Tibial Bowing 

There are multiple etiologies for tibial bowing (see Etiology). Tibial bowing specifically refers to bowing of the diaphysis of the tibia with the apex of the deformity directed anterolaterally, anteromedially, or posteromedially. Each type of bowing tends to have a classic etiology.^[1]

Anterolateral bowing is associated with pseudarthrosis of the tibia and neurofibromatosis.^[2] Anteromedial bowing is associated with fibular hemimelia. The focus of this article is posteromedial tibial bowing, shown in the images below.

Posteromedial bowing is a congenital bowing of the tibia (with the apex directed posteriorly and medially) and a calcaneovalgus foot deformity.^{[3, 4, 5]} Both of these deformities tend to resolve with little clinical disability; however, a leg-length inequality commonly develops that often requires treatment. If a significant leg-length inequality results, the patient will have an abnormal gait and may be at risk for increased back pain or deformity. Treatment options vary depending on the degree of limb-length inequality, age of the patient, expected height, and desires of the patient or family. Treatment options include slowing the growth of the longer limb or lengthening the shorter limb.

Limb-length equalization procedures have primarily been performed using 1 of 2 general approaches: slowing the growth of the longer limb with an epiphysiodesis or lengthening the shorter limb.

Phemister described his classic technique for epiphysiodesis.^{[6, 7]} He removed a section of the epiphysis, rotated it 90°, and replaced the bone. Today, the most common technique is the percutaneous drill epiphysiodesis, performed with the aid of an image intensifier. This technique has been reported to result in physeal closure in 85-100% of patients with few complications.^[8]

The first published report of a limb-lengthening procedure in the English literature dates to 1904 in Italy (Codivilla).^[9] Newer techniques, such as the Ilizarov and Wagner techniques, have been performed for 50 years. The Ilizarov technique and variations thereof are the procedures most often used today.^{[10, 11]} It is named after Gavril Abramovich Ilizarov, a Russian physician who used his technique to treat injured World War II veterans. Lengthening is usually performed using corticotomy and gradual distraction with a ring fixator and fine wires. This technique can result in an increase of 25% or more in bone length.

Posteromedial bowing is a congenital anomaly associated with a severe calcaneovalgus foot deformity. These deformities usually improve significantly with little or no treatment, as shown in the images below. Ultimately, limb-length inequality is usually of the greatest concern with tibial bowing.

Frequency

The true incidence of tibial bowing is unknown, although this is a relatively infrequent disorder.

Each type of tibial bowing tends to have its own etiology (see Introduction). Etiologies of tibial bowing include the following:

• Posteromedial bowing^[12]
• Anteromedial bowing (fibular hemimelia)^[13]
• Anterolateral bowing (tibial pseudarthrosis)
• Blount disease (infantile tibia vara)
• Physiologic bowing
• Rickets
• Focal fibrous dysplasia
• Trauma (ie, Cozen fracture)
• Dysplasias

The developmental etiology of posterior medial bowing is unknown, but most authors believe it occurs secondary to abnormal fetal positioning, with the dorsiflexed foot plastered against the anterior aspect of the tibia. Primary abnormal embryologic development, such as limb bud or circulatory abnormalities and intrauterine fracture,^[14] has also been suggested as a possible developmental etiology.

The pathophysiology of the resultant limb-length inequality may be related to the bowing. The degree of initial tibial deformity (which largely resolves by age 8 y) has been shown to be ultimately associated with the severity of tibial shortening and resulting limb-length inequality. Animal models have demonstrated that unbalanced longitudinal pressures affect physeal growth. It is speculated that bowing results in unbalanced longitudinal pressures and, ultimately, in a decreased rate of growth. This theory is contradicted by the fact that tibial growth inhibition remains constant as the child grows even though the deformity improves. The rate of growth of the affected tibia would be expected to approach that of the unaffected leg as the bowing resolves; this is not the case. Additionally, in the few patients who underwent early realignment osteotomy, tibial growth was still inhibited, resulting in a subsequent limb-length inequality.

Tibial bowing is often obvious and is present at birth. The foot is usually dorsiflexed to such a degree that it makes contact with the anterior aspect of the distal tibia. The posterior bow of the tibia is less obvious but can be easily palpated. A dimple may be present in the skin posterior to the apex of the bow.^[15]

The Galeazzi test, shown below, typically used to assess hip dislocation, can also be used to assess any congenital disorder that results in a significant limb-length inequality. The examination is performed with the patient supine and the hips and knees flexed. The result is considered positive if knee height is asymmetrical. It is also helpful to assess whether the limb-length inequality is primarily from the femur or from the tibia and to assess limb length in someone with knee or hip flexion contractures.

Differential diagnoses include the other types of tibial bowing, such as anterolateral and anteromedial bowing. Intrauterine fracture or osteogenesis imperfecta may also result in tibial bowing.^{[16, 17]} These are often easily differentiated based on physical examination findings in which the direction of the tibial bowing and the associated foot deformity are noted. Anteromedial bowing is often associated with congenital loss of the lateral rays of the foot and fibular deficiency. Anterolateral bowing is associated with a pseudarthrosis of the tibia that may be obvious radiographically at birth or may develop with growth. Approximately 50% of children with anterolateral bowing are eventually diagnosed with neurofibromatosis.

Initial treatment of the tibial bowing foot deformity includes stretching, serial casting, or splinting. The bowing deformity rapidly corrects. A 50% correction is usually seen by age 2 years, although a mild deformity often persists, as depicted below. The rationale for corrective tibial osteotomy is less clear, as a tibial osteotomy is rarely indicated; however, a significant deformity that interferes with development, especially if little or no correction is seen by age 2 years or a symptomatic and persistent deformity is seen in children older than 10 years, may be an indication for tibial osteotomy.^[18]

Performing a tibial osteotomy does not seem to decrease the need for later limb equalization. Most children with posteromedial bowing will require a limb equalization procedure. The type of procedure depends on the degree of projected limb-length inequality at skeletal maturity. Typically, limb-length inequality is 2-6 cm at skeletal maturity. Usually, an appropriately timed epiphysiodesis can restore limb-length equality, although a lengthening procedure may be indicated for more severe projected limb-length inequalities (>5 cm), especially in children of short stature.^{[19, 20]}

Posteromedial bowing is defined by the apex of the tibial curve being directed posteriorly and medially. Bowing in other directions is usually associated with different disorders.

Understanding the nature of the deformity and establishing the correct diagnosis are very important. Tibial osteotomies in children with anterolateral deformities can be disastrous. This type of tibial deformity can be associated with persistent pseudarthrosis even without any surgical procedures, and performing an osteotomy may promote or instigate an early nonunion. If the patient has a metabolic etiology for their bowing, treat the metabolic disorder before considering surgical options. Posteromedial bowing typically self-resolves, leaving only the limb-length inequality to be addressed.