Background

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.

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 and lengthening the shorter limb.

Limb-length equalization procedures have primarily been performed by following one of two 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] Subsequently developed 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.

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Anatomy and Pathophysiology

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.

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 years) 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 observation 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.

Etiology

Each type of tibial bowing tends to have its own etiology. Causes 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.

Epidemiology

The true incidence of tibial bowing is unknown. It is generally agreed that this is a relatively infrequent disorder.

Prognosis

Although the angulation and foot deformity associated with posteromedial bowing improve dramatically, some degree of deformity, including tibial torsion and muscle atrophy, often remains. This is usually not a significant disability.

Clinical Presentation