Orthopaedic Surgery - Posteromedial Bow of the Tibia

Basics

Posteromedial bowing of the tibia is a congenital deformity characterized by:

Posterior and medial angulation of the distal tibia

that is apparent at birth.

The affected foot is typically positioned in:

Calcaneovalgus, with excessive dorsiflexion and eversion.

The deformity arises primarily from abnormal curvature of the:

Tibia

rather than from an isolated foot abnormality.

Natural History

In most children, the tibial bow gradually:

Corrects spontaneously during growth.

However, the associated shortening of the affected tibia generally:

Persists

and may increase proportionally as the child grows.

Therefore, while the angular deformity often improves dramatically, the major long-term issue is usually:

Limb-length discrepancy.

Epidemiology

Posteromedial tibial bowing is:

Rare.

It is recognized:

At birth.

Boys and girls appear to be affected:

Approximately equally.

Laterality

The disorder is almost always:

Unilateral.

Risk Factors

No established environmental, maternal, or mechanical risk factors are known.

Genetics

There is no recognized Mendelian inheritance pattern.

Etiology

The exact cause is:

Unknown.

It may represent a congenital disturbance of:

Tibial growth

or asymmetric physeal development.

Growth Disturbance

One proposed mechanism is an intrinsic abnormality of:

Physeal growth

that produces both:

Angular deformity

and

Relative tibial shortening.

Birth Trauma

The disorder is unlikely to be the result of an unrecognized fracture because the limb demonstrates:

Persistent proportional shortening during growth

rather than the typical healing pattern of a traumatic fracture.

Associated Conditions

Posteromedial tibial bowing generally occurs as:

An isolated congenital deformity.

No consistent systemic or syndromic association is recognized.

Diagnosis

Diagnosis is usually straightforward based on:

Appearance at birth

Physical examination

and

Plain radiographs.

Signs and Symptoms

The typical newborn has:

Visible posteromedial bowing of the distal tibia

combined with a:

Calcaneovalgus foot position.

Foot Position

The ankle is usually held in:

Marked dorsiflexion

and the foot in:

Valgus or eversion.

The dorsum of the foot may approach the:

Anterior surface of the leg

in more pronounced cases.

Tibial Bow

The most obvious deformity is usually located in the:

Distal third of the tibia

just proximal to the ankle.

Pain

The condition is:

Painless.

Pain is not expected in an uncomplicated case.

Limb Shortening

The involved leg may already appear:

Shorter below the knee

at birth.

This discrepancy may become progressively more apparent during:

Childhood growth.

History

There is usually no history of:

Birth trauma

Difficult delivery

or

Gestational complication

that explains the deformity.

Physical Examination

A complete examination of both lower extremities should be performed.

Limb Length

Measure and compare:

Femoral length

Tibial length

Overall limb length

The shortening is typically concentrated in the:

Affected tibia.

Foot and Ankle Motion

Assess:

Dorsiflexion

Plantarflexion

Inversion

Eversion

The calcaneovalgus posture is often flexible.

Muscle Function

Confirm active function of:

Dorsiflexors

Plantarflexors

Invertors

Evertors

The surrounding muscles and tendons are generally intact.

Neurologic Examination

A routine neurologic assessment should confirm normal:

Motor function

Sensation

and

Reflexes, when age appropriate.

Laboratory Tests

No laboratory investigations are routinely required.

Imaging

Plain Radiographs

Plain radiographs demonstrate the:

Posteromedial tibial bow

and help exclude other congenital tibial disorders.

Degree of Angulation

The deformity may initially be substantial, with angulation reported up to approximately:

60°.

Bone Appearance

The tibia may appear:

Normally mineralized

or

Thickened.

Unlike congenital pseudarthrosis, there is typically no:

Cystic lesion

Dysplastic segment

or

Pseudarthrosis.

Fibula

The fibula should also be evaluated for:

Length

Shape

and associated deformity.

Pathological Findings

The principal abnormality is:

Bony bowing and thickening of the tibia.

The surrounding:

Muscles

Tendons

Ligaments

and other soft tissues are generally normal.

Muscle Development

The anterolateral musculature may appear:

Relatively underdeveloped

but remains functionally intact.

Differential Diagnosis

Important alternatives include:

Healed or congenital tibial fracture

Fibular hemimelia

Isolated calcaneovalgus foot

Congenital pseudarthrosis of the tibia

Neurofibromatosis-associated tibial dysplasia

Calcaneovalgus Foot

An isolated calcaneovalgus foot may resemble the associated foot position seen with posteromedial tibial bowing.

However, in isolated calcaneovalgus:

The tibial shaft itself is not substantially bowed.

Congenital Pseudarthrosis

Congenital pseudarthrosis of the tibia is an important distinction because it is typically associated with:

Anterolateral bowing

rather than posteromedial bowing.

It may also show:

Tibial dysplasia

Cortical narrowing

Cystic change

and may be associated with:

Neurofibromatosis type 1.

