow-up

Multidisciplinary Care:

• Pediatric orthopedic surgeon (primary)
• Physiotherapist (if calcaneovalgus needs stretching)
• Radiologist (for serial imaging)
• General practitioner (for routine follow-up)

Medicolegal Considerations:

• Informed consent: Explain benign nature and expected resolution
• Documentation: Document differentiation from anterior bow (CPT)
• Follow-up: Ensure appropriate monitoring until resolution
• Family counseling: Reassure about benign nature and good prognosis

Research and Outcomes:

• Australian centers follow international guidelines
• Registry data helps track outcomes
• Quality of life studies confirm excellent outcomes