Fibular Hemimelia

Fibular hemimelia may produce:

Limb shortening

Foot deformity

and

Abnormal tibial alignment

but is distinguished by deficiency or absence of the:

Fibula

and frequently by additional foot-ray abnormalities.

Treatment

General Principles

Initial treatment is usually:

Observation.

The angular deformity improves spontaneously in the majority of children as the tibia grows.

Spontaneous Correction

Most of the bowing remodels during early childhood.

A small amount of residual deformity may persist, often approximately:

6–8° or less.

Limb-Length Discrepancy

Unlike the angular deformity, limb shortening generally:

Does not completely correct.

At skeletal maturity, some patients may have a discrepancy of up to approximately:

5 cm, although many have considerably less.

Casting and Bracing

Routine:

Casting

Bracing

and

Stretching

do not substantially accelerate correction of the tibial bow and are therefore usually unnecessary.

Foot Splinting

In unusually severe cases, temporary splinting may help position the foot:

Plantigrade

so that walking and shoe wear are easier.

This is aimed at function rather than changing the natural history of the tibial bow.

Activity

No routine activity restriction is required.

Children can generally participate in:

Normal age-appropriate activities.

Shoe Lift

A:

Heel lift or shoe lift

may improve gait and comfort in children with a clinically important limb-length discrepancy.

Physical Therapy

Routine physical therapy is:

Not usually indicated.

Therapy may be useful only if there is an unusual secondary problem involving:

Motion

Strength

or

Gait.

Surgery

Surgery is directed primarily at:

Limb-length discrepancy

or, less commonly,

Persistent angular deformity.

Contralateral Epiphysiodesis

The most common operative strategy for a predicted moderate limb-length discrepancy is:

Epiphysiodesis of the longer contralateral limb.

This is usually performed:

Near adolescence

after most of the tibial bow has already corrected.

Indications for Limb-Length Equalization

If the predicted discrepancy at skeletal maturity is greater than approximately:

2 cm

surgical equalization may be considered.

The choice depends on:

Magnitude of predicted discrepancy

Remaining growth

Patient preference

and whether the family favors:

Shortening the longer limb

or

Lengthening the shorter limb.

Tibial Lengthening

Patients with a larger discrepancy or those wishing to avoid shortening the opposite leg may undergo:

Tibial lengthening.

This is a substantially more involved treatment than epiphysiodesis.

Corrective Osteotomy

Persistent clinically important angulation is uncommon but may require:

Tibial osteotomy.

This is generally reserved for patients with residual deformity that affects:

Mechanical alignment

Gait

or

Function.

Residual Angulation

Approximately:

5–10% of patients

have been reported to retain enough angular deformity to raise concern for corrective surgery.

Follow-Up

Long-term follow-up is important because:

The bow improves

while

The limb-length discrepancy may progressively increase.

Early Limb-Length Assessment

Formal radiographic assessment of limb length may be obtained by approximately:

5 years of age.

Options include:

Standing long-leg radiographs

or

Scanogram-type measurements.

Growth Prediction

Serial measurements can be plotted over time to estimate:

Expected discrepancy at skeletal maturity.

Posteromedial tibial bowing commonly produces:

Proportionate growth inhibition, so the relative discrepancy may remain fairly predictable.

Prognosis

The overall prognosis is:

Good.

Most children experience substantial spontaneous correction of the:

Angular deformity.

Long-Term Outcome

When clinically significant limb-length discrepancy is appropriately addressed, patients generally have:

Good function

Normal activity

and few long-term sequelae.

Complications

Limb-Length Discrepancy

The principal long-term complication is:

Persistent shortening of the affected tibia.

The discrepancy may increase as the child grows.

Growth Disturbance

The shortening is thought to result from:

Reduced growth of the involved tibial physis

possibly related to the developmental process responsible for the original bowing.

Residual Bowing

A small amount of posteromedial bowing may persist after growth.

In most patients this is:

Mild and asymptomatic.

Gait Asymmetry

A larger untreated limb-length discrepancy may produce:

Pelvic obliquity

Compensatory gait

or functional asymmetry.

Patient Monitoring

Children should be followed periodically during growth with attention to:

Tibial alignment

Limb-length discrepancy

Foot position

Gait

Lower-extremity function

Radiographic measurements are useful for predicting:

Final limb-length inequality

and deciding whether future:

Epiphysiodesis

Lengthening

or, rarely,

Corrective osteotomy

will be necessary.

Key Principle

Posteromedial bowing of the tibia is a rare congenital deformity recognized at birth, usually accompanied by a calcaneovalgus foot.

The tibial bow generally:

Remodels spontaneously with growth, while the associated:

Tibial shortening persists and may progressively increase.

For most children, management consists of:

Observation and serial monitoring of limb length.

Surgery is reserved primarily for:

Clinically important predicted limb-length discrepancy or persistent symptomatic angular deformity.